Escalona, T. (2003). Maternal effects on reproductive success in a river turtle (podocnemis unifilis) in southern venezuela. Unpublished thesis , University of Missouri St. Louis.
Added by: Admin (14 Aug 2008 20:37:14 UTC)
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Abstract
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Nest site selection and energy allocation to eggs are considered maternal effects that shape life history parameters of many oviparous organisms. Because they lack parental care, these effects are particularly important for a female turtle's reproductive fitness. I studied maternal effects from an ecological and evolutionary perspective in the freshwater turtle Podocnemis unifilis , a species for which maternal effects are poorly known. Nesting began with the onset of the dry season. Nesting was nocturnal and females nested in small to large groups. Larger groups were observed on bright nights, suggesting that females rely on visual cues to initiate nesting. Larger females laid larger clutches, composed of less elongated and relatively smaller eggs than clutches of smaller females. Increased egg size in small females provided evidence for female offspring optimization, but not in the direction expected by optimality trade-off models. Therefore, both large and small females contribute to population survival, but do so in different ways. Nests were clumped in all beaches and nesting locations differed from random locations in their environmental characteristics. However, spatial and environmental patterns were not consistent between beaches or among years. This suggests that adaptive explanations for these patterns are unlikely. An alternative explanation, social facilitation, is consistent with these observations, as well as observations of group nesting. Finally, nests at drier and warmer locations hatched sooner and produced smaller offspring than did nests in cool and moist settings. Heavier eggs produced larger hatchlings that hatched more successfully than smaller eggs. Nest predation was independent of nest density, nest spatial location, and female size, indicating that social nesting did not increase predation, and may in fact serve as an antipredatory mechanism. Nest loss to predators was related to nest age. Flooding was an important source of clutch mortality, while the effect of predators (not including humans) was very low. Overall, results of this study reveal that Podocnemis unifilis is a social nester that in some ways provisions energy to eggs to optimize fitness, but does not appear to track environmental conditions in selecting nest sites as a means to ensure reproductive success.
Added by: Admin
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