Scorched mussels (Brachidontesspp., Bivalvia: Mytilidae) from the tropical and warm‐temperate southwestern Atlantic: the role of the Amazon River in their speciation

Abstract

Antitropicality is a distribution pattern where closely related taxa are separated by an intertropical latitudinal gap. Two potential examples include Brachidontes darwinianus (south eastern Brazil to Uruguay), considered by some authors as a synonym of B. exustus (Gulf of Mexico and the Caribbean), and B. solisianus, distributed along the Brazilian coast with dubious records north of the intertropical zone. Using two nuclear (18S and 28S rDNA) and one mitochondrial gene (mtDNA COI), we aimed to elucidate the phylogeographic and phylogenetic relationships among the scorched mussels present in the warm‐temperate region of the southwest Atlantic. We evaluated a divergence process mediated by the tropical zone over alternative phylogeographic hypotheses. Brachidontes solisianus was closely related to B. exustus I, a species with which it exhibits an antitropical distribution. Their divergence time was approximately 2.6 Ma, consistent with the intensification of Amazon River flow. Brachidontes darwinianus, an estuarine species is shown here not to be related to this B. exustus complex. We suspect ancestral forms may have dispersed from the Caribbean to the Atlantic coast via the Trans‐Amazonian seaway (Miocene). The third species, B rodriguezii is presumed to have a long history in the region with related fossil forms going back to the Miocene. Although scorched mussels are very similar in appearance, their evolutionary histories are very different, involving major historical contingencies as the formation of the Amazon River, the Panama Isthmus, and the last marine transgression.

Multiple drainage reversal episodes and glacial refugia in a Patagonian fish revealed by sequenced microsatellites

“…Initially most phylogeographic studies focused on Northern Hemisphere taxa [4]. More recently, however, a number of studies have examined these questions on Southern Hemisphere species including species from tropical South America [5][6][7][8] and its temperate southern cone, Patagonia. In Patagonia, the focus area of the present study, phylogeographic patterns have been described for terrestrial [9][10][11][12], coastal marine [13][14][15]; freshwater [16][17][18][19][20][21][22][23] and diadromous species [24][25][26][27].…”

“…At the broadest scale, the tree distinguishes collections from Pacific draining systems north of 42°S from collections with headwaters east of the Andes that drain into the Atlantic and those that are trans-Andean south of 42°S and drain into the Pacific. Within the first group, collections from Maipo and Nilahue (1 and 2) and to a lesser extent, from the Biobío system (3-5) are distinguishable from those to the south(6)(7)(8)(9)(10)(11)(12)(13)(14). Within the second group the colouring reflects two glacial refugia east of Andes, one in northern and one in southern Patagonia.…”

Phylogeography of Petrolisthes armatus, an invasive species with low dispersal ability

“…Nevertheless, the isolation of Brazilian populations is obvious in the high F ST values and low estimates of migration in IMa2 (we consider the apparent migration from Georgia an artefact of the short COI-HL sequences). Isolation of Brazilian marine populations of other species from their conspecifics in the Caribbean is usually attributed to the fresh-water plume of the Orinoco and the Amazon 43 , 62 , 78 , 79 ; however, given the wide salinity tolerance of P. armatus , the isolation of its Brazilian populations may be due to the extensive mud habitat off the coast of Guyana and Surinam 80 .…”

Barriers to gene flow along the Brazilian coast: a synthesis and data analysis

“…Lastly, this region also coincides with the north end of the Rio Grande do Sul state, a region that include the world's longest beach, Cassino beach, with 220 kilometers of unconsolidated sandy substratum. Long stretches of sandy beaches have been considered putative BGF for hard bottom marine species (Nauer et al, 2019;Trovant et al, 2016). However, we could not test if Cassino beach can be considered a BGF because this region is located at the geographic extreme of our study area.…”

“…Several putative BGF have been proposed in the literature to explain genetic discontinuities along the Brazilian coast. Chiefly among them, we have: (a) the mouth of major rivers such as the Amazon, São Francisco, Paraguaçu, Jequitinhonha, Doce, and Paraíba do Sul (da Silva, Marceniuk, Sales, & Araripe, 2016;Machado et al, 2017); (b) the split of the South Equatorial Current (SEC) in two opposing boundary currents, giving rise to the southward Brazil Current and the northward North Brazil Current (Bezerra et al, 2018;Cortinhas et al, 2016); (c) the Cabo Frio coastal upwelling system (Cortinhas et al, 2016;Hurtado et al, 2016) and; (d) the Cassino beach, the longest stretch of sandy beach in the world located in southern Brazil between latitudes 29°S and 32°S (Nauer, Gurgel, Ayres-Ostrock, Plastino, & Oliveira, 2019;Trovant et al, 2016). In several phylogeographic studies, genetic discontinuities coincide with these coastal features, allowing researches to identify them as potential BGF (e.g.…”