Conditions for the evolution of soldier sperm classes.
There has been wide disagreement as to whether sperm competition among animals can produce a soldier class of sperm to fight against other males. Utilizing mathematical models, we analyze the appropriate conditions for the evolution and maintenance of a soldier sperm class. We conclude that: (1) soldier sperm evolve even if one soldier sperm can kill or block less than one competing sperm; (2) soldier sperm evolve faster when there is a large variance in the number of competing sperm; (3) soldier ratio increases until reproductive sperm are too scarce to fertilize all ova or a sperm intensely refuses to become a soldier; and (4) soldier sperm are more likely to be smaller than reproductive sperm. Our models suggest that the conditions for the evolution of a soldier sperm class are not stringent.
Department of Zoology, Graduate School of Science, Kyoto University, Japan. kura@ci.zool.kyoto-u.ac.jp
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Kura
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Nakashima
D000818:Animals; D005075:Biological Evolution; D005260:Female; D008297:Male; D008954:Models, Biological; D012098:Reproduction / Q000235:genetics / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology*