Frequencies of alternative mating strategies influence female mate preference in the swordtail Xiphophorus multilineatus (original) (raw)
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Animal Behaviour, 2010
The evolutionary importance of variation in female preferences has been ignored until recently, in part because evidence that variation in specific female preferences results in variation in mate choice in the wild has been lacking. In the laboratory, females of the swordtail fish Xiphophorus multilineatus prefer large males that court (courters) to small males that sneak (sneakers). However, variation in this preference is related to female size, with the strength of preference for courter males increasing with female size. In this study we found that both a female's size and her strength of preference for courter males were significantly related to whether or not she mated with a courter male. These results provide strong evidence for variation in female mate preference influencing the mating success of males in the wild. When combined with previous results demonstrating a correlation between female size distribution and frequency of the two types of males across populations, our results suggest that variation in female preference helps to promote variation in male alternative mating behaviours, and ultimately heritable variation in male traits. Ó
Male-male competition, female mate choice and their interaction: determining total sexual selection
Journal of Evolutionary Biology, 2009
Empirical studies of sexual selection typically focus on one of the two mechanisms of sexual selection without integrating these into a description of total sexual selection, or study total sexual selection without quantifying the contributions of all of the mechanisms of sexual selection. However, this can provide an incomplete or misleading view of how sexually selected traits evolve if the mechanisms of sexual selection are opposing or differ in form. Here, we take a two-fold approach to advocate a direction for future studies of sexual selection. We first show how a quantitative partitioning and examination of sexual selection mechanisms can inform by identifying illustrative studies that describe both male–male competition and female mate choice acting on the same trait. In our sample, the most common trait where this occurred was body size, and selection was typically linear. We found that male–male competition and female mate choice can be reinforcing or opposing, although the former is most common in the literature. The mechanisms of sexual selection can occur simultaneously or sequentially, and we found they were more likely to be opposing when the mechanisms operated sequentially. The degree and timing that these mechanisms interact have important implications for the operation of sexual selection and needs to be considered in designing studies. Our examples highlight where empirical data are needed. We especially lack standardized measures of the form and strength of selection imposed by each mechanism of sexual selection and how they combine to determine total sexual selection. Secondly, using quantitative genetic principles, we outline how the selection imposed by individual mechanisms can be measured and combined to estimate the total strength and form of sexual selection. We discuss the evolutionary consequences of combining the mechanisms of sexual selection and interpreting total sexual selection. We suggest how this approach may result in empirical progress in the field of sexual selection.
Animal Behaviour, 2007
Female preference variation over space and time could be an alternative to frequency-dependent selection as a mechanism maintaining alternative male reproductive strategies. In the swordtail fish, Xiphophorus nigrensis, males have alternative strategies where large courting males (courters) and smaller males (sneakers) have equal fitnesses due to a mating advantage for the courters and a higher probability of reaching sexual maturity for the sneakers. Variation in one of these advantages over space or time may be the mechanism that maintains these two strategies. We examined female preference variation for the courting strategy in Xiphophorus multilineatus, a species with the same strategies. Females had an overall significant preference for courters. The strength of this preference was positively related to female size, with smaller females having a weak preference for courters. If the relationship between female size and strength of preference is consistent over space and time, more smaller females would result in an weaker preference for courters, which would increase the relative mating advantage of sneakers. We assessed female size distribution and the frequency of each strategy across space and time and detected significant differences in mean female size across subpopulations and across time, as well as a relationship between mean female size and the relative frequencies of the two male strategies: courters were significantly more common in those samples with the largest females. These results suggest that variation across subpopulations of X. multilineatus in female preferences over space and/or time could shift the balance in fitness between the two strategies.