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In this study, we tested the significance of environmental influences on non-marine ostracod communities at high taxonomic levels across Patagonia, Argentina. We used a dataset compiled from 243 Patagonian freshwater bodies, representing an area of ~ 900,000 km2 and covering the main local and climatic gradients. We applied generalized linear models to test the effects of hydroperiod, local and climatic variables on the occurrence and abundance of Ostracoda, and the occurrence of the most frequent families (i.e., Cyprididae, Ilyocyprididae and Limnocytheridae). We found ostracods in 77% of the total sampled sites, driven mainly by dissolved oxygen levels and water temperature (local variables) as well as precipitation and air temperature (climatic variables). Specifically, warmer winters and dryer climates favored ostracod occurrences, which covered wide ecological ranges, such as peat bogs or high-altitude wetlands. For the Ilyocyprididae and Limnocytheridae families, precipitation and pH were important predictors of their occurrence. Furthermore, wind speed, nutrient levels and water depth had positive effects on ostracod abundance. This updated Patagonian freshwater dataset contributes towards filling those knowledge gaps related to the habitat suitability of ostracods communities in this vast region. Our findings could help us understand the past and future responses of ostracods to environmental changes. [ABSTRACT FROM AUTHOR]

Habitat fragmentation and loss threaten freshwater biodiversity worldwide. Habitats that are essential as fish spawning and nursery sites are critical, and must be identified for conservation purposes. Littoral zones within Patagonian lakes, especially shallow vegetated areas, represent important areas for the Creole perch, Percichthys trucha.Spawning behaviour has been little studied, so it is not known whether these movements are performed in groups. A particular area of a deep lake in northern Patagonia was studied to identify the environmental conditions under which spawning occurs, and to analyse spawning aggregation behaviour in relation to the lunar cycle.To identify spawning sites, spawning occurrence time, and the environmental parameters that determine it, fish capture data were analysed. Underwater cameras were also set up at three depth strata in the shallow zone to detect spawning aggregation behaviour. Aggregation was scored as the greatest number of individuals present in a single frame, and the number present per depth stratum. The relationship between the lunar cycle and Creole perch abundance by depth was then determined.This is the first visual record of a spawning bed and the spawning aggregation behaviour of Creole perch in Patagonian lakes. The abundance of mature Creole perch in the shallow strata during the austral spring suggests that vegetated areas constitute spawning sites. Spawning aggregation takes place at a shallow depth 2 days before the full moon.As the reproductive behaviours of Creole perch are important phenomena in the life history of the species, the results of this study have important implications for conservation and management. [ABSTRACT FROM AUTHOR]

Aim: To assess the relative importance of wind intensity and direction in explaining wetland invertebrate metacommunity organization. Location: Seventy‐eight wetland ponds in Patagonia (Argentina) covering a study area of 3.5 × 105 km2. Time period: Ponds were sampled once between 2006 and 2014. Major taxa studied: One hundred and fifty‐eight taxa of wetland aquatic invertebrates. Methods: We generated two beta diversity matrices (based on flying and non‐flying invertebrates) and six predictor matrices, including three environmental distance matrices, a topographic distance between ponds, and two wind pairwise matrices differing in wind speed. Using Moran spectral randomization of Mantel (MSR‐Mantel) tests (which account for spatial autocorrelation), we assessed the relationship between the response and the predictor matrices. We used a network‐constrained version of the nestedness metric based on overlap and decreasing fill (NODF), to assess if wind anisotropy (i.e., direction‐dependent) affected community nestedness among ponds. Results: Flying dispersers' dissimilarity was significantly explained by environmental variables, whereas non‐flying invertebrates' dissimilarity was not significantly explained by any of the distances tested. When wind direction was ignored, wind speed had a negligible effect on both types of communities, whereas when it was considered a consistent nested pattern emerged, with the eastern ponds (downwind) communities being subsets of those from the western ponds (upwind). Main conclusions: We found that the invertebrate communities were mainly assembled by a combination of environmental factors and wind directionality, although this depended on the dispersal ability of the organisms. [ABSTRACT FROM AUTHOR]

