Chapter 10 Mating

However, when resources are distributed heterogeneously and females are widespread and do not form groups, the only chance a male may have to find more than one female is to wait for females to come in search of him and his competitors (lek polygyny hypothesis

SETUP LEK WHEN SCATTERED RESOURCE, WAIT FOR FEMALES TO COME OR OTHER HETERO RESOURCE WHERE FEMALES DO NOT FORM GROUPS ARE scramble competition polygyny hypothesis)-scramble competition polygyny hypothesis When resources are distributed heterogeneously and females are widespread and do not form groups, males will seek out females.

In some species, males do not defend groups of females(fem defense polygyny) or resources that several females come to exploit(resource defense polygyny_ . Instead, they wait for females to come to them.

These males fight to control a very small area that is used only as a display arena. These mini-territories may be clustered in a traditional display ground called a lek, Despite the fact that leks do not contain food, nesting sites, or anything else of practical utility, females come to them anyway. They come to choose a mate, receive his sperm, and then depart to rear the offspring alone no parental male lek care Leks are often established in places where females need to pass through, as in the rocky intertidal areas that provide access for feeding in Galápagos marine iguanas If the female is receptive and chooses a partner, she flies to his perch for a series of mutual displays followed by copulation. Afterward, she leaves to begin nesting, and the male remains at the lek to court newcomers. fem quickly leave lek 1 male achieved nearly 75 percent of the total copulations; a second male mated 56 times (13 percent), while 6 other males together accounted for only 10 matings (Lill 1974). Preferred males tend to occupy sites near the center of the manakin lek, and they engage in more aggressive displays than less successful males a type of African antelope, older males tend to occupy the center of a lek, and therefore copulate much more often than younger rivals forced to the peripher Bradbury has argued that lekking evolves only when other mating tactics do not pay off for males, largely due to a wide and even distribution of females ( no grouping of females Hammer-headed bats do not live in permanent groups but instead travel over great distances in search of widely scattered sources of food Thus, the feeding ecology of females of these species makes it hard for males to monopolize them, directly or indirectly. Instead, males display their merits to choosy females that come to leks to inspect them.

Although promiscuity is most common in species ? parental care, it does occur in those in which parents play at least some role in caring for young.

young are precocial and can largely take care of themselves after hatching common when lacking parental care While both males and females have multiple partners in this species, only the father provides care. Males encounter dozens of receptive females each day during the mating season, and 15 to 23 males can sire clutches of 53 to 79 offspring. Whereas both sexes in this marine snail appear to mate indiscriminately and frequently, only the mother takes care of the young Promiscuity is even more common in species in which no parental care is provided by either the mother or the father. Take for example, the seaweed fly Coelopa frigida, which gets its name from the fact that it lives and breeds in seaweed washed up on beaches in the temperate Males and females in this species both desire larger mates (Pitafi et al. 1990), a mutual mate preference that is controlled by a chromosomal inversion However, this species has no courtship behavior, and males simply attempt to mount females when they find them. Females will struggle with males, but females often acquiesce to male mating attempts in a strategy that has been called convenience polyandry. In species such as this where male harassment is common, promiscuity resulting from convenience polyandry may be a consequence of sexual conflict between males and females Seaweed flies exhibit extreme promiscuity. When population densities are high, both males and females may copulate hundreds of times during their short, 3-week lives.

The question remains, why do these socially and genetically monogamous males fail to engage in fitness-boosting extra-pair fertilizations?

As we learned in Chapter 9, one answer is that females have something to say about who gets to mate with them, again indicating that sexual conflict is potentially present even in monogamous mating systems This is exactly what researchers discovered in a study of pied flycatchers (Ficedula hypoleuca) that experimentally decreased female flying ability (by tying together some wing feathers), making it harder for females to escape from unwanted copulations After manipulating female escape ability, the poorer fliers had nearly double the proportion of extra-pair young in their nests than control females, Thus, although both males and females can gain reproductive benefits from extra-pair matings, females appear to exert control over with whom they mate, both before and after a pair-bond has formed.

However, in nests containing extra-pair young sired by males from within the social group (within-group extra-pair young), there was no difference in heterozygosity between offspring sired by the extra-pair mates and social partners.

Extra-pair matings can boost the immune responses of offspring in the bluethroat. The mean wing-swelling response (an indicator of immune system strength) of young sired by their mother's social partner (within-pair young, or WPY) was less than that of young birds sired by their mother's extra-pair partner (extra-pair young, or EPY) in broods of mixed paternity a point established by injecting a foreign substance that triggers an immune response into the wing webs of nestling bluethroats and then measuring the swelling at the injection site linked genetic diversity in immune genes to female mate choice and offspring quality

In most polygynous species, it is critical to realize that it is the behavior of females that dictates the behavior of males, and ultimately the type of mating system that forms. This type of female defense polygyny is sometimes referred to as ? defense polygyny because females are socially bonded together in harems, making it easier for males to monopolize a group

