Annual dynamics variation of a landlocked Galaxias maculatus (Jenyns 1842) population in a Northern Patagonian river: occurrence of juvenile upstream migration

Galaxias maculatus, broadly distributed in the southern hemisphere, presents both diadromic and landlocked populations. The upstream migration of larvae and juveniles from the sea to freshwater habitats is a characteristic phenomenon of diadromous populations, but upstream migration has never been reported in those that are landlocked. The objective of this study was to establish the population dynamics of a peculiar riverine landlocked population that presents an upstream migration at the larvae–juvenile transition from the Piedra del Águila Reservoir to the Caleufú River (Argentina). A spawning season from September to November and the arrival of shoals of metamorphic larvae and juveniles from February to April to the adult habitat were coincidental with lacustrine landlocked populations, but not with diadromous populations. Growth rate and age at migration, 147 ± 22.6 days, were also similar to other landlocked and diadromous populations. The arrival of these shoals produced a 20‐fold increase in fish density while the two cohorts of G. maculatus overlapped in time and space. No significant differences in morphology or vertebrae number were detected when riverine and reservoir adults were compared. The great life history plasticity of G. maculatus, shown to be even greater in our results, could be the key to explain the wide distribution of this species in the southern hemisphere. Likewise, discovering this juvenile potamodromous behaviour in a landlocked population will provide a new view for the analysis of the ways of this species’ dispersion in continental waters.     

Metapopulation dynamics of a diadromous galaxiid fish and potential effects of salmonid aquaculture

1. Direct ecological effects of biological invasions have been widely documented, but indirect genetic effects on native species are poorly known. In many cases, this is because of the lack of information on the genetic structure of species affected by invasions. 2. We used microsatellite DNA loci to estimate the genetic structure and gene flow patterns of Galaxias maculatus, a galaxiid fish endemic to the southern hemisphere, which is increasingly being threatened by salmonid invasions. 3. Analysis of nine diadromous populations of G. maculatus in Chilean Patagonia (an area heavily impacted by farming of non‐native salmonids) indicates that dispersal is mostly a passive process, seemingly driven by wind and currents and resulting in high gene flow and weak population structuring. 4. Gene flow was asymmetrical, with three populations acting as sources and six populations acting as sinks. Sinks had lower habitat quality and had a greater incidence of adults than sources, which consisted mostly of juveniles. 5. Rivers invaded by salmonid escapees experienced significantly higher aquaculture pressure than rivers where salmonid escapees were apparently absent, but no effect on genetic diversity of G. maculatus could be detected. 6. We discuss whether salmonid aquaculture might affect the demography and connectivity of galaxiid metapopulations: indirectly through habitat alteration and directly through escapes of predatory fish.     

The effects of diadromy and its loss on genomic divergence: The case of amphidromous Galaxias maculatus populations

Understanding the evolutionary mechanisms that affect the genetic divergence between diadromous and resident populations across heterogeneous environments is a challenging task. While diadromy may promote gene flow leading to a lack of genetic differentiation among populations, resident populations tend to be affected by local adaptation and/or plasticity. Studies on these effects on genomic divergence in nonmodel amphidromous species are scarce. Galaxias maculatus, one of the most widespread fish species in the Southern Hemisphere, exhibits two life histories, an ancestral diadromous, specifically, amphidromous form, and a derived freshwater resident form. We examined the genetic diversity and divergence among 20 estuarine and resident populations across the Chilean distribution of G. maculatus and assessed the extent to which selection is involved in the differentiation among resident populations. We obtained nearly 4,400 SNP markers using a RADcap approach for 224 individuals. As expected, collections from estuarine locations typically consist of diadromous individuals. Diadromous populations are highly differentiated from their resident counterparts by both neutral and putative adaptive markers. While diadromous populations exhibit high gene flow and lack site fidelity, resident populations appear to be the product of different colonization events with relatively low genetic diversity and varying levels of gene flow. In particular, the northernmost resident populations were clearly genetically distinct and reproductively isolated from each other suggesting local adaptation. Our study provides insights into the role of life history differences in the maintenance of genetic diversity and the importance of genetic divergence in species evolution.     

