Patterns Of Sexual Selection Research Articles

Unifying quantification methods for sexual selection and assortative mating using information theory

Sexual selection plays a crucial role in modern evolutionary theory, offering valuable insight into evolutionary patterns and species diversity. Recently, a comprehensive definition of sexual selection has been proposed, defining it as any selection that arises from fitness differences associated with nonrandom success in the competition for access to gametes for fertilization. Previous research on discrete traits demonstrated that non-random mating can be effectively quantified using Jeffreys (or symmetrized Kullback-Leibler) divergence, capturing information acquired through mating influenced by mutual mating propensities instead of random occurrences. This novel theoretical framework allows for detecting and assessing the strength of sexual selection and assortative mating.In this study, we aim to achieve two primary objectives. Firstly, we demonstrate the seamless alignment of the previous theoretical development, rooted in information theory and mutual mating propensity, with the aforementioned definition of sexual selection. Secondly, we extend the theory to encompass quantitative traits. Our findings reveal that sexual selection and assortative mating can be quantified effectively for quantitative traits by measuring the information gain relative to the random mating pattern. The connection of the information indices of sexual selection with the classical measures of sexual selection is established.Additionally, if mating traits are normally distributed, the measure capturing the underlying information of assortative mating is a function of the square of the correlation coefficient, taking values within the non-negative real number set [0, +∞).It is worth noting that the same divergence measure captures information acquired through mating for both discrete and quantitative traits. This is interesting as it provides a common context and can help simplify the study of sexual selection patterns.

Behavioural plasticity in activity and sexual interactions in a social lizard at high environmental temperatures.

Sexual selection often shapes social behavioural activities, such as movement in the environment to find possible partners, performance of displays to signal dominance and courtship behaviours. Such activities may be negatively influenced by increasing temperatures, especially in ectotherms, because individuals either have to withstand the unfavourable condition or are forced to allocate more time to thermoregulation by increasing shelter seeking behaviour. Thus, they "miss" opportunities for social and reproductive interactions. Moreover, behavioural displays of ectotherms closely depend on temperature; consequently, mate choice behaviours may be disrupted, ultimately modifying sexual selection patterns. Therefore, it would be interesting to elucidate how increasing temperatures associated with global warming may influence activity and social interactions in the species' natural habitat and, specifically how high temperatures may modify intersexual interactions. Consequently, our aim was to explore differences in the daily pattern of social interactions in an ectotherm model, Tropidurus spinulosus, in two thermally different habitats and to determine how high temperatures modify mate choice. High environmental temperatures were found to be associated with a bimodal pattern in daily activity, which was closely linked to the daily variations in the thermal quality of the habitat; whereas the pattern and frequency of social displays showed less plasticity. The time allocated to mate choice generally decreased with increasing temperature since individuals increased the use of thermal refuges; this result supports the hypothesis of "missed opportunities". Moreover, at high temperatures, both sexes showed changes in mate selection dynamics, with females possibly "rushing" mate choice and males showing an increase in intermale variability of reproductive displays. In our ectotherm model, plastic adjustments in the behavioural activity pattern induced by high temperatures, plus the modification of the displays during courtship may ultimately modify mate choice patterns and sexual selection dynamics.

