Molecular and morphometric analysis of nominal Brachidontes exustus (Mollusca,Mytilidae) in Brazilian waters

Brachidontes exustus (Mollusca, Mytilidae) is mainly distributed in Central America, where it has been recognized as a _lataforma species. This study aimed to determine whether B. exustus extends beyond the Amazon Barrier and southward along the Brazilian West Atlantic coast. Mitochondrial genes coding for cytochrome-c oxidase, subunit I (COI) and 16S subunit of ribosomal _lataforma__ cid (16S rRNA) were analyzed with _lata parameters on Brazilian populations (Salvador, Arraial do Cabo and Fernando de Noronha) of scorched mussels previously recorded as B. exustus. Multivariate morphometric _latafor showed partial discrimination of species. Molecular _latafor confirmed B. exustus at Salvador, a population highly similar to Cartagena (Colombia), both belonging to the Atlantic Clade of the B. exustus complex. This fact adds evidence to the idea of the Amazon outflow as a semipermeable barrier. In the southeast of Brazil, B. exustus was not found; instead, B. darwinianus is the species represented at Arraial do Cabo (state of Rio de Janeiro), associated with brackish _lataf. Scorched mussels from Fernando de Noronha are most closely related to B. puniceus from Cape Verde with 4.4% differentiation. Demonstrating an independent evolutionary history since at least the beginning of the Pleistocene, its proposed new name is B. noronhensis.     

Allometric differences on the shell shape of two scorched mussel species along the Atlantic South American Coast

Scorched mussels (Bivalvia: Mytilidae) are an important component of rocky shore assemblages around the world. The mussel beds of the mid-intertidal coasts of the south-western Atlantic are composed of two species of scorched mussels, which dominate the physiognomy and structure of the rocky shore communities. The present study investigates the variation in the shell-shape allometric trajectories of both species of mussels throughout their distributional range in the southwestern Atlantic coast, from latitude 34°S to 53°S. Shells of Brachidontes rodriguezii were collected at two Uruguayan localities and four Argentinean localities, while shells of Perumytilus purpuratus were collected at six Argentinean localities. Shell shapes of the specimens were studied by geometric morphometrics using landmark and semi-landmark methods. Different evolutionary histories and thermal regimes characterize these two species. Brachidontes rodriguezii seems to have a long history in the region and is present in a restricted area, the warm temperate region of the south-western Atlantic, while P. purpuratus seems to have a recent history and is present in a wide thermal range, involving the cold-temperate regions of the south-western Atlantic and south-eastern Pacific and the warm-temperate region of the south-eastern Pacific. Based on these considerations, we prompt the hypothesis that allometric trajectories of P. purpuratus shell shape is more variable and adapted to a specific habitat than B. rodriguezii. The impact of allometry was larger in P. purpuratus than in B. rodriguezii. Graphical evidence was gathered, showing that these two species differ in allometric growth forms and that the allometric shell morphology changes reflect environmental constraints and adaptation. While the intertidal mussel beds of the South American coasts are ecologically similar in appearance, we found that the allometric variation of the scorched mussels occurs in response to diverging evolutionary processes such as phenotypic plasticity in P. purpuratus and canalization in B. rodriguezii.     

Explosive Pleistocene range expansion leads to widespread Amazonian sympatry between robust and gracile capuchin monkeys

