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[Display omitted] • Toxoplasma gondii DNA was detected in bivalves from the Kerguelen and Galapagos archipelagos. • Its occurrence differed between sampling sites in Kerguelen but not in Galapagos. • In both archipelagos, quantitative PCR-positive bivalves were found on islands without cats. • Our finding demonstrated the waterborne transport of oocysts over at least 20 km. • Exposure to currents and giant kelp density affect T. gondii detection in bivalves. Oocysts of the protozoan Toxoplasma gondii are found in felid feces and can be washed into coastal waters, where they persist for months, attaching to algae and accumulating in invertebrates. We used wild bivalves to assess contamination of coastal waters of the Kerguelen and Galapagos archipelagos by this zoonotic parasite. Additionally, we leveraged the contrasting situations of these archipelagos to identify some potential drivers of contamination. In the Galapagos, with a cat density reaching 142 per km2, 15.38% of the sampled oysters (Saccostrea palmula) tested positive for T. gondii by quantitative real-time PCR (qPCR) (n = 260), and positive samples were found in all eight sampling sites. In Kerguelen, with 1-3 cats per km2, 40.83% of 120 tested mussels (Mytilus edulis platensis) were positive, and positive samples were found in four out of the five sampling sites. These findings provide evidence of T. gondii contamination in the coastal waters of these archipelagos. Furthermore, T. gondii -positive bivalves were found on islands located 20 km away (Galapagos) and 5 km away (Kerguelen) from the nearest cat population, indicating that T. gondii oocysts can disperse through waterborne mechanisms over several kilometers from their initial deposition site. In the Galapagos, where runoff is infrequent and all sites are exposed to currents, the prevalence of qPCR-positive bivalves did not show significant variations between sites (p = 0.107). In Kerguelen where runoff is frequent and site exposure variable, the prevalence varied significantly (p < 0.001). The detection of T. gondii in Kerguelen mussels was significantly correlated with the site exposure to currents (odds ratio (OR) 60.2, p < 0.001) and the on-site density of giant kelp forests (OR 2.624, p < 0.001). This suggests that bivalves can be contaminated not only by oocysts transported by currents but also by consuming marine aggregates containing oocysts that tend to form in kelp forests. [ABSTRACT FROM AUTHOR]

El presente trabajo tiene por objetivo brindar información sobre el ciclo reproductivo y reclutamiento del mejillón Mytilus edulis platensis, una especie de importancia comercial, en bancos naturales intermareales de una localidad de la Provincia de Santa Cruz. Para ello, entre el 2013 y 2015 se realizaron muestreos biológicos y censos poblacionales estacionales y mensuales de la especie en un banco natural sobre sustrato fangoso y en otro asentado sobre sustrato rocoso en el interior de la Bahía San Julián. En el laboratorio, se determinó el largo total de los individuos, parte de los cuales fue luego procesado mediante técnicas histológicas convencionales para conocer el grado de madurez y desarrollo gonadal. Se realizaron también muestreos mensuales de zooplancton con el fin de detectar la época de mayor concentración de larvas de mejillón en el agua. Como resultado, se observó un alto grado de sincronismo en los estadios de madurez gonadal entre los individuos de Mytilus edulis platensis en la Bahía San Julián; la evacuación de gametas se produjo desde fines de primavera hasta fines de verano; las larvas presentaron su mayor abundancia en el plancton durante el mes de febrero, cuando la temperatura del agua alcanzó su valor máximo; los juveniles se incorporaron a la población principalmente durante el verano y el otoño; la abundancia de juveniles fue generalmente irregular a lo largo del tiempo y poco predecible en los bancos de Bahía San Julián.

Given the hybridization ability between species Mytilus edulis platensis and M. galloprovincialis, this research proposed to assess the genetic variability of the hybrid offspring in relation to pure species, using 8 loci microsatellites. The study found differences between hybrid offspring comparing to pure species. The hybrid offspring had the highest observed mean heterozygosity values (Ho = 0,63 ± 0,28) and low values of inbreeding, which tend to significant deviations to negative values of (Fis), demonstrating excess of heterozygote in hybrids comparing with pure species, which displayed significant deviations towards positive values of Fis. The principal component analysis shows three distinct groups among the samples analyzed, identifying the hybrid offspring as an intermediate group between pure species. [ABSTRACT FROM AUTHOR]

Abstract: It has been previously established that native smooth-shelled mussels in southern South America possess close evolutionary affinities with Northern-Hemisphere Mytilus edulis L. 1758 (McDonald et al. (1991) ). This result has since been challenged by authors claiming that Chilean mussels should be considered a local subspecies of M. galloprovincialis Lmk. 1819. Moreover, morphological, physiological, ecotoxicological and molecular genetic studies on Chilean smooth-shelled mussels still frequently refer to ‘M. chilensis’ Hupé 1854, even though the previous discovery of alien M. galloprovincialis and considerable heterogeneity in shell morphology among samples collected along the Chilean shores raise concerns that different Mytilus spp. species might have been included under ‘M. chilensis’. Here we reviewed the molecular and morphological data available on smooth-shelled mussels from Chile in an attempt to clarify both their genetic composition and their taxonomic status. Using multivariate analysis on sample×allozyme-frequency matrices, we confirmed the widespread occurrence of the Southern-Hemisphere form of M. edulis along the shores from the North Patagonia region of Chile to the southern tip of the South American continent. The populations sampled in southern central Chile showed some evidence of slight introgression from Southern-Hemisphere M. galloprovincialis. Morphological characterization of a sample from Dichato in southern central Chile was consistent with its previous genetic identification as Mediterranean M. galloprovincialis . The occurrence of Southern-Hemisphere M. galloprovincialis in Punta Arenas at the southern tip of the South American continent was also reported. Southern-Hemisphere M. edulis, including native Chilean smooth-shelled Mytilus, should be assigned subspecific rank and named M. edulis platensis d’Orbigny 1846. [Copyright &y& Elsevier]