Evolution of complex life cycles in helminths

Geoff Parker, University of Liverpool

Location: Cruciform LT2, time: 16:30

Helminth parasites often have complex life cycles in which the parasite must pass through more than one host during its lifetime.  Typically, reproduction occurs in only one (the definitive host). Why do these complex cycles evolve, and why does reproduction not occur in the first host? Hosts can be incorporated (i) by adding a new definitive host at a higher trophic level, after which reproduction in the original definitive host is suppressed so that it becomes an intermediate host (upward incorporation); (ii) by adding an intermediate host at a lower trophic level (downward incorporation).  Conditions favouring upward and downward incorporation differ: both may reduce predation mortality, but upward incorporation may allow greater parasite body size and enhanced reproduction, while downward incorporation may enhance transmission to the original definitive host.  The evolution of optimal parasite body size at which to stop growing in intermediate hosts (i.e. GALM = growth arrest at larval mortality) is a complex problem and depends on size- or time dependent mortality.  I also discuss (i) why paratenicity (i.e. larva does not grow or develop in an intermediate host) occurs, (ii) why do larvae in intermediate hosts avoid the host’s gut and migrate to the tissues, and (iii) some rules for intermediate host manipulation.

Geoff's webpage: http://tulip.liv.ac.uk/portal/pls/portal/tulwwwmerge.mergepage?p_template=rae_staff_bs&p_tulipproc=raestaff&p_params=%3Fp_func%3DSIBS%26p_select%3DRAE%26p_hash%3DA688867%26p_url%3D17%26p_template%3Drae_staff_bs

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