Abstract
Contemporary biological research has suggested that some host–microbiome multispecies systems (referred to as “holobionts”) can in certain circumstances evolve as unique biological individual, thus being a unit of selection in evolution. If this is so, then it is arguably the case that some biological adaptations have evolved at the level of the multispecies system, what we call hologenomic adaptations. However, no research has yet been devoted to investigating their nature, or how these adaptations can be distinguished from adaptations at the species-level (genomic adaptations). In this paper, we cover this gap by investigating the nature of hologenomic adaptations. By drawing on the case of the evolution of sanguivory diet in vampire bats, we argue that a trait constitutes a hologenomic adaptation when its evolution can only be explained if the holobiont is considered the biological individual that manifests this adaptation, while the bacterial taxa that bear the trait are only opportunistic beneficiaries of it. We then use the philosophical notions of emergence and inter-identity to explain the nature of this form of individuality and argue why it is special of holobionts. Overall, our paper illustrates how the use of philosophical concepts can illuminate scientific discussions, in the trend of what has recently been called metaphysics of biology.
Highlights
Adaptations are believed to be widespread in the biological world.1 The different types of beaks among bird species, the capacity of producing hemoglobin in vertebrates, or the ability to fly in some insects, are all considered adaptive traits
We argue for a form of recognizing and explaining the evolution of some biological adaptations that result from the interaction between a multicellular host and its microbiome, whose discovery relies on the consideration of the holobiont as a biological individual
Drawing on some recent research by Mendoza et al (2018), we show the existence of several hologenomic adaptations underlying the evolution of sanguivory, which suggests that the holobiont is the individual that manifests the adaptations and the reason why the adaptations evolved in the first place
Summary
Adaptations are believed to be widespread in the biological world. The different types of beaks among bird species, the capacity of producing hemoglobin in vertebrates, or the ability to fly in some insects, are all considered adaptive traits. We argue for a form of recognizing and explaining the evolution of some biological adaptations that result from the interaction between a multicellular host and its microbiome, whose discovery relies on the consideration of the holobiont as a biological individual. We use the notions of “emergence” and “inter-identity” as the driving notions of our account, i.e., we use these concepts to illuminate some features of the individuality of holobionts that would be masked if the theoretical resources that they provide were ignored. By placing emphasis in these theoretical resources, our paper shows how biological evolution may occasionally give rise to forms of individuality (manifestors of adaptation) that go beyond the traditional boundaries of organisms
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