Temporal diversification of Central American cichlids - PubMed (original) (raw)
Temporal diversification of Central American cichlids
C Darrin Hulsey et al. BMC Evol Biol. 2010.
Abstract
Background: Cichlid fishes are classic examples of adaptive radiation because of their putative tendency to explosively diversify after invading novel environments. To examine whether ecological opportunity increased diversification (speciation minus extinction) early in a species-rich cichlid radiation, we determined if Heroine cichlids experienced a burst of diversification following their invasion of Central America.
Results: We first reconstructed the Heroine phylogeny and determined the basal node to use as the root of Central American Heroine diversification. We then examined the influence of incomplete taxon sampling on this group's diversification patterns. First, we added missing species randomly to the phylogeny and assessed deviations from a constant rate of lineage accumulation. Using a range of species numbers, we failed to recover significant deviations from a pure-birth process and found little support for an early burst of diversification. Then, we examined patterns of lineage accumulation as nodes were increasingly truncated. We assumed that as we removed more recently diverged lineages that sampling would become more complete thereby increasing the power to detect deviations from a pure-birth model. However, truncation of nodes provided even less support for an early burst of diversification.
Conclusions: Contrary to expectations, our analyses suggest Heroine cichlids did not undergo a burst of diversification when they invaded from South America. Throughout their history in Central America, Heroine cichlids appear to have diversified at a constant rate.
Figures
Figure 1
Chronogram of CA Heroine diversification. Likelihood ancestral areas are reconstructed at nodes as either Central American (white) or South American + Greater Antilles (black). The tips as well as many of the nodes in the phylogeny are only one color and therefore are reconstructed with virtually 100% probability as one state. The pie diagrams that exhibit both colors represent ambiguous likelihood reconstructions of the area at that node and are depicted at larger sizes. Posterior probabilities of nodes are shown on the branch preceding the nodes and are indicated with an * if there is 100% Bayesian support for the node. Other numbers behind the nodes represent the percentage that that node was recovered among topologies saved in the Bayesian analysis. Only support values above 50% are depicted. The node calibrated with divergence of 7.5 million years before present (mybp) around the Punta del Morro is shown with an X. A temporal scale running from 15.0 mybp to the recent is shown below the chronogram. An image of a typical Central American Heroine cichlid, Herichthys cyanoguttatus, is shown nested within the phylogeny.
Figure 2
The lineage-through-time (LTT) plot of CA Heroine diversification. The black dots represent actual numbers of Heroine lineages estimated at a given time frame from the reconstructed phylogeny. The grey lines form an ellipse of simulated pure-birth phylogenies of 90 species used to compare to the CA Heroines. The dotted lines represent the 95% confidence interval of the number of lineages expected from the simulated pure-birth phylogenies. The CA Heroine LTT lies within the 95% null distribution expected for a radiation diversifying via a pure-birth process.
Figure 3
Species number and γ statistic. We used null distributions to test if γ exceeded the value of -1.645 (the critical value for α = 0.05) with a range of "true" total numbers of CA Heroine species in the clade. We examined γ with 90 species, the number of taxa sampled in the phylogeny, to 120 species. Increasing the number of species resulted in lower and lower probability of there being a burst early in the phylogeny. We therefore could not reject the hypothesis that CA Heroine cichlids exhibited a pure-birth model of constant lineage diversification if there are 122 species as current taxonomy suggests.
Figure 4
Node truncation and stability of γ. Nodes were truncated from the present to the root of the CA Heroine phylogeny in order to assess the stability of γ using our empirically estimated 90 species phylogeny. Because lineage sampling should become more complete towards the root of the phylogeny, truncation of nodes closer to the present should reduce the influence of incomplete lineage sampling on inferences made from γ. Node removal and γ recalculation is depicted temporally based on the last removed node's time-calibration from the CA Heroine chronogram. Importantly, once nodes from the present to 3.5 mybp are removed, γ is clearly not significant in our empirical phylogeny. Therefore, analyses of only the deeper nodes in the CA Heroine phylogeny cannot reject a pattern of pure-birth lineage diversification.
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