Arthropods are commonly infected with symbionts that are transmitted from mothers to
their offspring, often in egg cytoplasm. While many of these symbionts directly benefit
their hosts, a large number manipulate their hosts' reproduction, often in unusual ways,
in order to persist and spread – these are termed 'reproductive manipulators' or
'reproductive parasites' (of which the most widespread, versatile and certainly best known
is the alpha-proteobacterium Wolbachia). For example, some reproductive manipulators
transform male hosts into females (the transmitting sex). The most common type of
manipulation is cytoplasmic incompatibility (CI). In CI, uninfected females produce no
offspring after mating with infected males, whereas infected females can successfully mate
with either infected or uninfected males. As a result, infected females often rapidly
replace uninfected ones in a population. We are interested in how these reproductive
parasites are maintained and spread in host populations, in the mechanisms involved in
manipulation, and in the long-term effects of infection on hosts. We have focused on
Cardinium, a recently discovered intracellular symbiont in the Bacteroidetes that appears
to have converged on many of the same reproductive manipulations as Wolbachia, yet is
completely unrelated. In a long-term collaboration with Molly Hunter (U Arizona), we
have studied reproductive manipulation in Encarsia wasps, where diverse Cardinium strains
cause CI, as well as transform male hosts into females. We are also collaborating with
Jen White (U Kentucky). Finally, we have also studied Cardinium infections in Cybaeus
spiders, where infections appear to be highly prevalent, but the effects of the symbionts
on their hosts are still unknown.
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