FEM BEHAV DICTATE MALES This type of female defense polygyny is sometimes referred to as harem defense polygyny because females are socially bonded together in harems, making it easier for males to monopolize a group Male plains zebras attempt to defend a harem of females that forms to reduce the risk of predation, COMMON FEM DEF POLYGNY FOR ZEBRAS fem zebra group with dominant male, able to feed for 10 percent longer per day than those that associate with subordinate males, since dominant males successfully keep other males away, benefit from males guarding/monop this harem females directly benefit from joining a group controlled by a dominant male, and he in turn benefits by mating with a large number of females in his harem harems usually for predation risk reduced in fems And since females that group together have more eyes to spot predators, and those that associate with dominant (harem) males can forage longer without being harassed by other males, they are likely to join the harems of strong males

Thus, given the existence of female groups, IS the standard male tactic in mammals

Female defense polygyny

In some mammals, one helpful behavior a paternal male might do for females is to drive other males away from his brood, thereby blocking potential infant killers and preventing infanticide

In the mate-guarding prairie vole (Microtus ochrogaster), males can and do defend their offspring against infanticidal rivals, so both mate guarding and mate assistance may contribute to the tendency toward monogamy in this species monogamy has tended to evolve only in species that faced strong infanticidal pressures by males, making the defense by a long-term partner beneficial to males and females alike

Female defense polygyny is also quite common in vertebrates, particularly in species in which females form groups, which makes defending multiple females at the same time much easier.

Indeed, social monogamy in mammals never occurs when females live in groups-POLYGNY FAVORED IN MAMMAL FEMALE GROUPS western gorillas (Gorilla gorilla), groups of females that form in part for protection against predators attract males that compete to control sexual access to the entire group or harem

Just as the defense of resources or females was invoked to explain two types of defense polygyny (female versus resource), the absence of defensible clusters of females or resources has been invoked as an explanation for both nonterritorial scramble competition polygyny (see below) as well as for lek polygyny

One possibility is that congregated males may be relatives that assist one another in the attraction of mates in closer leks A lek polygynous mammal: the hammer-headed bat. Males cluster in dense groups at mating arenas where they defend DEFEND LEKS display territorie

As we have just seen, males may pay a reproductive cost if their partner mates multiply. But for females, there are a variety of potential benefits from mating multiply (just as there are for males, as Bateman's classic experiment suggested), particularly for their offspring. Indeed, females can potentially obtain several indirect genetic benefits for their offspring by mating polyandrously

Perhaps the best-studied genetic benefit linked to a polyandrous mating system has to do with improved offspring quality and viability. For example, in the grey foam nest treefrog (Chiromantis xerampelina), females build foam nests and multiple males fertilize the eggs that she lays without ever coming into contact with her According to this good genes hypothesis, females can receive a genetic benefit in terms of increased offspring viability by mating multiply yellow-toothed cavy (Galea musteloides), in which females will copulate with more than one male when given the opportunity In the dark-eyed junco (Junco hyemalis), a common North American songbird, not only are the genetic offspring of females and their extra-pair mates more likely to survive to reproduce, but when they do reproduce, they do better than the offspring of females and their social partners It seems that the sons of extra-pair liaisons appear to boost their lifetime reproductive success by mating with females outside of the pair-bond, and the daughters of these arrangements are more fecund Since extra-pair male juncos provide only genes to their sexual partners, the fitness benefits that females (and their offspring) gain from polyandry appear to be due to those genes females can, and sometimes do, make larger than usual eggs to be fertilized by the sperm of their extra-pair mates. The greater supply of nutrients can give extra-pair offspring an early developmental boost, enabling these young to become high quality sons and fecund daughters ( Carefully designed experiments can tease apart the potential roles of good genes versus maternal effects in studies examining the evolutionary maintenance of polyandry A major component of the fitness benefits gained by females through extra-pair copulations could be the production of sons that are so attractive that they repeat the extra-pair success of their fathers (Weatherhead and Robertson 1979). If sons inherit the very traits that made their fathers sexually appealing (and if their daughters inherit an affinity for seeking extra-pair copulations), these "sexy sons" increase the odds that their mothers will have many grandoffspring -inherit appealing traits of fathers A father's mating success can be transmitted to his sons. In experiment 1, two male field crickets were given an opportunity to compete for a female; one male (S) mated successfully, while the other male (U) was unsuccessful. When the sons of male S were placed in competition for a female with the sons of male U (which had been given a female to mate with after failing to win the initial competition), the sons of S were nearly twice as likely to mate with the female as were the sons of U. In experiment 2, a male that had won a mating competition was later allocated a female at random for breeding, as was a male that had lost the competition. The sons of the two males were then placed in an arena with a female, and as before, the sons of S were much more likely to mate with the female than were the sons of U.

