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

Lorena Y Ramos,Marta Alperin,Corina A Coviaga,Antje Schwalb,Alejandra Patricia Pérez,Daniel Ariztegui,Gabriela C Cusminsky

doi:10.1590/0001-3765202120200635

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.

Highlights

The study of the form and quantitative descriptions of the shell morphology of diverse aquatic invertebrates has already shown to have substantial implications to the taxonomy, functional morphology, phenotypic plasticity, ecology and biogeography
The main differences in valve outline between R. whatleyi juvenile and adults of C. silvestrii are found in the posterior area, which is more pointed in the juvenile stage of R. whatleyi than in adults of C. silvestrii (Figure 2b)
The non-metric multidimensional scaling (n-MDS) plot and ANOSIM, including recent and fossil specimens (Figure 2a, both solid and open symbols), evidence that it would be possible to discriminate between R. whatleyi juveniles and C. silvestrii using valve shape (ANOSIM Rglobal = 0.884; p = 0.1%)

Summary

Introduction

The study of the form (shape and size) and quantitative descriptions of the shell morphology of diverse aquatic invertebrates has already shown to have substantial implications to the taxonomy, functional morphology, phenotypic plasticity, ecology and biogeography. Geometric morphometric methods (Adams et al 2004) have further proven to be powerful tools to describe and compare fossil and modern shells of various taxonomic groups. They objectively discriminate between close taxa and characterize intraspecific variation and its possible causes MORPHOLOGICAL PATTERNS IN Cypridopsis silvestrii and genetic characteristics of the populations (Baltanás & Geiger 1998, Wrozyna et al 2018b). Based on their environmental sensibility and often excellent preservation in lake sediments, ostracods are biological proxies widely used to interpret past limnological, environmental and climatic changes (Griffiths & Holmes 2000). For that reason the precise identification of species as well as the knowledge of their morphological variability and ecological preferences are critical to the successful use of ostracods in paleoenvironmental and climatic reconstructions (Mezquita et al 2005, Coviaga et al 2018a, Ramos et al 2019)

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