Variable fitness effects of Wolbachia infection in Drosophila melanogaster

Abstract

Maternally inherited Wolbachia bacteria are extremely widespread among insects and their presence is usually associated with parasitic modifications of host fitness. Wolbachia pipientis infects Drosophila melanogaster populations from all continents, but their persistence in this species occurs despite any strong parasitic effects. Here, we have investigated the symbiosis between Wolbachia and D. melanogaster and found that Wolbachia infection can have significant survival and fecundity effects. Relative to uninfected flies, infected females from three fly strains showed enhanced survival or fecundity associated with Wolbachia infection, one strain showed both and one strain responded positively to Wolbachia removal. We found no difference in egg hatch rates (cytoplasmic incompatibility) for crosses between infected males and uninfected females, although there were fecundity differences. Females from this cross consistently produced fewer eggs than infected females and these fecundity differences could promote the spread of infection just like cytoplasmic incompatibility. More surprising, we found that infected females often had the greatest fecundity when mated to uninfected males. This could also promote the spread of Wolbachia infection, though here the fitness benefits would also help to spread infection when Wolbachia are rare. We suggest that variable fitness effects, in both sexes, and which interact strongly with the genetic background of the host, could increase cytoplasmic drive rates in some genotypes and help explain the widespread persistence of Wolbachia bacteria in D. melanogaster populations. These interactions may further explain why many D. melanogaster populations are polymorphic for Wolbachia infection. We discuss our results in the context of host-symbiont co-evolution.

Nuclear–Mitochondrial Epistasis and Drosophila Aging: Introgression of Drosophila simulans mtDNA Modifies Longevity in D. melanogaster Nuclear Backgrounds

“…All strains had been in laboratory culture for .5 years prior to analyses. Some data on longevity for Zim 2, Zim 53, and FTF 100 have been reported previously (Fry and Rand 2002;Fry et al 2004).…”

The effects of temperature on host–pathogen interactions in D. melanogaster: Who benefits?

“…While fecundity is reduced in many insects after infection (Cole et al, 2003;Elsawaf et al, 1994;Zerofsky et al, 2005), females still continue to produce eggs. In fact, some bacteria, such as Wolbachia, can even lead to increased fecundity in flies (Fry et al, 2004). While we did not examine fecundity in this experiment, flies held at cooler temperatures might lay a few more eggs while they are still alive.…”

Extensive Introgression of Mitochondrial Dna Relative to Nuclear Genes in the Drosophila Yakuba Species Group

“…Wolbachia could also provide direct fitness effects to its host, which could promote the spread of a Wolbachia infection in the absence of cytoplasmic incompatibility. Indeed, enhanced survival and/or fecundity effects associated with Wolbachia have been observed in four strains of D. melanogaster, while another strain responded positively to Wolbachia removal (Fry et al 2004). Nevertheless, none of these three species in the D. yakuba species group was found to be fixed for a specific Wolbachia strain.…”