Abstract: The West Indian (Trichechus manatus) and Amazonian (T. inunguis) manatees have a sympatric occurrence at the mouth of the Amazon River. A result of this interspecific encounter is the occurrence of hybrids, which are frequently found along the coasts of Amapá state in Brazil, French Guiana and Guyana. Here we present new genetic evidence indicating the occurrence of a hybrid swarm along the Guianas Shield coastline, which is an interspecific hybrid zone that also separates T. manatus populations located east (Brazil) and west (Caribbean, Gulf of Mexico, Florida and Antilles). In addition, we suggest that this hybrid population occupies a peculiar mangrove-rich environment under strong influence of the Amazon River plume, which requires an independent management and should be considered a special conservation area.
Espécimes recém coletados do raro roedor semi-aquático Neusticomys oyapocki (Rodentia: Sigmodontinae: Ichthyomyini) exibem variação individual no número de dentes. Considerando que esse ichthyomyineo das Guianas foi descrito como tendo apenas dois molares por quadrante mandibular, o nosso estudo examina 31 espécimes dos quais 12 apresentam de um a quatro terceiros molares adicionais. Espécimes com pelo menos um terceiro molar são provenientes de 6 localidades que abrangem Suriname, Guiana Francesa, e os estados brasileiros do Amapá e Pará. Os terceiros molares relatados para essa espécie são dentes muito pequenos (comprimento médio da coroa 0.55 mm), cerca da metade do tamanho dos segundos molares. Mostramos que N. oyapocki tem entre 8 e 12 molares, o que é uma variação extensa no número de dentes. Esse tipo de variação dentária encontrada no Ichthyomyineo das Guianas é rara em roedores murídeos, já que apenas alguns casos similares foram relatados para alguns ratos de água carnívoros e ratos-musgos da Nova Guiné.
Newly collected specimens of the rare semi-aquatic mouse Neusticomys oyapocki (Rodentia: Sigmodontinae: Ichthyomyini) exhibit individual variation in tooth number. Whereas this Guianan ichthyomyine had previously been described as having only two molars per jaw quadrant, our study examines 31 specimens, of which 12 exhibit from one to four additional third molars. Specimens with at least one third molar come from 6 localities spanning Suriname, French Guiana, and the Brazilian states of Amapa and Para. Third molars reported in this species are tiny (on average 0.55 mm crown length), about half the size of second molars. We show that N. oyapocki has between 8 and 12 molars, which represents extensive variation in the number of teeth. This kind of dental variation is rare in muroid rodents, as only a few such cases have been reported from some carnivorous water rats and moss mice from New Guinea.
Sea turtles are marine reptiles that undertake long migrations through their life, with limited information regarding juvenile stages. Feeding grounds (FGs), where they spend most of their lives, are composed by individuals from different natal origins, known as mixed stock populations. The aim of this study was to assess genetic composition, natal origins and demographic history of juvenile green turtles (Chelonia mydas) at the Paranaguá Estuarine Complex (PEC), Brazil, considered a Natural World Heritage site. Tissue samples of stranded animals were collected (n = 60), and 700 bp mitochondrial DNA sequences were generated and compared to shorter sequences from previously published studies. Global exact tests of differentiation revealed significant differences among PEC and the other FGs, except those at the South Atlantic Ocean. Green turtles at PEC present genetic signatures similar to those of nesting females from Ascension Island, Guinea Bissau and Aves Island/Surinam. Population expansion was evidenced to have occurred 20–25 kYA, reinforcing the hypothesis of recovery from Southern Atlantic refugia after the last Glacial Maximum. These results contribute to a better understanding of the dynamics of green turtle populations at a protected area by providing knowledge on the dispersion patterns and reinforcing the importance of the interconnectivity between nesting and foraging populations.
The genetic structure of Caiman crocodilus was investigated using a 1085 bp mtDNA fragment of the cytochrome b gene. Inferences were based on 125 individuals from nine localities in Peru, Brazil and French Guiana. With the exception of Mamirauá Lake, Anavilhanas Archipelago and the Tapará Community which show a signal of demographic expansion, the sampled localities are in a mutation-drift genetic equilibrium. Divergence between the Amazon basin and extra-Amazon basin localities is significant; however, inference from Nested Clade Analysis cannot distinguish between continuous range expansion, long distance colonization or past fragmentation; however, past fragmentation is unlikely due to low number of mutational steps separating these two regions. The divergence is probably maintained by the reduced ability of C. crocodilus to cross salt water barriers. Within the Amazon basin, continuous range expansion without isolation-by-distance is the most likely process causing genetic structuring. The observed genetic patterns are compatible with the ecology of C. crocodilus, and history of human exploitation. As commercial hunting depleted more valuable species, C. crocodilus expanded its range and ecological niche, prompting hunters to harvest it. Following a period of intense hunting, C. crocodilus is now experiencing recovery and a second population expansion especially in protected areas.