Female Fertilization: Effects of Sex-Specific Density and Sex Ratio Determined Experimentally for Colorado Potato Beetles and Drosophila Fruit Flies

Abstract

If males and females affect reproduction differentially, understanding and predicting sexual reproduction requires specification of response surfaces, that is, two-dimensional functions that relate reproduction to the (numeric) densities of both sexes. Aiming at rigorous measurement of female per capita fertilization response surfaces, we conducted a multifactorial experiment and reanalyzed an extensive data set. In our experiment, we varied the density of male and female Leptinotarsa decemlineata (Colorado potato beetles) by placing different numbers of the two sexes on enclosed Solanum tuberosum (potato plants) to determine the proportion of females fertilized after 3 or 22 hours. In the reanalysis, we investigated how the short-term fertilization probability of three Drosophila strains (melanogaster ebony, m. sepia, and simulans) depended on adult sex ratio (proportion of males) and total density. The fertilization probability of female Leptinotarsa decemlineata increased logistically with male density, but not with female density. These effects were robust to trial duration. The fertilization probability of female Drosophila increased logistically with both sex ratio and total density. Treatment effects interacted in m. sepia, and simulans. These findings highlight the importance of well-designed, multifactorial experiments and strengthen previous experimental evidence for the relevance of sex-specific densities to understanding and prediction of female fertilization probability.

Adult sex ratios: causes of variation and implications for animal and human societies

“…Population density, however, may modify male and female mating strategies and the response of individuals towards skewed ASRs. In fruit flies and beetles, fertilization success increases with both male-skewed ASRs and population density 101 . The effects of the ASR and density, however, is not simply additive because fertilization success increases more quickly with male-skewed ASR at high population densities than at low densities.…”

Divorce and Infidelity Are Associated with Skewed Adult Sex Ratios in Birds

“…Furthermore, there may be feedbacks between ASR and behavior, resulting in quick parallel changes in ASR, mating behavior, and breeding systems [4,42,43]. Experimental manipulations in laboratory and in seminatural conditions have made promising advances toward revealing these relationships [44][45][46][47][48][49], although further studies are needed to reveal the full implications of the positive and negative feedbacks between ASR and mating behavior.…”

Sex-biased survival predicts adult sex ratio variation in wild birds

“…For example, at male-biased ASR, rates of aggression increase; males harass females, which in turn induces increased female mortality [14]. Moreover, in species with male-biased ASR, courtship behaviour and male-male competition intensify [15,16], and/or males are more likely to provide care for their young than at female-biased ASRs [5,13,17]. Furthermore, ASR is a significant predictor of sex roles: birds with female-biased (or even) ASR typically exhibit conventional sex roles whereby males compete for females and females look after the young, whereas species with malebiased ASR often exhibit sex role reversal: males care for the young, whereas females compete for access to males [13].…”