Research
Evolution of immune systems
It's not easy to predict how much an organism should invest in defence. Induced immune defence costs little when pathogens are absent, but mounting an induced response can be time-consuming. To ensure timely protection, organisms often rely on constitutive defence even though always having one's guard up is uneconomical. Another layer of complexity is coevolutionary arms-race. If your enemy has an upper hand, is your defence really worth the cost? My colleagues and I developed a theoretical model inspired by the invertebrate innate immune system to ask how parasite coevolution affects the optimal combination of constitutive and induced defence. Our model tells us that coevolution of parasites can shift the host’s optimal allocation from induced towards constitutive immunity. A parasite population subjected to a specific immune receptor can evolve heightened genetic diversity, which makes parasite detection more difficult for the hosts. We show that this coevolutionary feedback makes the induced immune response less efficient, forcing the hosts to invest more heavily in constitutive immunity. Our results highlight that evolutionary feedback between host and parasite populations is a key factor shaping the selection regime for immune systems.
- Kamiya, T., Oña, L., Wertheim, B., and van Doorn, G. S. (2016). Coevolutionary feedback elevates constitutive immune defence: a protein network model. BMC Evolutionary Biology, 16:92, DOI: 10.1186/s12862-016-0667-3.
Sociality in parasitic flatworms (trematodes)
Division of labour in animal societies is not limited to ants and bees. The social clonal stage of trematode parasites in snail intermediate hosts form two castes: reproductive members and non-reproductive members that are considered as soldiers. Inspired by the classic theoretical and empirical works on social insects, we investigated potential determinants of colony success in these unique clonal organisms. We found that the effect of competition from other trematode parasite species interacts with social conditions, such as caste ratio, to influence the growth of individual caste members and ultimately determine the reproductive output of those colonies. In the process, we also discovered that reproductive colony members adjust their competitive behaviour according to the number of non-reproductives in the colony, as previously seen in termite colonies.
- Kamiya, T., & Poulin, R. (2013). Caste ratios affect the reproductive output of social trematode colonies. Journal of Evolutionary Biology, 26(3), 509-516.
- Kamiya, T., & Poulin, R. (2013). Behavioural plasticity of social trematodes depends upon social context. Biology Letters, 9(1), 20121027.
- Kamiya, T., O’Dwyer, K., Nuy, J., & Poulin, R. (2013). What determines the growth of colony members in caste-forming trematodes?, Evolutionary Ecology, 27:1235–1247.
Biodiversity of parasites
Understanding patterns of biodiversity, and evaluating its roles in ecosystem functions are important goals for ecologists. But, parasites are often rather neglected by the mainstream biodiversity crisis debate despite their richness and functional importance to ecosystems and evolutionary processes. Using meta-analytic techniques, we explored major determinants of parasite species richness.
- Kamiya, T., O’Dwyer, K., Nakagawa, S., & Poulin, R. (2014). Host diversity drives parasite diversity: meta-analytical insights into patterns and causal mechanisms. Ecography, 37: 001–009, DOI: 10.1111/j.1600-0587.2013.00571.x
- Kamiya, T., O’Dwyer, K., Nakagawa, S., & Poulin, R. (2013) What determines species richness of parasitic organisms? A meta-analysis across animal, plant and fungal hosts. Biological Reviews, Published online. DOI: 10.1111/brv.12046
Parasite-induced behavioural alteration
Parasites are known to alter behaviours of their hosts through pathogenic side effects or sometimes in order to adaptively improve their chance of transmission to the next host. I investigate how trematode infection affects the trade-off between foraging and predator evasion in a marine snail. I found that some species of parasites make their host less sensitive to predator odours, leaving the snail host more vulnerable to crab predators.
We have also looked into how trematode parasites affect the use of microhabitat of their rockyshore snail hosts. Through a mark-recapture study, we found that infected snails spend more time on the rocky surface instead of in crevice; this altered behaviour is likely to make the snails more vulnerable to predation by birds which serve as the definitive hosts for the trematode.
We have also looked into how trematode parasites affect the use of microhabitat of their rockyshore snail hosts. Through a mark-recapture study, we found that infected snails spend more time on the rocky surface instead of in crevice; this altered behaviour is likely to make the snails more vulnerable to predation by birds which serve as the definitive hosts for the trematode.
- Kamiya, T., & Poulin, R. (2012). Parasite-induced behavioural changes to the trade-off between foraging and predator evasion in a marine snail. Journal of Experimental Marine Biology and Ecology, 438, 61-67.
- O’Dwyer, K., Kamiya, T., & Poulin, R. (2014). Altered microhabitat use and movement of littorinid gastropods: the effects of parasites. Marine Biology, DOI: 10.1007/s00227-013-2349-7
