Ref ID : 7660
Jacques Berger and George Hatzidimitriou; Multivariate Morphometric Analyses of Demic Variation in Ancistrum mytili (Ciliophora: Scuticociliatida) Commensal in Two Mytilid Pelecypods. Protistologica XIV(2):133-153, 1978
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Having previously described the somatic morphology and morphogenesis of the widespread commensal scuticociliate, Ancistrum mytili, we now have analyzed by uni- and multivariate statistical methods the morphometric variability of a constellation of taxonomic attributes (characters) in several populations of this species from the northeast Atlantic O. This study was undertaken to elucidate the mechanisms of incipient speciation (adaptive radiation) in sexually reproducing ciliates inhabiting invertebrates. Ciliates were collected from two common species of mussels, Mytilis edulis and Modiolus modiolus (Pelecypoda, Filibranchia), from several localities off the Canadian and American coasts. All measurments were made on either Chatton-Lwoff or protargol-impregnated interphasic specimens. Principal components as well as multiple and stepwise discriminant analyses of 20 continuous and one discrete (meristic) attribute have unequivocally confirmed the presence of three morphologically distinguishable sympatric "forms" within A. mytili. These forms differ in somtic size and number of kineties. ANOVA and non-parametric univariate analysis demonstrate that significant variation exists among ten monodemes from Modiolus modiolus. Data describing xeno- and topodemic variability in several important taxonomic attributes are also presented for A. mytili. The evolutionary and systematic implications of demic variation in A. mytili are discussed. Emphasis is placed on a caudal analysis of demic variation. Comparison of the relative variability (C.V.) within vs. that present among monodemes for 25 attributes indicates that the Kluge-Kerfoot phenomenon exists in A. mytili. The nomenclatural history of A. mytili's confusion with other so-called species of Ancistrum is reviewed. Based on our demic and taxonomic analyses, we synonomize A. modioli Raabe, 1970, with A. mytili. The morphological attributes that define this species and each of its three "forms" as well as the evolutionary, systematic, and nomenclatural inferences of our study of this polymorphic species are discussed in detail.