Abstract
BackgroundInterspecific divergence along a benthic to pelagic habitat axis is ubiquitous in freshwater fishes inhabiting lentic environments. In this study, we examined the influence of this habitat axis on the macroevolution of a diverse, lotic radiation using mtDNA and nDNA phylogenies for eastern North America’s most species-rich freshwater fish clade, the open posterior myodome (OPM) cyprinids. We used ancestral state reconstruction to identify the earliest benthic to pelagic transition in this group and generated fossil-calibrated estimates of when this shift occurred. This transition could have represented evolution into a novel adaptive zone, and therefore, we tested for a period of accelerated lineage accumulation after this historical habitat shift.ResultsAncestral state reconstructions inferred a similar and concordant region of our mtDNA and nDNA based gene trees as representing the shift from benthic to pelagic habitats in the OPM clade. Two independent tests conducted on each gene tree suggested an increased diversification rate after this inferred habitat transition. Furthermore, lineage through time analyses indicated rapid early cladogenesis in the clade arising after the benthic to pelagic shift.ConclusionsA burst of diversification followed the earliest benthic to pelagic transition during the radiation of OPM cyprinids in eastern North America. As such, the benthic/pelagic habitat axis has likely influenced the generation of biodiversity across disparate freshwater ecosystems.
Highlights
Interspecific divergence along a benthic to pelagic habitat axis is ubiquitous in freshwater fishes inhabiting lentic environments
We addressed the question: Was the first major evolutionary shift from benthic to pelagic habitats in eastern North America followed by a period of accelerated lineage diversification in open posterior myodome (OPM) cyprinids?
Phylogenetic reconstruction Phylogenetic analysis of the cytochrome b (Cytb) and recombination activating gene 1 exon 3 (Rag1) loci provided substantial resolution of relationships among members of the OPM radiation (Additional file 1). Both maximum clade credibility (MCC) gene trees and the MCC concatenated analysis included moderately to well-supported clades (>90% posterior probability) containing the benthic genera Campostoma, Exoglossum, Nocomis, and Rhinichthys as the earliest diverging OPM lineages in eastern North America (Additional file 1 and Figures 1 and 2)
Summary
Interspecific divergence along a benthic to pelagic habitat axis is ubiquitous in freshwater fishes inhabiting lentic environments. The generality of this pattern has largely been inferred from fishes that inhabit lentic, or lake-like, environments, such as sticklebacks, perch, arctic charr, and cichlids [1,2,3,4,5,6,7] Most of these studies have examined microevolutionary processes of interspecific divergence. Cyprinid fishes have radiated extensively within flowing water environments across eastern North America to exploit both benthic and pelagic habitats This group should provide an ideal study system to test consistently recovered as arising following the initial divergence of several depauperate and strictly benthic lineages that display inferior mouths and often posses maxillary barbels [9,10,11]. A much more exhaustively sampled phylogeny combined with data on benthic/pelagic habitat use should facilitate a more robust phylogenetic examination of whether this ecological axis has influenced diversification within OPM cyprinids
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