Although females tend to exert more control than males over mating in most polyandrous systems, there are polyandrous species in which males maintain at least some control over their mating decisions and can reduce the probability that they will care for eggs fertilized by other males. For example, males of the red-necked phalarope (P. lobatus), like those of its relative the red phalarope, care for broods on their own

Polyandrous females almost always draw their second mates from those males that have lost a first clutch to predators. Such a male, however, favors his original sexual partner over a novel female more than nine times out of ten (Schamel et al. 2004). By copulating with this female again and then accepting her eggs, the male reduces the risk that the eggs that he receives will have been fertilized by another male's sperm. male w orig sex partner

The existence of constraints imposed by choosy females and competitors may also help explain the evolution of polyandrous mating systems in which most breeding females form social bonds with several males

Polyandry appears to be associated with a scarcity of suitable territories, which leads to a highly male-biased operational sex ratio since males outnumber the limited number of territorial,, breeding females The intense competition for these females and the territories on which they live has favored males capable of forming a cooperative defense team to hold an appropriate site. A breeding female may acquire as many as eight mates prepared to pair-bond with her for years If females do give all of their mates an equal chance at fertilizations, the mean fitness of each mate is certainly higher than that of males that fail to be part of a team. The territorial female then mates with all of the members of her harem, providing each male with his own clutch of eggs, which he cares for exclusively by himself. However, males that pair with a polyandrous female are also likely to care for offspring sired by other males, since 75 percent of the clutches laid by polyandrous female jacanas are of mixed paternity but male jacanas and phalaropes may have to accept the eggs that their partners lay if they are to leave any descendants at all. And in some cases, these males are able to gain additional reproductive success by having other males care for their eggs in other nests. First, the adult sex ratio is slightly biased toward males, meaning that the opportunities for polygyny are limited for males and that females may need to compete for access to mates Polyandrous female spotted sandpipers fight for males. Two female spotted sandpipers (A) about to fight and (B) fighting for a territory that may attract several monogamous, paternal males to the winner. Thus, male spotted sandpipers must deal with polyandrous females if they are to have any chance of reproducing, even if the female's ability to control the reproductive process puts the male at a major disadvantage.

way of testing between the hotspot and hotshot hypotheses is by temporarily removing males that have been successful in attracting females

REMOVING HOTSHOTS But if the hotshot hypothesis is correct, removal of attractive males will cause the cluster of subordinate males to disperse to other popular males or to leave the site altogether DISPERSE IF HOTSHOT NOT THERE-SECOND HYPO In a study of the great snipe (Gallinago media), an Old World sandpiper that displays at night, removal of central dominant males caused their neighboring subordinates to leave their territories (Höglund and Lundberg 1987). In contrast, removal of a subordinate while the alpha snipe was in place resulted in his quick replacement on the vacant territory by another subordinate. the presence of attractive hotshots, not the real estate per se, determines where clusters of males form. According to the female preference hypothesis, a female preference for quick and easy comparisons might make it advantageous for males of the Uganda kob Female density in the Kafue lechwe is not correlated with lek formation. Four leks of the antelope (open circles) are not located in the areas of highest female density, providing evidence against the hotspot hypothesis for this species Female Uganda kob do not aggregate disproportionately at leks with large numbers of males. (A) Female attendance at leks is simply proportional to the number of males displaying there. (B) As a result, the female-to-male ratio does not increase as lek size increases Contrary to this prediction, however, the operational sex ratio is the same for leks across a spectrum of sizes, so males are no better off in large groups than in small ones (FIGURE 10.35) (Deutsch 1994). For this species at least, the female preference hypothesis can be rejected LARGER LEK NOT GETTING MORE FEM If so, those leks with a relatively large number of males should attract disproportionately more females than leks with fewer males

Fathers provide care for young in a variety of other taxonomic groups besides birds, including in the extreme in the seahorse Hippocampus whitei, in which males take on the responsibility of "pregnancy" by carrying a clutch of eggs in a sealed brood pouch for about 3 weeks (FIGURE 10.7). Each male has a durable relationship with a single female that provides him with a series of clutches

Since a male's brood pouch can accommodate only one clutch of eggs, he gains nothing by courting more than one female at a time. In fact, in another species of Hippocampus, genetic data indicate that males do not accept eggs from more than one female a male seahorse may not benefit by switching mates if his long-term mate can supply him with a new complement of eggs as soon as one pregnancy is over. a male might be able to match his reproductive cycle with that of his partner. When the two individuals were in sync, the male would complete one round of brood care just as his partner had prepared a new clutch. If this is true, the experimental removal of a female partner should lengthen the interval between spawning for the male, which it does in at least some species related to seahorses

monogamy is uncommon in most animals, it is exceptionally rare in mammals, a group notable because internal gestation and lactation are largely limited to females

Since the types of care a male can therefore provide offspring are relatively fewer than those a female can provide, particularly at the earliest developmental stages, sexual selection theory suggests that males should instead try to mate with many females of those rare mammalian species that exhibit paternal behavior should tend to be monogamous (Woodroffe and Vincent 1994). One monogamous mammal with paternal males is the Djungarian hamster (Phodopus sungorus), in which males actually help deliver their partner's pups (FIGURE 10.8) (Jones and Wynne-Edwards 2000). Male parental care contributes to offspring survival in this species

In the typical bee, a single mating suffices to supply the female with all the sperm that she will need for a lifetime of egg fertilizations (queens of stingless bees can live for several years), thanks to her ability to store and maintain the abundant sperm that she receives from her single partner

