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A key challenge in ecology and evolutionary biology is to explain the origin, structure and temporal patterns of phenotypic diversity. With regard to the potentially complex determinism of phenotypic differences, the issue should be comprehended in a general view, across multiple scales and an increasing number of phenomic studies investigate shape variation through large taxonomic, biogeographic or temporal scales. In this context, there is an ever-increasing need to develop new tools for a coherent understanding of morphospace occupation by disentangling and quantifying the main determinants of phenotypic changes. The present study briefly introduce the possibility to use multivariate regression tree technique to cope with morphological data, as embedded in a geometric morphometric framework. It emphasizes that hierarchical partitioning methods produce a hierarchy between causal variables that may help analyzing complexity in multi-scale ecological and evolutionary data. I therefore suggest that morphological studies would benefit from the combined use of the classical statistical models with rapidly emerging and diversifying methods of machine-learning. Doing so allows one to primary explore in an extensive exploratory manner the hierarchy of nested organisational levels underlying morphological variation, and then conduct hypothesis-driven analysis by focusing on a relevant scale or by investigating the appropriate model that reflects hypothesized nested influence of explanatory variables. The outlined approach may help investigating morphospace occupation in an explicitly hierarchical quantitative context.

Environmental sex determination (ESD) has been detected in a range of vertebrate reptile and fish species. Eels are characterized by an ESD that occurs relatively late, since sex cannot be histologically determined before individuals reach 28 cm. Because several eel species are at risk of extinction, assessing sex at the earliest stage is a crucial management issue. Based on preliminary results of RNA sequencing, we targeted genes susceptible to be differentially expressed between ovaries and testis at different stages of development. Using qPCR, we detected testis-specific expressions of dmrt1 , amh , gsdf and pre - miR202 and ovary-specific expressions were obtained for zar1 , zp3 and foxn5 . We showed that gene expressions in the gonad of intersexual eels were quite similar to those of males, supporting the idea that intersexual eels represent a transitional stage towards testicular differentiation. To assess whether these genes would be effective early molecular markers, we sampled juvenile eels in two locations with highly skewed sex ratios. The combined expression of six of these genes allowed the discrimination of groups according to their potential future sex and thus this appears to be a useful tool to estimate sex ratios of undifferentiated juvenile eels.

Efforts to limit the impact of invasive species are frustrated by the cryptogenic status of a large proportion of those species. Half a century ago, the state of Hawai'i introduced the Bluestripe Snapper, Lutjanus kasmira, to O'ahu for fisheries enhancement. Today, this species shares an intestinal nematode parasite, Spirocamallanus istiblenni, with native Hawaiian fishes, raising the possibility that the introduced fish carried a parasite that has since spread to naïve local hosts. Here, we employ a multidisciplinary approach, combining molecular, historical, and ecological data to confirm the alien status of S. istiblenni in Hawai'i. Using molecular sequence data we show that S. istiblenni from Hawai'i are genetically affiliated with source populations in French Polynesia, and not parasites at a geographically intermediate location in the Line Islands. S. istiblenni from Hawai'i are a genetic subset of the more diverse source populations, indicating a bottleneck at introduction. Ecological surveys indicate that the parasite has found suitable intermediate hosts in Hawai'i, which are required for the completion of its life cycle, and that the parasite is twice as prevalent in Hawaiian Bluestripe Snappers as in source populations. While the introduced snapper has spread across the entire 2600 km archipelago to Kure Atoll, the introduced parasite has spread only half that distance. However, the parasite faces no apparent impediments to invading the entire archipelago, with unknown implications for naïve indigenous Hawaiian fishes and the protected Papahānaumokuākea Marine National Monument.

