Morphometric Methods for Applied Ostracodology: Tools for Outline Analysis of Nonmarine Ostracodes

Abstract

Morphometric techniques for the analysis of shape change in organisms have experienced a noteworthy development in the last decade. But despite the significant contributions that ostracodologists made to the field, their use in standard ostracode research is far from common. This contribution stresses the usefulness of morphometric methods to describe ostracode valve outlines and to summarize shape changes cued by environmental factors. Focus is on nonmarine ostracodes which are generally poorly ornamented so that their carapaces offer few landmarks for characterization of morphological change. Out of several alternatives three techniques for shape analysis are applied here: the B-splines method for approximative description of ostracode contours, Elliptic Fourier Analysis (EFA) and a Generalized (Resistant Fit) Procrustes Analysis. B-splines method is presented here for the first time within a biological framework and both its mathematical basis and practical usage are discussed. Additionally a computer program, Morphomatica, developed for performing B-splines analyses of ostracod outlines is briefly documented.Three case studies exemplify here how morphometric analysis might help either to detect environmental influences in ostracode shape or to show how morphological diversity of ostracode valve reflects environmental change. First, morphological variability within a clonal lineage of Heterocypris barbara (Gauthier and Brehm) is shown to be related to environmental variables (mainly temperature) when raised under controlled conditions in the lab. Second, carapace variability at the population level is explored in a widely distributed species (Limnocythere inopinata Baird) sampled from distant localities. Morphometric analyses illustrate how such variability is not related to geographic distance but to environmental conditions. Finally, patterns of temporal change in morphological diversity of a widely distributed ostracode group, the Candoninae, are elucidated by using the B-splines method combined with multivariate statistical analysis.It is concluded that morphometric methods deserve to be included in the methodological toolbox of practicing ostracodologists as they can provide useful information in ecological and paleoecological research.