Chapter 7- Sexual selection Flashcards

Question

Sexual selection pressure on male scorpionflies

Answer 1

Nuptial prey size has a strong effect on mating opportunities and sperm transfer, so there is strong sexual selection pressure on males to bring large nuptial gifts to females. Finding prey that is large enough is time consuming and dangerous, because increased foraging time puts males at risk of predation. Males will often sample and then discard prey that is too small, while females would never discard small prey. Selection pressure has also resulted in males stealing large prey from each other in order to obtain mating opportunities.

Answer 2

Proposes that selection favors that females choose the males with genes best suited to their particular environment. Females receive indirect benefits because their offspring receive some of the good genes that caused their mother to choose a specific mate.

Answer 3

Female pronghorns make a long search to find mates by visiting different males that already have harems of females. Females select males as mates based on a male's ability to defend his harem, and they end up mating with a small subset of males. This leads to high variance in harem size among males and to males with large harems siring a disproportionate number of offspring.

Answer 4

Researchers hypothesized that females were using current harem defense as an indicator of good genes in males. If so, males with large harems should have offspring that are more likely to survive. Researchers followed females during mating season and recorded which males were selected as mates. Offspring were marked when born and their survival was measured. The results were consistent with the hypothesis- offspring from attractive males had higher survival rates- suggests that females were selecting males based on some measure of a male's genetic quality.

Answer 5

Indicators of genetic quality that can't be manipulated by males- male pronghorns, for example, could "cheat" by pretending they have a larger harem than they actually do, so females would mate with them. Selection would actually favor males who do this.

Answer 6

Parasite resistance could be an honest indicator because it is a costly trait that is difficult to fake. Females receive an indirect benefit by selecting males with this trait. Some parasites can't be seen, but females can use other observable traits, such as body coloring, to determine which males are infected- infected males tend to have duller colors. Female birds and female sticklebacks tend to prefer brighter males.

Answer 7

A set of genes involved in disease resistance. Proteins produced by MHC genes guide the body in identifying self vs foreign cells. The MHC is extremely variable and very few people have the exact same MHC

Answer 8

Researchers predicted that animals prefer mating with others that have a dissimilar MHC. This can lead to offspring with strong immune systems. Diseases evolve so rapidly that a constantly changing set of MHC genes helps them to hit a "moving target". Females can use odors to determine whether a male is a good MHC match

Answer 9

Researchers tested undergraduate students in Switzerland, and had their blood samples tested for MHC analysis. Men were instructed to wear a cotton T-shirt for 2 nights. Women not on oral contraceptives consistently found the odors of the T-shirts from males with dissimilar MHCs more attractive. This suggests that MHC has a significant effect on female mate choice in humans.

Answer 10

Researchers hypothesized that to produce disease-resistant offspring, individuals should prefer mates with many MHC alleles rather than choosing a mate that is dissimilar in MHC related genes. Researchers capture fish from 3 populations that live in interconnected lakes. When females were given a choice between males- some had few MHC alleles and some had many- they consistently preferred the males with a greater number of MHC alleles.

Answer 11

Females use chemical cues. The greater the number of MHC alleles in an individual, the greater the number of MHC peptides (short strings of amino acids displayed on the cell surface). It was hypothesized that female sticklebacks were able to use odor to assess a male's diversity of MHC peptides, and that MHC peptide ligands (molecules that bind to proteins) were the key underlying proximate mechanism of female mate choice. Females were exposed to two water columns- one had water that had had a male swimming in it, one had water supplemented with MHC peptide ligands. The peptide ligand diversity of both the male and female were known. It was found that when a pair had a less than optimal number of MHC peptide ligands, the addition of synthetic ligands to one side of the water column made the odor on that side more attractive. When the male and female had the optimal number of MHC peptide ligands, the addition of ligands made that water column less attractive. This suggests that the number of peptide ligands was the proximate cue used to select males with good genes.

