Vertebrate History Research Articles

Problems in Fish-to-Tetrapod Transition: Genetic Expeditions Into Old Specimens.

The fish-to-tetrapod transition is one of the fundamental problems in evolutionary biology. A significant amount of paleontological data has revealed the morphological trajectories of skeletons, such as those of the skull, vertebrae, and appendages in vertebrate history. Shifts in bone differentiation, from dermal to endochondral bones, are key to explaining skeletal transformations during the transition from water to land. However, the genetic underpinnings underlying the evolution of dermal and endochondral bones are largely missing. Recent genetic approaches utilizing model organisms—zebrafish, frogs, chickens, and mice—reveal the molecular mechanisms underlying vertebrate skeletal development and provide new insights for how the skeletal system has evolved. Currently, our experimental horizons to test evolutionary hypotheses are being expanded to non-model organisms with state-of-the-art techniques in molecular biology and imaging. An integration of functional genomics, developmental genetics, and high-resolution CT scanning into evolutionary inquiries allows us to reevaluate our understanding of old specimens. Here, we summarize the current perspectives in genetic programs underlying the development and evolution of the dermal skull roof, shoulder girdle, and appendages. The ratio shifts of dermal and endochondral bones, and its underlying mechanisms, during the fish-to-tetrapod transition are particularly emphasized. Recent studies have suggested the novel cell origins of dermal bones, and the interchangeability between dermal and endochondral bones, obscuring the ontogenetic distinction of these two types of bones. Assimilation of ontogenetic knowledge of dermal and endochondral bones from different structures demands revisions of the prevalent consensus in the evolutionary mechanisms of vertebrate skeletal shifts.

Expansion, retention and loss in the Acyl-CoA synthetase “Bubblegum” (Acsbg) gene family in vertebrate history

Fatty acids (FAs) constitute a considerable fraction of all lipid molecules with a fundamental role in numerous physiological processes. In animals, the majority of complex lipid molecules are derived from the transformation of FAs through several biochemical pathways. Yet, for FAs to enroll in these pathways they require an activation step. FA activation is catalyzed by the rate limiting action of Acyl-CoA synthases. Several Acyl-CoA enzyme families have been previously described and classified according to the chain length of FAs they process. Here, we address the evolutionary history of the ACSBG gene family which activates, FAs with >16 carbons. Currently, two different ACSBG gene families, ACSBG1 and ACSBG2, are recognized in vertebrates. We provide evidence that a wider and unequal ACSBG gene repertoire is present in vertebrate lineages. We identify a novel ACSBG-like gene lineage which occurs specifically in amphibians, ray finned fishes, coelacanths and cartilaginous fishes named ACSBG3. Also, we show that the ACSBG2 gene lineage duplicated in the Theria ancestor. Our findings, thus offer a far richer understanding on FA activation in vertebrates and provide key insights into the relevance of comparative and functional analysis to perceive physiological differences, namely those related with lipid metabolic pathways.

Histology and 3D Modeling of the Connective Tissue Skeleton in the Trunk of a Lamprey (Petromyzon marinus)

Agnathan lampreys play a key role in the reconstruction of the evolutionary history of vertebrates and, more specifically, in the analysis of the biomechanics underlying piscine undulatory locomotion. However, the morphology of the fibrous skeletal framework for their trunk musculature is still incompletely understood, mainly because of the complex spatial configuration of the segmentally arranged myosepta and muscle fibers within the myomeres. To contribute to a better understanding of how contractile muscular forces are transmitted via the fibrous skeletal framework of the trunk, the architecture and composition of the connective tissue structures (dermis, dorsal longitudinal ligament, hypodermis, myosepta, perimysial lamellae, notochord, fasciae) and their relationship to the muscle fibers of the myomeres were analyzed through histological techniques (in addition to MRI and microdissection described elsewhere) and 3D modeling based on a 3D reconstruction of serial histological sections treated with special stains (e.g., Movat Pentachrome, Ladewig Trichrome). These stains, however, did not differentiate tissue types as expected, probably because lamprey tissue fiber types differ biochemically from mammalian ones, but they discriminate a wide range of fiber types. As to the distribution of connective tissue fibers, the dermis comprises about 25 layers of helically arranged collagen fibers with the most superficial layers anchoring to the basement membrane of the epidermis and the deepest layers connecting to fibers of the hypodermis, which is separated by the pigment layer from the dermis. Radially arranged collagen fibers interconnect the basement membrane and hypodermis. Also within the hypodermis, the dorsal longitudinal ligament collects and interbraids collagen fibers from the dermis, hypodermis, and dorsal vertical septum, and, ultimately, the myosepta. The latter comprise tendon fibers connecting the roughly longitudinally oriented muscle fibers of adjacent myomeres and are traversed by thick collagen fiber bundles that run from the dermis to the central periaxial and perivisceral fasciae, as well as by thin reticulated fibers that support intramyoseptal nerves and blood vessels. The muscle blocks of the myomeres are separated by radially arranged perimysial lamellae running from the hypodermis to the periaxial and perivisceral fasciae. During undulations, contracting muscle fibers between the myosepta shorten and expand radially. This expansion is resisted by the radially arranged collagen fibers within the myosepta and perimysial lamellae. As a result, the internal pressure and, hence, the turgidity of the trunk is raised. A detailed understanding of the connective tissue fiber configuration in lampreys provides the necessary basis for building dynamic 3D models of the biomechanics involved in locomotion and other behaviors.Support or Funding InformationGrant‐In‐Aid of Research from Sigma Xi, the Scientific Research Society, to Bradley M. Wood; LSU Foundation support to Dominique G. HombergerThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Early establishment of vertebrate trophic interactions: Food web structure in Middle to Late Devonian fish assemblages with exceptional fossilization

