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Size at first maturity of Brachidontes rodriguezii (d'Orbigny, 1846) from the South-western Atlantic Ocean

Published online by Cambridge University Press:  29 November 2016

María Eugenia Torroglosa  and
Juliana Giménez
María Eugenia Torroglosa
Affiliation:
Instituto de Biodiversidad, Biología Experimental y Aplicada (IBBEA), CONICET-UBA, Argentina
Juliana Giménez*
Affiliation:
Instituto de Biodiversidad, Biología Experimental y Aplicada (IBBEA), CONICET-UBA, Argentina Departamento de Biodiversidad y Biología Experimental, FCEN UBA, Argentina
*
Correspondence should be addressed to: J. Giménez IBBEA, CONICET-UBA, Departamento de Biodiversidad y Biología Experimental, FCEN UBA, Argentina email: jgimenez@bg.fcen.uba.ar
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Abstract

The size at first maturity of the bivalve Brachidontes rodriguezii was estimated in a population located in the northernmost limit of its distribution along Argentinean coast. Specimens were collected in two consecutive reproductive seasons from December 2011 to February 2012 and from December 2012 to February 2013. Individuals were evaluated using biometric and histological analyses of the gonads. This study intended to provide important information about the development of gonadal tissue according to shell length increase. Our results showed immature specimens lack gonads or exhibited groups of cells undergoing mitosis adjacent to the epithelium of the mantle and the tubules of the digestive gland. Male and female gonad development extended to mantle lobes and visceral mass as long as maturation occurred to reach sexual maturity. Using a logistic model our results showed that the size at which 50% of females were mature at a gonadal level was 7.05 mm in shell length; in males, 50% of the population were mature at 8.13 mm in shell length. The minimum shell length at which maturity was observed was 6.99 mm in shell length in females and 6.00 mm in shell length for males.

Keywords

Musselsintertidal coastsecosystem engineergonadal maturity

Information

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 98 , Issue 3 , May 2018 , pp. 457 - 462
Copyright
Copyright © Marine Biological Association of the United Kingdom 2016 

INTRODUCTION

The mussel Brachidontes rodriguezii (d'Orbigny, 1846) dominates intertidal rocky coasts and is distributed from Uruguay to north Patagonia along the Argentinean coast (Penchaszadeh, Reference Penchaszadeh1973; Adami et al., Reference Adami, Pastorino and Orenzans2013; Arribas et al., Reference Arribas, Bagur, Klein, Penchaszadeh and Palomo2013; Torroglosa & Giménez, Reference Torroglosa and Giménez2015). Mussels constitute diverse assemblages of several species (Scelzo et al., Reference Scelzo, Elías, Vallarino, Charrier, Lucero and Alvarez1996; Vallarino et al., Reference Vallarino, Rivero, Gravina and Elías2002; Adami et al., Reference Adami, Tablado and López Gappa2004; Calcagno et al., Reference Calcagno, Curelovich, Fernández, Thatje and Lovrich2012), becoming an ecosystem engineer (Borthagaray & Carranza, Reference Borthagaray and Carranza2007; Carranza et al., Reference Carranza, Defeo, Beck and Castilla2009; Arribas et al., Reference Arribas, Donnarumma, Palomo and Scrosati2014), so it is an important component of benthic intertidal coast communities. Brachidontes rodriguezii is commonly found in hard substrates of rocky coasts, but as a consequence of the introduction of artificial hard substrates (e.g. fishery piers and seawalls), it is also found in sandy coasts. These artificial hard substrates (vertical surfaces mostly) comprise a novel habitat along the coastline that might introduce changes into local and regional biodiversity modifying patterns of dispersal, establishment and spread of species (Bulleri & Chapman, Reference Bulleri and Chapman2010; Martins et al., Reference Martins, Jenkins, Neto, Hawkins and Thompson2015). To establish and colonize new habitats, species need a successful reproductive strategy (Mackie, Reference Mackie1991; Barber et al., Reference Barber, Fajans, Baker and Baker2005). Size at first maturity together with the reproductive cycle constitutes reproductive aspects that maximize reproductive effort of species (Todd, Reference Todd, Moore and Seed1985; Gage, Reference Gage1995). In addition, size at first maturity is useful to determine measures for adequate natural resource management (Chung, Reference Chung2007, Reference Chung2008), spatial monitoring (Camacho-Mondragón et al., Reference Camacho-Mondragón, Arellano-Martínez and Ceballos-Vázquez2012) and temporal changes associated with commercial exploitation (Giménez & Penchaszadeh, Reference Giménez and Penchaszadeh2003; Torroglosa & Giménez, Reference Torroglosa and Giménez2010). Brachidontes rodriguezii is a small mytilid (35 mm shell length) that often forms multi-layer beds on vertical intertidal substrates reaching high densities (170 000 ind. m−2) (Penchaszadeh, Reference Penchaszadeh1973: Gutiérrez et al., Reference Gutiérrez, Palomo, Bagur, Arribas and Soria2015). Some aspects of the reproductive biology of the species are known; B. rodriguezii recruits continuously during the year, with peaks during summer and autumn (Penchaszadeh, Reference Penchaszadeh1973; Adami et al., Reference Adami, Tablado and Sodor2008). The spawning peak occurs at the end of summer, however, mature males and females were recorded all year round suggesting minor spawning events that explain the continuous recruitment (Torroglosa, Reference Torroglosa2015). Knowledge of the reproductive cycle and the spawning season, together with size at first maturity will provide necessary information for further determination of recruitment rate during the spawning period, and the impacts on the structure population of B. rodriguezii in the south-western Atlantic Ocean. The objectives of this study were to characterize the gonad development according to shell length and to estimate the size at first maturity of B. rodriguezii in Villa Gesell.

