¹ DEZFULI B.S., ¹ VOLPONI S. , ¹ BELTRAMI I. & ² POULIN R.

Intra- and interspecific density-dependent effects on growth in helminth parasites of the cormorant Phalacrocorax carbo sinensis

PARASITOLOGY 2002, 124

ABSTRACT - The action of intra- and interspecific competition, mediated by density-dependent effects on growth, was investigated among the three helminth species found in the alimentary tract of 104 cormorants, Phalacrocorax carbo sinensis. Intraspecific density-dependent effects on worm sizes were observed in the abundant nematode Contracaecum rudolphii, as shown by a negative correlation between mean worm size and intensity of infection. Higher intensities of infection by C. rudolphii were also associated with more variable worm sizes in the nematode Syncuaria squamata, suggesting a one-sided and density-dependent interspecific effect. There was also clear evidence of some form of negative interaction between the nematode S. squamata and the acanthocephalan Southwellina hispida from two fronts. First, there was a strong negative correlation between the intensities of infection of the two species across hosts. Second, sizes of worms of one species became more variable as the number of worms of the other species per host increased, and vice versa. This interspecific density-dependent effect on growth was thus apparently symmetrical. We also found evidence that worm size is a predictor of egg output in the three helminth species, indicating that intra- and interspecific density-dependent effects on growth can affect population dynamics in these worms. These results illustrate the complex nature of density-dependence in helminth growth, and how its effects can act both within and among species.

Key words: competition, egg output, Contracaecum rudolphii, size dimorphism, Southwellina hispida, Syncuaria squamata, variability.

Address:
¹ Dipartimento di Biologia, Università di Ferrara, Via Borsari 46, 44100 Ferrara, Italy
² Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand
* corresponding Author

Page created on 27-02-2002
by S. Volponi