Benjamín Morales-Vela

Phylogeography of the West Indian manatee (Trichechus manatus): how many populations and how many taxa?

To resolve the population genetic structure and phylogeography of the West Indian manatee (Trichechus manatus), mitochondrial (mt) DNA control region sequences were compared among eight locations across the western Atlantic region. Fifteen haplotypes were identified among 86 individuals from Florida, Puerto Rico, the Dominican Republic, Mexico, Colombia, Venezuela, Guyana and Brazil. Despite the manatee’s ability to move thousands of kilometres along continental margins, strong population separations between most locations were demonstrated with significant haplotype frequency shifts. These findings are consistent with tagging studies which indicate that stretches of open water and unsuitable coastal habitats constitute substantial barriers to gene flow and colonization. Low levels of genetic diversity within Florida and Brazilian samples might be explained by recent colonization into high latitudes or bottleneck effects. Three distinctive mtDNA lineages were observed in an intraspecific phylogeny of T. manatus, corresponding approximately to: (i) Florida and the West Indies; (ii) the Gulf of Mexico to the Caribbean rivers of South America; and (iii) the northeast Atlantic coast of South America. These lineages, which are not concordant with previous subspecies designations, are separated by sequence divergence estimates of d = 0.04–0.07, approximately the same level of divergence observed between T. manatus and the Amazonian manatee (T. inunguis, n = 16). Three individuals from Guyana, identified as T. manatus, had mtDNA haplotypes which are affiliated with the endemic Amazon form T. inunguis. The three primary T. manatus lineages and the T. inunguis lineage may represent relatively deep phylogeographic partitions which have been bridged recently due to changes in habitat availability (after the Wisconsin glacial period, 10 000 BP), natural colonization, and human‐mediated transplantation.

Phylogeography, phylogeny and hybridization in trichechid sirenians: implications for manatee conservation

The three living species of manatees, West Indian (Trichechus manatus), Amazonian (Trichechus inunguis) and West African (Trichechus senegalensis), are distributed across the shallow tropical and subtropical waters of America and the western coast of Africa. We have sequenced the mitochondrial DNA control region in 330 Trichechus to compare their phylogeographic patterns. In T. manatus we observed a marked population structure with the identification of three haplotype clusters showing a distinct spatial distribution. A geographic barrier represented by the continuity of the Lesser Antilles to Trinidad Island, near the mouth of the Orinoco River in Venezuela, appears to have restricted the gene flow historically in T. manatus. However, for T. inunguis we observed a single expanding population cluster, with a high diversity of very closely related haplotypes. A marked geographic population structure is likely present in T. senegalensis with at least two distinct clusters. Phylogenetic analyses with the mtDNA cytochrome b gene suggest a clade of the marine Trichechus species, with T. inunguis as the most basal trichechid. This is in agreement with previous morphological analyses. Mitochondrial DNA, autosomal microsatellites and cytogenetic analyses revealed the presence of hybrids between the T. manatus and T. inunguis species at the mouth of the Amazon River in Brazil, extending to the Guyanas and probably as far as the mouth of the Orinoco River. Future conservation strategies should consider the distinct population structure of manatee species, as well as the historical barriers to gene flow and the likely occurrence of interspecific hybridization.

The Tanaid Hexapleomera robusta (Crustacea : Peracarida) from the Caribbean Manatee, With Comments on Other Crustacean Epibionts

The tanaidaceans are among the most conspicuous and ecologically relevant benthic microcrustaceans in the marine realm but there are only a few records of species of tanaids associated with other marine organisms. During a long-term survey on the biology and distribution of the Caribbean manatee Trichechus manatus manatus Linnaeus in Mexican waters, parasites and epibionts were collected from 47 individuals that were captured for tagging in two bay systems. Well-established epibiotic communities of the tanaidacean Hexapleomera robusta (Moore) were found on eight of these animals; this tanaid crustacean formed patches of tubes adhered to the skin surface. Patches were distributed in different parts of the body surface but mainly along the backbone depression, the caudal zone, and on the lateral margins; in some instances they were related to clusters of barnacles. Highly significant differences of infestation rates were revealed between Chetumal Bay and Ascension Bay, the latter representing better conditions (high salinity and hydrodynamism) for tanaid invasion and settlement on the manatee. It is speculated that the tanaid is a commensal; no visible damage was found in the host and its presence was not related to skin lesions. The tanaid probably captures suspended particles as the manatee feeds. This is the first confirmed record of a symbiotic association involving a tanaid and the Caribbean manatee. The tanaid species recorded ( H. robusta ) and the harpacticoid copepod Balaenophilus manatorum (Ortiz, Lalana & Torres), have both been recorded also as epibionts of sea turtles. The tanaid has been known from sea turtles for some time, but the copepod was first recorded from a manatee and was subsequently found on sea turtles a few years later.

