Larval growth of the polychaete Arenicola marina under different temperature and food conditions: consequences on bioenergetic models.

Arenicola marina, a marine benthic polychaete, is widespread on sandy beaches in Europe and considered as an ecosystem engineer despite commonly used as bait by fishermen. Data regarding the bioenergetics of the lugworm larval stages are still incomplete. Trochophore is initially lecithotroph and then becomes planktotroph while growing as metatrochophore on subtidal area, a quite stable daily temperature environment compared with the foreshore, where juveniles and adult live, with daily temperature fluctuating up to 15°C. These discrepancies in temperature ranges may influence the temperature corrections (TCs) that control metabolic rates during the life cycle of A. marina. We carried out laboratory experiments in microcosms by inducing artificial spawning of lugworms, and then undertaken in vitro fertilization to obtain embryos and, finally, to follow, the larval development up to 10 segments with chaetae for 50 days under three temperature conditions (13°C, 15°C and 17°C) and two food conditions ('fed' and 'non-fed'). The first feeding ('birth') of A. marina larvae was deciphered anatomically for a size between 450 and 500 µm and described at 17 days post-fertilization for larvae reared at 15°C and 17°C. Using a biphasic model with a von Bertalanffy growth before 'birth' and an exponential growth after 'birth', among the three temperature treatments, the 15°C condition exhibited the best larval performance. TC based on embryonic and larval metabolic rates gave an Arrhenius temperature of ~6661 K and a higher boundary temperature tolerance range of ~294.5 K. Both temperature values differ from those calculated from TC based mostly on juvenile and adult metabolic rates. We claim to use two sets of Arrhenius temperatures according to the life history stages of A. marina while using Dynamic Energy Budget model. This model was developed initially in order to manage the conservation of the lugworm species.

Gonadal transcriptomes associated with sex phenotypes provide potential male and female candidate genes of sex determination or early differentiation in Crassostrea gigas, a sequential hermaphrodite mollusc.

BACKGROUND: In the animal kingdom, mollusca is an important phylum of the Lophotrochozoa. However, few studies have investigated the molecular cascade of sex determination/early gonadal differentiation within this phylum. The oyster Crassostrea gigas is a sequential irregular hermaphrodite mollusc of economic, physiological and phylogenetic importance. Although some studies identified genes of its sex-determining/-differentiating pathway, this particular topic remains to be further deepened, in particular with regard to the expression patterns. Indeed, these patterns need to cover the entire period of sex lability and have to be associated to future sex phenotypes, usually impossible to establish in this sequential hermaphrodite. This is why we performed a gonadal RNA-Seq analysis of diploid male and female oysters that have not changed sex for 4 years, sampled during the entire time-window of sex determination/early sex differentiation (stages 0 and 3 of the gametogenetic cycle). This individual long-term monitoring gave us the opportunity to explain the molecular expression patterns in the light of the most statistically likely future sex of each oyster. RESULTS: The differential gene expression analysis of gonadal transcriptomes revealed that 9723 genes were differentially expressed between gametogenetic stages, and 141 between sexes (98 and 43 genes highly expressed in females and males, respectively). Eighty-four genes were both stage- and sex-specific, 57 of them being highly expressed at the time of sex determination/early sex differentiation. These 4 novel genes including Trophoblast glycoprotein-like, Protein PML-like, Protein singed-like and PREDICTED: paramyosin, while being supported by RT-qPCR, displayed sexually dimorphic gene expression patterns. CONCLUSIONS: This gonadal transcriptome analysis, the first one associated with sex phenotypes in C. gigas, revealed 57 genes highly expressed in stage 0 or 3 of gametogenesis and which could be linked to the future sex of the individuals. While further study will be needed to suggest a role for these factors, some could certainly be original potential actors involved in sex determination/early sex differentiation, like paramyosin and could be used to predict the future sex of oysters.

Determination of annual reproductive cycle in male sterlet, Acipenser ruthenus using histology and ultrasound imaging.

The aim of this study was to evaluate seasonal testicular development in the cultured sterlet, Acipenser ruthenus. During annual sexual cycle of male sterlet, stages of gonad maturity were examined using histology and ultrasonography approaches. The histology identified males at different stages of maturity among fish sampled monthly. According to the seasonal changes in the testes, reproductive cycle was divided into four stages including resting, pre-spawning, spawning, and post-spawning. The histology examination revealed considerable variation in testicular developmental stages. These changes were identified based on persistent spermatogenesis and asynchronous gonad development in testes, showing that regulation of annual gonadal cycle is influenced by season. Also, the results obtained using ultrasound suggested that reproductive stages can be identified based on morphology and tissue echogenicity. At each phase of testicular development, gonadosomatic index (GSI) and number of spermatogenic cysts were variable. The present study focused on determination of annual reproductive development in cultured male sterlet which clearly identifies reproductive stage in each season as valuable guide for future researches on reproductive biology of sterlet. This study presents basic knowledge about reproductive biology in sterlet contributing to optimal broodstocks management that allows comparison of reproductive development among sturgeon species.