Extreme genetic structure in a small-bodied freshwater fish, the purple spotted gudgeon, Mogurnda adspersa (Eleotridae)

Cryptic species, biogeography, and patterns of introgression in the fish genus Mogurnda (Eleotridae) from the Australian wet tropics: A purple patch for purple-spots

Accurately delimiting species is an essential first step towards understanding the true biodiversity of an ecosystem and any subsequent efforts to identify and protect taxa at risk of extinction. Current molecular evidence suggests that purple-spotted gudgeons (genus Mogurnda) harbour high levels of cryptic biodiversity across their broad distributional range. The present study uses a large single nucleotide polymorphism (SNP) dataset plus a companion allozyme dataset to clarify taxonomic uncertainty, patterns of introgression, and biogeographic relationships among Mogurnda populations within the Queensland Wet Tropics (QWT), a known biodiversity hotspot. Both datasets were strongly concordant in identifying a total of seven taxa split among distinct southern, northern, and lowlands groups. No two taxa were found in strict sympatry, but many appear to be parapatric and occur within the same drainage basin. Although clear evidence of introgression was only evident at six sites (∼4%), the genomic signature of modest historic admixture between proximally-distributed taxa was detected at multiple other sites. Nevertheless, all primary genetic and phylogenetic analyses strongly supported the integrity and diagnosability of these seven taxa. We therefore nominate these as novel candidate species for what appears to be yet another hyper-cryptic complex within the Australian freshwater ichthyological fauna. These results offer up intriguing ecological scenarios and conservation implications for multiple candidate species with narrow ranges in specialised habitat. We conclude by exploring the major biogeographic patterns displayed by QWT Mogurnda.

Factors Beyond Karstification Have Shaped the Population Structure of a Surface-Dwelling Minnow (Phoxinus lumaireul) Able to Disperse Underground

The Dinaric Karst, a biodiversity hotspot, features complex surface and subterranean hydrological networks that influence aquatic species distribution. This study investigates how karst hydrology shapes the genetic structure of the surface-dwelling minnow Phoxinus lumaireul, examining both large-scale and small-scale population patterns. Using mitochondrial DNA and genome-wide single nucleotide polymorphism (SNP) data of 827 specimens of P. lumaireul, three hypotheses were tested: (1) karst underground water connections facilitate genetic connectivity within and across river systems, whereas non-karst rivers exhibit genetic connectivity mostly within the same system; (2) historical and occasional hydrological connections have shaped present-day population structure, leaving genetic signatures of relatedness where no contemporary hydrological links exist; and (3) genomic approaches provide additional insights into biologically relevant connections that may not be captured by classical tracing tests. The large-scale analyses confirmed three main genetic groups (1a-c), whose structure was likely shaped by Pleistocene glaciations and associated microrefugia rather than by karst hydrology. Small-scale structure analyses revealed that while karst hydrology facilitated gene flow within specific areas, connectivity was uneven and influenced by local hydrological dynamics and historical admixture events. Furthermore, some underground pathways identified by classical tracing tests lacked evidence of genetic connectivity, underscoring the limitations of traditional methods and the added value of genomic data in indirectly detecting biologically relevant hydrological connections. These findings highlight the influence of both historical processes and contemporary karst hydrology on P. lumaireul populations, emphasizing their vulnerability in karst ecosystems and the need for targeted conservation efforts.

Genetic structure of Australian glass shrimp, Paratya australiensis, in relation to altitude

Paratya australiensis Kemp (Decapoda: Atyidae) is a widely distributed freshwater shrimp in eastern Australia. The species has been considered as an important stream organism for studying genetics, dispersal, biology, behaviour and evolution in atyids and is a major food source for stream dwelling fishes. Paratya australiensis is a cryptic species complex consisting of nine highly divergent mitochondrial DNA lineages. Previous studies in southeast Queensland showed that “lineage 4” favours upstream sites at higher altitudes, with cooler water temperatures. This study aims to identify putative selection and population structure between high elevation and low elevation populations of this lineage at relatively small spatial scales. Sample localities were selected from three streams: Booloumba Creek, Broken Bridge Creek and Obi Obi Creek in the Conondale Range, southeast Queensland. Six sample localities, consisting of 142 individuals in total were sequenced using double digest Restriction Site Associated DNA-sequencing (ddRAD-seq) technique. Among the 142 individuals, 131 individuals shared 213 loci. Outlier analysis on 213 loci showed that 27 loci were putatively under selection between high elevation and low elevation populations. Outlier analysis on individual streams was also done to test for parallel patterns of adaptation, but there was no evidence of a parallel pattern. Population structure was observed using both the 27 outliers and 186 neutral loci and revealed similar population structure in both cases. Therefore, we cannot differentiate between selection and drift here. The highest genetic differentiation was observed between high elevation and low elevation populations of Booloumba Creek, with small levels of differentiation in the other two streams.

