Male sperm storage compromises sperm motility in guppies.
Sperm senescence can have important evolutionary implications due to its deleterious effects on sperm quality and offspring performance. Consequently, it has been argued that polyandry (female multiple mating) may facilitate the selection of younger, and therefore competitively superior, sperm when ejaculates from multiple males compete for fertilization. Surprisingly, however, unequivocal evidence that sperm ageing influences traits that underlie sperm competitiveness is lacking. Here, we used a paired experimental design that compares sperm quality between 'old' and 'young' ejaculates from individual male guppies (Poecilia reticulata). We show that older sperm exhibit significant reductions in sperm velocity compared with younger sperm from the same males. We found no evidence that the brightness of the male's orange (carotenoid) spots, which are thought to signal resistance to oxidative stress (and thus age-related declines in sperm fitness), signals a male's ability to withstand the deleterious effects of sperm ageing. Instead, polyandry may be a more effective strategy for females to minimize the likelihood of being fertilized by aged sperm.
Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia clelia.gasparini@uwa.edu.au.
Clelia
C
Gasparini
Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
Jennifer L
JL
Kelley
Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
Jonathan P
JP
Evans
D000818:Animals; D002338:Carotenoids / Q000502:physiology; D005260:Female; D008297:Male; D010858:Pigmentation; D011036:Poecilia / Q000502:physiology*; D012726:Sexual Behavior, Animal; D013081:Sperm Motility; D013094:Spermatozoa / Q000502:physiology*
D002338:Carotenoids
postcopulatory sexual selection; sperm age; sperm competition; sperm velocity; sperm viability