Aim Capuchin monkey species are widely distributed across Central and South America. Morphological studies consistently divide the clade into robust and gracile forms, which show extensive sympatry in the Amazon Basin. We use genetic data to test whether Miocene or Plio‐Pleistocene processes may explain capuchin species’ present distributions, and consider three possible scenarios to explain widespread sympatry. Location The Neotropics, including the Amazon and Atlantic Coastal Forest. Methods We sequenced the 12S ribosomal RNA and cytochrome b genes from capuchin monkey specimens. The majority were sampled from US museum collections and were wild‐caught individuals of known provenance across their distribution. We applied a Bayesian discrete‐states diffusion model, which reconstructed the most probable history of invasion across nine subregions. We used comparative methods to test for phylogeographic association and dispersal rate variation. Results Capuchins contained two well supported monophyletic clades, the morphologically distinct ‘gracile’ and ‘robust’ groups. The time‐tree analysis estimated a late Miocene divergence between Cebus and Sapajus and a subsequent Plio‐Pleistocene diversification within each of the two clades. Bayesian analysis of phylogeographic diffusion history indicated that the current wide‐ranging sympatry of Cebus and Sapajus across much of the Amazon Basin was the result of a single explosive late Pleistocene invasion of Sapajus from the Atlantic Forest into the Amazon, where Sapajus is now sympatric with gracile capuchins across much of their range. Main conclusions The biogeographic history of capuchins suggests late Miocene geographic isolation of the gracile and robust forms. Each form diversified independently, but during the Pleistocene, the robust Sapajus expanded its range from the Atlantic Forest to the Amazon, where it has now encroached substantially upon what was previously the exclusive range of gracile Cebus. The genus Cebus, as currently recognized, should be split into two genera to reflect the Miocene divergence and two subsequent independent Pliocene radiations: Cebus from the Amazon and Sapajus from the Atlantic Forest.     

Hidden Floridian biodiversity: mitochondrial and nuclear gene trees reveal four cryptic species within the scorched mussel, Brachidontes exustus, species complex

The well-documented Floridian 'Gulf/Atlantic' marine genetic disjunction provides an influential example of vicariant cladogenesis along a continental coastline for major elements of a diverse nearshore fauna. We are engaged in a two-part study that aims to place this disjunction into a regional Caribbean Basin phylogenetic perspective using the scorched mussel Brachidontes exustus as an exemplar. Our first step, documented here, is to thoroughly characterize the genetic structure of Floridian scorched mussel populations using mitochondrial (mt) and nuclear markers. Both sets of markers recovered the expected disjunction involving sister clades distributed on alternate flanks of peninsular Florida and lineage-specific mt molecular clocks placed its origin in the Pliocene. The two sister clades had distinct population genetic profiles and the Atlantic clade appears to have experienced an evolutionarily recent bottleneck, although plots of the relative estimates of N through time are consistent with its local persistence through the last Ice Age Maximum. Our primary novel result, however, was the discovery that the Gulf/Atlantic disjunction represents but one of three cryptic, nested genetic discontinuities represented in Floridian scorched mussel populations. The most pronounced phylogenetic split distinguished the Gulf and Atlantic sister clades from two additional nested cryptic sister clades present in samples taken from the southern Florida tropical marine zone. Floridian populations of B. exustus are composed of four cryptic taxa, a result consistent with the hypothesis that the Gulf/Atlantic disjunction in this morphospecies is but one of multiple latent regional genetic breakpoints.     

Phylogenetic and phylogeographic inferences based on two DNA markers reveal geographic structure of the orangeclaw hermit crab Calcinus tibicen (Anomura: Diogenidae) in the western Atlantic

The hermit crab Calcinus tibicen has an extensive distribution along the coasts of the western Atlantic Ocean, from the USA to southern Brazil. The present study aimed to test the hypothesis of the presence of phylogeographic structure of C. tibicen throughout its distribution, evaluating the genetic and morphological variabilities of the species. The molecular data, genetic diversity and demographic history were inferred from 16 different localities for the mitochondrial genes cytochrome oxidase subunit I (COI) (75 specimens) and 16S rRNA (20). The morphological information was based on 99 individuals from the same 16 localities. Results were obtained by the construction of haplotype networks and a phylogenetic tree, an Analysis of Molecular Variance (AMOVA), Tajima’s D and Fu’s Fs tests, pairwise mismatch distributions under the sudden expansion model, and by estimating divergence times. The haplotype networks show the existence of two genetically well-defined groups that do not share haplotypes. The phylogenetic tree and the matrix of genetic distances suggest lack of gene between North and South Atlantic groups, also corroborated by AMOVA for the COI gene. The genetic distance can be attributed to at least two ecological factors: the existence of a physiological barrier caused by the Amazon River freshwater plume, and the effect of the bifurcation of the westerly flowing South Atlantic oceanic currents creating a gap along the Brazilian coastline. Demographic history analyses suggest that C. tibicen experienced population expansion, probably after the Amazon River changed its direction. Despite the molecular evidence for the existence of a phylogeographic structure, no morphological pattern for each genetic group was observed. Therefore, based on the described molecular differences and the ecological and historical factors suggested, the question arises whether a cryptic species should be recognized for some of the populations of C. tibicen.     

