Sperm Competition and Sperm Length in Shorebirds ’

We investigated how sperm morphology varies across 16 species of shorebirds in the Scolopacidae, Charadriidae, and Jacanidae. Sperm were significantly longer in nonmonogamous than in socially monogamous species. Nonmonogamous species also I Received 27 January 1999. Accepted 22 June 1999. 2Current address: Department of Zoology, Private Bag 4800, University of Canterbury, Christchurch, New Zealand. had significantly longer midpieces and tails than monogamous species. As the midpiece houses the mitochondria for powering the tail, this suggests that sperm competition may select for greater investment inmobilitv. After controlling for phvlogenv and male bodv mass, sperm tail lengih was co&elated positively tb relative testis size. There was no evidence that variation in sperm morphology was related to either male body mass (through allometry) or egg size (via linkage disequilibrium). Instead, our results suggest that sperm size in shorebirds increases with the intensity of sperm competition. SHORT COMMUNICATIONS 849