Lamprey Species Research Articles

Major threats to European freshwater fish species

In Europe, freshwater fish are the richest group amongst European vertebrates and the second most threatened animal group, surpassed only by freshwater molluscs. The identification of threats is a major benefit for conservation efforts, as it allows actions to be bespoke to specific threats imperilling fish communities in sensitive areas. In this work, we analyse all threats identified under the International Union for Conservation of Nature (IUCN) Red List of Threatened Species for all European native freshwater dependent fish and lamprey species and relate them with the species distribution, conservation status and migratory phenology. Results show that the current level of imperilment of European freshwater fish fauna is high, especially in the Iberian Peninsula fish communities where low richness is combined with a proportion of threatened species surpassing 50% in several catchments The most relevant threats affecting European freshwater fish are: “Dams & Water Management/Use”, “Droughts”, “Invasive Non-Native/Alien Species/Diseases”, “Agricultural & Forestry Effluents” and “Fishing & Harvesting Aquatic Resources”. The present work contributes to the ultimate goal of species conservation by highlighting the main threats affecting freshwater fish species in Europe and by demonstrating how specific regions need particular attention. Increasing longitudinal connectivity stands out as a measure with the potential to increase species' resilience to the several threats affecting them, and it should be coupled with additional efforts to reduce water pollution, control alien species and effectively manage fishing.

Beyond fish eDNA metabarcoding: Field replicates disproportionately improve the detection of stream associated vertebrate species

Fast, reliable, and comprehensive biodiversity monitoring data are needed for environmental decision making and management. Recent work on fish environmental DNA (eDNA) metabarcoding shows that aquatic diversity can be captured fast, reliably, and non-invasively at moderate costs. Because water in a catchment flows to the lowest point in the landscape, often a stream, it can collect traces of terrestrial species via surface or subsurface runoff along its way or when specimens come into direct contact with water (e.g., when drinking). Thus, fish eDNA metabarcoding data can provide information on fish but also on other vertebrate species that live in riparian habitats. This additional data may offer a much more comprehensive approach for assessing vertebrate diversity at no additional costs. Studies on how the sampling strategy affects species detection especially of stream-associated communities, however, are scarce. We therefore performed an analysis on the effects of biological replication on both fish as well as (semi-)terrestrial species detection. Along a 2 km stretch of the river Mulde (Germany), we collected 18 1-L water samples and analyzed the relation of detected species richness and quantity of biological replicates taken. We detected 58 vertebrate species, of which 25 were fish and lamprey, 18 mammals, and 15 birds, which account for 50%, 22.2%, and 7.4% of all native species to the German federal state of Saxony-Anhalt. However, while increasing the number of biological replicates resulted in only 24.8% more detected fish and lamprey species, mammal, and bird species richness increased disproportionately by 68.9% and 77.3%, respectively. Contrary, PCR replicates showed little stochasticity. We thus emphasize to increase the number of biological replicates when the aim is to improve general species detections. This holds especially true when the focus is on rare aquatic taxa or on (semi-)terrestrial species, the so-called ‘bycatch’. As a clear advantage, this information can be obtained without any additional sampling or laboratory effort when the sampling strategy is chosen carefully. With the increased use of eDNA metabarcoding as part of national fish bioassessment and monitoring programs, the complimentary information provided on bycatch can be used for biodiversity monitoring and conservation on a much broader scale.

An assessment of terminology for intraspecific diversity in fishes, with a focus on "ecotypes" and "life histories".

Understanding and preserving intraspecific diversity (ISD) is important for species conservation. However, ISD units do not have taxonomic standards and are not universally recognized. The terminology used to describe ISD is varied and often used ambiguously. We compared definitions of terms used to describe ISD with use in recent studies of three fish taxa: sticklebacks (Gasterosteidae), Pacific salmon and trout (Oncorhynchus spp., “PST”), and lampreys (Petromyzontiformes). Life history describes the phenotypic responses of organisms to environments and includes biological parameters that affect population growth or decline. Life‐history pathway(s) are the result of different organismal routes of development that can result in different life histories. These terms can be used to describe recognizable life‐history traits. Life history is generally used in organismal‐ and ecology‐based journals. The terms paired species/species pairs have been used to describe two different phenotypes, whereas in some species and situations a continuum of phenotypes may be expressed. Our review revealed overlapping definitions for race and subspecies, and subspecies and ecotypes. Ecotypes are genotypic adaptations to particular environments, and this term is often used in genetic‐ and evolution‐based journals. “Satellite species” is used for situations in which a parasitic lamprey yields two or more derived, nonparasitic lamprey species. Designatable Units, Evolutionary Significant Units (ESUs), and Distinct Population Segments (DPS) are used by some governments to classify ISD of vertebrate species within distinct and evolutionary significant criteria. In situations where the genetic or life‐history components of ISD are not well understood, a conservative approach would be to call them phenotypes.

