RESUMEN

Models reveal that sexually antagonistic co-evolution exaggerates female resistance and male persistence traits. Here we adapt an established model by including directional sexual selection acting against persistence. We find similar equilibria to previous models showing that sexually antagonistic co-evolution can be limited by counteracting sexual, as well as, natural selection. We tested the model using empirical data for the seaweed fly, Coelopa ursina, in which body size acts as a persistence and a resistance trait. Our model can generate continuous co-evolutionary cycles and stable equilibria, however, all simulations using empirically derived parameter estimates reach stable equilibria. Thus, stable equilibria might be more common in nature than continuous co-evolutionary cycles, suggesting that sexual conflict is unlikely to promote speciation. The model predicts male biased sexual size dimorphism for C. ursina, comparable with empirically observed values. Male persistence is shown to be more sensitive than female resistance to changes in model parameters.

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RESUMEN

The seaweed fly, Coelopa frigida, exhibits LMSP. A large chromosomal inversion system affects many traits including egg-to-adult viability via heterosis. Consequently, there is also considerable potential for cryptic female mate choice to operate on the basis of sperm karyotype. Here, we investigated the effect of time interval and chromosomal inversion karyotype on postcopulatory sexual selection. Homokaryotypic females were mated with a male of the same and a male of the opposite homokaryotype. The order of the matings was varied so cryptic female mate choice could operate either in concert or antagonistically with LMSP. LMSP was found when there was a 24 h time interval between matings, irrespective of the order in which the males were mated. However, when the males were mated in quick succession the order of mating was important. When LMSP and cryptic female mate choice work in concert a high level of LMSP was found. However, when the male of opposite homokaryotype mated first, then first male sperm precedence was observed. This suggests that polyandrous females might be able to bias paternity but only when matings occur in quick succession. Consequently, population density is likely to affect the operation of postcopulatory sexual selection.

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RESUMEN

The seaweed fly mating system is characterized by pre-mating struggles during which females exhibit a mate rejection response involving kicking, shaking and abdominal curling. Males must resist rejection until females become passive and allow copulation to take place. However, despite the vigorous nature of the struggle males frequently dismount passive females without attempting copulation. Here we show that rejected females suffered higher post-encounter mortality rates than those accepted by males in the seaweed fly Gluma musgravei. Furthermore, we show that males also preferentially mounted females with higher future longevity. We propose that this male mate choice for female survivorship has evolved as a result of females often having to survive for long periods after mating until suitable oviposition sites become available. Such male preferences for female survivorship may be common in species in which oviposition must sometimes be substantially delayed after mating.

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RESUMEN

The mating preferences of female seaweed flies Coelopa frigida were determined by observing their acceptance or rejection of males of known size. The inversion karyotype of both males and females was also determined. Females exhibited a preference to mate with large males, and evidence is presented that a genetic correlation exists between the female preference and the preferred trait. Females carrying the inversion karyotype associated with large male size showed a strong preference for large males; females carrying the inversion associated with small male size also exhibited a preference for large males, but it was significantly less strong. This finding suggests that a Fisherian process may be operating.