Genetic diversity and aquaculture conservation for a threatened Neotropical catfish

Abstract Due to the ecological importance of Lophiosilurus alexandri, the present work evaluated its genetic representativeness by comparing wild stocks to broodstocks that were kept at three restocking hatcheries along the São Francisco River. A total of 97 samples were genotyped for newly developed microsatellite markers. Low levels of genetic diversity (average alleles number of 4.2 alleles) were detected in all cases, being more severe in captive groups. Significant pairwise FST and DEST values, Structure, and DAPC analyses showed that wild animals were structured in two groups, and a third group was formed by captive animals, evidencing the need to adopt genetic criteria to retain genetic diversity in the hatcheries. For this reason, three full-sib families were constructed to select the best relatedness estimator for L. alexandri and establish a cut-off value aimed to avoid full-sibling matings in the hatcheries. Two estimators, Wang (RW) and Lynch & Li (RLL), were accurate in reflecting the relatedness level for full-sibs in this species. According to them, less than 50% of the potential breeding matings in the three hatcheries are advisable. The innate low diversity of L. alexandri highlights the importance of minimizing inbreeding and retaining genetic diversity towards the species recovery.

Effects of landscape features on population genetic variation of a tropical stream fish, Stone lapping minnow, Garra cambodgiensis, in the upper Nan River drainage basin, northern Thailand

Spatial genetic variation of river-dwelling freshwater fishes is typically affected by the historical and contemporary river landscape as well as life-history traits. Tropical river and stream landscapes have endured extended geological change, shaping the existing pattern of genetic diversity, but were not directly affected by glaciation. Thus, spatial genetic variation of tropical fish populations should look very different from the pattern observed in temperate fish populations. These data are becoming important for designing appropriate management and conservation plans, as these aquatic systems are undergoing intense development and exploitation. This study evaluated the effects of landscape features on population genetic diversity of Garra cambodgiensis, a stream cyprinid, in eight tributary streams in the upper Nan River drainage basin (n = 30–100 individuals/location), Nan Province, Thailand. These populations are under intense fishing pressure from local communities. Based on 11 microsatellite loci, we detected moderate genetic diversity within eight population samples (average number of alleles per locus = 10.99 ± 3.00; allelic richness = 10.12 ± 2.44). Allelic richness within samples and stream order of the sampling location were negatively correlated (P < 0.05). We did not detect recent bottleneck events in these populations, but we did detect genetic divergence among populations (Global F_ST = 0.022, P < 0.01). The Bayesian clustering algorithms (TESS and STRUCTURE) suggested that four to five genetic clusters roughly coincide with sub-basins: (1) headwater streams/main stem of the Nan River, (2) a middle tributary, (3) a southeastern tributary and (4) a southwestern tributary. We observed positive correlation between geographic distance and linearized F_ST (P < 0.05), and the genetic differentiation pattern can be moderately explained by the contemporary stream network (STREAMTREE analysis, R² = 0.75). The MEMGENE analysis suggested genetic division between northern (genetic clusters 1 and 2) and southern (clusters 3 and 4) sub-basins. We observed a high degree of genetic admixture in each location, highlighting the importance of natural flooding patterns and possible genetic impacts of supplementary stocking. Insights obtained from this research advance our knowledge of the complexity of a tropical stream system, and guide current conservation and restoration efforts for this species in Thailand.

A Risk-Based Ecohydrological Approach to Assessing Environmental Flow Regimes

For several decades there has been recognition that water resource development alters river flow regimes and impacts ecosystem values. Determining strategies to protect or restore flow regimes to achieve ecological outcomes is a focus of water policy and legislation in many parts of the world. However, consideration of existing environmental flow assessment approaches for application in Queensland identified deficiencies precluding their adoption. Firstly, in managing flows and using ecosystem condition as an indicator of effectiveness, many approaches ignore the fact that river ecosystems are subjected to threatening processes other than flow regime alteration. Secondly, many focus on providing flows for responses without considering how often they are necessary to sustain ecological values in the long-term. Finally, few consider requirements at spatial-scales relevant to the desired outcomes, with frequent focus on individual places rather than the regions supporting sustainability. Consequently, we developed a risk-based ecohydrological approach that identifies ecosystem values linked to desired ecological outcomes, is sensitive to flow alteration and uses indicators of broader ecosystem requirements. Monitoring and research is undertaken to quantify flow-dependencies and ecological modelling is used to quantify flow-related ecological responses over an historical flow period. The relative risk from different flow management scenarios can be evaluated at relevant spatial-scales. This overcomes the deficiencies identified above and provides a robust and useful foundation upon which to build the information needed to support water planning decisions. Application of the risk assessment approach is illustrated here by two case studies.

