Effects of steroid hormones on reproduction- and detoxification-related gene expression in adult male mosquitofish, Gambusia affinis

The molecular mechanisms that mediate fish reproduction and detoxification in response to steroid hormones were studied by using adult male western mosquitofish (Gambusia affinis) as sentinel species. The expression patterns of three vitellogenins (VtgA, VtgB and VtgC), two estrogen receptors (ERα and ERβ), two androgen receptors (ARα and ARβ), metallothionein (MT) and cytochrome P450 1A (CYP1A) in the liver and testis of adult male mosquitofish were assessed through exposure treatments with progesterone (P), testosterone (T) and 17β-estradiol (E2), alone and in combination for eight days. The results showed that expression patterns of Vtg subtype, ER subtype, AR subtype, MT and CYP1A genes in male mosquitofish varied according to tissue and specific hormone stress. Vtg subtype mRNA expression was induced in the liver in E2-added treatments, and an up-regulation of ERα mRNA expression was also observed. In addition, hormone treatments increased three Vtg subtype mRNA expression levels in the testis, at least to some extent. All hormone treatments significantly inhibited ERα, ERβ and ARβ mRNA expression in the testis. Some of hormone treatments could affect MT and CYP1A gene expression in mosquitofish. In general, multiple hormone treatments showed different effects on target gene expression compared with corresponding hormone alone. The results from the present study provided valuable information on the toxicological effects of steroid hormones in mosquitofish.     

Female sexual polymorphism and fecundity consequences of male mating harassment in the wild

Genetic and phenotypic variation in female response towards male mating attempts has been found in several laboratory studies, demonstrating sexually antagonistic co-evolution driven by mating costs on female fitness. Theoretical models suggest that the type and degree of genetic variation in female resistance could affect the evolutionary outcome of sexually antagonistic mating interactions, resulting in either rapid development of reproductive isolation and speciation or genetic clustering and female sexual polymorphisms. However, evidence for genetic variation of this kind in natural populations of non-model organisms is very limited. Likewise, we lack knowledge on female fecundity-consequences of matings and the degree of male mating harassment in natural settings. Here we present such data from natural populations of a colour polymorphic damselfly. Using a novel experimental technique of colour dusting males in the field, we show that heritable female colour morphs differ in their propensity to accept male mating attempts. These morphs also differ in their degree of resistance towards male mating attempts, the number of realized matings and in their fecundity-tolerance to matings and mating attempts. These results show that there may be genetic variation in both resistance and tolerance to male mating attempts (fitness consequences of matings) in natural populations, similar to the situation in plant-pathogen resistance systems. Male mating harassment could promote the maintenance of a sexual mating polymorphism in females, one of few empirical examples of sympatric genetic clusters maintained by sexual conflict.     

Food availability and competition do not modulate the costs of Plasmodium infection in dominant male canaries

Understanding the different factors that may influence parasite virulence is of fundamental interest to ecologists and evolutionary biologists. It has recently been demonstrated that parasite virulence may occur partly through manipulation of host competitive ability. Differences in competitive ability associated with the social status (dominant or subordinate) of a host may determine the extent of this competition-mediated parasite virulence. We proposed that differences between subordinate and dominant birds in the physiological costs of infection may change depending on the level of competition in social groups. We observed flocks of domestic canaries to determine dominant or subordinate birds, and modified competition by providing restricted (high competition) or ad libitum food (low competition). Entire flocks were then infected with either the avian malaria parasite, Plasmodium relictum or a control. Contrary to our predictions we found that the level of competition had no effect on the outcome of infection for dominant or subordinate birds. We found that dominant birds appeared to suffer greater infection mediated morbidity in both dietary treatments, with a higher and more sustained reduction in haematocrit, and higher parasitaemia, than subordinates. Our results show that dominance status in birds can certainly alter parasite virulence, though the links between food availability, competition, nutrition and virulence are likely to be complex and multifaceted.     

Female proximity stimulates development of male competition in juvenile brown-headed cowbirds, Molothrus ater

