Surviving historical Patagonian landscapes and climate: molecular insights from Galaxias maculatus

<p>Abstract</p> <p>Background</p> <p>The dynamic geological and climatic histories of temperate South America have played important roles in shaping the contemporary distributions and genetic diversity of endemic freshwater species. We use mitochondria and nuclear sequence variation to investigate the consequences of mountain barriers and Quaternary glacial cycles for patterns of genetic diversity in the diadromous fish <it>Galaxias maculatus </it>in Patagonia (~300 individuals from 36 locations).</p> <p>Results</p> <p>Contemporary populations of <it>G. maculatus</it>, east and west of the Andes in Patagonia, represent a single monophyletic lineage comprising several well supported groups. Mantel tests using control region data revealed a strong positive relationship when geographic distance was modeled according to a scenario of marine dispersal. (<it>r </it>= 0.69, <it>P = 0.055</it>). By contrast, direct distance between regions was poorly correlated with genetic distance (<it>r </it>= -0.05, <it>P </it>= 0.463). Hierarchical AMOVAs using mtDNA revealed that pooling samples according to historical (pre-LGM) oceanic drainage (Pacific vs. Atlantic) explained approximately four times more variance than pooling them into present-day drainage (15.6% vs. 3.7%). Further <it>post-hoc </it>AMOVA tests revealed additional genetic structure between populations east and west of the Chilean Coastal Cordillera (coastal vs. interior). Overall female effective population size appears to have remained relatively constant until roughly 0.5 Ma when population size rapidly increased several orders of magnitude [100× (60×-190×)] to reach contemporary levels. Maximum likelihood analysis of nuclear alleles revealed a poorly supported gene tree which was paraphyletic with respect to mitochondrial-defined haplogroups.</p> <p>Conclusions</p> <p>First diversifying in the central/north-west region of Patagonia, <it>G. maculatus </it>extended its range into Argentina via the southern coastal regions that join the Pacific and Atlantic oceans. More recent gene flow between northern populations involved the most ancient and most derived lineages, and was likely facilitated by drainage reversal(s) during one or more cooling events of the late Pleistocene. Overall female effective population size represents the end result of a widespread and several hundred-fold increase over approximately 0.5 Ma, spanning several climatic fluctuations of the Pleistocene. The minor influence of glacial cycles on the genetic structure and diversity of <it>G. maculatus </it>likely reflects the access to marine refugia during repeated bouts of global cooling. Evidence of genetic structure that was detected on a finer scale between lakes/rivers is most likely the result of both biological attributes (i.e., resident non-migratory behavior and/or landlocking and natal homing in diadromous populations), and the Coastal Cordillera as a dispersal barrier.</p

Biogeography, habitat transitions and hybridization in a radiation of South American silverside fishes revealed by mitochondrial and genomic RAD data

Rivers and lake systems in the southern cone of South America have been widely influenced by historic glaciations events, carrying important implications on the evolution of aquatic organisms including prompting transitions between marine and freshwater habitats and by triggering hybridization among incipient species via waterway connectivity and stream capture events. Silverside fishes (Odontesthes) in the region comprise a radiation of 19 marine and freshwater species that have been hypothesized on the basis of morphological or mitochondrial DNA data to have either transitioned repeatedly into continental waters from the sea or colonized marine habitats following freshwater diversification. New ddRAD data presented here provide a robust framework to investigate biogeographic history and habitat transitions in Odontesthes. We show that Odontesthes silversides originally diversified in the Pacific but independently colonized the Atlantic three times, producing three independent marine-to-freshwater transitions. Our results also indicate recent introgression of marine mitochondrial haplotypes into two freshwater clades, with more recurring instances of hybridization among Atlantic- vs. Pacific-slope species. In Pacific freshwater drainages, hybridization with a marine species appears to be geographically isolated and may be related to glaciation events. Substantial structural differences of estuarine gradients between these two geographic areas may have influenced the frequency, intensity, and evolutionary effects of hybridization events.Laboratorio de Sistemática y Biología EvolutivaFacultad de Ciencias Naturales y Muse

Session D3: Drivers of Migratory Life Histories of Riverine Galaxias maculatus in Chile: Implications for Management

