Sexual Selection in the Gift-Giving Dance Fly, Rhamphomyia Sulcata, Favors Small Males Carrying Small Gifts

Abstract

. In some species of insects males transfer a gift to females during courtship or copulation. In the dance flies these nuptial gifts vary from nutritious prey items to inedible tokens such as a leaf, stone, or silk balloon. Nuptial gifts in dance flies are presumed to increase male mating success. We examined the strength and form of sexual selection on male Rhamphomyia sulcata, an empidid in which males provide females with a nutritious prey item as a nuptial gift. We found that whereas large males carried large gifts, neither large males nor gifts were targets of sexual selection. Indeed, correlational selection analysis and nonparametric examination of the fitness surfaces revealed that small males carrying small gifts were the most successful. Males may be more maneuverable or flight efficient with small gifts, or small males with large gifts may be unable to carry both a large gift and a female in the paired descent flight. These results suggest carrying constraints may be an important factor in determining selection on nuptial gift size. The largest target of sexual selection was old males. Old males were also paired with the largest and most fecund females, highlighting the role mate quality can further contribute to selection on males. Correlational selection analysis also revealed selection for an increase in covariance between male wing length and body size, and for an increase in slope between these traits. Males who deviate away from the optimal phenotypic relationship for two tightly related morphological traits, such as tibia and wing length, may have overall reduced performance. These findings highlight the role correlational sexual selection can play in optimizing nonsexual male morphology and scaling relationships. This study questions the role of the nuptial gift in dance flies as a resource for females.

Stabilizing sexual selection for female ornaments in a dance fly

“…Like many other assessments of sexual selection in insects including dance flies (Sadowski et al. , 1999; LeBas et al. , 2003, 2004; Bussière et al.…”

“…Unlike many other empidines (e.g. Svensson & Petersson, 1987; Preston‐Mafham, 1999; LeBas et al. , 2003, 2004; Daugeron & Grooterat, 2005), copulation occurs ‘on the wing’ so that inflated mating females remain in flight while consuming the nuptial gift.…”

The Importance of Female Choice, Male-Male Competition, and Signal Transmission as Causes of Selection on Male Mating Signals

“…All signal parameters were first log‐transformed and standardized within year. The selection gradients were calculated using partial regression coefficients and significance testing was done using a logistic regression, as in Fairbairn and Preziosi (1996) and LeBas et al (2004). The model included both linear and nonlinear forms of each signal parameter.…”

All that Glisters is not Gold: Sensory Bias, Sexual Conflict and Nuptial Feeding in Insects and Spiders

“…Furthermore, token gifts have the additional advantage of having a large volume relative to their weight, providing a large visual target to females, while potentially minimizing carrying costs (LeBas & Hockham 2005), although the large surface area could increase drag (Sadowski et al. 1999; LeBas et al. 2004).…”