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No evidence of tradeoffs in the evolution of sperm numbers and sperm size in mammals

Tourmente, M and DelBarco-Trillo, J and Roldan, ERS (2015) No evidence of tradeoffs in the evolution of sperm numbers and sperm size in mammals. Journal of Evolutionary Biology. ISSN 1420-9101

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Abstract

Postcopulatory sexual selection, in the form sperm competition, has influenced the evolution of several male reproductive traits. However, theory predicts that sperm competition would lead to tradeoffs between numbers and size of spermatozoa because increased costs per cell would result in a reduction of sperm number if both traits share the same energetic budget. Theoretical models have proposed that, in large animals, increased sperm size would have minimal fitness advantage compared with increased sperm numbers. Thus, sperm numbers would evolve more rapidly than sperm size under sperm competition pressure. We tested in mammals whether sperm competition maximizes sperm numbers and size, and whether there is a tradeoff between these traits. Our results showed that sperm competition maximizes sperm numbers in eutherian and metatherian mammals. There was no evidence of a tradeoff between sperm numbers and sperm size in any of the two mammalian clades since we did not observe any significant relationship between sperm numbers and sperm size once the effect of sperm competition was taken into account. Maximization of both numbers and size in mammals may occur because each trait is crucial at different stages in sperm's life; e.g., size determined sperm velocity is a key determinant of fertilization success. In addition, numbers and size may also be influenced by diverse energetic budgets required at different stages of sperm formation.

Item Type: Article
Additional Information: This is the peer reviewed version of the following article: "No evidence of tradeoffs in the evolution of sperm numbers and sperm size in mammals", which has been published in final form at: http://dx.doi.org/10.1111/jeb.12698. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Uncontrolled Keywords: 0603 Evolutionary Biology, 0608 Zoology
Subjects: Q Science > QL Zoology
Divisions: Natural Sciences and Psychology
Publisher: Wiley
Date Deposited: 15 Jul 2015 11:08
Last Modified: 11 Sep 2017 10:23
DOI or Identification number: 10.1111/jeb.12698
URI: http://researchonline.ljmu.ac.uk/id/eprint/1578

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