My research interests focus mostly on the impact of geographic fragmentation and small population size on the evolutionary dynamics of threatened, natural populations.

In my PhD dissertation I analyzed the relative role of competition to the expression of inbreeding depression in a small isolated population of Cyclura carinata rock iguanas. Previous genetic work on C. carinata population on Little Water Cay highlighted the possibility that iguanas on this small isolated cay may be experiencing inbreeding depression (Berk, 2013).

Cyclura carinata, Turks and Caicos Islands
Cyclura carinata, Turks and Caicos Islands

The ultimate cause of inbreeding depression can be found in the expression of a certain proportion of the genetic load (Charlesworth & Willis, 2009). Although generally true, high genetic load not necessarily corresponds to intense inbreeding depression. For example, populations that have been small and isolated for many generations may present reduced genetic variation due to the long term influence of genetic drift acting on them. When this happens the variance in inbreeding values between inbred and non-inbred individuals is expected to be very low, if any, despite the fact that the entire population presents high levels of genetic load (Hedrick, 2005). Different population dynamics could contribute to the expression of inbreeding depression in such situations.

If competition is responsible for exposing the genetic load to selection, then populations are potentially robust and not in imminent risk of extinction. In contrast, if inbreeding depression reflects the expression of lethal genotypes, then small populations may be ephemeral and hence should be targeted with specific and immediate conservation programs. Thus an important question to ask is: what proportion of attrition is attributable to soft and hard selection, respectively, in natural populations? Differences in demographic parameters across populations could be used to quantify the relative importance of different evolutionary forces and make inferences on the way they interact at the local scale to purge the genetic load in small isolated populations.

Literature cited: 

  • Berk, J. W. (2013). Inbreeding and heterozygosity-fitness correlations in a small, isolated population of Turks and Caicos Rock Iguanas, Cyclura carinata. Master Thesis. Mississippi State University
  • Charlesworth, D., & Willis, J. H. (2009). The genetics of inbreeding depression. Nature Reviews. Genetics, 10(11), 783–96.
  • Hedrick, P. W. (2005). Genetics of Populations (Third). Sudbury, MA: Jones and Bartlett.


Jesus told me "Come forth, and you will have eternal life!" But I came fifth, and I got a toaster…