Abstract
Many species interactions are dependent on environmental context, yet the benefits of obligate, mutualistic microbial symbioses to their hosts are typically assumed to be universal across environments. We directly tested this assumption, focusing on the symbiosis between the sap‐feeding insect Megacopta cribraria and its primary bacterial symbiont Candidatus Ishikawaella capsulata. We assessed host development time, survival, and body size in the presence and absence of the symbiont on two alternative host plants and in the insects' new invasive range. We found that association with the symbiont was critical for host survival to adulthood when reared on either host plant, with few individuals surviving in the absence of symbiosis. Developmental differences between hosts with and without microbial symbionts, however, were mediated by the host plants on which the insects were reared. Our results support the hypothesis that benefits associated with this host–microbe interaction are environmentally contingent, though given that few individuals survive to adulthood without their symbionts, this may have minimal impact on ecological dynamics and current evolutionary trajectories of these partners.OPEN RESEARCH BADGES This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.kg4bc56
Highlights
Environmental factors have long been shown to mediate the out‐ come of biotic interactions within and between species (Agrawal, 2001)
We find that developmental benefits of symbiosis for this host are contingent on the environmental context of host plant, though survival of individuals to adulthood without symbionts is rare, suggesting that the symbiosis is obligate in the invasive range and regardless of the nutrients provi‐ sioned by alternative hosts plants
In both field and laboratory experiments, we found that develop‐ ment time, survival, and body size were significantly impacted by the status of the symbiosis, by the host plant, and, interestingly, by the interaction between these factors
Summary
Environmental factors have long been shown to mediate the out‐ come of biotic interactions within and between species (Agrawal, 2001). By removal or heat treatment of symbiont capsules, Fukatsu and Hosokawa (2002) demonstrated that preventing estab‐ lishment of a symbiont population within Megacopta punctatissima, when feeding on soybean in controlled laboratory conditions, can delay development, decrease body weight, and lessen adult color‐ ation, suggesting an essential need for symbiosis for this Megacopta species. This method of disrupting the symbiosis requires no antibiotics, which can have off‐target effects that can influence host phenotypes, in part by altering other components of the host microbiome. We find that developmental benefits of symbiosis for this host are contingent on the environmental context of host plant, though survival of individuals to adulthood without symbionts is rare, suggesting that the symbiosis is obligate in the invasive range and regardless of the nutrients provi‐ sioned by alternative hosts plants
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