MATERIALS AND METHODS

Specimens of Brachidontes rodriguezii were collected by hand from the basal area of the pier pilings in a sandy beach at Villa Gesell (37°16′S 56°53′W). Sampling was carried out on middle intertidal at 20 cm below the sea level at low tide during two consecutive reproductive seasons (Torroglosa, Reference Torroglosa2015): the period December 2011–February 2012 and December 2012–February 2013.

The shell length (SL) of all individuals was measured with stereomicroscope or a digital caliper to the nearest 0.01 mm. Individuals with SL < 8 mm were decalcified in Jenkins solution for 96 h. Tissues were removed from shells and fixed in Bouin for 12 h. They were then dehydrated in alcohol, embedded in metacrylate resin and sectioned at 5 µm. The sections were stained with haematoxylin and eosin (H & E) (Howard et al., Reference Howard, Lewis, Keller and Smith2004). Individuals were considered sexually mature when gonads were completely developed in both mantle lobes and the visceral mass.

The percentages of individuals arranged in 1 mm size class were plotted against SL and data fitted using a non-linear modelling procedure to the logistic equation (Roa et al., Reference Roa, Ernst and Tapia1999): P m = [1/1 + exp (-a (SL – SL0)] 100. Where Pm is the proportion of mature males and females, SL0 and a (slope of the logistic function) were constants. The parameters for the equation were estimated by using the Solver function in the Excel statistical package (Microsoft® Excel 2007). The logistic function was fitted to data on maturity status at shell length using the least-squares method. Each size class comprised between 20 and 27 individuals. The shell length at which 50% of individuals exhibited mature gonads was considered the size at first maturity (SL50) for the population (Roa et al., Reference Roa, Ernst and Tapia1999). To evaluate sex ratio, chi-square test (χ2) was used to assess significant differences between two random samples (N = 100) taken each reproductive season (shell length between 8.10–28.30 mm).

RESULTS

A total of 355 mussels with shell lengths ranging from 2.10 to 25.50 mm were studied. Sex ratio for B. rodriguezii was not significantly different from 1:1 (χ2, P > 0.05). The histological examination showed sexually immature individuals with undeveloped gonads with shell length (SL) < 3.99 mm. The tubules of the digestive gland were distributed entirely in the dorsal region adjacent to the stomach and the digestive diverticula. In both mantle lobes there was connective tissue. For some individuals with shell length between 4.00 and 4.75 mm SL, adjacent to the epithelium of the mantle, there were groups of cells (clusters) undergoing mitosis (Figure 1) suggesting an early development stage of undifferentiated gonad. These individuals were considered undifferentiated because no sex determination was possible. For individuals with shell length > 5.00 mm, the observation of these clusters was in low proportion.

