Direct detection of male quality can facilitate the evolution of female choosiness and indicators of good genes: Evolution across a continuum of indicator mechanisms

The evolution of mating displays as indicators of male quality has been the subject of extensive theoretical and empirical research for over four decades. Research has also addressed the evolution of female mate choice favoring such indicators. Yet, much debate still exists about whether displays can evolve through the indirect benefits of female mate choice. Here, we use a population genetic model to investigate how the extent to which females can directly detect male quality influences the evolution of female choosiness and male displays. We use a continuum framework that incorporates indicator mechanisms that are traditionally modeled separately. Counter to intuition, we find that intermediate levels of direct detection of male quality can facilitate, rather than impede, the evolution of female choosiness and male displays in broad regions of this continuum. We examine how this evolution is driven by selective forces on genetic quality and on the display, and find that direct detection of male quality results in stronger indirect selection favoring female choosiness. Our results imply that displays maybe more likely to evolve when female choosiness has already evolved to discriminate perceptible forms of male quality. They also highlight the importance of considering general female choosiness, as well as preference, in studies of “good genes.”     

Hidden antibiotics: Where to uncover?

The struggle of humans versus pathogens is a never ending battle. Since the discovery of antibiotics humans have tipped the scales in their favour, but today bacteria are nullifying this advantage by developing resistance mechanisms against these molecules. The plethora of different antibiotics active against pathogens is shrinking while the discovery of new molecules is arduous. Especially the development of drugs active against Gram^? pathogens continues slowly. New strategies to discover novel, potent antibiotics are hence needed. Adopting the optimistic view of technological singularity, innovative and disruptive approaches are required and hence proposed to lift the current conundrum. In this review, questions are answered on where and how to look for new natural product hit molecules with antibacterial activity, on how the field of synthetic biology can aid the contemporary pharmaceutical challenge and whether we are ready to make the transition towards other approaches, such as narrow-spectrum antibiotics and phage therapy.     

Female preference for males that have exclusively marked or invaded territories depends on male presence and its identity in the subterranean rodent Ctenomys talarum

Territorial scent‐marking provides chemical records of male competitive interactions that are available to females, who gain valuable information to assess and identify best quality partners. In this context, the solitary subterranean rodent tuco‐tuco (Ctenomys talarum) offers excellent possibilities to evaluate the effects of male exclusive scent‐marking of territories on female assessment. For evaluation, we used wild caught individuals of C. talarum, manipulated their scent marks within the territories in captive conditions and staged preference tests where females were able to choose between exclusive and invaded territories. The evaluation was performed in two scenarios considering the identity of the intruder scent mark: territories invaded by a strange male and territories invaded by a neighbour male. Females investigated the chemical cues deposited on the substrate of the exclusively marked territory more frequently. Next, females displayed equal interest to scent samples of both males presented in a Y‐maze. Finally, when females could gain access to both individually isolated males and their scent‐marked territories, they spent more time within invaded territories despite they visited them with the same frequency. Moreover, females tried to get in contact by scratching the mesh of the owner of the invaded territory more frequently. We found that females of C. talarum evaluate the homogeneity (exclusiveness) of scent marks within a male territory and then show preferences in relation to the identity of the intruder's scent –whether strange or neighbour.     

Male mate choice in the chameleon grasshopper (Kosciuscola tristis)

In many species, males can increase their fitness by mating with the highest quality females. Female quality can be indicated by cues, such as body size, age and mating status. In the alpine grasshopper Kosciuscola tristis, males can be found riding on subadult females early in the season, and as the season progresses, males engage in fights over ovipositing females. These observations suggest that males may be competing for females that are either unmated (early season) or sperm‐depleted (late season). We thus hypothesised that male K. tristis may be choosy in relation to female mating status, and specifically, we predicted that males prefer females that are unmated. We conducted behavioural experiments in which males were given the choice of two females, one mated and one unmated. Contrary to our prediction, males did not mate preferentially with unmated females. However, copulation duration with unmated females was, on average, 24 times the length of copulation with mated females. While female K. tristis can reject mates, we did not observe any evidence of overt female choice during our trials. Females may gain additional benefits from mating multiply and may therefore not readily reject males. While our experiment cannot definitively disentangle female from male control over copulation duration, we suggest that males choose to invest more time in copula with unmated females, perhaps for paternity assurance, and that male mate assessment occurs during copulation rather than beforehand.     

Mating plugs and sexual cannibalism in the Colombian orb‐web spider Leucauge mariana

In Leucauge orb‐web spiders, females form mating plugs, which play a part in cryptic female choice after they evaluate male performance during courtship and mating. Our aim was to assess sexual behavior and mating plug formation of Leucauge mariana from Colombia (CO). We carried out mating trials to describe in detail courtship and mating behavior of sexual pairs from the CO population, and then compared the results to previously collected data from a Costa Rican population (CR). In addition, we assessed the amount of sperm transferred during mating predict plug formation in CO pairs. All CO virgin females mated (n = 23), and mating plug formation occurred in only 11 cases (48%). In contrast, all CR virgin females mated (n = 43) and 74% formed mating plugs. None of the male courtship or mating behaviors that we measured in CO pairs predicted mating plug formation, in contrast to previous reports from CR. Mating plugs of CO consisted of a matrix of unknown composition (77.2%) and encapsulated and decapsulated sperm (22.8%). In CR, plug composition varied in color and consistency, but also comprised a matrix with encapsulated and decapsulated sperm. We observed female cannibalism of males in CO pairs, which had never been reported in CR pairs. Some female displays during courtship and mating were unique to each population. Different female preferences could explain the observed geographic differences between L. mariana in male traits and behaviors that could, in turn, promote reproductive isolation. More studies are needed to test this hypothesis.     

