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Exceptional sperm cooperation in the wood mouse


Spermatozoa from a single male will compete for fertilization of ova with spermatozoa from another male when present in the female reproductive tract at the same time1. Close genetic relatedness predisposes individuals towards altruism, and as haploid germ cells of an ejaculate will have genotypic similarity of 50%, it is predicted that spermatozoa may display cooperation and altruism to gain an advantage when inter-male sperm competition is intense2. We report here the probable altruistic behaviour of spermatozoa in an eutherian mammal. Spermatozoa of the common wood mouse, Apodemus sylvaticus, displayed a unique morphological transformation resulting in cooperation in distinctive aggregations or ‘trains’ of hundreds or thousands of cells, which significantly increased sperm progressive motility. Eventual dispersal of sperm trains was associated with most of the spermatozoa undergoing a premature acrosome reaction. Cells undergoing an acrosome reaction in aggregations remote from the egg are altruistic in that they help sperm transport to the egg but compromise their own fertilizing ability.

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Figure 1: Morphology of wood mouse sperm head.
Figure 2: Development of sperm train.
Figure 3: The change in progressive motility (average path velocity) of sperm trains (solid line) and single spermatozoa (dotted line) with increasing viscosity of medium.
Figure 4: Histogram of the proportion of spermatozoa displaying deployment of the apical hook, the acrosome reaction and hyperactivated motility in relation to sperm aggregation in vitro at different time points.


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We thank J. Waters for advice on wood mice husbandry. K.D. was supported by an Erasmus Exchange studentship.

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Correspondence to Harry Moore.

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Moore, H., Dvoráková, K., Jenkins, N. et al. Exceptional sperm cooperation in the wood mouse. Nature 418, 174–177 (2002).

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