Fig. 1.

Brachidontes rodriguezii sexually immature (4.45 mm SL) with early stages of gametogenesis. Between the digestive gland and the epithelium of the mantle, there were clusters of cells undergoing mitosis (arrowhead) within acini. arrow, acinus wall cells; dg, digestive gland; mfe, epithelium of the mantle. Scale bar: 20 µm.

The histological examination showed differentiated gonads, allowing differentiation between immature males and females. The gonad consisted of acini distributed dorsal and laterally to the digestive gland and stomach (Figure 2A, B). The development of the connective tissue next to the gonad and into both mantle lobes was reduced. Immature males also exhibited few acini with early spermatogenic stages: spermatogonia, spermatocytes and spermatids (Figure 2C). This early development condition for males was registered between 4.00 and 7.38 mm SL. In immature females there were a few acini with early stages of oogenesis: oogonia, previtellogenic and early vitellogenic oocytes (Figure 2D). This early development condition for females was registered between 4.97 and 6.46 mm SL. The minimum SL with spermatozoa within acini was 6.00 mm SL, while the minimum SL with vitellogenic oocytes (mature oocytes) was 5.75 mm SL. However, the criteria for maturity included (besides the presence of mature gametes) acini increased in size and number and the decrease of the connective tissue. Mature males and females showed a well-developed gonad where the acini were distributed into the visceral mass next to the epithelium of the mantle and the tubules of the digestive gland. Also both mantle lobes were full of acini while the connective tissue was completely reduced. Gonads of mature males consisted of acini almost entirely filled with spermatozoa (Figure 2E) while mature females exhibited growing (early vitellogenic) and vitellogenic oocytes (Figure 2F). The first record of maturity according to the histological criteria described above was at 6.00 mm SL for males and 6.99 mm SL for females.

Fig. 2.

Transverse sections of immature B. rodriguezii. (A) Detail of male gonad (4.60 mm SL) with spermatogonia within acini next to the digestive gland. (B) Detail of a female gonad (4.97 mm SL) with aggregated oogonia. (C) Male gonad showing spermatocytes and spermatids (7.60 mm SL). (D) Female gonad showing ogonia, previtellogenic oocytes, and early vitellogenic oocytes (8.00 mm SL). (E) Mature male with gonad completely expanded into the mantle lobe full with spermatozoa in lumen (*) of the acini. (F) Female gonad with early vitellogenic and vitellogenic oocytes, arrowhead indicated wall of the acini. dg, digestive gland; evo, early vitellogenic oocytes; mfe, epithelium of the mantle; oo, oogonia; pvo, previtellogenic oocytes; spc, spermatocytes; spg, spermatogonias; spm, spermatids; vo, vitellogenic oocyte. Scale bars = A–D, 20 µm; E–F = , 50 µm.

The record of gametogenic activity according to shell length was summarized graphically based on histological characterization (Figure 3A–C). The proportion of mussels with different maturation conditions in each size class showed a high proportion of undifferentiated individuals with undeveloped gonads at smaller sizes; the proportion of males increased faster with respect to the size than females until both reached maturity and sex ratio showed no differences between males and females (Figure 3D).

Fig. 3.

Development of the gonad of B. rodriguezii as shell length increased. (A) Sexually immature and undifferentiated individuals. (B) Immature differentiated with an early development of gonad (shading). (C) Sexually mature. Between parentheses: shell length intervals for each stage. (D) Frequency of undifferentiated and differentiated individuals (males and females).

Size at first maturity

For differentiated individuals, males and females, the parameters of the logistic equation were: a = 1.07 and SL0 = 8.1 for males and f = 0.90 (∑dif2 0.01) and SL0 = 7.1 (∑dif2 0.16) for females. The value of the slope of the logistic function was higher in females than in males. The size at first maturity estimated was found to be 8.13 mm for males and 7.05 mm for females. For shell length larger than 14.00 mm all males were mature while all females larger than 13.00 mm were sexually mature (Figure 4).

