Evolution and development towards a synthesis of macro and microevolution with ecology

hans zauner and ralf j. sommer

Until our population-based evolutionary theory can be reconciled with our homology-based evolutionary theory, we live without a true synthesis of evolutionary thought.

Amundson 2005: 249-250

Evolutionary theory is the philosophical backbone of biology. Interestingly, contemporary research in evolutionary biology involves several parallel lines of investigations that build on different philosophies and aim for different kinds of explanations and mechanisms. At its extreme, at least three independent research activities are actively promoted in evolutionary biology: neo-Darwinism with a population genetics research agenda analyses the evolution of populations by natural selection (Amundson 2005). Molecular phylogeny tries to reconstruct historical patterns and the phylogenetic relationship of organisms using cladistic approaches. And finally, comparative morphology, and more recent 'evo-devo' research, build on the evolution of ontogeny and try to show how modifications of development (ontogeny) result in evolutionary novelties (Valentine 2004, Kirschner and Gerhard 2005).

All of these agenda are actively propagated and they all consider themselves to follow the Darwinian logic. Surprisingly, however, there is hardly any cross-talk between these disciplines and even worse, these research fields ignore each other to a certain extent. Several authors have emphasised the different research strategies and philosophies in contemporary evolutionary biology, i.e. neo-Darwinism and

Evolving Pathways: Key Themes in Evolutionary Developmental Biology, ed. Alessandro Minelli and Giuseppe Fusco. Published by Cambridge University Press. # Cambridge University Press 2008.

evolutionary developmental biology (Wilkins 2002, Amundson 2005). Despite these obvious problems and lack of interactions, we are in need of a true synthesis of evolutionary thought. And such a synthesis must include both population genetic and developmental thinking. In this context, homology could be an important concept. Homology has been a central aspect of comparative morphology and evolutionary developmental biology, but was long considered to be of limited importance in population genetics (Mayr 1966).

Here, we will summarise our attempts to bring these research fields together. Building on and believing in the 'case study' philosophy of experimental biology, we summarise our research on nematode macro- and micro-evolution of developmental processes, population genetics and nematode ecology. We hope that such studies will help - in the long run - to bridge barriers and to bring together different research strategies from evolutionary developmental biology over population genetics all the way to ecology.

the system: vulva formation in the nematode caenorhabditis elegans

The nematode Caenorhabditis elegans was introduced as a model system in genetics and developmental biology more than 30 years ago (Brenner 1974). Several features made this organism attractive to developmental biologists. For example, the adult organism consists of roughly 1000 somatic cells that develop through a fixed cell lineage, which is identical among the individuals of the species. Building on the complete description of post-embryonic development, genetic and molecular studies have helped to identify the molecular principles of ontogenetic processes in C. elegans (Sulston and Horvitz 1977). The formation of several organs and tissues during post-embryogenesis has been studied in great depth, providing a detailed understanding of developmental mechanisms.

One well-studied developmental process is the formation of the vulva, the egg-laying structure of nematode females and hermaphrodites (Sternberg 2005). The vulva is formed during the third larval stage by a subset of ventral epidermal precursor cells. Like all other nematodes studied to date, C. elegans have a total of 12 ventral epidermal cells, called P1.p to P12.p from anterior to posterior (Figure 9.1). Three of these cells, P(5-7).p are selected in wild-type animals to form vulval tissue. These cells adopt one of two alternative cell fates. P6.p generates eight progeny, which form the central part of the vulva, and this cell has been designated as the cell with the 1° (primary) fate (see below). P(5,7). p generate seven progeny each and form the anterior and posterior part

P1.p P2.p P3.p P4.p P5.p P6.p P7.p P8.p P9.pP10.pP11.pP12.pa

P1.p P2.p P3.p P4.p P5.p P6.p P7.p P8.p P9.pP10.pP11.pP12.pa

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