Annual Variation in the Levels of Transcripts of Sex-Specific Genes in the Mantle of the Common Mussel, Mytilus edulis

Abstract

Mytilus species are used as sentinels for the assessment of environmental health but sex or stage in the reproduction cycle is rarely considered even though both parameters are likely to influence responses to pollution. We have validated the use of a qPCR assay for sex identification and related the levels of transcripts to the reproductive cycle. A temporal study of mantle of Mytilus edulis found transcripts of male-specific vitelline coat lysin (VCL) and female-specific vitelline envelope receptor for lysin (VERL) could identify sex over a complete year. The levels of VCL/VERL were proportional to the numbers of sperm/ova and are indicative of the stage of the reproductive cycle. Maximal levels of VCL and VERL were found in February 2009 declining to minima between July – August before increasing and re-attaining a peak in February 2010. Water temperature may influence these transitions since they coincide with minimal water temperature in February and maximal temperature in August. An identical pattern of variation was found for a cryptic female-specific transcript (H5) but a very different pattern was observed for oestrogen receptor 2 (ER2). ER2 varied in a sex-specific way with male > female for most of the cycle, with a female maxima in July and a male maxima in December. Using artificially spawned animals, the transcripts for VCL, VERL and H5 were shown to be present in gametes and thus their disappearance from mantle is indicative of spawning. VCL and VERL are present at equivalent levels in February and July–August but during gametogenesis (August to January) and spawning (March to June) VCL is present at lower relative amounts than VERL. This may indicate sex-specific control mechanisms for these processes and highlight a potential pressure point leading to reduced reproductive output if environmental factors cause asynchrony to gamete maturation or release.

Transcriptomic and Network Analyses Reveal Mechanistic-Based Biomarkers of Endocrine Disruption in the Marine Mussel, Mytilus edulis

“…Results of the RT-qPCR sex identification assay for mussels exposed to 5 ng/L and 50 ng/L EE2 for 39 days. Sex of mussels were identified by using the difference of a female specific egg protein, the vitelline envelope receptor for lysin (VERL), and a male specific sperm protein, vitelline coat lysin (VCL) . If the difference between transcripts ΔCt­(VERL-VCL) is positive the mussel is male, while negative values represent females.…”

“…Sex of mussels were identified by using the difference of a female specific egg protein, the vitelline envelope receptor for lysin (VERL), and a male specific sperm protein, vitelline coat lysin (VCL). 39 If the difference between transcripts ΔCt(VERL-VCL) is positive the mussel is male, while negative values represent females. A: Individual lines represent one mussel with 16 mussels analyzed per treatment.…”

“…Five sites throughout the Northeast including Jamaica Bay, NY; Port Jefferson NY; Boston Harbor, MA; Falmouth, MA; and Savin Hill Cove, MA (Table S7, Figure S1) were selected to validate the laboratory developed biomarkers in the field or to determine if sites may be susceptible to endocrine disruption. From each site 15 mussels were collected for sex identification in mantle tissue 39 and for biomarker analysis in the digestive gland. Each sample was dissected in the field, placed in RNA later on ice, and stored in RNA later at −20 °C when returned to the laboratory.…”

Local interspecies introgression is the main cause of extreme levels of intraspecific differentiation in mussels

“…While most of the genome is resistant to current introgression in European M. edulis , identification of within‐species outliers between American and European M. edulis populations showed a putative case of adaptive introgression in Europe. A gene expressed solely in females (H5, Anantharaman & Craft ) has swept through M. edulis and M. galloprovincialis across the hybrid zone, while being structured between American M. edulis and Mediterranean M. galloprovincialis (Fig. B).…”

DNA fragmentation in blue mussel (Mytilus edulis) sperm: aquaculture and fisheries implications

“…Blue mussels ( Mytilus edulis ) are sessile, filter‐feeding organisms that inhabit coastal areas over a broad geographical area (Anantharaman & Craft ). In their natural environment, mussels reproduce by broadcast‐spawning with synchronization between males and females to produce mature gametes at the same time based on environmental cues (Anantharaman & Craft ). In recent years, commercial hatcheries have shown interest in producing blue mussel spat (Pronker, Nevejan, Peene, Geijsen & Sorgeloos ).…”