Factors Shaping Gender Role in the Freshwater Hermaphrodite Snail Physella acuta

Reproductive investment theory assumes that females invest more in mate choice than males do because eggs are more energetically costly to produce than sperm. However, recent studies indicate that the relationship between initial investment and patterns of sexual selection is more nuanced. Simultaneous hermaphrodite mating systems offer unique opportunities to explore reproductive investment theory, as individuals exhibit fluid preferences for donating or receiving sperm and eggs. Shifts in gender role can depend on environmental or physiological conditions such as size. However, environment factors (e.g. temperature) that affect mating role preference or behavior (e.g. latency to copulate, reciprocity) have not been explored, despite evidence that the physiological consequences of elevated temperature interfere with reproductive success. By constraining the amount of energy available during copulation, elevated temperature may directly impact individual investment, reflected in changes in gender role. We observed courtship and gender roles in Physella acuta (Draparnaud 1805) at standard (19-20°C) and elevated (28-29°C) temperature. Elevated temperature reduced duration and frequency of copulation but had no effect on latency to copulate or reciprocity. Contrary to previous studies, gender role was not found to be size-dependent in either temperature treatment. Lack of size dependence across temperature treatments could be due to low population density or climate in situ. Combined results indicate that although elevated temperature clearly has negative physiological consequences, its impact is not reflected in changes to gender role patterns. This relationship is more complicated than previously expected and requires further study.

Phylogeny and secondary sexual trait evolution in Schizocosa wolf spiders (Araneae, Lycosidae) shows evidence for multiple gains and losses of ornamentation and species delimitation uncertainty

Members of the Nearctic spider genus Schizocosa Chamberlin, 1904 have garnered much attention in behavioral studies and over many decades, a number of species have developed as model systems for investigating patterns of sexual selection and multimodal communication. Many of these studies have employed a comparative approach using putative, but not rigorously tested, sister species pairs that have distinctive morphological traits and attendant behaviors. Despite past emphasis on the efficacy of these presumably comparative-based studies of closely related species, generating a robust phylogenetic hypothesis for Schizocosa has been an ongoing challenge. Here, we apply a phylogenomic approach using anchored hybrid enrichment to generate a data set comprising over 400 loci representing a comprehensive taxonomic sample of 23 Nearctic Schizocosa. Our sampling also includes numerous outgroup lycosid genera that allow for a robust evaluation of genus monophyly. Based on analyses using concatenation and coalescent-based methods, we recover a well-supported phylogeny that infers the following: 1) The New World Schizocosa do not form a monophyletic group; 2) Previous hypotheses of North American species require reconsideration along with the composition of species groups; 3) Multiple longstanding model species are not genealogically exclusive and thus are not “good” species; 4) This updated phylogenetic framework establishes a new working paradigm for studying the evolution of characters associated with reproductive communication and mating. Ancestral character state reconstructions show a complex pattern of homoplasy that has likely obfuscated previous attempts to reconstruct relationships and delimit species. Important characters presumably related to sexual selection, such as foreleg pigmentation and dense bristle formation, have undergone repeated gain and loss events, many of which have led to increased morphological divergence between sister-species. Evaluation of these traits in a comparative framework illuminates how sexual selection and natural selection influence character evolution and provides a model for future studies of multimodal communication evolution and function.

Genomic Insights Into the Molecular Basis of Sexual Selection in Birds

Sexual selection is a well-known biological process, yet the genomic basis and patterns of sexual selection are not fully understood. The extravagant ornamental plumage of peacock (Pavo cristatus) was instrumental in shaping Charles Darwin's theory of sexual selection and is considered to be an honest signal of its immunocompetence. Here, we used the recently generated draft genome sequence of peafowl (Pavo cristatus) and carried out a comparative analysis across 11 bird genomes that encompass a range of sexual selection and also had high-quality genomic and phenotypic data publically available to study the genomic basis of sexual selection. We found that varying degree of purifying selection was the predominant mechanism of action for sexual selection at the genome-wide scale and observed that sexual selection mostly influences genes regulating gene expression and protein processing. Specifically, the genome-wide phylogenetically corrected regression analysis supported the continuous or ongoing model of sexual selection. Genes involved in nucleic acid binding and gene expression regulation, including a specific regulator of sex-determination known as TRA2A to be under positive selection in the species with high post-copulatory sexual selection manifested as high sperm competition. We also detected specific feather-related and immune-related gene-pairs evolving under similar selection pressures across the 11 species, including peacock (Pavo cristatus), which is consistent with the Hamilton-Zuk hypothesis. The comparative genomics analysis of 11 avian taxa has provided new insights on the molecular underpinnings of sexual selection and identifies specific genomic regions for future in-depth analysis.

