ch. 24

How long does it take new species to form on Earth?

the time required varies considerably. (Read examples of both rapid and slow speciation events.)

Item 1, Part C - Gene flow and the biological species concept: Recall that the biological species concept defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring. This means that all members of these populations (called conspecifics) can contribute to a common gene pool. Conspecifics are organisms or populations that belong to the same species. Genes are transferred between conspecific populations through both direct and indirect gene flow. Biologists studying disease susceptibility in mice used genetic techniques to look for gene flow in 12 wild populations of mice. The populations (designated A through L) were located along a 210-km transect line. The researchers found evidence of gene flow between some, but not all, pairs of populations. In the grid below, a "+" indicates a pair of populations in which direct gene flow was detected, and a "-" indicates a pair that showed no evidence of direct gene flow. For help reading this grid, see Hint 2. BCDEFGHIJKLA---------+-B---------+C---+--+--D---++-+-E------+F----+-G-----H----I---J--K- The researchers discovered that the 12 populations could be organized into 3 distinct species. Populations A, B, and C each belong to a different species. Use the data in the grid to sort each population to the species to which it belongs.

Species 1 (includes populationA): k, d, f, h, i Species 2 (include population B): l, e Species 3 (includes population C): g, j (Based on the gene flow data in the grid, populations A, D, F, H, I, and K belong to one species, populations B, E, and L belong to a second species, and populations C, G, and J belong to a third species. Just as different species are kept separate by barriers to gene flow, species integrity is maintained by gene flow between populations. Even populations that are separated by large distances (such as A and K in this example) may be connected through gene flow. Gene flow can also occur between two populations that do not directly interbreed. As genes are exchanged between some populations, and those populations then exchange genes with other populations, genes can flow throughout all populations of a species.)

Item 13, Part B: Which of the following statements is best supported by the data on matings in the experimental groups? a.) The starch-adapted flies and maltose-adapted flies are not different species, but a reproductive barrier is forming between the populations. b.) The starch-adapted flies and maltose-adapted flies appear to now be separate species as defined by the biological species concept. c.) There is no evidence of reproductive isolation between the starch-adapted flies and maltose-adapted flies.

a

Which of the following has been shown to cause speciation most rapidly? a.)autopolyploidy b.) hybridization c.) differential resource exploitation d.) sexual selection e.) punctuated equilibrium

a (Autopolyploidy has been shown to produce nearly instantaneous speciation in plants.)

Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification? a.) The two forms have many genes in common. b.) The two forms interbreed often in nature, and their offspring have good survival and reproduction. c.) The two forms live in similar habitats. d.) The two forms are very similar in coloration. e.) The two forms have similar food requirements.

b

Item 13, Part D: A similar control experiment was performed with flies adapted to maltose, and similar results were obtained. What were these control experiments testing? a.) These control experiments tested whether in the process of becoming adapted to different food sources, the flies had lost the ability to reproduce. b.) These control experiments tested whether flies were more likely to choose mates from their own population than from another population adapted to the same medium. c.) These control experiments tested whether the starch-adapted flies had a greater preference for like-adapted flies than did the maltose-adapted flies.

b

Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals. These rituals involve fighting other males and making stylized movements that attract females. What type of reproductive isolation does this represent?

behavioral isolation

Item 1, Part A- Comparing Species Definitions: Three of the most prominent definitions of species are the biological species concept, the phylogenetic species concept, and the morphological species (morphospecies) concept.

biological: not applicable for extinct species morphological: relies on similarities in structures phylogenetic: based on evolutionary history morphological and phylogenetic: accommodates asexual reproduction, species acceptance criteria can be subjective morphological, phylogenetic, and biological: used by scientists in classification

Item 13, Part C: Which of the following statements is supported by the data from the control group matings? a.) Female starch flies from population #2 were more likely to mate with male flies from their own population than with flies from a different starch population. b.) Male starch-adapted flies were less likely to mate with female starch-adapted flies than with female maltose-adapted flies. c.) Flies were about as likely to mate with flies from different starch-adapted populations as with flies from their own starch-adapted population.

