Marian Alejandra Camacho-Mondragón

Unnoticed sex change in Atrina maura (Bivalvia: Pinnidae): Histological and size structure evidence

Abstract: Sex-change (protandry or protogyny) has gone unnoticed in many bivalves due to the rapid occurrence of this process. In this paper, histological evidence and analyses of the size structure of three geographically separated populations on the northwestern coast of México together with theoretical considerations strongly suggest that Atrina maura (Sowerby I, 1835) is a protandric species. The gonads of a total of 931 A. maura specimens collected in the three study sites were analyzed: Ojo de Liebre lagoon (27°55′N, 114°20′W from March 2002 through February 2003), Ensenada de La Paz (24°11′N, 110°26′W, from May 2004 through June 2005 and during 2007), and Bahía Magdalena (24°30′N, 111°48′W, from March through October 2008). Microscopic analysis of gonads of hermaphrodite specimens enabled the reconstruction of a detailed histological sequence during the male-to-female transition. Analysis of the sex ratio by size class revealed that males occur primarily in the smaller classes, females in the larger classes and hermaphrodites in intermediate size classes. All the evidence substantiate the hypothesis that this species is not gonochoric.

Ultrastructural and Histological Study of Oogenesis and Oocyte Degeneration in the PenshellAtrina maura(Bivalvia: Pinnidae)

Abstract The successive stages of oogenesis and the changes involved in the oocyte degeneration process in the penshell Atrina maura were examined using light and transmission electron microscopy. The ovarian maturation process is asynchronous, as oocytes at different developmental stages can be found simultaneously. Oocytes develop from oogonia and then undergo three distinct stages of oogenesis: previtellogenesis, vitellogenesis and postvitellogenesis with mature oocytes. Atrina maura displays a solitary oogenesis type, in which follicular cells become associated with oocytes from the earliest stages of development and seem to play an integral role in vitellogenesis. The cytoplasm of vitellogenic oocytes contains numerous whorls of rough endoplasmic reticulum and Golgi bodies, suggesting that auto-synthetic vitellogenesis may occur in this species. In addition, the degeneration process of postvitellogenic oocytes triggered by a seasonal increase in water temperature (> 25°C) is described.

Ultrastructure of the Spermatogenic Process in the Penshell Atrina maura (Bivalvia: Pinnidae)

ABSTRACT The ultrastructural features of the spermatogenic development and mature spermatozoa morphology of Atrina maura were investigated through transmission electron microscopy. The testis displays a diffuse tubular structure in which gametes develop within a concentric arrangement according to the degree of development. Within the tubules also appear Sertoli cells, which contain a large amount of lipid droplets and glycogen granules in the cytoplasm, suggesting a nutritive role in the first spermatogenesis stage (spermatogonia). Four gamete maturation stages co-occurred in the same individual: spermatogonia (4–8 &mgr;m), spermatocytes (3–4 &mgr;m) (including primary and secondary), spermatids (2.5 &mgr;m) and spermatozoa (∼ 2 &mgr;m head length). The proacrosomal vesicle and flagellum occur only until the first stages of spermiogenesis, contrasting with the early formation of both structures in spermatogonia and spermatocytes in other bivalves. In A. maura, the material in the acrosomal vesicle of mature spermatozoa shows a characteristic electron density pattern, which seems to be an exclusive taxonomic feature of the family Pinnidae. However, A. maura displayed only four mitochondria in the midpiece, contrasting with five in all other species in this family.

Ultrastructure of Sperm Development and Mature Sperm Morphology in Spondylus calcifer and S. Princeps (Bivalvia: Spondylidae)

ABSTRACT The entire spermatogenesis process and the presence of accessory cells in sperm development in Spondylus princeps Broderip, 1833, and S. calcifer Carpenter, 1857, were described for the first time. Spermatogenesis in both species showed similar anatomical and ultrastructural features. The testis contained amoeboid somatic cells inside the acini, frequently associated with developing gametes. Overall, spermatogenesis followed the typical pattern reported for other bivalve species, except for a few specific details. In S. princeps, intercellular bridges between spermatogonia, as well as one spermatocyte with seven mitochondria were observed. Both species had mature sperm of the ect-aquasperm type, consisting of a head, which contains a spherical-pyriform nucleus and a conical acrosome bounded by two regions of different density, four spherical mitochondria and two centrioles in the middle piece; the flagellum showed a standard 9 + 2 microtubule arrangement.

REPRODUCTIVE AND LARVAL PERFORMANCE OF THE PEN SHELL ATRINA MAURA IN RELATION TO THE ORIGIN AND CONDITION OF BROODSTOCK

ABSTRACT The pen shell Atrina maura has economic importance in northwestern Mexico, but limitations to rear larvae in hatcheries increased the interest of scientists and producers to study aspects of reproduction and larval cultivation. Reproductive and larval performances of the species were studied in relation to the origin (depth, phases of tidal cycle) and gross condition of broodstock. The results were correlated to variations in water temperature and concentration of chlorophyll a. Tide influenced spawning response, which was between 40% and 100% successful in broodstock collected during rising and falling tides and only 10% at high or low tides (this percentage corresponds tomales only). The number and size of released and fertilized eggs and the survival of larvae were higher in pen shells collected at 5–8 m depth, compared with those collected at less than 1m. The number and size of released and fertilized eggs, number of veliger larvae, and the survival and growth rate of larvae were significantly higher in January 2012 and correspond to low temperatures, high concentrations of food, high percent of ripe gonads, high-condition index (CI), and low-muscle index (MI). These indicators were significantly lower in March 2012, when broodstock had the lowest percent of ripe gonads, the lowest CI, and the highest MI of all samples. The number and size of released eggs was positively correlated with concentration of chlorophyll a and negatively correlated with temperature, indicating that both factors play a different role in regulating reproductive output.