Geography and seasonality of an environmentally-acquired symbiosis: is the bug-Burkholderia relationship spatially or temporally structured?

Many members of animal-associated microbial communities are acquired from their host’s environment. Acquisition of free-living symbionts presents a unique set of potential challenges, including failure to find the symbiont or acquisition of a sub-optimal strain. The leaf footed bug Leptoglossus zonatus (Coreidae) is a promising model system for investigating the costs (and benefits) of environmental symbiont acquisition because it acquires its Burkholderia symbiont from the environment (presumably local soil). Despite large contributions to insect fitness, nymphs must re-acquire Burkholderia every generation.

To understand how the local reservoir of symbiont strains may shape the insect’s biology, we characterized turnover in insect- and soil-associated Burkholderia strains across a range of spatial scales, comparing samples from a single tree, from trees within a plot, from plots within the same city, and from different cities in Arizona and California. We also repeatedly sampled insects within a single pomegranate orchard over two years. We found that with increasing distance between samples, fewer Burkholderia strains were shared. The location where a bug develops therefore appears to have a large influence on the symbiont strain it acquires, consistent with a process of passive spatial turnover in hosted symbiont strains. Since strains vary in quality, with some promoting higher host fitness than others, we might expect this to represent a cost of the environmental mode of symbiont acquisition.