Research carried out on a large and diverse family of fish in 46 African lakes is helping answer important questions about the formation of new species, or speciation. Although previous studies have shown that both environmental and species-specific factors influence the diversification of species, it was not known exactly how these variables interact in the process.
While some species carry on virtually unchanged from generation to generation for millions of years, other groups change and diversify into new species in timescales of only a few thousand years. Understanding why this is the case is one of the key issues which face evolutionary biologists, especially those concerned with biodiversity (or the lack of it).
The cichlid family of fish were chosen as the ideal subject for a study led by Eawag (Swiss Federal Institute of Aquatic Science and Technology) and the University of Bern, as they have developed immense richness and diversity from just a few original species. Cichlids are one of the largest vertebrate families, with more than 800 distinct species recorded in Lakes Malawi and Victoria alone.
Appearing in the latest edition of Nature
, the study details the way in which the likelihood of ‘adaptive radiation’ (another term for diversification) is dependent on a combination of extrinsic and intrinsic factors. In terms of environmental variables, diversification is more likely to arise where solar radiation is relatively high and when lakes are deeper.
In contrast to speciation in terrestrial animals – where the extent of habitat available significantly impacts on the probability of new species developing – lake size did not seem to have much of an influence on rates of diversification.
As far as species-specific traits were concerned the intensity of sexual selection – or choosing a mate – was found to be important, as reflected by the correlation between adaptive radiation and sexual dichromatism, where males and females display distinctly different colouration.
It was found that diversification could therefore be partly predicted by the extent of concordance between optimum extrinsic and intrinsic factors. The findings also hint at the possibility of being able to predict the knock-on effects for biodiversity of human activities which alter environmental conditions such as lake depth.