Evolution of interspecific variation in size of attachment structures in the large tapeworm genus Acanthobothrium (Tetraphyllidea: Onchobothriidae)

Parasites have evolved a myriad of attachment structures closely adapted to their hosts and sites of attachment. Here, using members of the genus Acanthobothrium van Beneden, 1850 (Cestoda: Tetraphyllidea: Onchobothriidae), we (i) examined the influence of host body size and phylogeny, in addition to morphological features of these tapeworms, on the size of 3 structures used in attachment (bothridia, accessory suckers and hooks) by means of general linear models and phylogenetic-independent contrasts methods, and (ii) quantified the scaling exponents of relationships between size of attachment structures and tapeworm body size. Our results indicate that there exists a positive relationship, albeit not directly proportional, between size of attachment structures and Acanthobothrium spp. body size, and hook size and size of bothridia and accessory suckers. These results suggest that the resource investment in whole-body growth is greater than that in attachment structures, and that a greater investment in development of bothridia and accessory suckers is required to maintain an equivalent functional efficacy to hooks. In addition, host body size also influences, though less markedly, the size of attachment structures in Acanthobothrium spp. independently of parasite size itself. Acanthobothrium species have evolved a generalized mode of attachment that is successful in maintaining their position on various intestinal mucosal topographies across a variety of hosts exploiting different food resources.