![]() ![]() ![]() Bacot and Martin noticed that fleas harboring plague exhibited blocked proventriculi that limited their success in blood feeding ( Bacot and Martin, 1914). Not surprisingly, given its implications for human health, one of the earliest clear demonstrations of the role of altered behavior in parasite transmission came from an arthropod vector, the flea. Carus in 1835 (see Kagan, 1952), both the ecological influence of the parasite and the mechanism by which it accomplishes its visibility have remained more of a puzzle than one might expect (see Casey et al., 2003). Leucochloridium and its snail hosts can be difficult to keep in the laboratory and are patchily distributed in nature, so in the almost 200 years since its description by C. Of course, Leucochloridium in snails is highly visible – the snails are said to crawl out into lighted areas, and the striped broodsacs pulsate this visibility is something to keep in mind as I continue my brief review. I hesitate to call this suggestion one about transmission, because in 1853, when Siebold wondered whether the pulsating tentacles of snails infected with Leucochloridium might attract predators, the first trematode life cycle had yet to be discovered. Indeed, what seems to be the earliest suggestion of parasite manipulation of a host was tied to possible trophic consequences. When we think of manipulative parasites, the challenge of getting to the host occupies much of our attention, although enhancing parasite survival and reproduction does not lag far behind. Within this broad description we can find a wealth of detail I reviewed much of that detail in a 2002 book ( Moore, 2002), and will describe a fraction of it here. In particular, what does the larger world of animal behavior tell us about how to go about seeking insights – or at least, what not to do? By asking questions about the sensory–perceptual world of hosts, we can identify those associations that hold the greatest promise for neuroethological studies of parasite-induced behavioral alterations, and those studies can, in turn, help guide our understanding of how parasite-induced alterations evolved, and how they are maintained. This paper will provide an overview of the conflicting (and coinciding) demands on parasite and host, using examples from a wide range of taxa and posing questions for the future. In other cases, the altered behavior has an almost curative, if not prophylactic, effect in those cases, the host benefits. Some cases of parasite-induced behavioral change are truly manipulative, with the parasite standing to benefit from the changed behavior. For instance, at first glance, the growing list of altered behaviors tells us very little about how those alterations happen, much less how they evolved. This is a simple enough concept, one that is now widely recognized as true, but if we move beyond that statement, the light that it casts on behavior fades quickly: the world of parasites, hosts and behavior is shadowy, and boundaries are ill-defined. ![]() An animal with a parasite is not likely to behave like a similar animal without that parasite. ![]()
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