The widespread nature of bee monogamy indicates that this trait was the ancestral mating pattern, with polyandry in the genus Apis a more recently derived characteristic (see Chapter 12). Some of the best support for these group-level benefits of genetic diversity includes the results of an experiment in which some honey bee colonies were set up with queens that had been artificially inseminated just once and some set up with queens that had been supplied with the sperm of ten drones. Both types of colonies were then infected with a bacterium that causes the disease American foulbrood, a killer of honey bee larvae. The researchers found that colonies with polyandrous queens had lower disease intensity and larger and more robust colonies at the end of the summer because the increased genetic diversity within the colony meant that fewer workers were infected honey bees is the result of individual differences in innate immunity, or the nonspecific defense mechanisms of the immune system ( within-colony variance among samples in the upregulation of hymenoptaecin (but not of abaecin) in response to immune challenge significantly decreased with increasing genetic diversity In other words, more genetically diverse colonies exhibited less variation in individual immune responses. Thus, individual larval immunocompetence alone may be the mechanism explaining colony-level immunity in honey bees and other eusocial insects

In some animals, polyandry enables females to indirectly access resources through greater parental assistance from their several mates (additional care hypothesis). For example, in the dunnock (Prunella modularis), a small European songbird, a female that often lives in a territory controlled by one (alpha) male may actively encourage another, subordinate male to stay around by seeking him out and copulating with him when the alpha male is elsewhere

The benefit to a polyandrous female of distributing her copulations between two males is that both sexual partners will help her rear her brood—provided that they have both copulated often enough with her. Adjustment of copulation frequency by polyandrous female dunnocks. (A) A female dunnock (B) living in a territory with two males solicits copulations more often from the male that has spent less time with her, whether that is the alpha or the beta male. By copulating with an additional male, the polyandrous female has in effect made it advantageous for the "other male" to invest parentally in her offspring.

In species of birds in which males and females form partnerships for one or more breeding seasons (Lack 1968), males tend to contribute in a major way to the welfare of the offspring produced by their mates (Orians 1969). In the yellow-eyed junco (Junco phaeonotus), for example, the male takes care of his mate's first brood of fledglings while the female incubates a second clutch of egg

The paternal help provided is essential for the survival of these young and highly inept foragers (Weathers and Sullivan 1989). The value of male assistance has also been documented for European starlings (Sturnus vulgaris). In a population in which some males helped their mates incubate their eggs and others did not, the clutches with biparental attention stayed warmer (FIGURE 10.5) and so could develop more rapidly. Indeed, 97 percent of the eggs that had been incubated by both parents hatched, Thus, in many bird species the high costs of parental care that require both parents to share the workload (see Chapter 11) may promote (social) monogamy.

10.2 Polyandry: Multiple Mating by Females

These include indirect benefits in the form of genetic advantages to a female's offspring, as well as direct benefits (such as parental care, access to resources, safety from predators, or reduced harassment by other males We now know that polyandry is much more common than monogamy, not just in birds but in most taxonomic groups. A review led by Nina Wedell found evidence that mating with more than one male per female occurs in all of the 14 major taxonomic groups explored One explanation for this type of behavior is that the male may be able to take advantage of his own opportunity for extra-pair copulations with females other than his social partner A male of this sort may be able to fertilize at least some of the eggs of his social partner while also inseminating other females whose offspring will receive care, but not from him. These males, which often exhibit ornaments and displays thought to be indicative of superior physical condition (Griffith et al. 2002), avoid some or most of the costs of monogamy

Resource defense polygyny occurs not only in zebras and other mammals, but in many other vertebrates, including the African cichlid fish Lamprologus

This fish exhibits the most extreme sexual size dimorphism among animals, as males are more than 12 times heavier than females (Schütz and Taborsky 2000). Females of this species deposit a clutch of eggs in an empty snail shell and then swim inside to remain with the eggs and hatchlings until they are ready to leave the nest Territorial males of this species need to be larger than their tiny mates to not only defend suitable nest sites but also to collect shells from the lake bottom and steal them from the nests of rival males to create middens of up to 86 shells ( shell groups=middens Because as many as 14 females may nest simultaneously in different shells in one male's midden, the owner of a shell-rich territory can have extraordinary reproductive success females nest in these male cichlid dominated territories with shells these shells are a defensible resource that cichlids use to build territories

Consistent with the idea that polygynous males were of higher quality, the researchers found that sons of polygynous fathers defended more nest boxes and produced more courtship song than did sons of monogamous fathers.

Together these results confirmed that sons may inherit from their fathers behavioral qualities for the successful acquisition of nest sites and attraction of mates, and that these qualities are not the result of maternal effects from hormones deposited in the eggs

As we noted in Chapters 7 and 9, there is a point at which a female can gain more by mating with a polygynist on a good territory than by pairing off with a male occupying a resource-poor or predator-vulnerable territory

What should a female do when the selection of an already mated male means that she must share the resources under his control with other females "polygyny threshold" (after Emlen and Oring's "polygamist threshold"; Emlen and Oring 1977) at which a female will gain higher fitness by mating with an already mated male than with a bachelor with poor territory

No one hypothesis for why lekking males form groups holds for every species. Nevertheless, the interactions among males on a lek usually seem to enable individuals of high physiological competence to demonstrate their superior condition to their fellow males and to visiting females

Whatever the basis for lek formation is, lekking males are forced to compete in ways that separate the strong from the weak, making it potentially advantageous for females to come to a lek in order to compare and choose,

genetic compatibility hypothesis Females mate polyandrously to increase the odds of receiving genetically complementary sperm.