In past and present ecosystems, trophic interactions determine material and energy transfers among species, regulating population dynamics and community stability. Food web studies in past ecosystems are helpful to assess the persistence of ecosystem structure throughout geological times and to explore the existence of general principles of food web assembly. We determined and compared the trophic structure of two Devonian fish assemblages [(1) the Escuminac assemblage (ca. 380 Ma), Miguasha, eastern Canada and (2) the Lode assemblage (ca. 390 Ma), Straupe, Latvia] with a closer look at the Escuminac assemblage. Both localities are representative of Middle to Late Devonian aquatic vertebrate assemblages in terms of taxonomic richness (ca. 20 species), phylogenetic diversity (all major groups of lower vertebrates) and palaeoenvironment (palaeoestuaries). Fossil food web structures were assessed using different kinds of direct (i.e. digestive contents and bite marks in fossils) and indirect (e.g. ecomoiphological measurements, stratigraphic species co-occurrences) indicators. First, the relationships between predator and prey body size established for the Escuminac fishes are comparable to those of recent aquatic ecosystems, highlighting a consistency of aquatic food web structure across geological time. Second, non-metric dimensional scaling on ecomorphological variables and cluster analysis showed a common pattern of functional groups for both fish assemblages; top predators, predators, primary and secondary consumers were identified. We conclude that Devonian communities were organized in multiple trophic levels and that size-based feeding interactions were established early in vertebrate history.

Histological evidence for a dynamic dental battery in hadrosaurid dinosaurs

The first histological study of an entire hadrosaurid dental battery provides a comprehensive look at tooth movement within this complex structure. Previous studies have focused on isolated teeth, or in-situ batteries, but this is the first study to examine an entire dental battery of any dinosaur. The absence of direct tooth-to-tooth contact across the entire battery and a unique arrangement of the dental tissues in hadrosaurids led us to compare their teeth with the ever-growing incisors of mammals. The similarity in the distributions of tissues along the incisor, coupled with continuous eruption, make for helpful comparisons to hadrosaurid teeth. The mammalian ever-growing incisor can be used as a model to extrapolate the soft tissue connections and eruptive mechanisms within the hadrosaurid dental battery. Serial sections across the adult dental battery reveal signs of gradual ontogenetic tooth migration. Extensive remodeling of the alveolar septa and the anteroposterior displacement of successive generations of teeth highlight the gradual migration of tooth generations within the battery. These eruptive and ontogenetic tooth movements would not be possible without a ligamentous connection between successive teeth and the jaws, underscoring the dynamic nature of one of the most unique and complex dental systems in vertebrate history.

Next Generation Sequencing of Chromosome-Specific Libraries Sheds Light on Genome Evolution in Paleotetraploid Sterlet (Acipenser ruthenus).

Several whole genome duplication (WGD) events followed by rediploidization took place in the evolutionary history of vertebrates. Acipenserids represent a convenient model group for investigation of the consequences of WGD as their representatives underwent additional WGD events in different lineages resulting in ploidy level variation between species, and these processes are still ongoing. Earlier, we obtained a set of sterlet (Acipenser ruthenus) chromosome-specific libraries by microdissection and revealed that they painted two or four pairs of whole sterlet chromosomes, as well as additional chromosomal regions, depending on rediploidization status and chromosomal rearrangements after genome duplication. In this study, we employed next generation sequencing to estimate the content of libraries derived from different paralogous chromosomes of sterlet. For this purpose, we aligned the obtained reads to the spotted gar (Lepisosteus oculatus) reference genome to reveal syntenic regions between these two species having diverged 360 Mya. We also showed that the approach is effective for synteny prediction at various evolutionary distances and allows one to clearly distinguish paralogous chromosomes in polyploid genomes. We postulated that after the acipenserid-specific WGD sterlet karyotype underwent multiple interchromosomal rearrangements, but different chromosomes were involved in this process unequally.

Phylotranscriptomic consolidation of the jawed vertebrate timetree.

