Clone-specific immune reactions in a trematode-crustacean system

Abstract

Variability of immune responses is an essential aspect of ecological immunology, yet how much of this variability is due to differences among parasite genotypes remains unknown. Here, variation in immune response of the crab, Macrophthalmus hirtipes, is examined as a function of experimental exposure to 10 clonal cercarial lineages of the trematode Maritrema novaezealandensis. Our goals were (1) to assess the variability of the host immune reaction elicited by 10 parasite clones, (2) to test if the heterozygosity-fitness correlation, whereby organisms with higher heterozygosities achieve a higher fitness than those with lower heterozygosities, applies to heterozygous parasites eliciting weak immune responses, and (3) to see how concomitant infections by other macroparasites influence the crab's immune response to cercariae. Parasite clones were distinguished and heterozygosities calculated using 20 microsatellite markers. We found that exposure to cercariae resulted in increased haemocyte counts, and that although interclonal differences in immune response elicited were detected, parasite heterozygosity did not correlate with host immune response. Additionally, the presence of other pre-existing parasites in hosts did not influence their immune response following experimental exposure to cercariae. Overall, the existence of variability in immune response elicited by different parasite clones is promising for future ecological immunology studies using this system.

Specific Gene Expression Responses to Parasite Genotypes Reveal Redundancy of Innate Immunity in Vertebrates

“…We also have little knowledge on the degree of discrimination that the innate immune system can achieve, although some phenotypic studies suggest distinction among parasite genotypes in three-spined sticklebacks, rainbow trout and monarch butterflies [5] [6] [7], but also in a wide range of other species as reviewed by Lazzaro & Little [8]. In line with these findings, host immune reactions were found to be parasite-genotype specific in crabs [9] and gene expression differences could be attributed to host-parasite genotype interactions in bumblebees [10]. But the genes responsible for host immune reactions to parasite genotypes have yet to be shown in vertebrates.…”

“…This parasite has a complex life cycle, using freshwater snails and fish as intermediate hosts, before reproducing sexually in piscivorous birds [17]. Since digenean trematodes undergo clonal expansion in the snail host, they are ideal candidates to investigate genotype-specific performance of parasites [9]. After penetration of the skin and migration through tissues and blood vessels, larvae of D. pseudospathaceum invade the fish’s eye lens within 24 h to evade the adaptive immune system [17].…”

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

“…References . Dittmer et al (2011); Fredensborg and Poulin (2005a, 2005b); Keeney et al (2007a); Koehler and Poulin (2010, 2012); Leung, Donald, et al (2009); Martorelli et al (2004); Poulin et al (2003).…”

Somatic Dimorphism in Cercariae of a Bird Schistosome

“…The most intriguing example of an extreme somatic polymorphism in clonal trematode larval stages is the existence of reproductive and soldier redial castes differing in morphology and size, in addition to their function, behavior, and site location within the snail body (e.g., [ 23 , 24 , 25 ]). The use of experimental and/or genotyping molecular methods enabled phenotypic variation studies also in clonal cercariae such as output rates, activity and survival patterns, photo- and geotaxis behavior, or infection success [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. As mammalian and bird schistosomes serve as model organisms for studying various biological and ecological aspects of parasitism and host–parasite interactions, research on their polymorphism is more advanced than in other trematode groups, focusing on host-induced morphometrical alterations (e.g., [ 33 , 34 ]), genetic diversity of different developmental stages (e.g., [ 35 , 36 , 37 , 38 , 39 ]), or a compatibility polymorphism in snail-schistosome interactions (reviewed in [ 40 , 41 ]).…”