Evolution of the body snatchers, or the secret lives of parasites

Friday 19th February 6 pm, Presbyterian Community Centre, Tenby St Wanaka, $5 admission.

Evolution of the body snatchers, or the secret lives of parasites.

Professor Robert Poulin
Department of Zoology, University of Otago, Dunedin.

Although they account for maybe half of current biodiversity, parasites are often ignored by biologists because they are small and generally not visible, but also because of their repugnant lifestyle. However, far from the degenerate organisms running counter to progressive evolution often depicted in textbooks, parasites display some remarkably sophisticated adaptations allowing them to better exploit their hosts and complete their life cycle. Using examples drawn from our research on parasitic trematodes (flatworms) endemic to New Zealand aquatic ecosystems, I explore three ways in which evolution has shaped these fascinating creatures. First, as in colonies of ants and termites, there exist ‘social’ trematodes living in groups of genetically related individuals, in which a division of labour occurs: large individuals that lack mobility handle all the reproduction while small and highly mobile individuals defend the colony against other parasites trying to invade the host. Specialisation into a soldier caste and a reproductive caste leads to improved colony fitness. Second, as trematodes must be transmitted from an intermediate (prey) host to a final (predator) host via consumption, many of them have evolved the ability to alter the behaviour or appearance of their intermediate host to make it more susceptible to predation by the next host. Parasites use different mechanisms to usurp control of host behaviour, negating the host’s elaborate anti-predator adaptations. Third, as an alternative way to overcome this transmission-by-predation bottleneck in their life cycle, other trematodes have evolved the ability to indirectly detect, via odour cues, the presence of the predatory host while still inside the prey host. In the presence of cues from the predator host, the parasites await transmission; in the absence of such cues, however, the parasites accelerate their development and reach maturity precociously inside the prey intermediate host, thereby by-passing the need for transmission. These are only a few of the sophisticated adaptations shown by parasites that belie their simplified morphology, and allow them to be key players in natural ecosystems.

Professor Robert Poulin is a Canadian who has been at Otago University since 1992. He was elected a Fellow of the Royal Society of NZ in 2001 and has been awarded many medals and distinctions for his research. He has also been a recipient of major Marsden Fund Grants since 2001 through to 2018.