Fig. 4.

Brachidontes rodriguezii. The proportion of mature females and males as a function of shell length (SL) modelled with a logistic function: the model fitted (females: continuous line and males: dotted line) (N = 270).

DISCUSSION

According to the results of this study, the development of gonads in B. rodriguezii occurred together with the start of gametogenic activity and size of gonads increased with shell length. The first acini were located laterally and dorsally to the digestive gland; while maturation progressed, the acini of the gonad increased their size and number and changed its distribution, reaching both mantle lobes. While development of gonad tissue occurred the connective tissue tended to become less abundant. Mature males and females exhibited a well-developed gonad which extended from the dorsal region of the visceral mass to both mantle lobes with mature gametes within acini. Our observation about gonad development coincided with descriptions made by Allen (Reference Allen1962) for Brachidontes recurves; the gonad is a branched organ with ducts which end in follicles. The early development of gonadal tissue begins in the mantle and spreads to the mesosoma. When individuals reach maturity the gonad occupies the entire mantle, mesosoma and penetrates into the foot and is adjacent to the stomach and digestive tubules. The morphology of gonadal tissue of B. rodriguezii resembles those mentioned for Perna viridis, Brachidontes exustus (Barber et al., Reference Barber, Fajans, Baker and Baker2005) and Mytilus galloprovincialis (Suárez et al., Reference Suárez, Alvarez, Molist and San Juan2005).

According to Stearns (Reference Stearns1992) females of species with external fertilization tend to delay maturity so females become mature at bigger sizes than males. Our results showed that B. rodriguezii males reached gonadal maturity at slightly shorter shell length than females, but 50% of the female population reached gonadal maturity at a smaller size than males: 7.05 mm for females and 8.13 mm shell length for males. The steep slope of the logistic function estimated for females suggested a faster transition from immature to mature population in females than in males.

Many studies showed that reproductive seasonality is related to temperature and food intake (Giese & Pearse, Reference Giese, Pearse, Giese and Pearse1974; Lubet et al., Reference Lubet, Gimázane and Prunus1981; Suárez et al., Reference Suárez, Alvarez, Molist and San Juan2005; Fearman & Moltschaniwskyj, Reference Fearman and Moltschaniwskyj2010). Franz (Reference Franz1996) studied gametogenic activity in Geukensia demissa exposed to a gradient of wave exposition and observed that individuals exposed to immersed condition during prolonged periods of time reached maturity at shorter sizes than individuals exposed to aerial conditions. Intertidal coast organisms are able to obtain food and oxygen and to avoid desiccation (stress conditions are reduced) only during the period of immersion (Petes et al., Reference Petes, Menge and Murphy2007, Reference Petes, Menge and Harris2008). Previous studies for a population of B. rodriguezii inhabiting a rocky coast, in the high level of the middle intertidal, reported a size of first maturity between 6.2 and 7 mm shell length (Nugent-Rincón, Reference Nugent-Rincón1989). In our study specimens were collected from the lower zone of pier pilings (middle intertidal) where mussels were under water even in low tides, suggesting an intake of resources and more appropriate conditions to grow and develop. Delgado & Defeo (Reference Delgado and Defeo2007) observed that Donax hanleyanus delayed maturity in beaches where individuals were able to allocate more resources for reproduction and somatic growth.

Size at first maturity together with the reproductive cycle constitute reproductive aspects that maximize reproductive effort of species (Todd, Reference Todd, Moore and Seed1985; Gage, Reference Gage1995). Size at first maturity could be useful in determining measures for adequate natural resource management (Chung, Reference Chung2007, Reference Chung2008) and spatial monitoring (Camacho-Mondragón et al., Reference Camacho-Mondragón, Arellano-Martínez and Ceballos-Vázquez2012). The mussel B. rodriguezii lacks fishery or artisanal exploitation at present, although it is considered an ecosystem engineer encouraging species to the landscape (Borthagaray & Carranza, Reference Borthagaray and Carranza2007; Carranza et al., Reference Carranza, Defeo, Beck and Castilla2009; Arribas et al., Reference Arribas, Donnarumma, Palomo and Scrosati2014); a key species that structures the intertidal benthic community from Buenos Aires Province to north Patagonia (Adami et al., Reference Adami, Tablado and Sodor2008; Arribas et al., Reference Arribas, Bagur, Klein, Penchaszadeh and Palomo2013), hence the importance of understanding as many population aspects as possible with special regard to reproductive biology. Further studies should focus on evaluating changes in settlement and population structure according to substrate and environmental conditions, due to the progressive increase in the use of man-made structures and its impact in coastal areas and biodiversity.

