Influence of lighting environment on social preferences in sticklebacks from two different photic habitats.I.mate preferences of wild-caught females

Ultraviolet(UV)A signals(320-400 nm)are important in mate choice in numerous species.The sensitivity for UV signals is not only assumed to be costly,but also expected to be a function of the prevailing ecological conditions.Generally,those signals are favored by selection that efficiently reach the receiver.A decisive factor for color signaling is the lighting environment,especially in aquatic habitats,as the visibility of signals,and thus costs and benefits,are instantaneously influenced by it.Although ecological aspects of color signal evolution are relatively well-studied,there is little data on specific effects of environmental UV-light conditions on signaling at these shorter wavelengths.We studied wild-caught gravid female 3-spined sticklebacks Gasterosteus aculeatus of 2 photic habitat types(tea-stained and clear-water lakes),possessing great variation in their UV transmission.In 2 treatments,tea-stained and clear-water,preferences for males viewed under UV-present(UV-1-)and UV-absent(UV-)conditions were tested.A preference for males under UV+conditions was found for females from both habitat types,thus stressing the significance of UV signals in stickleback's mate choice decisions.However,females from both habitat types showed the most pronounced preferences for males under UV-h conditions under clear-water test conditions.Moreover,reflectance measurements revealed that the carotenoid-based orange-red breeding coloration in wild-caught males of both habitat types differed significantly in color intensity(higher in clear-water males)and hue(more red shifted in clear-water males)while no significant differences in UV coloration were found.The differential reflection patterns in longer wavelengths suggest that sticklebacks of both habitat types have adapted to the respective water conditions.Adaptations of UV signals in a sexual context to ambient light conditions in both behavior and coloration seem less evident.

Influence of lighting environment on social preferences in sticklebacks from two different photic habitats.II.Shoaling and mate preferences of lab-bred fishes

Different environmental conditions may lead to diverse morphological,behavioral,and physiological adaptations of different populations of the same species.Lighting conditions,for example,vary vastly especially between aquatic habitats,and have been shown to elicit adaptations.The availability of short-wave ultraviolet(UV)light is especially fluctuating,as UV wavelengths are attenuated strongly depending on water properties.The island of North Uist,Scotland,comprises 2 differential habitat types,tea-stained and clear-water lakes,varying considerably in UV transmission.In previous studies,wild-caught 3-spined stickleback Gasterosteus aculeatus populations(3 populations of each habitat type)were tested with respect to their shoaling and mate preferences for fish viewed under UV-present and UV-absent conditions.The results revealed a habitat-dependent preference of UV cues during shoal choice(tea-stained populations:preference for UV-absent condition in tea-stained water;clear-water populations:no preference in clear-water)but an overall preference for UV-present conditions during mate choice.To assess genetic influences on these behavioral patterns,similar experiments were conducted with lab-bred F1-gen-erations of the same stickleback populations that were raised in a common environment(i.e.standardized clear-water conditions).Offspring of sticklebacks from tea-stained lakes tended to prefer shoals viewed under UV-absent conditions(only in tea-stained water),while sticklebacks from clear-water lakes showed a significant preference for the shoal viewed under UV-present conditions in clear-water but not in tea-stained water.Mate-preference experiments demonstrated that females from the tea-stained lakes significantly preferred and females from the clear-water lakes preferred by trend the male viewed under UV-present conditions in the clear-water treatment.The results for both shoaling-and mate-preference tests were largely similar for wild-caught and lab-bred sticklebacks,thus hinting at a genetic basis for the preference patterns.

