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International Journal of Morphology

versión On-line ISSN 0717-9502

Int. J. Morphol. v.28 n.2 Temuco jun. 2010

http://dx.doi.org/10.4067/S0717-95022010000200038 

Int. J. Morphol.,28(2):569-573, 2010.

Hermaphroditism in Marine Mussel Perumytilus purpuratus (Lamarck, 1819), (Mollusca: Mytilidae)

 

Hermafroditismo en el Chorito Perumytilus purpuratus (Lamarck, 1819), (Mollusca: Mytilidae)

*Diana Montenegro Villalobos; **Alberto Olivares Paz & *María Teresa González

* Instituto de Investigaciones Oceanológicas. Facultad de Recursos del Mar, Universidad de Antofagasta, Casilla 170, Antofagasta, Chile.

**Departamento de Acuicultura. Facultad de Recursos del Mar, Universidad de Antofagasta, Casilla 170, Antofagasta, Chile.

Corresponence to:


SUMMARY: Marine bivalves are essentially gonochoric species. However, some occasional hermaphrodites specimens can be found. A histological description of two (among 179) hermaphrodites of the marine mussel Perumytilus purpuratus (Lamarck, 1819) that were collected in San Jorge Bay (24S) is given. The low proportion of hermaphrodites suggests that P. purpuratus hermaphroditism could be an accidental phenomenon; nevertheless other causes are also discussed in the present study.

KEY WORDS: Bivalve; Hermaphroditism; Perumytilus purpuratus.


RESUMEN: Los bivalvos marinos son principalmente especies gonocoricas. Sin embargo, ocasionales especímenes hermafroditas pueden encontrarse. Una descripción histológica de dos (de 179) especímenes hermafroditas del chorito Perumytilus purpuratus (Lamarck, 1819) es registrada, los que fueron colectados en la bahía de San Jorge (24S). La baja proporción de hermafroditas de Perumytilus purpuratus sugiere que podría ser un fenómeno accidental, aun así otras posibles causas son discutidas en el presente estudio.

PALABRAS CLAVE: Bivalvos; Hermafroditismo; Perumytilus purpuratus.


INTRODUCTION

Bivalves (also known as lamellibranchs or pelecypods) include groups such as clams, mussels, scallops, and oysters (Brink, 2001). Among the more than 10,000 species belonging to the class Pelecypoda may be found in different degrees of sexual differentiation from species that are strictly of separated sexes in relations to those that are almost invariably functionally hermaphroditic (Coe, 1943). Especially, freshwater bivalves are often hermaphroditic (Morton, 1991). However, hermaphroditic individuals occasionally have been found in species strictly considered gonochoric (Heller, 1993), such as clams Ruditapes decussatus (L.) (Delgado & Perez, 2002), Anadara granosa (L.) and Anadara Antiqua (L.), which have simultaneously male and female tissue in the same follicle (Afiati, 2007). Similarly, Ceuta et al. (2007) recorded hermaphroditism in two clams species Tagelus plebeius (Lightfoot, 1786) and Iphigenia brasiliana (Lamark, 1818), Vinuesa (1977) reported the first hermaphrodite in mussel Aulacomya ater (Molina) and Villalon (1965) reported one of 4309 (0.023%) specimen of Perumytilus purpuratus (Lamarck, 1819) with male and female gonads.

Perumytilus purpuratus is a common marine mussel in the rocky intertidal habitats from Ecuador to Strait of Magellan, extending up to the Atlantic coast of Santa Cruz, Argentina. This specie is diocious, the female mantle is brown and the mantle of male is yellow (Osorio & Bahamonde, 1968; Paredes & Tarazona, 1980).

In the present paper, a histological description as an evidence of hermaphroditism in Perumytilus purpuratus from the Northern Chilean coast is recorded.

MATERIAL AND METHOD

Between September and November 2009, at low tides, 179 specimens of Perumytilus purpuratus were collected in lower intertidal layer along the coastal area of San Jorge Bay. The specimens were measured by using a digital caliper (precision 0.01 mm). Taking into account that reproductive tissue in mytilids expand and invade soft tissues in the visceral mass and mantle lobes (Field, 1922), sex was determined based on gonad tissue color and the mantle: male (Fig. 1), female (Fig. 2) and in the case of the hermaphrodites specimens, one lobe of the mantle was browner and the other was yellow (Fig. 3). Hermaphrodites were found in intertidal zone of Las Petroleras beach (2336´S; 7023´W). The gonads were fixed with Davidson solution, dehydrated, embedded in paraplast, sectioned at 5 µm with Microtome Minot and stained with haematoxylin and eosin (Bancroft & Steves, 1990).

