Inbreeding reveals mode of past selection on male reproductive characters in Drosophila melanogaster
Ecology and Evolution
© 2013 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/3.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Directional dominance is a prerequisite of inbreeding depression. Directionality arises when selection drives alleles that increase fitness to fixation and eliminates dominant deleterious alleles, while deleterious recessives are hidden from it and maintained at low frequencies. Traits under directional selection (i.e., fitness traits) are expected to show directional dominance and therefore an increased susceptibility to inbreeding depression. In contrast, traits under stabilizing selection or weakly linked to fitness are predicted to exhibit little-to-no inbreeding depression. Here, we quantify the extent of inbreeding depression in a range of male reproductive characters and then infer the mode of past selection on them. The use of transgenic populations of Drosophila melanogaster with red or green fluorescent-tagged sperm heads permitted in vivo discrimination of sperm from competing males and quantification of characteristics of ejaculate composition, performance, and fate. We found that male attractiveness (mating latency) and competitive fertilization success (P2) both show some inbreeding depression, suggesting they may have been under directional selection, whereas sperm length showed no inbreeding depression suggesting a history of stabilizing selection. However, despite having measured several sperm quality and quantity traits, our data did not allow us to discern the mechanism underlying the lowered competitive fertilization success of inbred (f = 0.50) males.
We thank M. Puurtinen for helpful comments on an earlier draft of this manuscript and T. Ketola for insightful discussions. This research was supported by grants from the Academy of Finland (135684 and 250999) and Ella and Georg Ehrnrooth's Foundation to O. A.-H., and from the U.S. National Science Foundation (DEB-0814732 and DEB-1021240) to S. P., J. M. B., and M. K. M., and by a fellowship of the Swiss National Science Foundation (PBSKP3_130878) to S. L.
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Vol. 3 (7), pp. 2089 - 2102
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