Allocation of Reproductive Investment in the Redbelly Snake Storeria occipitomaculata

Reproductive traits of a population of the redbelly snake Storeria occipitomaculata were studied for 2 consecutive years and assessed for congruence with optimal egg size models. Litter size and total litter mass were correlated with female size but mean offspring size was not, indicating that larger females invested more in total reproduction but partitioned it into more rather than larger offspring. After adjusting for female size differences, yearly variation was observed in offspring mass, but not in total litter mass or litter size, suggesting that factors determining total investment and investment per offspring may be different. Within-litter variance in offspring size was generally small, but in some cases was substantial. Whether this variation was due to a physiological inability to produce uniform litters or selection for variation in offspring size is unknown. Finally, we discuss why an observed positive correlation between total litter mass and offspring size need not be viewed as evidence against the optimal egg size concept if the fractional clutch problem is considered.