Mating Trials Research Articles

Mate competition and evolutionary outcomes in genetically modified zebrafish (Danio rerio).

Demonstrating relationships between sexual selection mechanisms and trait evolution is central to testing evolutionary theory. Using zebrafish, we found that wild-type males possessed a significant advantage in mate competition over transgenic RFP Glofish® males. In mating trials, wild-type males were aggressively superior to transgenic males in male-male chases and male-female chases; as a result, wild-type males sired 2.5× as many young as did transgenic males. In contrast, an earlier study demonstrated that female zebrafish preferred transgenic males as mates when mate competition was excluded experimentally. We tested the evolutionary consequence of this conflict between sexual selection mechanisms in a long-term study. The predicted loss of the transgenic phenotype was confirmed. More than 18,500 adults collected from 18 populations across 15 generations revealed that the frequency of the transgenic phenotype declined rapidly and was eliminated entirely in all but one population. Fitness component data for both sexes indicated that only male mating success differed between wild-type and transgenic individuals. Our predictive demographic model based on fitness components closely matched the rate of transgenic phenotype loss observed in the long-term study, thereby supporting its utility for studies assessing evolutionary outcomes of escaped or released genetically modified animals.

Sexual cannibalism in the spiderAlpaida veniliae(Keyserling 1865) (Araneae: Araneidae)

Postmating cannibalism where a female attacks, kills and consumes a male after a sexual encounter is frequently influenced by certain male morphological and behavioral characteristics. We conducted behavioral assays in the laboratory to test the predictions that male Alpaida veniliae (Keyserling 1865) with larger absolute and relative size in relation to their mate and those having longer courtship and copulation duration would have lower probability of being cannibalized by females after a sexual encounter. We performed a set of mating trials exposing males of different sizes to virgin females. We observed copulation in 88.8% of mating trails; its duration was very brief compared to courtship. Only a few attempts (16.7%) of recopulations with the same female were recorded, and in all these cases the first copulation was significantly shorter than the mean copulation duration of those who had only one copulation. The percentage of postcopulatory cannibalism was 47.6%. There was no correlation between the relative and absolute male size and duration of courtship and copulation. Postcopulatory cannibalism was independent of courtship and mating durations but was affected by absolute and relative male size. Smaller males were more frequently cannibalized than large ones. However, it remains unclear whether sexual cannibalism in A. veniliae may be explained by female mate choice or whether smaller males are less able to escape or defend themselves. More studies are needed to understand the underlying factors of postcopulatory cannibalism of A. veniliae, as well as to elucidate their possible ecological and evolutionary implications.

Conspicuous female ornamentation and tests of male mate preference in threespine sticklebacks (Gasterosteus aculeatus).

Sexual selection drives the evolution of exaggerated male ornaments in many animal species. Female ornamentation is now acknowledged also to be common but is generally less well understood. One example is the recently documented red female throat coloration in some threespine stickleback (Gasterosteus aculeatus) populations. Although female sticklebacks often exhibit a preference for red male throat coloration, the possibility of sexual selection on female coloration has been little studied. Using sequential and simultaneous mate choice trials, we examined male mate preferences for female throat color, as well as pelvic spine color and standard length, using wild-captured threespine sticklebacks from the Little Campbell River, British Columbia. In a multivariate analysis, we found no evidence for a population-level mate preference in males, suggesting the absence of directional sexual selection on these traits arising from male mate choice. Significant variation was detected among males in their preference functions, but this appeared to arise from differences in their mean responsiveness across mating trials and not from variation in the strength (i.e., slope) of their preference, suggesting the absence of individual-level preferences as well. When presented with conspecific intruder males, male response decreased as intruder red throat coloration increased, suggesting that males can discriminate color and other aspects of phenotype in our experiment and that males may use these traits in intrasexual interactions. The results presented here are the first to explicitly address male preference for female throat color in threespine sticklebacks.

