Crocodilian evolution, systematics and population genetics: Recovery and ecological interactions of the American crocodile (Crocodylus acutus)

Date

2007-08

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Publisher

Texas Tech University

Abstract

The goals of this research were to explore the use of genetic markers to infer biological information about crocodilian species and populations. Given that the range of the American crocodile (Crocodylus acutus) is much larger than its sympatric congeners; this species was used as the focal point for my study. The American crocodile is sympatric in Cuba with the Cuban crocodile (C. rhombifer), in Meso-America with Morelet’s crocodile (C.moreletii) and in South America with the Orinoco crocodile (C. intermedius). The New World Crocodylus system, due to its geographic arrangement, presents an interesting opportunity to model broad-scale evolutionary process. Modern conservation biology requires the integration of both ecological and molecular data. The grand purpose of this work is to provide a genetic context spanning a scale from the species level to specific populations, including inter-species interactions in wild populations and breeding strategies. I begin by using mitochondrial markers to infer the phylogenetic relationships of New World crocodiles. I continue with an examination of the genetic structure of American crocodiles in Florida compared to other populations from Meso-America. Then I later relate those findings with breeding strategies of a specific wild population that has colonized and successfully utilized an artificial habitat. I also inspect putative hybridization zones between Morelet’s crocodile and the American crocodile in the Yucatan Peninsula using a combination of multiple microsatellite loci, mitochondrial sequences and morphological assignments.

All New World crocodiles formed a highly supported clade with C. niloticus as a sister taxon. ND4-tRNAHis-tRNASer sequences did not provide sufficient resolution among populations of C. acutus, therefore partial control region sequence data were used to make population-based inferences. Two haplotypes were most prevalent within the Florida population, but surprisingly distant haplotypes were also found, indicating the migration of foreign haplotypes into Florida. This hypothesis is supported by government documentation of foreign releases into Florida waters. In Mexico hybridization was found to be not only widespread but bidirectional between the American and Morelet’s crocodile. The majority of hybrids were classified as F2 and C. moreletii-backcrosses. Using microsatellite data from 10 loci I found that nesting efforts within Turkey Point Power Plant (Florida, USA) are the result of inbreeding, and thus this site exhibits very low genetic diversity compared to other crocodilian populations. Relatedness values were very high among (r = 0.5624) and within nests (r = 0.5910 – 0.7457). Additionally, I could not detect multiple paternity within 8 nests due to minimal allelic diversity.

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