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Although studies on sperm competition examined a wide range of taxa, little is known about the selection pressures on male traits in systems with simultaneous risk of sperm competition and sexual cannibalism. Here, we experimentally studied how the risk of sperm competition affects male copulatory behavior in the sexually cannibalistic praying mantis Mantis religiosa. We recorded the onset and duration of copulations following the introduction of virgin, adult praying mantises into mating arenas with three different sex ratio treatments: polyandrous, monogamous, and polygynous. We did not detect any female phenotypic trait predicting cannibalism. The chance of male survival was related to his condition, with males in better condition being cannibalized significantly less often. In contrast, we did not identify any male trait that would favor some males to obtain copulations. Our results on copulation duration support sperm competition theory in that the copulations in the male-biased treatment, where the perceived risk of sperm competition was greatest, were significantly longer than those in single-male treatments. Importantly, males in better condition copulated significantly longer regardless of sex ratio. Overall, our study suggests that males can adjust their copulation behavior in response to the risk of sperm competition even in a system with frequent sexual cannibalism. [ABSTRACT FROM AUTHOR]

Abstract Sexual selection models usually predict directional selection for ornamental traits because of intra- as well as inter-sexual selection. Animals frequently face reproductive trade-offs, such as between mating and parental effort. Provided that both are essential and have opposite effects on ornament expression, we may however not necessarily expect directional selection for ornament size. The house sparrow is an ideal species to study such a trade-off, as the size of the male ornament, the black throat badge, seems to be inversely related to mating and parental effort. It has been suggested that large-badged males invest more in female attraction and territory defence, while small-badged males may invest more in parental care. In a nest-box study, we show that females started to breed earliest and produced the largest clutches when mated to males with average-sized badges that invested in paternal care more than other males. These results are discussed in view of inter- as well intra-sexual selection. Overall, average-badged males experienced the highest hatching failures, their chicks were in the poorest physical condition and they did not fledge more chicks than other males. It is therefore unlikely that the mating advantages that we observed could by themselves lead to stabilizing selection for badge size. Our results rather suggest that badge size in male house sparrows signals different reproductive tactics, which are adapted flexibly according to their physical condition and socio-ecological situations. [ABSTRACT FROM AUTHOR]