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Verísimo, P., Bernárdez, C., González-Gurriarán, E., Freire, J., Muiño, R., and Fernández, L. 2011. Changes between consecutive broods in the fecundity of the spider crab, Maja brachydactyla. – ICES Journal of Marine Science, 68: . An analysis of the fecundity of Maja brachydactyla and the possible causes for its variability was carried out during two breeding cycles in the Ría de Arousa (Galicia, NW Spain). Based on brood samples with known weight data, subsample counts were taken of the number of eggs (125 081–530 309 eggs), and dry weight and volume of individual eggs were recorded. The main cause of variability in egg number and dry weight of the broods was female body length. Moreover, the size of the broods during the two breeding cycles and of subsequent broods exhibited significant differences in terms of both fecundity (p < 0.05) and brood dry weight (p< 0.05). The first broods contained fewer, larger eggs (a greater energy investment per egg), whereas subsequent broods contained more, smaller eggs (less energy investment per egg).

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Mitochondria are mostly inherited by maternal via, that is, only mitochondria from eggs are retained in the embryos. However, this general assumption of uniparentally transmitted, homoplasmic and non-recombining mitochondrial genomes is becoming more and more controversial. The presence of different sequences of mtDNA within a cell or individual, known as heteroplasmy, is increasingly reported in several taxon of animals, such as molluscs, arthropods and vertebrates. In this work, a considerable frequency of heteroplasmy were detected in the COI and 16S genes of the spider crab Maja brachydactyla, possibly associated to hybridisation with the congeneric species Maja squinado. This finding is a fact to keep in mind before addressing molecular analyses based on mitochondrial markers, since the assumption of maternal inheritance could lead to erroneous results. As M. brachydactyla is a commercial species, heteroplasmy is an important aspect to take into account for the fisheries management of this resource, since effective population size could be overestimated. OPEN ACCESSCitation: Rodríguez-Pena E, Verísimo P, Fernández L, González-Tizón A, Bárcena C, Martínez-Lage A (2020) High incidence of heteroplasmy in the mtDNA of a natural population of the spider crab Maja brachydactyla. PLoS ONE 15(3): e0230243.

SummarY: Patterns of habitat use by spider crab juveniles, Maja brachydactyla, from two geographic areas on the nW coast of the iberian Peninsula were studied through the analysis of carbon and nitrogen stable isotope relations in muscle and hepatopancreas. main potential preys of spider crab juveniles in rocky and sandy habitats and different organic matter sources in coastal food webs were also analysed. isotopic ratios showed no difference between rocky and sandy habitats. the use of carapace colour and epibiosis as an indicator of habitat use was not supported by our data. these results suggest that movements between the two habitats are much more frequent than suggested in previous studies. in the coastal food web, two main trophic compartments were identified according to their organic matter source: one based on plankton and seaweeds (rocky habitats), and one based on sedimentary particulate organic matter (sandy bottoms). by means of the model of Phillips and Gregg (2003), it was found that juveniles of Maja brachydactyla from both habitats consumed approximately two thirds of the preys in rocky habitats and one third in sedimentary habitats. the results indicate that in exposed environments large juveniles spend most of the time on sedimentary bottoms, where they find more refuge, moving frequently to nearby rocky substrates to feed.Keywords: coastal ecosystems, food webs, feeding, life history, marine crustaceans, stable isotopes, trophic level, energetic condition. reSumen: Patrones de uso del hábitat de la centolla Maja brachydactyla mediante el uso de isótopos estables. -el patrón de uso del hábitat de los juveniles de centolla, Maja brachydactyla, de dos áreas geográficas en la costa no de la Península ibérica, se estudió a través del análisis de las relaciones de los isótopos estables del Carbono y del nitrógeno en músculo y hepatopáncreas. Se analizaron las presas potenciales de los juveniles de centolla en hábitats rocosos y arenosos y las diferentes fuentes de materia orgánica de las redes tróficas costeras. las relaciones isotópicas no mostraron ninguna diferencia entre hábitats arenosos y rocosos. el uso del color del caparazón y la epibiosis como indicadores del hábitat no se vio apoyado por nuestros datos. los resultados sugieren que los movimientos entre hábitats son más frecuentes que los sugeridos en estudios previos. en la red trófica costera se identificaron dos compartimentos tróficos principales en base a la fuente de materia orgánica: uno basado en el plancton y macroalgas (hábitats rocosos) y otro basado en la materia orgánica particulada sedimentada (fondos arenosos). en base al modelo de Phillips y Gregg (2003) se estimó que los juveniles de Maja brachydactyla de ambos tipos de hábitat consumirían, aproximadamente, dos tercios de sus presas de hábitats rocosos y un tercio de hábitats sedimentarios. los resultados obtenidos indican que, en ambientes expuestos, los juveniles pasan la mayor parte del tiempo en los fondos arenosos, donde encuentran refugio, moviéndose frecuentemente ...

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