Intertidal mussel beds from the South-western Atlantic show simple structure and uniform appearance: does environmental harshness explain the community?

Communities of the rocky mid-intertidal zone of the South-western Atlantic are uniform in appearance, dominated by dense monocultures of small-size mussels (Brachidontes rodriguezii and Perumytilus purpuratus). To explain this, two hypotheses have been advanced in the literature: environmental harshness due to high potential evaporation and historical contingency after the Last Glacial Maximum. In this study of Uruguayan and Argentine shores, we address the implications and predictions of these two hypotheses from a biogeographic perspective by studying the regional distribution and composition of mid-intertidal mussels. We conducted an extensive latitudinal sampling survey (21 locations, 34–54°S), along with a compilation of available information on mussel bed composition and mussel predators present along the coastline. Then we constructed latitudinal profiles of ecologically significant environmental variables with specific emphasis on potential evaporation, a proxy for desiccation stress. The results show that mussel beds are composed of two species of small mussels, which coexist over a biogeographic transition zone (40–42°S) related to sea surface water temperature. The distribution of mussels along the coastline studied is not consistent with the environmental harshness hypothesis. In addition, in the Central Patagonian zone (44–50°S), two invertebrate predators also inhabit the intertidal rocky shores. However, these localities showed higher environmental harshness (potential evaporation rate) than non-Patagonian localities. We suggest that further attention should be given to historical contingency in order to advance towards a hypothesis consistent with current knowledge on the post-glacial biogeographic history of the South-western Atlantic.     

EVOLUTIONARY RELATIONSHIPS BETWEEN FOUR SPECIES OF CLADOPHORA (CLADOPHORALES,CHLOROPHYTA) BASED ON DNA–DNA HYBRIDIZATION1

Analysis of the reassociation kinetics of the DNA from Cladophora pellucida (Huds.) Kütz. indicates that the genome of this benthic alga is comprised of approximately 75% repetitive sequences. Single-copy sequences reassociated with a rate constant of 1.8 × 10^?3 M^?1· s^?1, which corresponds to a haploid genome size of 4.7 × 10⁸ bp. Genotypic relationships between members of the form section Longiarticulatae were determined by the method of DNA–DNA hybridization. No significant divergence was observed between the single-copy sequences of C. pellucida isolates from the East Atlantic coast and Mediterranean Sea. Cladophora feredayi Harv. and C. att. ad pellucida from Australia and C. pellucidoidea van den Hoek from the West Atlantic coast were highly and about equally divergent from C. pellucida. The data support the hypothesis that the West Atlantic–West Pacific divergence reflects the middle Miocene closure of the Mediterranean–Indo-Pacific seaways, and the hypothesis that the Northwest Atlantic–Northeast Atlantic divergence reflects the middle Miocene thermal separation of these coasts.     

Molecular phylogeny, biogeography and insights into the origin of parthenogenesis in the Neotropical genus Leposoma (Squamata: Gymnophthalmidae): Ancient links between the Atlantic Forest and Amazonia

