Role of drainage and barriers in the genetic structuring of a tessellated darter population

摘要

While population genetic structuring is easily identified, the causes of the structure can be difficult to determine. Habitat fragmentation in aquatic systems has often been identified as a major source of increased population structure and decreased genetic diversity in fish, including benthic resident species such as darters. However, these findings are often not replicated across natural and manmade barriers and come from endangered or threatened populations where the genetic structure is likely already compromised due to small population size. To evaluate the factors involved in structuring a healthy darter population, we genotyped 506 tessellated darters from 18 sites in three different river drainages and one large lake. Sites were all in the same watershed but separated from one another by one or more of three different types of barriers: dams, natural fall lines and causeways. We found that while diversity and allele frequency varied largely by drainage, within drainage variation was minimal even across multiple barriers. No single barrier type appeared to be more formidable than any other. Our results indicate that healthy populations of darters may naturally be structured by drainage, but likely disperse across barriers enough to retain drainage-wide homogeneity.