Life history strategies
It has been indicated in section 1.4.1 that the residual component in the life cycles of many species of parasitic organisms represents an important strategy for local transmission as well as dispersal. Among those parasites with a residual component in their life cycle, many have larval stages that can remain in a habitat long after the definitive host has deposited the parasite’s propagules and disappeared from the scene. On the other hand, not all parasites have complicated life cycles. Many have direct life cycles where an egg, for example, may be directly ingested and the host thus infected. Despite the route of infection, whether direct or indirect, many parasites have co-evolved with their hosts to the extent that their survival strategies involve mechanisms that increase their reproductive fitness. Some strategies include those that ensure spatial or temporal overlap with a potential host. Indeed, as stated by Janovy and Kutish (1988), some’ studies suggest that temporal and spatial aggregation of infective stages may have equivalent effects on the structure of parasite populations’ (emphasis added); in other words, time and space are of equal importance in affecting the aggregation of parasites. Other parasites may repress a host’s immune responsiveness, allowing the parasite to successfully establish and thrive. Whatever the strategy, the outcome permits fecundity levels to remain high enough to sustain the parasite’s suprapopulation density above some threshold level.
KeywordsIntermediate Host Hydatid Cyst Asexual Reproduction Definitive Host Digenetic Trematode
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