Abstract
The contrasting distribution of species diversity across the major lineages of cichlids makes them an ideal group for investigating macroevolutionary processes. In this study, we investigate whether different rates of diversification may explain the disparity in species richness across cichlid lineages globally. We present the most taxonomically robust time-calibrated hypothesis of cichlid evolutionary relationships to date. We then utilize this temporal framework to investigate whether both species-rich and depauperate lineages are associated with rapid shifts in diversification rates and if exceptional species richness can be explained by clade age alone. A single significant rapid rate shift increase is detected within the evolutionary history of the African subfamily Pseudocrenilabrinae, which includes the haplochromins of the East African Great Lakes. Several lineages from the subfamilies Pseudocrenilabrinae (Australotilapiini, Oreochromini) and Cichlinae (Heroini) exhibit exceptional species richness given their clade age, a net rate of diversification, and relative rates of extinction, indicating that clade age alone is not a sufficient explanation for their increased diversity. Our results indicate that the Neotropical Cichlinae includes lineages that have not experienced a significant rapid burst in diversification when compared to certain African lineages (rift lake). Neotropical cichlids have remained comparatively understudied with regard to macroevolutionary patterns relative to African lineages, and our results indicate that of Neotropical lineages, the tribe Heroini may have an elevated rate of diversification in contrast to other Neotropical cichlids. These findings provide insight into our understanding of the diversification patterns across taxonomically disparate lineages in this diverse clade of freshwater fishes and one of the most species-rich families of vertebrates.
Highlights
Recent studies that focused on groups long considered to be the product of rapid evolution have demonstrated that these lineages have undergone periods of increased diversification in their evolutionary history that may explain their exceptional present-day diversity (e.g. [1,2,3])
A monophyletic Cichlidae was recovered with strong statistical support and an estimated divergence of the family in the Mesozoic, during the Late Cretaceous (95% higher posterior densities (HPD) 96–67 Mean Age (Ma), Fig. 1)
Our results indicate that the common ancestor of each of the monophyletic cichlid subfamilies most likely arose during the Cenozoic (Fig. 1), which is consistent with the known fossil distributions of the oldest described cichlid taxa from these geographic lineages, extending to the Eocene approximately 40 to 49 Ma (e.g. [28,32,33])
Summary
Recent studies that focused on groups long considered to be the product of rapid evolution (e.g., skinks, perch-like fishes, passerine birds) have demonstrated that these lineages have undergone periods of increased diversification in their evolutionary history that may explain their exceptional present-day diversity (e.g. [1,2,3]). Cichlids have often been regarded as a lineage that exhibits elevated diversification rates in comparison to other freshwater-fish lineages Hybridization has possibly acted as an aid to diversification in these fishes [11,12] Groups such as the haplochromin cichlids of Lakes Victoria and Malawi, known for their colorful species flocks [13,14], are considered to be the product of adaptive radiations. They have been thought to have evolved with an increased diversification rate relative to other cichlid lineages [6]. A comparative study of cichlid diversification across all major lineages is required to tease apart the patterns of diversification that have shaped present day cichlid diversity
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