Abstract
BackgroundDistichodus is a clade of tropical freshwater fishes currently comprising 25 named species distributed continent-wide throughout the Nilo-Sudan and most Sub-Saharan drainages. This study investigates the phylogenetic relationships, timing of diversification, and biogeographic history of the genus from a taxonomically comprehensive mutilocus dataset analyzed using Maximum Likelihood and Bayesian methods of phylogenetic inference, coalescence-based species-tree estimation, divergence time estimation, and inference of geographic range evolution.ResultsAnalyses of comparative DNA sequence data in a phylogenetic context reveal the existence of two major clades of similar species-level diversity and provide support for the monophyletic status of most sampled species. Biogeographic reconstruction on a time-scaled phylogeny suggest that the origins of the genus date back to the late Oligocene and that current geographic distributions are the result of a Congo Basin origin followed by dispersal and range expansion into adjacent ichthyofaunal provinces at different times during the evolutionary history of the group.ConclusionsWe present the most comprehensive phylogenetic, chronological, and biogeographic treatment yet conducted for the genus. The few instances of species paraphyly (D. teugelsi, D. fasciolatus) revealed by the resulting phylogenies are likely a consequence of post-divergence introgressive hybridization and/or incomplete lineage sorting due to recent speciation. Historical biogeographic findings are both in agreement and conflict with previous studies of other continent-wide African freshwater fish genera, suggesting a complex scenario for the assemblage of Africa’s continental ichthyofaunal communities.
Highlights
Distichodus is a clade of tropical freshwater fishes currently comprising 25 named species distributed continent-wide throughout the Nilo-Sudan and most Sub-Saharan drainages
No morphological synapomorphies have yet been identified for Distichodus, the genus can be distinguished from all other distichodontid genera by the combination of: an upper jaw only slightly mobile with respect to the cranium; an edentulous maxilla not tightly applied posteriorly to the premaxilla; two rows of gracile, long stalked, bicuspid teeth in each jaw; a highly mobile joint between the angulo-articular and dentary; a reduced dentary portion of the mandibular sensory canal; and a completely pored lateral line [13, 14]
The spatiotemporal framework for the diversification of African freshwater fish genus Distichodus presented provides a significant advance in our knowledge of the evolutionary history of this ecologically and socioeconomically important group of fishes
Summary
Distichodus is a clade of tropical freshwater fishes currently comprising 25 named species distributed continent-wide throughout the Nilo-Sudan and most Sub-Saharan drainages. Distichodus species are distributed across the continent, occurring throughout the freshwaters of most of sub-Saharan Africa and the river basins of the Nilo-Sudan, with representation in six of the nine ichthyofaunal provinces of continental Africa (Fig. 1). Besides playing an important role as a major constituent of the ecologically important herbivore/detrivore guilds in African freshwaters [8], Distichodus is of considerable socio-economic importance, as many species constitute a highly valued, but increasingly over-exploited, component of artisanal and commercial fisheries across the continent [9], and due to their high fecundity and herbivorous diet are increasingly being cultured in fish farms and lentic water bodies, in western Africa [4]. No morphological synapomorphies have yet been identified for Distichodus, the genus can be distinguished from all other distichodontid genera by the combination of: an upper jaw only slightly mobile with respect to the cranium; an edentulous maxilla not tightly applied posteriorly to the premaxilla; two rows (generally) of gracile, long stalked, bicuspid teeth in each jaw; a highly mobile joint between the angulo-articular and dentary (i.e., a Distichodus-type lower jaw [13]); a reduced dentary portion of the mandibular sensory canal; and a completely pored lateral line [13, 14]
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