Corynosoma cetaceumin the Stomach of Franciscanas,Pontoporia blainvillei(Cetacea): an Exceptional Case of Habitat Selection by an Acanthocephalan

Abstract

Adult acanthocephalans are typically found in the intestine of vertebrates, where they can readily absorb nutrients. However, Corynosoma cetaceum has been frequently reported in the stomach of cetaceans from the Southern Hemisphere. The ecological significance of this habitat was investigated by examining data on number, sex ratio, maturity status, biomass, and fecundity of C. cetaceum in different parts of the digestive tract of 44 franciscanas Pontoporia blainvillei. Individual C. cetaceum occurred in the pyloric stomach (PS) and, to lesser degrees, in the duodenal ampulla (DA) and the main stomach (MS). Females outnumbered males in all chambers, although the sex ratio was closer to 1:1 in the MS; there also was a higher proportion of nongravid females, with a smaller biomass in the MS than in the PS and the DA. This evidence suggests that cystacanths are released from prey tissues in the MS, where entire prey are reduced to semi-fluid chyme. The 3 chambers harbored gravid females that did not differ significantly in mean biomass or fecundity. The maturity status of females was nearly identical between the PS and the DA. In the MS, the higher proportion of non-gravid females is probably due to the occurrence of newly recruited females to this site. Mean biomass and fecundity of gravid females covaried strongly and positively among chambers within hosts. These results suggest that there are no major differences between the 3 chambers with respect to the suitability for reproduction by C. cetaceum. However, although the MS is the largest chamber, it harbored the smallest number of gravid females. Interestingly, worms were largely restricted to the aboral portion of the MS, a sheltered region where a concentration of chyme, and thus nutrient availability, likely occurs. Linear distribution differences of gravid female C. cetaceum at increasing intensities suggest that reproductive females occupy chambers according to available space. In summary, the stomach should be considered the main habitat for C. cetaceum. The choice of this habitat is puzzling because other Corynosoma species occur in the intestine, and because the stomach of cetaceans is not an absorptive site.

GASTROINTESTINAL HELMINTHS OF THE FRANCISCANA Pontoporia blainvillei (MAMMALIA: CETARTIODACTYLA) IN THE NORTHERN COAST OF RIO GRANDE DO SUL STATE, SOUTHERN BRAZIL

“…The acanthocephalan C. cetaceum is known to infect mainly the pyloric stomach of P. blainvillei (Aznar et al 1995, Andrade et al 1997. In the present study, C. cetaceum had lower prevalence and mean intensity of infection levels than those reported for the southern coast of RS (Andrade et al 1997) (Tables 4 and 5), Uruguay and Argentina (Aznar et al 1995(Aznar et al , 2001. Possibly, these observed differences are related to a low availability of intermediate hosts for this parasite in the northern RS.…”

Evaluation of three methods for biomass estimation in small invertebrates, using three large disparate parasite species as model organisms

“…Direct biomass estimates of the specimens were used as a benchmark for the other methods, enabling quantifying the error associated with indirect methods. Mean biomass was estimated using the method described in the literature 16 . Since specimens had been stored in 70° ethanol for 10–30 years, they were placed in 0.9% saline solution (9 g NaCl per 1 L distillated water) for 1 to 5 days to allow the tissues to re-hydrate.…”

“…Invertebrates are often the cornerstone of ecosystems 12 , 13 and recent studies have shown that their biomass is greater than that previously thought 14 , 15 . Different methods have been proposed to study the allocation of biomass between various taxonomic groups of invertebrates, mostly arthropods, but also considered groups include sponges, cnidarians, platyhelminths, annelids, acanthocephalans, nematodes, molluscs, nemerteans, echinoderms, bryozoans and urochordates have been considered 14 , 16 – 24 . As direct measurements of biomass of small invertebrates (i.e.…”

From mammals back to birds: Host-switch of the acanthocephalan Corynosoma australe from pinnipeds to the Magellanic penguin Spheniscus magellanicus

“…Trunk length, disk diameter, and body volume (assuming a conical shape) of these specimens were measured following Hernández-Orts et al [ 46 ]. Fecundity was estimated as the number of acanthors per female [ 47 ] in 10, 30 and 30 gravid females, randomly selected, from 4 penguins, 3 sea lions and 4 fur seals, respectively. The contents of each worm were washed into a beaker and the volume made up to 10 ml, then continually agitated using a magnetic stirrer for at least 5 min.…”

“…Fully developed eggs were distinguished by having a completely formed acanthor inside. Mean numbers of each egg type obtained from these samples were then extrapolated to the total volume [ 47 ].…”