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Taking advantage of the unique system of doubly uniparental inheritance (DUI) of mitochondria, we developed a reliable molecular method to sex individuals of the marine bivalve Macoma balthica rubra. In species with DUI (~100 known bivalves), both sexes transmit their mitochondria: males bear both a male‐ and female‐type mitogenome, while females bear only the female type. Male and female mitotypes are sufficiently divergent to reliably PCR‐amplify them specifically. Loop‐mediated isothermal amplification (LAMP) is a precise, economical and portable alternative to PCR for molecular sexing and we demonstrate its application in this context. We used 154 individuals sampled along the Atlantic coast of France and sexed microscopically by gonad examination to test for the congruence among gamete type, PCR sexing and LAMP sexing. We show an exact match among the sexing results from these three methods using the male and female mt‐cox1 genes. DUI can be disrupted in inter‐specific hybrids, causing unexpected distribution of mitogenomes, such as homoplasmic males or heteroplasmic females. To our knowledge, DUI disruption at the intra‐specific scale has never been tested. We applied our sexing protocol to control for unexpected heteroplasmy caused by hybridization between divergent genetic lineages and found no evidence of disruption in the mode of mitochondrial inheritance in M. balthica rubra. We propose LAMP as a useful tool to accelerate eco‐evolutionary studies of DUI. It offers the opportunity to investigate the potential role of, previously unaccounted‐for, sex‐specific patterns such as sexual selection or sex‐specific dispersal bias in the evolution of free‐spawning benthic species. [ABSTRACT FROM AUTHOR]

Mercury concentration [Hg] was assessed in 20 adult Allis shad Alosa alosa (54–59 cm) and 20 adult Twaite shad Alosa fallax (36–44 cm) collected during their spawning migration in the Dordogne and the Garonne rivers (France). [Hg] was measured in the gills, dorsal muscle, liver and kidney. Twaite shad exhibited higher [Hg] than Allis shad. Median [Hg] values were [Hg]Gills = 0.33 μg g−1 (dw), [Hg]Muscle = 1.22 μg g−1, [Hg]Liver = 1.99 μg g−1, [Hg]Kidney = 1.93 μg g−1 for Twaite shad and [Hg]Gills = 0.06 μg g−1, [Hg]Muscle = 0.20 μg g−1, [Hg]Liver = 1.18 μg g−1, [Hg]Kidney = 1.08 μg g−1 for Allis shad. In order to understand such differences, we investigated some life history traits of the two species: migratory history, age (3–6 years), size at age (an expression of growth) and the number of spawning events (0–2 events). The difference in estuarine residence time between the juveniles of both species, which was assumed to influence [Hg], was investigated using otolith Sr:Ca ratio. The microchemical analysis revealed a significant difference in the residence time of juveniles in the estuary (medians are 21 d and 10 d for Twaite shad and Allis shad, respectively) but this residence time seems too short to influence [Hg] (Allis shad: r spearman < 0.128; Twaite shad: r spearman < −0.340). As both species show the same age structure, the influence of age on [Hg] was negligible. The literature shows that the differences in growth and in the number of spawning events reported in our study are in favour of a higher [Hg] for Twaite shad than for Allis shad. Although trophic status was not investigated here, the literature reveals that it is another factor that could produce higher [Hg] in Twaite shad, since its diet includes higher trophic levels than Allis shad. [ABSTRACT FROM AUTHOR]