Evidence of two genetic clusters of manatees with low genetic diversity in Mexico and implications for their conservation

Abstract

The Antillean manatee (Trichechus manatus manatus) occupies the tropical coastal waters of the Greater Antilles and Caribbean, extending from Mexico along Central and South America to Brazil. Historically, manatees were abundant in Mexico, but hunting during the pre-Columbian period, the Spanish colonization and throughout the history of Mexico, has resulted in the significantly reduced population occupying Mexico today. The genetic structure, using microsatellites, shows the presence of two populations in Mexico: the Gulf of Mexico (GMx) and Chetumal Bay (ChB) on the Caribbean coast, with a zone of admixture in between. Both populations show low genetic diversity (GMx: N(A) = 2.69; H(E) = 0.41 and ChB: N(A) = 3.0; H(E) = 0.46). The lower genetic diversity found in the GMx, the largest manatee population in Mexico, is probably due to a combination of a founder effect, as this is the northern range of the sub-species of T. m. manatus, and a bottleneck event. The greater genetic diversity observed along the Caribbean coast, which also has the smallest estimated number of individuals, is possibly due to manatees that come from the GMx and Belize. There is evidence to support limited or unidirectional gene flow between these two important areas. The analyses presented here also suggest minimal evidence of a handful of individual migrants possibly between Florida and Mexico. To address management issues we suggest considering two distinct genetic populations in Mexico, one along the Caribbean coast and one in the riverine systems connected to the GMx.

Phylogeography and Sex-Biased Dispersal across Riverine Manatee Populations (Trichechus inunguis and Trichechus manatus) in South America

“…However, marine West Indian manatees presented population structure contrasting with gene flow in riverine populations [19], [20], [21] We suggest that habitat differences between marine and riverine environments impose different barriers to male dispersal, on which marine T. manatus male migrations are limited by freshwater resources to avoid osmoregulation stressors [67], strong currents, and presence of seagrass beds which restricts them from dispersing across deep waters [68], [69], while riverine males are mostly limited by strong currents and water levels [8], [10], being able to move for longer distances, relying more on behavioral, acoustic or chemical signals to pursue females [4].…”

“…Microsatellite data supported population division between Florida and Puerto Rican populations [21], the wetlands systems of the Gulf of Mexico and the Caribbean coast of Mexico [20], as well as between Belize City Cayes and the Southern Lagoon system in Belize [19].…”

“…Using multiple unlinked loci for populations with smaller sampling sizes improves accuracy in population genetics estimates [13], [14], [15], and provides a solution to study population dynamics in manatee populations. Primers for amplification of highly polymorphic bi-parentally inherited nuclear microsatellite loci have been developed for the Florida manatee [16], [17], [18], and effectively used to study manatee population structure in Florida, Puerto Rico, Belize and Mexico [19], [20], [21].…”

Sighting demographics of the West Indian manatee Trichechus manatus in the north-central Gulf of Mexico supported by citizen-sourced data

“…Because manatee calves show philopatry to natal ranges and migration pathways (USFWS 2001, Deutsch et al 2003, manatee calves seen in Alabama and Mississippi may amass knowledge of local habitats from their mothers, increasing the likelihood that future generations of manatees will continue to occur in these areas. Genetic techniques may be useful to resolve connections between north-central Gulf of Mexico migrants and other groups of manatees through time (Nourisson et al 2011, Tucker et al 2012). …”

SEASONAL PREVALENCE OF ANTIBODIES TOLEPTOSPIRA INTERROGANSIN ANTILLEAN MANATEES FROM A LANDLOCKED LAKE IN TABASCO, MEXICO

“…In Mexico, Antillean manatees inhabit coastal and inland waters from the Gulf of Mexico and the Caribbean lowlands, forming two discrete population units (Nourisson et al 2011). The largest population is in the Gulf of Mexico watershed, encompassing most of the state of Tabasco, northern Chiapas, and southern Campeche, associated with the Usumacinta and Grijalva rivers, which carry approximately 30% of the surface runoff in Mexico.…”