Hadfield, J. D. | Search bioRxiv

bioRxiv2018

The Evolution of Phenotypic Plasticity when Environments Fluctuate in Time and Space

Most studies have explored the evolution of plasticity when the environment, and there-fore the optimal trait, varies in time or space. When the environment varies in time and space we show that genetic adaptation to temporal fluctuations depends on the between-generation autocorrelation in the environment in exactly the same way that genetic adaptation to spatial fluctuations depends on the probability of philopatry. This is because both measure the correlation in parent-offspring environments and therefore the effectiveness of a genetic response to selection. If the capacity to genetically respond to selection is stronger in one dimension (e.g. space) then plasticity mainly evolves in response to fluctuations in the other dimension (e.g. time). If the relationship between the environments of development and selection are the same in time and space then the evolved plastic response to temporal fluctuations is useful in a spatial context and genetic differentiation in space is reduced. However, if the relationship between the environments of development and selection are different then the optimal level of plasticity is different in the two dimensions. In this case the plastic response that evolves to cope with temporal fluctuations may actually be maladaptive in space. This can result in the evolution of hyperplasticity or negative plasticity, the effects of which are mitigated by spatial genetic differentiation. However, genetic differentiation acts in opposition to plasticity resulting in counter-gradient variation. These results highlight the difficulty of making space-for-time substitutions in empirical work but identify the key parameters which need to be measured in order to test whether space-for-time substitutions are likely to be valid.

evolutionary biology↗

bioRxiv2018

Changes in temperature alter susceptibility to a virus following a host shift

Host shifts - where a pathogen jumps between different host species - are an important source of emerging infectious disease. With ongoing climate change there is an increasing need to understand the effect changes in temperature may have on emerging infectious disease. We investigated whether species susceptibilities change with temperature and ask if susceptibility is greatest at different temperatures in different species. We infected 45 species of Drosophilidae with an RNA virus and measured how viral load changes with temperature. We found the host phylogeny explained a large proportion of the variation in viral load at each temperature, with strong phylogenetic correlations between viral loads across temperature. The variance in viral load increased with temperature, whilst the mean viral load did not, such that as temperature increased the most susceptible species become more susceptible, and the least susceptible less so. We found no significant relationship between a species susceptibility across temperatures and proxies for thermal optima; critical thermal maximum and minimum or basal metabolic rate. These results suggest that whilst the rank order of species susceptibilities can remain the same with changes in temperature, the likelihood of host shifts into a given species may increase or decrease.\n\nAuthor SummaryEmerging infectious diseases are often the result of a host shift, where a pathogen jumps from one host species into another. Understanding the factors underlying host shifts is a major goal for infectious disease researchers. This effort has been further complicated by the fact that host-parasite interactions are now taking place in a period of unprecedented global climatic warming. Here, we ask how host shifts are affected by temperature by carrying out experimental infections using an RNA virus across a wide range of related species, at three different temperatures. We find that as temperature increases the most susceptible species become more susceptible, and the least susceptible less so. This has important consequences for our understanding of host shift events in a changing climate, and suggests that temperature changes may affect the likelihood of a host shift into certain species.

evolutionary biology↗