CONICET-Universidad Nacional del Comahue INIBIOMA, Quintral 1250, Bariloche, CP 8400, Río Negro, Argentina.
Technische Universität Braunschweig, Institute of Geosystems and Bioindication, Langer Kamp 19c, D-38106, Braunschweig, Germany.
An Acad Bras Cienc. 2021 Aug 4;93(suppl 2):e20200635. doi: 10.1590/0001-3765202120200635. eCollection 2021.
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.
几何形态测量方法是区分密切相关的介形虫类群以及研究它们形态变化、分类和古生态学之间关系的有力工具。在这项研究中，壳瓣轮廓分析可以区分淡水介形虫 C. silvestrii 和 R. whatleyi 的幼体，指出后壳瓣区域和表面装饰的差异。从位于空间横截线上的 23 个地点采集的 23 个地点的现代雌性 C. silvestrii 标本表现出广泛的形态变异性，基于此确定了三种形态型（尖突型、过渡型、次截断型）。多元分析表明，尖突型和过渡型并没有分组排列，而是次截断型形态型，之前被描述为 E. cecryphalium，似乎与低水导率（372 µS cm-1）、主导低温（5°C）和大风（8.6 m s-1）的气候条件有关。包含九个核心的化石群跨越了过去 15600 年，仅包括尖突型和过渡型，这可能表明这些谱系可能比次截断型形态型更古老。此外，生殖方式的形态差异表明，孤雌生殖的雌性比有性生殖的雌性后缘更尖突。这些结果为在巴塔哥尼亚进行更精确的生态和古环境研究奠定了基础。
