Meeting Abstract
Embryos are highly sensitive to environmental conditions experienced during development. For oviparous reptiles, the hydric conditions and temperature of a nest are the key environmental factors shaping phenotypic variation. Weather is the primary determinant of nest temperature and hydric conditions, yet the effects of weather are mediated through the nest microhabitat selected by the mother. For example, there is a well-documented relationship between canopy cover above a nest and the nest thermal regime. Some aspects of the microhabitat have received considerably less attention, yet are plausibly also important in influencing nest conditions. Soil characteristics of nests vary substantially within and among populations, and these characteristics may influence temperature and/or water potential of the nest. Surprisingly, then, the influence of nest substrate type on phenotypes has not been experimentally assessed in the field. In this experiment, we incubate painted turtle (Chrysemys picta) eggs in three substrate types that are commonly selected by turtles within our study population. In a common area, we constructed six pits, which were refilled with loamy soil, sand, or gravel. Artificial nests were created in each substrate, and eggs were randomly assigned to a substrate type in a randomized block design. Eggs remained in these nests for ~90% of incubation, and were returned to the lab for hatching. Nest temperatures were measured, and preliminary analyses reveal that substrate type influenced nest temperatures. Thus, we expect that offspring phenotypes, including developmental rate, body size, and sex will also be influenced by substrate type. These findings suggest that soil characteristics are important aspects of the microhabitat for oviparous reptiles, and should be more carefully considered in future research.
