We report that Western Sandpipers （Calidris mauri） on Alaska’s Yukon-Kuskokwim River Delta exhibited aggregated breeding behavior at a relatively small spatial scale. Prior to clutch initiation, males performing so...We report that Western Sandpipers （Calidris mauri） on Alaska’s Yukon-Kuskokwim River Delta exhibited aggregated breeding behavior at a relatively small spatial scale. Prior to clutch initiation, males performing song flight displays on a 36 ha plot were aggregated as were subsequent initial nesting attempts on the plot. We tested three hypotheses commonly invoked to explain aggregated breeding in territorial species （social mate choice, predation, and material resources hypotheses）, and found support for the material resources hypothesis, as dispersed individuals were more often associated with tundra habitat patches, and aggregated individuals nested more often in undulating-tundra habitat patches compared to patch availability. The pattern of habitat occupancy conformed to an ideal despotic distribution with aggregated nesting birds in undulating-tundra patches experiencing lower reproductive success. On our study plot, older, more aggressive males solicited females more often, and defended larger, more dispersed sites in tundra habitat patches, compared to younger, less aggressive males that were aggregated in undulating-tundra habitat patches. Breeding aggregations are often concentrated on or near a critical resource. In contrast, Western Sandpiper breeding aggregations occur when dominant and/or older individuals exclude younger, subordinate individuals from preferred habitat. Although many taxa of non-colonial birds have been reported to aggregate breeding territories, this is the first quantitative report of aggregated breeding behavior in a non-colonial monogamous shorebird species prior to hatch.展开更多
Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recogn...Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recognized. Therefore, studying the trade-offs between natural selection and sexual selection is crucial to a better understanding of the ecology underlying the evolution of sexual dimorphism. The freshwater blenny Salaria fluviatilis, a fish inhabiting lakes and rivers around the Mediterranean Sea, displays strong sexual dimorphism in size, shape, and behavior （i.e., larger body and head size for males and higher swimming requirements for females during the reproductive period）. We tested for differences in sexual dimorphism in size and shape between the populations from lake and river habitats with the goal of identifying the trade-offs between natural and sexual se- lection that underlie variations in sexual dimorphism in this species. Our results show i） differences in sexual size dimorphism （SSizeD） in accordance to Rensch＇s rule （i.e., larger individuals in rivers associated with higher SSizeD）, and ii） a decrease in shape differentiation between males and fe- males in lake populations. Together, this suggests that the different environmental conditions between lake and river habitats （e.g., resource limitations, predation pressure, water velocity） affect the relative importance of sexual selection in the display of sexual dimorphism within the species. This study highlights the importance of considering the environmental conditions to which populations are exposed to better understand the ecology underlying the evolution of sexual dimorphism.展开更多
文摘We report that Western Sandpipers （Calidris mauri） on Alaska’s Yukon-Kuskokwim River Delta exhibited aggregated breeding behavior at a relatively small spatial scale. Prior to clutch initiation, males performing song flight displays on a 36 ha plot were aggregated as were subsequent initial nesting attempts on the plot. We tested three hypotheses commonly invoked to explain aggregated breeding in territorial species （social mate choice, predation, and material resources hypotheses）, and found support for the material resources hypothesis, as dispersed individuals were more often associated with tundra habitat patches, and aggregated individuals nested more often in undulating-tundra habitat patches compared to patch availability. The pattern of habitat occupancy conformed to an ideal despotic distribution with aggregated nesting birds in undulating-tundra patches experiencing lower reproductive success. On our study plot, older, more aggressive males solicited females more often, and defended larger, more dispersed sites in tundra habitat patches, compared to younger, less aggressive males that were aggregated in undulating-tundra habitat patches. Breeding aggregations are often concentrated on or near a critical resource. In contrast, Western Sandpiper breeding aggregations occur when dominant and/or older individuals exclude younger, subordinate individuals from preferred habitat. Although many taxa of non-colonial birds have been reported to aggregate breeding territories, this is the first quantitative report of aggregated breeding behavior in a non-colonial monogamous shorebird species prior to hatch.
文摘Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recognized. Therefore, studying the trade-offs between natural selection and sexual selection is crucial to a better understanding of the ecology underlying the evolution of sexual dimorphism. The freshwater blenny Salaria fluviatilis, a fish inhabiting lakes and rivers around the Mediterranean Sea, displays strong sexual dimorphism in size, shape, and behavior （i.e., larger body and head size for males and higher swimming requirements for females during the reproductive period）. We tested for differences in sexual dimorphism in size and shape between the populations from lake and river habitats with the goal of identifying the trade-offs between natural and sexual se- lection that underlie variations in sexual dimorphism in this species. Our results show i） differences in sexual size dimorphism （SSizeD） in accordance to Rensch＇s rule （i.e., larger individuals in rivers associated with higher SSizeD）, and ii） a decrease in shape differentiation between males and fe- males in lake populations. Together, this suggests that the different environmental conditions between lake and river habitats （e.g., resource limitations, predation pressure, water velocity） affect the relative importance of sexual selection in the display of sexual dimorphism within the species. This study highlights the importance of considering the environmental conditions to which populations are exposed to better understand the ecology underlying the evolution of sexual dimorphism.
