Morphological diversity and discrimination tools of the non-marine ostracod Cypridopsis silvestrii across temporal and spatial scales from Patagonia

Abstract

Geometric morphometric methods are powerful tools to discriminate between closely related ostracods taxa as well as to study the relationship between their morphological variations, taxonomy and paleoecology. In this study, valve outline analysis allows the discrimination between the non-marine ostracod C. silvestrii and R. whatleyi juveniles, pointing out differences in the posterior valve area and surface ornamentation.Modern female specimens of C. silvestrii from 23 sites located in a spatial transect (41 to 51 °S) exhibited extensive morphological variability, on the basis of which three morphotypes (acuminated, transitional, subtruncated) were determined. Multivariate analyses showed that acuminated and transitional shapes are not arranged in groups but the subtruncated morphotype, previously described as E. cecryphalium, seems to be associated with low water conductivity (372 µS cm -1 ), dominant cold (5 ºC) and windy (8.6 m s -1 ) climatic conditions. The fossil cluster which included nine cores spanning the last 15.6 kyr, only covered acuminated and transitional shapes, which may indicate that these lineages might be older than the subtruncated morphotype. In addition, morphological differences between reproduction modes suggested that parthenogenetic females exhibit de posterior margin more acuminate than sexual females. These results set the ground for more precise ecological and paleoenvironmental studies in Patagonia.

Diversification of the shell shape and size in Baikal Candonidae ostracods inferred from molecular phylogeny

“…Earlier studies 27 showed that Candonidae have the highest diversity of shell shape among freshwater ostracod lineages, although this might be slightly exaggerated due to an old classification used. Quantitative analyses of the shell shape have sometime been applied in ostracodology to address problems of homoplasies 28 , 29 , correlation with ecological variables 30 – 32 , or cryptic species 33 , 34 . Although the use of morphometrics (both linear and geometric) in evolutionary studies has been constantly on the rise 35 , there are very few on ostracod shells, and only on the subgenus level and using morphology-based phylogeny 36 , 37 .…”

Diversification of the shell shape and size in Baikal Candonidae ostracods in the light of molecular phylogeny

“…Quantitative analyses of the shell shape have sometime been applied in ostracodology to address problems of homoplasies 28,29 , correlation with ecological variables 30,31,32 , or cryptic species 33,34 . Although the use of morphometrics (both linear and geometric) in evolutionary studies has been constantly on the rise 35 , there are very few on ostracod shells, and only on the subgenus level and using morphology-based phylogeny 36,37 .…”