Whose Kids Did You Eat? Genetic Identification of Species and Parents of Larval Lampreys in Fish Predator Guts

AbstractThe Pacific Lamprey Entosphenus tridentatus is an important species both ecologically and culturally, but their population numbers and range have declined severely in the past several decades in the Columbia Basin. In freshwater ecosystems, larval lampreys are candidate prey species for many fish predators, but little is known regarding the magnitude of predation they currently experience. Predation on larval Pacific Lampreys may be substantially underestimated by morphological gut content analysis because their soft bodies are quickly digested and leave no hard evidence, such as bones and scales. We conducted an experimental predation study and analyzed larval Pacific Lampreys in the gut contents of predators’ digestive tracts via both morphological and molecular methods. Whereas most consumed larval lampreys (67–100%) were morphologically unidentifiable within two nights, genetic species identification rates using four single nucleotide polymorphisms from stomachs were high (83%). The single nucleotide polymorphisms optimized for parentage in Pacific Lamprey also successfully identified the parents of four out of five Pacific Lampreys with complete genotypes. When a genetic baseline of candidate parents is available, this molecular technique using parentage‐based tagging offers a novel method for determining precise characteristics of predation behavior in field studies, including the ages and natal origins of larvae being consumed.

Invasion of the European River Lamprey Lampetra fluviatilis in the Upper Volga

The European river lamprey came to the Upper Volga from the Baltic Sea most probably via a system of shipways developed in the 18th and 19th centuries. The Vyshnii Volochek, Tikhvin, and Mariinskaya water systems are possible invasion pathways for this species. Dispersal and colonization of the Caspian Basin was likely a combination of upstream and downstream migrations. Analysis of museum and our own samples showed that lamprey possibly migrated upstream (for spawning) along rivers of the Baltic Basin until they reached the watershed boundary from which they could disperse downstream (in the juvenile period) into rivers of the Caspian Basin. Dispersal in the Volga River could occur in accordance with the migration cycle of this opportunistic lamprey species and lead to the present distribution. Key features (dentition and number of trunk myomeres) showed that lamprey from the studied area are similar to lampreys from the Baltic basin, although specimens in each population have their own peculiarities in morphology (size and coloration). Genetic data (Cyt-b) support the idea of a relatively recent invasion of lamprey into the Upper Volga. The haplotype, found in three rivers, is one of the most widespread in Europe and is found along the supposed route of invasion.

Species-environment relationships of fish and map-based variables in small boreal streams: Linkages with climate change and bioassessment.

Species–environment relationships were studied between the occurrence of 13 fish and lamprey species and 9 mainly map‐based environmental variables of Finnish boreal small streams. A self‐organizing map (SOM) analysis showed strong relationships between the fish species and environmental variables in a single model (explained variance 55.9%). Besides basic environmental variables such as altitude, catchment size, and mean temperature, land cover variables were also explored. A logistic regression analysis indicated that the occurrence probability of brown trout, Salmo trutta L., decreased with an increasing percentage of peatland ditch drainage in the upper catchment. Ninespine stickleback, Pungitius pungitius (L.), and three‐spined stickleback, Gasterosteus aculeatus L., seemed to benefit from urban areas in the upper catchment. Discovered relationships between fish species occurrence and land‐use attributes are encouraging for the development of fish‐based bioassessment for small streams. The presented ordination of the fish species in the mean temperature gradient will help in predicting fish community responses to climate change.

