Tracing the routes of speciation in Mesocyclops woutersi - superspecies [Copepoda: Cyclopoida]

Morphological comparisons among three allopatric representatives of the Mesocyclops thermocyclopoides-group - Mesocyclops parentium sp. nov. (southern India, Sri Lanka), Mesocyclops woutersi Van de Velde, 1987 (New-Guinea-Indochina-Ryukyu Is.) and Mesocyclops dissimilis Defaye et Kawabata, 1993 (Honshu, Kyushu Is.) - revealed a very slight degree of divergence, as compared to that of sympatric species of the group. Clear-cut differences in some characters (presence/absence of spinules at base of antero- and posterolateral furcal setae, hair rows on dorsum of pediger 5) do nevertheless indicate genetic discontinuity among the species. The separation of M. dissimilis is also expressed in quantitative traits, some of them (increase of relative length of the apical exopod and baseoendopod setae of leg 5, the dorsal furcal setae and third endopodal segment of leg 4) being very probably adaptations for pelagic life. Mesocyclops guangxiensis Reid et Kay, 1992 is synonymyzed with M. woutersi Van de Velde, 1987, syn. nov. Parsimony, zoogeographical and ecological considerations leave two hypotheses of relationships within the trio likely: either the ancestor of the group was M. parentium-like; or the ancestor was different from all three.