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Exaggerated ornaments provide opportunities to understand how selection can operate at different levels to shape the evolution of a trait. While these features aid their bearer in attracting mates or fending off competitors, they can also be costly and influenced by the environment and genetic variation. The eyestalks of the stalk-eyed fly, Teleopsis dalmanni, are of interest because eyestalk length is the target of both intra- and intersexual selection and is also reduced by loci on a highly-divergent sex ratio X chromosome (XSR), a meiotic driver accounting for up to 30% of wild X chromosomes. Male stalk-eyed flies fight to control access to females and over food using a combination of low-intensity displays and highintensity physical fights. We staged, filmed, and scored contests between pairs of eyespan-matched males to evaluate whether X chromosome type impacts the behavior and outcome of aggressive interactions. While our results broadly match expectations from previous studies, we found that XSR males used more high-intensity behaviors than males carrying a non-driving, standard X chromosome (XST), particularly when their eyestalks were of similar size or smaller than their opponents. Additionally, we found that when XSR males use high-intensity behaviors, they win more bouts than when they use low-intensity behaviors. Taken together, these results suggest that XSR impacts male aggressive behavior to compensate for the shorter eyestalks of XSR males and may help to explain how this selfish chromosome is maintained. [ABSTRACT FROM AUTHOR]

Experimental evolution provides an integrative method for revealing complex interactions among evolutionary processes. One such interaction involves sex-linked selfish genetic elements and sexual selection. X-linked segregation distorters, a type of selfish genetic element, influence sperm transmission to increase in frequency and consequently alter the population sex ratio and the opportunity for sexual selection, while sexual selection may impact the spread of X-linked distorters. Here we manipulated sexual selection by controlling female mating opportunities and the presence of a distorting X chromosome in experimental lines of the stalk-eyed fly, Teleopsis dalmanni, over 11 generations. We find that removal of sexual selection leads to an increase in the frequency of the X-linked distorter and sex ratio across generations and that post-copulatory sexual selection alone is sufficient to limit the frequency of distorters. In addition, we find that male eyestalk length, a trait under pre-copulatory sexual selection, evolves in response to changes in the strength of sexual selection with the magnitude of the response dependent on X chromosome type and the frequency of distorting X chromosomes. These results reveal how a selfish X can interact with sexual selection to influence the evolution of sexually selected traits in multiple ways. [ABSTRACT FROM AUTHOR]

Male pregnancy, a phenomenon unique to seahorses and their relatives, is facilitated by an elaborate brood pouch into which a female deposits eggs during mating (10,11). Far from being a [...], Male pregnancy in seahorses, pipefishes and sea dragons (family Syngnathidae) represents a striking reproductive adaptation that has shaped the evolution of behaviour and morphology in this group of fishes (1-4). In many syngnathid species, males brood their offspring in a specialized pouch, which presumably evolved to facilitate male parental care (5,6). However, an unexplored possibility is that brood pouch evolution was partly shaped by parent-offspring or sexual conflict, processes that would result in trade-offs between current and future pregnancies. Here we report a controlled breeding experiment using the sexually dimorphic Gulf pipefish, Syngnathus scovelli, to test for post-copulatory sexual selection within broods and for trade-offs between successive male pregnancies as functions of female attractiveness. Offspring survivorship within a pregnancy was affected by the size of a male's mate, the number of eggs transferred and the male's sexual responsiveness. Significantly, we also found that embryo survivorship in a current pregnancy was negatively related to survivorship in the prior pregnancy, clearly demonstrating fitness trade-offs between broods. Overall, our data indicate that post-copulatory sexual selection and sexual conflict occur in Gulf pipefishes. The conflict seems to be mediated by a strategy of cryptic choice in which males increase rates of offspring abortion in pregnancies from unattractive mothers to retain resources for future reproductive opportunities. Hence, the male brood pouch of syngnathid fishes, which nurtures offspring (7-9), also seems to have an important role as an arbiter of conflict between the sexes.

Environmental estrogens have been shown to affect populations of aquatic organisms in devastating ways, including feminization of males, alterations in mating behaviors, and disruption of sexual selection. Studies have shown 17α-ethinylestradiol (EE2) exposure to induce female-like secondary sexual traits in male Gulf pipefish, changing how females perceive affected males. We aimed to understand the effects of EE2 exposure on the sex-role-reversed mating system and the strength of selection in Gulf pipefish. We used artificial Gulf pipefish breeding aggregations and microsatellite-based parentage analysis to determine maternity. We then calculated the opportunity for selection and selection differentials on body size for both sexes during three consecutive episodes of selection. Exposure to EE2 did not affect the strength of selection, likely due to the unusual sex-role-reversed mating system found in this species. With respect to multiply mated females, EE2-exposed females produced more eggs with higher embryo survivorship than nonexposed females. Thus, short-term exposure to low concentrations (2.0 ng/L) of EE2 in Gulf pipefish enhanced female reproductive success. However, higher EE2 concentrations (5.0 ng/L) caused complete reproductive failure in Gulf pipefish males. These results call for more work on the long-term effects of EE2 exposure in Gulf pipefish in artificial and natural populations. [ABSTRACT FROM AUTHOR]

The use of molecular techniques for parentage analysis has been a booming science for over a decade. The most important technological breakthrough was the introduction of microsatellite markers to molecular ecology, an advance that was accompanied by a proliferation and refinement of statistical techniques for the analysis of parentage data. Over the last several years, we have seen steady progress in a number of areas related to parentage analysis, and the prospects for successful studies continue to improve. Here, we provide an updated guide for scientists interested in embarking on parentage analysis in natural or artificial populations of organisms, with a particular focus on computer software packages that implement various methods of analysis. Our survey of the literature shows that there are a few established methods that perform extremely well in the analysis of most types of parentage studies. However, particular experimental designs or study systems can benefit from some of the less well-known computer packages available. Overall, we find that parentage analysis is feasible and satisfying in most systems, and we try to provide a simple roadmap to help other scientists navigate the confusing topography of statistical techniques. [ABSTRACT FROM AUTHOR]