Dynamic micro-geographic and temporal genetic diversity in vertebrates: the case of lake-spawning populations of brown trout (Salmo trutta)

Conservation of species should be based on knowledge of effective population sizes and understanding of how breeding tactics and selection of recruitment habitats lead to genetic structuring. In the stream‐spawning and genetically diverse brown trout, spawning and rearing areas may be restricted source habitats. Spatio–temporal genetic variability patterns were studied in brown trout occupying three lakes characterized by restricted stream habitat but high recruitment levels. This suggested non‐typical lake‐spawning, potentially representing additional spatio–temporal genetic variation in continuous habitats. Three years of sampling documented presence of young‐of‐the‐year cohorts in littoral lake areas with groundwater inflow, confirming lake‐spawning trout in all three lakes. Nine microsatellite markers assayed across 901 young‐of‐the‐year individuals indicated overall substantial genetic differentiation in space and time. Nested gene diversity analyses revealed highly significant (≤P = 0.002) differentiation on all hierarchical levels, represented by regional lakes (F_LT = 0.281), stream vs. lake habitat within regional lakes (F_HL = 0.045), sample site within habitats (F_SH = 0.010), and cohorts within sample sites (F_CS = 0.016). Genetic structuring was, however, different among lakes. It was more pronounced in a natural lake, which exhibited temporally stable structuring both between two lake‐spawning populations and between lake‐ and stream spawners. Hence, it is demonstrated that lake‐spawning brown trout form genetically distinct populations and may significantly contribute to genetic diversity. In another lake, differentiation was substantial between stream‐ and lake‐spawning populations but not within habitat. In the third lake, there was less apparent spatial or temporal genetic structuring. Calculation of effective population sizes suggested small spawning populations in general, both within streams and lakes, and indicates that the presence of lake‐spawning populations tended to reduce genetic drift in the total (meta‐) population of the lake.     

Effect of waterfalls on fluvial fish distribution and landlocked Rhinogobius brunneus populations on Yakushima Island,Japan

The distribution of fluvial fish was surveyed at 55 sites on Yakushima Island, Japan, which has precipitous mountains and waterfalls (below- or no-waterfall sites: 31; above-waterfall sites: 24). Eleven diadromous and one river resident (introduced Oncorhynchus masou masou) species were found, but absolutely no fish were detected at the 18 above-waterfall sites. Statistical analyses revealed that the presence of waterfalls (> 5 m in height) below the sites had a significant negative effect on fish distribution, suggesting that waterfalls prevent migration of diadromous fishes. We found Rhinogobius brunneus populations above high waterfalls such as Nunobiki Falls (50 m) and Ohko Falls (88 m). Otolith Sr:Ca ratios and mitochondrial DNA (cyt-b region) were examined to determine the migratory history and genetic properties of these populations; the Sr:Ca ratios indicated that the populations had a landlocked life cycle, whereas the genetic endemism/isolation of landlocked populations was unexpectedly absent. There is no clear explanation for this phenomenon, but fairly infrequent individuals of nonlandlocked type might have migrated beyond the waterfalls with their sucker-like organ and mated with landlocked populations, disrupting the genetic isolation of landlocked populations.     

Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (<Emphasis Type="Italic">Gobiomorphus cotidianus</Emphasis>) – implications for incipient speciation in island freshwater fish species

Background  

Many postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species.     

Rapid divergence of mussel populations despite incomplete barriers to dispersal

Striking genetic structure among marine populations at small spatial scales is becoming evident with extensive molecular studies. Such observations suggest isolation at small scales may play an important role in forming patterns of genetic diversity within species. Isolation‐by‐distance, isolation‐by‐environment and historical priority effects are umbrella terms for a suite of processes that underlie genetic structure, but their relative importance at different spatial and temporal scales remains elusive. Here, we use marine lakes in Indonesia to assess genetic structure and assess the relative roles of the processes in shaping genetic differentiation in populations of a bivalve mussel (Brachidontes sp.). Marine lakes are landlocked waterbodies of similar age (6,000–10,000 years), but with heterogeneous environments and varying degrees of connection to the sea. Using a population genomic approach (double‐digest restriction‐site‐associated DNA sequencing), we show strong genetic structuring across populations (range F_ST: 0.07–0.24) and find limited gene flow through admixture plots. At large spatial scales (>1,400 km), a clear isolation‐by‐distance pattern was detected. At smaller spatial scales (<200 km), this pattern is maintained, but accompanied by an association of genetic divergence with degree of connection. We hypothesize that (incomplete) dispersal barriers can cause initial isolation, allowing priority effects to give the numerical advantage necessary to initiate strong genetic structure. Priority effects may be strengthened by local adaptation, which the data may corroborate by showing a high correlation between mussel genotypes and temperature. Our study indicates an often‐neglected role of (evolution‐mediated) priority effects in shaping population divergence.     