When gametes with especially compatible genotypes unite, they can result in highly viable progeny (Zeh and Zeh 1996, 1997). This genetic compatibility hypothesis has been tested by comparing the number of surviving offspring produced by polyandrous pseudoscorpions with the number produced by females that were experimentally paired with lone males (FIGURE 10.17) (Zeh 1997, Newcomer et al. 1999). When Jeanne Zeh compared the she found no correlation, which means that male pseudoscorpions cannot be divided into studs and duds. Instead, the effect of a male's sperm on a female's reproductive success depended on the match between the two gametic genomes, as predicted by the genetic compatibility hypothesis. we can predict that female pseudoscorpions should prefer to mate with new males rather than with previous partners eggs). Indeed, when a female was given an opportunity to mate with the same male 90 minutes after an initial copulation, she refused to accept his spermatophore in 85 percent of the trials

The researchers used the mean number of copulations for females of each species as a measure of its degree of polyandry. To quantify reproductive output, they measured the mass of eggs produced by a female in the laboratory and divided that figure by the body mass of the female in order to control for differences among species in weight. As

across these eight butterfly species, the more males a female mated with on average, the more spermatophores she received, and the greater her production of eggs

Females often mate multiply to gain access to resources that are necessary for successful reproduction (?). As we discussed in Chapter 9, female red-winged blackbirds (Agelaius phoeniceus) may be allowed to forage for food on the territories of males with which they have engaged in extra-pair copulations, whereas genetically monogamous females are chased away

additional resources hypothesis

? Females mate polyandrously to gain more caregivers to help rear young

additional care hypothesis Females in many insect species have an incentive to mate several times in order to receive direct benefits in the form of food gifts such as nutritious spermatophores from their partners. Indeed, the spermatophores of highly polyandrous butterfly species contain more protein than the spermatophores of monogamous species

This type of mating system in which males mate with multiple females but females mate with only a single male is referred to as polygyny

ale satin bowerbirds the green catbird (Ailuroedus crassirostris), males and females pair off for a given breeding season and rear offspring together, a mating system known as monogamy

Both the genetic compatibility hypothesis and the genetic diversity hypothesis may ultimately be related to the idea that females choose extra-pair mates to avoid inbreeding, which would likely result in the production of less heterozygous offspring. Studies from two species of fairy-wrens are consistent with this inbreeding avoidance hypothesis. Work in red-backed fairy-wrens (Malurus melanocephalus) showed that females paired to genetically similar males were more likely to produce young sired by extra-pair males,

and that those offspring were less inbred (more heterozygous) than within-pair offspring the effects of inbreeding on the likelihood of extra-pair matings because many Similarly, an analysis of 55 avian species by Erol Akçay and Joan Roughgarden found little support for the good genes or genetic compatibility hypotheses in more than half of the species studied (Akçay and Roughgarden 2007). Although these researchers showed that extra-pair males are on average larger and older than within-pair males, males were not different in terms of secondary sexual traits, body condition, or genetic relatedness to the female Moreover, no difference was found between extra-pair and within-pair young in survival to the next breeding season Thus, there is at least some good evidence from a variety of species to suggest that indirect benefits promote the evolution of polyandrous mating systems, but the importance of genetic benefits to offspring in the evolution of female mate choice and of polyandrous mating systems in particular remains a source of debate. Our focus thus far on the potential indirect genetic benefits of polyandry should not obscure the possibility that females sometimes mate with several males to secure direct benefits rather than genes alone. These direct benefits can take many forms, including access to additional resources or parental care (HYPOTHESES 10.3), as well as better protection from sexually harassing males and reduced risk of infanticide

Svein Dale and colleagues found that unmated female pied flycatchers (Ficedula hypoleuca) visit many males and do not rush into a paired relationship, suggesting that when they choose an already mated male, they do so voluntarily and with full knowledge

because the remaining unmated males have extremely poor territories ( As one might expect, pied flycatcher females that are already mated to a male are not typically receptive to their mates accepting another female. Indeed, female- female competition for access to mates (and other resources), a topic that we mentioned in Chapter 9 is often less well-studied than male-male competition, can be important to the evolution of mating systems. In some populations of pied flycatchers, almost half of the females express a white forehead patch, a Females with patches are also more aggressive to intruders, and intruders with patches are attacked less often than those lacking patches (Morales et al. 2014). Together, these results suggest that female pied flycatchers are under strong selection to prevent their mates from accepting another female

HYPOTHESES 10.5 Alternative hypotheses to explain why males congregate at leks hotspot hypothesis Males cluster in places (called "hotspots") where the routes frequently traveled by receptive females intersect. hotshot hypothesis Subordinate males cluster around highly attractive males to have a chance to interact with females drawn to these "hotshots." female preference hypothesis Males cluster because females prefer sites with large groups of males, where they can quickly or safely compare the quality of many potential mates.