Female control of mate plugging in a female-cannibalistic spider (Micaria sociabilis).

BackgroundSperm competition imposes a strong selective pressure on males, leading to the evolution of various physiological, morphological and behavioral traits. Sperm competition can be prevented by blocking or impeding the access to female genitalia by means of a mating plug. We investigated the factors responsible for plug production and function in the promiscuous female-cannibalistic spider Micaria sociabilis (Gnaphosidae).ResultsWe performed mating trials using females with and without a plug that consists of an amorphous mass. The mating trials demonstrated that the probability of male plugging increased non-linearly with the duration of copulation. Copulation duration and plug production seem to be controlled by the female. We found that females terminated matings later if males were fast at genital coupling. Whereas incomplete plugs had disappeared on the day following copulation, complete plugs persisted (40%). In matings with females with complete plugs, only a small proportion of males (7%) were able to remove the plug, indicating the high effectiveness of plugging. Moreover, males ceased attempts to copulate with plugged females with higher probability. 3D X-ray microscopy of the female and male genitalia showed that the plug material can extend far into the female genital tract and that the plug material is produced by a massive gland inside the palpal organ of the modified male pedipalps.ConclusionsOur study demonstrates that the mating plug in M. sociabilis constitutes an effective male strategy to avoid sperm competition that seems to be under female control.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0278-9) contains supplementary material, which is available to authorized users.

Immunization of Female Mice with a Plasmid DNA Vaccine Coding Eight Repeats of Gonadotrophin Releasing Hormone(Gnrh-I) and Eight T-Helper Epitopes Suppress Fertility In Vivo

Induction of an appropriate immune response against gonadotrophin releasing hormone (GnRH-I) disrupt fertility, reduce fecundity and regress tumours of reproductive system.To disrupt fertility a plasmid DNA vaccine was engineered coding eight repeats of GnRH-I and eight T-helper epitopes. Translation efficiency of the vaccine was evaluated in undifferentiated COS1 cells and found to release GnRH-I fusion protein in culture supernatant. Swiss albino female mice (N=24) were immunized with 50μg plasmid DNA construct in study weeks 0, 3, 6, 9 and 12. Group 2 mice were primed with the plasmid DNA in hemagglutinating virus of japanese envelope (HVJE) vector and subsequent boosts were carried out in phosphate buffer saline. Group 3 mice were immunized with the plasmid DNA in non-ionic surfactant vesicles (NISV) and Group 1 was served as untreated control. The effect of immunization was studied in terms of anti-GnRH-I antibody response (OD value at A540 ± SD), suppression of ovarian folliculogenesis, altered uterine histoarchitecture and impaired fertility in vivo in mating trials. In study week 24 OD values of anti- GnRH-I antibody response were 0.982 ± 0.231 in Group 3 mice, followed by 0.783 ± 0.191 in Group 2 in comparison with no response in Group 1 controls (0.237 ± 0.147). Results of mating trials showed conception failure in vaccinated mice; 51, 18 and 05 pups were seen in the uteri of Groups 1, 2 and 3 mice respectively. There was significant (p>0.001) reduction in the weight of ovaries in Group 2 (8.50 ± 2.38 mg) and Group 3 (7.25 ± 0.95 mg) mice compared to Group 1 control (15.00 ± 1.41 mg). Significant reduction of ovarian folliculogenesis was seen in Group 2 (p>0.001) and Group 3 mice (p>0.01). In conclusion, the plasmid DNA vaccine delivered in female mice with HVJE and NISV induced significantly (p>0.001) higher levels of anti-GnRH-I antibody response, suppressed ovarian and uterine function and impaired fertility in vivo.

