Abstract
One of the current problems in microbiology concerns the understanding of fitness in host-symbiont systems. A great deal of research and conceptual work has analysed how the host benefits from such associations; however, very little of this work has attempted to take the microbial perspective. Nevertheless, some scientists have argued that we should conduct more comparative studies of both microorganisms that interact with a host and their free-living counterparts in order to determine whether or not symbiosis is beneficial for these microorganisms. In this paper, by means of analysing heritable symbiosis as a case study, I intend to provide a different perspective on this subject. Mainly, I argue that asking how the fitness of a given microorganism was changed during the evolution of heritable symbiosis may be theoretically unjustified at both the early and late stages of this process. The reason for this, I argue, is that, during the evolution of heritable symbiosis, the fitness of a microorganism becomes incommensurable with that of its free-living counterparts because their contexts become radically different; therefore, comparing their fitness makes little sense. My analysis is driven by the use of the ecological concept of fitness; accordingly, my conclusions are bound to this specific interpretation of fitness.
Highlights
Host-microbe interactions have been studied mainly from the perspective of the host; many studies have attempted to determine how these interactions influence the fitness of hostsInnovation Programme, grant agreement #637647
It has been noted recently that we don’t know how these kinds of interactions influence the fitness of microbes; the need to compare the fitness of microbes that interact with a host with their free-living counterparts, in order to determine whether participation in these interactions offers any fitness benefits for the former (Garcia and Gerardo 2014; Mushegian and Ebert 2016; Lowe et al 2016)
I argue that the ecological fitness of heritable symbionts is incommensurable with that of their freeliving counterparts because the necessary conditions for comparison have not been fulfilled, and we are not in a position to argue that the ecological fitness of the microorganisms in question is enhanced or diminished during the evolution of heritable symbiosis
Summary
Host-microbe interactions have been studied mainly from the perspective of the host; many studies have attempted to determine how these interactions influence the fitness of hosts. I argue that sometimes it may be impossible to understand how host-microbe interactions shape the fitness of microbes, because it has become incommensurable with that of their free-living counterparts (Stencel 2016). Scientists, unsure of whether becoming a heritable symbiont enhances or diminishes the fitness of microbes, use metaphors such as ‘slavery’ (Maynard Smith and Szathmáry 1995, 141; Dyall et al 2004). I argue that the ecological fitness of heritable symbionts (at both the early and late stages of co-evolution with their hosts) is incommensurable with that of their freeliving counterparts because the necessary conditions for comparison have not been fulfilled, and we are not in a position to argue that the ecological fitness of the microorganisms in question is enhanced or diminished during the evolution of heritable symbiosis. I conclude the paper with some general remarks aimed at linking my analysis to the idea of niche construction (Odling-Smee and Laland 2011; Laland et al 2016)
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