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Sexual selection accounts for the geographic reversal of sexual size dimorphism in the dung fly, Sepsis punctum (Diptera: Sepsidae)


Puniamoorthy, Nalini; Schäfer, Martin A; Blanckenhorn, Wolf U (2012). Sexual selection accounts for the geographic reversal of sexual size dimorphism in the dung fly, Sepsis punctum (Diptera: Sepsidae). Evolution, International Journal of Organic Evolution, 66(7):2117-2126.

Abstract

Sexual size dimorphism (SSD) varies widely across and within species. The differential equilibrium model of SSD explains di- morphism 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 labo- ratory 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.

Abstract

Sexual size dimorphism (SSD) varies widely across and within species. The differential equilibrium model of SSD explains di- morphism 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 labo- ratory 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.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Date:2012
Deposited On:08 Mar 2013 14:19
Last Modified:07 Dec 2017 20:31
Publisher:Blackwell, Society for the Study of Evolution
ISSN:0014-3820
Additional Information:Author Posting. © The Authors 2012. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Evolution, 66(7), 2117-2126. http://dx.doi.org/10.1111/j.1558-5646.2012.01599.x.
Publisher DOI:https://doi.org/10.1111/j.1558-5646.2012.01599.x
PubMed ID:22759289

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