International Society for History, Philosophy, and Social Studies of Biology

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MONDAY, JULY 6  /  19:00 - 20:30  /  Salle Marie Gérin-Lajoie
Reassessing the Status of Holobionts in Evolution

Shijian Yang (Xiamen University, China); Zhiping Cao (Xiamen University, China)

A holobiont is a symbiotic collective formed by a multicellular animal/plant organism and the microbial community living inside its body. How shall we properly characterize the operation of natural selection on holobionts? Holobionts vertically transmitting their endosymbionts, like aphid-Buchnera holobionts, have been widely accepted as units of natural selection. Now controversies lie on holobionts horizontally picking up their symibonts, like squid-Vibrio holobionts. Zilber-Rosenberg and Rosenberg (2008) and Dupré and O’Malley (2012) insisted that this kind of holobionts are cohesive as units of natural selection, while Godfrey-Smith (2012) claimed that they have no clear parental lineage, thus are not reproducers and not qualified as units of natural selection. This paper proposes that what has been missing in previous discussions is a careful examination on various levels of biological organization in the holobiont. On the cellular and physiological level, acquisition and replication of symbionts could be better viewed as a part of development of the holobiont, and on the organism level, the parental lineage can be tracked by following the lineage of the host organism. In this way a horizontally transmitted holobiont can still be viewed as a reproducer and hence a unit of natural selection.