Song Choice Is Modulated by Female Movement in Drosophila Males

Mate selection is critical to ensuring the survival of a species. In the fruit fly, Drosophila melanogaster, genetic and anatomical studies have focused on mate recognition and courtship initiation for decades. This model system has proven to be highly amenable for the study of neural systems controlling the decision making process. However, much less is known about how courtship quality is regulated in a temporally dynamic manner in males and how a female assesses male performance as she makes her decision of whether to accept copulation. Here, we report that the courting male dynamically adjusts the relative proportions of the song components, pulse song or sine song, by assessing female locomotion. Male flies deficient for olfaction failed to perform the locomotion-dependent song modulation, indicating that olfactory cues provide essential information regarding proximity to the target female. Olfactory mutant males also showed lower copulation success when paired with wild-type females, suggesting that the male’s ability to temporally control song significantly affects female mating receptivity. These results depict the consecutive inter-sex behavioral decisions, in which a male smells the close proximity of a female as an indication of her increased receptivity and accordingly coordinates his song choice, which then enhances the probability of his successful copulation.     

Body Weight and Rearing Conditions of Males, Female Choice and Paternities in a Small Mammal, Cavia aperea

Patterns of mate choice may be important determinants of a species' social organisation and mating system. At least two different aspects of female mate choice can be distinguished: choice of a social partner and choice of the genetic father of the offspring. Different characteristics of males can qualify them for these two roles. Although social and reproductive partners have been shown to differ in many species, social association times are often used in laboratory choice tests to infer reproductive preferences. The traits for which females may choose partners are diverse. Body size can correlate with the male's strength in defending resources or other abilities benefiting the female and her offspring. In species living in social groups, social skills learned from group members during infancy can be important for later reproductive success. In this laboratory study, we conducted choice tests with wild cavies, Cavia aperea , a harem-living species of South American rodents, to determine social preferences of females towards two simultaneously available males. For offspring sired during these tests, paternities were determined by microsatellite DNA profiling. Males used in the tests differed in body weight and in rearing conditions: Half of the males had been reared in the presence or absence of their father, respectively. Male rearing conditions had no effect on either female social preferences or paternities. Females significantly preferred heavier males as social partners. In five of six tests, the heavier male also sired the offspring. Sires were in most cases but not consistently socially preferred. Heavier males may be preferable as social partners because they are better able to provide females with resources or have more experience in paternal care or predator avoidance as weight correlates with age. When choosing reproductive partners, females may prefer other male traits and the distribution of paternities may also be influenced by sperm competition.     

Female Mate Choice in a Paternal Brooding Blenny: The Process and Benefits of Mating with Males Tending Young Eggs

Female mate preference for males tending young offspring has been demonstrated in many fishes; however, not much is known about the choice process. Using the barred chin blenny Rhabdoblennius ellipes, a fish with male uniparental care, field experiments were conducted to investigate the female preference for males tending young eggs and then whether females choose the males with young eggs by discriminating young eggs from old eggs in the nests. Males tending young eggs (0‐ to 2‐d old) acquired new eggs nine times more frequently than those tending old eggs (3‐ to 5‐d old) regardless of other traits in males and nests. In the two egg‐switching field experiments (old to young and young to old), contrary to our expectation, male mating success was neither enhanced when given young eggs nor inhibited when given old eggs. These results suggested that females choose males with young eggs not by discriminating the developmental stage of eggs in the nests but by using other choice processes. By choosing males with young eggs, females may benefit from the dilution effects of egg predation and filial cannibalism risks and avoid male parental care failure.     

The Round-Eared Sengi and the Evolution of Social Monogamy: Factors that Constrain Males to Live with a Single Female

Animal dispersion in space and time results from environmental pressures, and affects the outcome of a species' social organization. When females are solitary, males may either roam or be pair-living. We studied possible environmental influences affecting the social organization of the round-eared sengi ( Macroscelides proboscideus ) in a semi-desert in South Africa, using trapping and radio-tracking across 2.5 yr. Adult sex ratios did not deviate from 1:1 and we found no indication of sexual dimorphism in body mass. Females maintained exclusive areas, which had little overlap (<4%) with neighbouring females (NF), and males overlapped predominately only with the home range of single females. Generally, inter- and intra-sexual overlap with neighbouring individuals was low (3–6%) for both sexes, indicating territoriality and pair-living. Pairs were perennial and territories were maintained year-round. However, males generally maintained much larger areas than females, which were sensitive to population density. Male space use appeared to be primarily limited by the presence of neighbouring males. Female home ranges were smaller-sized despite changes in population density, possibly for energetic efficiency. Some paired males attempted to take over widowed females, but shifted back to their original home range following the intrusion of an un-paired male. We conclude that social monogamy is the predominant social organization in round-eared sengis in a semi-desert that may have resulted from females living solitarily in small exclusive territories, balanced sex ratios, and from a low variation of body mass between males.     