We investigated how individual variation in social behaviour among group members interacts to affect social structure and development of reproductive skills. We randomly assigned juvenile male and juvenile and adult female cowbirds to four aviaries and observed patterns of singing and social assortment in each. Although social composition of each aviary was the same, juvenile males in one aviary engaged in more intra- and intersexual affiliation and singing interactions. We designed a series of rotations of individuals among the aviaries to determine which individual traits were responsible for the observed group differences. First, we rotated groups of three males from a less interactive aviary into a more interactive aviary, replacing interactive males. Within 4 days, the rotated males changed their behaviour to match the aviary into which they had been moved (i.e. interactive males became less interactive and vice versa). Next, we rotated juvenile females through the aviaries. After this rotation, the behaviour of the juvenile females remained the same, but the behaviour of the resident males changed, becoming like the males in the females' former aviaries (i.e. when juvenile females were moved from an interactive aviary into a noninteractive aviary, the males in the new aviary became more interactive and vice versa). Across the aviaries, the amount of female-male associations correlated positively with male-male competition. During the breeding season, males that had experienced more competition over the year received more copulations than males that had experienced little competition. Furthermore, more eggs were produced in aviaries containing competitive males than in aviaries containing less competitive males. Past work has shown that females can influence male vocal development; here we show that they can also influence male social development. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Effects of a parasitic nematode on male mate choice in a livebearing fish with a coercive mating system (western mosquitofish, Gambusia affinis)

I examined the effects of the parasitic larval nematode, Eustrongylides ignotus, on male mate choice in the western mosquitofish, Gambusia affinis. I hypothesized that parasite presence influences male mate choice either directly (via reduction in male mating behavior due to presence of parasite in females) or indirectly (via reduction in male mating behavior due to reduced condition of infected females). Specifically, I tested the predictions that (1) males would mate preferentially with uninfected over infected females (scoring both mating attempts and association time with females); (2) parasitized females would be in poorer condition than non-parasitized females (measured as soluble fat stores); and (3) parasitized females would have reduced fecundity (measured as number of developing embryos). Males preferred to mate with non-parasitized over parasitized females, but showed no differences in association time between females. The nematode did not decrease female body condition, but did decrease female mass, and appeared to decrease female fecundity via reduction in broods (# embryos). Results support that parasites affect male mate choice in mosquitofish; however, the mechanisms used by males to differentiate between parasitized and non-parasitized females remain untested. This study provides the first empirical evidence of parasite affects on male mate choice in livebearing fishes, and suggest a potentially important role for parasite-mediated sexual selection in organisms that use coercive mating as the primary mechanism of obtaining mates.     

Female choice and male competition in longear sunfish

Mating systems with spatial clumping of nests or display sitestheoretically can result from female preference for clumpedmales or from competitive interactions among males. We testedpredictions derived from these two types of models against observationsof nest dispersion, mating success, and alternative male matingtactics in a naturally occurring population of central longearsunfish (Lepomis megalotis megalotis). The data were consistentwith models for male-initiated spatial clumping of nest sites;no evidence of female preference for clumped nests was found.We observed that large males had greater mating success thansmall males and that solitarily nesting males were larger thancolonial males; the most successful males were solitary nesters.Mating success of large males did not increase with colony size.Furthermore, colonial males were often cuckolded by neighbors,whereas solitary males were not cuckolded. We propose that colonialnesting is maintained in longear sunfish because group nestingallows subordinate males to obtain access to females.     

Female remating, sperm competition and sexual selection in Drosophila

Female remating is fundamental to evolutionary biology as it determines the pattern of sexual selection and sexual conflict. Remating in females is an important component of Drosophila mating systems because it affects sperm usage patterns and sexual selection. Remating is common in females of many species of Drosophila in both natural and laboratory populations. It has been reported in many insect species and also in vertebrates. Female remating is a prerequisite for sperm competition between males, and the consequences of this competition, such as sperm precedence or sperm displacement, have been reported for many species of Drosophila. Female remating is dependent on the amount of sperm stored, the male seminal fluid components, nutrition, the quantity of eggs laid, experimental design and density of flies in laboratory. Remating by a female is an insurance against male sterility and sub-fertility and increases genetic heterogeneity of female offspring. Remating gives greater female productivity in many species of Drosophila. We examined female remating with respect to sperm competition and sexual selection in Drosophila and addressed the possible benefits for females. We also reviewed the role of accessory gland fluid in remating, costs associated with remating, the genetic basis of female remating and some possible mechanisms of sperm competition in the light of last male sperm priority and paternity assurance in Drosophila and other insects. We also suggest future areas of research.     

