Invertebrate Reproduction and Development, 52:1–2 (2008) 31–40 31 Balaban, Philadelphia/Rehovot 0792-4259/08/$05.00 © 2008 Balaban Reproductive cycle of the rissoid Alvania mediolittoralis Gofas, 1989 (Mollusca, Gastropoda) at São Miguel Island (Azores, Portugal) SÉRGIO P. ÁVILA1,2,3*, P.J. MELO1,4, ANA LIMA1, ANDRÉ AMARAL1,4, A.M DE FRIAS MARTINS1,3,5 and ARMINDO RODRIGUES1,4 1Departamento de Biologia, Universidade dos Açores, 9501-801 Ponta Delgada, Azores, Portugal 2Centro do IMAR da Universidade dos Açores, 9901-862 Horta, Azores, Portugal 3MPB–Marine Palaeobiogeography Working Group of the University of the Azores, Rua da Mãe de Deus, 9501-801 Ponta Delgada, Azores, Portugal Tel. +351 296 650 101/2; Fax: +351 296 650 100; email: [email protected] 4CIRN–Centro de Investigação de Recursos Naturais, Universidade dos Açores, 9501-801 Ponta Delgada, Azores, Portugal 5CIBIO-Pólo Açores–Centro de Investigação em Biodiversidade e Recursos Genéticos, and Departamento de Biologia, Universidade dos Açores, 9501-801 Ponta Delgada, Azores, Portugal Received 5 December 2007; Accepted 24 October 2008 Summary The reproductive cycle of an Alvania species is studied for first time. Alvania mediolittoralis Gofas, 1989 is an endemic Azorean rissoid very common in sheltered places and particularly abundant among the algal turf covering the lower half of the intertidal and upper subtidal rocky shores. This species reproduces throughout the year, with two spawning peaks, one during early spring and the other in late autumn. In an attempt to relate to current paleobiogeographical studies, inferences are made regarding the ecological advantages of species with a continuous type of reproduction, on Azorean shores, during glacial episodes. Key words: Alvania, Rissoidae, reproductive cycle, gametogenesis, Pleistocene Introduction malacofauna in the Mediterranean and Atlantic shores The Rissoidae are a family of small caenogastropod of Europe, the Madeira archipelago (Watson, 1873), the molluscs with a worldwide geographical distribution. Canary Islands (Moolenbeek and Faber, 1987a, 1987b, Shells are usually <5 mm long sometimes with elaborate 1987c; Moolenbeek and Hoenselaar, 1989, 1998) and sculpturing on both the protoconch and teleoconch also along west African shores (Gofas, 1999). They are (Ávila, 2005). Rissoidae are dioecious. Males have a the most represented family in the Azores Islands simple penis, located behind the right eye, females are (Gofas, 1990; Ávila, 2000b; Ávila, 2005), with 24 monaulic. The majority of species are marine, although species belonging to nine genera (Alvania, Botryphallus, some occur in brackish waters, and they are present in Cingula, Crisilla, Manzonia, Pusillina, Onoba, Rissoa the fossil record from the Upper Jurassic of Europe and Setia) (Moolenbeek and Faber, 1987b; Gofas, 1990; (Chenu, 1859; Ponder, 1985, 1988). Knudsen, 1995; Hoenselaar and Goud, 1998; Ávila, Rissoidae are a principal components of the littoral 2000a; Ávila, 2005). *Corresponding author. 32 S.P. Ávila et al. / IRD 52 (2008) 31–40 The Azorean rissoids are one of the best studied (Azores) (Fig. 1). According to Morton et al. (1998), mollusc families in the region, from MacAndrew (1856) this biologically diverse site (in both species number and Drouët (1858) to date. Ávila (2005) summarised all and density) is representative of the rocky shore the published information about this family in the environment in the Azores and has been studied archipelago of the Azores, including ecological, taxo- extensively (Hawkins et al., 1990; Costa, 1994; Britton, nomical, palaeontological, and geographical distri- 1995; Botelho and Costa, 2000). It is particularly bution data on all the 24 shallow water species. suitable for the collection of intertidal species, due to its Alvania mediolittoralis Gofas, 1989 is a small large and shallow rocky platform, which has a gentle mollusc (usually with a shell about 2.7 mm long and slope towards the sea. The bottom of this relatively 1.5 mm wide), with non-planktotrophic larval develop- protected bay is covered by small boulders, which rest ment, which inhabits the intertidal and upper subtidal on the underlying lava flow. Most of the boulders algal covered rocky shores (Martins, 2004; Ávila, possess a dense algal mat that makes the perfect habitat 2005). It is common and may be present in large for micro-molluscs such as Alvania mediolittoralis. numbers in sheltered places, especially under boulders (Ávila, 2000b). It is especially abundant in the lower half of the intertidal zone, among the intertidal algal turf Sampling and morphometry (Ávila et al., 2005) reaching a maximum density of During low tide, several rocks were collected, and 54,000 individuals/m2 in the Ilhéu de Vila Franca, São the upper