Animal Behavior: Infanticide and Infanticidal animals

Hanuman langur social groups

-3 social groups: A one-male group, a multi-male group (that has males and females of all ages), and an all-male group -Multi-male groups may be unstable.

Hanuman langur groups

-A group of female relatives is the permanent group. -There is one breeding male in a group of females. He has to fight hard to get that position. This is what all the males want. Other males live on the fringes or in all-male groups. The breeding male doesn't last in that position. He is constantly being challenged. -even in the multi-male groups, there is only ONE breeding male

Adolescent male lions life cycle

-Adolescent males leave their natal pride when their fathers (or the new male leaders of the pride) begin to view them as competition→ usually at about 2.5 years old -These males lead nomadic lives for two to three years, then form a coalition and seek a pride to take over -they take over a pride for a few years and during that time they have offspring

Female lion fighting behavior

-Female pride members tend not to compete or fight with each other and tend not to display the kinds of dominance behavior that are observed in many matriarchal social systems -sometimes the females will fight against coalitions trying to take over the pride. This is because the females do not want their cubs to be killed.

Jacana reproductive behaviors

-Female wattled jacanas are polyandrous (have more than one mate at a time) and have harems of up to four males. -She has a large territory that encompasses the small territories of four males. -The female lays the eggs, but the male takes care of them.

Comparison of infanticide hypotheses

-In all cases, new males (or for waterbugs and jacanas, new females) are taking over a breeding situation, and killing the kids of the previous males.

Madagascar giant water bug characteristics

-Lethocerus oculatus -over 100 different species -bigger species of giant water bugs can take vertebrate prey (ex: frog) -male parental care→ females lay the eggs and the males will take care of them. Male carries the eggs on his back

Gorillas infanticide

-Male gorillas are known to kill unweaned infants when trying to dislodge a dominant silverback male from his group. -Male gorillas that are in charge and secure can also care for infants that are not always their own. -Caring for infants is associated with increased reproductive success for male mountain gorillas

male water bug egg behavior

-Male wants to be sure that the eggs he is going to carry are his so he will mate with the female before he lets her lay eggs. -male uses its hind legs to brush debris and algae off the eggs -as the eggs hatch, male uses the scales on his hind legs to help the offspring out

waterbug infanticide process

-Male water bug guards the eggs (sometimes he carries eggs on back). He can't breed again while doing this. -Female waterbugs will stab these eggs and kill them. -Male will then mate with the infanticidal female.

Female lion reproduction

-Related females in the same pride tend to have synchronous reproduction, and they cross-suckle their cubs. -Not all litters are synchronous, but there is a big cost if you are a female and have a late batch of cubs. All your cubs are small and young compared to your sisters' cubs, and they are outcompeted. -Female lions tend to have cubs every 2 years. Litters are 1-6. The cubs are weaned between 7 and 10 months, however they are dependent upon adults in the pride until they are about 1.5 years old. -If a female's cubs are killed (after a male take over of the pride), then the female comes into estrus soon after and has more cubs. -Females are able to breed at 4 years of age and males at 5 years. -have a 2yr birth interval

Jacana infanticide process

-Territorial females sometimes attack the eggs or chicks of neighboring females. -The male who had been in the harem of the neighboring female, now mates with the infanticidal female and takes care of her eggs.

lion pride

-a group of close female relatives -a stable social unit of females that has persistence across generations -Pride sizes vary (2-40), and the pride is not always together in one place -'average' pride is 5-6 females, their offspring of both sexes, and 2-4 males

Male and female red phalarope

-have reverse sex characteristics: male is smaller and less colorful; female is larger and more colorful In photo, the left is the male and the right is the female

lion distribution

-historically, lions were found all around Africa and some parts of Europe and the Middle East -present distribution is restricted to certain areas of Africa -there is a small population of a lion species in India

hyenas and lions

-hyenas are big competitors to lions -Hyenas and other lions are the biggest competitors with lions for their own kills. -Hyenas will take carcasses from lions and lions will take carcasses from hyenas.

lions and prey

-lions can bring down really big prey -A carcass is a huge pile of resources, and everybody wants a piece→ other animals will stay around to get a piece of the carcass too (ex: hyenas and vultures)

Social states of lions: resident

-live in prides (group of female relatives) -have a pride area that they defend from other lions

animals that are infanticidal

-male lions -male Hanuman langurs (monkey species) in India -female waterbugs -female jacanas -male gorilla silverbacks

female and male water bug parental roles

-males care for the eggs -females are infanticidal and will kill eggs that are not hers; she then mates with the male and has her own eggs

Social states of lions: nomads

-singles or pairs or triplets of lions wandering widely with no fixed area. -majority of nomads are males, and all males go through the nomad stage. Some males are always nomads and are never successful at becoming pride males. -Some females are forced to become nomads if they are evicted from their pride (this is very bad news for a female because she is almost never able to join another pride)

Establishing the alpha male in the coalition

-some coalitions may have an alpha male; the alpha is decided through fighting -there is a trade off though because fighting leads to wounds and infection which will make it harder for that coalition to fight against another group of males that comes to try to take over the pride

Infanticide hypothesis: Population regulation

-states that infanticide is a form of population regulation -this is a group selection hypothesis ex: Langur groups that got too big ultimately went extinct from lack of resources. Groups that regulated their population were the ones that remained and spread.

