Host benefits of a novel endosymbiont: Interactions between a defensive spiroplasma and a specialist nematode in Drosophila
Date
2022
Authors
Hyggen, Thompson
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Abstract
Bacterial endosymbionts are widespread in insects, and can affect their hosts in many different ways, such as protecting them against diverse natural enemies. Drosophila flies host Spiroplasma symbionts that defend them from parasitic wasps, as well as a harmful, generalist nematode parasite. However, defence has never been tested for a specialist nematode, Parasitylenchus nearcticus, which can be equally or more damaging to its hosts, with infection often resulting in complete sterility. Here, I exposed Spiroplasma-positive and negative Drosophila putrida flies to P. nearcticus to test if this symbiont confers protection against this parasite. I measured infection success by counting the number of infective worms that successfully parasitized their hosts, and parasite fitness by counting the reproductive output of motherworms. I also measured the effect of nematodes on Drosophila fitness by counting the number of mature fly eggs. Although P. nearcticus infected its natural host, Drosophila subquinaria, at high rates in my experiment, infection rates in D. putrida were very low, limiting my ability to demonstrate any defensive effects of Spiroplasma against this nematode. However, I did find lower nematode fecundity in the one infected fly that harboured Spiroplasma, which contained few, sickly-looking nematode offspring. Interestingly, I also found that Spiroplasma-infected D. putrida flies had higher fecundity than symbiont-free ones, independent of nematode infection. This research provides multiple pieces of evidence for how Spiroplasma can benefit their hosts and will help guide future investigations in defensive symbiosis.