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. 2021 May 17;10(5):1227.
doi: 10.3390/cells10051227.

Can Sexual Selection Drive the Evolution of Sperm Cell Structure?

Leigh W Simmons  1 , Francisco Garcia-Gonzalez  1   2
Affiliations

Can Sexual Selection Drive the Evolution of Sperm Cell Structure?

Leigh W Simmons et al. Cells. .

Abstract

Sperm cells have undergone an extraordinarily divergent evolution among metazoan animals. Parker recognized that because female animals frequently mate with more than one male, sexual selection would continue after mating and impose strong selection on sperm cells to maximize fertilization success. Comparative analyses among species have revealed a general relationship between the strength of selection from sperm competition and the length of sperm cells and their constituent parts. However, comparative analyses cannot address causation. Here, we use experimental evolution to ask whether sexual selection can drive the divergence of sperm cell phenotype, using the dung beetle Onthophagus taurus as a model. We either relaxed sexual selection by enforcing monogamy or allowed sexual selection to continue for 20 generations before sampling males and measuring the total length of sperm cells and their constituent parts, the acrosome, nucleus, and flagella. We found differences in the length of the sperm cell nucleus but no differences in the length of the acrosome, flagella, or total sperm length. Our data suggest that different sperm cell components may respond independently to sexual selection and contribute to the divergent evolution of these extraordinary cells.

Keywords: Onthophagus; cryptic female choice; dung beetles; experimental evolution; sperm competition; sperm length.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Experimental evolution protocol. S, sexual selection; M, enforced monogamy; Ne, effective population size.
Figure 2
Figure 2
(A) A sperm bundle taken from the seminal vesicles of a sexually mature male (scale bar, 100 µm); (B) an individual sperm cell (scale bar, 100 µm); (C) the head region showing the acrosome (a) and nucleus (n) (scale bar, 10 µm). B and C reprinted by permission from Springer Nature: Springer, Naturwissenschaften, Ultrustructure of spermatozoa of Onthophagus taurus (Coleoptera, Scarabaeidae) exhibits heritable variation, Michael Werner and Leigh W. Simmons, ©Springer-Verlag 2011 [57].
Figure 3
Figure 3
Mean (±SE) total sperm length, and lengths of the acrosome, nucleus, and flagella of males derived from three replicate populations that had been evolving under enforced monogamy (1–3) and three replicate populations that had been evolving under sexual selection (4–6) for 20 generations.
See this image and copyright information in PMC

References

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