Convergent characteristics of cryptic species along environmental gradients

• Applicant: Dr. Jonas Jourdan
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448273043

The emergence of genetic methods has led to the discovery of an increasing number of species that previously could not be distinguished from one another on the basis of morphological characteristics. The family Gammaridae (Crustacea, Amphipoda) is a prime example of a group that has recently seen a high degree of genetic diversity uncovered. However, despite their frequency, cryptic species have so far rarely been considered in ecological and evolutionary work. Thus, especially the important question of ecological differentiation of closely related cryptic species – previously considered as a single morphospecies – is rarely addressed, although this is of key importance for evolutionary ecology and conservation biology. Our research project picks up this question and will examine the apparent paradoxon that we have found phenotypic differentiation even within a genetic line in a recent study. The widespread occurrence of cryptic species complex Gammarus roeselii made it an ideal model system to investigate phenotypic responses across repeated environmental gradients raising the question of whether phenotypic divergence (of a cryptic lineage) is present and even stronger within than between genetic lineages. This allows us to integrate quantitative analyses of phenotypic variation within a phylogeographic framework. In three work packages, we will investigate the following hypotheses: 1) Phenotypic differentiation occurs within genetic lineages along environmental gradients, where differences are more pronounced within than between genetic lineages and convergent changes occur along similar environmental conditions. 2) Genetic lineages fulfil different ecological roles in the riverine food web. Again, we expect to find differences not only between, but also within lineages. These differences can partly be explained by the observed phenotypic differentiation and are thus a prime example of eco-evolutionary dynamics. 3) One of the (at least) 13 cryptic lineages described shows a massive range expansion during the last 150 years, displacing other species in Central Europe. While native species disappear, e.g. from waters with high pesticide loads, we can find this genetic lineage in high densities in such habitats. We assume that the success of this lineage is due to a high degree of adaptive plasticity enabling them to adapt respond to anthropogenic stressors. We will exemplarily investigate the adaptability of different lineages using pesticide- and thermal tolerance tests. Our research project will identify mechanisms leading to phenotypic variation or morphological convergence and will provide important insights into the future management of cryptic species and show at which taxonomic level we need to consider biodiversity in terms of indicator and conservation status.

• DFG Programme: Research Grants