Identifying Robust Proxies of Gonad Maturation for the Protandrous HermaphroditeTridacna maxima(Röding, 1798, Bivalvia) from Individual to Population Scale

Abstract

Monitoring gonad maturation for protandrous and functional hermaphrodite species such as the giant clam Tridacna maxima is difficult due to the juxtaposition and relative proportion of male and female tissues in the gonad [gonadal sex ratio (GSR)].Here, the relevance of the widely used gonadosomatic index (GSI) as proxy of giant clam gonad maturation is tested with a large dataset (n ¼ 265). Gonadosomatic index is compared with other indices, namely the proportion of the male part harboring spermatozoids, the proportion of empty oocyte follicles, the mean oocyte diameter, and the oocyte elongation. At gonad scale, high index variability highlighted partial spawning. At individual scale, male and female maturation proxies were contrasted, showing either asynchronous emissions of male and female gametes or contrasted spermatogenesis and oogenesis duration. The GSI was mostly driven by the number and diameter of oocytes and therefore it is recommended here as primary proxy for female maturity. Except for the oocyte elongation, all indices were affected by the GSR, which ruled out drawing conclusions at population scale. These results highlight the need for maturation stage proxies that are optimized for functional hermaphrodite species.

Growth, Survival and Reproduction of the Giant Clam Tridacna maxima (Röding 1798, Bivalvia) in Two Contrasting Lagoons in French Polynesia

“…To date, very few studies have looked into the reproductive activity of giant clams [27, 44]. In particular, spawning periods and stimuli for spawning events in natural environments have not been clearly identified [45].…”

“…The proportion of female versus male tissues (The “Gonadal Sex Ratio”, GSR) and the proportion of male tissues harbouring spermatozoids (SPZ) were also calculated using histological treatments and used as proxy of sexual maturity, following the procedure recommended by a recent study [27]. …”

Shell dimension-weight relationships in the blood cockle Larkinia grandis (Bivalvia: Arcidae) on the southeastern coast of the Gulf of California

“…The CV for BW showed high dispersion (24%-45%), suggesting a possible reproductive event during sampling (Khalil et al 2017). The shell measurement ranges, the 2 peaks observed for BW, and consequently the higher CV obtained for BW suggest the gonad maturation index as the main cause of the BW fluctuation (Menoud et al 2016). The regression equations for the relationships between BW and the 3 shell measurements indicate negative allometric growth in L. grandis, with values of b < 3.…”

“…Esto coincide con lo reportado por Borda y Cruz (2004), que indicaron que la edad adulta reproductiva en Anadara tuberculosa se presenta a los 25 mm LT. El CV para BW mostró una alta dispersión (24%-45%), lo que sugiere que posiblemente ocurrió un evento reproductivo durante el muestreo (Khalil et al 2017). Los intervalos de las medidas de las conchas, los 2 picos observados para el BW y el consecuente mayor CV obtenido para el BW sugieren que el índice de maduración de las gónadas es la principal causa de la fluctuación del BW (Menoud et al 2016). Las ecuaciones de regresión para las relaciones entre el BW y las 3 medidas de la concha indican un crecimiento alométrico negativo en L. grandis, con valores de b < 3.…”

Identifying conserved molecular mechanisms of thermo-acclimation in symbiotic organisms

“…Only one individual was used in an effort to reduce assembly polymorphism biases. For this individual, sexual status was confirmed by gonad biopsy and histology following a previously detailed procedure ( 84 ). This individual was not included in the differential expression analysis.…”