Ecology and evolution of the malaria parasites: Integrating molecules, morphology, and traits across scales
Why study the malaria parasites?
The malaria parasites represent a global radiation of blood pathogens that infect all major vertebrate lineages (even fish!). Four species of malaria parasite commonly infect humans, but the human parasites comprise less than 1% of described malaria parasite biodiversity. I use microscopic, DNA barcoding, and genomic approaches to study the neglected 99% of malaria diversity. My research is focused largely on the avian malaria parasites, represented by the genera Haemoproteus, Parahaemoproteus, Plasmodium, and Leucocytozoon, which in total make up the majority of described malaria parasite species. My current research is focused on addressing the pattern and process of malaria diversification and adaptation across space and time, from the entire order (Haemosporida) to the species level. Current and former projects include:
Evolution of the Order Haemosporida
Haemosporidian phylogeny from Galen et al. (2018) Roy. Soc. Open Sci.
The phylogeny of the Haemosporida has long vexed parasitologists, as historically it has been difficult to not only obtain samples of the broad diversity of malaria parasites, but also to generate sequence data from more than just a few loci. Our recent paper assembled the most comprehensive phylogenetic dataset for the malaria parasites, revealing many previously unknown relationships. We are now in the process of using transcriptomic data to assemble an even larger dataset – stay tuned for that.
I am also interested in understanding the relationships among malaria parasites at the species level. Unfortunately, our understanding of how to identify malaria parasite species is limited. I have been investigating malaria parasite species limits in the genus Leucocytozoon, an odd group of malaria parasites that have bizarre, highly variable morphologies that greatly distort the host cell, do not produce the distinctive hemozoin pigment that is characteristic of all other malaria parasites, and is most abundant in cold high-latitude and high-elevation regions of the world. As a result Leucocytozoon has been neglected among malaria biologists, with our understanding of species diversity, host specificity, and geographic distributions muddled at best. I used an integrative approach combining morphology, ecological host associations, and multi-locus statistical species delimitation analyses to investigate species diversity in this group. I found that cryptic host-specificity has caused Leucocytozoon species diversity to be vastly underestimated, supporting previous research that has suggested that the avian malaria parasites are incredibly diverse globally.
Leucocytozoon species delimitation from Galen et al. (2018) BMC Evol. Biol.
Malaria parasite community ecology
Avian malaria parasites form diverse communities that engage in complex interactions with their often equally diverse hosts. What determines the malaria parasite species that are found together in the same communities, the same host species, or even the same host individuals? I am using DNA barcoding surveys of avian malaria parasite communities throughout the world to determine how evolutionary history and malaria parasite traits (such as host specificity and climatic niche) structure parasite assemblages. For example, I have found that malaria parasite “infracommunities” within single host individuals tend to be phylogenetically overdispersed. This pattern appears to be caused primarily by convergent evolution of similar host preferences in distantly related parasite species.
Leucocytozoon malaria parasites are phylogenetially overdispersed within hosts. From Galen et al. 2019 J. Animal Ecol.
Blood parasite metatranscriptomics
A major challenge for the study of blood parasites has been the difficulty of building genomic resources for studies of parasite phylogenomics, population genomics, molecular evolution, and more. I have been working on approaches to expand and improve blood parasite genomic research, primarily through transcriptomics and sequence capture.
I have previously used a metatranscriptomic approach to generate the largest genomic dataset for malaria parasites of wildlife to date. This study also found that transcriptomics is more sensitive than traditional methods such a microscopy and DNA barcoding, and is capable of detecting upwards of 20% more infections than these more commonly used methods. I am building off of this research to improve sequence capture methods for haemosporidian parasites that will allow the generation of 100’s of loci for any malaria parasite lineage.
Avian ecology and evolution
I have previously studied avian ecology and evolution, and I maintain research interests in these areas.
Avian ecology and evolution publications:
Elevational generalism of Andean songbirds
Mutation-biased adaptation in Andean house wrens
Natural history and conservation
In addition to my primary research program, I seek to contribute to advances to our understanding of natural history and conservation using molecular approaches. Previous projects that I have contributed to include a non-invasive molecular survey of the endangered San Joaquin kit fox, the identification of the first Pacific-slope Flycatcher in Illinois, and parentage analysis of a putative hybrid hawk from California.
Previous natural history and conservation publications:
- Conservation genetics of the San Joaquin kit fox
- A new method for identifying Empidonax flycatchers leads to the discovery of Illinois’s first “Western” flycatcher
- Using molecular and morphological approaches to determine parentage of a putative hybrid Buteo
Spencer C. Galen 