Sociosexuality as predictor of sexual harassment and coercion in female and male high school students

Sexual harassment and coercion have mainly been considered from a sex difference perspective. While traditional social science theories have explained harassment as male dominance of females, the evolutionary perspective has suggested that sex differences in the desire for sex are a better explanation. This study attempts to address individual differences associated with harassment from an evolutionary perspective. Considering previous research that has found links between sociosexual orientation inventory (SOI) and harassment, we consider whether this association can be replicated in a large, representative sample of high school students (N=1199) from a highly egalitarian culture. Expanding the previous studies which mainly focused on male perpetrators and female victims, we also examine females and males as both perpetrators and as victims. We believe that unrestricted sociosexuality motivates people to test whether others are interested in short-term sexual relations in ways that sometimes might be defined as harassment. Furthermore, unrestricted individuals signal their sociosexual orientation, and while they do not desire all individuals that react to these signals with sexual advances, they attract much more sexual advances than individuals with restricted sociosexual orientations, especially from other unrestricted members of the opposite sex. This more or less unconscious signaling thus makes them exploitable, i.e., harassable. We find that SOI is a predictor for sexual harassment and coercion among high school students. The paper concludes that, as expected, unrestricted sociosexuality predicts being both a perpetrator and a victim of both same-sex and opposite-sex harassment.     

Female tail wagging enhances sexual performance in male goats

Preference testing has shown that sexually experienced male goats choose females that are tail wagging, a behavior that may function as both attractivity and proceptivity, over those that are not. We hypothesized that exposure to females expressing high rates of tail wagging would arouse males, increasing sexual performance. Tail wagging rate could be manipulated because we have shown previously that flutamide treatment increases the frequency of tail wagging in estrous goats. Sexually experienced males observed different stimuli for 10 min before a 20 min sexual performance test (SPT). The stimuli were an empty pen (MT), or groups of three females that were all estrous (E), non-estrous (NE), estrous + flutamide (E_F) or non-estrous + flutamide (NE_F). During the stimulus observation period, tail wagging was recorded. During SPT, frequencies and latencies of sexual behaviors were recorded. E_F females displayed the most tail wagging. Viewing E_F females before SPT increased the number of ejaculations attained by males and decreased the latencies to first and second ejaculation, as well as the inter-ejaculatory interval. Viewing estrous females (E and E_F) before SPT decreased the latency to first mount, as compared to non-estrous females (NE and NE_F). We conclude that male goats are sexually aroused by tail wagging. This study and previous work demonstrate that tail wagging functions as both attractivity and proceptivity in goats.     

Balancing sexual selection through opposing mate choice and male competition

Male–male competition and female mate choice act contemporaneously in the cockroach Nauphoeta cinerea and the social pheromone of males influences the outcome of both forms of sexual selection. We therefore examined the joint and separate effects of male–male competition and female mate choice to determine if the selective optima for the pheromone were the same or different. Dominant males in a newly established hierarchy mated more frequently, but not exclusively. Manipulations of the multi-component social pheromone produced by males of N. cinerea showed that both long- and close-range attraction of females by males were influenced by the quantity and composition of the pheromone. The most attractive composition, however, differed from that which was most likely to confer high status to males. Since the outcome of male–male competition can conflict with mating preferences exhibited by females, there is balancing sexual selection on the social pheromone of N. cinerea. Such balancing selection might act to maintain genetic variation in sexually selected traits. We suggest that the different forms of sexual selection conflict in N. cinerea because females prefer a blend different to that which is most effective in male–male competition in order to avoid mating with overly aggressive males.     

Increased density and male-male interactions reduce male longevity in the medfly, Ceratitis capitata

We investigated the effect of adult density on male and female longevity and behavioural interactions in a mass-reared strain of the medfly. Male survival decreased significantly, and male-male behavioural interactions increased significantly, with increasing male density (males were kept at 1, 2, 6 and 10 flies per 285 cm²in pots of 5.5 cm in diameter and 12 cm high). No such effects were observed in females over the same density range. This suggests that male survival decreased in response to the deleterious effects of male-male behavioural interactions. At the highest density, courtship wing fanning directed towards other males decreased significantly over time. In addition, as either density or male-biased sex ratio increased, males were increasingly likely to be engaged in courtship wing fanning that was not directed towards females. These results suggest that high adult density may significantly reduce male reproductive success, by decreasing survival and mating success. The results highlight the potentially high survival costs of male-male interactions and indicate differences in the nature of reproductive costs in the two sexes.     

Female preferences drive the evolution of mimetic accuracy in male sexual displays

Males in many bird species mimic the vocalizations of other species during sexual displays, but the evolutionary and functional significance of interspecific vocal mimicry is unclear. Here we use spectrographic cross-correlation to compare mimetic calls produced by male satin bowerbirds (Ptilonorhynchus violaceus) in courtship with calls from several model species. We show that the accuracy of vocal mimicry and the number of model species mimicked are both independently related to male mating success. Multivariate analyses revealed that these mimetic traits were better predictors of male mating success than other male display traits previously shown to be important for male mating success. We suggest that preference-driven mimetic accuracy may be a widespread occurrence, and that mimetic accuracy may provide females with important information about male quality. Our findings support an alternative hypothesis to help explain a common element of male sexual displays.