Sperm morphometry variations and its role on sperm competition: the snakes as a model

TOURMENTE, MAXIMILIANO; GIOJALAS, LAURA C.; CHIARAVIGLIO, MARGARITA

Villa Giardino

Jornada; XV Jornadas Científicas. Sociedad de Biología de Córdoba; 2005

Sociedad de Biología de Córdoba

Extensive variation in sperm size, even among close related species, is probably a reflection of the risk of sperm competition and the environment in which it takes place. Although the production of long sperm can be costly, an increment in sperm size may either increase its longevity if size signifies energy reserve. Conversely, this could lead to a trade off with swimming speed by increasing tail length plus its associated mitochondria in the mid-piece. Sperm competition may also select for bigger sperm because they are able to displace smaller competing sperm or serve as an indicator of male genetic quality. Snakes are excellent study subjects to test sperm competition hypotheses as they show reproductive characteristics like promiscuous mating systems, long and short-term sperm storage and unique structural spermatic features. The objective of this work was to detect variations in sperm morphometry across snake taxa and to relate it to differential sperm competition pressures. The length of the head, acrosome, midpiece and principal piece of spermatozoa of three snake taxa: Boinae, Crotalinae and Xenodontinae, was measured using phase contrast and fluorescence light microscopy. Data were controlled for normality and a parametric analysis of variance (ANAVA) was performed for each variable. Pairwise differences among means were tested a posteriori. Although head length did not varied significatively among taxa, the acrosome, principal piece and particularly midpiece length showed significant variation. The high variationdegree detected in midpiece length would have an important influence in the metabolic features of these cells, as this region is the responsible for generation and maintenance of motility. The studied snake species also show differences in life histories, reproductive cycles and mating systems. Thus, it would be possible that variations in sperm length, especially in the midpiece and tail regions, were influenced by sperm competition risk derived from such differences.