Diet affects ejaculate traits in a lizard with condition-dependent fertilization success

Sexually selected traits are often driven to costly extremes by persistent directional selection. Energy acquisition and allocation can therefore influence variation in traits subject to both precopulatory and postcopulatory sexual selection, though the later have received much less attention. We tested the condition dependence of sperm morphology, sperm count, and fertilization success in a promiscuous lizard (Anolis sagrei) by 1) collecting sperm samples from wild males that varied naturally in body condition, 2) experimentally altering the body condition of captive males through dietary restriction, and 3) analyzing genetic paternity data from competitive mating trials between captive males that differed in body condition. In both wild and captive males, the length of the sperm midpiece decreased with body condition. Experimental food restriction decreased sperm production, decreased length of the sperm head, increased length of the sperm midpiece, and increased variance in sperm morphology within individuals. When restricted to a single copulation, males on high-intake diets exhibited a slight but nonsignificant fertilization advantage. Reanalysis of a previous experiment in which high- and low-condition males were sequentially allowed to copulate ad libitum for 1 week revealed a significant fertilization bias in favor of high-condition males. When controlling for mean treatment effects on the proportion of offspring sired and on sperm phenotypes, multiple regression revealed negative correlations between fertilization success and sperm head length, midpiece length, and sperm count. Collectively, our results suggest that condition-dependent fertilization success in A. sagrei may be partially mediated by underlying condition dependence of sperm morphology and sperm count.

Male fertility is reduced by chronic intermittent hypoxia mimicking sleep apnea in mice.

Obstructive sleep apnea (OSA) is characterized by intermittent hypoxia and oxidative stress. However, it is unknown whether intermittent hypoxia mimicking OSA modifies male fertility. We tested the hypothesis that male fertility is reduced by chronic intermittent hypoxia mimicking OSA in a mouse model. Case-control comparison in a murine model. University research laboratory. Eighteen F1 (C57BL/6xCBA) male mice. Mice were subjected to a pattern of periodic hypoxia (20 sec at 5% O2 followed by 40 sec of room air) 6 h/day for 60 days or normoxia. After this period, mice performed a mating trial to determine effective fertility by assessing the number of pregnant females and fetuses. After euthanasia, oxidative stress in testes was assessed by measuring the expression of glutathione peroxidase 1 (Gpx1) and superoxide dismutase-1 (Sod1) by reverse-transcription polymerase chain reaction. Sperm motility was determined by Integrated Semen Analysis System (ISAS). Intermittent hypoxia significantly increased testicular oxidative stress, showing a reduction in the expression of Gpx1 and Sod1 by 38.9% and 34.4%, respectively, as compared with normoxia (P < 0.05). Progressive sperm motility was significantly reduced from 27.0 ± 6.4% in normoxia to 12.8 ± 1.8% in the intermittent hypoxia group (P = 0.04). The proportion of pregnant females and number of fetuses per mating was significantly lower in the intermittent hypoxia group (0.33 ± 0.10 and 2.45 ± 0.73, respectively) than in normoxic controls (0.72 ± 0.16 and 5.80 ± 1.24, respectively). These results suggest that the intermittent hypoxia associated with obstructive sleep apnea (OSA) could induce fertility reduction in male patients with this sleep breathing disorder.

Attractant, sexual competitiveness enhancing and toxic activities of the essential oils from Baccharis spartioides and Schinus polygama on Ceratitis capitata Wiedemann

The sterile insect technique is currently used to control the fruit fly pest, Ceratitis capitata Wiedemann. The problem with this technique is a decreased sexual competitiveness of the sterile males. We tested the semiochemical properties of essential oils from non-host species as sexual performance enhancers of C. capitata as well as the attractant activity and toxic effect of the oils on adults. By GC–MS analysis, thirty-seven compounds were identified in the essential oil from Schinus polygama (Anacardiaceae) with relative proportions of the compounds up to 5%. The essential oil from Baccharis spartioides (Asteraceae) presented three monoterpenes hydrocarbon dominating the chemical profile. Prior exposure of males to both essential oils increased the sexual competitiveness compared to untreated males in mating trials. In olfactometry tests, males were slightly attracted by the oil of S. polygama, and the essential oil of B. spartioides significantly attracted the females. We postulate these two aromatic species as new sources of essential oils that can enhance the sexual performance of sterile medfly males used in SIT programs. Moreover, the attractant and toxic properties of the oils suggest they can be candidate substances for lure-and-kill technologies.

