Definition of regional ostracod (Cytheridella) morphotypes by use of landmark-based morphometrics

Abstract

Geometric morphometric analyses were performed on the Neotropical ostracod Cytheridella including recent populations from Florida, Yucatán, Colombia, and Brazil. Generalized least-squares Procrustes analyses were applied to left and right valves of adult females and males and to A-1 to A-3 juveniles. The analyses show that the prevailing shape variability is in the outline of the valves. Further characters defining the variability range are the anterior pore conuli 2 and 4 (LM 2, LM 4) and the connection point between transversal sulcus and the extension of the posterior lobe (LM 6). Relative Warps Analysis enabled delineation of the whole-shape disparity and revealed a geographical pattern in the morphological variability that is apparent in adults and juveniles. Females show greatest morphological disparity, whereas juveniles are more variable on the population scale. Differences in hard- and soft-part morphology identify the specimens from Yucatán as new a morphospecies. Different hydrological or hydrochemical conditions may have led to the evolution of the new species. Cytheridella has occurred in the Neotropics since the Oligocene with a similar distribution to that in the Recent. Avian dispersal may repeatedly reintroduce C. ilosvayi to Yucatánian populations possibly explaining the sympatric occurrence of 2 Cytheridella morphospecies. Our findings promote the benefit of investigating morphological variability quantitatively to detect regional morphotypes and ultimately to contribute to evaluations of biodiversity.