Browsing by Subject "Sexual selection"

Now showing 1 - 11 of 11

Condition-dependent signaling in a neotropical frog
(2022-05-05) Wilhite, Kyle Osborne; Ryan, Michael J. (Michael Joseph), 1953-; Taylor, Ryan C; Gilbert, Lawrence E; Phelps, Steve M
Communication facilitates almost every interaction between animals. Sexual selection produces signals that happen to be very energetically costly to produce. Only males who are in high condition should be able to produce these signals after basic individual needs are met. Here we investigate the effect of food intake/the ability to forage on condition and how condition influences the production of these sexual signals in the túngara frog. We recorded male calls in acoustic boxes for 9 days. After a period of no food, we found that males change certain aspects of their sexual advertisement call that are usually attractive to females. We then tested to see if females show a preference for a high or low condition male to which they preferred the high condition male. We then show that condition can predict a male’s ability to compete against other males for access to females. Males in low condition call less, make fewer complex calls, show changes in stereotypically sexually selected traits, and are less attractive to females.
Counter‐perfume : using pheromones to prevent female remating
(2018-09-05) Malouines, Clara; Gilbert, Lawrence E.
Strong selection to secure paternity in polyandrous species leads to the evolution of numerous chemicals in the male’s seminal content. These include antiaphrodisiac pheromones, which are transmitted from the male to the female during mating to render her unattractive to subsequent males. An increasing number of species have been shown to use these chemicals. Herein, I examine the taxonomic distribution of species using antiaphrodisiac pheromones, the selection pressures driving their evolution in both males and females, and the ecological interactions in which these pheromones are involved. The literature review shows a highly skewed distribution of antiaphrodisiac use; all species currently known to use them are insects with the exception of the garter snakes Thamnophis sirtalis parietalis and T. radix. Nonetheless, many taxa have not yet been tested for the presence of antiaphrodisiacs, in groups both closely and distantly related to species known to express them. Within the Insecta, there have been multiple cases of convergent evolution of antiaphrodisiac pheromones using different chemical compounds and methods of transmission. Antiaphrodisiacs usually benefit males, but their effect on females is variable as they can either prevent them from mating multiple times or help them reduce male harassment when they are unreceptive. Some indirect costs of antiaphrodisiacs also impact both males and females, but more research is needed to determine how general this pattern is. Additional research is also important to understand how antiaphrodisiacs interact with the reproductive biology and sexual communication in different species.
Deviation from panmixia via assortative mating and divergent habitat preferences
(2014-12) Jiang, Yuexin, Ph. D.; Bolnick, Daniel; Kirkpatrick, Mark, 1956-; Singer, Michael; DeAngelis, Donald; Leibold, Mathew
The speciation process is often viewed to start from panmictic populations. Understanding the evolutionary mechanisms that cause populations to deviate from panmixia is essential to understanding the initial stage of population divergence that may lead to speciation. My dissertation focuses on the evolution of two mechanisms that cause deviation from panmixia: assortative mating and divergent habitat preferences. The first chapter is a meta-analysis on published measures of the strength of assortative mating within natural animal populations. Results showed that deviation from panmixia via weak positive assortative mating was typical within natural animal populations, while disassortative mating was rare or absent. Results also suggested that assortative mating did not typically evolve adaptively, but instead as an incidental consequence of other mechanisms, such as spatial segregation. Divergent habitat uses are important drivers of spatial segregation. The second chapter revealed a behavioral mechanism of divergent habitat uses between parapatric lake and stream threespine stickleback populations. The results showed strong divergent rheotaxis between lake and stream fish during their breeding season. The divergence is likely to contribute to the sorting of lake and stream fish into their natal habitats and promote habitat-based assortative mating. The third chapter focused on the neuroanatomical and morphological mechanisms of rheotaxis. Results showed significant correlations between the numbers of neuromasts (functional units of the lateral line) and rheotaxis in both lab-reared and wild-caught threespine stickleback. Results also showed heritable divergence in lateral line structure between parapatric lake and stream stickleback, suggesting that divergent rheotaxis and the resulting divergent habitat uses are likely to have a heritable component. In summary, my dissertation revealed ultimate evolutionary mechanisms of assortative mating and proximate evolutionary mechanisms of divergent habitat uses. These results shed light on the understanding of the beginning of population divergence and ultimately speciation.
Influences of predation risk on mate evaluation and choice in female túngara frogs, Physalaemus pustulosus
(2010-05) Bonachea, Luis Alberto; Ryan, Michael J. (Michael Joseph), 1953-; Muller, Ulrich G.; Pianka, Eric R.; Bolnick, Daniel I.; Bell, Chris J.
