Tradeoffs limit the evolution of male traits that are attractive to females

Tradeoffs occur between a variety of traits in a diversity of organisms, and these tradeoffs can have major effects on ecological and evolutionary processes. Far less is known, however, about tradeoffs between male traits that affect mate attraction than about tradeoffs between other types of traits. Previous results indicate that females of the variable field cricket, Gryllus lineaticeps, prefer male songs with higher chirp rates and longer chirp durations. In the current study, we tested the hypothesis that a tradeoff between these traits affects the evolution of male song. The two traits were negatively correlated among full-sibling families, consistent with a genetically based tradeoff, and the tradeoff was stronger when nutrients were limiting. In addition, for males from 12 populations reared in a common environment, the traits were negatively correlated within populations, the strength of the tradeoff was largely invariant across populations, and the within-population tradeoff predicted how the traits have evolved among populations. A widespread tradeoff thus affects male trait evolution. Finally, for males from four populations assayed in the field, the traits were negatively correlated within and among populations. The tradeoff is thus robust to the presence of environmental factors that might mask its effects. Together, our results indicate there is a fundamental tradeoff between male traits that: (i) limits the ability of males to produce multiple attractive traits; (ii) limits how male traits evolve; and (iii) might favor plasticity in female mating preferences. Includes Supplementary Materials

The Phylogenetic Distribution of a Female Preference

Robust phylogenetic information can be instrumental to the study of the evolution of female mating preferences and preferred male traits. In this paper, the evolution of a preexisting female bias favoring a sword in male swordtail fish and the evolution of the sword, a complex character, are used to demonstrate how the evolution of mating preferences and preferred traits can be examined in a phylogenetic context. Phylogenetic information suggests that a preference for a sword arose prior to the evolution of the sword in the genus Xiphophorus and that the sword was adaptive at its origin. A phylogenetic approach to the study of female preferences and male traits can also be informative when used in conjunction with mate choice theory in making predictions about evolutionary changes in an initial bias, both prior to the appearance of the male trait it favors and subsequent to the appearance of the trait

The Relative Importance of Different Direct Benefits in the Mate Choices of a Field Cricket

Discussions about the evolution of female mating preferences have often suggested that females should express multiple strong preferences when different male traits are correlated with different mating benefits, yet few studies have directly tested this hypothesis by comparing the strength of female preferences for male traits known to be correlated with different benefits. In the variable field cricket, Gryllus lineaticeps, females receive fecundity and fertility benefits from mating with males with higher chirp rates and life-span benefits from mating with males with longer chirp durations. Although females prefer higher chirp rates and longer chirp durations when the other trait is held constant, it is possible that they give priority to one of these song traits when both vary. In this study, we examined the relative importance of chirp rate and chirp duration in female mate choice using single-stimulus presentations of songs that varied in both chirp rate and chirp duration. Females expressed both directional and stabilizing preferences based on chirp rate, responding most strongly to a chirp rate approximately one standard deviation above the population mean. Females did not express preferences based on chirp duration, and did not express correlational preferences. These results suggest that females may give priority to the reproductive benefits provided by males that produce higher chirp rates

Variation in Response to Artificial Selection for Light Sensitivity in Guppies (\u3ci\u3ePoecilia reticulate\u3c/i\u3e)

We performed artificial selection on the visual system in guppies (Poecilia reticulate), using the optomotor reaction threshold as the selection criterion. Two lines were selected for increased sensitivity to blue light, two were selected for increased sensitivity to red light, and two were unselected controls. There was significant response to selection in all four selected lines and significant heritability for sensitivity. An examination of the spectral sensitivity function showed that the form of the response differed between the red and blue lines and among the red lines. Such divergence is likely because there are many different mechanisms allowing response to selection for spectral sensitivity. Diverse mechanisms allow a divergent response by different populations to the same selective pressures. Such a mechanism can promote diversity in vision and visual signals, and any multicomponent system where different components can respond to the same selective regime

Predator exposure alters female mate choice in the green swordtail

Female green swordtails, Xiphophorus helleri, show a mating preference for males with brightly colored, elongated swords. This preference is thought to be due to a preexisting receiver bias favoring longer sworded males. In this study, we examined variation in the expression of this sword bias in females. Specifically, we tested the hypothesis that an increase in perceived predation risk will decrease female response to males with longer swords. We used a video playback experiment to evaluate female choice between two recordings of a displaying male that differed only in sword length. We scored responses of females to these recordings immediately before and after they had been exposed to a video recording of a predation event between a cichlid and a male possessing a long sword. We found that prior to exposure to this predation event, females preferred the male with the longer sword. However, after exposure to the predator, females altered their mating response, preferring the male with the sword removed. Exposure to the predator also caused an increase in the frequency with which females moved from potential mating positions to a neutral zone. The results presented here suggest that the female preference for males with longer swords can be modulated based on the perceived risk of predation. Copyright 2003.