Mate choice based on body size similarity in sexually dimorphic populations causes strong sexual selection

Traditionally it has been suggested that sexual selection can cause sexual size dimorphism (SSD). However, a recent review in gastropods shows that SSD itself can also cause sexual selection (Ng et al., 2019. Animal Behaviour, 148, 53–62). This may be the case if mate choice exists, with males preferring to mate with females similar in body size but somewhat larger than themselves (female-biased preference). We formally investigated this verbal explanation by computer simulations using a Gaussian mating preference function. Parameters of that function were also estimated from empirical data. Our results suggest that sexual selection (estimated as selection differential) is strong when mate choice is high and exerted by only one of the sexes, being influenced by SSD and the magnitude of the female-biased preference. All these factors cause a negative relationship between SSD and the (sexual) selection differential, similar to that observed in Ng et al.‘s review on gastropods. Empirical estimates of male mate choice from wild-captured mating pairs of different gastropod species confirm that mate choice by males is biased towards females slightly larger than themselves. Our results also illustrate that if mate choice is truly involved in determining SSD, present-day sexual selection cannot be used to estimate the past magnitude of mate choice, as SSD influences present-day patterns of sexual selection.

Multi-model inference of non-random mating from an information theoretic approach

Non-random mating has a significant impact on the evolution of organisms. Here, I developed a modelling framework for discrete traits (with any number of phenotypes) to explore different models connecting the non-random mating causes (mate competition and/or mate choice) and their consequences (sexual selection and/or assortative mating).I derived the formulaefor the maximum likelihood estimates of each model and used information criteria to perform multi-model inference. Simulation results showed a good performance of both model selection and parameter estimation. The methodology was applied to ecotypes data of the marine gastropod Littorina saxatilis from Galicia (Spain), to show that the mating pattern is better described by models with two parameters that involve both mate choice and competition, generating positive assortative mating plus female sexual selection. As far as I know, this is the first standardized methodology for model selection and multi-model inference of mating parameters for discrete traits. The advantages of this framework include the ability of setting up models from which the parameters connect causes, as mate competition and mate choice, with their outcome in the form of data patterns of sexual selection and assortative mating. For some models, the parameters may have a double effect i.e. they produce sexual selection and assortative mating, while for others there are separated parameters for one kind of pattern or another. From an empirical point of view, it is much easier to study patterns than processes and, for this reason, the causal mechanisms of sexual selection are not so well known as the patterns they produce. The goal of the present work is to propose a new tool that helps to distinguish among different alternative processes behind the observed mating pattern.The full methodology was implemented in a software called InfoMating (available at http://acraaj.webs6.uvigo.es/InfoMating/Infomating.htm).

Differential female sociality is linked with the fine-scale structure of sexual interactions in replicate groups of red junglefowl, Gallus gallus.

Recent work indicates that social structure has extensive implications for patterns of sexual selection and sexual conflict. However, little is known about the individual variation in social behaviours linking social structure to sexual interactions. Here, we use network analysis of replicate polygynandrous groups of red junglefowl (Gallus gallus) to show that the association between social structure and sexual interactions is underpinned by differential female sociality. Sexual dynamics are largely explained by a core group of highly social, younger females, which are more fecund and more polyandrous, and thus associated with more intense postcopulatory competition for males. By contrast, less fecund females from older cohorts, which tend to be socially dominant, avoid male sexual attention by clustering together and perching on branches, and preferentially reproduce with dominant males by more exclusively associating and mating with them. Collectively, these results indicate that individual females occupy subtly different social niches and demonstrate that female sociality can be an important factor underpinning the landscape of intrasexual competition and the emergent structure of animal societies.

