Evolution of Mating Systems - Behavior of Animal - Solved Quiz, Exercises of Biology

Download Evolution of Mating Systems - Behavior of Animal - Solved Quiz and more Exercises Biology in PDF only on Docsity! Chapter 11: The Evolution of Mating Systems 11.1 We began this chapter with a mention of male monogamy in the honey bee. Try to explain the male’s suicidal mating behavior in light of the alternative hypotheses on male monogamy discussed on pages 370–373 in the textbook. Also include in your list one hypothesis based on group selection theory. What predictions follow from the different explanations you have considered? What data are required to resolve the issue? A mate guarding hypothesis is perhaps the most plausible, with the male sacrificing a portion of his body to seal the genitalia of his partner as the cost of losing any additional chances to mate. But this action could be explained in terms of mate-assistance if females gain by having males provide them with a shield that could block any unwanted mating attempts by other males. And the male’s sacrifice could even be construed as the by- product of female-enforced monogamy if the genitalia of a queen honeybee are such that they can hold the male’s genital apparatus and not let go, forcing him to sacrifice all if he is to mate. A group selectionist hypothesis is that the deaths of males helps keep the population of honey bees under control so that they do not become too large for their own good. The mate guarding and mate assistance hypotheses yield the prediction that females with male genitalia in place are less likely to mate again than unmated females or females from whom the genitalic plug has been removed. The female-enforced hypothesis leads to the prediction that the male’s sacrifice is not voluntary but reflects special design features of the female’s genitalia. The group selectionist hypothesis predicts that the males’ deaths keep some females from mating, thereby lowering the overall potential for growth in some honey bee populations. In order to resolve the issue, data on the frequency of multiple mating by females and the reproductive anatomy of the female are needed as well as information on the number of unmated queens in an area. The fact is that almost all females mate with large numbers of males, thanks in part to their ability to remove the mating sign from their body. However, it is possible that they would be mated more often if they did not have the option of leaving the sign in place after having mated a sufficient number of times (from their perspective). 11.2 In the starling, some males acquire several mates but do not assist them, while other monogamous males work with their only partner to rear their brood together. Sometimes when there are two females nesting on a male’s territory, the first female to settle there attacks the clutch of the other female, piercing her companion’s eggs with her beak. Why might she do so, and what kind of monogamy could result from her actions? Under what circumstances would the female’s behavior actually qualify as a form of parental investment? Perhaps by destroying the eggs of a companion female, the killer female drives her rival away and thereby restores the parental option of her male partner. If so, we have here a case of female-enforced monogamy that requires the female to take costly actions, given Docsity.com that the egg-destroying female may well encounter strong resistance from the mother of those eggs. These costs could be outweighed by the benefit of receiving greater care for her current crop of eggs from her necessarily monogamous mate, in which case her destructive behavior can be considered a kind of parental investment. 11.3 In a small African antelope called Kirk’s dik-dik, most males and females live in monogamous pairs. Evaluate alternative hypotheses for monogamy in this species in light of the following evidence: the presence of males does not affect the survival of their offspring; males conceal the female’s estrous condition by scent-marking over all odors deposited by their mates in their territory; males sire their social partner’s offspring; females left unaccompanied wander from the pair’s territory; some territories contain five times the food resources of others; the few polygynous associations observed do not occupy larger, or richer, territories than monogamous pairs of dik-diks. The fact that male presence does not boost offspring survival would seem to rule out the mate assistance hypothesis; the fact that males conceal female estrous condition is consistent with the mate guarding hypothesis for monogamy as is the finding that males actually sire their partner’s offspring. Mate guarding is also implicated in the tendency of unaccompanied females to wander away to places where they might be contacted by other males. Male territoriality is not focused on resources, judging from the disparity in resources contained within dik-dik territories, but instead is apparently focused directly on the female herself. Because females do not cluster in richer sites, it is hard for a male to acquire multiple mates and so he instead attempts to insure that his one and only mate will copulate only with him. 11.4 In their classic