The Trophic Role of the Endangered Caribbean Manatee Trichechus manatus in an Estuary with low Abundance of Seagrass

Chetumal Bay is a refuge for the manatee, Trichechus manatus, a large and strictly herbivorous aquatic mammal. The ecosystem is notoriously poor in subaquatic vegetation, the main components of manatees’ diet. Due to the constant presence of manatees in the bay and their ability to consume large volumes of plant material, it is assumed that the species has a relevant trophic impact on the system. A mass–balance trophic model was designed to describe the flows of energy and matter in the bay, with the goal of assessing the role of manatees in the system. The system was aggregated in eight effective trophic levels. The biomass was intensely concentrated in the detritus, suggesting that the matter on the bottom sediment is the main regulator of the energy flow in the system. Primary producers comprised of detritus, mangrove, benthic autotrophs, and phytoplankton. The apex predators were dolphins and large piscivorous fishes. Manatees occupied the trophic level 2.0. Manatees were directly or indirectly impacted by autotrophs, mangrove, and detritus; but the competition between manatees and other groups was insignificant. In comparison to other ecosystems where manatees occur, Chetumal Bay (BCh) has the lowest relative biomass of seagrasses. Several ecological and behavioral mechanisms to compensate the lack of macrophytes biomass (or a combination of several) are suggested. Ecopath with Ecosim models are useful to describe the flow of energy and matter in the ecosystems. However, there are still critical gaps in the knowledge of BCh and its manatee population. It is difficult to assess the uncertainty associated with the estimates obtained; therefore, results should be interpreted with caution. Improving this preliminary model with robust local information on the Chetumal Bay ecology and its manatee population is recommended.

The copepod Balaenophilus manatorum (Ortíz, Lalana and Torres, 1992) (Harpacticoida), an epibiont of the Caribbean manatee

The harpacticoid copepod Balaenophilus manatorum (Ortíz, Lalana and Torres, 1992) was originally described based on a few specimens collected from a single manatee in Cuba. Since its description it has been recorded exclusively as a symbiont of sea turtles worldwide; there were no further records of this species from the manatee and this association remained unconfirmed. During a long-term survey on the biology and ecology of the manatee Trichechus manatus manatus L. in Mexican waters of the western Caribbean, epibionts were collected from 54 individuals, including males, females and juveniles. Many specimens of B. manatorum were recorded from several manatees and analysed morphologically; a comparison is made with specimens from turtles of the Mexican Pacific. Manatees captured in two different bay systems were examined, but only those from Chetumal Bay were positive for copepods. Infestation comprised 14 manatees (26%), eight females and six males; incidence was higher than that previously found for other crustacean epibionts. Copepods were found as soft yellowish masses arranged along skin folds and wrinkles of the muzzle, the base of the fins, and the nipple area; there was no evidence of skin damage caused by the copepod. The presence of B. manatorum on manatees is confirmed and the first data are provided on the prevalence of this epibiont in one of the main populations of this mammal in the western Caribbean.

Using craniometrical predictors to infer body size of Antillean manatees

Abstract Body size determines many physiological and ecological variables; however, there are few studies on this parameter for the Antillean manatee (Trichechus manatus manatus). We studied an osteological collection and databases of Antillean manatees in Mexico to infer body measurements and to determine the body mass (BM)/body length (BL) relationship. The studied sample included 165 specimens: skulls (n=60), necropsies (n=51), and individuals captured for health assessment purposes (n=54). Specific regression equations for estimating BM were derived using the following craniometrical parameters: condylobasal length (BSL), occipital condyle width (OCW), and foramen magnum width (FMW). OCW and FMW were not significantly correlated with BL. The equation of the fitted model was BL=-121.644+10.8861×BSL (p<0.05, r2=0.93, SE=14.72). The allometric equation of weight/length relationship was defined as BM=exp (2.7477+0.0110957×BL) (p<0.05, r2=0.99, SE=0.07). The model showed a significant relationship between BL and BSL (>95%). Regression equations proved to be useful in estimating BL when only highly decomposed carcasses or skull dry bones are available, and in estimating weight when it is impossible to do it directly. Studies on biology history and age determination in T. m. manatus are required in order to establish an adequate age classification.