Experimental evidence for the evolution of numerous, tiny sperm via sperm competition

Gage, Matthew J G and Morrow, Edward H (2003) Experimental evidence for the evolution of numerous, tiny sperm via sperm competition. Current Biology, 13 (9). pp. 754-757. ISSN 09609822

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Abstract

Sperm competition, when sperm from different males compete to fertilize a female's ova [1], is a widespread and fundamental force in the evolution of animal reproduction [2]. The earliest prediction of sperm competition theory was that sperm competition selected for the evolution of numerous, tiny sperm, and that this force maintained anisogamy [3]. Here, we empirically test this prediction directly by using selective breeding to generate controlled and independent variance in sperm size and number traits in the cricket Gryllus bimaculatus. We find that sperm size and number are male specific and vary independently and significantly. We can therefore noninvasively screen individuals and then run sperm competition experiments between males that differ specifically in sperm size and number traits. Paternity success across 77 two-male sperm competitions (each running over 30-day oviposition periods) shows that males producing both relatively small sperm and relatively numerous sperm win competitions for fertilization. Decreased sperm size and increased sperm number both independently predicted sperm precedence. Our findings provide direct experimental support for the theory that sperm competition selects for maximal numbers of miniaturized sperm [3]. However, our study does not explain why G. bimaculatus sperm length persists naturally at ∼1 mm; we discuss possibilities for this sperm size maintenance

Item Type: Article
Schools and Departments: School of Life Sciences > Evolution, Behaviour and Environment
Subjects: Q Science > QH Natural history > QH0301 Biology > QH0359 Evolution
Depositing User: Ted Morrow
Date Deposited: 12 Nov 2012 13:35
Last Modified: 12 Nov 2012 13:35
URI: http://sro.sussex.ac.uk/id/eprint/40257
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