Genetic Research Needs
Genetic research should address four major issues facing conservation efforts for West Indian iguanas: 1) genetic distinctiveness and taxonomic status of species, subspecies, and populations, 2) hybridization of genetically distinct species or subspecies in captive and natural populations, 3) pedigree relationships among individuals used in breeding programs and reintroduction efforts, and 4) retention of genetic variation during long-term management of small West Indian iguana populations.
Given the limited resources available for conservation of West Indian Iguanas, it is important that any recommended conservation actions are based on accurate taxonomy. At present, most island populations of rock iguanas are recognized as distinct species or subspecies, but there are only limited genetic data to support this classification. Based on the experiences of researchers in other groups, it seems likely that a genetic survey of rock iguanas will identify unique genetic entities (species or subspecies) that are currently unrecognized. It may also point to significant genetic differentiation between conspecific rock iguana populations on some of the larger islands (e.g., Cuba). Finally, such a survey may identify subspecies of rock iguanas that are not genetically distinct and thus not deserving of their current taxonomic status. In combination, these findings would allow future conservation action to focus on preserving the unique gene pools within the genus. A sequence study based on mitochondrial DNA of all extant species, subspecies, and populations of rock iguanas is currently underway at Texas A & M University.
As species become rare, it is common for problems with hybridization to occur. The subspecies of Cyclura nubila provide a classic example of the impact of hybridization on conservation efforts. The Grand Cayman iguana has been under intense pressure by man through the alteration of habitat and introduction of feral predators. One of the largest rock iguanas, the Grand Cayman iguana occurs only on Grand Cayman (Grant 1940). Two other subspecies, the Cuban iguana and the Lesser Caymans iguana are also recognized, with their ancient distribution limited to Cuba and the Isla de Pinos, and Little Cayman and Cayman Brac, respectively (Schwartz and Carey 1977).
In 1990, the Lizard Advisory Group of the American Zoo and Aquarium Association (AZA) designated the Grand Cayman iguana as a high priority for conservation and captive management. Although this subspecies represented an excellent candidate for intensive captive breeding, two problems complicated implementation of a managed breeding program. First, reports of recent introductions of Lesser Caymans iguanas onto Grand Cayman raised the possibility that subspecific hybridization had occurred in nature (Schwartz and Carey 1977). Second, concern existed among the zoo community that some of the founders of the existing captive population may have been hybrids of Lesser Caymans iguanas and Grand Cayman iguanas. Obviously, the existence of subspecific hybridization within the population would create problems for efforts to conserve the genetic purity of this taxon.
Life Fellowship Sanctuary (Seffner, Florida) produced all of the founding stock of captive bred Grand Cayman iguanas, which were dispersed to several zoos and returned to the Cayman Islands. The Life Fellowship group was founded with five males and two females imported from the Cayman Islands and an additional female and two of her offspring purchased from a Florida herpetologist in 1987 and 1984, respectively. Unfortunately, the two offspring purchased in 1984 may have been produced using a male Lesser Caymans iguana, and would thus be hybrids. In addition, the female parent of these potential hybrids was herself of unknown origin. These three questionable animals had made a significant contribution to the captive population; thus many of the animals under consideration for a managed program and destined for release in the wild were potentially of hybrid origin. The American Zoo and Aquarium Assocation's Lizard Advisory Group decided to proceed by authorizing a genetic study on the existing breeding stock.
Genetic data collected at Texas A & M University demonstrated that the questionable female was of hybrid origin (probably from a male Grand Cayman iguana and a female Lesser Caymans iguana) and thus her offspring and approximately 50% of the existing captive population, including animals returned to Grand Cayman for captive breeding, were of hybrid origin. The hybrids have now been removed from the program, but the problems with this iguana point out the importance of collecting genetic data as early as possible.
Reports of an introduction of Lesser Caymans iguanas into the wild population of Grand Cayman iguanas were apparently unfounded. However, genetic data from the remaining wild Grand Cayman iguanas will provide an unequivocal answer. For most species of West Indian iguanas, a very real possibility of human translocation exists.
Another use for genetic data is the clarification of relationships among founders of captive breeding programs in order to maximize retention of genetic variation and minimize problems due to inbreeding depression. An example of the need for such data is provided by the Jamaican iguana. The Hope Zoo in Kingston, Jamaica, in collaboration with the AZA Lizard Advisory Group, began a headstart program for this species with over 100 individuals collected from clutches laid by wild females between 1991 and 1994. Without genetic data it was impossible to ascertain the number of wild founders represented. If each wild clutch was produced by a different pair, there could be 30 or more founders, but in the worst case, all offspring could have been the product of three females bred by a single male.
To evaluate this situation, 1ml of blood was drawn from the caudal vein (Esra et al. 1975; Gorzula et al. (1976) of each of the hatchlings, and, where possible, from egg-laying females. A genetic analysis of the DNA in these blood samples using microsatellite markers allowed the characterization of both maternal and paternal genetic contributions. Genetic input from at least two male and four female founders was documented and this information was used in selecting founders for the captive breeding program that would maximize initial genetic diversity and avoid inbreeding. Similar analyses would benefit captive breeding programs for other West Indian iguanas.
Lateral entry technique for collecting blood smaples from the caudal vein of iguanas.
Ventral entry technique for collecting blood smaples from the caudal vein of iguanas.
Genetic research depends on the availability of marker systems, a variety of which have been used for genetic analyses of vertebrate populations, including protein electrophoresis, karyotyping, mitochondrial DNA restriction fragment length polymorphisms, and DNA fingerprinting. In recent years, two techniques have emerged as ideal tools for genetic analyses of populations: mitochondrial DNA sequences and nuclear DNA microsatellites. Both of these techniques provide high level resolution and both are based on the polymerase chain reaction (PCR). PCR technology offers the tremendous advantage of utilizing only minute amounts of sample and of providing data even when available samples are of very poor quality (such as museum specimens or shed skins). Mitochondrial DNA is a maternally inherited marker and microsatellites are nuclear, biparentally inherited markers. Microsatellites are similar to DNA fingerprints but are single locus, co-dominant, Mendelian markers and are therefore much easier to interpret in pedigrees. In combination, mtDNA allows the identification of unique maternal lineages and reconstruction of evolutionary relationships, while microsatellites allow the characterization of both maternal and paternal contributions to the gene pool. Both marker systems are in place for rock iguanas, and all that is needed are samples from the appropriate animals.
