Reduction and variability of trunk spines in the acanthocephalan Corynosoma cetaceum: the role of physical constraints on attachment

Abstract

Abstract. In this study, we investigated a functional trade‐off between trunk attachment and trunk‐spine development in the acanthocephalan Corynosoma cetaceum. The worms live attached to the stomach and upper intestine of their cetacean definitive hosts, using the proboscis and spiny foretrunk as the main holdfast; the spiny hindtrunk can also attach by bending ventrally. When the hindtrunk bends, ventral compression generates an anterior fold (AF) and a posterior fold (PF). A morphological analysis based on 7,823 individuals collected from 10 franciscana dolphins, Pontoporia blainvillei, revealed that spines were smaller and more variable in size and occurrence in the folds than on neighboring areas; the growth of fold spines seemed to be inhibited to various degrees. Spines were more reduced in the AF than in the PF, and spines of both folds were more reduced in females than in males. Patterns of reduction appeared to be directly related to the intensity of fold compression associated with hindtrunk bending. Fold compression could induce plastic inhibition of spine growth, and/or could make fold spines maladaptive, spines being reduced by natural selection. Apparently, fold spines neither contact the substrate, nor are they exposed to the environment when the hindtrunk attaches. Therefore, fold spines could have reduced, or lost, their primary function, at least in the definitive host. The reduction and variability of spines in C. cetaceum seem to be unique among Corynosoma species.

Corynosoma australe Johnston, 1937 and C. cetaceum Johnston & Best, 1942 (Acanthocephala: Polymorphidae) from marine mammals and fishes in Argentinian waters: allozyme markers and taxonomic status

“…Specimens of C. cetaceum examined in the present paper agree in general terms with the characteristics that define the species; however, some differences in the number of proboscis hook rows (20-21 versus 18-9) and in the number of hooks per row (13-15 versus 12-13 or 14-16) were observed. The ventrally transverse folds delimiting a blunt lobe between the fore-and hind-trunks in the female, described by Aznar et al (1999bAznar et al ( , 2002b, were also observed in cystacanths in the present study.…”

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

“…Being exposed to the strongest frictional drag, C. cetaceum exhibits not only the greatest development of Ds and VNR, but also the largest body spines of all Corynosoma species examined thus far [ 17 ]. As an interesting twist, females of C. cetaceum also have shorter bodies than males, contrary to most acanthocephalans [ 28 ], and are able to deeply fold the hindtrunk thanks to VNR contraction [ 29 ]. These features additionally reduce frictional drag, which helps females withstand the harsh microhabitat conditions in the stomach longer than males [ 14 ].…”

Patterns of trunk spine growth in two congeneric species of acanthocephalan: investment in attachment may differ between sexes and species

“…2 i.e. the disk border, the interfold area, and the posterior hind-trunk (see Aznar et al 2002 a for details). For brevity, we will refer to the spines from these sites as Spines 1, 2 and 3, respectively.…”

“…Acanthocephalans, in particular, have developed a proboscis armed with hooks that anchor to the gut of their definitive host (Taraschewski, 2000). Many species also have trunk spines that engage on the gut surface, sometimes playing a significant role in attachment (Van Cleave, 1952;Aznar et al 1999aAznar et al , 2002a. It has been argued that investment in these primary holdfast structures is optimized for the species of host and the particular microhabitat where each species of acanthocephalan lives (Poulin, 2007).…”