Aversive Responses of Female Mice to the Odors of Parasitized Males: Neuromodulatory Mechanisms and Implications for Mate Choice

The detection and avoidance of parasitized conspecifics is proposed to have important consequences for the behavior of animals, especially as related to mate choice. A reduction in pain sensitivity (i.e. analgesia) is a major correlate of exposure to real or potential danger and threatening stimuli, facilitating the expression of various active (e.g. fleeing) and passive (e.g. immobilization) defense responses. The present study examined pain sensitivity (latency of a foot-lifting response to 50 ° C thermal surface) of female mice, Mus musculus, that were exposed to the urine and other odor secretions of male mice subclinically infected with the naturally occurring, enteric, sporozoan parasite, Eimeria vermiformis. A 30-min exposure to the odors of a parasitized male induced an analgesia in the female mice that was found to be mediated by the increased activity of endogenous opioid peptide systems. A brief 1-min exposure to the male odors induced a shorter duration and lower amplitude analgesia of a non-opioid (serotonergic) nature. Maximum analgesic responses were induced by the odors of pre-infective [5 days post-infection (PI)] and infective (day 10 PI) males, with significantly lower responses elicited by the odors of post-infective (day 17 PI) male mice. Exposure to the odors of unparasitized males had no significant effects on the pain sensitivity of female mice. These results indicate that female mice can distinguish between the odors of parasitized and non-parasitized male mice, and find the odors of parasitized males threatening and/or stressful. These odor-induced analgesic responses and their neurohormonal correlates may be part of an adaptive preparatory defense mechanism that facilitates the detection and avoidance of parasitized males by female mice and contributes to female mate choice.     

Female Mate Choice Can Drive the Evolution of High Frequency Echolocation in Bats: A Case Study with Rhinolophus mehelyi

Animals employ an array of signals (i.e. visual, acoustic, olfactory) for communication. Natural selection favours signals, receptors, and signalling behaviour that optimise the received signal relative to background noise. When the signal is used for more than one function, antagonisms amongst the different signalling functions may constrain the optimisation of the signal for any one function. Sexual selection through mate choice can strongly modify the effects of natural selection on signalling systems ultimately causing maladaptive signals to evolve. Echolocating bats represent a fascinating group in which to study the evolution of signalling systems as unlike bird songs or frog calls, echolocation has a dual role in foraging and communication. The function of bat echolocation is to generate echoes that the calling bat uses for orientation and food detection with call characteristics being directly related to the exploitation of particular ecological niches. Therefore, it is commonly assumed that echolocation has been shaped by ecology via natural selection. Here we demonstrate for the first time using a novel combined behavioural, ecological and genetic approach that in a bat species, Rhinolophus mehelyi: (1) echolocation peak frequency is an honest signal of body size; (2) females preferentially select males with high frequency calls during the mating season; (3) high frequency males sire more off-spring, providing evidence that echolocation calls may play a role in female mate choice. Our data refute the sole role of ecology in the evolution of echolocation and highlight the antagonistic interplay between natural and sexual selection in shaping acoustic signals.     

Males Prefer Small Females in a Dichotomous Choice Test in the Poeciliid Fish Heterandria formosa

Male choice is expected to evolve when females differ in quality, even if male investment in each mating is low. The family Poeciliidae is an example of fishes in which males show little parental investment as they only provide sperm. Up until now, a preference for large females has been found in all species studied. Here we show that unexpectedly, males of the least killifish (Heterandria formosa) prefer to interact with small instead of large females in a dichotomous male choice test, even though large females are more fecund. During a free‐swimming choice experiment, males did not discriminate between females based on their size. We suggest that this unique preference for small females, or the lack of preference for large females, results from strong first male sperm precedence in this species. Smaller females are younger and therefore more likely to be virgin, which probably makes them more profitable mates for males. When presented with a virgin and a mated female of similar size, males showed no preference for either type. This suggests that males do not use pheromone cues to assess female mating status but that they are likely to use female size as a proxy for it.     

