Support for the evolutionary speed hypothesis from intraspecific population genetic data in the non-biting midgeChironomus riparius

Abstract

The evolutionary speed hypothesis (ESH) proposes a causal mechanism for the latitudinal diversity gradient. The central idea of the ESH is that warmer temperatures lead to shorter generation times and increased mutation rates. On an absolute time scale, both should lead to an acceleration of selection and drift. Based on the ESH, we developed predictions regarding the distribution of intraspecific genetic diversity: populations of ectothermic species with more generations per year owing to warmer ambient temperatures should be more differentiated from each other, accumulate more mutations and show evidence for increased mutation rates compared with populations in colder regions. We used the multivoltine insect species Chironomus riparius to test these predictions with cytochrome oxidase I (COI) sequence data and found that populations from warmer regions are indeed significantly more differentiated and have significantly more derived haplotypes than populations from colder regions. We also found a significant correlation of the annual mean temperature with the population mutation parameter u that serves as a proxy for the per generation mutation rate under certain assumptions. This pattern could be corroborated with two nuclear loci. Overall, our results support the ESH and indicate that the thermal regime experienced may be crucially driving the evolution of ectotherms and may thus ultimately govern their speciation rate.

Genomic processes underlying rapid adaptation of a natural Chironomus riparius population to unintendedly applied experimental selection pressures

“…The species spends most of its life‐cycle as larva in freshwater habitats like small streams, ditches and puddles (Pfenninger & Nowak, ). Chironomus riparius is characterised by a broad ecological tolerance (Armitage, ): in Europe it experiences a wide amplitude of water temperatures throughout its range and throughout the breeding season from late spring over the summer into autumn (Oppold et al, ). Chironomids, like most insects, are generally susceptible to temperature, the general pattern being an initial increase in growth and developmental rate with increasing temperature above a lower threshold temperature up to a maximum, followed by an increasingly negative effect on larval survival at higher temperatures (above ~ 27˚C) (Frouz, Ali, & Lobinske, ; Sankarperumal & Pandian, ; Stevens, ).…”

Chironomus riparius (Diptera) genome sequencing reveals the impact of minisatellite transposable elements on population divergence

“…This is probably due to a large effective population size and high gene flow in this species rather than short divergence time (Oppold et al . ). The population differentiation on the level of Cla‐elements , and TEs in general, was significantly stronger than anticipated.…”

“…These results fit very well to a recent study showing that the evolutionary ‘speed’ of the very same C. riparius populations depends on the temperature‐dependent number of generations per year and the possibly also increased mutation rate (Oppold et al . ). It is conceivable that the observed quantitative differences in population TE content are also temperature‐related.…”

“…Previous studies in C. riparius have revealed that genetic diversity and the population mutation parameter theta are correlated with ambient temperatures (Oppold et al . ). Considering new TE insertions as mutations in a classical sense, the rate of TE transposition might also correlate with temperature.…”

“…To start F 0 , we raised 360 larvae of each of the three parental pure populations, distributed over six replicates and under constant conditions at 20 °C (Oppold et al . ). Larvae were fed with a developmental stage‐adjusted amount of ground TetraMin (Tetra GmbH, Germany).…”