Leposoma is a conspicuous component of leaf litter herpetofauna of South and Central American rainforests. The 15 bisexual and one parthenogenetic species are allocated to the parietale and scincoides groups based on morphology. Phylogenetic analyses of 1830 bp (mtDNA + nuclear) were performed on 63 specimens of four species from Amazonian and Panamanian rainforests, and six species and one undescribed form from the Atlantic Forest. Different methods of tree reconstruction were explored, with Anotosaura vanzolinia and Colobosauroides cearensis as outgroups. The monophyly of the parietale and scincoides groups is strongly supported. Contrary to previous hypotheses suggesting a recent contact between Atlantic and Amazon forests, our estimates point to an initial split in Miocene. The position of Leposoma baturitensis, endemic to relictual forests in the semiarid Caatingas northeastern Brazil, and its divergence from the remaining species of the Atlantic Forest, suggests an ancient isolation with no indication of a secondary contact with forests of the eastern coast. Our data do not permit unambiguous assignment of parental species of the unisexual Leposoma percarinatum or the mechanism involved in the origin of parthenogenesis, but revealed two highly divergent diploid and triploid lineages within L. percarinatum, indicating that the unisexuals represent a species complex.     

Phylogeography of the Hypnea musciformis species complex (Gigartinales,Rhodophyta) with the recognition of cryptic species in the western Atlantic Ocean

Populations of the marine benthic red macroalgae Hypnea musciformis and Hypnea pseudomusciformis along the Atlantic and Pacific Oceans were tested for phylogeographic structure using the DNA barcode COI‐5P combined with rbcL for the construction of the phylogenetic tree. Strong patterns of genetic structure were detected across 210 COI‐5P DNA sequences, and 37 COI‐5P haplotypes were found, using multiple statistical approaches. Hypnea musciformis was found in the Northeast and Northwest Atlantic, the Mediterrean Sea, Namibia, and along the Pacific coast of Mexico. Two new putative species were detected, Hypnea sp. 1 in the Caribbean Sea and Hypnea sp. 2 in the Dominican Republic. Three distinct marine phylogeographic provinces were recognized in the Southern Hemisphere for H. pseudomusciformis: Uruguay, South‐Southeast Brazil, and Northeast Brazil. The degree of genetic isolation and distinctness among these provinces varied considerably. The Uruguay province was the most genetically distinct, as characterized by four unique haplotypes not shared with any of the Brazilian populations. Statistically significant results support both, isolation by distance and isolation by environment hypotheses, explaining the formation and mantainance of phylogeographic structuring along the Uruguay‐Brazil coast. Geographic, taxonomic and molecular marker concordances were found between our H. pseudomusciformis results and published studies. Furthermore, our data indicate that the Hawaiian introduced populations of H. musciformis contain Hypnea sp. 1 haplotypes, the current known distribution of which is restricted to the Caribbean.     

New records of the snow bass Serranus chionaraia (Perciformes: Serranidae) confirm an established population in the Brazilian Province

The snow bass Serranus chionaraia is a small-bodied reef fish presumed to be restricted to the Caribbean Province, with a single specimen captured south of the Amazon River mouth. Recent surveys with baited remote underwater stereo-video systems detected the species c. 1900 km southward. Meristic and morphometric characters of two specimens examined in this study confirmed the species identity, which greatly extends the speciesʼ range southward on the eastern coast of Brazil and indicates the presence of an established population of S. chionaraia in the Brazilian Province.     

Two deep evolutionary lineages in the circumtropical glasseye Heteropriacanthus cruentatus (Teleostei,Priacanthidae) with admixture in the south‐western Indian Ocean

A phylogeographic study of the circumtropical glasseye Heteropriacanthus cruentatus was conducted. Molecular analyses indicate two mitochondrial cytochrome c oxidase subunit I (coI) lineages that are 10·4% divergent: one in the western Atlantic (Caribbean) and another that was detected across the Indo‐Pacific. A fixed single nucleotide polymorphism (SNP) was detected at a nuclear locus (S7 ribosomal protein) and is consistent with this finding. There is evidence of recent dispersal from the Atlantic to the Indian Ocean with individuals of mixed lineages detected in South Africa and the Mozambique Channel. Using coalescent analyses of the mitochondrial dataset, time of divergence between lineages was estimated to be c. 15·3 million years. The deep divergence between these two lineages indicates distinct evolutionary units, however, due to the lack of morphological differences and evidence of hybridization between lineages, taxonomic revision is not suggested at this time.     

