Experimental evolution of sex ratio and sex-determining mechanisms in C. elegans

To complement our work on the evolution and ecology of sex-determining mechanisms, especially temperature-dependent sex determination (TSD), in reptiles, we are developing strains of the nematode "worm" Caenorhabditis elegans as a model system.

Anthropogenic influences on turtle populations

Many reptiles, including many turtle species, are increasingly impacted by human activity. Wild populations can be harmed by direct exploitation of the animals themselves, habitat loss and fragmentation due to development, pollution such as agricultural run-off, global climate change, and even recreational activities by humans, as well as a combination of these factors. A thorough understanding of the effects of these influences on populations, as well as the mechanisms by which populations might cope with their changing surroundings, is crucial for developing successful, cost-effective management and conservation strategies.

Evolutionary ecology of sex-determining mechanisms in reptiles

A fundamental problem in biology is understanding the ecology, genetics, and evolution of diverse sex-determining mechanisms. To address these questions, we have focused on reptiles as model organisms because they exhibit a tremendous diversity in modes of sex determination, including temperature-dependent sex determination (TSD) (Janzen and Paukstis, 1991, Quart. Rev. Biol.; Valenzuela et al., 2003, Am. Nat.; Janzen and Krenz, 2004). In the past we have studied the adaptive significance of TSD (Janzen and Paukstis, 1991, Evolution; Janzen, 1995, Evolution; Valenzuela and Janzen, 2001, Evol. Ecol. Res.; Janzen and Morjan, 2002, J. Herpetol.; Morjan and Janzen, 2003, Copeia; Janzen and Phillips, 2006, J. Evol.

Life-history evolution and functional ecology of reptiles

Egg and offspring size, as well as other morphological and behavioral performance traits, play important roles in life-history models yet they vary greatly both within and among populations and taxa and temporally (Tucker et al., 1998, J. Herpetol.; Bowden et al., 2004, Funct. Ecol.; Schwanz et al., 2009, Ecology; Janzen and Warner, 2009, J. Evol. Biol.). We have investigated physiological mechanisms underlying this variation in snapping turtles (Janzen et al., 1990, J. Exp. Zool.) and in painted turtles (Harms et al., 2005, Physiol. Biochem. Zool.), differences in size variation between sympatric populations of map turtles (Graptemys) (Janzen et al., 1995, Funct.

Phylogenetics, molecular ecology, and phylogeography of North American reptiles

The structure of natural populations and the intraspecific relationships among these populations provides a crucial context for understanding the historical, current, and future evolution of organismal phenotypes. This fact is becoming increasingly clear to biologists of all stripes, and analysis of microsatellite markers and mtDNA and nuDNA sequences are providing the substrate to add a geneological perspective to such studies. We are using this approach with various molecular techniques to evaluate the pedigrees and phylogenies of species and populations of certain North American reptiles.