Rapid radiation in a diverse marine environment

Abstract

Rapid diversification can often be observed when new species invade habitats that offer ecological opportunities for adaptive radiation. Most of the Earth’s diversity was created in diverse environments with limited ecological opportunities. This is a striking example of rapid radiation in a marine habitat that is rich in diversity. The hamlets, which are a group of reef fishes originating from the Caribbean, have radiated into an astonishing diversity of color patterns, but show low divergence across all other ecological axes. The hamlet’s lineage is 26 Mys in age, but the radiation occurred in the last 10,000 generations in an explosion of diversification that ranks amongst fishes’ fastest. The hamlets are a compelling context to reveal the genomic elements involved in phenotypic diversification. They also offer an excellent opportunity for building a comparative framework that will allow us to understand the drivers and consequences of adaptive radiation. An analysis of 170 genomes revealed that color pattern diversity is caused by different combinations of alleles at just a few large-effect loci. This modular genomic architecture of diversity has been previously documented in HeliconiusThree other tropical radiations occurred in extremely diverse and complex environments. The hamlet radiation occurred in a context with a large effective population size, which is typical for marine populations. This allows for the accumulation and retention of genetic variation through mutation, which are both important in this radiation.