Ecological disturbance influences adaptive divergence despite high gene flow in golden perch (Macquaria ambigua): Implications for management and resilience to climate change

Populations that are adaptively divergent but maintain high gene flow may have greater resilience to environmental change as gene flow allows the spread of alleles that have already been tested elsewhere. In addition, populations naturally subjected to ecological disturbance may already hold resilience to future environmental change. Confirming this necessitates ecological genomic studies of high dispersal, generalist species. Here we perform one such study on golden perch (Macquaria ambigua) in the Murray-Darling Basin (MDB), Australia, using a genome-wide SNP data set. The MDB spans across arid to wet and temperate to subtropical environments, with low to high ecological disturbance in the form of low to high hydrological variability. We found high gene flow across the basin and three populations with low neutral differentiation. Genotype-environment association analyses detected adaptive divergence predominantly linked to an arid region with highly variable riverine flow, and candidate loci included functions related to fat storage, stress and molecular or tissue repair. The high connectivity of golden perch in the MDB will likely allow locally adaptive traits in its most arid and hydrologically variable environment to spread and be selected in localities that are predicted to become arid and hydrologically variable in future climates. High connectivity in golden perch is likely due to their generalist life history and efforts of fisheries management. Our study adds to growing evidence of adaptation in the face of gene flow and highlights the importance of considering ecological disturbance and adaptive divergence in biodiversity management.

Landscape genetics informs mesohabitat preference and conservation priorities for a surrogate indicator species in a highly fragmented river system

Poor dispersal species represent conservative benchmarks for biodiversity management because they provide insights into ecological processes influenced by habitat fragmentation that are less evident in more dispersive organisms. Here we used the poorly dispersive and threatened river blackfish (Gadopsis marmoratus) as a surrogate indicator system for assessing the effects of fragmentation in highly modified river basins and for prioritizing basin-wide management strategies. We combined individual, population and landscape-based approaches to analyze genetic variation in samples spanning the distribution of the species in Australia's Murray-Darling Basin, one of the world's most degraded freshwater systems. Our results indicate that G. marmoratus displays the hallmark of severe habitat fragmentation with notably scattered, small and demographically isolated populations with very low genetic diversity-a pattern found not only between regions and catchments but also between streams within catchments. By using hierarchically nested population sampling and assessing relationships between genetic uniqueness and genetic diversity across populations, we developed a spatial management framework that includes the selection of populations in need of genetic rescue. Landscape genetics provided an environmental criterion to identify associations between landscape features and ecological processes. Our results further our understanding of the impact that habitat quality and quantity has on habitat specialists with similarly low dispersal. They should also have practical applications for prioritizing both large- and small-scale conservation management actions for organisms inhabiting highly fragmented ecosystems.

Genetic Diversity and Structure Analysis of Percocypris pingi (Cypriniformes: Cyprinidae): Implications for Conservation and Hatchery Release in the Yalong River

Percocypris pingi is a near threatened cyprinid species, which has suffered a dramatic decline due to anthropogenic factors. As one response to this decline, hatchery release for P. pingi has been conducted in the lower reaches of the Yalong River since 2012. To understand the conservation status of this species and the potential impact of the release of hatchery-reared fish, we studied the genetic diversity and population structure of wild and hatchery populations of P. pingi. Two hatchery populations (Jinping [JPH] and Ya’an [YAH]) and two wild populations (Muli [MLW] and Woluo [WLW]) of P. pingi were analyzed based on microsatellite markers and the mitochondrial DNA control region. The results showed that P. pingi possesses moderate levels of genetic diversity, with observed heterozygosities ranging from 0.657 to 0.770 and nucleotide diversities ranging from 0.00212 to 0.00491. Our results also suggested WLW harbors considerable proportions of genetic diversity in this species and serves as a refuge for P. pingi during anthropogenic disturbance, thus playing an important role for the conservation of P. pingi populations. Microsatellite and mitochondrial markers both indicated close genetic relationships between YAH and MLW, JPH and WLW, respectively. The results to some extent reflected the geographical provenances for original broodstocks of the two hatchery populations, which provide some practical guidance for hatchery release of P. pingi. The existence of remarkable genetic divergence distributed along limited geographical range (approximately 10 kilometers) suggests the two wild populations should be regarded at least as two distinct evolutionary significant units (ESUs) and management units (MUs). Considering reduced intra-population genetic variation in hatchery population for release and significant genetic compositions of the two hatchery populations, some appropriate breeding strategies were proposed to benefit conservation of P. pingi.