Answer 12

After females give birth, they avidly forage and raid the nest of other sticklebacks to eat their eggs. Males guard nests from female attacks. Females are actually repelled by the MHC peptide ligand odor of their former mates, because repulsion reduces the chance of a female accidentally raiding the nest of her mate and cannibalizing her own eggs

Answer 13

Centers on the relationship between alleles at two loci. One locus houses alleles that code for female preference, and the other houses alleles associated with the male trait that females prefer. Over evolutionary time, specific alleles from the two genes become associated with each other- when one allele is present in male offspring in a clutch, the other allele is likely to be present in female offspring from that clutch. It results in a feedback loop because selection will produce exaggerated traits (like color pattern in males and preference genes for color in females) in both sexes. It has a "snowball effect" where traits change dramatically over time.

Answer 14

Female flies prefer to mate with males who have eyes at the end of long stalks- variation in this trait is due to genetics. In one treatment of a study, males with the largest eye stalks were allowed to breed with females. In the second treatment, males with the shortest eye stalks were allowed to breed. In the long stalk treatment, average stalk length increases over generations, while in the short stalk group, average stalk length decreased. The study also found a positive link between the length of the male eye stalk and the female preference for this trait. Over time, when females from the short stalk line were given the choice of mating with males of different eye stalk lengths, they actually chose males with short eye stalks. Female preference changed due to selection pressure on males. In the long eye stalk line, females preferred long eye stalks, but no more so than control flies. Therefore, the evidence was contrary to predictions of the runaway selection model that selection on males produced significant changes in female eye stalk length preference.

Answer 15

State that when a male trait first emerges it is preferred by females because it elicits a neurobiological response that is already in place in females, and that this response is not associated with mating preferences initially. For example, if red berries are the most nutritious food source available to a bird species, females that eat this berries will be better at surviving and reproducing. Natural selection should therefore favor the neurobiological circuitry that allows females to hone in on red items in their environment. If red feather arose in males of the species, birds with red feathers might be chosen as mates because the female's nervous system to set to respond preferentially to red.

Answer 16

The female preference trait should predate the appearance of the male trait on a phylogenetic tree. The model describes the origin, not the maintenance, of the female preference trait.

Answer 17

Males in two species (pustulosus and coloradorum) of frog use calls to attract females. Both species have calls beginning with a high frequency whine- females pick up the whine part using the basilar papilla of the inner ear. Pustulosus frogs add a low frequency "chuck" sound to the end of their call. Pustulosus females usually prefer to mate with males that make the chuck sound, which is detected using the amphibian papilla section of the inner ear. The hypothesis was that the preference for chucks in these females was due to a pre existing sensory bias in favor of low frequency sounds. In the analysis of phylogenetic data, it was found that the common ancestor of both frog species did not use a chuck call. However, coloradorum females prefer chuck calls if a prerecorded chuck call is played. This suggests that auditory circuitry in both species is designed to prefer low frequency sounds. The preference for chucks predated the actual appearance of the chuck trait.

Answer 18

After exposure to a conditioned sexual stimulus, males are quicker to copulate, become better competitors than other males, display higher levels of courtship, and produce more sperm and more offspring. For example, male quails learned to pair an experimental chamber with a chance to mate. Males that had been conditioned to expect mating produced more sperm.

Answer 19

Young individuals imprint on the behavior and morphology of adults (usually their parents) and use these characteristics to guide their selection of mates. Imprinting usually occurs during a small window of development

Answer 20

Researchers can test the hypothesis that offspring raised by adoptive parents show different mating preferences than by those raised by biological parents. It can also examine whether mating preferences are linked to something about the behavior or morphology of the adoptive parents.

Answer 21

Offspring are raised by parents that have some novel trait introduced by a researcher

Answer 22

Researchers added a red feather to the forehead of adult mannikins as a novel trait. They hypothesized that offspring that were raised in the presence of adults with the red head feather would display a sexual preference for individuals with red feathers when they were older. Group 1 was a control where offspring were raised with their parents who did not have a feather, in group 2 both parents had the feather, in group 3 only the father had the feather, and in group 4 only the mother had the red feather. It was found that males raised with a mother with the feather preferred females with red head feathers as mates, and females raised with a father with a red feather preferred males with the feather.

Answer 23

When animals rely less on learning (like with imprinting), there is a decrease in dendritic spine density after an individual has imprinted on the phenotype of the opposite sex. Male zebra finches exhibit a decrease in dendritic spine density in the MNH area after exposure to a female. There were also fewer dendritic spines in males who had completed the process of sexual imprinting.

