Eco-Evolution and Malaria Increase in a Blue Tit Population

In Southern Sweden my colleagues have monitored a Blue Tit population since 1983 and since 1996 they have collected blood samples from individual birds. These blood samples can be thought of as time capsules that provide us with the opportunity to understand how malaria parasite populations have changed across decades. Notably, we have found an overall significant increase for all the parasites that we study (Haemoproteus, Plasmodium, and Leucocytozoon). We seek to understand the drivers of this increase. In recent decades, Southern Sweden has experienced observable climatic shifts, and this may be a contributing factor. However, evolution is always at play. Using a combination of host natural history, lab methods, climate modeling, and genomic analyses, my team and I are unravelling how the interactions between genomes and the environment can translate into an observable pattern of long-term prevalence increase.   

While many parasites are highly host and/or habitat-specific, some are generalists that are capable of infecting a myriad of species in a diversity of environments. For example, Plasmodium relictum, one of the world’s most invasive parasites, is known to infect species in over 30 avian families. During my PhD, I found that a strain of P. relictum (SGS1) was infecting some of the birds that I sampled in Boulder County, Colorado. SGS1 is not native to North America, but given the availability of suitable vectors and host species, it has been able to expand its range. Currently, our group is working to understand how SGS1 might be evolving in North America compared to within its native range. 

Habitats shift with elevation change. I am interested in understanding how parasite communities are shaped by changes in elevation. Birds that are not long-distance migrants are excellent study systems for these investigations as their parasites reflect the environment that they were sampled in. I have studied the influence of elevation on parasite communities in Black-capped Chickadees, Mountain Chickadees, and Brown-Capped Rosy Finches, all of whom are found in the high alpine. Chickadees in Boulder County inhabit a wide array of elevations, and this is reflected in their parasite communities. At low elevations, chickadees tend to have more Plasmodium infections, and at higher elevations a majority harbor Leucocytozoon parasites. We don’t yet know how these parasite distributions affect chickadee ranges, and whether these infections have associated fitness consequences. This work was part of broader project in my PhD lab group, The Boulder Chickadee Study.