Print PageMaternally-transmitted associations between endosymbiotic bacteria and their insect hosts are pervasive in nature. Inherited microbes with imperfect transmission are expected to be lost from their host lineages in the absence of other mechanisms to enhance their transmission (e.g., host reproductive manipulation and fitness benefits to host). Indeed many inherited facultative endosymbionts are reproductive manipulators, and several others are reported to defend their hosts against natural enemies, but it is unclear whether these mechanisms alone or in combination guarantee endosymbiont persistence. Two closely related strains of heritable Spiroplasma infecting distantly related Drosophila hosts, protect their respective hosts against a parasitic wasp (Leptopilina heterotoma; Lh) and a nematode. Although these Spiroplasma defensive strains are not male-killers, several closely related strains are, such as MSRO, which naturally infects D. melanogaster. Goal 1: Examine whether the male-killing MSRO strain also has the ability to enhance its host’s survival against wasp parasitism by Lh. Goal 2: Determine whether MSRO protects its host against another species of Leptopilina (L. boulardi; Lb), which differs from Lh in host evasion/suppression strategies. Goal 3: Because Wolbachia is another common heritable endosymbiont of D. melanogaster, we evaluated the potential interacion of Wolbachia with this protective mechanism. In this study, we examined whether larval to adult survival of D. melanogaster subjected to oviposition attacks by two different species of wasps differed among: uninfected flies, Spiroplasma MSRO infected flies, Wolbachia infected flies, and doubly-infected flies.
Results/Conclusions
Our preliminary results suggest that Spiroplasma MSRO and Wolbachia wMel do not affect fly larva-to-adult survival in the absence of wasps (mean survival 88%). Spiroplasma MSRO caused high mortality of the two species of wasps (~99% in both wasps). MSRO-infected flies subjected two wasp attacks had significantly higher larva-to-adult survival against Lh and Lb (~21% and 22% respectively), compared to their MSRO-uninfected counterparts (~5% and 0.6%; respectively). This degree of protection is lower than that reported for the non-male-killing Spiroplasma strain of D. hydei. The role of Wolbachia was less clear: it enhanced fly survival against Lh, but countered the protection by Spiroplasma against Lb, but neither of these observations were significant. The observation that the male-killer MSRO provides weaker protection to its host than the non-male-killer of D. hydei, suggests that the male-killing and defensive mechanisms are complimentary strategies of Spiroplasma MSRO to achieve persistence in its host population.
