Abstract
BackgroundMales and females differ in many ways and might present different opportunities and challenges to their parasites. In the same way that parasites adapt to the most common host type, they may adapt to the characteristics of the host sex they encounter most often. To explore this hypothesis, we characterized host sex-specific effects of the parasite Pasteuria ramosa, a bacterium evolving in naturally, strongly, female-biased populations of its host Daphnia magna.ResultsWe show that the parasite proliferates more successfully in female hosts than in male hosts, even though males and females are genetically identical. In addition, when exposure occurred when hosts expressed a sexual dimorphism, females were more infected. In both host sexes, the parasite causes a similar reduction in longevity and leads to some level of castration. However, only in females does parasite-induced castration result in the gigantism that increases the carrying capacity for the proliferating parasite.ConclusionsWe show that mature male and female Daphnia represent different environments and reveal one parasite-induced symptom (host castration), which leads to increased carrying capacity for parasite proliferation in female but not male hosts. We propose that parasite induced host castration is a property of parasites that evolved as an adaptation to specifically exploit female hosts.
Highlights
Males and females differ in many ways and might present different opportunities and challenges to their parasites
In a series of experiments using the crustacean host D. magna and P. ramosa, its bacterial parasite, we investigated if parasites exposed to male versus female host individuals differ in the likelihood of successful infection (Experiments 1 and 2), in parasite fitness, in the rate of proliferation within the host (Experiments 2 and 3), and in induced disease symptoms (Experiments 2, 4 and 5)
In the same way that parasites are expected to be better adapted to the most common host types [5], we propose that parasites can adapt to the characteristics of the host sex they encounter more often
Summary
Males and females differ in many ways and might present different opportunities and challenges to their parasites. In the same way that parasites adapt to the most common host type, they may adapt to the characteristics of the host sex they encounter most often To explore this hypothesis, we characterized host sexspecific effects of the parasite Pasteuria ramosa, a bacterium evolving in naturally, strongly, female-biased populations of its host Daphnia magna. A given species may have differences in gametes, primary and secondary sexual characters, quality and quantity of hormones, and differences in behavior, somatic structures, immune response and gene expression [1,2,3,4] These differences can make males and females distinct types of hosts, offering different challenges and opportunities to their parasites. Parasites of D. magna will typically encounter females considerably more often than males and might be adapted to exploit that particular host type
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