Consistent sexual differences in trunk spine growth between cystacanths and adults of two species of Corynosoma (Acanthocephala: Polymorphidae): do each sex exhibit a different strategy to attach to the definitive host?

HERNÁNDEZ-ORTS, J.S., E.A. CRESPO, J.A. TIMI, J.A. RAGA & F.J. AZNAR

Melbourne, Australia

Congreso; THE XIITH INTERNATIONAL CONGRESS OF PARASITOLOGY (ICOPA); 2010

It is generally assumed that the proboscis and trunk armature (if present) of  acanthocephalans are fully developed at the juvenile (cystacanth) stage in the intermediate / paratenic hosts. Primary investment in attachment devices would maximize the likelihood of an effective attachment just after recruitment to the gut of the definitive host. Extensive evidence suggests that armature patterning is determined prior to the adult stage, but whether or not growth of armature occurs in the definitive host is still an open question. We compared size differences of trunk spines between cystacanths and adults of two polymorphid species, Corynosoma australe and C. cetaceum collected from paratenic hosts (fish) and definitive hosts (otariids and cetaceans, respectively) off the Argentine coast. Spines were measured at three points: the disk border, the anterior hindtrunk and the posterior hindtrunk. Our results revealed that (1) the trunk was significantly larger in adults than in juveniles of both species, regardless of sex; (2) no significant differences were found between the size of spines in juvenile and adult males of any species; (3) in females of C. australe, disk spines were significantly larger in adults than in juveniles and (4) in females of C. cetaceum, spines at the 3 points were significantly larger in adults. Adult females of Corynosoma live longer than males and carry the (presumably heavy) load of the offspring. Therefore, it is possible that females experience stronger selective pressures to develop more plastic responses avoiding dislodgment from the gut. Interestingly, the effect is more apparent in C. cetaceum, which inhabits the stomach (a site with an intense physical disturbance), than in C. australe, which lives in the intestine.