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Abstract
BackgroundLife history traits like developmental time, age and size at maturity are directly related to fitness in all organisms and play a major role in adaptive evolution and speciation processes. Comparative genomic or transcriptomic approaches to identify positively selected genes involved in species divergence can help to generate hypotheses on the driving forces behind speciation. Here we use a bottom-up approach to investigate this hypothesis by comparative analysis of orthologous transcripts of four closely related European Radix species.ResultsSnails of the genus Radix occupy species specific distribution ranges with distinct climatic niches, indicating a potential for natural selection driven speciation based on ecological niche differentiation. We then inferred phylogenetic relationships among the four Radix species based on whole mt-genomes plus 23 nuclear loci. Three different tests to infer selection and changes in amino acid properties yielded a total of 134 genes with signatures of positive selection. The majority of these genes belonged to the functional gene ontology categories “reproduction” and “genitalia” with an overrepresentation of the functions “development” and “growth rate”.ConclusionsWe show here that Radix species divergence may be primarily enforced by selection on life history traits such as (larval-) development and growth rate. We thus hypothesise that life history differences may confer advantages under the according climate regimes, e.g., species occupying warmer and dryer habitats might have a fitness advantage with fast developing susceptible life stages, which are more tolerant to habitat desiccation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0434-x) contains supplementary material, which is available to authorized users.
Highlights
Life history traits like developmental time, age and size at maturity are directly related to fitness in all organisms and play a major role in adaptive evolution and speciation processes
Mitochondrial genome nucleotide divergence ranges from 0.04 % between the two sister species R. balthica and MOTU3 and 0.24 % between MOTU3 and R. auricularia
We hypothesized that the distribution ranges differ in climatic niche properties, leading to species divergences based on selection on species specific physiological traits
Summary
Life history traits like developmental time, age and size at maturity are directly related to fitness in all organisms and play a major role in adaptive evolution and speciation processes. Various mechanisms can lead to the evolution of reproductive isolation between populations and to speciation [2, 3]. One of these mechanisms is ecology-driven diversifying selection imposed by the demands of adapting to niche-specific biotic and abiotic factors [3,4,5]. One major target of these adaptive processes is the evolution of life history traits such as lifespan, growth, development and most local environmental variables are affected by climate, which is especially the case in fresh water systems where climate is a major driver of abiotic and biotic processes [13]. Variation in air temperature leads to changes in water temperature but might lead to alterations in additional water body conditions such as reduced oxygen availability, increased salinity and the desiccation of the water body
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