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Host ploidy, parasitism and immune defence in a coevolutionary snail–trematode system
Author(s) -
OSNAS E. E.,
LIVELY C. M.
Publication year - 2006
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/j.1420-9101.2005.00994.x
Subject(s) - biology , ploidy , snail , parasite hosting , parasitism , host (biology) , zoology , asexual reproduction , freshwater snail , trematoda , ecology , helminths , genetics , gene , world wide web , computer science
We studied the role of host ploidy and parasite exposure on immune defence allocation in a snail–trematode system ( Potamopyrgus antipodarum‐Microphallus sp.). In the field, haemocyte (the defence cell) concentration was lowest in deep‐water habitats where infection is relatively low and highest in shallow‐water habitats where infection is common. Because the frequency of asexual triploid snails is positively correlated with depth, we also experimentally studied the role of ploidy by exposing both diploid sexual and triploid asexual snails to Microphallus eggs. We found that triploid snails had lower haemocyte concentrations than did diploids in both parasite‐addition and parasite‐free treatments. We also found that both triploids and diploids increased their numbers of large granular haemocytes at similar rates after parasite exposure. Because triploid P. antipodarum have been shown to be more resistant to allopatric parasites than diploids, the current results suggest that the increased resistance of triploids is because of intrinsic genetic properties rather than to greater allocation to defence cells. This finding is consistent with recent theory on the advantages of increased ploidy for hosts combating coevolving parasites.