RESUMO
Competitive fertilization success can depend on the relative abilities of competing males to fertilize available ova, and on mechanisms of cryptic female choice that moderate paternity. Competitive fertilization success is thus an emergent property of competing male genotypes, female genotype and their interactions. Accurate estimates of intrinsic male effects on competitive fertilization success are therefore problematic. We used a cross-classified nonbreeding design in which rival male family background was standardized to partition variation in competitive fertilization success among male and female family backgrounds in the field cricket Teleogryllus oceanicus. Male effects were close to zero, supporting previous quantitative genetic designs in which male competitors were assigned at random. In contrast, some 22% of the variance in competitive fertilization success was explained by female effects, suggesting that paternity in this species is influenced strongly by cryptic female choice.
Assuntos
Gryllidae/fisiologia , Preferência de Acasalamento Animal/fisiologia , Espermatozoides/fisiologia , Animais , Comportamento Competitivo/fisiologia , Feminino , Fertilização/fisiologia , Genótipo , Modelos Lineares , Masculino , Repetições de Microssatélites/genética , Reação em Cadeia da Polimerase , Reprodução/fisiologia , Análise de Sequência de DNA , Austrália OcidentalRESUMO
The size of the vertebrate brain is shaped by a variety of selective forces. Although larger brains (correcting for body size) are thought to confer fitness advantages, energetic limitations of this costly organ may lead to trade-offs, for example as recently suggested between sexual traits and neural tissue. Here, we examine the patterns of selection on male and female brain size in pinnipeds, a group where the strength of sexual selection differs markedly among species and between the sexes. Relative brain size was negatively associated with the intensity of sexual selection in males but not females. However, analyses of the rates of body and brain size evolution showed that this apparent trade-off between sexual selection and brain mass is driven by selection for increasing body mass rather than by an actual reduction in male brain size. Our results suggest that sexual selection has important effects on the allometric relationships of neural development.
