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Lampreys aren't just freaky because of their funnel-shaped mouth or many species' appetite for blood. They're an invasive species slowly entering North American waters and causing harm to native species. Readers learn about the problems invasive species cause as well as details about the parasitic relationships between lampreys and other fish. This title covers how they suck blood and more about the lamprey life cycle, habitat, and more.

The brain of the hagfish, a cyclostome related to the lamprey, develops domains equivalent to the median ganglionic eminence and the rhombic lip, resembling the brains of gnathostomes (jawed vertebrates), suggesting that brain regionalization in jawed vertebrates occurred before the divergence of cyclostomes and gnathostomes more than 500 million years ago. The early vertebrate brain revisited The brains of vertebrates are much more complex than those of their immediate invertebrate relations — tunicates and the amphioxus — raising questions about the origins and development of the brain. The jawless lamprey, an ancient vertebrate, was also thought to have a primitive 'ancestral' brain. In particular, the embryonic lamprey was thought to have characteristics resembling those of mutant mice lacking a structure called the medial ganglionic eminence (MGE). Shigeru Kuratani and colleagues now show that the hagfish, a close relative of the lamprey, develops domains equivalent to the MGE and also the rhombic lip, resembling the brains of jawed vertebrates (gnathostomes). A closer look at lampreys reveals that they too have similar structures. These findings suggest that brain regionalization as seen in jawed vertebrates dates back to the latest vertebrate ancestor prior to the divergence of cyclostomes and gnathostomes more than 500 million years ago. The vertebrate brain is highly complex, but its evolutionary origin remains elusive. Because of the absence of certain developmental domains generally marked by the expression of regulatory genes, the embryonic brain of the lamprey, a jawless vertebrate, had been regarded as representing a less complex, ancestral state of the vertebrate brain. Specifically, the absence of a Hedgehog- and Nkx2.1 -positive domain in the lamprey subpallium was thought to be similar to mouse mutants in which the suppression of Nkx2-1 leads to a loss of the medial ganglionic eminence 1 , 2 . Here we show that the brain of the inshore hagfish ( Eptatretus burgeri ), another cyclostome group, develops domains equivalent to the medial ganglionic eminence and rhombic lip, resembling the gnathostome brain. Moreover, further investigation of lamprey larvae revealed that these domains are also present, ruling out the possibility of convergent evolution between hagfish and gnathostomes. Thus, brain regionalization as seen in crown gnathostomes is not an evolutionary innovation of this group, but dates back to the latest vertebrate ancestor before the divergence of cyclostomes and gnathostomes more than 500 million years ago.

Jawed vertebrates have inner ears with three semicircular canals, the presence of which has been used as a key to understanding evolutionary relationships. Ostracoderms, the jawless stem gnathostomes, had only two canals and lacked the lateral canal 1 – 3 . Lampreys, which are modern cyclostomes, are generally thought to possess two semicircular canals whereas the hagfishes—which are also cyclostomes—have only a single canal, which used to be regarded as a more primitive trait 1 , 4 . However, recent molecular and developmental analyses have strongly supported the monophyly of cyclostomes 5 – 7 , which has left the evolutionary trajectory of the vertebrate inner ear unclear 8 . Here we show the differentiation of the otic vesicle of the lamprey Lethenteron camtschaticum and inshore hagfish Eptatretus burgeri . This is the first time, to our knowledge, that the development of the hagfish inner ear is reported. We found that canal development in the lamprey starts with two depressions—which is reminiscent of the early developmental pattern of the inner ear in modern gnathostomes. These cyclostome otic vesicles show a pattern of expression of regulatory genes, including OTX genes, that is comparable to that of gnathosomes. Although two depressions appear in the lamprey vesicle, they subsequently fuse to form a single canal that is similar to that of hagfishes. Complete separation of the depressions results in anterior and posterior canals in gnathostomes. The single depression of the vesicle in hagfishes thus appears to be a secondarily derived trait. Furthermore, the lateral canal in crown gnathostomes was acquired secondarily—not by de novo acquisition of an OTX expression domain, but by the evolution of a developmental program downstream of the OTX genes. The differentiation of the inner ear in the lamprey Lethenteron camtschaticum and hagfish Eptatretus burgeri sheds light on the evolution of the semicircular canals of jawed vertebrates.

The southern Italian peninsula has been suggested to be an important European district for lampreys’ genetic diversity. All lamprey species ever described throughout the Italian peninsula are protected within European legislation and listed in Annex II of the EU Habitats Directive (92/43/EEC) and Annex III of the Bern Convention (82/72/CEE) as species of conservation concern, and the Habitats Directive ensures the designation of “sites of community interest” (SICs) for threatened species. During a survey to collect preliminary data on lampreys’ presence in the Cilento, Vallo di Daino, and Alburni National Park (PNCV) located in the Campania region, where 28 sites of community interest (SICs) have been established by the EU Habitats Directive (92/43/EEC), two specimens of sea lamprey (Petromyzon marinus, Linnaeus, 1758) were detected for the first time. The specimens were genetically characterized through the sequencing of the mtDNA control region locus. The study highlighted the significant importance of the Campania region for lampreys, which, concerning Lampetra sp., was found to have peculiar genetic characteristics and unique alleles that have not been described elsewhere. Furthermore, the recognition of the sea lamprey, P. marinus, emphasized the value of this area, especially in terms of laying the groundwork for future habitat protection strategies.