Infanticide hypothesis: Social pathology

-suggests that under unnatural, overcrowded conditions (ex: feeding by humans) male-male competition gets intense, males get hyperaggressive, and their aggression spills over into assaulting females and killing infants ex: This hypothesis points out that, because of human feeding, many langur groups got huge causing the males to get aggressive

lions and social ability

-the only cat species that live in groups -the only "social" cat species -The main social unit is the pride

Infanticide hypothesis: cannibalism

-this hypothesis suggests that males commit infanticide after takeovers in order to eat meat and replenish their reserves that were dangerously depleted by the effort of a takeover. -taking over takes a lot of energy; the males want replenishing food so they eat the infants

Infanticide hypothesis: Sexual competition

-this hypothesis suggests that males just taking over a group are killing the offspring of nursing females in order to shorten the time it takes for those females to come into estrus (a recurring period of sexual receptivity and fertility in many female mammals) -thereby to get more offspring during their tenure (their "reign" over the group) than they otherwise would, new despots kill nursing infants. -A new male's tenure in a group is always at risk, and males who wait for kids that aren't theirs to be weaned or raised, lose out. -developed from observations of langurs. It also fits gorillas and lions.

tigers vs lions

-tigers are another cat species -tend to be more solitary except for mothers and their offspring -tiger range is over east and south Asia; Siberian tigers are in Russia

Infanticide hypotheses

1. population regulation 2. social pathology 3. sexual competition 4. cannibalism

water bug mating

After every few eggs that the female produces, the male and female will mate again so that she can produce more eggs. This is done to ensure that the eggs she is producing are the male's eggs.

why are lions social?

Carcass defense may be the biggest reason lions are social (there is no agreement in the literature as to what the reason is).

What determines whether a lion pride stays together in one place or not?

Ecology, seasonality, and prey availability

coalitions

Groups of 2-4 male lions (brothers and cousins)

hyenas similarities to lions

Hyenas are another group living species - the group is often called a "clan" and it is a group of related females.

waterbugs and jacanas infanticide

In Jacanas (a bird, the lilytrotter) and in waterbugs, both species in which males care for kids, females have been observed to be infanticidal and then mate with the male who has been just freed from parental care (of some other female's kids).

Hanuman langur social groups and infanticide

Infanticide is most common in one-male groups, but it has been observed in multi-male groups.

Coalition size and years of pride take over

Male coalitions of two lions tend to rule a pride for no more than 2.5 years, long enough for one set of cubs to be reared. Coalitions of three and four tend to rule a pride for longer than 3 years.

Male lions and infanticide

Male lions are infanticidal, and will kill all unweaned cubs when they take over a pride. These are the cubs of the previous males. Females come into estrus quickly after their cubs are killed and mate with the killers. *If a female is still nursing, she is not ready to breed again. Male lions that take over a pride will kill the unweaned cubs so that the mothers may breed again. Male lions want to have offspring as quickly as possible

How do males become members of a pride?

Males become a member of a pride only by fighting with and ousting the previous pride males. They must take over a pride. Single males are almost never able to take over a pride. They try to take over a pride in groups called coalitions

Sex and lion pride

Males: -The males in the pride only stay in group for about 2 or 2.5 years on average. -Male pride members are typically each other's brothers or cousins. They are not related to the females. Females: -females in a pride are typically sisters and/or cousins (relatives) -Female membership in a pride only changes with births and deaths.

Social states of lions

Resident and nomad

water bug egg hatching

The offspring first pop the top of the egg open. Then the bug starts squeezing the top part of their bodies out of the egg. Once they get about half way out of the egg, they start swaying back and forth to help them get out of the egg. Eventually they are able to free their legs. Once the legs are free, they rest for a few minutes. The offspring fall out of the eggs in order (front eggs first and then back eggs) and then they drop into the water and then they will scleratize (harden). The bugs are soft and yellow when they first hatch and will turn hard and dark.

Hanuman langurs

Used as an example for infanticide in addition to the example with lions

Infanticide

act of killing an infant