Incidence of lamprey marks on Lake Sturgeon ( Acipenser fulvescens Rafinesque, 1817) in the St. Clair – Detroit River System: Implications for Sea Lamprey ( Petromyzon marinus Linnaeus, 1758) effects

Laurentian Great Lakes Lake Sturgeon (Acipenser fulvescens) are hosts to lamprey species, including native Silver Lamprey (Ichthyomyzon unicuspis) and invasive Sea Lamprey (Petromyzon marinus). Silver Lamprey coevolved with Lake Sturgeon and cause negligible mortality, but Sea Lamprey can negatively affect Lake Sturgeon populations. Sea Lamprey abundance in Lake Erie has been above targets set by resource managers, with the St. Clair – Detroit River System (SCDRS) suspected as a source of Sea Lamprey production into Lake Erie. This study summarizes lamprey marking on Lake Sturgeon captured during agency assessment surveys in the SCDRS since 1996 and provides insight on the potential for Sea Lamprey to negatively affect Lake Sturgeon in the SCDRS. Lamprey marks (any lamprey species) were noted on 48.2% of Lake Sturgeon (2.5 marks/fish) and 3.3% of Lake Sturgeon assumed to be susceptible to mortality by Sea Lamprey (<760 mm TL; 0.06 marks/fish). Silver Lamprey were the only lamprey species found attached to Lake Sturgeon and there was no difference between oral disc diameters of Silver Lamprey and marks measured on Lake Sturgeon in Lake St. Clair and the lower St. Clair River (p = .45). Based on logistic regression, probability of at least one lamprey mark increased with Lake Sturgeon total length and was highest in Lake St. Clair. The probability of observing at least one lamprey mark on a 760 mm Lake Sturgeon was 8.1% or less for each sampling location in the SCDRS aside from Lake St. Clair (28.1%). Results suggest that parasitism of Lake Sturgeon by Sea Lamprey in the SCDRS is rare, particularly for Lake Sturgeon <760 mm TL. Low incidence of lamprey marks on Lake Sturgeon assumed to be susceptible to mortality from Sea Lamprey parasitism and zero occurrence of Sea Lamprey being observed attached to a Lake Sturgeon suggest Sea Lamprey at their current abundance likely have little effect on the Lake Sturgeon population in the SCDRS. Caution should be taken when using mark size to assign marks to lamprey species as there is substantial overlap among species oral disc diameters, potentially inflating the perceived impact of Sea Lamprey on Lake Sturgeon in areas with native lampreys.

Beyond fish eDNA metabarcoding: Field replicates disproportionately improve the detection of stream-associated vertebrate species

Fast, reliable, and comprehensive biodiversity monitoring data are needed for environmental decision making and management. Recent work on fish environmental DNA (eDNA) metabarcoding shows that aquatic diversity can be captured fast, reliably, and non-invasively at moderate costs. Because freshwater ecosystems act as sinks in the landscape, they also collect traces of terrestrial species via surface runoff or when specimens come into direct contact with water (e.g., for drinking purposes). Thus, fish eDNA metabarcoding data can provide information on fish but also on other, even terrestrial vertebrate species that live in riparian habitats. This data become available and may offer a much more comprehensive approach for assessing vertebrate diversity at no additional costs. Studies on how the sampling strategy affects species detection especially of stream-associated communities, however, are scarce. We therefore performed an analysis on the effects of biological replication on both fish as well as (semi-)terrestrial species detection. Along a 2-km stretch of the river Mulde (Germany), we collected 18 1L water samples and analyzed the relation of detected species richness and quantity of biological replicates taken. We detected 58 vertebrate species, of which 25 were fish and lamprey, 18 mammals, and 15 birds, which account for 50%, 24% and 7% of all native species to the German federal state of Saxony-Anhalt. However, while increasing the number of biological replicates resulted in only 25 % more detected fish and lamprey species, mammal and bird species richness increased disproportionately by 69 % and 84 %, respectively. Contrary, PCR replicates showed little stochasticity. We thus emphasize to increase the number of biological replicates when the aim is to improve general species detections. This holds especially true, when the focus is on rare aquatic taxa or on (semi-)terrestrial species, the so-called ‘bycatch’. As a clear advantage, this information can be obtained without any additional sampling or laboratory effort when the sampling strategy regarding biological replication is chosen carefully. With the consideration of frequent eDNA metabarcoding as part of national biomonitoring programs, the additional information provided by the bycatch can be used to further investigate the state of the environment and its biodiversity on a much broader scale.

Transcriptomic analysis of gonadal development in parasitic and non-parasitic lampreys (Ichthyomyzon spp.), with a comparison of genomic resources in these non-model species.