Answer 24

Researchers hypothesized that classical conditioning as an adult might override the effects of sexual imprinting as a juvenile. Each trial of the experiment contained a male, a female, and another female with lighter colored feathers. The brown males were raised with other brown quail, and had already sexually imprinted on the brown females. In the first phase, the male was allowed to mate with the blond female. In the second phase, the male could see the brown female but not mate with her, and he learned that the blond female's presence meant an opportunity to mate while the brown female's did not. In the last phase, time near each female was measured. It was found that blond female quails elicited a stronger response. Therefore, learning in adulthood overrode the effects of sexual imprinting.

Answer 25

When a male's probability of being preferred as a mate increases as a result of having been preferred by a female in the past. If a male has an X percent chance of mating if he hasn't recently mated and Y percent chance of mating if he has recently mated, female mate copying if found using the formula Y-X.

Answer 26

Black grouse mating arenas that are found in Finland, Wales, and Scotland. Male black grouse gather at leks and each one defends a small territory.

Answer 27

Male grouse have specific behaviors used to attract females. However, a single male grouse will usually obtain 80% of all matings on a lek. Females looking for mates will often travel to leks in groups before mating, so they will synchronize their trips to male territories in an arena. Mate choice copying seems to occur among younger females, as older females tend to mate earlier than younger females.

Answer 28

Researchers placed stuffed dummy females on 7 randomly chosen male territories in a lek before real females arrived. Males courted the dummy females and even attempted to mate with them. After observing the males, the real females were more interested in mating with a male they had observed mating, even if the mate wasn't real. This suggests that mate choice copying explains the skew in male reproductive success than a specific trait or characteristic of a territory

Answer 29

Researchers studied female mate choice in two different leks. They hypothesized that the agreement in female mate choice would increase as more females mated on a specific day, because there would be more opportunities to observe and copy mate choice. Researchers observed all interactions on a lek and compared the data with a computer simulation that estimated how often females would have chosen the same male on a lek if they hadn't been copying each other. The results supported mate choice copying, as the agreement in female mate choice increased as more females appeared. The increase occurred more quickly than would be expected by chance

Answer 30

A neurohormone secreted by the pituitary gland, plays an important role in social behaviors like mate choice, maternal bonds, and individual recognition.

Answer 31

Researchers studied mate choice copying in 3 lines of mice, two of which were normal and one of which had an OT knockout. A female was allowed to choose between two males, one of which had recently associated with an estrous female and had traces of odor in his area, and one of which hadn't. Normal females copies the mate choice of other females. However, OT knockout females did not exhibit mate choice copying- there were no other differences in learning, so the results suggest that knocking out the gene for OT has the effect of inhibiting mate choice copying behavior in mice.

Answer 32

OT "knockout" mice are mice that have deletions of the OT gene. These mice appear to learn normally, except in the context of social learning and mate choice.

Answer 33

They learn the songs from others, who are referred to as tutors.

Answer 34

Juvenile and adults cowbirds were selected from two different populations (Indiana and South Dakota), which had different social behaviors and different songs between species. Researchers conducted a cross-fostering experiment where juvenile SD birds were raised with either SD adults or IN adults. When juvenile cowbirds matured, they were observed with unfamiliar birds from the SD and IN populations. The birds tended to mate with others that came from the same rearing regime (IN or SD) in which they were raised- SD birds raised with SD adults preferred SD birds as mates. Therefore, mating preferences were dependent on the social environment in which the birds were raised. This is likely due to copying and sexual imprinting. Males copied the songs of the adult males with which they were raised regardless of the adult's population. Females also preferred songs that were like those of the males with which they were raised. This could be due to females copying the song preferences of adult females in their population or to females imprinting on the songs of males they were exposed to during development.

Answer 35

Male red deer form harems during mating season and fight off other males to defend their harems. Many males are injured while fighting, suggesting there is a strong selection pressure for accurately assessing an opponent's strength in order to avoid injury.