Asymmetrical mate preference in recently adapted White Sands and black lava populations of Sceloporus undulatus

Speciation can proceed rapidly when natural and sexual selection act in concert. For example speciation can be ac- celerated when traits that confer a selective advantage in a particular habitat also influence mate preference. Studying parallel but evolutionarily independent instances of ecological divergence can illuminate the interaction between natural and sexual selection during speciation. Locally adapted populations of the eastern fence lizard Sceloporus undulatus have recently evolved in three different habitats in the Chihuahuan desert： blanched color morphs occur on the gypsum dunes of White Sands, melanic color morphs occur on the Carrizozo lava flow, and brown color morphs occur in the surrounding desert scrubland. In addition to dif- ferences in cryptic dorsal coloration, populations also differ in the size and color of ventral patches used for social signaling. This system therefore provides an opportunity to investigate the interplay of natural and sexual selection during rapid ecological speci- ation. We used mate preference experiments to determine whether locally adapted populations may exhibit the early stages of be- havioral reproductive isolation. We observed an asymmetrical mate preference in this system; White Sands males preferentially courted local females, while males from dark soils and black lava populations did not exhibit a preference for local mates. We also found that female behavior and ventral patch phenotype were associated with male courtship. Our results suggest that the observed preference for local mates evolved at White Sands, and we discuss the possible link between local adaptation and traits involved in mate preference in this system [Current Zoology 59 （1）： 20-30, 2013].

No Male Preference for Large Females in the Asian Common Toad(Duttaphrynus melanostictus):Effect of the Sex Ratio and Breeding System

Mating preferences are common in natural populations of animals.Numerous studies have shown that male mate choice can occur in a wide range of taxa.However,male mating preferences are still poorly understood in anurans.Sexual selection theory predicts that male mate choice is not expected to arise if 1) adult population exhibited a highly male-biased sex ratio which will diminish male mating success;2) males provide less parental care;3) mating success of males is associated with chorus tenure in which males would maximize their fitness by mating with multiple mates.We tested these predictions in the Asian common toad Duttaphrynus melanostictus from southeastern Tibet,China.Our field experimental results indicated that,the breeding population exhibited a highly male-biased sex ratio,called males did not defend sites which contain significant resources required by females and offspring,both sexes provided no parental care after egg-laying,and the toad species was characterized with prolonged breeding season chorus attendance.In male mate choice experiment,males did not show preferences for a larger gravid female over a smaller gravid female.We suggest that male mating success in the Asian common toad is likely determined by the number but not the quality of mates.Future research should focus on how sexual selection on male acoustic signaling and how female preference exert different types of selection pressure on male call traits in this Tibet toad.

The influence of female age on male mating preference and reproductive success in cabbage beetle, Colaphellus bowringi

The influence of female age on male mating preference and reproductive success has been studied using a promiscuous cabbage beetle, Colaphellus bowringi Baly （Coleoptera： Chrysomelidae）. In a simultaneous choice test, middle-aged females had significantly greater mating success than young and old females. In single pair trials, when paired with middle-aged virgin males, middle-aged females mated faster, copulated longer, and had greater fecundity and fertility than young or old females, while the longevity of males was not significantly affected by female age. This study on C. bowringi suggests that middle-aged females are more receptive to mating, which can result in the highest male reproductive success.

The evolution of male mate choice and female ornamentation： a review of mathematical models

The evolution of male preferences and of female ornaments in species with traditional sex roles （i.e., polygyny） have been highlighted as areas in need of more active research by an accumulation of recent findings. The theoretical literature on these topics is relatively small and has centered on the evolution of male choice. Mathematical models have emphasized that, under polygyny, the evolution of male preferences faces much greater competition costs than does the evolution of female preferences. We discuss ways in which costly male choice can nonetheless evolve, via （1） direct selection that favors preferences, primarily through mating with highly fecund females, （2） mechanisms that rely on indirect selection, which weakly counters competitive costs of male preferences, and （3） genetic constraints, primarily in the form of pleiotropy of male and female preferences and traits. We also review a variety of mathematical models that have elucidated how costs to male preferences can be avoided. Finally, we turn our attention to the relatively scant theoretical literature on the effects of male mate choice on the evolution of female traits. We emphasize the finding that the presence of male preferences cannot be assumed to lead to the evolution of female ornaments during polygyny, and point out situations where models have elucidated ways in which female ornaments can nevertheless evolve.

