Wolbachia in Eurema butterflies : endosymbiont effects on host sex ratios and population genetics

Abstract

Many insect species are infected with endosymbiotic bacteria that live in the cytoplasm of their host cells. Most of these bacteria are maternally inherited and can manipulate reproduction of their insect hosts by inducing cytoplasmic incompatibility (CI), thelytokous parthenogenesis, male killing and feminisation, and some of these manipulations distort the sex ratio of their hosts. This PhD research studied Wolbachia infections in Eurema butterflies (Lepidoptera: Pieridae), the effects of Wolbachia on their sex determination system, and the effects on gene flow and genetic diversity across different Eurema species in Australia. The genus Eurema was chosen because Wolbachia had previously been identified in three species of this genus. In two species, E. hecabe and E. mandarina, Wolbachia induced CI and feminisation. CI is caused by the wCI strain and feminisation by the wFem strain. Both species are two out of only three known examples of Wolbachia caused feminisation in insects. Prior to this study details about the feminisation mechanisms were unknown except that it was expected that Wolbachia changes homogametic (ZZ) males into functional females that do not possess the female sex chromosome (W) found in uninfected heterogametic ZW females. It was also unknown whether Australian E. hecabe and other Australian Eurema species are infected with the feminising or any other Wolbachia strains (with the exception of previous preliminary and unpublished work on E. hecabe). Australia is home to six Eurema species of the two subgenera Terias and Eurema. In response to the Australian climate with seasonal and often unpredictable rainfall, these Australian Eurema species evolved different adaptation strategies such as reproductive diapause and migration behaviour.

Date of Award	2015
Original language	English