Conservation Genetics at the Species Boundary: Case Studies From African and Caribbean Crocodiles (Genus: Crocodylus)

EPA Grant Number: U915922
Title: Conservation Genetics at the Species Boundary: Case Studies From African and Caribbean Crocodiles (Genus: Crocodylus)
Investigators: Hekkala, Evon R.
Institution: Columbia University in the City of New York
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $88,319
RFA: STAR Graduate Fellowships (2001) RFA Text |  Recipients Lists
Research Category: Fellowship - Molecular Biology/Genetics , Academic Fellowships , Biology/Life Sciences


The objective of this research project is to examine boundaries within and between species using the combined tools of mitochondrial and nuclear genetic markers. Such marker systems provide specific levels of resolution which, when combined, have the ability to clarify patterns of evolution at local, regional, and continental geographic scales. The perspective afforded by this approach is brought to bear on the conservation and management of the true crocodiles in Africa and the Caribbean.


I will address problems in crocodile taxonomy and how one can hope to combat some of the threats to members of this group using the tools of conservation genetics. To explore the hypothesis of the monophyly of the widespread type species, Crocodylus niloticus, the Nile crocodile, I will complete a phylogeographic analysis based on data from five mitochondrial and four nuclear regions. The findings suggest a deep and early split between crocodile lineages in East and West Africa rendering the species C. niloticus paraphyletic and indicating two distinct species of true crocodiles currently inhabiting Africa. Populations of C. niloticus are examined at a finer level, using microsatellite markers to evaluate levels of population identity and differentiation. Measures of population differentiation (Fst and Rst) depict low levels of interpopulation dispersal and suggest a close association between populations and regional drainage systems. The assignment test allows for clear identification of individuals from source populations in Kenya, Zimbabwe, South Africa, and Madagascar, and will provide a valuable enforcement mechanism for monitoring trade in Nile crocodile products. I will examine the presence and extent of a hybrid zone between two protected species of Caribbean crocodiles using both mitochondrial and nuclear markers. Although some hybrid individuals can be identified using morphological characters, additional hybrids are detected by multilocus genotyping. In addition, the molecular markers indicate a unidirectional pattern of hybridization and suggest that it is a relatively localized occurrence. I will review the use of genetic markers for crocodile conservation and their application at differing scales to elucidate meaningful boundaries for the maintenance of biodiversity.

Supplemental Keywords:

fellowship, Nile crocodiles, Crocodylus niloticus, conservation genetics, paraphyletic, Africa, Caribbean, mitochondrial genetic markers, nuclear genetic markers, population identity, population differentiation, biodiversity.

Progress and Final Reports:

  • 2001
  • 2002
  • Final