Female mate choice based on pheromone content may inhibit reproductive isolation between distinct populations of Iberian wall lizards

The Iberian wall lizard Podarcis hispanica forms part of a species complex with several morphologically and geneti- cally distinct types and populations, which may or may not be reproductively isolated. We analyzed whether female mate choice based on males＇ chemical signals may contribute to a current pre-mating reproductive isolation between two distinct populations of P. hispanica from central Spain. We experimentally examined whether females choose to establish territories on areas scent-marked by males of their own population, versus areas marked by males of the other population. Results showed that fe- males did not prefer scent-marks of males from their own population. In contrast, females seemed to attend mostly to among-individual variation in males＇ pheromones that did not differ between populations. Finally, to test for strong premating re- productive isolation, we staged intersexual encounters between males and females. The population of origin of males and females did not affect the probability nor the duration of copulations. We suggest that the different environmental conditions in each population might be selecting for different morphologies and different chemical signals of males that maximize efficiency of communication in each environment. However, females in both populations based mate choice on a similar condition-dependent signal of males. Thus, male signals and female mate choice criteria could be precluding premating reproductive isolation between these phenotypically ＂distinct＂ populations [Current Zoology 59 （2）： 210-220, 2013].

Preference status does not indicate intrinsic quality differences in Drosophila pseudoobscura

The good genes hypothesis states that choosers prefer individuals of high intrinsic quality to individuals of lower intrinsic quality.Variation in longevity is thought to reflect,in part,intrinsic quality differences of individuals in addition to the costs of mating and reproduction.Here we report longevity variation of Drosophila pseudoobscura,a species in which previous experiments have demonstrated that individual mate preferences(pre-touching mate assessments)of females and males are associated with enhanced numbers of eclosed(adult)offspring and higher egg-to-adult survival(offspring viability).Using mate assessment arenas and protocols similar to those in a previous experiment that demonstrated fitness benefits to breeders and their offspring of mating with individuals they preferred,we tested the following predictions:(i)preferred discriminatees live longer than non-preferred discriminatees;(ii)males live longer than females;and(iii)virgins live longer than mated individuals.The experiment yielded 938 individuals for longevity analysis.Sex and mating status affected longevity:males lived longer than females,virgin females lived longer than mated females,but there were no differences in longevity for mated and virgin males.Non-preferred discriminatees of both sexes survived as long as preferred discriminatees,a result inconsistent with the prediction of the good genes hypothesis for mate preferences.To our knowledge,this is the first demonstration of the cost of reproduction for females in D.pseudoobscura and of longevity variation of preferred and non-preferred discriminatees.

The evolution of sexual imprinting in socially monogamous populations

Sexual imprinting is a common mechanism of mate preference learning. It is thought to influence how traits evolve and in some cases to promote speciation. Recently there has been increasing interest in how sexual imprinting itself evolves. Theoretical work on polygynous mating systems predicts that females will evolve paternal imprinting, which means they learn to prefer phenotypes expressed by their fathers. In nature however, females of some species learn to prefer phenotypes expressed by their mothers instead. We used a dynamical systems model and tools from adaptive dynamics to study how sexual imprinting evolves in species with socially monogamous mating systems. We considered cases in which the target trait for imprinting is un- der viability selection but is not a reliable signal of paternal investment. Thus, the target trait signals the genetic benefits rather than the parental care benefits of mate choice. When mating is socially monogamous and there is some extra-pair patemity, we show that maternal imprinting can be favored over paternal imprinting. Counterintuitively, females often become choosier when selecting social partners in systems where extra-pair mating is more frequent. That is, females may be more selective when choosing social partners that will sire a smaller percentage of their offspring. Our results offer new testable hypotheses, and ad- vance our understanding of the mechanisms that drive the evolution of mate choice strategies in nature .