FINANCIAL SUPPORT

This work was partially supported by Universidad de Buenos Aires (grant UBACyT 086) and the Banco Interamericano de Desarrollo (grant PICT 1159).

References

REFERENCES

Adami, M., Pastorino, G. and Orenzans, J.M. (2013) Phenotypic differentiation of ecologically significant Brachidontes species co-occurring in intertidal mussel beds from the southwestern Atlantic. Malacologia 56, 59–68.Google Scholar
Adami, M.L., Tablado, A. and López Gappa, J.J. (2004) Spatial and temporal variability in intertidal assemblages dominated by the mussel Brachidontes rodriguezii (d'Orbigny, 1846). Hydrobiologia 520, 49–59.CrossRefGoogle Scholar
Adami, M.L., Tablado, A. and Sodor, M.A. (2008) Population dynamics of the intertidal mytilid Brachidontes rodriguezii (Bivalvia) on a rocky shore. Thalassas 24, 21–27.Google Scholar
Allen, F. (1962) Gonad development and spawning of Brachidontes recurvus in Chesapeake Bay. The Nautilus 75, 149–156.Google Scholar
Arribas, L.P., Bagur, M., Klein, E., Penchaszadeh, P.E. and Palomo, M.G. (2013) Geographic distribution of two mussel species and associated assemblages along the northern Argentinean coast. Aquatic Biology 18, 91–103.CrossRefGoogle Scholar
Arribas, L.P., Donnarumma, L., Palomo, M.G. and Scrosati, R.A. (2014) Intertidal mussels as ecosystem engineers: their associated invertebrate biodiversity under contrasting wave exposures. Marine Biodiversity 44, 203–211.CrossRefGoogle Scholar
Barber, B.J., Fajans, J.S., Baker, S.M. and Baker, P. (2005) Gametogenesis in the non-native green mussel, Perna viridis, and the native scorched mussel, Brachidontes exustus, in Tampa bay, Florida. Journal of Shellfish Research 24, 1087–1095.Google Scholar
Borthagaray, A.I. and Carranza, A. (2007) Mussels as ecosystem engineers: their contribution to species richness in a rocky littoral community. Acta Oecologica 31, 243–250.Google Scholar
Bulleri, F. and Chapman, M.G. (2010) The introduction of coastal infrastructure as a driver of change in marine environments. Journal of Applied Ecology 47, 26–35.CrossRefGoogle Scholar
Calcagno, J.A., Curelovich, J.N., Fernández, V.M., Thatje, S. and Lovrich, G.A. (2012) Effects of physical disturbance on a sub-Antarctic middle intertidal bivalve assemblage. Marine Biology Research 8, 937–953.Google Scholar
Camacho-Mondragón, M.A., Arellano-Martínez, M. and Ceballos-Vázquez, B.P. (2012) Particular features of gonadal maturation and size at first maturity in Atrina maura (Bivalvia: Pinnidae). Scientia Marina 76, 539–548.Google Scholar
Carranza, A., Defeo, O., Beck, M. and Castilla, J.C. (2009) Linking fisheries management and conservation in bioengineering species: the case of South American mussels (Mytilidae). Reviews in Fish Biology and Fisheries 19, 349–366.Google Scholar
Chung, E.Y. (2007) Oogenesis and sexual maturation in Meretrix lusoria (Röding 1798) (Bivalvia: Veneridae) in western Korea. Journal of Shellfish Research 26, 71–80.CrossRefGoogle Scholar
Chung, E.Y. (2008) Ultrastructural studies of oogenesis and sexual maturation in female Chlamys (azumapecten) farreri farreri (Jones and Preston, 1904) (Pteriomorphia: Pectinidae) on the western coast of Korea. Malacologia 50, 279–292.Google Scholar
Delgado, E. and Defeo, O. (2007) Tisular and population level responses to habitat harshness in sandy beaches: the reproductive strategy of Donax hanleyanus. Marine Biology, 152, 919–927.Google Scholar
Fearman, J.A. and Moltschaniwskyj, N.A. (2010) Warmer temperatures reduce rates of gametogenesis in temperate mussels, Mytilus galloprovincialis. Aquaculture 305, 20–25.Google Scholar
Franz, D.R. (1996) Size and age at first reproduction of the ribbed mussel Geukensia demissa (Dillwyn) in relation to shore level in a New York salt marsh. Journal of Experimental Marine Biology and Ecology 205, 1–13.CrossRefGoogle Scholar
Gage, M.J. (1995) Continuous variation in reproductive strategy as an adaptive response to population density in the moth Plodia interpunctella. Proceedings of the Royal Society of London 261, 25–30.Google Scholar
Giese, A.C. and Pearse, J.S. (1974) Introduction: general principles. In Giese, A.C. and Pearse, J.S. (eds) Reproduction of marine invertebrates, Vol. 1. New York, NY: Academic Press, 1–49.Google Scholar