paper on mating systems, Steve Emlen and Lew Oring suggested that two ecological factors could promote the evolution of monogamy: a high degree of synchrony in reproductive cycling within a population and a highly dispersed distribution of receptive females. Try to reconstruct the logic of these predictions and then make counterarguments to the effect that synchronized breeding could facilitate acquisition of multiple mates while a relatively dense population of receptive females might actually promote monogamy. Emlen and Oring’s argument was that when most females are receptive at the same time, then a male will not have time to go from one female to the next, and so will be constrained to be monogamous. This outcome would be particularly likely if females were highly dispersed because of the time costs of travel between females. On the other hand, synchronized breeding by females creates a large pool of potential mates for the male that can attract several females to him more or less simultaneously. And if a female became unreceptive immediately or soon after mating because of the restricted period of breeding, then a male that left one female for another would run a relatively low risk of having her copulate with a competitor. And, although it seems at first glance that a dispersed distribution of females would facilitate monogamy, on the other hand, if females are densely packed, then so too would Docsity.com Female dunnocks adjust their copulatory tactics so as to increase the number of matings with the male who has copulated relatively few times with them. Alpine accentor females should, in contrast, bias their matings toward the male that has mated most often with them (i.e., the alpha male) and to avoid mating with the beta male, a response that increases the likelihood of maximizing the assistance received from the alpha male. 11.10 Todd Shelly did an experiment with the Mediterranean fruit fly, a lekking species, in which he placed two cups with wire mesh tops containing different numbers of males in a coffee bush [1092]. After the cups were in position, he released 400 females in another coffee bush about 10 meters away. He then counted, at 10-minute intervals, the number of males in each cup releasing pheromones (signaling males evert an abdominal pheromone gland) and the number of females perched on or near each cup. Each trial lasted 80 minutes, and he did 30 trials in all. The data he collected are presented in Figure 11.39 in the textbook. Reconstruct the science underlying this research, working from the graphs in whatever direction makes sense until you have the causal question, hypothesis, prediction, test, and scientific conclusion. You should be able to relate the work to one of the hypotheses described in this section on why males aggregate at leks. Causal question: Why do males of the Mediterranean fruit fly form groups when attracting females? Hypothesis: Males in large group attract a disproportionately large number of females to them, thereby boosting the reproductive success of individual males. Prediction: If you were to do an experiment in which females had a choice between a large and a small group of lekking males, the females should accumulate at the site with the greater number of males so that the ratio of females to individual males was higher at this site. Test: Do the experiment that Shelly did and collect the data shown in Figure 11.39, which show that the frequency distribution of the ratios of female sightings to calling males is skewed toward the higher ratios for the larger of the two groups tested. Conclusion: The hypothesis is supported. 11.11 One of the possible benefits to females of participating in lek mating systems is the selection of mates of exceptional genetic quality. This form of sexual selection should tend to reduce genetic variation among males of lekking species over time. (Why?) What significance would the elimination of genetic variation among males have for the argument that females of modern species go to leks to choose a superior mate? Might the phenomenon of genetic compatibility help us out of this pickle? But is the finding that a very few males monopolize matings at most leks consistent with the suggestion that females visit leks to secure sperm from a genetically compatible partner? If females gain from going to leks because they secure the very best genes from the very best males, then after a relatively few generations, there will be little remaining genetic Docsity.com variation within such a species. If genetic variation is low or nil among males, then females have little to gain by going to leks, which should lead to the evolution of some other mating system. But if females were really trying unconsciously to get compatible genes, not the very best ones in some absolute sense, then different alleles could persist within a species over the long haul because some forms matched well with some female genotypes while others were compatible with different female genotypes. Nonetheless, the fact that in typical lekking species a great many females mate with the same handful of males is not consistent with the idea that females visit leks to get genetically compatible sperm for their eggs. Docsity.com