Lateral gene flow and arthropods

I’ve long been a fan of A Thousand Plateaus, the epic second volume of Capitalism and Schizophrenia by Gilles Deleuze and Félix Guttari, in good measure because it is a philosophical work that makes a number of statements directly relevant to evolutionary biology. In particular, Deleuze and Guttari spend some time criticizing the idea that the gene flow from parent to offspring (vertical gene flow) is far more important than any other form of gene flow. Instead, they argue that we should be paying more attention to lateral gene flow, the flow between organisms not involved in a parent-offspring relationship. 

While evidence of lateral gene transfer in micro-organisms is well accepted (think, for example, of plasmid transfer among bacteria by conjugation), there seems to remain some skepticism about the importance of this phenomenon in more complicated organisms. Despite this skepticism, Deleuze and Guttari’s suggestion that lateral gene flow is generally important was recently reinforced by a paper out of Yale describing the first evidence of de novo carotenoid synthesis in animals, effected by genes incorporated into the aphid genome from a probable fungal origin (Moran and Jarvik 2010). 

Fast forward to 2012 when two papers make this story a little longer, and a little more remarkable. First, the April issue of Biology Letters contained a paper by Altincicek et al. describing genes for carotenoid synthesis present in spider mites. These genes cluster phylogenetically close to the aphid carotenoid synthesis genes (and therefore are also likely to be of fungal origin). Second, an August 16th paper in Scientific Reports by Valmalette et al. suggests that the carotenoids in aphids may actually form a sort of photosynthetic system capable of reducing NAD+, and therefore fueling ATP synthesis. 

While the results are new, and therefore are sure to come with a number of unanswered questions, there is no denying that these papers are going to shake up our understanding of both ecology and evolution. First, the previously accepted wisdom that animals have to obtain carotenoids from their diet has been challenged in two disparate arthropod groups, which suggests that the power to synthesize these physiologically important pigments may actually be widespread. Second, we may have to abandon the notion that animals are not necessarily pure heterotrophs if they can perform some  photosynthesis-like process, which adds a whole new level of complexity to food webs. Finally, it may be time to begin accepting that lateral gene flow has relevance to metazoans, and at least sometimes in functionally important ways.