A Continuum of Behavioral Plasticity in Urban and Desert Black Widows

AbstractBehavioral plasticity marks an individual's ability to modulate behavior across functional contexts. Behavioral syndromes, on the other hand, appear as consistent individual variation in behavior that is both repeatable for individuals within a functional context (e.g., consistent voracity toward prey) and correlated across contexts (e.g., high voracity toward prey and high levels of boldness toward enemies). Thus, adaptive plasticity and syndromes represent two extremes of a behavioral plasticity continuum upon which most behavioral phenotypes fall. We tested for both adaptive plasticity and behavioral syndromes in the western black widow spider, Latrodectus hesperus. We measured behavior in three contexts: startle, startle + prey, and startle + mate, and found (1) classic behaviorally plastic responses to predation risk, (2) high repeatability of behavior within contexts, and (3) evidence of a correlation between startle + prey and startle + mate contexts, indicative of a behavioral syndrome. As relative behavioral plasticity may vary across populations, we also compared urban and desert populations to test whether spiders from these habitats exhibit different behaviors and/or behavioral syndromes. While we found that urban males used in mating trials courted urban females significantly more than desert females, we found no other differences in the behavior of urban and desert black widows. Thus, black widows, regardless of habitat, are characterized by both context‐specific behavioral plasticity and across‐context correlations, presenting a phenotypic complexity that is likely exhibited, to varying degrees, by most organisms.

Forced copulation as a conditional alternative strategy in camel crickets

In the animal kingdom, males typically acquire reproductive access to females through courtship, nuptial gifts, or combat. In many species, small or poor-condition males that are unable to produce an attractive display, proffer an adequate mating gift, or dominate in male–male competition may resort to forced copulation. Forced copulation has been previously demonstrated in the camel cricket Pristoceuthophilus marmoratus and is uniquely facilitated by male hind leg weaponry that functions in both intrasexual competition and sexual coercion. Because male leg armaments are positively allometric, the largest males would seem best equipped to force-copulate, although they might be the most attractive to females, and so least likely to adopt a forced copulation strategy. In order to resolve this potential paradox and determine which males are in fact most likely to force-copulate, we manipulated male body size using diet and performed mating trials. Results showed that (1) male size increased with diet quality, (2) females appear to prefer larger males, and (3) smaller males were more likely to attempt forced copulation. Our results thus suggest that forced copulation is a condition-dependent alternative mating tactic used by small males unattractive to females.

Tactical adjustment of signalling leads to increased mating success and survival

Most sexually reproducing animals overcome the challenge of searching for and attracting mates by utilizing signals that are broadcast through a spatially and temporally varying environment. A diverse suite of behavioural solutions exist for overcoming such environmental variability, including the adjustment of signalling behaviour based upon receiver feedback. Few studies have directly examined the relationship between such tactical signalling adjustments and proxies of male fitness; the few that have, failed to find a relationship. Using the wolf spider, Schizocosa rovneri, we set out to first quantify among-male variation in the form and degree of responsiveness to female feedback. Following exposure to female receptivity cues, some males increased their signalling on an effective signalling substrate (filter paper) while others decreased signalling on the effective substrate. These groups of males were then run through mating trials, conducted in a heterogeneous environment, to examine the relationship between male signalling adjustments and subsequent mating success. Males that adaptively adjusted their signalling (i.e. increased signalling on a more effective substrate) were (1) more likely to copulate, (2) achieved a copulation more quickly and (3) were less likely to be attacked; thus establishing a positive relationship between tactical adjustments of courtship signalling and male fitness.

Sexual selection on Drosophila serrata male pheromones does not vary with female age or mating status.