Lampreys are jawless fishes that diverged ∼550 million years ago from other vertebrates. Sequencing of the somatic and the germline genomes of the sea lamprey (Petromyzon marinus) in 2013 and 2018, respectively, has helped to improve our understanding of the genes and gene networks that control many aspects of lamprey development. However, little is known about the genetic basis of gonadal differentiation in lampreys, partly due to the prolonged period during which their gonads remain sexually indeterminate. We performed RNA-sequencing on gonadal samples from four chestnut lamprey (Ichthyomyzon castaneus) and six northern brook lamprey (I. fossor) to identify differentially expressed genes (DEG’s) and pathways associated with transcriptomic differences in: (1) larvae during early gonadal differentiation versus definitive females (i.e., with oocytes in the slow cytoplasmic growth phase); and (2) females versus definitive males undergoing spermatogonial proliferation. We compared the mapping percentages of these transcriptomes to the two available sea lamprey reference genomes and three annotation files (Ensembl and UCSC for the somatic genome and SIMRbase for the germline genome). We found that mapping the RNA-seq reads to the germline genome gave superior results and, using Trinotate, we provided new putative annotations for 8161 genes in the somatic assembly and 880 genes for the germline assembly. We identified >2000 DEG’s between stages and sexes, as well as biological pathways associated with each. Interestingly, some of the upregulated genes (e.g., DEG’s associated with spermiation) suggest that changes in gene expression can precede morphological changes by several months. In contrast, only 81 DEG’s were evident between the chestnut lamprey (that remains sexually immature during an extended post-metamorphic parasitic feeding phase) and the nonparasitic northern brook lamprey (that undergoes sexual maturation near the end of metamorphosis), but few replicates were available for comparable stages and sexes. This work lays the foundation for identifying and confirming the orthology and the function of genes involved in gonadal development in these and other lamprey species across more developmental stages.

Visual opsin expression and morphological characterization of retinal photoreceptors in the pouched lamprey (Geotria australis, Gray)

Lampreys are extant members of the agnathan (jawless) vertebrates that diverged ~500 million years ago, during a critical stage of vertebrate evolution when image-forming eyes first emerged. Among lamprey species assessed thus far, the retina of the southern hemisphere pouched lamprey, Geotria australis, is unique, in that it possesses morphologically distinct photoreceptors and expresses five visual photopigments. This study focused on determining the number of different photoreceptors present in the retina of G. australis and whether each cell type expresses a single opsin class. Five photoreceptor subtypes were identified based on ultrastructure and differential expression of one of each of the five different visual opsin classes (lws, sws1, sws2, rh1, and rh2) known to be expressed in the retina. This suggests, therefore, that the retina of G. australis possesses five spectrally and morphologically distinct photoreceptors, with the potential for complex color vision. Each photoreceptor subtype was shown to have a specific spatial distribution in the retina, which is potentially associated with changes in spectral radiance across different lines of sight. These results suggest that there have been strong selection pressures for G. australis to maintain broad spectral sensitivity for the brightly lit surface waters that this species inhabits during its marine phase. These findings provide important insights into the functional anatomy of the early vertebrate retina and the selection pressures that may have led to the evolution of complex color vision.

Changes in native lamprey populations in the Great Lakes since the onset of sea lamprey (Petromyzon marinus) control

The control of invasive sea lamprey in the Great Lakes basin has been highly successful, but has deleteriously affected native lamprey species. American brook, northern brook, silver and chestnut lampreys are all susceptible to lampricide treatments. Incidental catch from surveys that targeted sea lamprey were used to determine changes in distributions and catch rates of these native species within the Great Lakes basin since the onset of the sea lamprey control program. Over 2.4 million native lampreys were collected during sea lamprey control operations between 1947 and 2018. Native lampreys were no longer captured from many treated and untreated streams. Silver lamprey and northern brook lamprey distributions were reduced most substantially. These species were no longer found in about three quarters of the number of streams in which they were historically present. The number of streams inhabited by chestnut lamprey has diminished by half. American brook lamprey were still present in the majority of streams previously occupied. Catch rates declined in northern brook lamprey and Ichthyomyzon larvae in some Great Lakes basins, but changes in collection gear and methods made comparisons difficult. Trap and weir data show drastic declines in silver lamprey and chestnut lamprey. Streams that have not been treated with lampricide have suffered similar or greater declines in both the number of streams occupied and catch rates for all four species when compared to untreated streams. Therefore reductions in native lamprey populations were likely due to a number of environmental changes, and not exclusively from lampricide treatments.

Chromosome-level genome assembly of Lethenteron reissneri provides insights into lamprey evolution.

