My Ph.D. research has examined the evolution of mating preferences and their role in speciation. I have addressed these topics empirically, using sympatric species pairs of limnetic and benthic threespine sticklebacks, and theoretically, with multilocus population genetics. Sticklebacks are small fish that occur in lakes, streams and estuaries throughout British Columbia. Most lakes contain one type of stickleback, however, several lakes support two differentially adapted sympatric species: a large benthic form (benthic), and a smaller zooplanktivorous form (limnetic). Chapter 2 examines the role of species interactions in shaping male mating preferences. I determined that the mate preferences of the small species have shifted from preferring large females (the ancestral state) to preferring small females due either to selection against hybrids (reinforcement), or to egg predation by the larger benthic species. Chapter 3 explores the idea that sexual imprinting may facilitate assortative mating between benthic and limnetic sticklebacks. Sexual imprinting occurs when individuals imprint on the phenotype of their parents, and subsequently prefer mates that resemble their parents. The results suggested that sexual imprinting does not contribute to assortative mating between the sympatric species pairs, implying that genetics are more important than early learning for the formation of mate preferences. Chapter 4 focuses on differences in male breeding colour between benthics and limnetics. The results reveal that limnetic males have more intense red and blue coloration than benthic and solitary males. These differences in colour could be due to reinforcement, to differences in visual sensitivity of females, or to territorial interactions between males. Chapter 5 examines the evolution of female mating preferences under different scenarios of sex-linkage, when the male display trait is sexually antagonistic. Theoretical analysis suggests that sexually antagonistic traits on the X chromosome (males XY, females XX), females will evolve to prefer mates carrying alleles beneficial to their daughters. In contrast, with a Z-linked trait (males ZZ, females ZW), females more often evolve preferences for mates carrying alleles beneficial to their sons (e.g., flashy displays). This provides an explanation for why males in ZW species have more elaborate sexual displays than males in XY species.

My Ph.D. research has examined the evolution of mating preferences and their role in speciation. I have addressed these topics empirically, using sympatric species pairs of limnetic and benthic threespine sticklebacks, and theoretically, with multilocus population genetics. Sticklebacks are small fish that occur in lakes, streams and estuaries throughout British Columbia. Most lakes contain one type of stickleback, however, several lakes support two differentially adapted sympatric species: a large benthic form (benthic), and a smaller zooplanktivorous form (limnetic). Chapter 2 examines the role of species interactions in shaping male mating preferences. I determined that the mate preferences of the small species have shifted from preferring large females (the ancestral state) to preferring small females due either to selection against hybrids (reinforcement), or to egg predation by the larger benthic species. Chapter 3 explores the idea that sexual imprinting may facilitate assortative mating between benthic and limnetic sticklebacks. Sexual imprinting occurs when individuals imprint on the phenotype of their parents, and subsequently prefer mates that resemble their parents. The results suggested that sexual imprinting does not contribute to assortative mating between the sympatric species pairs, implying that genetics are more important than early learning for the formation of mate preferences. Chapter 4 focuses on differences in male breeding colour between benthics and limnetics. The results reveal that limnetic males have more intense red and blue coloration than benthic and solitary males. These differences in colour could be due to reinforcement, to differences in visual sensitivity of females, or to territorial interactions between males. Chapter 5 examines the evolution of female mating preferences under different scenarios of sex-linkage, when the male display trait is sexually antagonistic. Theoretical analysis suggests that sexually antagonistic traits on the X chromosome (males XY, females XX), females will evolve to prefer mates carrying alleles beneficial to their daughters. In contrast, with a Z-linked trait (males ZZ, females ZW), females more often evolve preferences for mates carrying alleles beneficial to their sons (e.g., flashy displays). This provides an explanation for why males in ZW species have more elaborate sexual displays than males in XY species.