c

Which of the following factors would not contribute to allopatric speciation? a.) A population becomes geographically isolated from the parent population. b.) Different mutations begin to distinguish the gene pools of the separated populations. c.) Gene flow between the two populations is extensive. d.) The isolated population is exposed to different selection pressures than the ancestral population. e.) The separated population is small, and genetic drift occurs.

c

Which of the following is the first step in allopatric speciation? a.) polyploidy b.) formation of a reproductive barrier c.) geographic isolation d.) genetic drifthy e.) bridization

c (Allopatric speciation occurs when a population of organisms is geographically separated long enough for significant changes to occur. After a period of time, the populations may no longer be able to interbreed.)

Which of these is an example of temporal isolation? a.) One species is found only in New York, the other only in London. b.) One species performs a specific courtship dance. the other species does not. c.) One species is nocturnal, and the other species is not. d.) The average weight of the individuals in one species is 45 kg; in the other species the average is 290 kg. e.) One is a type of primate, the other is a type of marsupial. Submit

c (In temporal isolation, two species that breed during different times of the day cannot mix their gametes.)

Select the correct statement describing sympatric speciation. a.) Sympatric speciation has never been observed in nature. b.) Sympatric speciation is always initiated by geographic isolation of two populations. c.) Sympatric speciation can occur in a single generation.

c (Read about autopolyploidy and sympatric speciation. Return to Assignment)

According to the biological species concept, two animals are considered members of different species if they _____.

cannot mate and produce viable, fertile offspring (If two individuals cannot interbreed and produce viable, fertile offspring, they are members of different species.)

Item 13, Part A: Of the 59 matings in the experimental groups, how many were between like-adapted flies (flies adapted to the same medium)? a.) 17 b.) 22 c.) 30 d.) 42

d

True or false? A mating between a tetraploid individual and a diploid individual produces biologically fit offspring.

false (Offspring produced from this mating would be triploid and likely produce nonviable gametes with an uneven number of chromosomes.)

What prevents speciation from occurring in sympatric populations?

gene flow (Gene flow prevents speciation in sympatric populations.)

What is the most important factor that holds a gene pool of a species together and prevents speciation?

gene flow (Gene flow refers to the transfer of alleles among populations. As long as populations are exchanging alleles, speciation is unlikely.)

According to the punctuated equilibria model, ____.

most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species

Item 1, Part B- Classifying Reproductive Barriers: According to the biological species concept, individuals belong to the same species if they can interbreed in nature and produce viable, fertile offspring. Prezygotic and postzygotic barriers ensure that members of different species do not reproduce with one another. This diagram shows some of these barriers along with examples of the barriers at work. Complete the diagram by following these steps: Drag blue labels onto blue targets only to identify the two main types of reproductive barriers. Drag pink labels onto pink targets only to identify specific barriers. Drag white labels onto white targets only to identify examples of barriers.

prezygotic barriers (a): • behavioral isolation (c)... beetle mating show different spot patterns • mechanical isolation (d)... flowers accommodate different insect pollinators • habitat isolation... two fish species spawn at different depths (h) • temporal isolation (e)... birds are active during different times of the day • gametic isolation (f)... a coral's sperm can't fertilize another's eggs (i) postzygotic barriers (b): • reduced hybrid fertility (g)... offspring of two newts are sterile (j) • reduced hybrid viability... lion-tiger hybrids don't reach maturity (k)

According to the _____ model, evolution occurs in spurts; species evolve relatively rapidly then remain unchanged for long periods.

punctuated equilibrium

The largest unit within which gene flow can readily occur is a _____.

species

Which term is used to describe populations that live close enough to interbreed?

sympatry (Sympatry describes populations that live close enough to interbreed.)

Sympatric speciation is _____.

the appearance of a new species in the same area as the parent population (It is due to a radical change in the genome.)