A model for studying isolation mechanisms in parasite populations—the genus Lepeophtheirus (Copepoda, Caligidae). J Exp Zool

Laboratoire de Parasitologie Comparée, UA 698, CNRS, Université des Sciences et Techniques du Languedoc, Montpellier, France.
Journal of Experimental Zoology 05/1990; 254(2):207-14. DOI: 10.1002/jez.1402540213
Source: PubMed


In the Mediterranean, the parasitic copepod Lepeophtheirus thompsoni Baird, 1850 specifically infests turbot (Psetta maxima L., 1758), whereas L. europaensis Zeddam, Berrebi, Renaud, Raibaut, and Gabrion, 1988 infests brill (Scophthalmus rhombus L., 1758) and flounder (Platichthys flesus L., 1758). Experimental infestation of turbot by copepods from each of the three fish species showed an absence of any physiological incompatibility preventing natural development of the two parasite species, at least on one host species, i.e., the turbot. Moreover, interspecific hybrids were obtained experimentally, which implies that 1) there is no strict genetic barrier between the two species and 2) the natural prezygotic isolation results from a choice of the most favorable habitat. We discuss the origin and possible consequences of the presence, in the Mediterranean, of L. europaensis on brill and flounder, two hosts separated by their taxonomic status and ecobiology.

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    • "ntrast , S . andegavinus showed no initial choice for any of the two host species , which were seemingly colonized at random . Thus , differences in strength of host preference were detected between the two parasite species . Similar divergent patterns of host preference in closely - related species have been observed in various parasite taxa ( de Meeûs et al . 1990 , 1995 ; Le Brun et al . 1992 ; Du Preez and Kok 1997 ; Du Preez et al . 1997 ; Thresher et al . 2000 ) As described above , preference should evolve according to parasite fitness and dispersal ability . In mites , difference in host preference should occur because the strength of one or both of these conditions ( parasite population dy"
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    ABSTRACT: In parasites, host specificity may result either from restricted dispersal capacity or from fixed coevolutionary host-parasite adaptations. Knowledge of those proximal mechanisms leading to particular host specificity is fundamental to understand host-parasite interactions and potential coevolution of parasites and hosts. The relative importance of these two mechanisms was quantified through infection and cross-infection experiments using mites and bats as a model. Monospecific pools of parasitic mites (Spinturnix myoti and S. andegavinus) were subjected either to individual bats belonging to their traditional, native bat host species, or to another substitute host species within the same bat genus (Myotis). The two parasite species reacted differently to these treatments. S. myoti exhibited a clear preference for, and had a higher fitness on, its native host, Myotis myotis. In contrast, S. andegavinus showed no host choice, although its fitness was higher on its native host M. daubentoni. The causal mechanisms mediating host specificity can apparently differ within closely related host-parasite systems.
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    • "All three hosts are of northern origin (Quignard 1972). They colonized the Mediterranean Sea during the course of the last glaciation events, during which £ounder may have lost their original parasites and become infected with L. europaensis from brill (De Meeuª s et al. 1990). The absence of L. europaensis on £ounder in the Atlantic suggests that parasite competition has a role in determining the host range for these copepods (De Meeuª s et al. 1995), but there is no direct evidence for the e¡ect of such competition. "
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    ABSTRACT: Lepeophtheirus thompsoni and Lepeophtheirus europaensis are two parasitic copepods naturally isolated on their sympatric hosts, i.e. turbot (Psetta maxima L.) and brill (Scophthalmus rhombus L.), respectively They are able to meet, mate and hybridize on turbot experimentally but they are naturally prevented from doing so by a strong host preference when given a choice. Theory suggests that such a pattern is possible, but only under conditions of competition for the resource. In the present study the attachment rates of the two copepods were studied experimentally under various conditions of competition, infectious dose and number of available hosts. The results suggest a greater sensitivity to competition for the generalist species L. europaensis than for the specialist L. thompsoni, which is in agreement with theoretical predictions.
    Full-text · Article · Nov 2000 · Proceedings of the Royal Society B: Biological Sciences
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    • "After settlement, viability selection occurs, followed by the production of the next generation's propagules, which again disperse. This life-cycle corresponds to many parasites (parasitic copepods: Kabata, 1981; Raibaut, 1985; de Meeûs et al., 1990), marine species (polychaetes: Doyle, 1975; bivalves: Bayne, 1976; ascidians: Stoner, 1994) or species producing a large number of highly dispersible propagules (procaryotes, fungi, plants, protozoa) (e.g. Bazzaz, 1991, for plants). "
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    ABSTRACT: The stable co-existence of two haploid genotypes or two species is studied in a spatially hetero-geneous environment submitted to a mixture of soft selection (within-patch regulation) and hard selection (outside-patch regulation) and where two kinds of resource are available. This is analysed both at an ecological time-scale (short term) and at an evolutionary time-scale (long term). At an ecological scale, we show that co-existence is very unlikely if the two competitors are symmetrical specialists exploiting different resources. In this case, the most favourable con-ditions are met when the two resources are equally available, a situation that should favour generalists at an evolutionary scale. Alternatively, low within-patch density dependence (soft selection) enhances the co-existence between two slightly different specialists of the most avail-able resource. This results from the opposing forces that are acting in hard and soft regulation modes. In the case of unbalanced accessibility to the two resources, hard selection favours the most specialized genotype, whereas soft selection strongly favours the less specialized one. Our results suggest that competition for different resources may be difficult to demonstrate in the wild even when it is a key factor in the maintenance of adaptive diversity. At an evolutionary scale, a monomorphic invasive evolutionarily stable strategy (ESS) always exists. When a linear trade-off exists between survival in one habitat versus that in another, this ESS lies between an absolute adjustment of survival to niche size (for mainly soft-regulated populations) and absolute survival (specialization) in a single niche (for mainly hard-regulated populations). This suggests that environments in agreement with the assumptions of such models should lead to an absence of adaptive variation in the long term.
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