2015 Díaz Interim Report
Studying the effects of habitat fragmentation and hunting on the genetic diversity of the threatened Oaxacan Spiny-tailed Iguana, Ctenosaura oaxacana

Submitted by Gabriela Díaz-Juárez and Víctor Hugo Reynoso

Depto. de Zoología, Instituto de Biología, Universidad Nacional Autónoma de México (UNAM).

 

This study aims to determine the structure and genetic diversity of populations of the Oaxacan Spiny-tailed Iguana by combining sequencing analysis of mitochondrial DNA (mtDNA), nuclear DNA (nDNA), and microsatellite markers. This project aims to establish the effect of habitat fragmentation and hunting on the genetic diversity and structure of populations of Ctenosaura oaxacana throughout its distribution and determine population trends for the future. All this information will contribute to establishing well-sustained local and national conservation and management programs for this species.

 

The first field season began February 2–26, 2015, at nine selected sub-populations in the Isthmus of Tehuantepec in Oaxaca, México. Iguanas were captured by exhaustive searching within hollow tree trunks in the dry forest for 2–3 days. Thirty samples were collected among three sites with continuous forest where iguanas are not hunted, three sites with continuous forest and a high hunting rate, and three fragmented areas where iguanas are not hunted. In the first sampling, we captured 270 iguanas (40.4% females, 45.2% males, and 14.4% sexually immature). The second sampling was conducted April 11–May 15. Fifteen were observed, but only ten of them were captured. Ten iguanas were captured in each site throughout the coast of Oaxaca and the Isthmus of Tehuantepec. In this sampling we captured 100 iguanas (39% females, 50% males, and 11% sexually immature).

 

We withdrew 0.5 ml of blood from each iguana’s caudal vein and preserved it in 96% alcohol. We also recorded the snout-vent length (SVL), head length (HL), head width (HW), tail length (T), the length of the tibia (Tib), weight, and sex of each iguana.

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Females showed an average length of 12.5 ± 1.26 cm (range 9.5 to 15.5 cm). Average weight of females was 64.6 ± 21.15 g (range 26 to 140 g). Males showed an average length of 14.2 ± 1.8 cm (range 8-18 cm). Average male weight was 104.2 ± 35.5 g (range 24 to 200 g).

 

DNA extraction from each sampled iguanas began June 1. DNA concentration and quality were measured in 1% agarose gels, obtaining good results for all populations. Gene amplifications of mitochondrial and nuclear microsatellite genome fragments will be analyzed during August, 2015 at the Institute of Biology, UNAM, México.

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Complementary activities in the field included interviewing people in different localities from the Isthmus and the coasts of Oaxaca, considering our knowledge of the use and practices related to iguanas within their communities. We observed that the capture of iguanas is a common practice and varies according to the species. Ctenosaura pectinata represents the highest hunted rate (36%), while C. oaxacana is lower (33%), and Iguana iguana represents 16%. Hunting of iguanas is more common during the nesting season and is done mostly for meat consumption.

 

The townspeople know that populations of spiny-tailed iguana, and iguanas in general, have been reduced and some of them are endangered. They agreed to develop programs and projects for protection and controlled use of iguana populations. We talked with the municipal presidents of the different towns on the importance and status of C. oaxacana. Furthermore, we talked with local communities on the importance of C. oaxacana, about the objectives of our study, and how they would benefit by knowing and protecting the Oaxaca Spiny-tailed Iguana.