Phylogeography of the Sponge Suberites diversicolor in Indonesia: Insights into the Evolution of Marine Lake Populations

The existence of multiple independently derived populations in landlocked marine lakes provides an opportunity for fundamental research into the role of isolation in population divergence and speciation in marine taxa. Marine lakes are landlocked water bodies that maintain a marine character through narrow submarine connections to the sea and could be regarded as the marine equivalents of terrestrial islands. The sponge Suberites diversicolor (Porifera: Demospongiae: Suberitidae) is typical of marine lake habitats in the Indo-Australian Archipelago. Four molecular markers (two mitochondrial and two nuclear) were employed to study genetic structure of populations within and between marine lakes in Indonesia and three coastal locations in Indonesia, Singapore and Australia. Within populations of S. diversicolor two strongly divergent lineages (A & B) (COI: p = 0.4% and ITS: p = 7.3%) were found, that may constitute cryptic species. Lineage A only occurred in Kakaban lake (East Kalimantan), while lineage B was present in all sampled populations. Within lineage B, we found low levels of genetic diversity in lakes, though there was spatial genetic population structuring. The Australian population is genetically differentiated from the Indonesian populations. Within Indonesia we did not record an East-West barrier, which has frequently been reported for other marine invertebrates. Kakaban lake is the largest and most isolated marine lake in Indonesia and contains the highest genetic diversity with genetic variants not observed elsewhere. Kakaban lake may be an area where multiple putative refugia populations have come into secondary contact, resulting in high levels of genetic diversity and a high number of endemic species.     

Hierarchical population structure and genetic diversity of lake trout (Salvelinus namaycush) in a dendritic system in Northern Labrador

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Genetic and phenotypic differentiation among Galaxias maculatus populations in a Patagonian postglacial lake system

Understanding the influence of landscape features on population differentiation is fundamental to evolutionary biology studies. We examined spatial patterns of genetic and phenotypic variability among Galaxias maculatus populations in a complex of four postglacial lakes in northwestern Patagonia differing in size and connectivity among them. A hierarchical Bayesian analysis grouped the individuals collected from eleven localities into three genetic clusters, first defining the populations of the two large lakes and separating the two small lakes in subsequent analysis. Genetic structuring was restricted within large lakes. It is known that the larval stage of Galaxias maculatus migrate to the limnetic zone of Patagonian lakes, possibly exerting an homogenizing effect on gene flow within lakes. Gene flow asymmetry and divergences among lakes can be explained by a combination of landscape characteristics and the presence of predators in the short streams that connect them. Individuals from the small lakes are the most divergent morphologically and genetically. The population in the isolated Redonda Lake, exhibits meristic differences as well, suggesting strong drift and environmental effects. This population is likely to have been isolated following the decline in water level of a paleolake that existed in this region approximately 13.2 kya BP. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Surviving historical Patagonian landscapes and climate: molecular insights from <Emphasis Type="Italic">Galaxias maculatus</Emphasis>

Background  

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 Galaxias maculatus in Patagonia (~300 individuals from 36 locations).     

Migratory behaviour shapes spatial genetic structure of cyprinid fishes within the Lake Malawi catchment

• Genetic differences among freshwater fish populations are dependent on life‐history characteristics of the species, including the range of adult dispersal and the extent of homing to natal breeding grounds. However, the effects of variation in such characteristics on population genetic connectivity are rarely studied comparatively among closely related species.
• We studied population genetic structure within three congeneric cyprinid species from the Lake Malawi catchment that differ substantially in life‐history traits and conservation status, using a combination of microsatellite and mitochondrial DNA markers. Mpasa (Opsaridium microlepis) is a large (70 cm total length) migratory species that spawns in rivers, but as an adult is exclusively known from the main lake body. Sanjika (Opsaridium microcephalum), is a medium size (30 cm total length) species that exists in lake breeding, river‐lake migratory and apparently landlocked populations. Dwarf sanjika (Opsaridium tweddleorum) is a small non‐migratory species (15 cm total length) that persists in small tributaries surrounding the main lake and adjoining rivers.
• The results revealed striking differences among the three species in spatial genetic structuring. The river‐lake migratory mpasa showed only weak yet significant population genetic structure within the main Lake Malawi catchment, suggesting that there is no strong natal homing. The habitat‐generalist sanjika showed only weak spatial genetic differentiation at microsatellite loci within the Lake Malawi catchment, but moderate structure in mitochondrial DNA, potentially reflecting male‐biased dispersal. The river‐restricted dwarf sanjika showed strong genetic structure in both microsatellite and mitochondrial DNA, suggesting strictly limited dispersal at both adult and juvenile stages.
• We conclude that contrasting migration life histories have resulted in dramatically different patterns of population genetic structure among these congeneric species. The observed patterns demonstrate how divergent life‐history evolution may strongly influence broader patterns of population genetic connectivity in freshwater fish, with consequences for management and conservation. Specifically the results suggesting gene flow among Lake Malawi populations of mpasa, an IUCN red‐listed ‘Endangered’ species endemic to the lake catchment, imply that conservation initiatives operating at both local and catchment scales are needed to reverse local population decline.