The reissner lamprey Lethenteron reissneri, belonging to the class Cyclostomata, serves as a bridge between invertebrates and jawed vertebrates, and is considered the sister group of jawed vertebrates. However, despite this evolutionary significance, the genetic mechanisms underlying the adaptive evolution of the lamprey lineage remain unclear. Here, we assembled a 1.06Gb chromosome-level draft genome of L. reissneri, with 72 chromosomes (ranging in length from 4.5Mb to 25.9Mb) and a scaffold N50 length of 13.23Mb. Genome quality comparisons revealed that the reissner lamprey genome has higher completeness and contiguity than the previously published sea lamprey and Japanese lamprey genomes. Moreover, reissner lamprey, sea lamprey, and Japanese lamprey species share similar transposable element profiles and Hox gene cluster compositions, suggesting that a burst of transposable element activity and whole genome duplication occurred before their divergence. Additionally, the Lip gene copy numbers, which have been studied for their functions in the host defence system, were found to be expanded uniquely in lamprey lineages, suggesting key roles for these genes in lamprey evolution and adaptation. We also identified two neural-related genes, Nrn1 and Unc13a, with copy number expansions in jawed vertebrates, which may be functionally relevant to the origin of lamprey brains. Hence, this study not only provides the first chromosome-level reference genome for Cyclostomata, but also highlights features of the unique biology and adaptive evolution of the lamprey lineage.

The role of local ecological knowledge for the conservation and sustainable fisheries of the sea lamprey (Petromyzon marinus Linnaeus, 1758) in the Iberian Peninsula

Anadromous sea lamprey (Petromyzon marinus Linnaeus, 1758) uses many environments in its life cycle, which makes them even more susceptible to any environmental changes. Due to the potential of local ecological knowledge (LEK) in fishing villages on the Minho River, this study provided information on trophic chain, conservation, gastronomy, taboos, and food aversions of the sea lamprey. The discharge of pollutants, physical barriers, and climate change were considered a threat to the conservation of sea lamprey. Fishers’ LEK highlighted some preys from Osteichthyes and two potential predators (European otter and the Great Cormorant). Artisanal fishing was carried out predominantly at night and close to the village of Caminha, with the average of the largest sea lamprey caught was 2.6 kg. The price of this fishing resource could vary between 10 and 40 euros. Food taboos did not influence the conservation of this lamprey species. Local beliefs can assist in the promotion of eco-labels and greater recognition of local gastronomy. Alternative approaches to current scientific research can lead fishing villages that depend on these natural resources to contribute to the conservation of sea lamprey in the Minho river watershed.

Predicting larval metamorphosis of Pacific lamprey Entosphenus tridentatus through measurements of length and mass.

The utility of length and mass measurements to predict the larval metamorphosis of Pacific lamprey Entosphenus tridentatus was evaluated. During 2004-2008, larval E. tridentatus were collected from Cedar Creek (Washington, USA) in either the spring or autumn, measured for total length and total mass, reared in captivity and monitored for metamorphosis. The minimum total length, total mass and condition factor of larvae that were observed to go through metamorphosis were 102 mm, 2.0 g and 1.52, respectively. Logistic models indicated that total length and condition factor in both spring and autumn were the most significant variables for predicting metamorphosis of Pacific lamprey during the subsequent summer. Mass in the autumn also appeared important to predict whether metamorphosis occurred in the subsequent summer. Collectively, all models using specific minimums of total length, total mass or condition factor of larvae as criteria for them to metamorphose were sometimes (5 of 14 cases) able to predict the percentage of larvae that would metamorphose but rarely (1 of 12 cases) able to predict which individual larvae would metamorphose. Similar to other anadromous species of lampreys, the size and condition of larval E. tridentatus have utility for predicting metamorphic fate.