Answer 36

Researchers hypothesized that the main indicator of strength and fighting ability in males was roaring- roaring was likely used to assess an opponent's fighting ability in the context of harem holding. The more a male roared, the more likely he was to win a subsequent fight. Researchers used males of different sizes and abilities, and played tapes of other males roaring at different rates. When the tapes included sounds from a larger opponent, male red deer responded by being more attentive to the calls and increasing their own rate of roaring. Male-male competition for females has led to a social system involving fine tuned communication designed to maximize access to females and minimize injuries

Answer 37

A subset of male-male interactions involve one male interfering with a second who is attempting to mate with a female. This is common in amphibians and insects- in earwigs, males may displace lighter males during mating to gain access to the female. In some cases, females may solicit males to try to remove a rival during the mating event

Answer 38

It may increase the probability of mating with the highest ranking male in a group

Answer 39

Male elephant seals form large harems of females where the males are much larger than the females, Harems can include up to 40 females which are defended by a large and dominant bull seal. There is a big variation in reproductive success among males. A small percentage of males will mate, but those that do will inseminate many females.

Answer 40

Researchers marked estrous female elephant seals and tracked attempted matings with these females. Most attempted matings were protested by the females- protesting included many behaviors, like loud calls. Protesting was effective, because over 60% of attempted mating was interrupted by another male to some extent, opposed to 25% of mating that went unprotested. Females often protested subordinate males mounting more than they did dominant males, which led to an increased probability of mating between high ranking males and protesting females

Answer 41

Researchers studied the relationship between sexual size dimorphism and male-male competition in pinnipeds (seals, walruses, and sea lions). They hypothesized that sexual size dimorphism (males larger than females) would be greatest when harem size is larger and therefore when there is more male-male competition. Sexual selection for large body size in pinnipeds should act more strongly on males than females, so researchers predicted that as harem size increased, female body size would remain constant. To test these hypotheses, researchers gathered data for 38 species of pinnipeds. There was a positive correlation between harem size and sexual size dimorphism- the larger the harem size, the larger the relative size of males compared to females. The relative size of females remained constant

Answer 42

Parental, sneaker, and satellite- they can coexist within populations.

Answer 43

These males are light bodied, build nests, and are highly territorial to chase off males that come near their territory. In the days before their eggs hatch, males fan the eggs to oxygenate them and defend the nest against predators

Answer 44

Sneaker males are smaller, less aggressive, and don't hold territories. They have hiding places near a parental male and swim into a territory while the parental male and shed their sperm. Therefore, sneakers are trying to outcompete other males by sneaking into the parental male's territory and cuckolding the parental male. Sneaker males invest most heavily in sperm production due to their mating strategy, and they have the highest ratio of testes size to body size

Answer 45

Satellite males look like females and position themselves between a mating parental male and female. The parental male may treat a satellite male and a female and attempt to mate with both of them- at this point the satellite male will release its own sperm

Answer 46

Sneaker males produce more sperm per ejaculate. This is because sneaker sperm is always competing with parental sperm, but not all parentals are cuckolded. Sneakers also experience a shorter lifespan than parental fish as a cost of producing so much sperm. Sneaker sperm was found to be less likely to fertilize eggs than parental sperm.

Answer 47

Sneakers invest in producing many short lived, lower quality sperm, parentals invest in producing fewer but higher quality sperm.

Answer 48

Studies have found that males can adjust the number and quality of sperm they produce in response to competition to other males. There is a confound- males adjust sperm quality and number in response to the females they are attempting to mate with. Ideally, research should be conducted without direct male-female interactions. This occurs in some insect species

Answer 49

In some species, sperm transfer is disassociated with male-female interactions. Males deposit a capsule of sperm and proteins at the tip of a stalk, and females can pick up a spermatophore to fertilize her eggs

Answer 50

Females in this species pick up only one spermatophore and receive indirect benefits from discriminating between spermatophores. Researchers tested whether males adjusted the size and quality of spermatophores in response to male competitors, and if this impacted female choice of spermatophores. Treatment 1 was a lone male control, treatment 2 placed a male with another male who was producing spermatophores, treatment 3 placed a male with another male who was not producing sperm. It was found that males in treatment 1 produced the most spermatophores of the 3 treatments. In the presence of other males, males trade off quantity vs attractiveness of spermatophore production as a result of indirect competition from others