SEXUAL SELECTION ACCOUNTS FOR THE GEOGRAPHIC REVERSAL OF SEXUAL SIZE DIMORPHISM IN THE DUNG FLY, SEPSIS PUNCTUM (DIPTERA: SEPSIDAE)
Article first published online: 16 MAR 2012
© 2012 The Author(s).
Volume 66, Issue 7, pages 2117–2126, July 2012
How to Cite
Puniamoorthy, N., Schäfer, M. A. and Blanckenhorn, W. U. (2012), SEXUAL SELECTION ACCOUNTS FOR THE GEOGRAPHIC REVERSAL OF SEXUAL SIZE DIMORPHISM IN THE DUNG FLY, SEPSIS PUNCTUM (DIPTERA: SEPSIDAE). Evolution, 66: 2117–2126. doi: 10.1111/j.1558-5646.2012.01599.x
- Issue published online: 3 JUL 2012
- Article first published online: 16 MAR 2012
- Received November 25, 2011 Accepted January 30, 2012
- Body size;
- natural selection;
- population differentiation;
- sepsid flies;
- sexual selection
Sexual size dimorphism (SSD) varies widely across and within species. The differential equilibrium model of SSD explains dimorphism as the evolutionary outcome of consistent differences in natural and sexual selection between the sexes. Here, we comprehensively examine a unique cross-continental reversal in SSD in the dung fly, Sepsis punctum. Using common garden laboratory experiments, we establish that SSD is male-biased in Europe and female-biased in North America. When estimating sexual (pairing success) and fecundity selection (clutch size of female partner) on males under three operational sex ratios (OSRs), we find that the intensity of sexual selection is significantly stronger in European versus North American populations, increasing with male body size and OSR in the former only. Fecundity selection on female body size also increases strongly with egg number and weakly with egg volume, however, equally on both continents. Finally, viability selection on body size in terms of intrinsic (physiological) adult life span in the laboratory is overall nil and does not vary significantly across all seven populations. Although it is impossible to prove causality, our results confirm the differential equilibrium model of SSD in that differences in sexual selection intensity account for the reversal in SSD in European versus North American populations, presumably mediating the ongoing speciation process in S. punctum.