Chimerism and altruism

Abstract

Chimerism spans the tree of life, from mammals and corals to plants and fungi. In such organisms, individuals contain within them cells and genomes from another once distinct member of the population. This chimeric genetic composition may subsequently alter patterns of relatedness not only within those individuals, but also between them. Consequently, we may expect unique patterns of social behaviour in such species. To explore the social evolutionary consequences of chimerism, here we develop a kin-selection model of a structured population. First, we show how somatic and germline chimerism influence patterns of relatedness and thus the potential for altruism. We find that the partitioning of genetic variation within individuals plays an important role in modulating social behaviour between individuals. We then explore how chimerism may generate within-organism differences in the valuation of social partners and thus foment conflicts between tissues and organs. Finally, we show how differences in the development of male and female germlines in chimeras provides a novel source of relatedness asymmetry between maternal-origin and paternal-origin genes. Overall, we find that chimerism introduces additional opportunities for internal conflicts over the development of behavioural phenotypes, most of which have been unexplored by empiricists.