Biological and morphological aspects ofBranchiobdella italica(Annelida: Clitellata) in a native crayfish population of central Italy

Abstract

The present study aimed to improve the knowledge of the biology of Branchiobdella italica, a symbiontic worm on the whiteclawed crayfish Austropotamobius pallipes, with particular attention to the feeding strategy, infestation and colonization ability, and morphology. Branchiobdellids occurred most frequently on adult crayfish rather than juveniles, due to the larger size of the former that permit a higher colonization by epizoic organisms, and to the high moult rate of smaller crayfish. We did not observe massive infestations of branchiobdellids, and the few specimens found do not seem to influence crayfish health. The higher occurrence of branchiobdellids took place on the A. pallipes carapace where worms find trophic resources. Gut content analysis of B. italica showed a generalist feeding strategy. The presence of fungal hyphae found within the gut of B. italica could lead us to infer that branchiobdellids could contribute to limit the fungal growth on the exoskeleton or on eggs of their host. Histological analysis of reproductive traits does not show structural differences from those referred to previous descriptions; the observation of one or two ciliated funnels (not always two), and the absence of hooks or spines on the penis surface, represent the main exceptions. Additional studies are needed to assess the true nature of the symbiosis between branchiobdellids and their hosts.

Preliminary data on the distribution, morphology and genetics of white-clawed crayfish and on their ectosymbionts in Lunigiana (Tuscany, Italy)

“…Some species of branchiobdellidans can positively influence their hosts' body size and mass (Keller, 1992;Brown et al, 2002;DeWitt et al, 2013;Vedia et al, 2016). On the contrary, other species, when occurring at high density, can show parasite habits by consuming host tissues and thus affecting crayfish growth (Scalici et al, 2010a;Brown et al, 2012;Skelton et al, 2013;Skelton et al, 2016). On average, branchiobdellidan worms occurred at high density on Verdesina crayfish, which showed smaller CL values when compared to those from the Civasola stream.…”

“…On average, branchiobdellidan worms occurred at high density on Verdesina crayfish, which showed smaller CL values when compared to those from the Civasola stream. Although we cannot rule out other hypotheses, such as those above mentioned, we tentatively suggest that B. italica could act as parasite on A. italicus, with the abundance of branchiobdellidans either directly affecting host growth (Scalici et al, 2010a;Brown et al, 2012;Skelton et al, 2013;Skelton et al, 2016) or indirectly decreasing the fitness of the largest individuals.…”

“…Nevertheless, the occurrence of Branchiobdellida in only one of the two streams deserves some attention. Branchiobdellidans are obligate ectosymbionts of crayfish and, depending on different environmental conditions, they can act as commensals, mutualists or parasites (Scalici et al, 2010a;Brown et al, 2012;DeWitt et al, 2013;Skelton et al, 2013;Vedia et al, 2014;Skelton et al, 2016;Vedia et al, 2016). Some species of branchiobdellidans can positively influence their hosts' body size and mass (Keller, 1992;Brown et al, 2002;DeWitt et al, 2013;Vedia et al, 2016).…”

Annelid symbiont assemblage and European stone crayfish − a deterministic relationship with implications for conservation management

“…Recent studies indicate that the relationship between Branchiobdellida and their hosts is highly complex. Due to their larger body surface and lower moulting rate, adult crayfish specimens, for instance, display higher infestation rates than young ones (Scalici et al, 2010;Vedia et al, 2016). Moreover, a link between the Branchiobdellida community and the hosts ontogeny was suggested, as adult North-American crayfish Cambarus sciotensis showed not only a higher Branchiobdellida diversity, but also were inhabited by Branchiobdellida species with larger body sizes than young specimens (Skelton et al, 2016).…”

Molt and gastroliths inAustropotamobius pallipes(Lereboullet, 1858)

“…Ecdysis seems not only to be an important phenomenon for growth but also for the sanitary state of crustaceans. In fact, after molting, crayfish have the opportunity to leave parasites (Gherardi et al, 2002;Scalici et al, 2010b), so that the latter do not damage integument tissues. The ecdysis cycle determines the typical stepwise growth pattern of crustaceans, sometimes making studies on the population structure and dynamics hard when non-invasive marking methods are used (Scalici et al, 2010a).…”