Tibisay Escalona

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Current Research

I am currently a Minority PostDoctoral NSF Research Fellow (2006-present) at Iowa State University. My research project involves estimating the population structure of Podocnemis unifilis.

Podocnemis unifilis or "Terecay" is a widely distributed freshwater turtle inhabiting the Orinoco, Amazon, and Essequibo river basins and eastern Guianas. It belongs to the family Podocnemidae (Testudines: Pleurodira). This turtle represents an important economic and cultural resource for local people in Colombia, Bolivia, Brazil, Ecuador, Peru, Venezuela, and the Guyanas. Unfortunately, overexploitation and habitat destruction has caused drastic population declines which may cause loss of genetic variation and fixation of deleterious alleles, with consequent inbreeding depression and reduced adaptive potential. Despite the implications of genetic information for conservation issues no study has been conducted to date describing the basic genetic parameters of populations of P. unifilis at a large scale. My ongoing research represents the first such endeavor to alleviate this deficiency. For this project, the main goal was to carry out a genetic study of microsatellite DNA and mitochondrial DNA to look at the population structure of P. unifilis throughout its distributional range with the aim of providing crucial information for conservation of this endangered species and future comparative studies of evolutionary ecology in the genus. A total of 11 localities, including six from Venezuela (NICH, CAU, MAT, RFTA, MET, CQ), one from Colombia (CUT), and three from Peru (MC, PI, SC) corresponding roughly to a North-South transect, plus one farther Eastern locality in Brazil (TRO) were used in this study. This sampling is the first step of a more geographically comprehensive study that will be completed in the future, once samples from Brazil, Ecuador, Bolivia and Guyana become available. This study included (1) the analysis of genetic variability within populations, (2) the analysis of genetic structure among populations, (3) the analysis of genetic bottleneck in each sampled location, (4) tested the hypotheses that the flooded forests rather than the river channels are the main conduits for gene flow and (5) made recommendations for conservation. These objectives were accomplished only for microsatellite DNA and a research article title “Population genetics of the endangered South American freshwater turtle, Podocnemis unifilis, inferred from microsatellite DNA data”is already in press for publication in Conservation Genetics (DOI 10.1007/s10592-008-9746-3). Currently I am exploring the population structure using as marker the control region of the mitochondrial DNA from the same samples. This will provide a better understanding of the patterns of population subdivision and migration, such as whether females exhibit natal homing.

My research is partially funded by