A Wolbachia-associated fitness benefit depends on genetic background in Drosophila simulans

Abstract

The alpha-proteobacteria Wolbachia infect a number of insect species and influence host reproduction to favour the spread of infected females through a population. The fitness effect of this infection is important in understanding the spread and maintenance of Wolbachia within and among host populations. However, a full elucidation of fitness effect requires careful control of host genetic background. Here, I transferred a single clone of Wolbachia (the wHa strain) into three genetically distinct isofemale lines of the fly Drosophila simulans using microinjection methodology. These lines carried one of the three described mitochondrial haplogroups (siI, siII or siIII) and differ in nuclear genome as well. Population cage assays showed that wHa-infected siIII flies enjoyed a dramatic fitness benefit compared to uninfected siIII. In contrast, wHa did not affect the fitness of siI or siII flies. This study points to the importance of host-by-symbiont interaction terms that may play an important role in organismal-fitness.

Figure 1

Proportion of D. simulans versus CyO/Sp through 10 generations at two temperatures. The first set of population cages involved competition between CyO/Sp and (a) siI at 20 °C or (b) 25 °C; (c) siII at 20 °C or (d) 25 °C; siIII at (e) 20 °C or (f) 25 °. The second set of population cages involved competition between w118 and (g) siIII at 20 °C or (h) 25 °C. Straight lines indicate an uninfected host line; dashed lines indicate transfected counterparts.