Mate preferences are costly and are thought to evolve due to the direct and/or indirect benefits they provide. Such costs and benefits may vary in response to intrinsic and extrinsic factors with important evolutionary consequences. Limited attention has been given to quantifying such variation and understanding its causes, most notably with respect to the direction and strength of preferences for multivariate sexual displays. In Drosophila serrata, female preferences target a pheromone blend of long-chain cuticular hydrocarbons (CHCs). We used a factorial design to test whether female age and mating status generated variation in the strength and direction of sexual selection on male CHCs. Replicate choice mating trials were conducted using young and old females (4 or 10 days post-emergence) that were either virgin or previously mated. The outcome of such trials is known to capture variation in female mate preferences, although male-male interactions may also contribute. Directional sexual selection on male CHCs was highly significant within each treatment, but there was little evidence of any variation among treatments. The absence of treatment effects implies that the multivariate combination of male CHCs preferred by females was constant with respect to female age and mating status. To the extent that male-male interactions may also contribute, our results similarly imply that these did not vary among treatments groups. With respect to D. serrata mate preferences, our results suggest that either plasticity with respect to age and mating status is not beneficial to females, or preference expression is somehow constrained.

Aggressive male mating behavior depends on female maturity in Octopus bimaculoides

This laboratory study examined the combined effects of male and female behaviors on the outcome of mating encounters in Octopus bimaculoides. We found that male–male competition for mating opportunities depends on female maturity; the presence of immature females elicited significantly higher levels of aggression between competing males. We conclude that males are able to assess the reproductive status of females. The study also found that immature and mature females resisted male mating attempts to a similar extent but that males that showed more aggression toward male competitors were able to spend more time in contact with females. We suggest that the lack of prominent visual displays in these mating trials indicates the importance of chemical cues in Octopus mating systems, as has been demonstrated for other cephalopods. This study contributes to the growing research on cephalopod mating systems and in particular shows that Octopus mating dynamics may be more behaviorally complex than initially assumed.

Impaired Sperm Maturation in Rnase9 Knockout Mice1

Ribonuclease, RNase A family, 9 (RNASE9) is a ribonuclease A superfamily member that is expressed only in the epididymis. It is a small, secreted polypeptide, it lacks ribonuclease activity, and its function(s) is unknown. However, epididymis-specific expression suggests a role in sperm maturation. We generated Rnase9(-/-) mice to study RNASE9 function in vivo. We confirm that RNASE9 expression is restricted to the epididymis. Within the epididymis, RNASE9 is first detected in midcaput, persists through the distal caput and corpus, and wanes in the cauda. Rnase9(-/-) mice are born at the expected Mendelian ratio, have normal postnatal growth and development, and have no outwardly apparent phenotype. Spermatogenesis is normal, and Rnase9-null sperm are morphologically normal. Rnase9(-/-) males have normal fertility in unrestricted mating trials, and fertilization rates in in vitro fertilization assays are indistinguishable from wild-type mice. Visual observations coupled with analyses of sperm velocities shortly after swim out from the corpus shows that motility of Rnase9-null sperm is significantly impaired. However, no differences between wild-type and Rnase9-null sperm are detected by computer-assisted sperm analysis 10-90 min after sperm isolation from the corpus or cauda. Assessment of capacitation-dependent signaling pathways in Rnase9-null sperm showed that, while levels of tyrosine phosphorylation of sperm proteins were normal, there was decreased phosphorylation of protein kinase A substrates upon capacitation compared to wild-type mice. In conclusion, RNASE9 is dispensable for fertility, but the absence of RNASE9 during epididymal transit results in impaired sperm maturation.

