Meeting Abstract
Local adaptation cannot occur unless traits under selection have a genetic basis; therefore, it is essential to determine patterns of trait heritability. However, the evolutionary trajectory of traits is also dependent on the genetic correlations among traits, potentially leading to constraints on adaptive change. We identified four fish farms with large populations of diamond-backed watersnakes (Nerodia rhombifer) that specialized in the species of fish they raised (either small-bodied fish or large-boded fish). We hypothesized that snakes at farms raising large-bodied fish would likely experience stronger pressure to ingest larger prey and would adapt to this pressure with changes in relative head size. We determined that in at least one large-bodied fish farm neonate snakes had larger heads, but establishing differences in head size does not necessarily imply an adaptive response. We estimated heritabilities, phenotypic correlations, and genetic correlations among traits using a full-sibling design and determined that measured cranial characteristics were, in fact, heritable, and the among-population pattern for heritability and relative quadrate length is generally in agreement with the theoretical relationship between heritability and selection; suggesting the snakes with the longest quadrates have been selection. Within each population, the skull length and mandible are most strongly correlated with one another, both genetically and phenotypically, while the quadrate has the weakest correlations suggesting it may have fewer intrinsic constraints on adaptive change than the skull length and mandible.