Current patterns of genetic and morphological diversity are the product of historical climatic and geomorphological events, and of contemporary selection processes acting upon this diversity. Here we examine the phylogeographic and phenotypic patterns of diversity within Percichthys trucha, a widely distributed Patagonian fish species complex that inhabits Andean and steppe freshwater environments. Molecular analysis (mtDNA control region) of 21 populations distributed throughout its latitudinal range revealed little evidence of phylogeographic structure and no evidence of species-level genetic divergence east of the Andes. The complex, however, exhibits high levels of intra- and interpopulation phenotypic variation. Patterns of among-population divergence in morphology were most easily explained by differences in predation pressure among populations; dorsal fin spines (commonly a defensive characteristic) were longer in environments with greater densities of potentially piscivorous fish. Trophic characters were highly variable within populations, suggesting an important role for resources in generating within-population morphological variation. The very shallow levels of divergence shown by the molecular data most likely reflect the historical mixing of populations as a result of the climatic and landscape changes that affected Patagonia throughout the Quaternary. The phenotypic divergences, in contrast, are probably the result of differing contemporary selection regimes acting on currently disjoint populations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, , 514-529. Los patrones de diversidad genética y morfológica que pueden observarse en poblaciones existentes son el producto de la influencia conjunta de procesos históricos (climáticos, geomorfológicos) y de la selección natural. En este trabajo examinamos los patrones de diversidad filogeográfica y fenotípica en Percichthys trucha, una especie o complejo de especies de amplia distribución en Patagonia andina y esteparia. Análisis molecular (Region de Control ADN mitocondrial) de 21 poblaciones a lo largo y ancho del rango distribucional del grupo reveló poca evidencia de estructura filogeográfica (estructura poco profunda) y ninguna evidencia de divergencia genética a nivel de especie al este de los Andes. El complejo exhibe sin embargo, altos niveles de variación fenotípica tanto intra-, como interpoblacional. Los patrones de divergencia morfológica entre poblaciones se correlacionan con diferencias interpoblacionales en la intensidad de predación; las espinas dorsales (comúnmente una característica defensiva) son más largas en ambientes con mayor densidad de peces potencialmente piscívoros. Los caracteres tróficos exhiben alta variación intrapoblacional sugiriendo que los recursos tróficos cumplen un rol importante en la generación de variación morfológica dentro de poblaciones. Los bajos niveles de divergencia molecular y de estructura filogeográfica son probablemente el resultado de la mezcla histórica de individuos y poblaciones como consecuencia de los cambios climáticos y geográficos (paisaje) que afectaron la región Patagónica durante el Cuaternario. Las divergencias fenotípicas por el contrario, son el resultado de diferencias en los regímenes de selección natural operantes en poblaciones de Percichthys trucha actualmente disjuntas. [ABSTRACT FROM AUTHOR]

Rainbow trout Oncorhynchus mykiss have successfully colonized almost all available water bodies in Patagonia. Introduction and restocking practices have taken place since the beginning of the 20th century without prior consideration of differences between environments in terms of fish community composition and trophic food web structure. We assessed how observed growth, growth efficiency, production, and biomass of rainbow trout populations from four Patagonian lakes were influenced by food web structure and prey quality, and we evaluated the growth strategies adopted by this species in response to environmental differences. Fish communities vary in terms of species composition and dominance. Bioenergetics simulations showed that size and growth patterns of rainbow trout varied between lakes, mainly owing to dietary differences. Fewer and lower-quality food items led to low growth efficiency and stunted growth, while a more diverse and higher-energy diet base led to higher growth efficiency and larger sizes. Rainbow trout density, production, and biomass were higher in the larger, more structurally complex lakes, although rainbow trout production values in the smallest lake were comparable with those in a lake twice its size. This study provides comparative evidence of the high plasticity of rainbow trout, for which the adoption of different growth strategies facilitates the successful colonization of environments where diet bases range widely in quality. [ABSTRACT FROM AUTHOR]

