RESEARCH ARTICLE Tamara Rubilar Æ Catalina T. Pastor de Ward Marı´a E. Dı´az de Vivar Sexual and asexual reproduction of Allostichaster capensis (Echinodermata: Asteroidea) in Golfo Nuevo Received: 19 January 2004 / Accepted: 1 November 2004 / Published online: 12 January 2005 Ó Springer-Verlag 2005 Abstract Sexual and asexual reproduction of the ﬁs- siparous starﬁsh Allostichaster capensis were examined for 24 months at Bahı´a Kaiser, Golfo Nuevo, Chubut, Argentina. Gonad indices revealed an annual repro- ductive cycle, with peak development occurring in late winter (August). Spawning occurred in spring (Sep- tember). Pyloric caeca indices displayed a clear annual cycle and a reciprocal relationship with gonad indices, showing the storage function of pyloric caeca. The starﬁsh population appears to be largely maintained by ﬁssion, as only two females were found. A. capensis also showed an annual cycle of ﬁssion, with the highest frequency in spring and summer (from November to January), just after spawning. Incidence of ﬁssion was correlated with environmental factors such as photo- period, seawater temperature, and salinity. Introduction Asexual reproduction by ﬁssion is one of the repro- ductive methods of some starﬁsh: they split their bodies into two or three parts. Each resulting part regenerates a complete individual, which can split again (Ottessen and Lucas 1982). Fissiparous starﬁsh are commonly asymmetrical, with a set of smaller regenerating arms and a set of large arms; they typically have more than ﬁve arms and they often possess multiple madreporites and ani. Fission is known to occur in about 21 species of three families. It is apparently an uncommon mode of reproduction within starﬁsh (Emson and Wilkie 1980; Mladenov and Burke 1994; Karako et al. 2002). The contribution of ﬁssiparity in the maintenance of local populations is not well known, but asexual reproduction is an obligatory reproductive method in populations of Stephanasterias albula (Mladenov et al. 1986) and Asterina burtoni (Achituv and Sher 1991) and it appears that populations of Coscinasterias ten- uispina are sustained only by ﬁssion (Alves et al. 2002). The factors regulating asexual reproduction are unknown, but it appears to be regulated by both exogenous (seasonal changes, environmental stimuli) and endogenous factors (humoral and nervous factors; Thorndyke et al. 1998). As ﬁssiparous starﬁsh are normally able to produce gametes, they can reproduce sexually as well, and like other starﬁsh, most ﬁssiparous species show an annual gonadal cycle with a seasonal pattern. The nature of the interaction between sexual reproduction and ﬁssion is variable and complex. Allostichaster capensis (Perrier, 1875) is a known ﬁs- siparous species that is widely distributed in the South Atlantic (from Buenos Aires to Tierra del Fuego) and the Falkland Islands (Islas Malvinas). It ranges from the subtidal zone to 100 m depth, usually on hard bottoms (Clark and Downey 1992). This work is part of a larger study of the repro- ductive cycle of a population of A. capensis from Golfo Nuevo regarding the histological and biochemical ap- proaches. The aim of this research was to examine (1) seasonality of gonadal development and ﬁssion, (2) environmental factors that might be correlated with reproduction, and (3) the relationship between sexual and asexual reproduction. Similar research was per- formed on C. tenuispina from Rio de Janeiro, (Brazil) by Alves et al. (2002). Communicated by P.W. Sammarco, Chauvin T. Rubilar (&) Æ M. E. Dı´az de Vivar Fac. de Ciencias Naturales, Universidad Nacional de la Patagonia ‘‘San Juan Bosco’’, Puerto Madryn, Chubut, Argentina E-mail: rubilar@cenpat.edu.ar Tel.: +54-2965-451024 Fax: +54-2965-451543 C. T. Pastor de Ward Centro Nacional Patago´nico, CONICET, Puerto Madryn, Chubut, Argentina Marine Biology (2005) 146: 1083–1090 DOI 10.1007/s00227-004-1530-4