The 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. Phylogenetic 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. Our 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.

Jawless vertebrates use variable lymphocyte receptors (VLR) comprised of leucine-rich-repeat (LRR) segments as counterparts of the immunoglobulin-based receptors that jawed vertebrates use for antigen recognition. Highly diverse VLR genes are somatically assembled by the insertion of variable LRR sequences into incomplete germline VLRA and VLRB genes. Here we show that in sea lampreys ( Petromyzon marinus ) VLRA and VLRB anticipatory receptors are expressed by separate lymphocyte populations by monoallelic VLRA or VLRB assembly, together with expression of cytosine deaminase 1 ( CDA1 ) or 2 ( CDA2 ), respectively. Distinctive gene expression profiles for VLRA + and VLRB + lymphocytes resemble those of mammalian T and B cells. Although both the VLRA and the VLRB cells proliferate in response to antigenic stimulation, only the VLRB lymphocytes bind native antigens and differentiate into VLR antibody-secreting cells. Conversely, VLRA lymphocytes respond preferentially to a classical T-cell mitogen and upregulate the expression of the pro-inflammatory cytokine genes interleukin-17 ( IL-17 ) and macrophage migration inhibitory factor ( MIF ). The finding of T-like and B-like lymphocytes in lampreys offers new insight into the evolution of adaptive immunity. Double immunity in lampreys Lampreys and hagfish, the last of the jawless vertebrates, attract the attention of immunologists as their adaptive immune system rivals that of humans in its flexibility. In humans, each lymphocyte expresses a unique anticipatory receptor for an antigen, constructed from variable, diversity and joining segments. Jawless vertebrates use variable lymphocyte receptors composed of leucine-rich-repeat protein segments with a non-varying stalk tethered to the lymphocyte surface. New work on the sea lamprey reveals yet more parallels with humans: they have a compartmentalized adaptive immune system containing cells that resemble cytokine-secreting T cells and antibody-secreting B cells of the mammalian adaptive immune system. This points to a split in lymphocyte differentiation along T- and B-like cell lineages much earlier in evolution than previously appreciated, such that their system was either a precursor of, or evolved alongside, our own immune system. Variable lymphocyte receptors (VLRs) are used for antigen recognition in jawless vertebrates. Distinctive gene expression profiles for VLRA + and VLRB + lymphocytes in lampreys are now shown to resemble those of mammalian T and B cells, offering insight into the evolution of adaptive immunity.

The lamprey's thymoid and vertebrate immunity The immune system of lampreys — jawless fish with roots in the early separation of the vertebrates into jawed and jawless lines — is of particular interest to evolutionary biologists. Much has been made of the differences between the 'alternative' immune system in the lamprey and that of today's jawed vertebrates, but the recent discovery that lampreys have lymphocytes resembling B and T cells, which are central to the adaptive immune response of the jawed vertebrates, puts more emphasis on the search for similarities. Histological surveys of lampreys have failed to reveal an organ equivalent to the mammalian thymus, the organ that generates the development of T lymphocytes. Now, gene expression analysis reveals previously unrecognized thymus-like structures — termed thymoids — at the tips of gill filaments of lamprey larvae. This suggests that the common ancestor of the jawed and jawless vertebrates may have had not only T- and B-like lymphocytes, but also anatomically distinct tissues for their development. Jawless fish were recently shown to possess T- and B-like lymphocytes expressing diverse assembled antigen receptors. This study identifies and characterizes lympho-epithelial thymus-like structures at the tips of gill filaments of lamprey larvae, thus providing evidence that the similarities underlying the adaptive immune systems of both types of vertebrate appear to extend to primary lymphoid organs. Immunologists and evolutionary biologists have been debating the nature of the immune system of jawless vertebrates—lampreys and hagfish—since the nineteenth century. In the past 50 years, these fish were shown to have antibody-like responses and the capacity to reject allografts 1 but were found to lack the immunoglobulin-based adaptive immune system of jawed vertebrates 2 . Recent work has shown that lampreys have lymphocytes that instead express somatically diversified antigen receptors that contain leucine-rich-repeats, termed variable lymphocyte receptors (VLRs) 3 , 4 , and that the type of VLR expressed is specific to the lymphocyte lineage: T-like lymphocytes express type A VLR ( VLRA ) genes, and B-like lymphocytes express VLRB genes 5 . These clonally diverse anticipatory antigen receptors are assembled from incomplete genomic fragments by gene conversion 6 , 7 , 8 , 9 , which is thought to be initiated by either of two genes encoding cytosine deaminase 9 , cytosine deaminase 1 ( CDA1 ) in T-like cells and CDA2 in B-like cells 5 . It is unknown whether jawless fish, like jawed vertebrates, have dedicated primary lymphoid organs, such as the thymus, where the development and selection of lymphocytes takes place 10 , 11 . Here we identify discrete thymus-like lympho-epithelial structures, termed thymoids, in the tips of the gill filaments and the neighbouring secondary lamellae (both within the gill basket) of lamprey larvae. Only in the thymoids was expression of the orthologue of the gene encoding forkhead box N1 (FOXN1) 10 , a marker of the thymopoietic microenvironment in jawed vertebrates 12 , accompanied by expression of CDA1 and VLRA . This expression pattern was unaffected by immunization of lampreys or by stimulation with a T-cell mitogen. Non-functional VLRA gene assemblies were found frequently in the thymoids but not elsewhere, further implicating the thymoid as the site of development of T-like cells in lampreys. These findings suggest that the similarities underlying the dual nature of the adaptive immune systems in the two sister groups of vertebrates extend to primary lymphoid organs.