     

Landscape genetics and spatial pattern of phenotypic variation of Eristalis tenax across Europe

A study of population connectivity of the migratory insect species, such as dronefly Eristalis tenax (Diptera, Syrphidae), has an essential importance in understanding the relative influence of the evolutionary forces and environmental features that interact in the spatial distribution of molecular and morphological diversity. However, specific study aiming to understand spatial genetic structure of dronefly populations and its migratory potential is lacking. Hence, we studied a spatial pattern of genetic and phenotypic variation of seven European populations of E. tenax incorporating landscape genetic methods using allozyme data, wing size and shape and abdominal colour pattern. Based on the observed lack of genotypic structuring, we suggested that there has been sufficient long‐distance gene flow to effectively homogenize population structuring at a broader geographical scale. Wing shape similarity among populations and an overlap of abdominal colour variation showed no clear clustering related to geography, which is in congruence with genetic data. However, genetic (F_ST values) and phenotypic (wing size) data and landscape genetics indicated subdivision between the Balkan populations (four Serbian samples) and populations from Central (Germany and Switzerland) and Northern (Finland) Europe. These findings indicated a potential connection between the Central and Northern Europe supporting the Central European origin of the flies caught in Finland. Thus, by performing spatial analysis and combining genetic–morphological approach, we shed light on the movement pattern in complex landscapes and thus provided the necessary guidelines to a broad‐scale analysis of this widespread generalist pollinator.     

Effects of ultraviolet radiation on the eggs of landlocked Galaxias maculatus (Galaxiidae, Pisces) in northwestern Patagonia

• 1 Ultraviolet radiation (UVR) damages early life stages of several fish species. Galaxias maculatus is a small catadromous fish, with landlocked forms occurring in many lakes within the Nahuel Huapi National Park (Patagonia, Argentina). In this work, the vulnerability of G. maculatus eggs exposed to both natural and artificial UVR was investigated in relation to water transparency.
• 2 Field experiments were performed in two lakes differing in UVR attenuation. Galaxias maculatus eggs were exposed to in situ levels of UVR in quartz tubes incubated at various depths. For laboratory experiments, the eggs were exposed to five levels of artificial UVB radiation.
• 3 Exposure to natural UVR causes various degrees of egg mortality depending on water transparency and incubation depth. In the less transparent lake (K_d320 = 3.08 m^‐1), almost complete mortality was observed near the surface. At a depth of 43 cm the observed mortality was only 22%, but was still significantly different from the dark control. In the most transparent lake (K_d320 = 0.438 m^‐1), almost total mortality was observed in tubes incubated at 2.56 m or shallower. A gradual decline in mortality was recorded from that depth to 3.78 m where the values approached those in the dark control treatments.
• 4 A monotonic relationship between mortality and UV exposure could be observed both in field and laboratory experiments. Using the results from field incubations, a LD₅₀ of 2.5 J cm^‐2 nm^‐1 was estimated. In a few mountain lakes, this value would be exceeded even if the eggs were laid at the maximum depth of the lake. Thus UVR seems a sufficient cause to explain the absence of G. maculatus populations in some mountain lakes. For most lakes, however, UVR is probably one of several important environmental factors, which together determine the habitat suitability.

     

Lasting through the ice age: The role of the proglacial refugia in the maintenance of genetic diversity,population growth,and high dispersal rate in a widespread freshwater crustacean