Two highly related odorant receptors specifically detect α-bile acid pheromones in sea lamprey (Petromyzon marinus)

Pheromones play critical roles in habitat identification and reproductive behavior synchronization in the sea lamprey (Petromyzon marinus). The bile acid 3-keto petromyzonol sulfate (3kPZS) is a major component of the sex pheromone mixture from male sea lamprey that induces specific olfactory and behavioral responses in conspecific individuals. Olfactory receptors interact directly with pheromones, which is the first step in their detection, but identifying the cognate receptors of specific pheromones is often challenging. Here, we deorphanized two highly related odorant receptors (ORs), OR320a and OR320b, of P. marinus that respond to 3kPZS. In a heterologous expression system coupled to a cAMP-responsive CRE-luciferase, OR320a and OR320b specifically responded to C24 5α-bile acids, and both receptors were activated by the same set of 3kPZS analogs. OR320a displayed larger responses to all 3kPZS analogs than did OR320b. This difference appeared to be largely determined by a single amino acid residue, Cys-792.56, the C-terminal sixth residue relative to the most conserved residue in the second transmembrane domain (2.56) of OR320a. This region of TM2 residues 2.56-2.60 apparently is critical for the detection of steroid compounds by odorant receptors in lamprey, zebrafish, and humans. Finally, we identified OR320 orthologs in Japanese lamprey (Lethenteron camtschaticum), suggesting that the OR320 family may be widely present in lamprey species and that OR320 may be under purifying selection. Our results provide a system to examine the origin of olfactory steroid detection in vertebrates and to define a highly conserved molecular mechanism for steroid-ligand detection by G protein-coupled receptors.

Corticotropin-Releasing Hormone (CRH) Gene Family Duplications in Lampreys Correlate With Two Early Vertebrate Genome Doublings

The ancestor of gnathostomes (jawed vertebrates) is generally considered to have undergone two rounds of whole genome duplication (WGD). The timing of these WGD events relative to the divergence of the closest relatives of the gnathostomes, the cyclostomes, has remained contentious. Lampreys and hagfishes are extant cyclostomes whose gene families can shed light on the relationship between the WGDs and the cyclostome-gnathostome divergence. Previously, we have characterized in detail the evolution of the gnathostome corticotropin-releasing hormone (CRH) family and found that its five members arose from two ancestral genes that existed before the WGDs. The two WGDs resulted, after secondary losses, in one triplet consisting of CRH1, CRH2, and UCN1, and one pair consisting of UCN2 and UCN3. All five genes exist in representatives for cartilaginous fishes, ray-finned fishes, and lobe-finned fishes. Differential losses have occurred in some lineages. We present here analyses of CRH-family members in lamprey and hagfish by comparing sequences and gene synteny with gnathostomes. We found five CRH-family genes in each of two lamprey species (Petromyzon marinus and Lethenteron camtschaticum) and two genes in a hagfish (Eptatretus burgeri). Synteny analyses show that all five lamprey CRH-family genes have similar chromosomal neighbors as the gnathostome genes. The most parsimonious explanation is that the lamprey CRH-family genes are orthologs of the five gnathostome genes and thus arose in the same chromosome duplications. This suggests that lampreys and gnathostomes share the same two WGD events and that these took place before the lamprey-gnathostome divergence.

Revalidation of the Argentinian pouched lamprey Geotria macrostoma (Burmeister, 1868) with molecular and morphological evidence.

BackgroundThe Argentinian pouched lamprey, classified as Petromyzon macrostomus Burmeister, 1868 was first described in 1867 in De La Plata River, in Buenos Aires, Argentina, and subsequently recorded in several rivers from Patagonia. Since its original description, the validity of P. macrostomus was questioned by several ichthyologists and 36 years after its original discovery it was considered a junior synonym of Geotria australis Gray, 1851. For a long time, the taxonomic status of G. australis has been uncertain, largely due to the misinterpretations of the morphological alterations that occur during sexual maturation, including the arrangement of teeth, size and position of fins and cloaca, and the development of an exceptionally large gular pouch in males. In this study, the taxonomic status of Geotria from across the “species” range was evaluated using both molecular analysis and examination of morphological characteristics.Methodology/principal findingsPhylogenetic and species delimitation analyses based on mitochondrial DNA sequences of Cytochrome b (Cyt b) and Cytochrome C Oxidase Subunit 1 (COI) genes, along with morphological analysis of diagnostic characters reported in the original descriptions of the species were used to assess genetic and morphological variation within Geotria and to determine the specific status of the Argentinian lamprey. These analyses revealed that Geotria from Argentina constitutes a well differentiated lineage from Chilean and Australasian populations. The position of the cloaca and the distance between the second dorsal and caudal fins in sub-adult individuals, and at previous life stages, can be used to distinguish between the two species. In addition, the genetic distance between G. macrostoma and G. australis for the COI and Cyt b mitochondrial genes is higher than both intra- and inter-specific distances reported for other Petromyzontiformes.Conclusions/significanceOur results indicate that the Argentinian pouched lamprey, found along a broad latitudinal gradient on the south-west Atlantic coast of South America, should be named as Geotria macrostoma (Burmeister, 1868) and not as G. australis Gray 1851, returning to its earliest valid designation in Argentina. Geotria macrostoma can now be considered as the single lamprey species inhabiting Argentinian Patagonia, with distinct local adaptations and evolutionary potential. It is essential that this distinctiveness is recognized in order to guide future conservation and management actions against imminent threats posed by human actions in the major basins of Patagonia.