Interaction Between Sexually Antagonistic Selection and Mate Choice in the Evolution of Female Responses to Male Traits

Theoretical analyses of selection on mutations affecting female responsiveness to male traits suggested that sexually antagonistic selection and traditional female choice are not exclusive alternatives. They can act simultaneously on the same female traits, and can either reinforce or act against each other. These analyses do not yield theoretical predictions regarding the relative frequency and importance of the two types of selection on female responsiveness, as the balance between them is affected by complex factors, including the frequency distribution of male traits, and the mechanisms of male action. Male–female interactions differ from many other evolutionary interactions involving potential evolutionary conflict, in that male and female genomes are irretrievably mixed in their offspring, thus increasing the possibility of indirect payoffs to one participant from the traits of its partner.     

Harassment of Mature Female Chimpanzees by Young Males in the Mahale Mountains

Juvenile and adolescent male chimpanzees sometimes threaten older, apparently stronger individuals such as mature females. I label the behavior harassment. Harassment comprises 25 behaviors, 14 of which are accompanied by the use of objects such as branches: Clubbing, flailing and throwing are the most common. Females respond to harassment with 10 behaviors, including scream, avoid, ignore, and retaliate. Females tend to respond to harassment by juvenile males by ignoring them. However, they are more likely to retaliate, scream or avoid in response to harassment by adolescent males. I propose the rank improvement hypothesis that harassment initiates the process of male domination of females, and compare the predictions derived from it with those of the exploratory aggression hypothesis. Males stopped harassing females significantly earlier when females ignored them versus when they did not ignore them. This is not consistent with the exploratory aggression hypothesis. Males harassed adult females significantly longer when females retaliated than when they did not, which is consistent with the rank improvement hypothesis. Although the observations are congruent with my hypothesis, we need more data to test it.     

Highly Competitive Reindeer Males Control Female Behavior during the Rut

During the rut, female ungulates move among harems or territories, either to sample mates or to avoid harassment. Females may be herded by a male, may stay with a preferred male, or aggregate near a dominant male to avoid harassment from other males. In fission-fusion group dynamics, female movement is best described by the group’s fission probability, instead of inter-harem movement. In this study, we tested whether male herding ability, female mate choice or harassment avoidance influence fission probability. We recorded group dynamics in a herd of reindeer Rangifer tarandus equipped with GPS collars with activity sensors. We found no evidence that the harassment level in the group affected fission probability, or that females sought high rank (i.e. highly competitive and hence successful) males. However, the behavior of high ranked males decreased fission probability. Male herding activity was synchronous with the decrease of fission probability observed during the rut. We concluded that male herding behavior stabilized groups, thereby increasing average group size and consequently the opportunity for sexual selection.     

Possible Female Choice During Copulation in Ozophora baranowskii (Heteroptera: Lygaeidae): Female Behavior, Multiple Copulations, and Sperm Transfer

The remarkable behavior of female Ozophora baranowskii of lightly tapping the male with the hind legs during copulation was studied in relation to multiple copulations, copulation length, and sperm transfer. Multiple copulations did not affect female fecundity, fertility, or longevity. The incidence of tapping was higher in shorter copulations, which did not result in sperm transfer to the female. Female tapping behavior may be a mechanism for choosing between males after copulation has begun.     

Parasites and Female Choice in the Ring-necked Pheasant

The Hamilton and Zuk hypothesis is based on several assumptions:1) The parasites adversely affect host fitness, and susceptibilityto parasites is heritable. 2) Expression of secondary sexualcharacteristics is, at least to some extent, dependent on hostcondition and vigor, and therefore on host ability to controlparasites. 3) Females evolve appropriate discriminatory preferencefor secondary sexual characteristics that best reveal susceptibilityto parasites. This paper presentsthe results of experimentsdesigned to test these assumptions, using the Ring-necked Pheasant,Phasianus colchicus. The results show that resistance to diseasecan be heritable. Preliminary analysis of the mate choice testsdoes not reveal that these resistant offspring have better developedsecondary sexual characters, or that females prefer them. However,there is a correlation between display rate; coccidian parasiteload, and female choice in male pheasants.     

Possible Balancing Selection in Human Female Homosexuality

A growing number of researchers suggest that female homosexuality is at least in part influenced by genetic factors. Unlike for male homosexuality, few familial studies have attempted to explore maintenance of this apparently fitness-detrimental trait in the population. Using multiple recruitment methods, we explored fecundity and sexual orientation within the pedigrees of 1,458 adult female respondents. We compared 487 homosexual and 163 bisexual with 808 heterosexual females and 30,203 of their relatives. Our data suggest that the direct fitness of homosexual females is four times lower than the direct fitness of heterosexual females of corresponding ages. The prevalence of nonheterosexuality within the homosexual female respondents’ families (2.83%) appear to be more than four times higher than the basal prevalence in the Italian population (0.63%). Pedigree size and relative fecundity in both the paternal and maternal sides of the homosexual women’s families were significantly higher than in the heterosexuals’ families. If confirmed, the relative average fecundity increase within the family seems to offset the loss in fitness due to the low direct fitness of homosexual females. Therefore, the balanced fecundity in the homosexual females’ families may allow the trait to be maintained at a low-frequency equilibrium in the population.     