Genetic detection of cryptic species in the frillfin goby Bathygobius soporator

We compared, through allozyme and cytochrome b sequence analyses, populations of Bathygobius soporator from four localities on the Brazilian coast with those from the Oceanic Islands of the Rocas Atoll (230 km off the Brazilian coast) and the Bahamas (5700 km northwest from Rocas). The population from the Rocas Atoll was genetically more similar to the geographically distant Bahamas (gene identity, I=0.92) than to the supposedly conspecific populations from the Brazilian coast (I<0.55). Five diagnostic allozyme loci and a high level of nucleotide divergence (Kimura 2-parameters=0.21) were found between the two groups, further confirming that they must belong to different biological species. Since the type locality of B. soporator is in the Caribbean, the binomial should be maintained for the Bahamas/Rocas Atoll populations, and the other Brazilian populations of Bathygobius analysed either represent the occurrence of a species of Bathygobius hitherto not cited for the Brazilian coast, or belong to a new species. The coastal populations of this species were also found to be highly structured (F_ST=0.18; p<0.05), indicating that, even along the coast, levels of gene flow of this species are limited. This could be related to their reproductive biology (adhesive benthic eggs with parental care and short length of larval life). The timings of the divergence between the Caribbean and the Southwest Atlantic species found here, estimated from allozymes and cytb sequences, are very similar (around 10 MY bp), and correlate with the start of the Amazon river outflow. The colonization of the Rocas Atoll by populations from the Caribbean seems to have taken place after the Caribbean and the Brazilian coast species had diverged.     

Evaluating Intertidal Oyster Reef Development in South Carolina Using Associated Faunal Indicators

Eastern oyster (Crassostrea virginica) habitat is increasingly being restored for the ecosystem services it provides rather than solely as a fishery resource. Community‐based projects with the goal of ecological restoration have successfully constructed oyster reefs; however, the habitat benefits of these restoration efforts are usually not assessed or reported. In this study, we examined oyster habitat development at five community‐based oyster restoration sites in South Carolina using oyster population parameters, resident fauna densities, and sedimentation (percent sediment coverage) as assessment metrics. All sites included multiple‐aged reefs (1–3 years old) at the time of the fall 2004 sampling. Resident crabs and mussels were abundant at all five sites and crab assemblages were related to the size structure of the oyster microhabitat. Scorched mussel (Brachidontes exustus) abundances were most frequently correlated with oyster and other resident species abundances. Associations among oysters and resident crabs and mussels were not evident when analyses were conducted with higher level taxonomic groupings (e.g., total number of crabs, mussels, or oysters), indicating that species‐level identifications improve our understanding of interactions among reef inhabitants and oyster populations. Community‐based restoration sites in South Carolina provide habitat for mussels and resident crabs, in some cases in the absence of dense populations of relatively large oysters. Monitoring programs that neglect species‐level identifications and counts of mussels and crabs may underestimate the successful habitat provision that can arise independent of large, dense oyster assemblages.     

Comparative Phylogeography of the Atlantic Forest Endemic Sloth (Bradypus torquatus) and the Widespread Three-toed Sloth (Bradypus variegatus) (Bradypodidae, Xenarthra)

The comparative phylogeographic study of the maned sloth (Bradypus torquatus) and the three-toed sloth (Bradypus variegatus) was performed using a segment of mitochondrial DNA (mtDNA) control region. We examined 19 B. torquatus from two regions and 47 B. variegatus from three distant regions of Atlantic forest. This first characterization of molecular diversity indicates a great diversity (B. torquatus: h = 0.901 ± 0.039 and π = 0.012 ± 0.007; B. variegatus: h = 0.699 ± 0.039 and π = 0.010 ± 0.006) and very divergent mitochondrial lineages within each sloth species. The different sampled regions carry distinct and non-overlapping sets of mtDNA haplotypes and are genetically divergent. This phylogeographic pattern may be characteristic of sloth species. In addition, we infer that two main phylogeographic groups exist in the Atlantic forest representing a north and south distinct divergence.     

