Phenotypic plasticity in relation environmental quality and sperm competition in snakes

CHIARAVIGLIO, MARGARITA; TOURMENTE, MAXIMILIANO; CARDOZO, G.A.; GIOJALAS, LAURA C.

Manaos

Congreso; 6th World Congress of Herpetology; 2008

Society for the Study of Amphibians and Reptiles

Reproductive costs impose an adjustment of the reproductive tactics to local conditions and phenotypic plasticity is an important mechanism generating substantial intraspecific variation in reproductive traits (Shine, 2003). Since variations in the local environmental conditions influence the energetic costs and benefits balance, males of many species modify their reproductive behavior. Sperm competition (Parker, 1970) constitutes a major evolutive force imposing intense selective pressures on sperm traits related to fertilization efficiency (Snook, 2005). The objective of this work is to analyze the variation of reproductive and life history traits of males of Boa constrictor occidentalis in two environments of different qualities and to relate them to variations in seminal quality. Study areas, called Pocho and Loreto, were characterized using Landsat 7 ETM+ satellite images. Pocho was considered as a more suitable environment than Loreto since the forest habitat requirements of this species were more abundant in this location. Males were examined to obtain snout vent length (SVL), weight and body condition (BC). Reproductive structures were observed by ultrasound scanning (Sonosite 180 Plus, linear 5-10 Mhz transducer). For the males from Loreto curvilinear velocity (VCL), linear velocity (VSL) and motile cells proportion (MOV) of the ejaculates were examined at 25°C in culture conditions. Male reproductive frequency differed between populations being higher in Pocho. Also, reproductive frequency within SVL size classes varied since reproductive large males were more abundant in Pocho (X2=15.44, p=0.0796). Males belonging to Pocho region had higher testicular volume. Testicular volume and SVL were correlated in Loreto (p=0.01, R2= 0.42) but not in Pocho (p=0.25, r=0.19). Positive associations were registered between sperm velocity and male SVL (VCL p=0.0021, R2=0.82; VSL p=0.0041, R2=0.77). These results show that low quality environments may decrease male reproductive potential. Since habitat loss difficult males dispersion (Cardozo et al., 2007) it would be possible that larger males display a less dispersive behavior because of their increased movement costs (Bonnet et al., 2000; Pearson et al., 2002). However, a higher seminal quality would counterbalance the loss of large males reproductive success in sperm competition conditions. Phenotypic plasticity in reproductive and life-history traits would be an advantageous mechanism to adjust reproductive strategies to local conditions.