Call recognition and female choice in a treefrog with a multicomponent call

Acoustic mating signals are typically species‐specific, and often additionally are subject to directional female preferences. Male executioner treefrogs, Dendropsophus carnifex, produce a multicomponent advertisement call composed of an introductory screech note followed by two or more click notes. Here, we tested (i) call recognition by comparing female directed phonotaxis towards individual and combined call components: screech vs. clicks vs. screech + clicks, (ii) female preferences for greater numbers of click notes and (iii) female preferences for faster call rates. The results demonstrated that screeches and clicks, presented either separately or together as a complete call, evoke similar female responses, suggesting that either note was sufficient to elicit a mate‐recognition response. Additionally, females preferred calls with greater numbers of click notes and with faster call rates. We interpret these results within the context of female mate selection in natural choruses.     

Ecology can inform genetics: Disassortative mating contributes to MHC polymorphism in Leach’s storm‐petrels (Oceanodroma leucorhoa)

Studies of MHC‐based mate choice in wild populations often test hypotheses on species exhibiting female choice and male–male competition, which reflects the general prevalence of females as the choosy sex in natural systems. Here, we examined mutual mate‐choice patterns in a small burrow‐nesting seabird, the Leach’s storm‐petrel (Oceanodroma leucorhoa), using the major histocompatibility complex (MHC). The life history and ecology of this species are extreme: both partners work together to fledge a single chick during the breeding season, a task that requires regularly travelling hundreds of kilometres to and from foraging grounds over a 6‐ to 8‐week provisioning period. Using a 5‐year data set unprecedented for this species (n = 1078 adults and 925 chicks), we found a positive relationship between variation in the likelihood of female reproductive success and heterozygosity at Ocle‐DAB2, a MHC class IIB locus. Contrary to previous reports rejecting disassortative mating as a mechanism for maintaining genetic polymorphism in this species, here we show that males make significant disassortative mate‐choice decisions. Variability in female reproductive success suggests that the most common homozygous females (Ocle‐DAB2*01/Ocle‐DAB2*01) may be physiologically disadvantaged and, therefore, less preferred as lifelong partners for choosy males. The results from this study support the role of mate choice in maintaining high levels of MHC variability in a wild seabird species and highlight the need to incorporate a broader ecological framework and sufficient sample sizes into studies of MHC‐based mating patterns in wild populations in general.     

The influence of developmental environment on courtship song in cactophilic Drosophila

Closely related species often differ in the signals involved in sexual communication and mate recognition. Determining the factors influencing signal quality (i.e. signal's content and conspicuousness) provides an important insight into the potential pathways by which these interspecific differences evolve. Host specificity could bias the direction of the evolution of sexual communication and the mate recognition system, favouring sensory channels that work best in the different host conditions. In this study, we focus on the cactophilic sibling species Drosophila buzzatii and D. koepferae that have diverged not only in the sensory channel used for sexual communication and mate recognition but also in the cactus species that use as primary hosts. We evaluate the role of the developmental environment in generating courtship song variation using an isofemale line design. Our results show that host environment during development induces changes in the courtship song of D. koepferae males, but not in D. buzzatii males. Moreover, we report for the first time that host rearing environment affects the conspicuousness of courtship song (i.e. song volume). Our results are mainly discussed in the context of the sensory drive hypothesis.     

Women's attractiveness is linked to expected age at menopause

A great number of studies have shown that features linked to immediate fertility explain a large part of the variance in female attractiveness. This is consistent with an evolutionary perspective, as men are expected to prefer females at the age at which fertility peaks (at least for short‐term relationships) in order to increase their reproductive success. However, for long‐term relationships, a high residual reproductive value (the expected future reproductive output, linked to age at menopause) becomes relevant as well. In that case, young age and late menopause are expected to be preferred by men. However, the extent to which facial features provide cues to the likely age at menopause has never been investigated so far. Here, we show that expected age at menopause is linked to facial attractiveness of young women. As age at menopause is heritable, we used the mother's age at menopause as a proxy for her daughter's expected age of menopause. We found that men judged faces of women with a later expected age at menopause as more attractive than those of women with an earlier expected age at menopause. This result holds when age, cues of immediate fertility and facial ageing were controlled for. Additionally, we found that the expected age at menopause was not correlated with any of the other variables considered (including immediate fertility cues and facial ageing). Our results show the existence of a new correlate of women's facial attractiveness, expected age at menopause, which is independent of immediate fertility cues and facial ageing.     

Change in male coloration associated with artificial selection on foraging colour preference

Sensory drive proposes that natural selection on nonmating behaviours (e.g. foraging preferences) alters sensory system properties and results in a correlated effect on mating preferences and subsequently sexual traits. In colour‐based systems, we can test this by selecting on nonmating colour preferences and testing for responses in colour‐based female preferences and male sexual coloration. In guppies (Poecilia reticulata), individual functional links of sensory drive have been demonstrated providing an opportunity to test the process over more than one link. We measured male coloration and female preferences in populations previously artificially selected for colour‐based foraging behaviour towards two colours, red and blue. We found associated changes in male coloration in the expected direction as well as weak changes in female preferences. Our results can be explained by a correlated response in female preferences due to artificial selection on foraging preferences that are mediated by a shared sensory system or by other mechanisms such as colour avoidance, pleiotropy or social experiences. This is the first experimental evidence that selection on a nonmating behaviour can affect male coloration and, more weakly, female preferences.