but we still need to know what benefit a male derives from defending a small display territory at a group lek only a few males on leks monopolize most of the matings. Here we review three hypotheses related to female choice According to the hotspot hypothesis, males cluster in places ("hotspots") where the routes frequently traveled by receptive females intersect ( In contrast, the hotshot hypothesis argues that subordinate males cluster around highly attractive males to have a chance to interact with females drawn to these "hotshots" FEM PREF FOR LARGER SITES WHERE THEY COMPARE MATE QUALITIES Males cluster because females prefer sites with large groups of males, where they can quickly or safely compare the quality of many potential mates. Female decoys failed to draw in males, leading to the rejection of the hotspot hypothesis. In contrast, male decoys regularly attracted both females and males, particularly if those decoys had been painted to resemble individuals with highly symmetrical plumage patterns. Therefore, the hotshot hypothesis may apply to little bustards However, the fact that more females per decoy were attracted to clusters of four decoys than to smaller groups is consistent with the female preference hypothesis as well, though more than four decoys did not draw in additional females. Thus, this experiment ruled out the hotspot hypothesis but could not distinguish between the hotshot and female preference hypotheses.

But one does not have to be hyperaggressive to practice female defense polygyny. For example, males of tiny siphonoecetine amphipods construct elaborate ?

cases composed of pebbles and fragments of mollusk shells found in the shallow ocean bays where they live PEBBLE MOLUSK SHELLS AND MOVE AROUND IN THESE They move about in these houses and capture females by gluing the females' houses to their own, eventually creating an apartment complex containing up to three potential mates

Female defense and resource defense tactics by competitive males ONLYmake intuitive sense when either females or resources are ?

clumped emales or resources

Some male black-winged damselflies (Calopteryx maculata), for example, defend floating vegetation that attracts a series of sexually receptive females,

each of which mates with the male and then lays her Resource defense polygyny is also common in insects, in which a safe location for eggs often constitutes a defensible resource Ultimately, the more of this resource a territorial male holds or the longer he holds it, the more likely he is to acquire several mates. In effect, the male's parental care, in addition to the safe burrow that he defends, constitutes a resource for receptive females,

Another form of scramble competition polygyny is influenced not by the distribution of females but by the length of the breeding period. An explosive breeding assemblage occurs in species with a highly compressed breeding season in which females may be receptive only during a short window of time

explosive breeding assemblage=scramble competition polygynyinfluenced by ength of the breeding period. vOne such species is the horseshoe crab Limulus polyphemus, in which females lay their eggs on just a few nights each spring and summer. Males are under the gun to be near the egg-laying beaches at the right times and to accompany females to the shore, where egg laying and fertilization occur On that night or nights in spring in the temperate Northern Hemisphere, most of the adult male wood frogs in a population are present at the ponds that females visit to mate and lay their eggs. Therefore, male wood frogs eschew territorial behavior and instead hurry about trying to encounter as many egg-laden females as possible before the one-night orgy ends And because females are available only on this one night, a few highly aggressive territorial males cannot monopolize a disproportionate number of mates by displaying territorial behavior of driving certain other males away , they scramble

that we discussed in previous chapters, females mate with multiple males but males only mate with a single female, a mating system called polyandry

extreme version of polyandry is exhibited by the honey bee Apis mellifera, in which young queens fly out from their hives into aerial swarms of drones that pursue, capture, and mate with them in midair. The The average queen is highly polyandrous, coupling with many males and storing the sperm of perhaps a dozen 2002). In contrast, drones never mate with more than one queen because a drone violently propels his genitalia into his first and only mate, a suicidal act that ensures that he is only able to mate once because shortly thereafter, he is dead (

mechanism resource def polygyny-If the distribution of females is controlled by the distribution of key ?, and if male mating tactics are in part dictated by this fact of life, then it should to be possible to alter the mating system of a species by moving resources around, thereby altering where females are located

fem following resources control male mating tactics alter the mating system of a species by moving resources around, measured male territories and female foraging ranges in the dunnock, a species that we introduced above in our discussion of polyandry. In this drab little songbird, females hunt for widely dispersed food items over such large areas that the ranges of two males may overlap with those of several females, creating a polygynous-polyandrous mating system (also known as polygynandry; see below). Those females with the most reduced ranges had, as predicted, fewer social mates than other females whose ranges had not diminished in size (FIGURE 10.29). In other words, as a female's home range contracted, the capacity of one male to monitor her activities increased, with the result that female polyandry tended to be replaced by female monogamy. males attempt to monopolize females within the constraints imposed on them by the spatial distribution of potential partners monopolize fem with smaller ranges

This means that most mating systems are plastic and can vary among populations of the same species

framework builds from the principles of sexual selection theory, namely that a population's mating system is the result of the ability of one sex to gain—and even monopolize—access to the other sex, either by associating with that sex directly or by defending territories and other resources Members of the limited sex should therefore attempt to control access to members of the limiting sex, often by regulating the resources that they need to survive and reproduce. In many species, the spatial dispersion of food or other key resources, as well as the temporal availability of receptive mates, influences one sex's ability to do this. In general, the greater the potential to monopolize mates or resources, the greater the likelihood that mating systems in which one sex mates multiply will evolve Thus, polygyny can evolve when males are able to monopolize access to multiple females,

that one or both mates in most birds that form monogamous pair-bonds are not as faithful as they seem. Social monogamy (the pairing of a male and female) does not equate to genetic monogamy (when pairs produce and rear only their own genetic offspring).