Female choice is an important selective force shaping the evolution of communication and speciation in animals. However, predation risk can impose severe costs on longer searches and choosiness, thereby limiting the expression of female preferences for specific male traits. The work detailed in this dissertation explores how mate choice and sexual selection can be influenced by predation risk in túngara frogs. I begin by examining the effects of multiple simulated cues of predation risk on female search behavior and mate choice, taking a departure from the standard presence/absence paradigm used in similar studies to explore responses to quantitative variation in perceived predation risk. I demonstrate that light, longer travel times, and acoustic cues of predators are all sufficient to sway females away from otherwise more attractive conspecific males. Next, I explore the role of predation risk in altering female permissiveness, or the range of signals females will respond to. Using an artificial series of calls intermediate between heterospecific and conspecific, I demonstrate that predation risk dramatically increases the range of signals females will respond to, including a small number of females choosing pure heterospecific calls. Next I attempt to bridge a logical gap with our understanding of search costs, testing questions about how female search paths change with increasing distance. I demonstrate that females use more direct paths and move faster under higher light conditions, potentially reducing sampling but also reducing encounter rates with predators. Lastly, I examine factors that influence how individual females vary in their response to perceived risk, particularly hormonal state and experience. I demonstrate that naïve, captive-bred females respond to acoustic cues produced by natural predators in a manner similar to wild females and that, while hormonal state is obviously important in determining female receptivity, it has little effect directly on how females respond to predators. Together, these studies demonstrate that predation risk not only changes how females respond to conspecific males, but also increases female permissiveness and constrains search behavior. Predation risk can strongly influence and potentially even negate the expression of female preferences, having profound consequences for communication and the evolution of reproductive isolation between populations.
The Intersexual Genetic Correlation for Lifetime Fitness in the Wild and Its Implications for Sexual Selection
(Public Library of Science, 2007-08-15) Brommer, Jon E.; Kirkpatrick, Mark; Qvarnström, Anna; Gustafsson, Lars
Background -- The genetic benefits of mate choice are limited by the degree to which male and female fitness are genetically correlated. If the intersexual correlation for fitness is small or negative, choosing a highly fit mate does not necessarily result in high fitness offspring. Methodology/Principal Finding -- Using an animal-model approach on data from a pedigreed population of over 7,000 collared flycatchers (Ficedula albicollis), we estimate the intersexual genetic correlation in Lifetime Reproductive Success (LRS) in a natural population to be negative in sign (−0.85±0.6). Simulations show this estimate to be robust in sign to the effects of extra-pair parentage. The genetic benefits in this population are further limited by a low level of genetic variation for fitness in males. Conclusions/Significance -- The potential for indirect sexual selection is nullified by sexual antagonistic fitness effects in this natural population. Our findings and the scarce evidence from other studies suggest that the intersexual genetic correlation for lifetime fitness may be very low in nature. We argue that this form of conflict can, in general, both constrain and maintain sexual selection, depending on the sex-specific additive genetic variances in lifetime fitness.
Intrasexual selection and warning color evolution in an aposematic poison dart frog
(2014-05) Crothers, Laura Rose; Cummings, Molly E.; Bolnick, Daniel; Hofmann, Hans; Ryan, Michael; Summers, Kyle
Flamboyant colors are widespread throughout the animal kingdom. While many of these traits arise through sexual selection, bright coloration can also evolve through natural selection. Many aposematic species, for example, use conspicuous warning coloration to communicate their noxiousness to predators. Recent research suggests these signals can also function in the context of mate choice. Studies of warning color evolution can therefore provide new insights into how the interplay of natural and sexual selection impact the trajectory of conspicuous signal evolution. For my dissertation, I investigated the potential for male-male competition to impact the warning color evolution of a species of poison frog. I focused my work on an exceptionally bright and toxic population of the strawberry poison frog (Oophaga pumilio) where males are brighter than females, a classic signature of sexual selection. In Chapter 1, I used theoretical models of predator and frog visual systems to determine which can see the variation in bright warning coloration within this population. I found that birds, the presumed major predator, likely cannot see this variation, indicating that sexual selection can work under the radar of predators in this species. In Chapter 2, I tested the aggressive responses of males using a two-way choice paradigm that manipulated the perceived brightness of stimulus males. I found that males directed more of their behaviors to bright stimulus frogs, and brighter focal frogs more readily approached stimuli and directed more of their attention to the brighter rival. In Chapter 3, I tested the outcomes of dyadic interactions between males of varying brightness and observed male reactions to simulated intruders in their territories. I found that brighter males initiated aggressive interactions with rivals more readily, and brightness asymmetries between males settled interactions in a way that is consistent with classic hypotheses about male sexual signals. In Chapter 4 I sought to describe physiological correlates of male warning color brightness. While male brightness did not co-vary with classic measures of body condition (circulating testosterone and skin carotenoids), it did correlate with toxins sequestered from the diet and thus appears to be a reliable signal of toxicity in this population.
