Variation of parasite load and immune parameters in two species of New Zealand shore crabs

Abstract

While parasites are likely to encounter several potential intermediate hosts in natural communities, a parasite's actual range of compatible hosts is limited by numerous biological factors ranging from behaviour to immunology. In crustaceans, two major components of immunity are haemocytes and the prophenoloxidase system involved in the melanisation of foreign particles. Here, we analysed metazoan parasite prevalence and loads in the two sympatric crab species Hemigrapsus crenulatus and Macrophthalmus hirtipes at two sites. In parallel, we analysed the variation in haemocyte concentration and amount of circulating phenoloxidase (PO) in the haemolymph of the same individuals in an attempt to (a) explain differences in parasite prevalence and loads in the two species at two sites and (b) assess the impact of parasites on these immune parameters. M. hirtipes harboured more parasites but also exhibited higher haemocyte concentrations than H. crenulatus independent of the study site. Thus, higher investment in haemocyte production for M. hirtipes does not seem to result in higher resistance to parasites. Analyses of variation in immune parameters for the two crab species between the two sites that differed in parasite prevalence showed common trends. (a) In general, haemocyte concentrations were higher at the site experiencing higher parasitic pressure while circulating PO activity was lower and (b) haemocyte concentrations were influenced by microphallid trematode metacercariae in individuals from the site with higher parasitic pressure. We suggest that the higher haemocyte concentrations observed in both crab species exposed to higher parasitic pressure may represent an adaptive response to the impact of parasites on this immune parameter.

Interpreting immunological indices: The importance of taking parasite community into account. An example in blackbirdsTurdus merula

“…; Dittmer et al . ). However, interactions among different parasite species play a crucial role in determining the parasite community composition and relative abundance of each parasite species, as well as the host's immune responses.…”

“…This study not only highlighted the difficulties in drawing conclusions based on these data but also that ecoimmunologists must consider different species of parasites infecting the same host to understand the significance of a particular immune index. Such studies simultaneously investigating variation in multiple immune indices and relating them to the parasite community are still very rare (but see Lamkov a et al 2007;Roulin et al 2007;Dittmer et al 2011). However, interactions among different parasite species play a crucial role in determining the parasite community composition and relative abundance of each parasite species, as well as the host's immune responses.…”

Annotated checklist and genetic data for parasitic helminths infecting New Zealand marine invertebrates

“…References . Brockerhoff and Smales (2002); Dittmer et al (2011); Fredensborg and Poulin (2005b); Koehler and Poulin (2010); Latham and Poulin (2002a, 2002b, 2003); Poulin et al (2003).…”

Long-term change in the parasite burden of shore crabs ( Hemigrapsus oregonensis and Hemigrapsus nudus ) on the northwestern Pacific coast of North America

“…Hemigrapsus spp. crabs mount an immune challenge to infection by microphallid trematodes [39] that could be compromised by stressful environmental conditions. By contrast, rising temperatures can also lead to mismatches in host and parasite thermal performance that result in declines of parasite abundance [40].…”