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REPRODUCTION OF THE LIMPET NACELLA (P.) DEAURATA. 417
SCI. MAR., 63 (Supl. 1): 417-426 SCIENTIA MARINA 1999MAGELLAN-ANTARCTIC: ECOSYSTEMS THAT DRIFTED APART. W.E. ARNTZ and C. ROS (eds.)
Reproductive biology of the limpet Nacella (P.)deaurata (Gmelin, 1791) in Baha Lapataia
Centro Austral de Investigaciones Cientficas (CONICET), C.C. 92, (9410) Ushuaia, Tierra del Fuego, Argentina. E-mail: [email protected]
SUMMARY: The reproductive cycle of a Nacella (P.) deaurata population that inhabits the lower intertidal zone in Lapa-taia Bay (5452S; 6829W) was studied. Monthly samples were collected, and specimens were measured and weighed, fix-ing the gonads in Bouins fluid for histological analyses. The gonadosomatic index (GSI) was determined as a percentage ofthe ratio between gonadal and foot wet weight. Taking into account the presence and abundance of different cellular types,gonadal stages were established for males and females. The analyses of the variation of the gonadal stage percentages showedthe first mature males and females in July. In 1989, mature females maintained a percentage higher than 30% until January.Spawning began in September and was massive in November. In 1990, the maximum percentage of mature females was foundin September with all the specimens spawned in October. Nevertheless, the majority of the population was mature again inNovember. The male sexual cycle in 1989 showed the highest percentage of mature individuals in August, being high untilOctober and slightly diminishing in November. The highest percentage of evacuated males was observed in November-December. In 1990, the cycle was similar to the one shown by the females, but without recovery in November. The GSI vari-ability in males and females, and the adequate use of the GSI in determining the annual reproductive cycle were discussed.The biotic and environmental conditions that may act as a trigger for the spawning have been analyzed.
Key words: Archaeogastropods, Subantarctic limpets, reproductive cycle, spawning.
RESUMEN: BIOLOGA REPRODUCTIVA DE NACELLA (P.) DEAURATA (GMELIN, 1791) EN BAHA LAPATAIA (CANAL DEL BEAGLE). Se estudi el ciclo reproductivo de Nacella (P.) deaurata en una poblacin que habita el intermareal inferior en la costasur de Baha Lapataia (5452S; 6829O). Se realizaron muestreos mensuales, los ejemplares fueron medidos, pesndoselas vsceras, pie y gnada, siendo esta ltima fijada en Bouin para su posterior procesado histolgico. Se determin el ndi-ce Gonadosomtico (IGS) como la expresin porcentual del peso gonadal sobre el peso hmedo del pie. Se establecieronhistolgicamente estadios gonadales tanto en hembras como en machos, de acuerdo con la presencia y abundancia de losdiferentes tipos celulares. De acuerdo con el anlisis de los porcentajes mensuales de los estadios gonadales, los individuosde ambos sexos se encontraron maduros a partir de julio. Las hembras maduras durante 1989 se presentaron en porcentajessuperiores al 30% hasta enero. A partir de septiembre comenz el desove, hacindose masivo en la poblacin en noviem-bre. En 1990 el pico mximo de maduracin se alcanz en septiembre. En octubre todos los individuos habian desovado,mientras que durante noviembre una gran proporcin de la poblacin se recuper alcanzando nuevamente la madurez total.El ciclo sexual anual de los machos en 1989 mostr el mayor porcentaje de individuos maduros durante agosto, mante-nindose una alta proporcin hasta octubre con un ligero descenso en noviembre. El mximo porcentaje de individuos eva-cuados se observ entre noviembre y diciembre. En 1990 el ciclo fu similar al que presentaron las hembras para el mismoao pero no se produjo recuperacin de la maduracin gonadal en noviembre. Se discute la variabilidad del IGS en ambossexos y su validez para la determinacin de los ciclos reproductivos anuales, analizndose las condiciones biticas y ambien-tales que actuaran como desencadenantes del desove.
Palabras clave: Arqueogasterpodos, lapas subantrticas, ciclo reproductivo, desove.
*Accepted December 22, 1998.
Limpets are very common archaeogastropodmolluscs that inhabit intertidal rocky shores. Manyinvestigations have been made on their reproductione.g., Patella vulgata (L., 1758) (see Orton et al.,1956; Blackmore, 1969; Garwood, 1987), Cellanaradiata (Born) (see Balaparameswara Rao, 1973),seven species of Patella (see Branch, 1974), Cellanagrata (Gould, 1859) and Patelloida pygmaea(Dunker, 1860) (see Liu, 1994).
In cold waters the reproduction was studied inthe Subantarctic limpet Nacella maquarensis (Fin-lay, 1927) (see Simpson, 1982) and in the Antarcticand Subantarctic limpet Nacella concinna (Strebel,1908) (see Picken, 1980; Brthes et al., 1994). Nev-ertheless, there have not been histological studies ontheir reproductive cycles.