Metapopulation dynamics over the course of an invasion are usually difficult to grasp because they require large and reliable data collection, often unavailable. The invasion of the fish-free freshwater ecosystems of the remote sub-Antarctic Kerguelen Islands following man-made introductions of brown trout (Salmo trutta) in the 1950's is an exception to this rule. Benefiting from a full long term environmental research monitoring of the invasion, we built a Bayesian dynamic metapopulation model to analyze the invasion dynamics of 85 river systems over 51 years. The model accounted for patch size (river length and connections to lakes), alternative dispersal pathways between rivers, temporal trends in dynamics, and uncertainty in colonization date. The results show that the model correctly represents the observed pattern of invasion, especially if we assume a coastal dispersal pathway between patches. Landscape attributes such as patch size influenced the colonization function, but had no effect on propagule pressure. Independently from patch size and distance between patches, propagule pressure and colonization function were not constant through time. Propagule pressure increased over the course of colonization, whereas the colonization function decreased, conditional on propagule pressure. The resulting pattern of this antagonistic interplay is an initial rapid invasion phase followed by a strong decrease in the invasion rate. These temporal trends may be due to either adaptive processes or environmental gradients encountered along the colonization front. It was not possible to distinguish these two hypotheses. Because invasibility of Kerguelen Is. freshwater ecosystems is very high due to the lack of a pre-existing fish fauna and minimal human interference, our estimates of invasion dynamics represent a blueprint for the potential of brown trout invasiveness in pristine environments. Our conclusions shed light on the future of polar regions where, because of climate change, fish-free ecosystems become increasingly accessible to invasion by fish species.

Otolith morphometrics have been shown to provide a practical basis for stock discrimination and subsequent fisheries management. However, the determinants of otolith shape are not fully understood and analysis does not distinguish between genotype and environmentally induced differences. In this context, understanding how those 2 components act synergetically on the otolith shape is fundamental. The use of non-indigenous fish of multiple origins provides an interesting tool for evaluating the relative importance of genetic and environmental components in determining otolith shape. This paper investigates to what extent a dual regulation (i.e. genetic and environmental) of the otolith shape from an introduced coral reef snapper (Lutjanus kasmira) exists, in order to determine how each component specifically acts on otolith morphology. Using geometric morphometrics, we discriminated between native and introduced range as well as between individuals belonging to different lineages (i.e. origins) but growing under the same environmental conditions (individuals cohabiting within the same shoals in the wild). Here we show that both genetic and environmental influences play a substantial role in determining the shape of the otolith. More specifically, while environment induces an overall change in otolith shape, genetically induced changes locally affect otolith shape. In addition, data suggest that both nuclear and mitochondrial components act synergetically. This information is fundamental if otolith shape is to be used as an effective tool for management of fisheries resources in the future.

Prey regurgitation during capture is a potential important confounding effect in fish dietary ecology studies as it may lead to overestimation of stomach vacuity and underestimation of prey consumption. This study investigates patterns of prey regurgitation and stomach vacuity among five grouper and three snapper species in shallow water off French Polynesia and tests the effectiveness of piercing swim-bladders after capture as a method to prevent regurgitation. Groupers exhibited a moderate overall regurgitation rate of 15.6% of full stomachs and a high true (i.e., after accounting for regurgitation) stomach vacuity rate of 40.5%. In contrast, snappers showed high regurgitation (mean 31.7%) and low true stomach vacuity (14.6%). Not accounting for regurgitation would have resulted in a moderate overestimation of stomach vacuity in groupers, but an almost 3-fold overestimation in snappers. Swim-bladder decompression by piercing after capture prove a highly effective method to reduce regurgitation (more than 2-fold for groupers and near 8-fold for snappers). This study enables a more general understanding of prey regurgitation in two commercially valuable fish families, thus improving understanding of the dietary ecology of these fishes. This information is particularly important in the context of prey consumption estimates and subsequent estimations of the impact of fish predators on ecosystems.

