Research in the Rostal Lab

Research in my lab has focused on the evolution of reproductive strategies in amniotic egg laying vertebrates, in particular Chelonians. Much of my work has been directed at understanding the biological roles of hormones from a comparative perspective. Many groups of hormones, particularly steroid hormones, appear highly conserved phylogeneticaly. However, their functions are poorly understood in many lower vertebrates. There are over 250 species of turtles and all produce eggs. Turtles have persisted since the Triassic and represent a valuable model system for studying the evolution of endocrine control of reproduction. This research has been applied to understanding the reproductive biology of endangered species such as the Kemp’s ridley sea turtle (Lepidochelys kempi), the leatherback sea turtle (Dermochelys coriacea), and the desert tortoise (Gopherus agassizii). This information has been applied to monitoring population trends and recovery plans.

The influence of environmental factors including habitat quality on the reproductive biology and physiological ecology of reptiles and amphibians has been a major component. Various environmental factors are essential as proximate cues to timing of reproductive patterns. Habitat quality and characteristics also plays a critical role in maintaining viable populations. Many forms of habitat fragmentation and degradation can be observed today, but their effect is often very difficult to assess, especially when working with long lived species such as chelonians. As well, many reptiles display temperature dependent sex determination, which is only partially understood. Through understanding seasonal reproductive cycles including endocrine patterns, we can better understand both the evolutionary patterns observed in many reptiles and amphibians as well as improve conservation efforts.

CURRENT RESEARCH
My students and I are currently involved in three areas of investigation. These include studies on:

1) Temperature-dependent Sex Determination (TSD) in the gopher tortoise (Gopherus polyphemus) in southeast Georgia. Gopher tortoises inhabit sandhill habitats throughtout the southeast. Habitat loss and fragmentation have resulted in population declines of 80% or more in areas. A complete understanding of their biology including TSD is critical to maintaining viable populations. TSD characteristics must be determined and microhabitat characteristics of remaining habitat must determined.

2) The reproductive biology of the loggerhead sea turtle (Caretta caretta) on Wassaw Island, Georgia. The biological role of island nesting populations of loggerhead sea turtles on the Atlantic coast of north America is poorly understood. How these smaller nesting populations such as that utilizing Wassaw Island contribute to the eastern Atlantic loggerhead population is unknown. Studies of mainland nesting populations in Florida suggest that these populations produce 90% female offspring. Do the smaller island nesting populations contribute critical male offspring?

3) Reproductive biology and TSD in Galapagos tortoises (Geochelone nigra) under natural conditions.

These studies all address critically important keystone species in their regions and will contribute to the long term management requirements of these species.