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Sexually selected traits are among the most costly, complex, and conspicuous elements of the phenotype. In polygynous reproductive systems, they evolve under strong selection by females. Why females favor those traits, however, is an on-going debate. Here, I use túngara frogs as a model system to study the evolution of communication under sexual selection. The wealth of available information on the behavior, neurophysiology, and reproductive biology of túngara frogs make them an ideal system to understand the patterns of signal evolution and explore the processes that have shaped them. In chapter 1 and 2, I review the taxonomy of túngara frogs (Engystomops) from western Ecuador. I describe three new species including their external morphology and advertisement calls. In chapter 3, I explore the phylogenetic relationships of túngara frogs, testing the support for alternative relationships previously reported for this group. The new phylogeny provides the framework for the comparative analysis carried out in chapters 4 and 5. In chapter 4, I present new female preference and male advertisement call data to test the sensory exploitation hypothesis of sexual selection. Using ancestral character reconstruction, I found that female preferences for complex calls did not originated before the appearance of complex calls, as predicted by sensory exploitation. Instead, my results suggest that the origin of complex calls and their preference originated at similar times. Finally, in chapter 5, I analyze the macroevolutionary patterns of call variation in male túngara frogs. A generalized least squares model demonstrates that advertisement calls have a strong phylogenetic signal. Although most species in Engystomops have distinctive calls, they share a common acoustic structure with two components that evolve at different rates. I did not found evidence of greater call differentiation among sympatric species relative to allopatric species.

Many species of caridean shrimp are protandrous hermaphrodites, maturing initially as males but developing into females as they age and grow. A unique sexual system was recently discovered in the peppermint shrimp, Lysmata wurdemanni. In this species, individuals are initially male, but become simultaneous functional hermaphrodites over time. As in most caridean shrimp, L. wurdemanni can mate as a male during the intermoult period, but can reproduce through female function for only a short period after moulting. Ecdysis does not occur en masse in this species, and thus the operational sex ratio found in populations of L. wurdemanni is extremely male-biased. Sexual selection theory suggests that these conditions will result in increased competition for access to mates. Evolutionary pressures should therefore have selected for mechanisms that permit individuals to quickly identify and locate potential mating partners. L. wurdemanni were exposed to chemical stimuli collected from recently moulted conspecifics of varying reproductive condition. Test animals were able to distinguish among the different conditions, and physically manipulated only the plastic nozzle used to pump solutions collected from shrimp with ovaries filled with vitellogenic oocytes. It was subsequently hypothesized that methyl farnesoate, a hormone associated with ovarian maturation in crustaceans, might be a key component of sex pheromones used by L. wurdemanni. However, a series of methyl farnesoate concentrations did not elicit responses, indicating this species does not use this hormone alone when determining reproductive condition. Reproductive behaviour in L. wurdemanni was observed to differ both before and after copulation, as well as with increasing population density. Intermoult individuals were more likely to approach, follow and remain in the vicinity of a near-moult shrimp before mating could occur, and under high density conditions. The near-moult shrimp approached conspecifics only under low density conditions, and performed rapid escape behaviours only after copulation had occurred. The unusual occurrence of epibiota upon L. wurdemanni was described, and the location, size and age of barnacles quantified. The effect of salinity upon grooming activities was tested. Results indicated that carapace grooming was depressed at low salinities, and could account for the considerable epibiota found in this region.

Sex-specific calls are used in male-male agonistic encounters and male-female courtship in many animal species. The ring-tailed lemur (Lemur catta) is a gregarious Malagasy strepsirhine with twenty-two distinct vocalizations for adults, including two male-specific vocalizations and an additional vocalization with male-specific functions: the howl, the squeal, and the purr. Proposed intra-sexual agonistic functions for these three vocalizations have never been empirically tested. This study’s purpose was to investigate the functions of howling, squealing, and purring in the ring-tailed lemur, and to assess the relationships between the rates of these vocalizations and male dominance. From March to July 2010, I collected 600 hours of total data and 480 hours of focal data on male ring-tailed lemurs aged three and older at Beza Mahafaly Special Reserve, Madagascar. I observed each male continuously for 30 minutes at a time and noted behaviours including all vocalizations and all agonism using one–zero sampling at 2.5-min intervals. I calculated male dominance rank and vocalization rates from these data. My results indicated that male dominance rank is correlated with male purring rate and with squealing rate, but not with howling rate. Male purring rate increased during intra-sexual agonism and was associated with aggression in agonistic encounters. Squealing rate increased during male-male agonism and indicated both aggression and submission in male-male encounters. Howling rate increased during inter-group encounters and a greater number of males participated in multi-male howling choruses when non-group members were present. Purring and squealing are agonistic vocalizations and used in male-male agonism in the ring-tailed lemur, while howling is used in inter-group encounters.

