Abstract
Phylogeographic studies have sought to explain the genetic imprints of historical climatic changes and geographic barriers within the Brazilian Atlantic Forest (AF) biota, and consequently two processes of diversification (refugia and barriers) have been proposed. Additionally, there is evidence that eustatic changes influenced the biogeographic history of the AF. Here we evaluate these contrasting diversification processes using two AF social wasp species – the mid-montane Synoeca cyanea and the lowland Synoeca aff. septentrionalis. We analyzed several sources of data including multilocus DNA sequence, climatic niche models and chromosomal features. We find support for idiosyncratic phylogeographic patterns between these wasps, involving different levels of population structure and genetic diversity, contrary suitable climatic conditions during the last glaciation, and contrasting historical movements along the AF. Our data indicate that neotectonics and refugia played distinct roles in shaping the genetic structure of these wasps. However, we argue that eustatic changes influenced the demographic expansion but not population structure in AF biota. Notably, these wasps exhibited chromosomal clines, involving chromosome number and decreasing of GC content, latitudinally oriented along the AF. Together, these results reinforce the need to consider individual organismal histories and indicate that barriers and refugia are significant factors in understanding AF evolution.
Highlights
Intense climatic swings during the late Quaternary had notable effects on the population dynamics, range and genetic diversity of many organisms[1]
Several phylogeographic studies are consistent with the CM model in showing higher genetic diversity, strong population structure and an absence of demographic expansion signals within populations in the north and central portion of the Atlantic Forest (AF), whereas populations in the southern portion show lower genetic diversity, signals of demographic expansion and weaker population structuring[14, 15, 17,18,19,20,21]
Our sequence data set contained a total of 3621–3622 base pairs composed of mtDNA protein-coding cytochrome oxidase subunit I (COI) (472 bp − 13.04% of data set), tRNA-Leu + cytochrome oxidase subunit II (COII) (47 + 582 bp − 17.37%), cytochrome b (CytB) (433 bp − 11.96%), mtDNA non-protein-coding 16 S ribosomal DNA (16 S) (508–509 bp − 14.03%), 12 S ribosomal DNA (12 S) (354 bp − 9.77%), and nDNA introns from CAD (361 bp − 9.97%) and EF1α (873 bp − 24.11%)
Summary
Intense climatic swings during the late Quaternary had notable effects on the population dynamics, range and genetic diversity of many organisms[1]. In contrast to refugia scenarios, genetic predictions regarding barrier hypotheses include older divergence times (due to vicariant events occurring deeper in the past), interruptions of gene flow that coincide with geographic barriers, and populations showing smooth demographic oscillations[27] Another alternative hypothesis to the phylogeographic patterns observed in AF species, termed the “Atlantis Forest hypothesis”, suggests that populations expanded, even during the LGM, in response to the expansion of the AF onto the Brazilian emerged continental shelf[26]. The two wasps possess similar behaviors (e.g., swarming, nesting and reproduction), generation times, vagility (i.e., due to similar size these wasps have similar capacity for relatively long-distance dispersal), and sensitivities to climate change[31], but remain ecologically distinct due to their putative thermal adaptations These social insects are promising candidates to test the diversification models (e.g., refugial, barriers and Atlantis hypotheses) proposed for AF biota
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