The reliability of achromatic displays is island‐dependent in nocturnal Storm Petrels

Nocturnal birds rely on achromatic visual signals to assess rivals and potential mates, but variation in the expression of these displays has been understudied. Here we use UV‐visible reflectance spectrometry to study colour variation and the potential signalling function of the dark brown chest and white rump plumage – a colour pattern conspicuously exhibited during twilight courtship displays – in nocturnal Mediterranean Storm Petrels Hydrobates pelagicus melitensis from three islands with different exposures to predation and human disturbance. Human activity may increase perceived predation risk and thus affect activity budgets and the physiological stress response, with possible consequences on the relationship between individual body condition and plumage coloration. We found that chest and especially rump feathers reflected in the ultraviolet (UV) but there was no evidence of sexual dichromatism. However, we found support for a male‐specific signalling role of plumage coloration. Indeed, chest yellow–red chroma and rump UV chroma were positively related to body condition in males, but only in the two islands representing the poorer environmental conditions. Therefore, environmental variability can potentially modify the reliability of achromatic displays, with possible consequences on sexual selection patterns in a nocturnal bird.

Competitively mediated changes in male toad calls can depend on call structure

Abstract Males of many species aggregate in large groups where they signal to attract females. These large aggregations create intense competition for mates, and the simultaneous signaling by many individuals can impair any given male’s ability to attract females. In response to this situation, male signals can be modified, either evolutionarily or facultatively, such that the detectability of the signal is enhanced. The way in which signals are modified varies among even closely related species, yet few studies have evaluated what causes such variation. Here, we address this issue using male spadefoot toads (Spea multiplicata and Spea bombifrons), which call to attract females. Using data from natural populations, we examined if, and how, male calls of 3 different call types (S. multiplicata with a slow call, S. bombifrons with a slow call, and S. bombifrons with a fast call) varied depending on competition with other males. We found that in both call types consisting of slow calls, call pulse rate decreased with increasing competition. By contrast, in the call type consisting of fast calls, call rate decreased with increasing competition. Moreover, we found that the relationship between competition and male call effort—a measure of the energy that males expend in calling––differed between the call types. Such variation in male signals in response to competition can have important implications for explaining diversity in male signals and patterns of sexual selection.

Temperature alters multimodal signaling and mating success in an ectotherm

Temperature affects ectotherms in a variety of ways. These effects can be especially complex in sexual behaviors, as different sexes may be affected differently by temperature. We examined this in the jumping spider, Habronattus clypeatus. In this species, males court females using visual and vibratory signals. We tested whether key intersexual behaviors would change with temperature in similar, predictable ways across males and females. We first measured temperature and apparent activity of individuals across the day. We found that H. clypeatus are active across a wide range of temperatures (11–56 °C) and are most active at times of day when temperature ranges from 13 to 46 °C. Next, we performed mating experiments across behaviorally relevant temperatures. Females were more likely to allow males to progress to later stages of courtship and had higher mating rates at higher temperatures. Male visual and vibratory courtship behaviors generally became faster, higher-pitched, and lower in amplitude at higher temperatures. This relationship between temperature and signal aspects attained a roughly curvilinear shape, with an asymptote around 40 °C. Intriguingly, mating rates in the lab were highest at temperatures potentially above those during peak spider activity in the field. Our results suggest that temperature’s effects on behavior are complex and can affect males and females differently. This work emphasizes that understanding temperature effects on mating is critical to understanding sexual selection patterns particularly in species which use complex signals. Temperature affects communication in most ectothermic species. Previous research has shown that temperature changes courter signals and chooser choice. However, this has never been investigated in species that use multimodal signals. We investigate how signals and choice change across temperatures in a desert-dwelling jumping spider. Using field temperature/activity modeling and a series of courtship experiments in the lab, we show that male signals and female choice change with temperature across biologically relevant ranges. Our results suggest that the temperatures at which mating is most likely occur at times of the day when animals are least active. These counterintuitive results highlight the importance of understanding how behavior in a controlled lab environment corresponds to natural field conditions as well as the importance of examining the effects of naturally occurring environmental variation on behavior.