1. The severe climatic changes during the Pleistocene ice ages have shaped the genetic structure and distribution of biota in Europe. We aimed to reveal in detail the genetic diversity, geographical population structure, historical and present demography, migration patterns, and the presence of possible glacial refugia within the nominative subspecies Asellus aquaticus aquaticus.
2. We analysed DNA sequences of the mitochondrial cytochrome c oxidase subunit I gene and nuclear noncoding internal transcribed spacer II region, from populations inhabiting post-glacial Europe (from the British Isles and Scandinavia to the northern Mediterranean and Black Sea coasts).
3. The origin of the taxon, including establishment in the Dinaric Western Balkans, dates to the Middle/Late Pliocene, but most of its genetic diversity emerged during the Middle/Late Pleistocene before the Last Glacial Maximum.
4. Despite the general absence of spatial genetic structure with population growth, we discovered two different phylogeographic stories across 11 clusters revealed by a coalescent approach. Firstly, the periglacial cluster group—spatially restricted mainly to the northern Balkans, Pannonian Basin, and Pontic Region—is older and more divergent. It apparently retained a relatively stable population size during the glacial-interglacial cycles. Conversely, the proglacial cluster group—widely distributed in areas close to the glacier margins (north of the Alps, Sudetes, Carpathians) and in the Pannonian Basin—is younger and composed of closely related individuals. It originated in Pleistocene and lasted continuously through the Last Glacial Maximum in numerous high latitude refugia. This was probably due to the vast network of proglacial lakes and rivers, which played a crucial role in the maintenance of genetic diversity, population growth, and high dispersal rate.
5. The evolutionary history of A. a. aquaticus reveals unexpected patterns and is an important lesson when making predictions for other aquatic taxa. Our results suggest that we should stop perceiving the proglacial habitats as lifeless ice desert.

     

Unique sympatric quartet of limnetic,benthic, profundal and piscivorous brown trout populations resolved by 3D sampling and focused molecular marker selection

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Low interbasin connectivity in a facultatively diadromous fish: evidence from genetics and otolith chemistry

Southern smelts (Retropinna spp.) in coastal rivers of Australia are facultatively diadromous, with populations potentially containing individuals with diadromous or wholly freshwater life histories. The presence of diadromous individuals is expected to reduce genetic structuring between river basins due to larval dispersal via the sea. We use otolith chemistry to distinguish between diadromous and nondiadromous life histories and population genetics to examine interbasin connectivity resulting from diadromy. Otolith strontium isotope (⁸⁷Sr:⁸⁶Sr) transects identified three main life history patterns: amphidromy, freshwater residency and estuarine/marine residency. Despite the potential for interbasin connectivity via larval mixing in the marine environment, we found unprecedented levels of genetic structure for an amphidromous species. Strong hierarchical structure along putative taxonomic boundaries was detected, along with highly structured populations within groups using microsatellites (F_ST = 0.046–0.181), and mtDNA (Φ_ST = 0.498–0.816). The presence of strong genetic subdivision, despite the fact that many individuals reside in saline water during their early life history, appears incongruous. However, analysis of multielemental signatures in the otolith cores of diadromous fish revealed strong discrimination between river basins, suggesting that diadromous fish spend their early lives within chemically distinct estuaries rather than the more homogenous marine environment, thus avoiding dispersal and maintaining genetic structure.     

Gene flow from multiple sources maintains high genetic diversity and stable population history of Common Moorhen Gallinula chloropus in China

In this study, we used mitochondrial control sequences and microsatellite data from 231 Common Moorhen Gallinula chloropus individuals sampled from 19 sites in China to analyse their genetic structure and evolutionary history. High genetic diversity was found for all populations, although microsatellite analysis showed that the genetic diversity in non‐migratory populations was significantly higher than in migratory populations. High gene flow occurred between neighbouring populations, although long‐distance gene flow also occurred. The Huazhong population was the single greatest genetic source for other populations. High gene flow probably led to the shallow genetic structure that we observed. Demographic expansion was found in migratory populations, non‐migratory populations and with all individuals combined. The expansion time for all populations combined was estimated to be 221 000 years ago. The Common Moorhen population grew rapidly during the interglacial before the last glacial maximum (LGM), then remained generally stable from the LGM to the present.     

Population structuring in the monogonont rotifer Synchaeta pectinata: high genetic divergence on a small geographical scale

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Genetic diversity,population structure and sex‐biased dispersal in three co‐evolving species

Genetic diversity and spatial structure of populations are important for antagonistic coevolution. We investigated genetic variation and population structure of three closely related European ant species: the social parasite Harpagoxenus sublaevis and its two host species Leptothorax acervorum and Leptothorax muscorum. We sampled populations in 12 countries and analysed eight microsatellite loci and an mtDNA sequence. We found high levels of genetic variation in all three species, only slightly less variation in the host L. muscorum. Using a newly introduced measure of differentiation (Jost’s D_est ), we detected strong population structuring in all species and less male‐biased dispersal than previously thought. We found no phylogeographic patterns that could give information on post‐glacial colonization routes – northern populations are as variable as more southern populations. We conclude that conditions for Thompson’s geographic mosaic of coevolution are ideal in this system: all three species show ample genetic variation and strong population structure.