INTRO

ADAPTIVE HOST MANIPULATION BY PARASITES

There are many examples of parasites capable of inducing phenotypic change (typically behaviour or morphology) in their hosts, in order to increase the likelihood of completing their life cycle. This is commonly known as adaptive host manipulation, a phenomenon that has often been misrepresented in both the popular media and the scientific literature. I have worked with several host-parasite systems in which parasite-induced changes in host phenotype provide a clear advantage to the parasite (cave wētā-hairworm, nematode-earwig, snail-trematode). However, attributing adaptive causation to these alterations requires an in-depth investigation of the proximate molecular mechanisms underpinning host phenotypic change. With this in mind, I am currently focusing my research on hairworms and their terrestrial insect hosts (see figure above for a general methodology):

Hairworms (phylum Nematomorpha) are parasites with a complex life cycle, including multiple invertebrate hosts, an aquatic and terrestrial phase, and five recognised life stages. Interestingly, mature hairworms must enter water in order to mate and lay their eggs. However, they reside within a land-dwelling host that actively avoids bodies of water, e.g., crickets and ground beetles. Currently, it is thought that hairworms adaptively manipulate their invertebrate hosts to somehow enter water and drown, once the hairworms are mature and ready to exit. Despite their notoriety, hairworms remain mysterious in several biological aspects. Since experimental infections are important in demonstrating that host behavioural change is indeed the result of a manipulative parasite ensuing infection, my overarching goal is to elucidate the hidden interactions between hairworms and their insect hosts by combining experimental infections, behavioural assays, high-throughput sequencing methods (comparative genomics, comparative transcriptomics, and proteomics), and gene editing (CRISPR-Cas9) to understand the proximate mechanisms that cause terrestrial insects to enter water and drown.

PARASITE AND DISEASE TRANSMISSION DYNAMICS

Parasites require hosts for their development or transmission to another host or environment. The presence of compatible host species and the interactions between these hosts dictate the successful transmission of parasites and disease in the environment (pictured above, a dormant hairworm cyst inside its aquatic insect host). Moreover, host defensive traits are important regulators of transmission, impacting successful infection rates and parasite survival. Apart from the parasite-induced host behaviours mentioned above, studying parasite transmission dynamics also requires an understanding of host immune systems and the parasite avoidance strategies of animals as they navigate through their landscape. These small-scale interactions are partly responsible for the large-scale dynamics of disease transmission, both regionally and worldwide.

INTEGRATIVE ETHOLOGY

Animal behaviour is an intrinsically complex phenomenon resulting from the interactions of the internal and external environments of an organism. A simple observed change in behaviour is likely the culmination of myriad cascading physiological processes triggered by the environmental cues experienced by an animal. Evolution has undoubtedly played a fundamental role in shaping and refining the processes underpinning behaviour, but the physiological bases still remain largely open to debate. Simple model organisms (laboratory mice, fruit flies, etc.) have been used to study the great complexity of behaviour. Although these studies have resulted in promising lines of research, there is still much to discover. Given the notable complexity of animal behaviour and our incomplete understanding of its physiological foundations, my ambition is to conduct multidisciplinary research on host behavioural manipulation by parasites, from the molecular to the ecosystemic, to understand the fundamental nature of parasite transmission and behavioural regulation. These host-parasite systems represent an untapped source of unique and non-traditional model organisms. Harnessing this integrative approach to ethology is essential if our goal is to understand behaviour from all relevant scientific perspectives.