Intraspecific morphological diversity of anostracan resting eggs: Chirocephalus ruffoi Cottarelli & Mura, 1984 as a study case

The extent of intraspecific morphological variability in the egg shells of anostracans, never previously assessed, was investigated in the 13 known Chirocephalus ruffoi populations, a species endemic to Italy. Twelve sampling sites were chosen in the Northern Apennines, with distances between neighbouring sampling sites ranging from a minimum of 23 m to a maximum of 63 km. Another site was located in the Calabrian Apennines at a distance between 643 and 703 km from the previous set of sampling points. The SEM (scanning electron microscopy) observations of 300 cysts per population revealed the existence of great morphological diversity for most of the analysed populations. Up to 12 different morphotypes were described, with highly variable frequencies among the populations. Outer and inner cyst diameters and height of the "ridges" ornamenting cyst surface were calculated on a randomly selected sub-sample of 391 cysts. Statistically significant differences among populations were found for all the measured characters. No relationships between either occurrence of morphotypes or morphometric profiles and characteristics of sampling sites were found. In addition, the amount of morphological variability of the cysts did not seem to depend on the distances between sites. The results of this study are discussed in the light of the debate on the taxonomic value of the anostracan cyst ornamentation and the factors that can be invoked to explain the presence of high intraspecific morphological diversity.