Trunk spines in cystacanths and adults of Corynosoma spp. (Acanthocephala): Corynosoma cetaceum as an exceptional case of phenotypic variability

Abstract

Adults of the acanthocephalan Corynosoma cetaceum deeply attach to the stomach of dolphins using the proboscis and its spiny foretrunk as a disk while the spiny hindtrunk bends to also embed its ventral spines. During deep attachment, two ventral folds of tegument, anterior and posterior, are created. Spine growth is inhibited to a variable degree in folds, generating an extraordinary phenotypic variability, with most individuals, especially females, having folds partially or totally devoid of spines. Little is known on how this variability is generated and why it is not apparently found in other Corynosoma spp. In this paper, we examined the trunk armature of 77 and 388 cystacanth larvae of C. cetaceum and C. australe, respectively, from teleosts, and over 8800 adult specimens of C. australe, C. bullosum, C. cetaceum, C. strumosum, C. villosum and C. wegeneri from marine mammals. Cystacanths and adults of C. cetaceum exhibited the same range of fold spine reduction and variability, suggesting that they are generated prior to the adult stage (i.e., before spines are functional) and do not result from phenotypic plasticity. The other Corynosoma species analyzed created only the anterior fold during deep attachment, but it was always spined. Females of C. cetaceum had significantly larger foretrunk and hindtrunk spines than the other species and likely suffer stronger fold compression during deep attachment. The exceptional colonization of a harsh microhabitat, the stomach, could have generated a trade-off in C. cetaceum, which must bend the trunk to attach (as other Corynosoma spp.) but must also produce large spines that, in the folds, presumably are maladaptive and must be reduced.

Morphology, performance and attachment function in Corynosoma spp. (Acanthocephala)

“…In deeply attached worms, this expansion would produce a ‘wedge’ effect against the gut wall because the disk is literally buried in the mucosa ([ 16 ]; F.J. Aznar, unpublished observations). Not surprisingly, disk spines are larger on the border than anywhere else on the disk [ 17 ].…”

“…Upward and downward movements of the hindtrunk are potentially related with at least two functions, i.e. copula, and attachment of the hindtrunk, respectively ([ 3 , 17 , 18 ], see below).…”

“…The 13 species of Corynosoma included in this study encompass the widest variation in body morphology found within this genus. Trunk size differed by an order of magnitude between the smallest ( C. australe and C. semerme ) and the largest ( C. bullosum and C. enhydri ) species [ 17 ] (Fig. 3 ).…”

“…At least in females of C. cetaceum , the VNR assists the animal in performing a downward movement to attach a relatively thick and short hindtrunk [ 3 , 17 , 18 ]. During the process, the hindtrunk somewhat shortens due to ventral folding, and the whole ventral spiny surface contacts the substratum ([ 17 ], Additional file 6 : Video S4). In C. hamanni and C. pseudohamanni , the hindtrunk is also short and wholly covered by spines, thus one could postulate a similar performance of the VNR.…”

Morphological and molecular characterization of two new species ofAndracantha(Acanthocephala: Polymorphidae) from New Zealand shags (Phalacrocoracidae) and penguins (Spheniscidae) with a key to the species

“…Nevertheless, the presence or absence of fields of genital and trunk spines, and their distribution, have been used in helping to characterize the species of Andracantha (see for example Schmidt, 1975; Aznar et al ., 2006; Monteiro et al ., 2006). The bare area on the ventral trunk of A. sigma between the posterior field of disc spines and the ventral field of spines may be an adaptive feature, improving attachment to the host (Aznar et al, 2016). The presence of a sparse scattering of small spines across otherwise bare fields of trunk spines has been noted as a distinguishing character for A. baylisi, A. leucocarboi and A. sigma (Zdzitowiecki, 1986; this study).…”