in the vast majority of bird species, one or both members of a pair-bond engage in extra-pair fertilizations being monogamous may be safer and more rewarding. Costs of mating multiply can include the time and energy spent searching for and mating with several partners (who may be spaced far apart because food resources are widely distributed), the risk of being killed by a predator during these forays and when mating, and the chance of acquiring a sexually transmitted disease from some mate then we would expect the immune systems of species that mate multiply to be stronger than those of related species that have a greater tendency toward monogamy. Nunn and his colleagues measured immune system strength across the spectrum of mating systems by looking at data on white blood cell counts from large numbers of adult females of a variety of primate species white blood cell counts of healthy individuals were indeed higher (but within the normal range) in females of the more polyandrous species (FIGURE 10.2) (Nunn et al. 2000). The same relationship between white blood cell count and the number of mating partners a female has was also found in carnivores (Nunn et al. 2003), and similar results have been observed in birds. This can occur when potential mates do not form groups and roam widely, making them costly to locate (mate limitation hypothesis), when individuals have the ability to restrict mating behavior in their partner (mate guarding hypothesis), As we saw in Chapter 9, many males guard their mates when they are receptive to prevent them from seeking extra-pair fertilizations, a behavior consistent with the mate guarding hypothesis. Recall also that mate guarding by males results in monogamy for certain species of spiders, in which the male gives his all, quite literally, to his first mate when resources are so critical to successful reproduction that both parents are necessary to rear young (mate assistance hypothesis) , or when the risk of infanticide is high and having a partner can help provide protection against infanticidal males (infanticide hypothesis)-Parental care plays a central role in the mate assistance hypothesis, which proposes that a male remains with a single female to help her in various ways but generally because paternal care and protection of offspring Spanish field using video cameras to monitor burrows showed that guarded females were much less likely than unguarded ones to fall victim to predators, primarily birds. Thus, male burying beetles may often be monogamous not because it is in their genetic interest but because females force them to be

but let's now consider multiple mating in males (polygyny), which is by far the most common form of mating system in nature.

in the vast majority of species, female resource needs and reproductive behaviors create the circumstances that determine which competitive and display maneuvers will provide payoffs for males

Dunnocks too receive some indirect genetic benefits in the form of an amelioration of the negative effects of inbreeding (Santos et al. 2015), in addition to the direct benefits. Together, these studies remind us that females can, and in some species do, receive both direct and indirect benefits from mating with several males

inbreeding avoidance=indirect

One reason that females might choose more genetically compatible males is to produce offspring that are more heterozygous (Westneat et al. 1990). According to this genetic diversity hypothesis, females benefit by increasing the heterozygosity (genetic diversity) of individual offspring

level, those offspring with two different forms of a given gene often enjoy an advantage over homozygotes, which are more likely to carry two recessive alleles that might cause defects no chance of two recessive alleles that might cause defects might allow at least some members of a colony to withstand a disease outbreak or some offspring produced in a single breeding bout to survive in a range of environmental conditions. females that are socially bonded with genetically similar individuals will be prime candidates to mate with other males that are either genetically dissimilar or highly heterozygous themselves Dustin Rubenstein found that female superb starlings (Lamprotornis superbus) that went looking for extra-pair mates outside of their social groups tended to have social partners that were less heterozygous than they were (

When resources are evenly distributed in space but females form groups to better access those resources or to help dilute the risk of predation,

males can simply FOLLOW THESE FEMALE GROUP and guard a group of females, more easily gaining access to reproductively ready females at the appropriate time (female defense polygyny hypothesis)

And if females are unlikely to go in search of groups of males or frequent places such as a potential lek site regularly, what is a male to do?

males may simply try to find scarce receptive females before other males do. Photinus firefly, for example, can appear almost anywhere over wide swaths of Florida woodland. Searching males of this species make no effort to be territorial; instead, they fly, and fly, and fly some more. In other words, they scramble to find females as quickly as they can Mating success in this species almost certainly goes to those searchers that are the most persistent, durable, and perceptive, not the most aggressive The first male to find an estrous female and copulate with her will fertilize about 75 percent of her ova, even if she mates again. Given the widely scattered distribution of females and the first-male fertilization advantage, the ability to keep searching should greatly affect a male's reproductive success scramble need persistence When researchers experimentally removed several females from their home sites, returning males spent more time searching for those missing females that had been on the verge of estrus. Moreover, the males did not simply inspect places that the females had used heavily, such as their burrows, but instead biased their searches in favor of the spots where they had actually interacted with about-to-become-receptive females small groups (3 females and 3 males) in large pools exhibited scramble competition, but when placed in small pools with large groups (12 females and 12 males), the same animals often exhibited female defense polygyny whereby the largest male drove other males into hiding