Spider Males Adjust Mate Choice but Not Sperm Allocation to Cues of a Rival

Spatial and temporal variation in ecological parameters selects for plastic responses to prevailing conditions. Males of web spiders have been shown to adjust developmental decisions to cues that relate to the degree of competition from other males. Here, we explore experimentally whether males of the spider Nephila senegalensis base behavioural decisions in the context of mate choice and sperm allocation to the presence of cues of a rival and to their own competitive dominance. Large and small males were offered a simultaneous choice between two penultimate instar females that varied in quality and in whether they were previously visited by a rival male. Large and small males avoided webs visited by a previous male, and this preference overrode differences in female quality. In a second experiment, males were assigned to copulate with a virgin female whose web was either previously visited by a rival male or not. We found substantial variation in male sperm allocation, but this variation was not related to our treatment. Our experiments demonstrate that males notice silk cues left behind by rival males on a female’s web and that they can utilize these cues in relation to decisions over whether to visit a web, but not in relation to sperm allocation.     

Males Under-Estimate Academic Performance of Their Female Peers in Undergraduate Biology Classrooms

Women who start college in one of the natural or physical sciences leave in greater proportions than their male peers. The reasons for this difference are complex, and one possible contributing factor is the social environment women experience in the classroom. Using social network analysis, we explore how gender influences the confidence that college-level biology students have in each other’s mastery of biology. Results reveal that males are more likely than females to be named by peers as being knowledgeable about the course content. This effect increases as the term progresses, and persists even after controlling for class performance and outspokenness. The bias in nominations is specifically due to males over-nominating their male peers relative to their performance. The over-nomination of male peers is commensurate with an overestimation of male grades by 0.57 points on a 4 point grade scale, indicating a strong male bias among males when assessing their classmates. Females, in contrast, nominated equitably based on student performance rather than gender, suggesting they lacked gender biases in filling out these surveys. These trends persist across eleven surveys taken in three different iterations of the same Biology course. In every class, the most renowned students are always male. This favoring of males by peers could influence student self-confidence, and thus persistence in this STEM discipline.     

Sexual Selection and the Psychophysics of Female Choice

Woodland birds of 20 species were captured in mist-nets in winter (September to February) and summer (April—August) and scored for whether or not they made distress calls while being handled. Birds of only two species showed significant tendencies to be consistent in calling or failing to call when recaptured, but most species had weak trends in. the same direction. Some species changed seasonally in the tendency to call, but there was no general pattern. In winter, but not summer, the incidence of calling was correlated across species with an index of the number of conspecifics likely to hear the call, but there was no comparable correlation with variations within species. In the long-tailed tit, calling was associated with struggling, and with eyelid colour, which reflects a bird's mood. This implies that calling may be directed at a captor as well as at flock companions.     

Costly signalling: a work in progress

The Evolution of Animal Communication is a detailed examination of a wide variety of animal signalling systems. The main focus of the book is explaining how such signalling systems remain reliable when there is apparent evolutionary pressure to deceive. The principle strategy is to appeal to signal costs: signals remain reliable because the potential benefits of deceit are outweighed by the costs of producing the deceptive signal. In this review I show just how difficult this idea is to test, even in the simplest cases.     

Sexual Selection in the Water Spider: Female Choice and Male–Male Competition

The water spider Argyroneta aquatica is the only spider spending its whole life under water, and one of the few spider species in which males are larger than females. Previous studies indicated that males can cannibalize females, which is uncommon among spiders. Here we aimed to further test for a potential influence of sexual selection on male body size. We examined the importance of female choice by testing whether females prefer the larger of two simultaneously presented males as mating partners. Further, we examined the influence of male–male competition by comparing the fighting behaviour between large and small males when alone or when together with a female, and we determined the outcome of fights. We found that females approach and choose large males as mating partners, despite the risk of male cannibalism. Additionally, males intensively compete for females, and large males clearly win against smaller ones. Hence sexual selection seems to be important for the evolution of the peculiar sexual size dimorphism of water spiders, as large size is beneficial for males in both the intra‐ and intersexual context. Previous studies have suggested an important role of natural selection in the sex‐specific body size of water spiders, but natural and sexual selection mechanisms apparently work in the same direction, favouring large male size.