Figs. 1-3. Observation of specimens male (Fig. 1),
female (Fig. 2) and hermaphrodite (Fig. 3)
of Perumytilus purpuratus: T: testis; O: ovary.

RESULTS AND DISCUSSION

Mussel sizes varied from 27.77 mm to 38.72 mm. The size frequency is shown in Table I. The lengths of hermaphrodite mussels were 34.18 mm and 29.5 mm. The proportion of sexes did not differ from 1:1 (c2= 6.635; p< 0.01) Zar (1996).

In the general structure of male gonads in P. purpuratus, the testis are formed by seminiferous follicles (Fig. 4), whose epithelium contains spermatogenic cells, organized in layers, and Sertoli cells (Pipe, 1987). In female, the ovary is organized by gonadal follicles (See figure 5); with mature oocytes inside of them (Mykhalow et al., 1995). Hermaphrodites presented in the testis, follicles with fully mature sperm and other follicles with total emission of male gametes but in the stratum basale a reduced number of oocytes (Figs. 6 and 7). In summary the presence of male follicles in the lumen and the presence of oocytes, are evidences of a hermaphroditism in mussels Perumytilus purpuratus.

Fig. 4. Observation of mature seminiferous tubule. Spermatogonia (Sg),
Spermatocyte (Sc). Round spermatid (Rst). Elongated
spermatid (Est) and spermatozoa (Sz).

Fig. 5. Ovarian follicle with a high number of mature
oocytes (Mo), and immature oocytes (Io).

Figs. 6 y 7. Gonads of hermaphrodite with
mature seminiferous tubule (St)
and ovarian follicles(Of), contain immature oocytes
(Io) and the lumen spermatozoa (Sz).

Figs. 4-7. Gonadal histology of Perumytilus
purpuratus. Stain Hematoxilene & Eosine.

Other cases of occasional hermaphroditism in mollusks have been recorded in Cephalopods (Ortiz & Re, 2006), Polyplacophora (Scarano & Ituarte, 2009), and Gastropoda (Olivares et al., 2009). The scarce records of hermaphrodite individuals indicate that it could be an accidental phenomenon (Calvo et al., 1998); however, mechanisms of sexual differentiation control are not absolutes. Beninger & Le Pennec (1991) mentioned that it is possible to find low frequency of hermaphrodite specimens, even within gonochoric species. In the similar line, Coe suggested that these occasional individuals with functional hermaphroditism can all be considered as a result from deviations in developmental processes, due to the failure of the sex differentiating mechanism to function normally.

The endocrine systems of invertebrates generally regulate the same processes that are found in vertebrates such as development, growth, and reproduction (Oehlmann & Shutlte-Oehlmann, 2003). Several compounds or groups are known to disrupt specific invertebrate endocrine systems, including development and reproductive function (Defur, 2004). Endocrine disruptors include organotin, organichlorine, pesticides, industrial chemical (biphenyls and polycyclic aromatic hydrocarbons) (Lintelmann et al., 2003). Some authors have found incidence of ovotestis (produce eggs and sperm) in bivalves, which suggest that associations with urban, industrial, or organotin presence could be established. However, they indicate that the mode of action remains largely unclear (Chesman & Langston, 2006; Horiguchi et al., 2000; Langston et al., 2007; Petridis et al., 2009). In our study the hermaphrodites (ovotestis) were found in a polluted location by polycyclic aromatic hydrocarbons and heavy metals (Salamanca et al., 2004; CREA, 2005). Despite this, more evidence is needed to confirm that this hermaphroditism is related to pollution.

In conclusion, evidence of hermaphroditism in Perumytilus purpuratus is recorded. Although these hermaphrodite specimens could be an occasional occurrence in Perumytilus purpuratus and additional studies will be necessary to link them to pollution, endocrine disruption and the sexual development of the mussel Perumytilus purpuratus.

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Corresponence to:

Alberto Olivares Paz.
Departamento de Acuicultura
Facultad de Recursos del Mar
Universidad de Antofagasta
Casilla 170, Antofagasta
CHILE

Email: aolivares@uantof.cl

Received: 26-03-2010
Accepted: 17-04-2010

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