Our understanding of sexual selection has greatly improved during the last decades. The focus is no longer solely on males, but also on how female competition and male mate choice shape ornamentation and other sexuall...Our understanding of sexual selection has greatly improved during the last decades. The focus is no longer solely on males, but also on how female competition and male mate choice shape ornamentation and other sexually selected traits in females. At the same time, the focus has shifted from documenting sexual selection to exploring variation and spatiotemporal dynamics of sexual selection, and their evolutionary consequences. Here, I review insights from a model system with exceptionally dynamic sexual selection, the two-spotted goby fish Gobiusculus flavescens. The species displays a complete reversal of sex roles over a 3-month breeding season. The reversal is driven by a dramatic change in the operational sex ratio, which is heavily male-biased at the start of the season and heavily female-biased late in the season. Early in the season, breeding-ready males outnumber mature females, causing males to be highly competitive, and leading to sexual selection on males. Late in the season, mating-ready females are in excess, engage more in courtship and aggression than males, and rarely reject mating opportunities. With typically many females simultaneously courting available males late in the season, males become selective and prefer more colorful females. This variable sexual selection regime likely explains why both male and female G. flavescens have ornamental colors. The G. flavescens model system reveals that sexual behavior and sexual selection can be astonishingly dynamic in response to short-term fluctuations in mating competition. Future work should explore whether sexual selection is equally dynamic on a spatial scale, and related spatiotemporal dynamics.展开更多
Studies in several songbird species have shown that treating females with the androgenic steroid hormone testoste- rone （T） can negatively affect female reproductive behaviors and breeding success. As the effects of...Studies in several songbird species have shown that treating females with the androgenic steroid hormone testoste- rone （T） can negatively affect female reproductive behaviors and breeding success. As the effects of T on females appear to be species-specific, it is not clear if similar effects of high T occur in non-songbird species. Here, we studied the effects of T supplementation on female reproductive behavior and oviposition in the budgerigar, Melopsittacus undulatus, a small monogamous parrot species with distinct sex differences in parental behavior. We experimentally increased T concentrations to male-like levels in T-treated females compared to controls and we allowed females to breed. We found no significant effects of treatment on the latency to enter the nestbox but T treatment significantly interfered with oviposition. Our results show that T-treated females were seven times less likely to produce a clutch than control females. As we found that T treatment had a strong inhibitory effect on oviposition, our results indicate that female budgerigars suffer fitness costs from male-like plasma T levels. Therefore, it may be possible that, also in non-songbird species, selection for higher T levels in males is constrained by a correlated response to selection which imposes fitness costs on females in terms of reproduction. Evaluating whether or not this is indeed the case requires further work combining different approaches to the study of the evolution of male and female testosterone levels [Current Zoology 61 （4）： 586-595, 2015].展开更多
基金The work on which this review article is based has been funded by grants from the Research Council of Norway [Gram Nos. 133553, 146744, 166596, and 178444], the Norwegian University of Science and Technology, the Norwegian Academy of Science and Letters, the Royal Swedish Academy of Sciences, the Nordic Marine Academy, the EU Transnational Access to Research Infrastructures Scheme, the Nordic Council program NORDFORSK, and the National Science Foundation [USA, Grant No. OISE/0701086].
文摘Our understanding of sexual selection has greatly improved during the last decades. The focus is no longer solely on males, but also on how female competition and male mate choice shape ornamentation and other sexually selected traits in females. At the same time, the focus has shifted from documenting sexual selection to exploring variation and spatiotemporal dynamics of sexual selection, and their evolutionary consequences. Here, I review insights from a model system with exceptionally dynamic sexual selection, the two-spotted goby fish Gobiusculus flavescens. The species displays a complete reversal of sex roles over a 3-month breeding season. The reversal is driven by a dramatic change in the operational sex ratio, which is heavily male-biased at the start of the season and heavily female-biased late in the season. Early in the season, breeding-ready males outnumber mature females, causing males to be highly competitive, and leading to sexual selection on males. Late in the season, mating-ready females are in excess, engage more in courtship and aggression than males, and rarely reject mating opportunities. With typically many females simultaneously courting available males late in the season, males become selective and prefer more colorful females. This variable sexual selection regime likely explains why both male and female G. flavescens have ornamental colors. The G. flavescens model system reveals that sexual behavior and sexual selection can be astonishingly dynamic in response to short-term fluctuations in mating competition. Future work should explore whether sexual selection is equally dynamic on a spatial scale, and related spatiotemporal dynamics.
文摘Studies in several songbird species have shown that treating females with the androgenic steroid hormone testoste- rone （T） can negatively affect female reproductive behaviors and breeding success. As the effects of T on females appear to be species-specific, it is not clear if similar effects of high T occur in non-songbird species. Here, we studied the effects of T supplementation on female reproductive behavior and oviposition in the budgerigar, Melopsittacus undulatus, a small monogamous parrot species with distinct sex differences in parental behavior. We experimentally increased T concentrations to male-like levels in T-treated females compared to controls and we allowed females to breed. We found no significant effects of treatment on the latency to enter the nestbox but T treatment significantly interfered with oviposition. Our results show that T-treated females were seven times less likely to produce a clutch than control females. As we found that T treatment had a strong inhibitory effect on oviposition, our results indicate that female budgerigars suffer fitness costs from male-like plasma T levels. Therefore, it may be possible that, also in non-songbird species, selection for higher T levels in males is constrained by a correlated response to selection which imposes fitness costs on females in terms of reproduction. Evaluating whether or not this is indeed the case requires further work combining different approaches to the study of the evolution of male and female testosterone levels [Current Zoology 61 （4）： 586-595, 2015].