Sexual Selection Mechanisms for Male Plumage Ornaments in Japanese Barn Swallows

The Barn Swallow Hirundo rustica is a model species for studying sexual selection. After its long tail was shown to be the target of female mate choice, its plumage characteristics, including the red throat patch and the size of white tail spots in addition to tail length, have attracted the attention of many researchers. Although there have been several reviews of sexual selection in this species, these reviews have focused mostly on general patterns of sexual selection within and among subspecies, rather than on the functional differences between plumage characteristics in sexual selection. Here, I review mechanisms of sexual selection for male plumage ornaments in Japanese Barn Swallows H. r. gutturalis. In the last decade, studies of sexual selection in Japanese Barn Swallows have focussed on tail length, the size of the white tail spots, and the size and coloration of red throat patches. Each ornamental trait appears to be involved in different sexual selection mechanisms: the size of the white tail spots is important for several mechanisms of intersexual selection, including the Darwin-Fisher mechanism and differential allocation, whereas throat coloration may be intra-sexually selected, at least in part. The size of the throat patch, in contrast, is the target of an intersexual selection mechanism, differential access, indicating a partially independent evolution of the two components of the red throat patch. Multiple mechanisms of sexual selection would explain the multiple ornaments and their geographical variation, and even the probability of speciation and extinction.

Are olfactory traits in a pair-bonded primate under sexual selection? An evaluation of sexual dimorphism in Aotus nancymaae.

Sexual selection has seemingly influenced chemical communication in numerous non-human primates, although it is unclear whether it has influenced strictly pair-living and pair-bonded taxa. The physical similarities between male and female owl monkeys suggest that disruptive selection has not played a role in this taxon. However, given their nocturnality, olfactory traits may show differing patterns of sexual selection than visual traits. If sexual selection has influenced chemical communication in owl monkeys, we expect larger scent glands and greater scent-marking in females given the high degree of paternal care, as has been proposed for callitrichines. We evaluated sex differences in the qualitative and quantitative descriptions of the subcaudal and perianal glandular regions of captive male (n = 39) and female (n = 36) owl monkeys (A. nancymaae), and in the olfactory behaviors performed within breeding pairs (n = 16). Males had larger areas of secretion retained in the hairs covering the subcaudal gland, and females had more and darker secretion than males covering the perianal region. Males inspected the genital region of their partners more frequently than females did, but the sexes did not differ much in other investigative and marking behaviors. The observed sex differences and variation in olfactory traits are consistent with the hypothesis that sexual selection has influenced chemical communication in owl monkeys, with males having larger subcaudal glands and spending more time investigating odors. Still, sex differences in monogamous owl monkeys were less extreme than those in other, non-monogamous, taxa.

Estimating encounter rates as the first step of sexual selection in the lizard Anolis sagrei.

How individuals move through their environment dictates which other individuals they encounter, determining their social and reproductive interactions and the extent to which they experience sexual selection. Specifically, females rarely have the option of mating with all males in a population-they can only choose among the males they encounter. Further, quantifying phenotypic differences between the males that females encounter and those that sire females' offspring lends insight into how social and reproductive interactions shape male phenotypes. We used an explicitly spatio-temporal Markov chain model to estimate the number of potential mates of Anolis sagrei lizards from their movement behaviour, and used genetic paternity assignments to quantify sexual selection on males. Females frequently encountered and mated with multiple males, offering ample opportunity for female mate choice. Sexual selection favoured males that were bigger and moved over larger areas, though the effect of body size cannot be disentangled from last-male precedence. Our approach corroborates some patterns of sexual selection previously hypothesized in anoles based on describing them as territorial, whereas other results, including female multiple mating itself, are at odds with territorial polygyny, offering insight into discrepancies in other taxa between behavioural and genetic descriptions of mating systems.