The optic tectum (called superior colliculus in mammals) is critical for eye–head gaze shifts as we navigate in the terrain and need to adapt our movements to the visual scene. The neuronal mechanisms underlying the tectal contribution to stimulus selection and gaze reorientation remains, however, unclear at the microcircuit level. To analyze this complex—yet phylogenetically conserved—sensorimotor system, we developed a novel in vitro preparation in the lamprey that maintains the eye and midbrain intact and allows for whole-cell recordings from prelabeled tectal gaze-controlling cells in the deep layer, while visual stimuli are delivered. We found that receptive field activation of these cells provide monosynaptic retinal excitation followed by local GABAergic inhibition (feedforward). The entire remaining retina, on the other hand, elicits only inhibition (surround inhibition). If two stimuli are delivered simultaneously, one inside and one outside the receptive field, the former excitatory response is suppressed. When local inhibition is pharmacologically blocked, the suppression induced by competing stimuli is canceled. We suggest that this rivalry between visual areas across the tectal map is triggered through long-range inhibitory tectal connections. Selection commands conveyed via gaze-controlling neurons in the optic tectum are, thus, formed through synaptic integration of local retinotopic excitation and global tectal inhibition. We anticipate that this mechanism not only exists in lamprey but is also conserved throughout vertebrate evolution. Significance Neurons in the optic tectum are involved in stimulus selection and also control gaze reorientation. This study relies on an in vitro preparation that allows visual activation of the retina while providing accessibility for whole-cell recordings from specific cells that control gaze action. We show the tectal (collicular in mammals) GABAergic interneurons generate rivalry between visual areas and that tectal gaze-controlling cells integrate this inhibition along with local retinal excitation to form stimulus selection commands that will move the eyes and head, and may also contribute to edge detection. We propose that this subcortical visuomotor circuit is phylogenetically conserved throughout vertebrate evolution.

Lampreys (Petromyzontiformes) are an ancient group of fishes with complex life histories. We created a life cycle model that includes an R Shiny interactive web application interface to simulate abundance by life stage. This will allow scientists and managers to connect available demographic information in a framework that can be applied to questions regarding lamprey biology and conservation. We used Pacific lamprey ( Entosphenus tridentatus ) as a case study to highlight the utility of this model. We applied a global sensitivity analysis to explore the importance of individual life stage parameters to overall population size, and to better understand the implications of existing gaps in knowledge. We also provided example analyses of selected management scenarios (dam passage, fish translocations, and hatchery additions) influencing Pacific lamprey in fresh water. These applications illustrate how the model can be applied to inform conservation efforts. This tool will provide new capabilities for users to explore their own questions about lamprey biology and conservation. Simulations can hone hypotheses and predictions, which can then be empirically tested in the real world.

As animals forage for food and water or evade predators, they must rapidly decide what visual features in the environment deserve attention. In vertebrates, this visuomotor computation is implemented within the neural circuits of the optic tectum (superior colliculus in mammals). However, the mechanisms by which tectum decides whether to approach or evade remain unclear, and also which neural mechanisms underlie this behavioral choice. To address this problem, we used an eye–brain–spinal cord preparation to evaluate how the lamprey responds to visual inputs with distinct stimulus-dependent motor patterns. Using ventral root activity as a behavioral readout, we classified 2 main types of fictive motor responses: (i) a unilateral burst response corresponding to orientation of the head toward slowly expanding or moving stimuli, particularly within the anterior visual field, and (ii) a unilateral or bilateral burst response triggering fictive avoidance in response to rapidly expanding looming stimuli or moving bars. A selective pharmacological blockade revealed that the brainstem-projecting neurons in the deep layer of the tectum in interaction with local inhibitory interneurons are responsible for selecting between these 2 visually triggered motor actions conveyed through downstream reticulospinal circuits. We suggest that these visual decision-making circuits had evolved in the common ancestor of vertebrates and have been conserved throughout vertebrate phylogeny.