Host-shift effects on mating behavior and incipient pre-mating isolation in seed beetle

Mating behavior is based on communication among mates and includes both sexual signaling and mating preferences. In phytophagous insects, shift to a novel host will expose associated traits to novel selection regimes and eventually cause assortative mating and sexual isolation between populations inhabiting diverse host plants. We investigated the relationship between short- and long-term changes in mating systems on Acanthoscelides obtectus. Mating preferences were evaluated using measures of copulation frequency in mating trials within and among populations and by measuring time spent in sexual interactions prior to copulation. Sexual signaling was previously analyzed by chemical detection of contact pheromones (i.e., cuticular hydrocarbons [CHCs]), and these results were used in this study. Laboratory populations evolved for 50 generations either on the optimal host (common bean) or on the suboptimal host (chickpea). To determine short-term effects, subsets of individuals from each population were exposed to the alternative host for 1 generation. We revealed higher level of indiscriminate mating in populations, which evolved on the suboptimal host. Males from these populations spent less time in assessing mates although they had the ability to discriminate between signals. Short-term larval experience on the suboptimal host also decreased selectivity of mates. The results imply that plastically induced reduction in mate discrimination, after a shift to suboptimal host, may have been canalized through long-term genetic changes underlying behavioral development. Significant reproductive isolation between the 2 sets of populations was revealed regardless of the short-term host treatment.

Precopulatory sexual selection in the seed bug Lygaeus equestris: a comparison of choice and no-choice paradigms

Mate choice has long been appreciated as a key component of sexual selection. However, how we measure mate choice, both in the field and in the laboratory, remains problematic. Mating preferences may be tested using either no-choice or choice tests, but explicit comparisons between these two experimental paradigms remain limited. It has been suggested that preferences may be stronger in choice tests as they allow simultaneous comparison, and some studies have indeed found stronger mating preferences in choice tests compared to no-choice tests. Here we explicitly tested the effect of experimental choice paradigm on the measurement of sexual selection on male and female morphology in the promiscuous seed bug Lygaeus equestris (Heteroptera, Lygaeidae). We performed mating trials in which we varied the amount of choice presented to each sex, giving four choice treatments: no-choice, male choice, female choice and mutual choice. Overall we found evidence for significant positive directional selection on female body length and stabilizing selection on an overall measure of male body size. However, we found no significant effect of choice paradigm on the patterns of sexual selection for males or females. We suggest this may be because of the method of mate assessment in L. equestris, which appears to be primarily via contact cues, which may limit simultaneous comparison between options. • We investigated sexual selection on male and female morphology in a lygaeid bug. • We varied the level of choice available to males and females during mating trials. • We found significant sexual selection on male and female morphology. • However we found no effect of choice paradigm on the strength of selection. • The mechanism of mate choice in this species may limit comparison between options.

The effect of social environment on alternative mating tactics in male Endler's guppy, Poecilia wingei

Variation in sexual behaviour has both genetic (no experience or social contact needed) and environmental (based on individual experience) components. Within species, males can maximize their fitness during inter- and intrasexual selection in a variety of ways. This may lead to evolution of alternative male mating behaviours resulting in a dichotomy between courting/guarding and sneaking tactics. We used Endler's guppies to investigate (1) whether individual sexually naive males have a preferred mating tactic (courting or sneaking), and (2) how male mating behaviour is affected by recent social history (male- or female-biased social environment). We found that individual males approached females by either courting or sneaking, even with no previous sexual experience. We further demonstrated that male sexual behaviour in standardized mating trials was strongly affected following exposure to a sex-biased social environment for 5 weeks. Males from female-biased social environments showed decreased mating effort overall compared to the baseline level (measured prior to assignment to a social environment treatment) but were more likely to court females rather than attempt sneak copulations. Males from male-biased social environments maintained a high level of mating effort and increased the rate of sneaking attempts compared to courtship displays. Our study highlights that both genetic and environmental sources of variation contribute to individual sexual behaviour. Current sexual behaviour was strongly modulated by recent social history, underpinning the importance of previous experience in the expression of sexual behaviour.