Random size‐assortative mating despite size‐dependent fecundity in a Neotropical amphibian with explosive reproduction

AbstractSexual selection theory predicts that, when body size is correlated with fecundity, there should be fitness advantages for mate choice of the largest females. Moreover, because larger males are expected to monopolise the largest females, this should result in an assortative mating based on body size. Although such patterns could be expected in both explosive and prolonged breeders, non‐assortative mating should be more widespread in species under time constraints. However, patterns of sexual selection are largely unexplored in explosive breeding species, and contrasting patterns have been found previously. We expect that the active choice of partners may be particularly risky when the time period during which sexual partners are available is severely limited. Therefore, to avoid missing an entire reproductive act, males and females should pair irrespective of traits, such as body size. We tested this hypothesis by investigating the mating patterns of the Pacific horned toad, Ceratophrys stolzmanni, a short‐lived fossorial species inhabiting Neotropical dry forests. This species is particularly adequate to test our prediction because it reproduces explosively over the course of a single night per year. Although the number of eggs laid was proportional to the size of females, and individuals of both sexes showed variation in body size, there was no assortative mating based either on size, body condition or age of mates. Egg size was not influenced by either female size or clutch size. The larger body size of females compared to males is likely due to fecundity selection, that is, the selective pressure that enhances reproductive output. Although we cannot dismiss the possibility that individuals could select their partners based on other criteria than those related to size or age, the results fit well our prediction, showing that the explosive breeding makes improbable an active choice of partners in both sexes and therefore favours a random mating pattern.

Within-season variation in sexual selection on flight performance and flight-related traits in a damselfly

While selection is a key mechanism of evolution, our understanding of within-season variation in sexual selection remains limited. Here, we studied within-season sexual selection on two key performance traits, flight speed and flight endurance, and a set of morphological and physiological phenotypic traits in a natural population of the territorial damselfly Chalcolestes viridis. We applied a path analysis approach to address whether the flight-related traits affected mating success directly or indirectly through their effect on the flight performance traits, and whether these selection patterns differed between the first and second half of the reproductive season. While some trait means did not differ between both parts of the season (flight speed, wing loading and non-allometric wing shape), most traits showed within-season differences (flight endurance, fat content, flight muscle ratio, wing centroid size, body mass and the allometric wing shape). Despite the within-season temporal differences in flight endurance, sexual selection consistently favoured males with a higher flight endurance. None of the detected patterns of sexual selection on the flight-related traits were consistently significant in both periods: while we detected selection on wing loading and wing centroid size in the first half of the season, we detected selection on body mass in the second half of the season. More studies focusing on understudied traits such as performance traits are needed to refine our knowledge of the temporal dynamics of selection patterns in nature. This is important to arrive at a better understanding of the adaptive evolutionary dynamics of traits in natural populations.

Multiple Mating, Paternity and Complex Fertilisation Patterns in the Chokka Squid Loligo reynaudii.

Polyandry is widespread and influences patterns of sexual selection, with implications for sexual conflict over mating. Assessing sperm precedence patterns is a first step towards understanding sperm competition within a female and elucidating the roles of male- and female-controlled factors. In this study behavioural field data and genetic data were combined to investigate polyandry in the chokka squid Loligo reynaudii. Microsatellite DNA-based paternity analysis revealed multiple paternity to be the norm, with 79% of broods sired by at least two males. Genetic data also determined that the male who was guarding the female at the moment of sampling was a sire in 81% of the families tested, highlighting mate guarding as a successful male tactic with postcopulatory benefits linked to sperm deposition site giving privileged access to extruded egg strings. As females lay multiple eggs in capsules (egg strings) wherein their position is not altered during maturation it is possible to describe the spatial / temporal sequence of fertilisation / sperm precedence There were four different patterns of fertilisation found among the tested egg strings: 1) unique sire; 2) dominant sire, with one or more rare sires; 3) randomly mixed paternity (two or more sires); and 4) a distinct switch in paternity occurring along the egg string. The latter pattern cannot be explained by a random use of stored sperm, and suggests postcopulatory female sperm choice. Collectively the data indicate multiple levels of male- and female-controlled influences on sperm precedence, and highlights squid as interesting models to study the interplay between sexual and natural selection.