Otolith shape analysis provides a practical basis for stock separation, useful in fisheries management. A wide range of factors affect otolith morphology and a fundamental challenge in morphometric stock identification is to develop a consensus on the biological interpretation of otolith shape variation. To date, there are few comprehensive reports that have examined various factors simultaneously at multiple scales in natural conditions. In this study, I identified sources of otolith shape variation across spatial and taxonomic scales using a new hierarchical partitioning method embedded in a geometric morphometric framework. Various environmental, taxonomic and endogenic factors which affect otolith shape were quantitatively investigated in 2077 coral reef fishes. Using the new partitioning method, allometry accounted for a considerable degree of otolith shape variation at all scales and contributed more variation to regional differences than did habitats or islands. While large-scale variations are expected to be associated with significant shape variation, the study provides quantitative evidence that both local environmental variables and large-scale patterns contribute equally to total otolith shape variation. Models that aim at discriminating stocks and forecasting stock boundaries implicitly assume that the within-stock morphological variation is negligible in regard to the variation that exists among stocks. The importance of local environmental variables may therefore act as an important confounding effect into those predictive models. More generally, the degree of contribution of some variables differed substantially among the taxonomic scales, as did their relationship among spatial scales. A scale-dependent understanding of factors affecting otolith morphology is critical in understanding the integrity of fish populations and is an effective tool in management of fisheries resources.

In ecology and evolution, the small population paradigm posits that reduced genetic variation will result in limited phenotypic variation that, in turn, will affect population resilience and potential for adaptation. Over the last decade though, such a paradigm has been questioned, with evidence that mechanisms independent of genetic variation may be also important in shaping phenotypic variation. However, there are few large-scale empirical examples, especially from aquatic ecosystems. Using the large-scale natural experiment afforded by the global invasion of brown trout (Salmo trutta), we quantify standing phenotypic variation in morphology among different introduced ranges, relative to the native range. By using shape variation and morphological integration as indicators of phenotypic variation, we show that neither founding population size nor time since founding (i.e., effect of selection regime) are correlated to the amount of morphological variation, contrarily to common expectations. Beyond founding population size and time since founding, the amount of morphological variation is mostly controlled by factors at the population level rather than at the region level, and is not lower in invaded regions compared to the native range. These results suggest that the dynamics of phenotypic variation may be largely independent of population size and mostly determined by site-specific patterns of selection.

Brown trout (Salmo trutta L.) was voluntarily introduced in some rivers of the Kerguelen Islands in the 1950s–1960s. Fish originating from hatcheries rapidly colonized other streams, thanks to the early occurrence of anadromous (i.e., migratory) form. Getting insight into the success of colonization requires investigating fitness-related traits such as growth and reproductive investment. In particular, increased growth and body size—traits that are broadly related to dispersal ability—are predicted on colonization front, to the possible detriment of reproductive ability. We here report such investigation on early data following the first natural reproductions in the founder populations of Kerguelen, from 1971 to 1994, assessing the main characteristic on growth at sea and reproductive investment for both sexes. Our results reveal that growth of sea trout is excellent with individuals fully benefiting from their relatively short period of growth at sea, sizes and weights ranking among the highest recorded to date. During the reproduction period, males lose on average 15–21% of their weight, whereas females lose 18–19% of their weight. Although a trade-off between growth and reproduction may arise at marginal distribution of invasive species, our study indicates that any potential advantages arising from increased growth and therefore potential dispersal ability may not be directly balanced by reduced reproductive investment, with respect to other published studies. Results overall shed light on intrinsic invasiveness of the brown trout in a post-glacial landscape with barely any interaction with human activities.

Invasive species provide unique and useful systems by which to examine various ecological and evolutionary issues, both in terms of the effects on native environments and the subsequent evolutionary impacts. While biological invasions are an increasing agent of change in aquatic systems, alien species also act as vectors for new parasites and diseases. To date, colonizations by hosts and parasites have not been treated and reviewed together, although both are usually interwoven in various ways and may have unpredictable negative consequences. Fish are widely introduced worldwide and are convenient organisms to study parasites and diseases. We report a global overview of fish invasions with associated parasitological data. Data available on marine and freshwater are in sharp contrast. While parasites and diseases of inland freshwater fish, ornamental, reared and anadromous fish species are well documented, leading to the emergence of several evolutionary hypotheses in freshwater ecosystems during the last decade, the transfer of such organisms are virtually unexplored in marine ecosystems. The paucity of information available on the parasites of introduced marine fish reflects the paucity of information currently available on parasites of non-indigenous species in marine ecosystems. However, such information is crucial as it can allow estimations of the extent to which freshwater epidemiology/evolution can be directly transferred to marine systems, providing guidelines for adapting freshwater control to the marine environment.