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Research

Introduction

Life on Earth resulted in an astonishing diversity of form and phenotype. But our understanding on how this diversity is generated as a result of historical processes is still limited. We use a highly interdisciplinary approach that integrates development, ecology and population genetics to unravel the mechanistic changes that give rise to evolutionary alterations and novelty (Sommer, 2009). For this to be achieved well-selected model organisms with a sophisticated analytical toolkit for functional investigations have to be developed. We have established the free-living nematode Pristionchus pacificus as a model system in evolutionary biology. P. pacificus combines in a unique manner, laboratory studies building on genetic, genomic and transgenic tools with field work in ecology and population genetics.

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Evo-devo: Developmental Systems Drift

One of our core activities is in evolutionary developmental biology (evo-devo). Investigating the evolution of developmental processes, we aim for a mechanistic understanding of phenotypic change. Our genetic, molecular and biochemical studies on vulva development in P. pacificus show that Caenorhabditis elegans and P. pacificus form their egg-laying structure from the same precursor cells, but use distinct molecular mechanisms (for review see Sommer, 2008). Most strikingly, an unusual Wnt pathway regulates vulva development in P. pacificus and represents an example of developmental systems drift (Wang & Sommer, 2011). This example indicates that evo-devo studies have to be integrated into evolutionary theory to better understand not only their proximate but also their ultimate causation.

Integrative Evolutionary Biology

Towards this end, our interdisciplinary research program tries to integrate evo-devo with population genetics and ecology. The interface with ecology can reveal how the environment influences development and how developmental processes evolve under changing environmental conditions. We have shown that P. pacificus lives on scarab beetles in a necromenic association. Worms rest on the living beetle in the dauer stage and only start feeding on microbes after the beetles´ death (Herrmann et al., 2007).

Studies at the interface of evo-devo with population genetics can indicate the contribution of natural variation to the evolution of development. More than 500 P. pacificus strains from around the world have been isolated, providing ample material for natural variation. In 2010 we have established a field station on La Réunion in the Indian Ocean, an island that harbors the complete worldwide genetic diversity of P. pacificus (Herrmann et al., 2010; Morgan et al., 2012). We use the La Réunion microcosm for the population level analysis of ecological and developmental traits by performing genome wide association studies and QTL analysis. In this tripartite system – evo-devo, ecology and island population genetics – we link micro– and macroevolutionary investigations to provide a comprehensive and integrative view of evolution (Sommer, 2009).

Developmental Plasticity

Developmental (phenotypic) plasticity describes the property of a genotype to respond to environmental variation by producing distinct phenotypes. A huge body of theoretical studies argues that plasticity is a facilitator of evolutionary diversity and novelty, and indeed, case studies in insects, nematodes and vertebrates provide experimental and phylogenetic support for this hypothesis using comparative analyses and cladistic methodology. However, little is known about the genetic basis of developmental plasticity. Our work aims at elucidating the genetic control of plasticity (Ragsdale et al, 2013; Sommer et al., 2017). Simultaneously, we study how abiotic and biotic factors interact with the genetic network to control plastic traits. Most recently, we also started to investigate the role of epigenetics in mouth-form plasticity (Serobyan et al., 2016). Our work on developmental plasticity in Pristionchus is by nature, highly interdisciplinary and involves genetic and epigenetic approaches similar to ecological, micro-evolutionary and macro-evolutionary considerations.

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