Evolution of diadromy in fish: insights from a tropical genus (Kuhlia species)

Diadromous species undergo regular migration between fresh and marine waters. This behavior is found in many species, including fish, mollusks, and crustaceans, some of which are commercially valuable species. Several attempts to trace the evolution of this behavior have been made in Salmonidae and Galaxiidae, but ambiguous phylogenies and multiple character state changes prevented unequivocal conclusions. The Kuhliidae family consists of 12 fish species that inhabit tropical islands in the Indo-Pacific region. The species have marine, partially catadromous, or fully catadromous life histories (i.e., they migrate from rivers to the sea to reproduce). The evolution of migratory behavior was traced on a well-resolved phylogeny. Catadromous Kuhlia species were basal, and partially catadromous and marine species formed derived monophyletic groups. This is, to our knowledge, the first time that a clear origin and polarity for the diadromous character has been demonstrated. We propose that the relative lack of resources in tropical, inshore, marine habitats and the ephemeral and isolated nature of freshwater environments of tropical islands, combined with phenotypic plasticity of migratory traits, play key roles in driving the evolution of diadromy in the Kuhliidae and probably in other groups. This work is an important starting point to understand the role of diadromy in speciation and adaptation in unstable habitats

Towards the development of ecosystem-based indicators of mangroves functioning state in the context of the EU water framework directive

European Water Framework Directive is enforced in five tropical French Oversea Territories where mangroves are present. Developing bioindication tools to support the ecosystem-based management approach of the Directive is needed. A series of expert workshops was organized and led to the proposal of a strategy and of an applied research program to develop bioindication tools. The proceedings of the workshops are presented as a case study, as this is the first time such an integrative ecosystem-based approach is proposed in mangroves, combining structural and functional aspects, from forest structure to benthic community functioning

Mécanismes de persistance des assemblages piscicoles en eau douce (des bassins côtiers continentaux aux îles océaniques)

Un assemblage piscicole est un ensemble d'espèces de poissons vivant à un moment donné dans un même milieu. La composition de l'assemblage piscicole d'eau douce dans un bassin versant est dépendante de facteurs intervenant à plusieurs échelles. Les milieux insulaires, tels les bassins côtiers continentaux ou les îles océaniques, sont intéressants pour examiner les conditions de persistance des espèces qui y vivent. A différents degrés d'insularité, ce travail de thèse étudie les mécanismes de persistance des espèces piscicoles dans les eaux douces sous l'angle de leurs stratégies reproductrices et migratrices. Nous avons eu l'opportunité d'analyser d'importants jeux de données dans des systèmes " insularisés ". Des bassins côtiers du nord-ouest de la France à l'île de La Réunion dans l'océan Indien, nous examinons le fonctionnement d'assemblages d'espèces différentes du point de vue taxonomique, mais comparables par certains traits de vie (capacités de déplacements ou de migration, stratégies de reproduction). Les mécanismes de persistance de l'assemblage piscicole sont considérés dans un premier temps à l'échelle du cours d'eau, grâce à des échantillonnages de suivi sur plusieurs années, dans un petit bassin côtier continental (Le Frémur) et dans les 13 rivières pérennes de La Réunion. L'observation des variations densitaires et les probabilités d'extinction à l'échelle du bassin nous permettent ensuite d'interpréter la composition spécifique des assemblages piscicoles dans les bassins côtiers continentaux et les îles océaniques à l'échelle régionale. Parmi les diverses stratégies représentées, migratrices ou sédentaires, potamotoques ou thalassotoques, anadromes, catadromes ou amphidromes, la stratégie dispersive des anguilles est présente dans tous les bassins étudiés. Les mécanismes de colonisation des anguilles de l'île de La Réunion sont présentés, du recrutement estuarien à la colonisation fluviale, illustrés par les résultats d'une année de suivi. Les modalités régionales de persistance de cette stratégie particulière sont discutées.LA ROCHELLE-BU (173002101) / SudocPARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceF

Fine-scale congruence in bacterial community structure from marine sediments sequenced by short-reads on Illumina and long-reads on Nanopore

