PRIMARY RESEARCH PAPER Intra-specific variability in the thirteen known populations of the fairy shrimp Chirocephalus ruffoi (Crustacea: Anostraca): resting egg morphometrics and mitochondrial DNA reveal decoupled patterns of deep divergence Paola Zarattini • Graziella Mura • Valerio Ketmaier Received: 11 December 2012 / Revised: 18 February 2013 / Accepted: 2 March 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Chirocephalus ruffoi is a fairy shrimp endemic to the Italian peninsula, where it is known only from thirteen high mountain locations. Twelve of these are in the Northern Apennines while the thirteenth is about 700 km away in the Calabrian Apennines (Southern Italy). We quantified degree of genetic divergence within the species by sequencing a fragment of the mitochondrial DNA encoding for Cytochrome Oxidase I. We then combined genetic data with the re-analysis of two different datasets on the morphometrics of the resting eggs (cysts) produced by the species as an adaptation to survive seasonal droughts. Genetic data revealed profound divergence; we identified four clusters of haplotypes within the species phylogeography, three in the Northern Apen- nines and one in the Calabrian Apennines with most of the genetic variation (&70%) being apportioned among haplogroups. We found high variability in cyst morphometrics, especially in cyst size and height of the spines ornamenting the surface. Genetic and morpho- metric data are decoupled suggesting that cyst mor- phology is either under selection or a plastic trait. We, therefore, caution against using cyst morphology for taxonomic purposes in anostracans. Keywords Anostraca Á Resting eggs Á Morphometrics Á Cytochrome oxidase I Á Population structure Introduction Since early scanning electron microscope (SEM) observations on the external morphology of anostr- acan resting eggs (cysts) (Gilchrist, 1978; Mura et al., 1978), a great number of morphological studies have been performed aimed at ascertaining whether this feature could represent an additional taxonomic crite- rion to tell species apart. The initial enthusiasm of having an additional tool to tackle taxonomic diffi- culties in anostracans, a group of crustaceans where reliable morphological characters are hard to find, rapidly subsided. As experimental evidences were increasingly accumulating, it became evident that species were not always characterized by constancy in Handling editor: Christian Sturmbauer P. Zarattini Department of Life Sciences, University of Trieste, Via Valerio 28, 34127 Trieste, Italy G. Mura Á V. Ketmaier (&) Department of Biology and Biotechnology ‘‘Charles Darwin’’, University of Rome ‘‘La Sapienza’’, V. le dell’Universita’ 32, 00185 Rome, Italy e-mail: ketmaier@uni.potsdam.de V. Ketmaier Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany 123 Hydrobiologia DOI 10.1007/s10750-013-1487-8