Geography, assortative mating, and the effects of sexual selection on speciation with gene flow.

Theoretical and empirical research on the evolution of reproductive isolation have both indicated that the effects of sexual selection on speciation with gene flow are quite complex. As part of this special issue on the contributions of women to basic and applied evolutionary biology, I discuss my work on this question in the context of a broader assessment of the patterns of sexual selection that lead to, versus inhibit, the speciation process, as derived from theoretical research. In particular, I focus on how two factors, the geographic context of speciation and the mechanism leading to assortative mating, interact to alter the effect that sexual selection through mate choice has on speciation. I concentrate on two geographic contexts: sympatry and secondary contact between two geographically separated populations that are exchanging migrants and two mechanisms of assortative mating: phenotype matching and separate preferences and traits. I show that both of these factors must be considered for the effects of sexual selection on speciation to be inferred.

Frequency-dependent sexual selection with respect to progeny survival is consistent with predictions from rock-paper-scissors dynamics in the European common lizard

Genetic polymorphism can be maintained over time by negative frequency-dependent (FD) selection induced by Rock-paper-scissors (RPS) social systems. RPS games produce cyclic dynamics, and have been suggested to exist in lizards, insects, isopods, plants, and bacteria. Sexual selection is predicted to accentuate the survival of the future progeny during negative FD survival selection. More specifically, females are predicted to select mates that produce progeny genotypes that exhibit highest survival during survival selection imposed by adult males. However, no empirical evidence demonstrates the existence of FD sexual selection with respect to fitness payoffs of genetic polymorphisms. Here we tested this prediction using the common lizard Zootoca vivipara, a species with three male color morphs (orange, white, yellow) that exhibit morph frequency cycles. In a first step we tested the congruence of the morph frequency change with the predicted change in three independent populations, differing in male color morph frequency and state of the FD morph cycle. Thereafter we ran standardized sexual selection assays in which we excluded alternative mechanisms that potentially induce negative FD selection, and we quantified inter-sexual behavior. The patterns of sexual selection and the observed behavior were in line with context-dependent female mate choice and male behavior played a minor role. Moreover, the strength of the sexual selection was within the magnitude of selection required to produce the observed 3-4-year and 6-8 year morph frequency cycles at low and high altitudes, respectively. In summary, the study provides the first experimental evidence that underpins the crucial assumption of the RPS games suggested to exist in lizards, insects, isopods, and plants; namely, that sexual selection produces negative-FD selection. This indicates that sexual selection, in our study exert by females, might be a crucial driver of the maintenance of genetic polymorphisms.

Sexual selection is influenced by both developmental and adult environments.

Sexual selection is often assumed to be strong and consistent, yet increasing research shows it can fluctuate over space and time. Few experimental studies have examined changes in sexual selection in response to natural environmental variation. Here, we use a difference in resource quality to test for the influence of past environmental conditions and current environmental conditions on male and female mate choice and resulting selection gradients for leaf-footed cactus bugs, Narnia femorata. We raised juveniles on natural high- and low-quality diets, cactus pads with and without ripe cactus fruits. New adults were again assigned a cactus pad with or without fruit, paired with a potential mate, and observed for mating behaviors. We found developmental and adult encounter environments affected mating decisions and the resulting patterns of sexual selection for both males and females. Males were not choosy in the low-quality encounter environment, cactus without fruit, but they avoided mating with small females in the high-quality encounter environment. Females were choosy in both encounter environments, avoiding mating with small males. However, they were the choosiest when they were in the low-quality encounter environment. Female mate choice was also context dependent by male developmental environment. Females were more likely to mate with males that had developed on cactus with fruit when they were currently in the cactus with fruit environment. This pattern disappeared when females were in the cactus without fruit environment. Altogether, these results experimentally demonstrate context-dependent mate choice by both males and females. Furthermore, we demonstrate that simple, seasonal changes in resources can lead to fluctuations in sexual selection.