A field cage test of the effects of the endosymbiont Wolbachia on Drosophila melanogaster

Abstract

Wolbachia endosymbionts are known to affect the fitness of their hosts, but most of this information is from laboratory studies. In Drosophila melanogaster, Wolbachia frequencies vary clinically in frequency in Australia and may confound climatic adaptation. Here we use field cages in a reciprocal exchange design to test for Wolbachia effects in D. melanogaster in winter at temperate and tropical sites. Infected flies of both populations had a lower fecundity in tropical north Queensland, whilst in temperate southern Victoria Wolbachia effects depended on the nuclear population background. Here infected flies from Victoria were more fecund. Wolbachia also influenced larval/pupal viability in the tropics but this was dependent on population background. In comparisons of the populations, there was no evidence for local adaptation for total fecundity, viability or survival over winter. However, in Victoria, a local population had a higher late-life fecundity than a tropical population from Queensland that had higher early-life fecundity. At a tropical site, local Queensland flies had a higher early fecundity than Victorian flies. In contrast to many laboratory studies, mortality rates in the field cages increased only slightly over time. Both the Wolbachia effects and population differences have not been previously detected in laboratory studies with D. melanogaster and highlight the utility of Drosophila field studies in fitness experiments.

Genetic Diversity, Population Structure and Wolbachia Infection Status in a Worldwide Sample of Drosophila melanogaster and D. simulans Populations

“…Given that Wolbachia causes only weak cytoplasmic incompatibility in the wild, the infection is predicted to be lost from populations, unless it also confers a fitness benefit to the host [62], [64]. There is some evidence suggesting positive effects of Wolbachia infection on fitness in D. melanogaster , although these effects vary depending on a number of factors, including the sex and the genetic background of the host [65]–[67]. The strength of Wolbachia -induced cytoplasmic incompatibility also varies with age, and can be much stronger when infected males mate very young, which has also been postulated to explain the persistence of infection in wild populations [68].…”

From Parasite to Mutualist: Rapid Evolution of Wolbachia in Natural Populations of Drosophila

“…Such rapid evolution helps to explain the diversity of effects of Wolbachia on host fitness noted in the literature: these effects range from negative [9,15,39] to positive [19,21,22] to the extreme where Wolbachia becomes essential for host survival [20] or host fertility [40,41]. It also helps to explain the inconsistent effects of Wolbachia on host fitness detected in previous experiments [22,42]; changes in the apparent host effects of Wolbachia over time or between experiments may well reflect selection among Wolbachia variants rather than residual effects of antibiotics or changes in Wolbachia density. The rapid evolution of w Ri, as well as rapid evolution of Wolbachia hosts [43], suggests a dynamic interaction between parasitic and mutualistic life modes and rapidly changing effects of endosymbionts in host insect evolution.…”

The Native Wolbachia Endosymbionts of Drosophila melanogaster and Culex quinquefasciatus Increase Host Resistance to West Nile Virus Infection

“…A variety of non-reproductive phenotypes have additionally been identified in Wolbachia -infected D . melanogaster , including effects on behavior, viability, insulin signaling, and iron homeostasis [25], [26], [27], [28], [29], [30], [31], [32], [33]. While the magnitude of most of these Wolbachia -dependent phenotypes is generally modest and frequently variable, some of these could, nonetheless, provide Wolbachia -infected flies with a selective fitness advantage [32], [33], [34].…”