Thirty-seven-collar-spined echinostomes in North American populations of pulmonates: The genetic and life history implications
Abstract
Parasites are thought to influence a variety of ecological and evolutionary processes in host species. Digenetic trematodes, a diverse group of parasitic flatworms, alter the genetic and life history characteristics of their hosts. However, although the Subclass Digenea is composed of 90 different families of flukes, the majority of studies examining the impact of trematodes on host traits involve species from less than one-tenth of these families. Utilization of such a select group of parasites could skew our understanding of parasite-host interactions. Members of the Family Echinostomatidae are often among the most frequently collected trematodes in both vertebrates and invertebrates in North America. Thus I used two 37-collar-spined echinostome species, Echinostoma revolutum and Echinostoma trivolvis, in studies assessing their genetic diversity and investigating the influence of parasitism on the life history traits of their host snails. I found that E. revolutum, although previously thought to exist only in Eurasia, is endemic within natural populations of L. elodes snails in Indiana, USA. This conclusion is based upon analysis of morphological characteristics of adult and larval stages of the parasite, as well as host-use criteria. I compared the rDNA ITS nucleotide sequences of several isolates of North American E. revolutum and E. trivolvis to previously published sequences. I detected significant levels of intraspecific genetic diversity in these comparisons and used this data to construct a phylogenetic hypothesis for this group of trematodes. Lastly, experimental infections demonstrated that both E. revolutum and E. trivolvis alter the expression of life history traits of their first-intermediate host snails. This influence included: cessation of host reproduction concurrent with patency and the absence of a fecundity compensation response prior to patency; increased host growth during the early stages of the infection; and increased mortality later in the infection. In the case of E. revolutum parasitism of L. elodes snails mortality was size- selective favoring larger individuals. The combined effects of increased host growth and size-selective mortality provide an explanation for the frequent occurrence of gigantism among naturally infected snails.
Degree
Ph.D.
Advisors
Minchella, Purdue University.
Subject Area
Ecology|Zoology|Genetics
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