Multilocus approach reveals cryptic lineages in the goby Rhinogobius duospilus in Hong Kong streams: Role of paleodrainage systems in shaping marked population differentiation in a city

Drainage history is a well-demonstrated factor that influences the population structure of freshwater inhabitants over a broad geographic scale. However, there has been little research undertaken on such a relationship with freshwater fish on a small geographical scale, especially in Asia. In this study, we investigated the role of local, small drainage systems in affecting the population genetic structure of a freshwater goby, Rhinogobius duospilus, in Hong Kong streams using a multilocus approach. Analyses on nine genetic markers (2 mitochondrial and 7 nuclear markers, including 5 microsatellite markers) reveal prominent and intensive genetic structuring (2.1-5.4% mtDNA sequence divergence) in R. duospilus in Hong Kong. The lineages and clusters recovered from mtDNA data and assignment analysis of nuclear markers coincide with the paleodrainage networks. Furthermore, marked population subdivision between streams located on different side branches (<20km apart) within the same paleodrainage area is observed and gene flow occurs only between closely situated streams that share common paleodrainage confluences. In an extreme case, gene flow is limited between streams that are less than 5km apart. Apparently, such an intensive population structure is attributed to the regional paleodrainage pattern, together with the highly sedentary life style of R. duospilus, which reduces contemporary gene flow and dispersal between populations in neighbouring streams.

Phylogeographical analysis of a cold-temperate freshwater fish, the Amur sleeper (Perccottus glenii) in the Amur and Liaohe River basins of Northeast Asia

The Amur sleeper Perccottus glenii (Perciformes, Gobioidei, Odontobutidae) is well known as an invasive fish in the river basins of Eastern and Central Europe, but its genetic background is unavailable across its native habitats in northeast Asia. In this study, we used the mitochondrial cytochrome b gene by sampling 19 populations of P. glenii across its native distributional areas of Liaohe and Amur River basins to explore its evolutionary history. Phylogenetic analyses identified three major clades within P. glenii, among which Clade A and Clade B were co-distributed in the Liaohe and Amur River basins, and Clade C was restricted to the latter. Molecular dating showed that the splits of Clades A, B and C have happened in the late Early-early Middle Pleistocene and the most recent common ancestors of these clades have been presented in the late Middle-early Late Pleistocene. The P. glenii showed very high levels of genetic structure among populations (ΦST = 0.801), probably due to the characters of its life histories with very limited dispersal ability. The admixture of different clades in some populations of P. glenii probably reflects historical secondary contact. These findings indicate that Pleistocene climatic oscillation and river capture were major determinants for genetic variations and evolutionary history of the P. glenii.

Catchment-scale conservation units identified for the threatened Yarra pygmy perch (Nannoperca obscura) in highly modified river systems

Habitat fragmentation caused by human activities alters metapopulation dynamics and decreases biological connectivity through reduced migration and gene flow, leading to lowered levels of population genetic diversity and to local extinctions. The threatened Yarra pygmy perch, Nannoperca obscura, is a poor disperser found in small, isolated populations in wetlands and streams of southeastern Australia. Modifications to natural flow regimes in anthropogenically-impacted river systems have recently reduced the amount of habitat for this species and likely further limited its opportunity to disperse. We employed highly resolving microsatellite DNA markers to assess genetic variation, population structure and the spatial scale that dispersal takes place across the distribution of this freshwater fish and used this information to identify conservation units for management. The levels of genetic variation found for N. obscura are amongst the lowest reported for a fish species (mean heterozygosity of 0.318 and mean allelic richness of 1.92). We identified very strong population genetic structure, nil to little evidence of recent migration among demes and a minimum of 11 units for conservation management, hierarchically nested within four major genetic lineages. A combination of spatial analytical methods revealed hierarchical genetic structure corresponding with catchment boundaries and also demonstrated significant isolation by riverine distance. Our findings have implications for the national recovery plan of this species by demonstrating that N. obscura populations should be managed at a catchment level and highlighting the need to restore habitat and avoid further alteration of the natural hydrology.