FISSION IN THE ZOANTHARIA PALYTHOA CARIBAEORUM(Duchassaing and Michelotii, 1860) POPULATIONS: A LATITUDINAL COMPARISON

Bol. Invest. Mar. Cost. 36 151-165 ISSN 0122-9761 Santa Marta, Colombia, 2007 FISSION IN THE ZOANTHARIA PALYTHOA CARIBAEORUM (Duchassaing and Michelotii, 1860) POPULATIONS: A LATITUDINAL COMPARISON Alberto Acosta and Ana M. González Pontificia Universidad Javeriana, Departamento de Biología, Unidad de Ecología y Sistemática (UNESIS), Edificio 53 Oficina 112, Bogotá, Colombia. E-mail: (AA) ABSTRACT There are few regional studies attempting to compare the asexual reproductive output of marine populations, particularly when they are exposed to different environmental conditions. In this study we compared Caribbean and Southwestern Atlantic Palythoa caribaeorum populations in terms of ramet production, the minimum colony size for fission, and the relationship between fission frequency and colony size. Fission process was quantified in Ponta Recife and Praia Portinho, Sao Paulo, Brazil, and in Punta de Betín, Colombia, during the summer (December-January) of 1997 and 1998, respectively. Fission started at small colony size in both populations studied (> 4 cm2). The number of ramets produced per colony increased with colony size in Brazil and Colombia. Colombian zoanthids produced more ramets by fission than Brazilian populations. The populations shared early reproduction characteristics, and production of large numbers of ramets, which increased with colony size, even though they differed in fission frequency. Fission seems to be a conservative trait in P. caribaeorum, although its expression could vary depending on habitat conditions related to biotic and / or abiotic factors. KEY WORDS: Asexual reproduction, Colony size, Fission, Latitudinal comparison, Palythoa caribaeorum. RESUMEN Fisión en poblaciones de Palythoa caribaeorum (Duchassaing and Michelotii, 1860): una comparación latitudinal. Existen pocos estudios regionales que intentan comparar el esfuerzo de reproducción asexual de poblaciones marinas, particularmente cuando éstas están expuestas a diferentes condiciones ambientales. En este estudio comparamos poblaciones de Palythoa caribaeorum del Caribe y del Atlántico Sur occidental en términos de producción de clones, mínimo tamaño de la colonia para fisionarse, y la relación que existe entre la frecuencia de fisión y el tamaño de la colonia. El proceso de fisión fue cuantificado en Ponta Recife y Praia Portinho, Sao Paulo, Brasil y en Punta de Betín, Colombia, durante el verano (Diciembre-Enero) de 1997 y 1998 respectivamente. La fisión comenzó en colonias de tamaño pequeño en las dos poblaciones estudiadas (> 4 cm2). El número de ramets producidos por colonia incrementó con el tamaño colonial en Brasil y en Colombia. Los zoantídeos de Colombia produjeron más ramets por fisión que poblaciones brasileras. Las dos Instituto de Investigaciones Marinas y Costeras - Invemar 151 poblaciones presentan ciertas características como reproducción temprana y producción de un gran número de ramets, los cuales incrementan con el tamaño colonial, aunque estas difieren en la frecuencia de fisión. La fisión parece ser una característica conservativa en P. caribaeorum, aunque su expresión podría variar dependiendo de las condiciones del hábitat relacionadas con factores bióticos y/o abióticos. PALABRAS CLAVE: Reproducción asexual, Tamaño colonial, Fisión, Comparación latitudinal, Palythoa caribaeorum. INTRODUCTION Asexual reproduction is the process by which an increase in colony numbers is achieved without the aid of genetic recombination. Clonality is a common feature of plants (Cook, 1985) and benthic marine organisms. In Cnidaria, new colonies (ramets) can be formed asexually through several mechanisms, including polyp bail-out (Sammarco, 1982), coral polyp expulsion (Kramarsky et al., 1997), fragmentation (see review in Highsmith, 1982), asexually produced planulae (Fautin, 2002), and colony fission (Pearse, 2002) among others. Fission is a primary mode of asexual reproduction in numerous anthozoans, such as zoanthids and scleractinian corals (Hughes and Jackson, 1980; Tanner, 1999), and play an important role in population size (Tanner, 1999), dynamics (Acosta et al., 2005), and structure in several species (Karlson, 1991; McFadden, 1991). Despite the fission importance for ecology (Tanner, 2002), biogeography (Skold et al., 2002), and evolution (contributions of fission expression to genetic structure and genet survival; Fautin, 2002; Geller et al., 2005), few spatial comparisons have been published regarding how many ramets are produced via fission (Miller and Ayre, 2004; Zilberberg et al., 2006) and how these reproductive strategies affect the population size (Tanner, 2000). Spatial variation in fission expression (i.e. frequency) between populations has been explained by a number of intrinsic (genetic) and extrinsic factors (Hughes, 1989; Skold et al., 2002; Zilberberg et al., 2006). The extrinsic abiotic factors proposed to control fission are: wave action, desiccation, temperature (Crump and Barker, 1985), seasonal variation (Mladenov, 1996), marginal habitats and disturbance level (Morris et al., 2004; Foster et. al., 2007), and biotic factors such as food availability (Tsuchida and Potts, 1994), and population density (Karlson et al., 1996; Tanner, 1999; 2002; Baums, et al., 2006). The magnitude of this change at regional scale (thousands of km) in populations exposed to different habitats however has been poorly studied (Zilberberg et al., 2006). Latitudinal variation in the frequency of asexual reproduction has been reported in an aquatic annual plant (Potamogeton pectinatus; Santamaría and García, 2004), marine sponges (Zilberberg et al., 2006), and corals (Miller and Ayre, 2004), but no causes have been explored. P. caribaeorum is a common sessile epibenthic shallow water species occurring in reef areas (reef crest or reef flats; Díaz et al., 2000) in the Caribbean (Gleibs, 1994; 152 Boletín de Investigaciones Marinas y Costeras - Vol. 36 - 2007 Mueller and Haywick, 1995) and rocky shores along the Southwestern Atlantic (Acosta, 1999; Oigman-Pszczol et al., 2004; Perez et al., 2005). This species is present in Colombia under nearly all oceanographic conditions in continental and oceanic islands (Acosta A. pers. obs.), including upwelling zones (i.e. Santa Marta; Gleibs, 1994). Along the Brazilian coast, P. caribaeorum is one of the dominant benthic species (Migotto, 1997; Oigman-Pszczol et al., 2004; Perez et al., 2005); however, in the southern latitudinal limit of geographical distribution (Sao Paulo coast) this zoanthid is exposed to frequent storms, constant turbid waters, and high sedimentation rates (Acosta et al., 2005). Nevertheless, the Caribbean and the Brazilian shallow water faunas are geographically separated due to freshwater and sediment discharged by the Orinoco and Amazon rivers (11 myo; Robertson, et al., 2006) which act as physical barrier (Lessios et al., 2001; Masson and Delecluse, 2001; Rocha, 2003). Fission in P. caribaeorum is (...truncated)