Non-native populations of Pacific oysters Crassostrea gigas (Thunberg 1793) are established around the United Kingdom (UK), with two genetically different stocks originating from separate introductions to the UK and France. In this study, we use a coupled biophysical model to simulate Pacific oyster larval transport, in order to investigate the dispersal of the species from a known population near their northern limit on the west coast of the UK (in the Milford Haven Estuary). The model included a pelagic phase, simulating different swimming behaviours, and a settlement phase based on a hydrospatial substrate map. Following successful settlement elsewhere, subsequent releases simulated potential population spread over successive generations. Our results suggest that, should there be sufficiently warm sea temperatures to allow reproduction, dispersal away from Milford Haven Estuary would most be southeast ward towards the Bristol Channel; but dispersal north and west to Ireland is also possible, depending heavily on pelagic swimming behaviour. Seasonal modifications to circulation were less influential. Our study increases understanding of factors that contribute to oyster population spread, and suggests methods for improved management through numerical predictions.
Since Darwin's time, degree of ecological similarity between exotic and native species has been assumed to affect the establishment success or failure of exotic species. However, a direct test of the effect of exotic–native similarity on establishment of exotics is scarce because of the difficulty in recognizing failures of species to establish in the field. Here, using a database on the establishment success and failure of exotic fish species introduced into 673 freshwater lakes, we evaluate the effect of similarity on the establishment of exotic fishes by combining phylogenetic and functional information. We illustrate that, relative to other biotic and abiotic factors, exotic–native phylogenetic and functional similarities were the most important correlates of exotic fish establishment. While phylogenetic similarity between exotic and resident fish species promoted successful establishment, functional similarity led to failure of exotics to become established. Those exotic species phylogenetically close to, but functionally distant from, native fishes were most likely to establish successfully. Our findings provide a perspective to reconcile Darwin's naturalization conundrum and suggest that, while phylogenetic relatedness allows exotic fish species to pre‐adapt better to novel environments, they need to possess distinct functional traits to reduce competition with resident native fish species.
Venomous animals are found through a wide taxonomic range including cartilaginous fish such as the freshwater stingray Potamotrygon motoro occurring in South America, which can injure people and cause venom-related symptoms. Ensuring the efficacy of drug development to treat stingray injuries can be assisted by the knowledge of the venom composition. Here we performed a detailed transcriptomic characterization of the venom gland of the South American freshwater stingray Potamotrygon motoro. The transcripts retrieved showed 418 hits to venom components (comparably to 426 and 396 hits in other two Potamotrygon species), with high expression levels of hyaluronidase, cystatin and calglandulin along with hits uniquely found in P. motoro such as DELTA-alicitoxin-Pse1b, Augerpeptide hhe53 and PI-actitoxin-Aeq3a. We also identified undescribed molecules with extremely high expression values with sequence similarity to the SE-cephalotoxin and Rapunzel genes. Comparative analyses showed that despite being closely related, there may be significant variation among the venoms of freshwater stingrays, highlighting the importance of considering elicit care in handling different envenomation cases. Since hyaluronidase represents a major component of fish venom, we have performed phylogenetic and selective pressure analyses of this gene/protein across all fish with the available information. Results indicated an independent recruitment of the hyaluronidase into the stingray venom relative to that of venomous bony fish. The hyaluronidase residues were found to be mostly under negative selection, but 18 sites showed evidence of diversifying positive selection (P < 0.05). Our data provides new insight into stingray venom variation, composition, and selective pressure in hyaluronidase.
In the last few decades, non-native freshwater fishes have been introduced all over the world for economic purposes, including aquaculture and aquarium trade, as well as improvement for wild stocks resulting in adverse environmental and socio-economic effects. The Guangdong province of China is at a high risk of fish invasions owing to its warm and humid climate, abundance of water courses, flourishing aquaculture and ornamental fish trade, and extensive sea ports. A total of 160 non-native freshwater species were introduced in the Guangdong province and 71.9% of them were imported for aquarium purposes. Fourteen species have established self-sustaining populations and 21 species were found in the main river basin of the Guangdong province. Propagule pressure, rapid evolution and abundant resources in the environment were the factors likely to contribute to successful invasion by non-native fishes. The invasion of non-native fishes in the Guangdong province has already resulted in economic losses, decline of native species, as well as negative impacts on the functional diversity of native fish assemblages. To mitigate these effects and prevent future non-native fish invasions, scientists, policy makers and stakeholders should collaborate on the management of non-native fish introductions by developing risk assessments, statutory regulations, public education and scientific research.
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