Abstract: A relationship between life histories and increasing latitude has been described for Northern Hemisphere riverine fish, whereby life cycles that complete most of the growth in the ocean are favoured at higher latitudes. In the riverine ecosystems of the Southern Hemisphere many species of galaxiids display highly flexible migratory life histories and the mechanisms driving employment of different strategies remain unclear. Our objective was to unravel the mechanisms driving the selection of migratory strategies of Galaxias maculatus from rivers across a gradient of latitude. Fifteen fish from three size classes as well as water samples were collected from upper, middle and lower sections of 10 river systems in Chile across latitudes 36°- 47°S. Otoliths and water samples were analysed for a suite of trace elements using Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Otolith elemental composition was analysed through depth profiling to assess the frequency of marine migrations in each section of each river. The propensity of marine migrations was strongly related to latitude as well as flow and temperature dynamics of each river system. Fish in river systems at higher latitudes more frequently displayed use of marine and brackish habitats, potentially enabling them to maximise foraging opportunities and increase recruitment success. River systems originating from large Andean lakes with more predictable flow pattern (large scale spring floodplain inundations and therefore more predictable food supplies) accommodated more resident individuals with no marine signatures even at higher latitudes. Therefore, climate as well as both longitudinal (headwaters-estuary) and lateral (main channel-floodplains) hydrologic connectivity seem to govern migratory strategies of riverine Galaxias maculatus. Consequently, management strategies that promote both lateral and longitudinal connectivity within riverine ecosystems are crucial to maximise habitat availability for native fish species. (Financial support: Fondecyt 3130690, DIUC 213.310.063-1AP

NEW RECORDS OF HATCHERIA MACRAEI (SILURIFORMES, TRICHOMYCTERIDAE) FROM CHILEAN PROVINCE NUEVOS REGISTROS DE HATCHERIA MACRAEI (SILURIFORMES, TRICHOMYCTERIDAE) EN LA PROVINCIA CHILENA

We describe collections oiHatcheria macraei (Patagonian catfish) from south-central Chile. This represents a significant range extension for this species. These new records have important biogeographic implications as H. macraei is now recorded within Chilean Province, far north of its previous distributional limit in Patagonian Province. We document a new character, the shape of the dorsal fin, which allows quick and easy discrimination between H. macraei and Trichomycterus areolatus in the field or laboratory. This study highlights the need for careful identification for trichomycterid catfishes from southern Chile.<br>RESUMEN Describimos nuevos registros de Hatcheria macraei (bagre Patagónico) en el área sur-central de Chile. Ello representa una ampliación significativa del rango de distribución de esta especie. Estos nuevos registros tienen importantes implicancias biogeográficas, dado que reportamos a H. macraei dentro de la Provincia Chilena, bastante más al norte de su límite distributional previo en Chile, restringido a la Provincia Patagónica. Además, informamos en este trabajo de un nuevo carácter, correspondiente a la forma de la aleta dorsal, el cual permite una rápida y fácil discriminación entre H. macraei y Trichomycterus areolatus, tanto en terreno como en laboratorio. Este estudio alerta sobre la necesidad de identificar cuidadosamente los bagres de la familia Trichomycteridae del sur de Chile

Historical and Contemporary Diversity of Galaxiids in South America: Biogeographic and Phylogenetic Perspectives

Galaxiid fishes from South America are represented by three genera (Aplochiton, Brachygalaxias and Galaxias) and eight species. Their genetic patterns have been studied over the last two decades to disentangle how historical and contemporary processes influenced their biogeographic distribution and phylogeographic patterns. Here we review and synthesize this body of work. Phylogeographic approaches reveal the important role played by orogeny and the expansion/melting of glacial ice during the Quaternary. Populations retreated to glacial refugia during glacial times and some systems experienced drainage reversals from the Atlantic to the Pacific following deglaciation. Although most species expanded their populations and increased their genetic diversity during the Holocene, the introduction of salmonids and the construction of dams are likely to lead to a decline in genetic diversity for at least some species. An improvement in our understanding of the processes that influenced historical and contemporary diversity patterns among galaxiid and other native fishes in South America is necessary for addressing the cumulative and synergistic impacts of human activity on this unique freshwater fauna

Data from: Phylogeography of the catfish Hatcheria macraei reveals a negligible role of drainage divides in structuring populations

