Studying the interactions between parasites and hybridization.
The relationship between parasites and hybrids is complex, to put it mildly. On the one hand, hybrids might be more prone to infection because of genetic or developmental defects. On the other hand, they might be able to fend of parasites due to hybrid vigor. Or perhaps they show intermediate infection rates compared to their parental species. In addition to these three broad scenarios, the likelihood and severity of a parasite infection can be influenced by several ecological and behavioral factors. In short, it’s complicated. A recent study in the journal Ecology and Evolution investigated the interplay between parasites and hybrids in a contact zone between California Quail (Callipepla californica) and Gambel’s Quail (Callipepla gambelii). Let’s see if they could untangle this complex interplay.
Allison Roth and her colleagues tested 193 quails (72 California Quail, 27 Gambel’s Quail and 94 hybrids) for the presence of Haemoproteus lophortyx, a parasite that can cause avian malaria. The screening indicated that Gambel’s Quail were more often infected compared to California Quail and hybrids. However, the intensity of infection was higher in the latter two groups. In other words, California Quail and hybrids were infected less often, but when experiencing an infection they had more parasites in their blood. A counterintuitive result that requires further explanation.
The researchers describe two possible scenarios to explain the discrepancy between infection rate and intensity. First, the ecology or behavior of Gambel’s Quail might increase the likelihood of encountering biting midges (the vector of the parasites), resulting in a higher infection rate. In addition, the social interactions between individual Gambel’s Quail might be conducive for the exchange of parasites (see this blog post on the social network of quails). The higher infection rates can drive co-evolution between the Gambel’s Quails and their parasites, culminating in a higher parasite resistance in this species. Hence, Gambel’s Quail will show lower infection intensities.
The second scenario suggests that both quail species are equally likely to become infected, but Gambel’s Quail have more difficulty in completely clearing parasites from their system. This might explain the less intense infection patterns in these birds. California Quail, however, might be able to recover from mild infection. Only the most intense infections will leave their signature in the blood.
The similarity between the California Quail and the hybrids suggests that hybrids are genetically and/or behaviorally similar to this species. However, the researchers analyzed the hybrids as one homogenous group, although they probably represent a range of first-generation hybrids and backcrosses. More detailed analyses, taking into account the genetic make-up of the hybrids, are warranted. Moreover, several other details remain to be determined, such as the fitness effects of parasite infections and the possibility of multiple parasite lineages that are circulating in these quails. Despite these open questions, the researchers indicate that “these findings suggest that infection by H. lophortyx has the potential to influence species barrier dynamics in this system.” Parasite-driven speciation, wouldn’t that be awesome?
Roth, A. M., Keiser, C. N., Williams, J. B., & Gee, J. M. (2021). Prevalence and intensity of avian malaria in a quail hybrid zone. Ecology and Evolution, 11(12), 8123-8135.
Featured image: Gambel’s Quail (Callipepla gambelii) © Alan D. Wilson | NaturesPicsOnline