Cutting the Gordian knot： Complex signaling in African cichlids is more than multimodal

The active transmission of information from sender to receiver is a fundamental component of communication, and is therefore a primary facet in evolutionary models of sexual selection. Research in several systems has underlined the importance of multiple sensory modalities in courtship signals. However, we still tend to think of individuals as having a relatively static signal in consecutive communicative events. While this may be true for certain traits such as body size or coloration, behaviorally modulated signals can quickly violate this assumption. In this work, we explore how intraspecific variation may be an important component of interspecific signal divergence using cichlid fishes from Lake Malawi. Behavioral analyses were made using six species of Malawian cichlids from two divergent genera. While interspecific differences were found between congeners based on species-level analyses of both acoustic and audiovisual signals, intraspecific variation was of a similar magnitude. Specifically, individual fishes were found to possess highly plastic signal repertoires. This finding was ubiquitous across all species and resuited in a great deal of overlap between heterospecific individuals, despite statistically distinct species means. These results demonstrate that some aspects of courtship in Malawian cichlids are more plastic than previously proposed, and that studies must account for signal variability within individuals. We propose here that behavioral variability in signaling is important in determining the communication landscape on which signals are perceived. We review potential complexity deriving from multimodal signaling, discuss the sources for such lability, and suggest ways in which this issue may be approached experimentally .

The relationship between intraspecific assortative mating and reproductive isolation between divergent populations

The term ＇assortative mating＇ has been applied to describe two very different phenomena： （1） the tendency for indi- viduals to choose phenotypically similar mates from among conspecifics; or （2） the tendency to prefer conspecific over hete- rospecific mates （behavioral reproductive isolation）. Both forms of assortative mating are widespread in nature, but the relation- ship between these behaviors remains unclear. Namely, it is plausible that a preference for phenotypically similar conspecifics in cidentally reduces the probability of mating with phenotypically divergent heterospecifics. We present a model to calculate how the level of reproductive isolation depends on intraspecific assortative mating and the phenotypic divergence between species. For empirically reasonable levels of intraspecific assortment on a single trait axis, we show that strong reproductive isolation requires very substantial phenotypic divergence. We illustrate this point by applying our model to empirical data from threespine stickleback Gasterosteus aculeatus and Darwin＇s Finches （Geospiza spp）. We conclude that typical levels of intraspecific assortment cannot generally be extrapolated to explain levels of interspecific reproductive isolation. Instead, reproductive isolation between species likely arises from different mate choice behaviors, or multivariate assortative mating [Current Zoology 58 （3）： 484-492, 2012].

Comparison of sexual compatibility in crosses between the southern and northern populations of the cabbage beetle Colaphellus bowringi

It is widely accepted that the genetic divergence and reproductive incompat- ibility between closely related species and/or populations is often viewed as an important step toward speciation. In this study, sexual compatibility in crosses between the southern XS population and the northern TA population of the polyandrous cabbage beetle Co- laphellus bowringi was investigated by testing their mating preferences, mating latency, copulation duration, and reproductive performances of post-mating. In choice mating ex- periments, the percentages ofmatings were significantly higher in intra-population crosses than in inter-population crosses. Both isolation index （/） and index of pair sexual isolation （/PSi） indicated partial mating incompatibility or assortative mating in crosses between the two different geographical populations. In single pair mating experiments, XS females in inter-population crosses mated significantly later and copulated significantly shorter than those in intra-population crosses. However, TA females in inter-population crosses mated significantly earlier and copulated longer than those in intra-population crosses, suggesting that larger XS males may enhance heterotypic mating. The lifetime fecundity was highest in XS homotypic matings, lowest in TA homotypic matings, and intermedi- ate in heterotypic rnatings between their parents. The inter-population crosses resulted in significantly lower egg hatching rate and shorter female longevity than intra-population crosses. These results demonstrated that there exist some incompatibilities in premating, postmating-prezygotic, and postzygotic stages between the southern XS population and northern TA population of the cabbage beetle Colaphellus bowringi.