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

Abstract

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.

How many species of goliath grouper are there? Cryptic genetic divergence in a threatened marine fish and the resurrection of a geopolitical species

“…Our data, along with other recent studies (e.g. Bass et al 2005, Quattro et al 2006, Vianna et al 2006 clearly show that the phenomenon of hidden genetic divergence is not restricted to understudied or difficult-tostudy organisms, as has been the basis of conventional wisdom. In fact, goliath grouper are at the forefront of conservation efforts, as is evidenced by their presence as the focus of recent symposia, their listing by the IUCN as 'Critically Endangered,' their prior listing as a species of concern in US waters by US Fish and Wildlife Service, and a moratorium on their capture in both Brazil and the US.…”

“…Although this phenomenon was thought to occur most commonly in small or difficult-to-study organisms, recent evidence shows that these cryptic genetic lineages also occur amongst Earth's largest and most well-studied marine animals (e.g. Bass et al 2005, Quattro et al 2006, Vianna et al 2006. In addition, these genetic studies often elucidate genetic patterns that reflect demographic connectivity, a critical aspect of population biology that is often unknown but imperative for effective conservation strategies.…”

Mitochondrial and nuclear DNA variability in the living fossil Triops cancriformis (Bosc, 1801) (Crustacea, Branchiopoda, Notostraca)

“…unexpected for the mitochondrial control region, a marker widely used for population analysis (Chu et al, 2003;Kang et al, 2005;Vianna et al, 2006). Also, the widening of the analysis to a higher number of individuals per population for the 16S gene confirms the low differentiation.…”

Hybridization phenomenon in cetacean and pinniped species

“…Nos mamíferos, a ocorrência de híbri-dos foi registrada tanto em espécies aquáticas quanto em terrestres, e tem sido registrada nas seguintes ordens: Marsupialia, Lagomorpha, Carnivora, Cetartiodactyla, Rodentia e Primates (Van Gelder, 1977;Sezaki et al, 1984;Goodman et al, 1999;Wirtz, 1999). Há registros, inclusive, da geração de híbridos entre espécies de gêneros diferentes (Wilson et al, 1974;Van Gelder, 1977;Kovacs et al, 1997;Gava e Freitas, 2002;Vianna et al, 2006). De acordo com Short (1975Short ( , 1997, o registro mais antigo identificado deste fenômeno refere-se à mula (resultante do cruzamento entre a égua e o jumento), a qual já era conhecida e utilizada durante o império romano (44 a.C.).…”