and lower surfaces brushed inside a plastic Miguel Island (Bullock, 1995). It is commonly asso- container filled with seawater. The residue was then ciated with other microgastropods such as Omalogyra sorted for living individuals. Water temperature was atomus (Philippi, 1841), Pisinna glabrata (Megerle von recorded on each sampling date. The largest twenty Mühlfeld, 1824) and Skeneopsis planorbis (Fabricius individuals of A. mediolittoralis were sampled once per O., 1780), and the bivalve Lasaea adansoni (Gmelin, month, from February 2003 to January 2004. In the 1791) (Ávila et al., 2005). laboratory, quantitative measurements of maximum Although reported from Madeira by Hoenselaar and shell length (SL) and shell width (SW) were recorded Goud (1998) (CANCAP expeditions, Sta.1.D48, 0-22 using a Wild M3 Stereo Microscope with a camera m/1 shell; Sta.1.K14, in the littoral/1 and Sta. 1.K16, in lucida. The length/width ratio was also calculated the littoral/2), we think these reports describe specimens (SL/SW). that reached the Madeira archipelago but were not able to establish a viable reproductive population. Recent collecting at Madeira and Porto Santo by Ávila (unpub- Gonadal maturation state lished data) at appropriate intertidal and sublittoral After measurement, specimens were fixed in Bouin’s habitats where A. mediolittoralis should occur did not solution in seawater for 15 h, dehydrated in ethanol and yield a single specimen, thus we believe this species to embedded in paraffin wax. Finally, 7 µm thick serial be endemic to the Azores archipelago. It was reported transversal sections cut with a microtome were stained for the Pleistocene of the Azores (Prainha and with Mayer’s haemalum and eosin (Martoja and Lagoinhas, Santa Maria Island) by Ávila et al. (2002), in Martoja-Pierson, 1970). Observations were made on the outcrops dated from the Marine Oxygen Isotope Sub- histological sections of the gonads of the specimens stage 5e (MISS 5e) high sea level interval (about 130– collected in March, May, July, September and 120 ka) (Ávila et al., 2008a). Dispersal events November 2003, and January 2004, and the relative (successful or not) are usually rare events. From all the volumetric density of gametes estimated according to endemic Azorean rissoids, A. mediolittoralis is the only the M168 Weibel Multipurpose Test System (Weibel, species of which shells are reported from sites other than 1979). the Azores archipelago (in the present case, the Madeira Three stages of development were distinguished archipelago, about 900 km apart from the Azores). This during oogenesis (Hill and Bowen, 1976; Rodrigues and provides indirect evidence that speciation occurred long Medeiros, 2005; Cúrdia et al., 2005) (Fig. 2): (1) pre- ago, thus surviving to several glacial-interglacial cycles, vitellogenic oocytes (PV)—small, rounded cells, with and making it a particularly interesting species for study. strong basophilic cytoplasm; (2) vitellogenic oocytes (V)—larger than the previous stage, irregular in shape, Materials and Methods sometimes with multiple visible nucleoles, and lightly basophilic cytoplasm with slight granulations; (3) ma- Study area turing oocytes (M)—larger than the vitellogenic Caloura (Lat 37º42N30ON, Long 24º30N30OW) is oocytes, round in shape with eosinophilic and granular located on the southern shores of São Miguel Island cytoplasm. S.P. Ávila et al. / IRD 52 (2008) 31–40 33 Fig. 1. Azores archipelago and São Miguel Island, with location of the sampling site, Caloura. Fig. 2. Histological section of a Alvania mediolittoralis female gonad. A. General view; B, C. Highlight of the oogenic stages. Arrows, germinal layer; arrowheads, previtellogenic oocytes; dgt, digestive tubule; n, nucleus; mo, maturing oocytes; vo, vitellogenic oocytes; yg, yolk granules. Scale bars: 50 µm. 34 S.P. Ávila et al. / IRD 52 (2008) 31–40 Fig. 3. Histological section of a Alvania mediolittoralis male gonad. A. General view. B. Highlight of the spermatogenic stages. Arrows, germinal layer; dgt, digestive tubule; sc, spermatocytes; sg, spermatogonia; st, spermatides; sz, spermatozoa; t, testis. Scale bars: 50 µm. Four stages of spermatogenesis were identified formed into a lower triangular resemblance matrix using (Griffond et al., 1991; Rodrigues and Medeiros, 2005; the Euclidean distance similarity index, and a dendro- Cúrdia et al., 2005) (Fig. 3): (1) spermatogonia — gram was constructed with the UPGMA method. A total medium-sized cells, with a large nucleus in relation to of 117 specimens of A. mediolittoralis were analysed the quantity of cytoplasm, always located near the acinar (71 females and 46 males). epithelium; (2) spermatocytes — larger than spermato- The mean gonad index (MGI) (Brown, 1982) was gonia with basophilic