The valve shape variability in ten species of Heterocypris occuring in Europe

Abstract

Worldwide distributed genus Heterocypris has mixed reproduction that is considered to be one of the reasons of its great morphological variability, especially in carapace morphology. On the other hand, features on the carapace and valves are considered as important taxonomic characters and most frequently the only available in palaeontological and palaeoecological studies. The aim of this study was to give an insight in valve shape variability by illustrating differences in valve shapes among 31 populations of this genus occurring in Europe, originated from Pannonian Plain, Balkan Peninsula and Iberian Peninsula. Utilizing Morphomatica software, 350 left and 350 right digitized valve outlines were compared. Males were present in eight populations belonging to seven species, with 52 left and 51 right valves processed. Separately for females and males, mean specimen outline was obtained for each population. The populations included in the analyses are: eight populations of Heterocypris incongruens, six populations of H. rotundata, three populations of H. barbara, H. salina and H. vitrea, two populations of H. bosniaca and H. reptans, and one population of H. bulgarica, H. erikae, H. exigua and H. gevgelica. Cluster analysis and Multidimensional scaling on the Mean delta quadrate matrices provided from Morphomatica were performed for left and right valves separately. Overall, greater distances are present in left valve shape variation among species, populations and sexes. All conspecific populations grouped together in Cluster diagrams and MDS plots, both for left and right valve, where Heterocypris salina was the most distant from other species by its defined left and right valve shape. In Heterocypris reptans, valve shapes showed greatest distance in their variability between two analyzed populations and between sexes, as they individually grouped closer to other species. This species is clearly distinctive by the short natatory setae on the second antenna, and its valve shape variability could be interpreted as a consequence of the environmental components. Similar separations of some populations happened in H. rotundata that grouped with H. bulgarica. With inclusion of soft part morphology in further investigations, these findings could bring more light on the status of some analyzed taxa, and possibly clarify synonymies and other taxonomical issues within this genus.