Abstract
Understanding the processes that shaped the strikingly irregular distribution of species richness across the Tree of Life is a major research agenda. Changes in ecology may go some way to explain the often strongly asymmetrical fates of sister clades, and we test this in the caridean shrimps. First appearing in the Lower Jurassic, there are now ~3500 species worldwide. Carideans experienced several independent transitions to freshwater from marine habitats, while many of the marine species have also evolved a symbiotic lifestyle. Here we use diversification rate analyses to test whether these ecological traits promote or inhibit diversity within a phylogenetic framework. We demonstrate that speciation rates are more than twice as high in freshwater clades, whilst symbiotic ecologies are associated with lower speciation rates. These lower rates amongst symbiotic species are of concern given that symbioses often occur in some of the most diverse, delicately balanced and threatened marine ecosystems.
Highlights
Understanding the processes that shaped the strikingly irregular distribution of species richness across the Tree of Life is a major research agenda
We test the hypothesis that two key ecological traits for Caridea—namely broad habitat type and symbioses—contributed to increased rates of diversification in the geological past via an adaptive radiation into new ecological space
We find that transitions into freshwater habitats resulted in net diversification rates more than double those found in marine clades
Summary
Understanding the processes that shaped the strikingly irregular distribution of species richness across the Tree of Life is a major research agenda. We test the hypothesis that two key ecological traits for Caridea—namely broad habitat type (marine/freshwater) and symbioses—contributed to increased rates of diversification in the geological past via an adaptive radiation into new ecological space. We posit that this subsequently shaped the global patterns of caridean species diversity that we see today. The evolution of symbioses is associated with a small decrease in net diversification rates The latter finding has implications for vulnerability assessments of symbiotic marine carideans, given that they are predominantly associated with coral reefs, which are amongst the most threatened ecosystems on Earth
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