Investigating the female mate preference brain : identifying molecular mechanisms underlying variation in mate preference in specific regions of a swordtail (Xiphophorus nigrensis) brain
(2011-05) Wong, Ryan Ying; Hofmann, Hans (Hans A.); Cummings, Molly E.; Ryan, Michael J.; Crews, David; Zakon, Harold
Choosing with whom to mate is one of the most important decisions a female makes in her lifetime and inter-individual variation of these preferences can have important evolutionary consequences. In order to get a complete understanding of why and how females choose a mate, we must identify factors that can contribute to variation of female mate choice. Many decades of research sought to understand ultimate mechanisms of female mate choice with proximate mechanisms receiving a lot more attention in recent years. For my thesis, I identify intrinsic and extrinsic factors that correlate with individual variation of female Xiphophorus nigrensis mate preference. I provide evidence that a female’s size (e.g. age and sexual experience) as well as male behavioral displays can predict female mate preference. Using genes associated with female mate preference (neuroserpin, neurologin-3), I identify four brain regions (Dl, Dm, HV, POA) that show significant differences in gene expression between females exhibiting high preference for males relative to females displaying little mate preference. Neuroserpin and neuroligin-3 gene expression within these brain regions are also positively correlated with female mate preference behavior. Two of these brain regions (Dm and Dl) integrate multisensory information and are found in the putative teleost mesolimbic reward circuitry; the other two regions (HV and POA) are involved in sexual behaviors. With the implication of the reward circuitry, I assess whether there are changes in dopamine synthesis (via tyrosine hydroxylase, TH) in dopaminergic brain regions associated with the degree of mate preference. I do not find evidence of rapid changes (within 30 minutes) of TH expression (i.e. dopamine synthesis) in dopaminergic brain regions related to variation in female mate preference. Collectively my results suggest that mate preference behavior in the brain may be coordinated not just through regions associated with sexual response but also through forebrain areas that may integrate primary sensory information, with no associated changes of a proxy for dopamine synthesis in dopaminergic brain regions.
Mate choice and hybridization within swordtail fishes (Xiphophorus spp.) and wood warblers (family Parulidae)
(2011-05) Willis, Pamela Margaret; Ryan, Michael J. (Michael Joseph), 1953-; Bolnick, Daniel I.; Mueller, Ulrich G.; Rosenthal, Gil G.; Singer, Michael C.
Behavioral isolation is an important barrier to gene flow, contributing to the formation and maintenance of animal species. Nevertheless, hybridization occurs more commonly than is generally recognized, occurring in over ten percent of animal species in the wild. Although the genetic consequences of hybridization are of considerable interest given their evolutionary implications, the reasons that animals choose to mate with other species are less clear. I apply mate choice theory to the question of hybridization, using wood warblers (family Parulidae) and swordtail fishes (genus Xiphophorus) as study systems. Over half of the 45 species of North American wood warbler have produced hybrids. Using comparative methods, I address the questions: Do ecological and demographic factors predict hybridization in this family? Similarly, how do phylogeny, song similarity, and sympatry with congeners correlate with hybridization? As with North American wood warblers, behavioral isolation is also considered of primary importance in isolating sympatric species of swordtail fishes. Two species, X. birchmanni and X. malinche, hybridize in several locations in the wild. Through experimentation with these and other Xiphophorus species, I investigate some of the factors that cause female mate choice to vary, possibly contributing to hybridization. Specifically, I address the following questions: Do females become less choosy when predation risk is high, or encounter rates with conspecifics are low? Are female preferences for conspecifics innate, or can they be modified by experience? And, do female preferences for conspecifics vary among species, populations, or experiments? These studies illustrate the utility of treating hybridization as just another possible outcome of variation in mate choice. I find that warbler hybridization correlates with ecological and other variables, that female swordtails become more responsive to heterospecifics when mate choice is costly, and that female preferences for conspecifics are species- and context-dependent. As animal hybridization can have important evolutionary consequences, studying the factors that contribute to this variation can enhance our understanding of the evolutionary process.
Olfactory communication and sexual selection in strepsirrhines
(2009-12) Toborowsky, Carl Joshua; Lewis, Rebecca J., 1972-; Kirk, Edward C.