Sex-specific calls are used in male-male agonistic encounters and male-female courtship in many animal species. The ring-tailed lemur (Lemur catta) is a gregarious Malagasy strepsirhine with twenty-two distinct vocalizations for adults, including two male-specific vocalizations and an additional vocalization with male-specific functions: the howl, the squeal, and the purr. Proposed intra-sexual agonistic functions for these three vocalizations have never been empirically tested. This study’s purpose was to investigate the functions of howling, squealing, and purring in the ring-tailed lemur, and to assess the relationships between the rates of these vocalizations and male dominance. From March to July 2010, I collected 600 hours of total data and 480 hours of focal data on male ring-tailed lemurs aged three and older at Beza Mahafaly Special Reserve, Madagascar. I observed each male continuously for 30 minutes at a time and noted behaviours including all vocalizations and all agonism using one–zero sampling at 2.5-min intervals. I calculated male dominance rank and vocalization rates from these data. My results indicated that male dominance rank is correlated with male purring rate and with squealing rate, but not with howling rate. Male purring rate increased during intra-sexual agonism and was associated with aggression in agonistic encounters. Squealing rate increased during male-male agonism and indicated both aggression and submission in male-male encounters. Howling rate increased during inter-group encounters and a greater number of males participated in multi-male howling choruses when non-group members were present. Purring and squealing are agonistic vocalizations and used in male-male agonism in the ring-tailed lemur, while howling is used in inter-group encounters.

A recent hypothesis for explaining blue-green eggs in birds suggests that they may be a sexually selected signal of female (and thus nestling) quality that males use to make parental investment decisions. Although this hypothesis has found mixed correlational support in a few species, well-controlled experimental support has been lacking in non-cavity-nesting species with vivid blue eggs. In this study, we isolate the influence of egg colour on male behaviour by replacing natural American robin Turdus migratorius clutches with four artificial eggs (all of the same colour) representing extremes in natural colour intensity. After incubation, three unrelated nestlings were fostered into each experimental nest immediately after the normal incubation period and parental behaviour was monitored when nestlings were 3, 6, and 9 days old. For the youngest nestlings, male provisioning rate significantly increased in the dark egg treatment, but the effect of egg colour disappeared at the older nestling stages. This result remains significant when controlling for variation in female behaviour. Male feeding rate at unmanipulated nests was also significantly related to natural egg colour. These results suggest that blue-green egg colour acts as post-mating signal of female quality in at least some cup-nesting species, but does not exclude the possibility that the blue-green pigment also serves other adaptive purposes. / Thesis (Master, Biology) -- Queen's University, 2009-05-28 13:21:06.941

The function of the complex song of the European Starling (Sturnus vulgaris) was examined. Song playback experiments showed that both male and female starlings were attracted by song, and complex song inhibited males from entering nestboxes. Wild starlings (at least two years old when first recorded) showed extensive changes in the composition of their song phrase repertoires and most also increased the size of their repertoires, which will result in a correlation between age and repertoire size in this species. Females prefer males that have more complex song, and this preference remained significant when preferences for certain nest sites were controlled. Males with larger repertoires did not spend more time incubating or make more feeding visits to nestlings than did males with smaller repertoires. The evolution of complex song in the European starling is consistent with an age-indicator model of sexual selection, in which aspects of male quality correlated with age are advertised by the complexity of male song.

The occurrence of three reproductive tactics in a population of American redstarts was estimated: extra-pair fertilization, egg-dumping, and male polyterritoriality. Using DNA fingerprinting we show that none of 108 nestlings samples were the result of egg dumping. In contrast, 40% of nestlings were the result of extra-pair fertilizations. Males sired a greater proportion of their broods as they aged. In addition, promiscuous females were never fertilized by males that were younger than their social mates. Whether the poor reproductive performance of younger males was caused by female preference for older males or by intra-sexual competition was not determined. In any case, females would have benefited by mating with older males, if the traits that allowed the survival of the father were inherited by the females' offspring. Only three of 80 males attracted two females through polyterritoriality. One male fledged two broods: he sired both nestlings from his first brood, but none of the four nestlings from his second brood. We concluded that male redstarts can improve their reproductive success by trying to obtain extra-pair copulations, but less so by establishing a second territory.