Habitat selection by Corynosoma australe (Acantocephala) in the intestine of the Southern Fur Seal, Arctocephalus australis.

AZNAR, F. J.; CAPPOZZO, H.L; RAGA, J. A.

Bulletin of the Scandinavian Society for Parasitology

NFI

Lugar: Bergen; Año: 2003 vol. 12 p. 29 - 31

0803-4907

We investigated the habitat selection by Corynosoma australe in the intestine of 28 Southern fur seals (>2 yrs old) harvested by authorized hunters in Uruguay in August 1990-91. The intestines (mean length  SD: 17.4  4.4 m) were divided into 5 equal sections, their contents being flushed through a sieve 0.2 mm mesh. C. australe was the only helminth species found. All hosts were heavily infected (mean intensity  SD: 2,561  2,178; median: 1,557). Intestine length (IL) was a strong predictor of intensity (I) (best model: I= 0.42 IL3 -52.2, r2 = 0.746). The percentage of juvenile females also was mainly accounted for by IL (linear relationship, partial r= 0.508). Apparently, seals are continuously infected in the winter and IL seems to be a good indicator of recruitment. Worms were found throughout the intestine, but sections 1-2 contained less than 5 % of the population. Intensity significantly differed between all sections; the concordance of differences across hosts indicated a strong site fidelity for the medium and, especially, posterior intestine. The distribution of males was significantly more anterior than that of females, so was the distribution of juvenile females compared with that of gravid females. The overall sex ratio was strongly biased against males, but the proportion of males significantly decreased from section 1 to 5. We interpret that cystacanths (with a sex ratio likely close to 1:1) excyst in the stomach, then pass along the anterior intestine to establish mainly in the medium-posterior intestine, where they develop into adults and copulate. Adult males would be lost disproportionately in the posterior intestine because of their shorter life span. The niche of gravid females significantly expanded with intensity; the position of their median worm also was negatively correlated with intensity, but the correlation actually resulted from a decrease of variability in position at higher intensities. The distribution of the reproductive population may spread and become more predictable mainly because there are more recruited individuals filling an apparently vast suitable habitat, i.e., the medium-posterior intestine