Mitochondrial DNA genome evidence for the existence of a third divergent lineage in the western Atlantic Ocean for the bull shark (Carcharhinus leucas)

We report for the first time a highly divergent lineage in the Caribbean Sea for the bull shark (Carcharhinus leucas) based on the analysis of 51 mitochondrial DNA genomes of individuals collected in the western North Atlantic. When comparing the mtDNA control region obtained from the mitogenomes to sequences reported previously for Brazil, the Caribbean lineage remained highly divergent. These results support the existence of a discrete population in Central America due to a phylogeographic break separating the Caribbean Sea from the western North Atlantic, Gulf of Mexico and South America.     

Patterns of diversification in two species of short‐tailed bats (Carollia Gray, 1838): the effects of historical fragmentation of Brazilian rainforests

The small‐sized frugivorous bat Carollia perspicillata is an understory specialist and occurs in a wide range of lowland habitats, tending to be more common in tropical dry or moist forests of South and Central America. Its sister species, Carollia brevicauda, occurs almost exclusively in the Amazon rainforest. A recent phylogeographic study proposed a hypothesis of origin and subsequent diversification for C. perspicillata along the Atlantic coastal forest of Brazil. Additionally, it also found two allopatric clades for C. brevicauda separated by the Amazon Basin. We used cytochrome b gene sequences and a more extensive sampling to test hypotheses related to the origin and diversification of C. perspicillata plus C. brevicauda clade in South America. The results obtained indicate that there are two sympatric evolutionary lineages within each species. In C. perspicillata, one lineage is limited to the Southern Atlantic Forest, whereas the other is widely distributed. Coalescent analysis points to a simultaneous origin for C. perspicillata and C. brevicauda, although no place for the diversification of each species can be firmly suggested. The phylogeographic pattern shown by C. perspicillata is also congruent with the Pleistocene refugia hypothesis as a likely vicariant phenomenon shaping the present distribution of its intraspecific lineages. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 527–539.     

Predator size interacts with habitat structure to determine the allometric scaling of the functional response

While both predator body size and prey refuge provided by habitat structure have been established as major factors influencing the functional response (per capita consumption rate as a function of prey density), potential interactions between these factors have rarely been explored. Using a crab predator (Panopeus herbstii) – mussel prey (Brachidontes exustus) system, we examined the allometric scaling of the functional response in oyster (Crassostrea virginica) reef habitat, where crevices within oyster clusters provide mussels refuge from predation. A field survey of mussel distribution showed that mussels attach closer to the cluster periphery at high mussel density, indicating the potential for saturation of the refuge. In functional response experiments, the consumption rate of large crabs was depressed at low prey density relative to small crabs, while at high prey density the reverse was true. Specifically, the attack rate coefficient and handling time both decreased non‐linearly with crab size. An additional manipulation revealed that at low prey densities, the ability of large crabs to maneuver their claws and bodies to extract mussels from crevices was inhibited relative to small crabs by the structured habitat, reducing their attack rate. At high prey densities, crevices were saturated, forcing mussels to the edge of clusters where crabs were only limited by handling time. Our study illuminates a potentially general mechanism where the quality of the prey refuge provided by habitat structure is dependent on the relative size of the predator. Thus anthropogenic influences that alter the natural crab size distribution or degrade reef habitat structure could threaten the long‐term stability of the crab –mussel interaction in reefs.     

Phylogeographic Analyses Suggest Multiple Lineages of Crystallaria asprella (Percidae: Etheostominae)

The crystal darter, Crystallaria asprella, exists in geographically isolated populations that may be glacial relicts from its former, wide distribution in the Eastern U.S. An initial phylogeographic survey of C. asprella based upon the mitochondrial cytochrome b (cyt b) gene indicated that there were at least four distinct populations within the species: Ohio River basin, Upper Mississippi River, Gulf coast, and lower Mississippi River. In particular, the most divergent population was the most recently discovered, from the Elk River, WV, in the Ohio River basin, and it was postulated that this population represents an undescribed, potentially threatened species. However, differentiation observed at a single gene region is generally not considered sufficient evidence to establish taxonomic status. In the present study, nucleotide variation at the mitochondrial control region and a nuclear S7 ribosomal gene intron were compared to provide independent verification of phylogeographic results between individuals collected from the same five disjunct populations previously surveyed. Variation between populations at the control region was substantial (except between Gulf drainages) and was concordant with patterns of sequence divergence from cyt b. Only the Elk River population was resolved as monophyletic based upon nuclear S7, but significant differences based upon Φ_ST statistics were observed between most populations. Morphometric data were consistent with molecular data regarding the distinctiveness of the Elk River population. It is proposed that populations of C. asprella consist of at least four distinct population segments, and that the Elk River group likely constitutes a distinct species.     

