Abstract:

Background: Ecologists have long been interested by the geographical distribution patterns of biodiversity and the underlying mechanisms. The evolutionary speed hypothesis (ESH) is one of the mainstream explanations for the latitudinal biodiversity gradient pattern. This hypothesis suggests that the higher temperatures in low-latitude regions accelerate speciation rates and thus increase the species richness through three mechanisms. Specifically, (1) high temperatures shorten generation times, thereby increase the effective evolutionary time (the number of effective generations per unit of absolute time); (2) high temperatures increase mutation rates and thus genetic variations — the raw material for natural selection; (3) high temperatures accelerate the process of natural selection. Though this hypothesis is widely debated based on observed data from nature, rigorous tests are rare. 

Progress: The experimental evolution approach has been recently adopted to test specific mechanisms for ESH; and those studies were performed under well-controlled environmental temperatures. This article presents a comprehensive review of these studies about the consequences of temperature for mutation rates, selection and adaptive diversification. The generality of conclusions from those studies needs to be tested in more complex systems. 

Prospects: The experimental evolution approach will further deepen our understanding of the evolutionary speed hypothesis and the mechanisms underlying the geographical patterns of biodiversity, and give insights for species conservation and disease control under climate warming.

Key words: latitudinal biodiversity gradient, microbial experimental evolution, adaptive radiation, mutation rates, selection, metabolic theory of ecology