The shaping of a species: the Azorian Drouetia Gude (Pulmonata: Zonitidae: Oxychilus) as a model

WA Museum Records and Supplements | Updated 7 years ago

ABSTRACT – The endemic Azorian zonitid subgenus Orouetia Gude, 1911 is spread throughout the archipelago and shows a wide range of variability. The spatial distribution of the Azores islands and their geomorphological history provide a privileged research ground to assess the interactions of isolation and time on the emergence of those variability patterns and thus to infer on the speciation process. Special attention is given to volcanic activity as a disturbing factor of the populational integrity.

From the observed patterns of distribution of intra- and interspecific shell morphology and anatomical variability in Orouetia the following speciation scenario may be advanced: Stage one: demic (allotopic) variability; it is postulated that volcanic instability (frequent cyclic eruptions) and intense erosion (deep ravines) create temporary isolates that (7200 yrs) later merge into a larger, genetically richer population. Stage two: close syntopic (interspecific) variability; it is postulated that short-term (>2,000 ys) volcanic stability contributes to consummate speciation. Stage three: extreme syntopic (interspecific) variability; it is postulated that long-term volcanic stability (>1 Mys) leads to supra-specific differentiation.