Flowing into the unknown: inferred paleodrainages for studying the ichthyofauna of Brazilian coastal rivers

Abstract

The eastern coastal basins of Brazil are a series of small and isolated rivers that drain directly into the Atlantic Ocean. During the Pleistocene, sea-level retreat caused by glaciations exposed the continental shelf, resulting in enlarged paleodrainages that connected rivers that are isolated today. Using Geographic Information System (GIS), we infer the distribution of these paleodrainages, and their properties for the east Brazilian coast. Specifically, using elevation/bathymetric data for the largest sea-level retreats during the Pleistocene, the paleodrainages, their area and the number of contemporary basins connected by each palaeodrainage, was inferred. For the 145 inferred paleodrainages, total paleodrainage area is strongly correlated with the contemporary area encompassed by each paleodrainage, as well as with the number of contemporary basins encompassed by a paleodrainage. Differences in the continental shelf exposure along the coast affected the degree of past connectivity among contemporary rivers. With our results freely available, we discuss how paleodrainages have tremendous utility in biological studies, especially in regions with limited geologic data. With respect to the diverse ichthyofauna of the Brazilian coast, and its high endemism, we highlight how the inferred paleodrainages provide a backdrop to test hypotheses about the effect of past riverine connectivity on diversity patterns.

Common barriers, but temporal dissonance: Genomic tests suggest ecological and paleo‐landscape sieves structure a coastal riverine fish community

“…When we consider shared geographic divisions among taxa, the question becomes what makes these regions standout in terms of their effectiveness as barriers? Two of the three geographic divisions are associated with areas of prominent mountainous relief of granite‐gneiss crystalline basement, which agrees with areas associated with paleodrainages boundaries (i.e., the elevated boundary between two areas that drain to different river systems; Thomaz & Knowles, ; Weitzman et al, ). Specifically, the northern division corresponds with the Cabo Frio Magmatic Lineament, and the southern division with the Serra do Tabuleiro (Villwock, Lessa, Suguiu, Angulo, & Dillenburg, ; Zalán & Oliveira, ).…”

“…These geologic features and paleodrainages have notably been invoked as barriers contributing to both speciation and faunal turnover in distributional patterns (Abell et al, 2008;Bizerril, 1994;Dias et al, 2014;Pereira et al, 2013). We note that other paleodrainages have been inferred along the Brazilian coast (Thomaz & Knowles, 2018), but they do not appear to be contributing equally to the regional genetic differentiation across the studied taxa. Additional geological evidence could help explain why some, but not all, paleodrainages are associated with gene divergence.…”

“…However, one possible explanation may be that the genetic divergence associated with the two specific paleodrainage boundaries detected across the four taxa studied here reflect their stability, especially given that they are associated with prominent geological features that might make them more likely to withstand strong erosion caused by periods of sea level change. On the other hand, the lack of evidence for a role of geologic uplift associated with the central division ( Figure 2) is puzzling, but we note that it is positioned in an active tectonic area (i.e., Ponta Grossa Arch; Ribeiro, 2006) with rivers draining to a common outlet based on paleodrainages reconstructions for the LGM (Thomaz & Knowles, 2018). Although this central division has not been identified for structuring communities, high genetic differentiation has been inferred in analyses of population variation in other studies (Thomaz, Malabarba, Bonatto, & Knowles, 2015;Tschá et al, 2017).…”

Ancient and contingent body shape diversification in a hyperdiverse continental fish radiation

“…South America and Africa have both experienced multiple uplift and stream capture events (Ribeiro ; Swartz et al. ; Thomaz and Knowles ), likely yielding a rich history of vicariant evolution. Yet, the frequency of drainage isolation on each continent remains unknown and no study has tested for differences in speciation rates between African and South American characiforms.…”

“…Large river systems, like the Amazon and Congo Basins, are particularly susceptible to allopatric speciation because of geologic events that increase drainage subdivision and stream capture events (Roberts 1975;Lundberg et al 1998;Briggs 2005;Albert et al 2006;Albert et al 2011). South America and Africa have both experienced multiple uplift and stream capture events (Ribeiro 2006;Swartz et al 2009;Thomaz and Knowles 2018), likely yielding a rich history of vicariant evolution. Yet, the frequency of drainage isolation on each continent remains unknown and no study has tested for differences in speciation rates between African and South American characiforms.…”