23 December, 2012
We would like to invite you to attend and contribute to the ESEB-sponsored symposium “Evolutionary consequences of an early germ-soma segregation”, to take place at the 14th Congress of the European Society for Evolutionary Biology (ESEB), in Lisbon, Portugal, 19 – 24 August 2013.
Norman Arnheim (University of Southern California, USA) $B!H(BGermline selection and the paternal-age effect in humans.$B!I(B
Andrew Bourke (University of East Anglia, UK) $B!H(BEarly germline segregation and social group transformation$B!I(B
Duur K. Aanen (Wageningen University)
Rick Michod (University of Arizona)
It has been 25 years since Leo Buss first proposed that an early segregation of a germ line from the rest of the body is an adaptation to limit the scope for selfish cell lineages. A number of recent discoveries make it timely to reevaluate this hypothesis. This symposium explores the evolutionary stability of multicellularity in organisms with and without an early germ-line sequestration, to discuss the relative importance of this characteristic for conflict resolution, in multicellular growth and, more generally, in other major transitions such as the transition to eusociality.
Most animals segregate, early in development, a small number of germ cells that are destined to give rise to reproductive cells, from somatic cells. Only a few cell divisions separate the germ cell from the gamete stage and germ-cell division is strictly regulated. It has been nearly 25 years since Leo Buss proposed that these individual-level adaptations reduce the scope for within-individual selection, at which level selection often will be deleterious for individual fitness. The early germ-soma segregation thus prevents conflict between selection at the level of the individual and selection at the level of the cell. There is much empirical support for this hypothesis. However, it has been argued that the regular single-cell bottleneck observed in most life cycles in combination with a low mutation rate is sufficient to limit intra-individual genetic variation required for among-cell selection. Furthermore, recently some cases have been identified that show that the germ-soma segregation does not provide perfect protection against lower-level selection. First, contagious cancers, transmitted horizontally from one individual to another, circumvent the germ line. Second, recently a mechanism has been discovered by which inherited diseases, caused by de novo mutations in the father$B!G(Bs germ line, are positively selected. Normally, male germ cells divide asymmetrically, with one daughter cell becoming the new germ cell, and the other giving rise to multiple gametes. However, some mutations increase the frequency of symmetrical division of the germ cells, thus increasing the number of germ cells with this mutation. This explains an observation, already made in the early 1900$B!G(Bs, that the incidence of some inherited diseases increases with the age of the father. On the occasion of these new discoveries, this symposium will discuss the importance of germ-soma differentiation for resolution of the potential conflict between the levels of selection in a multicellular individual. This symposium will bring together students working on the evolution of multicellularity and conflict resolution, both in organisms with and organisms without an early germ-soma differentiation, such as fungi. It will discuss the importance of an early germ-soma differentiation for conflict resolution relative to other stabilising factors, especially high among-cell genetic relatedness, seen in most multicellular organisms.