Echinoderms 2000, Barker (ed.), © 2001 Swets & Zeitlinger, Lisse, ISBN 90 5809 189 9 Morphological, physiological and genetic variability of the ophiuroid Amphipholis squamata from the lagoon system of Oliveri-Tindari (Sicily) J-P.Féral & A-M. Villard Observatoire Océanologique, UMR, Banyuls-sur-mer; France S.Dupont & J.Mallefet Laboratoire de Physiologie Animale, Université catholique de Louvain, Louvain-la-Neuve, Belgium ABSTRACT: Amphipholis squamata is considered to be the on! y echinoderm distributed world-wide, ex- cepted in polar regions. This vast distribution area contrasts with a low dispersal potential due to the Jack of a pelagie larval stage and an aggregative spatial distribution. Previous works have shown strong inter- and intra-population variability among adult individuals for both phenotype and genotype, although the species seems to be anatomically uniform. The aim of this work was to understand these individual variations at three different levels : (a) the morphological differences character- ized by the colour of arms and dise; (b) the physiological variations estimated by luminous capabilities and (c) the genetic variations as revealed by RAPDs. Four populations were sampled in the system of Oliveri-Tindari in Sicily which consists of severa! lagoons complete] y isolated from the open sea and from each other for various periods. This system constitutes a suit- able mode! for studying differentiation between closely neighbouring demes. Our results confirm that each colour variety possesses its own luminous capabilities; they also indicate that colour varieties are genetically differentiated. INTRODUCTION In spite of the absence of a larval phase, the si- multaneous hermaphrodite (Nisolle, 1990) and brood protecting ophiuorid Amphipholis squamata is re- garded as a cosmopolitan species. This species lives in ali the oceans except Antarctica and, in varied habitats, from tidal zone down to 1330 rn depth (Gage et al. 1983, Hendler 1995, Alvà 1996). A. squamata constitutes dense local populations often occupying microhabitats. There is a paradox of an extremely wide distribution of a species that Jacks a larval stage and often shows an aggregative spatial distribution. The reproductive biol ogy of the species can explain a high potential of colonization, e.g. by means of rafting (Mortensen (1933, 1941), recently confirmed by Highsmith (1985), Alvà & Vadon (1 989) and Murray(1989)), but it is still difficult to understand how it could maintain regular gene flow between distant populations (Poulin et al. 1999). Variability seems the rule within Amphipholis. Numerous colour varieties were reported for this species (Binaux & Boguet 1971, Deheyn 1998, Dupont 1998, Deheyn & Jangoux 1999, Dupont et al., this volume ). A. squamata is luminescent (Brehm & Morin 1977) and important infraspecific 261 vanat10ns of luminous capabilities were described (Deheyn et al. 1997). Poulin et al. (1999) have dem- onstrated the co-existence of selfing and outcrossing in this species (a result different from Murray (1989) who hypothetized that only outcrossing was occur- ring). They also demonstrated a great genetic differ- entiation of A. squamata at a very short distance. At another scale, Sponer et al. (1999) have showed that global populations are genetically highly differenti- ated and hypothetized that different clades were likely representing different species. The results of Deheyn and Jangoux (1999) dis- cussing the inheritance of body colour and biolumi- nescence characters and those of Poulin et al. (1999), Sponer et al. (1999) and Dupont et al. (this volume) discussing the relationships between phe- notypic characters and genetic structuring ques- tioned about the taxonomie status of A. squamata. The aim of this paper is to characterize the intra- and inter- population variability at 3 levels, mor- phological, physiological and genetic. It is also to evaluate the congruence between polychromatism, bioluminescence and genetic structure of very close local populations of A. squamata, recent! y separated from the open sea and from each other.