Report submitted by Gabriela Díaz-Juárez and Víctor Hugo Reynoso
Departamento de Zoología, Instituto de Biología, Universidad Nacional Autónoma de México (UNAM).
This project is Part Two of our IIF-supported grant “Effects of habitat fragmentation and hunting on the genetic diversity of the threatened Oaxacan Spiny-tailed Iguana” (see previous report). Here, we extended sample collection to their sister taxa, Ctenosaura flavidorsalis and Ctenosaura quinquecarinata with the main goal overall to establish genetic parameters of the three sister species’ populations by using molecular techniques. During the field work, we aimed to collect 30 samples from each of C. oaxacana’s sister species throughout their distribution area. Among the main expected results, we aimed to establish the genetic diversity, genetic structure, and effective population size of the three species. These results will provide essential information to develop management plans for their conservation and to re-evaluate their status within the IUCN Red List of Threatened Species.
Outcomes. We obtained field data and blood or tissue samples from 120 individuals of the Yellow-backed Spiny-tailed Iguana (C. flavidorsalis). Thirty samples were collected from El Salvador (La Cueva de Corinto, Morazán), 30 from Honduras (south of La Paz), and 60 from Guatemala (30 each from SE and NW Rincón, Jutiapa). We also collected 90 samples from the Five-keeled Spiny-tailed Iguana, C. quinquecarinata, from Nicaragua (Boaco, La Cruz, and San Francisco del Norte; 30 iguanas per locality).
Capture of C. flavidorsalis began on 14 May 2016 in the town of Rincón Jutiapa within the Department of Jutiapa (Guatemala). The habits of the species are similar to those reported for other species in the quinquecarinata complex. They were usually found living within tree trunk hollows, although sometimes they were captured within piles of volcanic rocks or sometimes in the cracks. Hasbun et al. (2005) considered the locality SE of Rincón Jutiapa as different from NW of Rincón Jutiapa. However, to our surprise, these localities were very close to one another (less than 1 km) and for purposes of our study we considered them to be the same. Within this zone, 28 iguanas were captured: 10 females, 16 males and two hatchlings. The surrounding habitat is very fragmented with very small remnants of dry forest within farming land. The iguanas were captured close to the hills, and sometimes within the areas of crops. We did not find iguanas in the plains.
In El Salvador, capturing iguanas was very challenging; the preferred habitat of C. flavidorsalis was substantially different to what we were expecting. The site was quite high in elevation, located just before the transition of dry forest to pine forest and iguanas preferred to use cracks of large volcanic rocks for refuges. The large size and weight of these rocks did not allow for easy search and capture of iguanas. However, in the Cueva de Corinto locality (Department of Morazan) we managed to capture 26 iguanas: six females, eight males, and 12 tail tissue samples (the iguana itself was not captured, just the tail). In La Paz (Department of La Paz, Honduras) we captured iguanas in tree holes, fences made from volcanic rock piles, and wooden pole fences. Here we captured 28 iguanas: 10 females, 14 males, and four hatchlings. In this zone, the habitat is fragmented principally by some urbanization and agriculture and cattle ranch uses. In total, we captured 82 Ctenosaura flavidorsalis, which we consider are enough for population genetics. Martínez-González (2015) showed that 22 samples is enough to obtain most of the genetic variation within a C. oaxacana population.
In Bocao and La Cruz, Nicaragua, iguanas were scarce, not easily observed, and difficult to capture our goal of 30 iguanas. Instead C. quinquecarinata samples were taken from Santa Rosa del Peñón, Department of Leon, and San Francisco del Norte, Department of Chinandega. In the first locality, we captured 13 males, six females, three hatchlings, plus nine tail tissue samples (N = 31). In the second locality we obtained 10 males, 15 females, five hatchlings, and 13 tail tissue samples (N = 43). In both areas, habitat features were very similar to those observed for C. oaxacana (Rioja et al. 2012, Diaz-Juarez 2014) and both species are similar in behavior.
In total, we captured 122 spiny-tailed iguanas. For each captured iguana we measured morphometric data (mass, snout-vent length, tail length, head length and width, and tibia length), extracted blood from the caudal vein, and took photographs in lateral, dorsal and ventral views. A sample duplicate was left with collaborators in each country. When it was impossible to extract the iguana from its refuge, we cut a small sample from the tail (N = 34 samples) to extract DNA from the muscle tissue. Unfortunately, we lost the opportunity for morphological information from these iguanas. In total, we obtained 156 samples of blood or tissue: 82 for C. flavidorsalis and 74 for C. quinquecarinata.
Conservation Concerns. During our fieldwork, we noted that both species (C. flavidorsalis and C. quinquecarinata) have reduced population sizes, evident in the big effort needed to capture 30 samples per locality. Their habitat is also very fragmented, mainly because of land use conversion for cattle ranches, agriculture, and urbanization. These activities generate open spaces, without vegetation cover or refuges that protect iguanas from the environment, predators, and limits their food availability. Their use of volcanic rock piles and cracks for refuges was unexpected and may be in response to forest lost. Contrary to C. oaxacana and C. quinquecarinata, C. flavidorsalis appears to have been actively adapting to human-modified habitats, since they were commonly observed in very altered sites, including burned corn and bean fields. However, more dense populations are still found in the preserved forests. We believe that the progressive isolation of populations will reduce genetic flow between populations and promote differentiation and loss of genetic variation within populations. Finally, we observed severe habitat deterioration in La Guegue, Department of Bocao, Nicaragua, and we were unable to find any iguanas. People in the area said they are very difficult to find.
Another important threat contributing to decreasing small spiny-tailed iguana populations is intentional killing because of fear. In all localities, C. flavidorsalis and C. quinquecarinata are considered to be poisonous. Some people are even certain that iguanas may poison their cattle by biting them or even when cattle step on them.
One important outcome from this project has been establishing contact with local academics, especially in the University of Honduras and Nicaragua National University. One student from Nicaragua came to learn molecular techniques in our lab at the Instituto de Biología, National Autonomous University of Mexico (UNAM). This collaboration will assure future collaborative research in Nicaragua, where C. quinquecarinata is mostly distributed.
Future. The information we have gained about the biology and condition of the populations of C. quinquecarinata and C. flavidorsalis is still very limited. We think it is necessary to exhaustively explore the distribution area of each species to identify remnant areas that preserve good populations, establish the actual limits of distribution, define the number of subpopulations and their distributional pattern (continuous or in patches), and determine population size estimates for each species. Additionally, the study needs to consider iguana seasonality to assure complete understanding of the needs for both species, as we have done with C. oaxacana. Finally, we believe it is important to interview local people to determine the social importance of iguanas in each locality and to work with local academics and authorities to design conservation plans.