Claudia Wrozyna

Phenotypical variation in Leucocytherella sinensis Huang, 1982 (Ostracoda): a new proxy for palaeosalinity in Tibetan lakes

Leucocytherella sinensis, a ubiquitous and the most abundant ostracod endemic to the Tibetan Plateau, can account for >98% of the ostracod association. These low-diversity associations are hard to interpret using community palaeoecology alone, but environmentally driven phenotypic variation may provide clues to palaeoenvironmental factors. L. sinensis displays several morphological forms, characterised by different tubercle formation on their valves. These morphological forms were described as diverse species. We present a taxonomical revision and a first description of the soft parts of L. sinensis. We also redescribe the genus and confirm its assignment to the subfamily Limnocytherinae Klie, 1938. Analysis of L. sinensis associations from surface sediments of 12 Tibetan lakes shows a connection between tubercle formation and specific conductivity (SC) of the ambient water with lower tubercle number at higher salinity. Tubercles are less common in low SC populations and highest within the beta-oligohaline range. However, high Ca2+ concentrations suggest a combined effect of salinity and Ca2+ ion concentration on tubercle formation. The phenomenon of tubercle formation can be used to trace salinity changes recorded by fossil L. sinensis valves from Tibetan Holocene lake sediments.

Morphotypes of Cytheridella ilosvayi (Ostracoda) detected by soft and hard part analyses

Quantitative approaches dealing with soft- and hard-part morphological variability of ostracods are very rare for most species. Here we present intraspecific limb and shell variability of the Neotropical freshwater ostracod species assumed as Cytheridella ilosvayi. For the first time such an analysis considered adult females and males, as well as juveniles. Variability of the appendages included the antennule, second antenna as well as the first and second thoracopod and was analysed in terms of ratios of podomeres, setae and limbs. Limb variability of adult and juvenile individuals (down to A-3) is generally low. The highest variation is shown in podomere proportions of the antennas, while thoracopods and setae provide minor and/or non-significant influence on the variability. Based on discrimination analyses shell parameters (i.e., shell length, position of the transversal sulcus) emerge to be more important for differentiation of groups than limb ratios. Adult females exhibit a large size range in which two clearly separated morphotypes exist. Although differences in limbs are small their existence can be proven also on the basis of proportions between podomeres of the antennas. Males and juveniles, however, do not display a separation into corresponding subgroups or morphotypes. The presence of two morphologically similar females and only one type of males indicates the coexistence of female morphotypes which may represent either two (cryptic) species or a mixed reproduction population in which parthenogenetic and sexual reproduction coexists.

Definition of regional ostracod (Cytheridella) morphotypes by use of landmark-based morphometrics

Geometric morphometric analyses were performed on the Neotropical ostracod Cytheridella including recent populations from Florida, Yucatán, Colombia, and Brazil. Generalized least-squares Procrustes analyses were applied to left and right valves of adult females and males and to A-1 to A-3 juveniles. The analyses show that the prevailing shape variability is in the outline of the valves. Further characters defining the variability range are the anterior pore conuli 2 and 4 (LM 2, LM 4) and the connection point between transversal sulcus and the extension of the posterior lobe (LM 6). Relative Warps Analysis enabled delineation of the whole-shape disparity and revealed a geographical pattern in the morphological variability that is apparent in adults and juveniles. Females show greatest morphological disparity, whereas juveniles are more variable on the population scale. Differences in hard- and soft-part morphology identify the specimens from Yucatán as new a morphospecies. Different hydrological or hydrochemical conditions may have led to the evolution of the new species. Cytheridella has occurred in the Neotropics since the Oligocene with a similar distribution to that in the Recent. Avian dispersal may repeatedly reintroduce C. ilosvayi to Yucatánian populations possibly explaining the sympatric occurrence of 2 Cytheridella morphospecies. Our findings promote the benefit of investigating morphological variability quantitatively to detect regional morphotypes and ultimately to contribute to evaluations of biodiversity.