Experimental evolution reveals habitat‐specific fitness dynamics among Wolbachia clades in Drosophila melanogaster

Abstract

The diversity and infection dynamics of the endosymbiont Wolbachia can be influenced by many factors, such as transmission rate, cytoplasmic incompatibility, environment, selection and genetic drift. The interplay of these factors in natural populations can result in heterogeneous infection patterns with substantial differences between populations and strains. The causes of these heterogeneities are not yet understood, partly due to the complexity of natural environments. We present experimental evolution as a new approach to study Wolbachia infection dynamics in replicate populations exposed to a controlled environment. A natural Drosophila melanogaster population infected with strains of Wolbachia belonging to different clades evolved in two laboratory environments (hot and cold) for 1.5 years. In both treatments, the rate of Wolbachia infection increased until fixation. In the hot environment, the relative frequency of different Wolbachia clades remained stable over 37 generations. In the cold environment, however, we observed marked changes in the composition of the Wolbachia population: within 15 generations, one Wolbachia clade increased more than 50% in frequency, whereas the other two clades decreased in frequency, resulting in the loss of one clade. The frequency change was highly reproducible not only among replicates, but also when flies that evolved for 42 generations in the hot environment were transferred to the cold environment. These results document how environmental factors can affect the composition of Wolbachia in D. melanogaster. The high reproducibility of the pattern suggests that experimental evolution studies can efficiently determine the functional basis of habitat-specific fitness among Wolbachia strains.

Wolbachia modifies thermal preference in Drosophila melanogaster

“…Wolbachia’ s ability to provide anti‐viral protection to their hosts has emerged as the most promising approach to combatting insect‐vector borne pathogens that pose serious health risks to humans, such as dengue fever and Zika (Moreira et al ., ; Iturbe‐Ormaetxe et al ., ; Dutra et al ., ). However, because the strength of anti‐viral protection is associated with higher Wolbachia densities (Chrostek et al ., ; Martinez et al ., ) and bacterial titres are a temperature sensitive trait (Hoffmann et al ., ; Reynolds et al ., ; Mouton et al ., ; ; Bordenstein and Bordenstein, ; Correa and Ballard, ; Chrostek et al ., ; Strunov et al ., ; Murdock et al ., ; Versace et al ., ), it is feasible that under certain thermal conditions such as lower environmental temperatures, Wolbachia‐ induced virus protection could be attenuated or absent (Chrostek, ). Furthermore, our findings, as demonstrated in a highly inbred lab strain of D. melanogaster , need to be tested first in different host backgrounds, which are naturally or artificially infected with the endosymbiont.…”

Idiosyncratic evolution of maternal effects in response to juvenile malnutrition in Drosophila

“…Kazancioglu & Arnqvist, ). There is also evidence that the presence of Wolbachia may affect life history in Drosophila (Fry et al ., ), and that the frequency of different Wolbachia strains may respond to selection imposed by thermal stress (Versace et al ., ), suggesting that genetic variation in Wolbachia may affect host stress tolerance. Our selected and control populations all carry Wolbachia (B. Erkosar, unpublished data).…”

Heritable symbionts in a world of varying temperature

“…At its most powerful, this may involve varying thermal environment within laboratory or caged populations over a number of generations and examining its impact on symbiont dynamics. For instance, Versace et al (2014) noted that the Wolbachia strain that spread in passage through Drosophila melanogaster population cages depended upon the temperature at which the population was maintained (Versace et al, 2014). However, studies such as this are logistically complex for many species.…”