Parasitic Life Cycles
1. How did complex life cycles in trematodes evolve? (What are the hypotheses to explain how these life cycles evolved to include multiple hosts and larval stages?)
In order to reduce mortality rate and increase efficiency two methods were found in the life cycles of trematodes. The upward incorporation has a new definitive host from a high level of the foodweb and this host preys on the old definitive host (become intermediate) and are then combined together as one which reduces reproduction. The downward incorporation has a new intermediate host combined to a lower level of the food web and therefore, reduces mortality and makes it easier to go to the original host. Having multiple host is usually facultative
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