Males may also be able to maintain some control over mating by influencing whether or not their sperm fertilizes a female's eggs. I

males strategically allocate sperm according to the number of mates a female has, though dominant and subordinate males do so differently (Pizzari et al. 2003). That is, as the number of mates a female had increased from one to three, dominant males increased their sperm investment, whereas subdominants maximized their investment in the presence of just one competitor Dominant males have privileged control over copulations, and the presence of other males may represent an increased risk of another male inseminating the same female. However, since subdominant males cannot prevent females from copulating with other males, they may be selected to save sperm for less competitive copulation opportunities in the future. dom males can prevent promisc from breeding with others Male red jungle fowl adjust their sperm investment according to how many other mates a female has. Relative sperm investment of dominant (dark blue bars) and subdominant (light blue bars) males according to female promiscuity: dominant males steadily increased relative sperm investment as the number of competitors increased, whereas subdominants decreased their investment when the number of competitors increased beyond one. Relative

In contrast, ? can evolve when ? sex is able to ? access to mates or resources. When resources or access to mates drive both sexes to live together in long-term associations because neither sex is able to gain an advantage over the other, ? can evolve

monogamy, neither monopolize polygynandry=neither big advantage on which sex is limiting and the degree to which the other sex controls resource access or monopolizes mates costs of parental care, and sexual conflict between males and females over mating decisions interact to influence the type of mating system that a population or species exhibits.

FIGURE 10.25 Female defense polygyny in the greater spear-nosed bat (Phyllostomus hastatus). A large male (bottom right) guards a roosting cluster of smaller females. A successful male may sire as many as 50 offspring with his harem females in a year

n the greater spear-nosed bat ( MALES GUARD ROOSTING CLUSTER Thus, given the existence of female groups, female defense polygyny is the standard male tactic in mammals

In many animal species, females do not live together permanently, but a male may still become polygynous if he can control access to resources that females visit on occasion

not following female groups but access resources they visit Female associations in Grevy's zebra are much shorter lived than those in the plains zebra, and groups of females are not overseen by a male. What explains this difference in group formation and mating system in these two closely related species? Plains zebras occur in slightly wetter regions of Africa where grass and water sources are more readily accessible and evenly spread on the landscape, whereas Grevy's zebras live in more arid regions where most females wander far and wide in search of water and grass that is both scarce and more heterogeneously distributed more scarce resource in plains area where resource-defense polygyny occurs Plains zebra males can monopolize both receptive and (temporarily) nonreceptive females by guarding groups for extended periods of time. But since receptive Grevy's females rarely associate with nonreceptive females, it pays males to set up territories near water where the receptive females spend most of their time Dominant Grevy's males are able to defend the best territories where more females are likely to be Once again, we can see how the distribution of females, which is affected by their resource needs and grouping decisions, dictates male reproductive decisions and the adoption of different forms of polygynous mating systems

However, there are several species in which both sexes mate multiply. Behavioral biologists refer to this type of mating system as polygynandry or promiscuity

polygynandry refers to cases where there are pair-bonds between males and females that tend to live together in multi-sex groups, whereas promiscuity describes cases when mating occurs in the absence of long-term relationships promiscuity=mating without social bond polygynandry does have pair-bonds between males and females via multi-sex group The dunnock is perhaps one of the prime examples of this plasticity in mating behavior. Dunnocks exhibit not just polyandry and polygyny, but also monogamy and polygynandry The majority of the polygynandrous groups consisted of two males and two females, but there were some cases of groups with two males and three females, and even some larger groups. This variation in dunnock mating systems is thought to be a result of resource availability and sexual conflict, and both monogamy and polygynandry are cases where neither sex is able to gain an advantage at the expense of the other Individuals form groups partly to have multiple individuals available to help rear young. Although dominant males typically gain a higher share of the reproduction than subordinates, both types of males actively engage in parental care at nests ( both types of males actively engage in parental care at nests (Hartley et al. 1995). Thus, in the dunnock and the alpine accentor, the density of both birds and resources drives grouping patterns. The need for additional parental care facilitates this grouping and influences multiple mating in both sexes

When these matings involve long-term relationships between the males and females, often necessary to rear the young, the mating system is known as ?. In contrast, when there is no formal association between mates beyond sperm transfer, the mating system is called ?

polygynandry, promiscuity=only sperm

This work in ? demonstrates that when there is a free choice between a superior territory and an inferior one, it can pay a female to pick the better site even if she has to share it with another female

red-winged blackbirds, even if she has to share it with another female with whom male already mated

male mating tactics are an evolved response to female ? needs and to the ecological factors that determine the ? of ? females.

reproductive spatial distribution of receptive females

In contrast, when resources are clumped, attract multiple females, and are easily defended by males, males will simply guard the resources—and by extension the females—by setting up a territory (?).

resource defense polygyny hypothesis=SETING UP TERRITORY

if they could experimentally boost the quality of territories held by already mated males while lowering the value of territories controlled by unmated males

then mate-searching females should reverse their usual preference. They tested this prediction by manipulating pairs of red-winged blackbird territories in such a way that one of the two sites contained one nesting female and some extra nesting habitat Females that made this choice reared almost twice as many young on average as latecomers that had to make do with an onshore nesting platform in what became a monogamous male's territory