Giménez, J. and Penchaszadeh, P.E. (2003) Size at first sexual maturity in Zidona dufresnei (Caenogastropoda: Volutidae) of the south-western Atlantic Ocean (Mar del Plata, Argentina). Journal of the Marine Biological Association of the United Kingdom 83, 293–296.Google Scholar
Gutiérrez, J.L., Palomo, M.G., Bagur, M., Arribas, L.P., and Soria, S.A. (2015) Wave action limits crowding in an intertidal mussel. Marine Ecology Progress Series 518, 153–163.Google Scholar
Howard, D.W., Lewis, E.J., Keller, B.J. and Smith, C.S. (2004) Histological techniques for marine bivalve mollusks and crustaceans. NOAA Technical Memorandum NOS NCCOS 5, 218.Google Scholar
Lubet, P., Gimázane, J.P. and Prunus, G. (1981) Etude du cycle de reproduction de Mytilus galloprovincialis (Lmk) (Moll. Lamelibranche) à la limite meridionale de son aire de repartition. Comparison avec les autres secteurs de cette aire. Haliotis 11, 157–170.Google Scholar
Mackie, G.L. (1991) Biology of the exotic zebra mussel, Dreissena polymorpha, in relation to native bivalves and its potential impact in Lake St. Clair. Hydrobiologia 219, 251–268.Google Scholar
Martins, G.M., Jenkins, S.R., Neto, A.I., Hawkins, S.J. and Thompson, R.C. (2015) Long-term modifications of coastal defences enhance marine biodiversity. Environmental Conservation 43, 109–116.Google Scholar
Nugent-Rincón, P.L. (1989) Ecología y biología de los mejillinares de Brachydontes rodriguezi (D'Orbigny, 1846), Lamy 1936, en el litoral bonaerense. PhD thesis. Universidad Nacional de La Plata, Argentina.Google Scholar
Penchaszadeh, P.E. (1973) Ecología de la comunidad del mejillín (Brachydontes rodriguezi d'Orb.) en el mediolitoral rocoso de Mar del Plata (Argentina): el proceso de recolonización. Physis 32, 51–64.Google Scholar
Petes, L.E., Menge, B.A. and Harris, A.L. (2008) Intertidal mussels exhibit energetic trade-offs between reproduction and stress resistance. Ecological Monographs 78, 387–402.Google Scholar
Petes, L.E., Menge, B.A. and Murphy, G.D. (2007) Environmental stress decreases survival, growth, and reproduction in New Zealand mussels. Journal of Experimental Marine Biology and Ecology 351, 83–91.Google Scholar
Roa, R., Ernst, B. and Tapia, F. (1999) Estimation of size at sexual maturity: an evaluation of analytical and resampling procedures. Fishery Bulletin 97, 570–580.Google Scholar
Scelzo, M.A., Elías, R., Vallarino, E.A., Charrier, M., Lucero, N. and Alvarez, F. (1996) Variación estacional de la estructura comunitaria del bivalvo intermareal Brachidontes rodriguezii (D'Orbigny, 1846) en sustratos artificiales (Mar del Plata, Argentina). Neritica 10, 87–102.Google Scholar
Stearns, S. (1992) The evolution of life histories. New York, NY: Oxford University Press.Google Scholar
Suárez, M.P., Alvarez, C., Molist, P. and San Juan, F. (2005) Particular aspects of gonadal cycle and seasonal distribution of gametogenic stages of Mytilus galloprovincialis cultured in the estuary of Vigo. Journal of Shellfish Research 26, 531–540.Google Scholar
Todd, C.D. (1985) Reproductive strategies of north-temperate rocky shore invertebrates. In Moore, P.G. and Seed, R. (eds) The ecology of rocky coasts. London: Hodder and Stoughton, pp. 203–219.Google Scholar
Torroglosa, M.E. (2015) Biología reproductiva y crecimiento de Brachidontes rodriguezii (d'Orbigny, 1846) en sustratos duros artificiales en playas arenosas de la provincia de Buenos Aires. PhD thesis. Universidad de Buenos Aires, Buenos Aires, Argentina. 143 pp.Google Scholar
Torroglosa, M.E. and Giménez, J. (2010) Temporal variation in size at maturity of the snail Zidona dufresnei from the Southwestern Atlantic Ocean after ten years of fishery exploitation. Aquatic Biology 11, 163–167.Google Scholar
Torroglosa, M.E. and Giménez, J. (2015) Sperm ultrastructure in two species of Brachidontes (Bivalvia, Mytilidae) from the Southwestern Atlantic Ocean. Journal of the Marine Biological Association of the United Kingdom 95, 991–998.Google Scholar
Vallarino, E.A., Rivero, M.S., Gravina, M.C. and Elías, R. (2002) The community-level response to sewage impact in intertidal mytilid beds of the Southwestern Atlantic and the use of the Shannon index to assess pollution. Revista de Biología Marina y Oceanografía 37, 25–33.Google Scholar
Figure 0