New Insights into the Distribution, Physiology and Life Histories of South American Galaxiid Fishes, and Potential Threats to This Unique Fauna

South American galaxiids occupy both Patagonia and the ichthyogeographic Chilean Province, encompassing glacial Andean deep lakes, shallow plateau lakes, reservoirs, short Pacific rivers and long Atlantic rivers. The total fish fauna includes 29 species, comprising Neotropical fishes (siluriforms and characids), galaxiids, percichthyids, atherinopsids and mugilids, two lamprey species, and several exotic fishes (salmonids, Gambusia spp. and common carp). The family Galaxiidae shares a common ancestry with the Gondwanan temperate fish fauna, played a major role in the post-glacial colonization of Andean lakes and streams, and contributes key species to the food webs. Galaxiid species occupy an enormous latitudinal gradient, show a wide variety of life history patterns and are the southernmost native freshwater fishes of the world. Knowledge of South American galaxiids has improved notably, but new challenges arise due to climate change, biological invasions, damming, aquaculture and contamination. In this changing environment, the future of South American galaxiids should be carefully considered as a legacy of the old Gondwana and a unique attribute of the freshwaters of southern South America.

Comparative phylogeographic inference with genome‐wide data from aggregated population pairs

Comparing divergences across multiple sister population pairs has been a focus in phylogeography since its inception. Initial approaches used organelle genetic data and involved qualitative comparisons of phylogenetic patterns to evaluate hypotheses of shared and variable evolutionary responses. This endeavor has progressed with coalescent model-based statistical techniques and advances in next-generation sequencing, yet there remains a need for methods that can exploit aggregated genomic-scale data within a unified analytical framework. To this end, we introduce the aggregate joint site frequency spectrum (ajSFS) by validating its use within a hierarchical Bayesian framework through several in silico experiments. Subsequently, we applied our method against two published restriction site-associated DNA marker datasets consisting of eight local replicates of a lamprey species pair and six co-distributed passerine taxon pairs, respectively, with the aim of inferring variability in co-divergence and co-migration histories. We found that the lamprey population pairs exhibited temporal synchrony in both co-divergence and collective secondary contact times, yet an idiosyncratic pattern in secondary migration intensities. In contrast, the bird population pairs displayed thoroughly asynchronous co-divergence histories. Our results demonstrate that the ajSFS can be exploited for complex and flexible co-demographic inference, opening up new possibilities for comparative phylogeography and population genomic studies.

Detection of lamprey in Southernmost South America by environmental DNA (eDNA) and molecular evidence for a new species

Lampreys are jawless fishes belonging to the order Petromyzontiformes. Geotria australis is the sole representative lamprey species of the Geotriidae family and is widely distributed around South America, Australia, New Zealand, and sub-Antarctic Islands. In South America, the presence and distribution of G. australis are well characterized in Western Patagonia, in rivers flowing into the Pacific Ocean. In contrast, there is scarce information about the presence of this species in Eastern Patagonia, in rivers flowing into the Atlantic Ocean. Here, we provide the first report on the distribution of lamprey at the extreme south of Patagonia and suggest the occurrence of a new lamprey species. We developed an environmental DNA (eDNA) method to detect G. australis from water samples and obtained positive results in five basins flowing into the Atlantic Ocean and one river basin flowing into the Beagle Channel. Lampreys were captured from two eDNA-positive basins and used for genetic analysis. An 875 bp-sequence of the cytochrome b mitochondrial gene was obtained, and a phylogenetic analysis was carried out with this sequence and those available in GenBank, revealing Argentinean lamprey reported here, as a sister species of G. australis from Chile, Australia, and New Zealand. Also, the genetic distance values between lamprey reported here and G. australis were consistent with the genetic distances between species of different genera. Our results suggest that the Argentinean lamprey corresponds to a new specific taxon that could represent a new monotypic genus in Geotriidae.