Although progress has been made in the protection of manatees against threats from human activities, many populations continue to exhibit limited growth or decline, and so the West Indian manatee (Trichechus manatus) remains an endangered species. Visible threats, such as fatal propeller wounds and habitat depletion, are not the only causes for concern when it comes to protecting the Florida manatee (Trichechus manatus latirostris), a subspecies of the West Indian manatee. Scientists have determined that animals of this subspecies face the additional threat of low genetic diversity, a trait that could make them more susceptible to diseases and more sensitive to climate changes.
Biologists in the Sirenia Project at the U.S. Geological Survey (USGS) Florida Integrated Science Center (FISC) in Gainesville, FL, are currently identifying and mapping the genetic material of manatees. Their goal is to better understand and predict the animals' ability to react to environmental stimuli, such as prolonged periods of cold weather, red tides, and viral diseases. The information obtained from genetic testing will ultimately be used to assist in making sound management decisions regarding the protection and restoration of the Florida manatee.
Limited population growth coupled with changing environmental conditions over time has altered the degree of genetic variation among Florida manatees, posing a threat to the health and vitality of current animals and future generations. "We know that in sexually reproducing organisms, genetic diversity is necessary for long-term survival," explains Bob Bonde, a biologist with FISC. "It's how we ensure that our offspring are armed with the appropriate mechanisms to adapt to a changing environment."
Historically, the warm waters of south Florida and the Everglades provided an ideal habitat for manatees. Coastal development in the past century, however, has forced the manatees northward, and they have now come to depend on artificially warm waters expelled by power plants to survive the winters. They are restricted in their movement by the loss of natural habitat and, as a result, make contact with fewer individuals.
"The limited distances manatees can travel because of water-temperature requirements restrict contact with a diverse group of animals. Over time, if a species is unable to move about and relocate because changing environmental characteristics force them to exist within a relatively confined space, inbreeding can occur," explains Bonde.
Bonde uses cytogenetic research and DNA fingerprinting to map the population structure of the Florida manateemuch like drawing a family tree. Early genetic studies of these animals revealed a high degree of genetic homogeneity within the Florida population. In addition to the physical abnormalities associated with inbreeding, genetic homogeneity jeopardizes a species' ability to adapt or adjust to changing environments and can also make a species susceptible to disease.
Having originated in the warmer waters of the Caribbean, West Indian manatees, for example, specifically adapted over a period of many years to the colder water temperatures of the Florida peninsula, making them hardier than their Caribbean or Central and South American counterparts. Genetic homogeneity, however, may compromise the manatees' ability to make similar adaptations in the future.
Genetic research arms scientists with more conclusive evidence about the vitality of the species and is a tool used to support or refute their hypotheses about manatee behaviors. "We aren't trying to influence the manatee population with this particular investigation," explains Bonde. "We're really trying to learn as much as we can about the way these animals respond to environmental stimuli, so that later on, other people can be more effective in their decision making and in the management of manatee habitats."
Genetic research can help determine, for example, whether it is healthy to introduce a captive manatee into a population without regard to genetic differences. Scientists are examining the feasibility and desirability of supplementing depleted manatee populations with animals from other areas. "If we don't pay attention to their genetic composition, we could inadvertently do a disservice to the population we're trying to recover by relocating captive animals into a wild population with similar genetic content. We want to discourage instances of inbreeding and preserve genetic diversity. These models help us do that," says Bonde.
Only time will tell whether a compromised gene pool will further threaten the existence of the Florida manatee, but Bonde remains hopeful that the genetic investigations carried out by USGS scientists and researchers with the University of Florida, the Florida Fish and Wildlife Conservation Commission, Mote Marine Laboratory, and other organizations will help protect future generations of these Florida treasures.
in this issue:
Using Genetic Modeling to Assess the Health and Status of Manatee Populations