Southern South America provides a set of unusual geographic features that make it particularly interesting for studying phylogeography. The Andes Mountains run along a north-to-south axis and act as a barrier to gene flow for much of the biota of this region, with southern portions experiencing extensive historic glaciation. Geological data reveal a series of drainage reversals, shifting from Pacific Ocean outlets to Atlantic Ocean outlets due to glacier formation that dammed and reversed rivers. Once glaciers melted around 13 000 years ago, drainages returned to the Pacific Ocean. This geologic history predicts that aquatic organisms in Pacific rivers should have their closest relationships to their counterparts in Atlantic rivers immediately to their east. We tested this prediction in the trichomycterid catfish Hatcheria macraei from 38 locations using the mitochondrial cytochrome b gene. Our results show that most populations found in Pacific rivers were closely related to fish found in the adjacent Atlantic draining Río Chubut. Surprisingly, one documented drainage reversal (from Río Deseado into Río Baker) did not result in movement of H. macraei. Overall, we found the lowest levels of genetic structure between most Pacific rivers that are adjacent to the Atlantic draining Río Chubut. We also found low levels of population structuring among three out of four river basins that drain to the Atlantic Ocean. Our findings suggest that drainage basin boundaries have historically not played an important long-term role in structuring between nine out of 11 drainages, an unusual finding in freshwater biogeography

CRUSTACEAN ZOOPLANKTON ASSEMBLAGES IN INLAND WATERS OF SOUTHERN PATAGONIA (ALACALUFES NATIONAL RESERVE), CHILE (49-51 degrees S)

The inland water crustacean communities in southern Chilean Patagonia (46-55 degrees S) are characterized by their marked low species number, and many recurrent species among a wide ecological and geographical gradient, that is due to oligotrophy of lakes and lagoons and the fluvial parameters (i.e., high flow velocities) in rivers. The aim of the present study was to describe the zooplankton communities in lakes and respective outflow river estuaries in Alacalufes National Reserve on islands of Chilean southern Patagonia (49-51 degrees S). Species abundance and presence/absence were considered. The results obtained revealed the presence of a low number of species and also multiple sites in which zooplankton was not recorded at all. This is probably due the low zooplankton diversity of cold lakes at these high latitudes and the often turbulent flow of the outflow rivers studied

Partitioning β-diversity reveals that invasions and extinctions promote the biotic homogenization of Chilean freshwater fish fauna.

AimExotic species' introductions together with extinction of native species represent the main mechanisms driving biotic homogenization of freshwater fish assemblages around the world. While generally ichtyofaunistic realms transit towards biotic homogenization, for conservation purposes it is essential to understand what specific mechanisms are promoting it on particular areas or regions. Here, we report the occurrence of biotic homogenization in 29 Chilean watersheds, analyzing its β-diversity (including turnover and nestedness) and predicting future trends.LocationContinental Chile (18o-56o S).MethodsWe determined fish composition per basin for historical and current assemblages; extant native, exotic, and extinct species were recorded as 1 (presence) or 0 (absence) in two matrices basins × species. For each matrix, we calculated the turnover (βsim), nestedness (βnes), and β-diversity (βsor); then, we obtained Δβsim, Δβnes, and Δβsor, as the arithmetical difference between basin pairs over time. In addition, we search for explanatory variables correlating Δβsim, Δβnes, and Δβsor with geographical and land use variables. Finally, simulating events of species introduction (i.e., invasion) and extinction, we generated 15 hypothetical assemblages, looking to establish future trends towards biotic change in Chilean basins.ResultsSpecies turnover and β-diversity significantly decreased from historical to current assemblages (Δβsim = -0.084; Δβsor = -0.061, respectively), while the species nestedness did not show significant changes (Δβnes = 0.08). Biotic changes have been driven mainly by the introduction of 28 exotic species, with a minor role of extinctions (one species) and translocations (0 species) of native species. Changes in β-diversity were negatively correlated with area, elevation, and geographical distance between basins but not with land-use nor human population. Finally, the analysis of 15 future assemblages predicts a significant decrease of β-diversity and turnover, and an increase for species nestedness, this time promoted by an increase in the extinction of native species.Main conclusionChilean basins show a significant decrease of the distributional β-diversity and species turnover of the freshwater fish fauna, evidencing a trend towards biotic homogenization. This trend is shared with other Neotropical basins; however, specific mechanisms driving it show different magnitude. Changes in the β-diversity components do not show correlation with variables associated to land use, thus suggesting that casual introductions of freshwater fishes in Chile follow an opportunistic mode related to commercial use. According to future scenarios simulated, biotic homogenization should increase further, mainly as consequence of increased native extinctions