ndean Patagonian lakes are ultraoligotrophic, highly transparent water bodies with very low densities of organisms at the different levels of their trophic food webs. Little is known about spatial distribution and habitat use by fish in these lakes. Hydroacoustic and active sampling techniques were used to study the distribution, composition, and displacement of organisms in an Andean lake throughout the diel cycle on two different moon phase days. Sound scattering layers (SSLs) were found both in the near-shore and pelagic habitats at different times of the day. These SSLs, formed by galaxiid larvae and adults, underwent displacement during the time periods of dawn and dusk, giving rise to the redistribution of organisms in the different habitats. The organisms show high sensitivity to light intensity, displaying different behaviors depending on moon phases. Extensive diel vertical migrations show that the deep pelagic habitats provide diurnal refuge for native galaxiids in Andean Patagonian lakes. Due to the high densities of galaxiid larvae and adults, it is likely that diel migrations generate an active flow of energy and matter between habitats, which could have a profound influence on whole lake dynamics. [ABSTRACT FROM AUTHOR]

Presents a study which hypothesized that a change in spawning site for the Patagonian stock of Argentine hake, or Merluccius hubbsi, can affect species recruitment. Background on Argentine hake; Relationship between egg production and recruitment; Abundance of hake and location of spawning females; Spatial pattern of M. hubbsi spawning aggregation inshore and offshore of the north Patagonian area in Argentina and Chile between 1988 and 2001.

Within-species differentiation in phenotypic characters related to resource use (resource polymorphism) is frequently thought to result from divergent natural selection in a heterogeneous environment with ‘open niches’. In this study we found consistent resource-based polymorphism within three different populations of Percichthys trucha , a lake-dwelling fish native to the southern Andes. In each of three lakes we found two morphotypes that could be clearly distinguished by differences in gill raker length. However, the magnitude of the polymorphism, and the suite of phenotypic characteristics associated with the polymorphism, differed between lakes. Patterns of divergence were more similar between the two northern lakes which ultimately drain into a common river, than between these two lakes and a more southern, unconnected lake. The southern population, which had the largest divergence in gill raker length (32% vs. 16% and 19%), also showed substantial differences in diet. Evidence from the southern population suggests that polymorphism in P. trucha is present early during ontogeny. We conclude that while there are some strong parallels among lakes in the development of a trophic polymorphism, differences in environmental ­conditions and/or colonization history have led to substantial differences in the evolutionary history, resulting in ­different ecological roles of common morphotypes within different lakes. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 497–515. [ABSTRACT FROM AUTHOR]

Argentinean hake, Merluccius hubbsi, is one of the most important fishery resources of the South-western Atlantic Ocean, but its spawning biomass decreased in the last fifteen years, mainly due to the increased fishing pressure. It is widely accepted that to understand recruitment variability is necessary to study the factors that determine survival of early stages of development. Nutritional condition indexes have been widely used to determine starvation in wild larvae. In the present investigation, condition of M. hubbsi larvae was estimated employing field collected material by means of RNA/DNA index. This is the first attempt to use this index in this species. The change in the RNA/DNA index showed a clear ontogenetic pattern: increasing from preflexion to postflexion stages, showing an apparent decrease at the end of postflexion stage and a conspicuous increase once transformation stage was achieved. This pattern could be indicating that the transition between postflexion and transformation stages might represent a critical phase along larval development. RNA/DNA index also showed significant differences between areas from the spawning grounds characterized by different chlorophyll a concentration and abundance of potential prey. The study of nutritional condition represents a useful tool for identifying favorable nursery areas, providing valuable information for a comprehensive management of a population subject to overfishing. [ABSTRACT FROM AUTHOR]