Diversity and disparity through time in the adaptive radiation of Antarctic notothenioid fishes.

M Colombo,M Damerau,M Matschiner,R Hanel,W Salzburger

doi:10.1111/jeb.12570

Abstract

According to theory, adaptive radiation is triggered by ecological opportunity that can arise through the colonization of new habitats, the extinction of antagonists or the origin of key innovations. In the course of an adaptive radiation, diversification and morphological evolution are expected to slow down after an initial phase of rapid adaptation to vacant ecological niches, followed by speciation. Such ‘early bursts’ of diversification are thought to occur because niche space becomes increasingly filled over time. The diversification of Antarctic notothenioid fishes into over 120 species has become one of the prime examples of adaptive radiation in the marine realm and has likely been triggered by an evolutionary key innovation in the form of the emergence of antifreeze glycoproteins. Here, we test, using a novel time-calibrated phylogeny of 49 species and five traits that characterize notothenioid body size and shape as well as buoyancy adaptations and habitat preferences, whether the notothenioid adaptive radiation is compatible with an early burst scenario. Extensive Bayesian model comparison shows that phylogenetic age estimates are highly dependent on model choice and that models with unlinked gene trees are generally better supported and result in younger age estimates. We find strong evidence for elevated diversification rates in Antarctic notothenioids compared to outgroups, yet no sign of rate heterogeneity in the course of the radiation, except that the notothenioid family Artedidraconidae appears to show secondarily elevated diversification rates. We further observe an early burst in trophic morphology, suggesting that the notothenioid radiation proceeds in stages similar to other prominent examples of adaptive radiation.

Highlights

Adaptive radiation, that is the evolution of a multitude of species as a consequence of the adaptation to new ecological niches, is considered to be responsible for much of the diversity of life on Earth (Simpson, 1953; Schluter, 2000)
Maximum likelihood trees resulting from these two alignments differ strongly in their topologies (Fig. S3), and one of the most obvious differences concerns the placement of Gobionotothen, which is the first lineage to diverge among Antarctic notothenioids in the mitochondrial tree, but appears nested within this clade based on nuclear data
As it has often been hypothesized that the notothenioid radiation in the freezing waters of Antarctica is linked to the evolution of antifreeze glycoproteins (AFGPs) (Eastman, 1993), numerous previous studies have attempted to time-calibrate the origin of this radiation to test for possible correlations with cooling events recorded from geological data

Summary

Introduction

That is the evolution of a multitude of species as a consequence of the adaptation to new ecological niches, is considered to be responsible for much of the diversity of life on Earth (Simpson, 1953; Schluter, 2000).

Methods

Results

Discussion

Conclusion