Nacella (Patinigera) deaurata (Gmelin, 1791)and Nacella (Patinigera) magellanica (Gmelin,1791) are the two most conspicuous limpet speciesin the Beagle Channel due to their abundance andtheir relatively large sizes. Nacella (P.) magellanicainhabits the medium and superior intertidal zoneswhile Nacella (P.) deaurata lives in the lower inter-tidal zone and the sublittoral zone (Morriconi andCalvo, 1993).
Few studies on the biology of these limpetspecies have been carried out although they areabundant along the Patagonian coast. Guzmn(1978) determined the spatial pattern and density ofN. magellanica in the Magellan Straits and Guzmnand Ros (1987) established the age and growth ofthis species. Morriconi and Calvo (1993) deter-mined the environmental influence on shell allomet-ric growth in the Nacella (P.) deaurata BeagleChannel population.
The aim of this study was to establish the annualreproductive cycle and the frequency and duration ofthe spawning cycle of Nacella (P.) deaurata based onthe histological description of gonadal tissues. More-over, the biological and environmental parametersthat could trigger the spawning were analyzed.
MATERIAL AND METHODS
Sampling was carried out from March 1989 toNovember 1990 in Baha Lapataia (5452 S;6829 W) in the Beagle Channel (Fig. 1). The sam-pling area is protected against the dominant south-westerly winds.
Monthly samples of around 30-40 individualswere collected by diving. The shell of each speci-men was measured along its greatest length usingvernier callipers to the nearest 0.5 mm. The individ-uals were removed from their shells and the somadissected out. The soft parts were fixed in Bouinsfixative for at least 48 hours, washed in tap waterand kept in 70 % ethyl alcohol. Afterwards the foot,the digestive mass and the gonad were separated andthe wet weight of each part was obtained. The gonadwas sectioned in three parts: anterior, central andposterior. Following dehydration and clearing, thegonads were embedded in Paraplast, sectioned (5m) and counterstained with hematoxylin-eosin. Atotal of 536 individuals, ranging from 15 to 65 mmin shell length, were described histologically.
The Gonosomatic Index (GSI) was expressed aspercentage (100 * wet gonad weight/wet footweight).The differences in the values of GSIbetween males and females were tested using theMann-Whitney U -Test (Sokal and Rohlf, 1995).
418 E. MORRICONI
FIG. 1. Sampling area (arrows) in Baha Lapataia (54 52S; 68 29W).
REPRODUCTION OF THE LIMPET NACELLA (P.) DEAURATA. 419
FIG. 2. Nacella (P.) deaurata. Gonadal female stages. Scale bar = 100 m; a) Early developing stage. Nests of oogonia (arrows). Numer-ous basophilic oocytes; b) Developing stage: oocytes with deposition of eosinophilic granules in the basal region of cytoplasm (arrow), aci-dophilic oocytes; c) Ripe stage: acidophilic oocytes fill the tubular lumen, small number of basophilic oocytes against the trabeculae; d) Ripestage: homogeneous eosinophilic matrix in the tubular lumen, between the free oocytes; e) Partially spawned with recovery stage: acidophilicoocytes free in the tubular lumen, basophilic and intermediate oocytes; f) Partially spawned with no recovery stage: small basophilic oocytesclose to the tubular wall, mature oocytes in the tubular lumen with a basophilic citoplasmic zone, oocytary remains in the lumina; g) Total-ly spawned stage: very scarce mature oocytes are free in the tubules, basophilic oocytes close to the tubular wall; h) Oocytes in different
degree of atresia.
Nacella (P.) deaurata is a dioecious species. Ithas an impaired gonad located at the ventral part ofthe animal, underneath the visceral mass. The gonadoccupies a small portion of the posterior region inthe immature specimens. The gonad grows in ante-rior and lateral directions, over the outer margins ofthe visceral mass, during maturation. In males, thegonad is yellow in maturing and ripe specimens,while it is brown-reddish in spawned individuals.The female gonad is brown during maturation andbecomes darker in totally spawned specimens.
In both sexes, the gonad is formed by tubules thatextend from the ventral towards the dorsal regionforming branches. The tubules support a germinalepithelium and are separated by connective tissuetrabeculae.
Developmental stages of the female
Early developing stage
The trabeculae are enlarged. The tubules have awide lumen occasionally containing cytoplasmicremains and phagocytes.
Oogonial clusters are attached to the tubule wall(Fig. 2a). They are more numerous in the ventralzone. These cells have a rounded central nucleus (5m in diameter) and a conspicuous nucleolus. Thebasophilic oocytes (13-50 m in diameter, Fig. 2a)usually show a pyriform shape and have an ovalnucleus with several peripheric nucleoli. Oocytes(40-80 m in diameter) with numerous small chro-mophobic vacuoles in their cytoplasm are present atthe end of this stage.