Historical biogeography of lowland species of toads (Bufo) across the Trans-Mexican Neovolcanic Belt and the Isthmus of Tehuantepec

Aim In this study, we investigate phylogeographic structure in two different species groups of lowland toads. First, we further investigate strict parapatry of the Pliocene‐vicariant Bufo valliceps/B. nebulifer species pair. Secondly, we test for similar phylogeographic structure in the distantly related toad B. marinus, a species we hypothesize will show a Pleistocene dispersal across the same area. Location The eastern extension of the Trans‐Mexican Neovolcanic Belt (TMNB) contacts the Atlantic Coast in central Veracruz, Mexico. Although it is not a massive structure at this eastern terminus, the TMNB has nonetheless effected vicariance and subsequent speciation in several groups of animals. The Isthmus of Tehuantepec unites the North American continent with Nuclear Central America and is also known to be a biogeographic barrier for many taxa. Methods We use sequence data from two mitochondrial DNA genes (c. 550 base‐pairs (bp) of 16S and c. 420 bp of cyt b) from 58 individuals of the B. valliceps/nebulifer complex, collected from 24 localities. We also present homologous sequence data from 23 individuals of B. marinus, collected from 12 localities. We conduct maximum‐parsimony, maximum‐likelihood and Bayesian analyses to investigate phylogeographic structure. We then use parsimony‐ and likelihood‐based topology tests to assess alternative phylogenetic hypotheses and use a previously calibrated molecular rate of evolution to estimate dates of divergence. Results Our results further define the parapatric contact zone across the TMNB between the Pliocene‐vicariant sister species B. valliceps and B. nebulifer. In contrast, phylogenetic structure among populations of B. marinus across the TMNB is much shallower, suggesting a more recent Pleistocene dispersal in this species. In addition, we found phylogeographic structure associated with the Isthmus of Tehuantepec in both species groups. Main conclusions The existence of a Pliocene–Pleistocene seaway across the Isthmus of Tehuantepec has been controversial. Our data depict clades on either side of the isthmus within two distinct species (B. valliceps and B. marinus), although none of the clades associated with the isthmus, for either species, are reciprocally monophyletic. In the B. valliceps/B. nebulifer complex, the TMNB separation appears to predate the isthmian break, whereas in B. marinus dispersal across the TMNB has occurred subsequent to the presence of a barrier at the Isthmus of Tehuantepec.     

Molecular phylogenetics of Atlantic Shield Platynectes diving beetles (Coleoptera: Dytiscidae): a first glance at the evolution of the genus in the Amazon Basin

Neotropical diving beetles of the genus Platynectes are distributed across Central America, the Andes and different Precambrian shields in the Amazon Basin. Species from the northern Guiana Shield form a monophyletic clade, yet the phylogenetic relationships of the eastern Atlantic Shield species remain unknown. Here, we augmented an existing molecular dataset with a species from the Atlantic Shield that was not previously sampled. We reconstructed the phylogenetic relationships and estimated divergence times to understand the evolution of lineages dwelling in this region. The newly sampled specimens from the Atlantic Shield are recovered as sister taxa to Guiana Shield species. The dating analyses suggest a split between these two lineages in the late Oligocene to mid-Miocene, contemporary with the Miocenic geological remodeling of the Amazon Basin. Additional sampling in the Atlantic and Central Brazilian Shields will be determinant to test the monophyly of Platynectes species distributed in these ancient shields, and to fully understand the biogeographical history of diving beetles in the Amazon Basin.