Fig. 1. Brachidontes rodriguezii sexually immature (4.45 mm SL) with early stages of gametogenesis. Between the digestive gland and the epithelium of the mantle, there were clusters of cells undergoing mitosis (arrowhead) within acini. arrow, acinus wall cells; dg, digestive gland; mfe, epithelium of the mantle. Scale bar: 20 µm.

Figure 1

Fig. 2. Transverse sections of immature B. rodriguezii. (A) Detail of male gonad (4.60 mm SL) with spermatogonia within acini next to the digestive gland. (B) Detail of a female gonad (4.97 mm SL) with aggregated oogonia. (C) Male gonad showing spermatocytes and spermatids (7.60 mm SL). (D) Female gonad showing ogonia, previtellogenic oocytes, and early vitellogenic oocytes (8.00 mm SL). (E) Mature male with gonad completely expanded into the mantle lobe full with spermatozoa in lumen (*) of the acini. (F) Female gonad with early vitellogenic and vitellogenic oocytes, arrowhead indicated wall of the acini. dg, digestive gland; evo, early vitellogenic oocytes; mfe, epithelium of the mantle; oo, oogonia; pvo, previtellogenic oocytes; spc, spermatocytes; spg, spermatogonias; spm, spermatids; vo, vitellogenic oocyte. Scale bars = A–D, 20 µm; E–F = , 50 µm.

Figure 2

Fig. 3. Development of the gonad of B. rodriguezii as shell length increased. (A) Sexually immature and undifferentiated individuals. (B) Immature differentiated with an early development of gonad (shading). (C) Sexually mature. Between parentheses: shell length intervals for each stage. (D) Frequency of undifferentiated and differentiated individuals (males and females).

Figure 3

Fig. 4. Brachidontes rodriguezii. The proportion of mature females and males as a function of shell length (SL) modelled with a logistic function: the model fitted (females: continuous line and males: dotted line) (N = 270).