Inbreeding depression of mating behavior and its reproductive consequences in a freshwater snail

Theoretical work predicts that the magnitude of inbreeding depression is particularly high in traits that are closely related to fitness. Despite the extensive work on inbreeding depression of male and female reproductive performance, relatively little is known on how inbreeding impairs male and female mating behavior. We studied inbreeding depression of male and female mating behavior in the simultaneously hermaphroditic freshwater snail Physa acuta to test 1) whether there is inbreeding depression of mating behavior, 2) whether the potential of mate competition and mate choice has an effect on the strength of inbreeding depression, 3) whether the magnitude of inbreeding depression differs between both sex functions, and 4) how inbreeding depression of mating behavior translates into inbreeding depression of reproductive success. For this, we compared the mating behavior between selfed (inbred) and outcrossed (outbred) focal snails in a series of mating trials, in which we manipulated experimentally the potential of mate competition and mate choice. Our results provide evidence for moderate inbreeding depression of the number of copulatory encounters, the number of copulations, and the total time spent mating in both sex functions. The magnitude of inbreeding depression did not differ between the levels of competition and between both sex functions. Finally, our results suggest that inbreeding depression of mating behavior only explains a small fraction of the observed inbreeding depression of reproductive success. We discuss the implications of these findings with respect to precopulatory sexual selection and sex-specific inbreeding depression.

No evidence for size‐assortative mating in the wild despite mutual mate choice in sex‐role‐reversed pipefishes

Size-assortative mating is a nonrandom association of body size between members of mating pairs and is expected to be common in species with mutual preferences for body size. In this study, we investigated whether there is direct evidence for size-assortative mating in two species of pipefishes, Syngnathus floridae and S. typhle, that share the characteristics of male pregnancy, sex-role reversal, and a polygynandrous mating system. We take advantage of microsatellite-based “genetic-capture” techniques to match wild-caught females with female genotypes reconstructed from broods of pregnant males and use these data to explore patterns of size-assortative mating in these species. We also develop a simulation model to explore how positive, negative, and antagonistic preferences of each sex for body size affect size-assortative mating. Contrary to expectations, we were unable to find any evidence of size-assortative mating in either species at different geographic locations or at different sampling times. Furthermore, two traits that potentially confer a fitness advantage in terms of reproductive success, female mating order and number of eggs transferred per female, do not affect pairing patterns in the wild. Results from model simulations demonstrate that strong mating preferences are unlikely to explain the observed patterns of mating in the studied populations. Our study shows that individual mating preferences, as ascertained by laboratory-based mating trials, can be decoupled from realized patterns of mating in the wild, and therefore, field studies are also necessary to determine actual patterns of mate choice in nature. We conclude that this disconnect between preferences and assortative mating is likely due to ecological constraints and multiple mating that may limit mate choice in natural populations.

Misalignment of natural and sexual selection among divergently adapted Drosophila melanogaster populations

The effect of sexual selection on nonsexual fitness is a major unanswered question in evolutionary biology that may have important implications for adaptation, diversification and the evolution of mate preferences. If reproductive success is condition dependent, the resulting sexual selection will tend to align with natural selection, promoting adaptation. One prediction under such a scenario is that adaptation to a novel environment should increase male mating success and hence sexual fitness. Environmentally induced plasticity in mate preferences could also contribute to an alignment of natural and sexual selection if the changes cause females to prefer locally adapted males as mates. We tested for both forms of alignment using a set of 10 independent populations of Drosophila melanogaster that were adapted to one of two environments. Competitive mating trials were performed between pairs of populations adapted to these two environments, with the trials designed to separate the effects of local adaptation on male mating success from plasticity of female mate preferences in response to these environments. Contrary to expectations under an alignment of natural and sexual selection, males did not have higher mating success when competing in the environment to which they were adapted. Furthermore, there was no evidence that females altered their mate choice based on their rearing environment, indicating the absence of any adaptive plasticity in mate preferences. Overall, despite previous evidence of reciprocal adaptation to these different environments, increased nonsexual fitness did not translate into higher mating success, indicating a lack of any alignment with natural selection of this component of male sexual fitness.