Hague, M. T. J. | Search bioRxiv

bioRxiv2020

Divergent effects of Wolbachia on host temperature preference

Heritable symbionts can modify a range of ecologically important host traits, including behavior. About half of all insect species are infected with maternally transmitted Wolbachia, a bacterial endosymbiont known to alter host reproduction, nutrient acquisition, and virus susceptibility. Here, we broadly test the hypothesis that Wolbachia modify host behavior by assessing the effects of eight different Wolbachia strains on the temperature preference of six Drosophila melanogaster-subgroup species. Four of the seven host genotypes infected with A-group Wolbachia strains (wRi in D. simulans, wHa in D. simulans, wSh in D. sechellia, and wTei in D. teissieri) prefer significantly cooler temperatures relative to uninfected genotypes. Contrastingly, when infected with divergent B-group wMau, D. mauritiana prefer a warmer temperature. For most strains, changes to host temperature preference do not alter Wolbachia titer. However, males infected with wSh and wTei experience an increase in titer when shifted to a cooler temperature for 24 hours, suggesting that Wolbachia-induced changes to host behavior may promote bacterial replication and influence Wolbachia transmission rates. Modifications to host temperature preference likely influence host thermoregulation, and understanding the fitness consequences of these effects is crucial for predicting evolutionary outcomes of host-symbiont interactions, including how Wolbachia spread to become common.

evolutionary biology↗

bioRxiv2020

Environmental and genetic contributions to imperfect wMel-like Wolbachia transmission and frequency variation

Maternally transmitted Wolbachia bacteria infect about half of all insect species. They usually show imperfect maternal transmission and often produce cytoplasmic incompatibility (CI). Irrespective of CI, Wolbachia frequencies tend to increase when rare only if they benefit host fitness. Several Wolbachia, including wMel that infects Drosophila melanogaster cause weak or no CI and persist at intermediate frequencies. On the island of Sao Tome off West Africa, the frequencies of wMel-like Wolbachia infecting D. yakuba (wYak) and D. santomea (wSan) fluctuate, and the contributions of imperfect maternal transmission, fitness effects, and CI to these fluctuations are unknown. We demonstrate spatial variation in wYak frequency and transmission on Sao Tome. Concurrent field estimates of imperfect maternal transmission do not predict spatial variation in wYak frequencies, which are highest at high altitudes where maternal transmission is the most imperfect. Genomic and genetic analyses provide little support for D. yakuba effects on wYak transmission. Instead, rearing at cool temperatures reduces wYak titer and increases imperfect transmission to levels observed on Sao Tome. Using mathematical models of Wolbachia frequency dynamics and equilibria, we infer temporally variable imperfect transmission or spatially variable effects on host fitness and reproduction are required to explain wYak frequencies. In contrast, spatially stable wSan frequencies are plausibly explained by imperfect transmission, modest fitness effects, and weak CI. Our results provide insight into causes of wMel-like frequency variation in divergent hosts. Understanding this variation is crucial to explain Wolbachia spread and to improve wMel biocontrol of human disease in transinfected mosquito systems.

evolutionary biology↗