How large is the hand in the puppet? Ecological and evolutionary factors affecting body mass of 15 trematode parasitic castrators in their snail host

Abstract

Parasitic castration is an adaptive strategy where the parasite usurps its host's phenotype, most notably the host's reproductive effort. Though castrators are loosely known to be large relative to their hosts (compared to typical parasites), their mass has rarely been quantified and little is known about size variation, even if such variation exists. By cross-sectioning snails, we examined intra-and inter-specific variation in the parasite/ host mass of 15 trematode species that castrate the California horn snail, Cerithidea californica. Trematode species occupied 14-39% (mean = 20.3%) of an infected snail's soft tissue mass. Intraspecific variation in castrator mass fluctuated with variables that covary with energy available for host reproduction. Specifically, trematode mass was 24% higher in summer than in winter, 15% greater in snails from intertidal flats than from tidal channels, and increased with host mass to the 1.37 power (a finding contrary to that previously documented for other types of parasites). Relative body mass differed across trematode species, varying interspecifically with: (1) taxonomic family, (2) host tissue use Electronic supplementary material The online version of this article ((larger species used more types of host-tissue), (3) position in the trematode interspecific competitive dominance hierarchy (the two most subordinate species were the largest, otherwise size tended to increase with dominance), and (4) type of host used by offspring (species whose offspring infect relatively predictably occurring benthic invertebrates were larger than those infecting transient vertebrates). Our findings suggest that ecological constraints and life history trade-offs between reproduction and survival influence the mass of these very large parasites.

Ecosystem energetic implications of parasite and free-living biomass in three estuaries

“…The larval parthenitae of 18 recognized trematode species parasitically castrated many of these snails, including almost all of the largest individuals. The trematodes average 22% of the total soft-tissue weight of individual infected snails 15 . In total, the trematode biomass in C. californica matched or exceeded the high winter biomass of birds and substantially exceeded their summer biomass (Fig.…”

Diversity increases biomass production for trematode parasites in snails

“…As presented in detail in Hechinger et al (2008), we studied the biomass of trematode parasite assemblages that castrate the California horn snail, Cerithidea californica (Haldeman 1840). We dissected 594 snails that were haphazardly collected from tidal channels and intertidal flats at Carpinteria Salt Marsh, CA, USA (34.408 N,119.538 W ), in winter and summer 2005.…”

“…We quantified trematode biomass (wet weight) in snails as detailed in Hechinger et al (2008). Briefly, we did so by (i) separating and weighing the infected regions of each snail (figure 1a), (ii) using serial cross sections (figure 1b) to quantify trematode tissue proportional volume in the infected regions, (iii) multiplying the trematode proportion by the mass of the infected region, and (iv) ensuring that tissue densities for trematode and snail tissue were at least approximately equal.…”

“…Because a single trematode infection theoretically uses all the resources (host reproductive effort) available for a parasitic castrator, it is unclear whether complementary mechanisms of resource acquisition among multiple trematode species could cause diversity to increase parasite biomass. However, recent analyses have indicated that trematode species differ in how they allocate resources (McCarthy et al 2002;Hechinger et al 2008). Also, trematode species can vary in spatial distribution within their host, i.e.…”

Subtle effect of Xenos vesparum (Xenidae, Strepsiptera) on the reproductive apparatus of its male host: Parasite or parasitoid?

“…Parasitic castrators (or sterilizers) are organisms that manage to exploit the reproductive pathways of the host for their own development and reproductive output: they do so by diverting energy from gonad development or by secreting castrating hormones (Kuris, 1974;Baudoin, 1975;Hechinger et al, 2009;Lefèvre et al, 2009a). Parasitic castrators can also influence host morphology, behaviour and the evolution of host life history traits (Lafferty, 1993a;Hiroki et al, 2004;Hughes et al, 2004;Beani et al, 2011).…”