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Ontogeny of Bradleya normani (Brady): Shape Analysis of Landmarks

1988; Elsevier BV; Linguagem: Inglês

10.1016/s0920-5446(08)70184-5

2352-2852

Roger L. Kaesler, David William Foster,

Marine and fisheries research

The choice of a method of shape analysis is limited by the purpose of the research to which the method is to be applied. Three areas of investigation to which shape analysis lends itself are describing morphology; studying environmental, geographical, or stratigraphical change of morphology; and comparing similarity of morphology. Selection of a method is further dependent on whether the shapes of the objects being studied are defined by homologous landmarks or are defined by outlines. We encourage investigators first to ask biologically important questions and then to select the appropriate method of shape analysis. Although these caveats may seem unnecessary, we believe that too little attention has been directed toward applications in the rush to develop new methodologies. Bradleya normani (Brady) is unusual among species of its genus because it lives in relatively shallow water. Its study may provide a better understanding of deep-water species of Bradleya that have been used extensively in paleoceanography. Our understanding of the evolution of ostracodes in general would be enhanced by investigation of heterochrony, but especially little is known of the ontogeny of deep-sea ostracodes because their immature instars are comparatively rare. Homologous landmarks on the carapaces of adults and five instars of B. normani (Brady) were studied by traditional multivariate morphometric methods that are orientated toward graphical representation of results, by tensor analysis, and by robust regression analysis. Multivariate discriminant function analysis and ordination by nonmetric multidimensional scaling provide useful graphical summaries of overall morphological difference, but they do not show directly in which areas of the carapace the change occurs. Tensor analysis gives a useful graphic and quantitative impression of ontogenetic changes of shape of regions of the carapace that are bounded by landmarks. Robust regression analysis focuses attention on changes of the relative positions of the landmarks themselves rather than on changes of shape of the regions bounded by landmarks. It also provides a numerical estimate of change between selected pairs of indivials, the average residual length. In general, different methods of analysis showed the same progressive change of shape from the youngest instar, A-5, to the adult, but the results of the methods also differed in minor ways. The greatest ontogenetic change in the location of the landmarks occurred in the growth from instars A-4 to A-3, and from instars A-3 to A-2. Sexual dimorphism is apparent but not pronounced among adults of B. normani (Brady). Few males were found, however, and dimorphism was not detected with the measurements taken. In choosing a method, one should bear in mind that results of analysis of shapes are most easily interpreted when they lend themselves to production of simple graphs.