Although most strepsirrhines do not exhibit apparent physical signs of sexually selected traits, researchers have suggested that olfactory communication is sexually selected. The goal of this thesis is to (1) review sexual selection theory with an emphasis on sensory communication, and (2) test whether olfactory communication is sexually selected in strepsirrhines. I examined the relationships between primate mating systems and several measures of olfactory communication in 22 species: scent marking rates, the number of scent marking methods, and the volume of the main and accessory olfactory bulbs. I also evaluated qualitative data on olfactory communication in three lemur species to determine whether they meet the criteria of a sexually selected trait. Polygynandrous and monogamous species did not significantly differ from each other in scent marking rates, scent glands, or volume of the main and accessory olfactory bulbs. Three species of strepsirrhine met all criteria of having sexually selected olfactory traits, suggesting that polygynandrous lemurs are subject to sexual selection on several levels of olfactory communication.
Polymorphic mating signals and female choice in an Amazonian frog
(2014-12) Guerra, Mónica Alexandra; Ryan, Michael J. (Michael Joseph), 1953-; Cannatella, David C.; Phelps, Steve; Mueller, Ulrich; Funk, Chris
Sexual selection, more specifically mate choice, is one of the most important mechanisms responsible for signal evolution and assortative mating. My thesis integrates genetic analysis, behavioral assays and morphological observations to understand the evolution of polymorphic male mating signals in the frog Peters’ Dwarf Frogs (Physalaemus petersi). In this frog, different populations form distinct genetic clades that coincide with the type of advertisement call males produce. My thesis has four chapters: the first chapter investigates the role of sexual selection in the origin and maintenance of polymorphic mating signals and its consequences for reproductive isolation. I demonstrate strong female mate choice for male signals at a sympatric site. I propose that sexual selection is responsible for the maintenance of different call morphs in sympatric populations, and it likely contributed to the origin of polymorphic male signals. Males of P. petersi form choruses. Males that produce different call morphs are found calling together in sympatric populations. This set up the question if Peters’ Dwarf Frogs use acoustic cues to join choruses in nature. In the second chapter, I demonstrated that the males perform phonotaxis to choruses of similar call frequency. Along with the previous studies of female phonotaxis, the results suggest the pattern of discrimination of males and females are similarly based on the frequency of the call. Evolution of some behaviors results from changes in morphology; for instance, advertisement calls are normally restricted to males, which have larger larynges and muscles than females. In the third chapter, I investigate the ontogenetic morphological differences between males and females of a model in animal communication and close relative of P. petersi, the túngara frog, Physalaemus pustulosus. The results constitute the first comparison between males and females in the ontogeny of the vocal apparatus of a common frog, and contribute to the general knowledge of developmental differences in sound-producing organs. Lastly, in the fourth chapter, I investigated the developmental differences between males of two populations of Peters’ Dwarf Frog that produce different types of calls. I found the laryngeal growth is significantly different between P. petersi males that produce different types of calls.
Sexual selection in complex choruses : the interplay of male signal variation, social structure, and female mate choice
(2016-05-23) Lea, Amanda Marie, Ph. D.; Ryan, Michael J. (Michael Joseph), 1953-; Hofmann, Hans (Hans A.); Phelps, Steven; Meyers, Lauren; Farris, Hamilton
Females in many species assess variation among males’ sexual signals when choosing mates. Despite substantial empirical data demonstrating this, the role of mate choice in the evolutionary elaboration of signals among natural systems is not well understood. A major challenge is that mate choice often occurs within complex, dynamic social networks such as leks and choruses, scenarios that combine multiple interacting males, multiattribute signals, and the emergence of spatial relationships, all with the potential to influence females’ decisions. I examined the interplay of males’ social associations and females’ mate choices in túngara frogs (Physalaemus pustulosus), a model system for female mate choice but for whom interactions between male competition and mate choice were unexplored. My aim was to understand ways in which this complexity might influence the relative mating success of advertising males and ultimately, sexual signaling evolution. I conducted field studies and behavioral experiments to deconstruct spatial and neighbor association preferences among males. I found that males are highly tuned to features of their competitors’ calls, exhibiting association biases that roughly paralleled females’ mate preferences, thus supporting a dual function of advertisement calls. I tested classic chorus formation models invoking conspecific association preferences and found that phonotaxis preferences support a central role for highly attractive “hotshot” males in social structuring. I then examined consequences of these interactions for females’ mate preferences. I first tested the importance of signalers’ spatial positions, showing centrality outweighs bout-leading benefits and substantially increases inferior males’ success. I then tested females’ susceptibility to “decoy effects” and demonstrated that mate preferences were similarly reversible by presenting females with an irrelevant third option. Finally, I explored preference patterns among multiattribute signals between males and females; I found that transitivity in females’ preferences broke down among superior signals, suggesting that cyclical competition may play a fundamental role in maintaining signal diversity. Females’ preferences, in contrast with theoretical assumptions, exhibit substantial context-specificity, often paralleled by males’ strategies. These studies highlight the inextricable linkage between male competition and female mate choice and the importance of integration when assessing the opportunity for, and potency of, sexual selection via mate choice.