Abstract Following the development of high-throughput sequencers, environmental prokaryotic communities are usually described by metabarcoding with genetic markers on the 16S domain. However, short-read sequencing encounters a limitation in phylogenetic coverage and taxonomic resolution, due to the primers choice and read length. On these critical points, nanopore sequencing, a rising technology, suitable for long-read metabarcoding, was much undervalued because of its relatively higher error rate per read. Here we compared the prokaryotic community structure in a mock community and 52 sediment samples from two contrasted mangrove sites, described by short-reads on 16SV4-V5 marker ( ca . 0.4kpb) analyzed by Illumina sequencing (MiSeq, V3), with those described by long-reads on bacterial nearly complete 16S ( ca . 1.5 kpb) analyzed by Oxford Nanopore (MinION, R9.2). Short- and long-reads retrieved all the bacterial genera from the mock, although both showing similar deviations from the awaited proportions. From the sediment samples, with a coverage-based rarefaction of reads and after singletons filtering, co-inertia and Procrustean tests showed that bacterial community structures inferred from short- and long-reads were significantly similar, showing both a comparable contrast between sites and a coherent sea-land orientation within sites. In our dataset, 84.7 and 98.8% of the short-reads were assigned strictly to the same species and genus, respectively, than those detected by long-reads. Primer specificities of long-16S allowed it to detect 92.2% of the 309 families and 87.7% of the 448 genera that were detected by the short 16SV4-V5. Long-reads recorded 973 additional taxa not detected by short-reads, among which 91.7% were identified to the genus rank, some belonging to 11 exclusive phyla, albeit accounting for only 0.2% of total long-reads

Spatial organisation of European eel (Anguilla anguilla L.) in a small catchment

Modelling governing patterns of European eel (Anguilla anguilla L.) distribution of four eel size classes ( 450 mm) in the Frémur basin (North-West France) was done using artificial neural network (ANN) techniques and ecological profiles. Our results demonstrate the high predictive power of the ANN models. Some macro and micro-scale factors, like distance from the sea, depth and flow velocity have the most significant influence in the models. Influence of distance from the sea appears to be very different from the spatial organisation usually described in river systems. In fact, the general tendencies of total eel densities according to distance from the sea showed that densities weakly increase upstream. Another outcome was the variations of habitat preference according to the eel size, even if this species is spread over practically every type of micro-habitat. Small eels were mainly found in shallow habitats with strong abundance of aquatic vegetation, whereas large eels tend to be found in intermediate to high depth with small to intermediate abundance of aquatic vegetation. Finally, we hypothesize that European eels change behaviour and microhabitat characteristic preference around a size of 300 mm

A Review of Upstream Migration and Movements in Inland Waters by Anguillid Eels: Toward a General Theory

Anguillid eels are well known as catadromous highly migratory species, with marine spawning grounds well separated from inshore and inland growth areas. However, invasion mechanisms of river systems are poorly documented. This theory is based upon the identification of four distinct movement behaviors: "founders" that colonize rivers until they settle in the first available suitable habitat they encounter; "pioneers" that migrate upstream to the upper boundaries of the system; "home range dwellers" that establish in a given area for several months to several years; and „nomads;“ which are erratic eels that perform a general upstream shift as they search for suitable areas to forage or to settle. These behaviors are not mutually exclusive, any eel shifting from one behavior to another, depending upon ontogenetic attributes (age, experience, morphology, physiological stage, etc.), population parameters that determine density-dependent movements; and environmental parameters such as food availability, temperature, flow, and the carrying capacity of the ecosystem

Development of a key using morphological characters to distinguish south-western Indian Ocean anguillid glass eels

International audienceTwo morphological characters were examined in 4099 anguillid glass eels sampled in four south-western Indian Ocean islands, and resulting identifications were tested using genetic analysis. Distance between the origin of the dorsal and anal fins as related to total length and tail and caudal fin pigmentation enabled formulation of a useful field identification key, which was able to discriminate 4036 glass eels of the regional species Anguilla bicolor bicolor, Anguilla marmorata and Anguilla mossambica, and excluded the occurrence of Anguilla nebulosa labiata in the sample