Are Quail hybrids more susceptible to avian malaria?

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.

Infection Rates

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.

Gambel’s Quail showed the highest prevalence of parasites (left figure), but California Quail and hybrids had the more parasites when infected (right figure). From: Roth et al. (2021).

Two Scenarios

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.

Hybrid Patterns

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?

References

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

The social network of hybrid quails

Recent study reveals a dynamic web of social interactions in a hybrid quail population.

In Southern California, Gambel’s Quail (Callipepla gambelii) and California Quail (C. californica) come into contact and interbreed. This hybrid zone has been extensively described from a morphological, behavioral and genetic perspective by Jennifer Gee in the early 2000s (see the Galliformes page for more details). Recently, David Zonana and his colleagues – including Jennifer Gee – provided another perspective on this hybrid zone by applying a social network approach. Using radio-frequency identification tags, they managed to obtain a detailed picture of the social interactions between individual birds. I have covered the results from a previous study in another blog post. The final paragraph of that post nicely summarizes the main findings:

Quails pair up with individuals that share particular plumage patterns with them. Outside the contact zone, this strategy works perfectly because they only encounter members of their own species. In the contact zone, however, they run into quails from another species. But instead of focusing in the species-specific differences, they keep using the shared plumage traits to pick their partner. And voila, hybrids!

A new study in the Journal of Animal Ecology builds on these results by adding another layer of complexity: genetics. What do these social interactions mean for patterns of gene flow? Do quails with similar genetic ancestry flock together or do they ignore relatives to avoid inbreeding?

Genetic Ancestry

Using genomic data, the researchers calculated the percentage of shared genetic ancestry between individual birds and incorporated this information in the network analyses. It turned out that social associations were structured randomly with respect to genetic ancestry in all networks. They concluded that these random patterns of assortment “provide further evidence that behavioral reproductive isolation is likely weak within the hybrid zone.”

However, the genetic data uncovered some hidden patterns in the social network. The genetic parentage analyses revealed offspring from three pairs that were not strongly connected within the networks. These offspring might be the outcome of extra-pair copulations that can happen quickly (and are thus not picked up by the radio tags). Such extra-pair copulations can affect the direction of gene flow between hybridizing species. Whether this is the case in Gambel’s and California Quail remains to be investigated.

The researchers incorporated information about genetic ancestry (figures a and b) into the social network (figure c). From: Zonana et al. (2020) Journal of Animal Ecology.

Network Rewiring

In addition to the genetic analyses, the researchers also studied the change in network structure over time. The rewiring of a network can occurs in two main ways: (1) changes in relationships or (2) changes in members of the network. The first way occurs when individuals associate with different birds at different times during the year, while the second way concerns members leaving (e.g., through migration or death) or new members joining the network. With regard to the quails, the rewiring of the network primarily involved changes in relationships between different members. It seems that there is a core breeding population with relatively stable membership but highly dynamic patterns of association.

Most social networks are thus a snapshot in time and can change dramatically throughout the year. This insight has important consequences for the study of hybrid zones, where mating is often considered random. However, changing social interactions can affect mating opportunities and potentially the incidence of hybridization. These dynamics will obviously differ between different hybrid zones, but need to be taken into account. More social network studies in hybrid zones, please.

The social network in the hybrid zone between Gambel’s and California Quail changed over time. From: Zonana et al. (2020) Journal of Animal Ecology.

References

Zonana, D. M., Gee, J. M., Breed, M. D., & Doak, D. F. (2021). Dynamic shifts in social network structure and composition within a breeding hybrid population. Journal of Animal Ecology, 90(1), 197-211.

Featured image: A Gambel’s Quail (Callipepla gambelii) © Alan D. Wilson | NaturesPicsOnline

This paper has been added to the Galliformes page.