Phylogenomics is extremely powerful but introduces new challenges as no agreement exists on “standards” for data selection, curation and tree inference. We use jawed vertebrates (Gnathostomata) as model to address these issues. Despite considerable efforts in resolving their evolutionary history and macroevolution, few studies have included a full phylogenetic diversity of gnathostomes and some relationships remain controversial. We tested a novel bioinformatic pipeline to assemble large and accurate phylogenomic datasets from RNA sequencing and find this phylotranscriptomic approach successful and highly cost-effective. Increased sequencing effort up to ca. 10Gbp allows recovering more genes, but shallower sequencing (1.5Gbp) is sufficient to obtain thousands of full-length orthologous transcripts. We reconstruct a robust and strongly supported timetree of jawed vertebrates using 7,189 nuclear genes from 100 taxa, including 23 new transcriptomes from previously unsampled key species. Gene jackknifing of genomic data corroborates the robustness of our tree and allows calculating genome-wide divergence times by overcoming gene sampling bias. Mitochondrial genomes prove insufficient to resolve the deepest relationships because of limited signal and among-lineage rate heterogeneity. Our analyses emphasize the importance of large curated nuclear datasets to increase the accuracy of phylogenomics and provide a reference framework for the evolutionary history of jawed vertebrates.

Selective Constraints on Coding Sequences of Nervous System Genes Are a Major Determinant of Duplicate Gene Retention in Vertebrates.

The evolutionary history of vertebrates is marked by three ancient whole-genome duplications: two successive rounds in the ancestor of vertebrates, and a third one specific to teleost fishes. Biased loss of most duplicates enriched the genome for specific genes, such as slow evolving genes, but this selective retention process is not well understood. To understand what drives the long-term preservation of duplicate genes, we characterized duplicated genes in terms of their expression patterns. We used a new method of expression enrichment analysis, TopAnat, applied to in situ hybridization data from thousands of genes from zebrafish and mouse. We showed that the presence of expression in the nervous system is a good predictor of a higher rate of retention of duplicate genes after whole-genome duplication. Further analyses suggest that purifying selection against the toxic effects of misfolded or misinteracting proteins, which is particularly strong in nonrenewing neural tissues, likely constrains the evolution of coding sequences of nervous system genes, leading indirectly to the preservation of duplicate genes after whole-genome duplication. Whole-genome duplications thus greatly contributed to the expansion of the toolkit of genes available for the evolution of profound novelties of the nervous system at the base of the vertebrate radiation.

Morphological evolution of the mammalian jaw adductor complex.

ABSTRACTThe evolution of the mammalian jaw during the transition from non‐mammalian synapsids to crown mammals is a key event in vertebrate history and characterised by the gradual reduction of its individual bones into a single element and the concomitant transformation of the jaw joint and its incorporation into the middle ear complex. This osteological transformation is accompanied by a rearrangement and modification of the jaw adductor musculature, which is thought to have allowed the evolution of a more‐efficient masticatory system in comparison to the plesiomorphic synapsid condition. While osteological characters relating to this transition are well documented in the fossil record, the exact arrangement and modifications of the individual adductor muscles during the cynodont–mammaliaform transition have been debated for nearly a century.We review the existing knowledge about the musculoskeletal evolution of the mammalian jaw adductor complex and evaluate previous hypotheses in the light of recently documented fossils that represent new specimens of existing species, which are of central importance to the mammalian origins debate. By employing computed tomography (CT) and digital reconstruction techniques to create three‐dimensional models of the jaw adductor musculature in a number of representative non‐mammalian cynodonts and mammaliaforms, we provide an updated perspective on mammalian jaw muscle evolution.As an emerging consensus, current evidence suggests that the mammal‐like division of the jaw adductor musculature (into deep and superficial components of the m. masseter, the m. temporalis and the m. pterygoideus) was completed in Eucynodontia. The arrangement of the jaw adductor musculature in a mammalian fashion, with the m. pterygoideus group inserting on the dentary was completed in basal Mammaliaformes as suggested by the muscle reconstruction of Morganucodon oehleri. Consequently, transformation of the jaw adductor musculature from the ancestral (‘reptilian’) to the mammalian condition must have preceded the emergence of Mammalia and the full formation of the mammalian jaw joint. This suggests that the modification of the jaw adductor system played a pivotal role in the functional morphology and biomechanical stability of the jaw joint.

Evolution of the β-adrenoreceptors in vertebrates

The study of the evolutionary history of genes related to human disease lies at the interface of evolution and medicine. These studies provide the evolutionary context on which medical researchers should work, and are also useful in providing information to suggest further genetic experiments, especially in model species where genetic manipulations can be made. Here we studied the evolution of the β-adrenoreceptor gene family in vertebrates with the aim of adding an evolutionary framework to the already abundant physiological information. Our results show that in addition to the three already described vertebrate β-adrenoreceptor genes there is an additional group containing cyclostome sequences. We suggest that β-adrenoreceptors diversified as a product of the two whole genome duplications that occurred in the ancestor of vertebrates. Gene expression patterns are in general consistent across species, suggesting that expression dynamics were established early in the evolutionary history of vertebrates, and have been maintained since then. Finally, amino acid polymorphisms that are associated to pathological conditions in humans appear to be common in non-human mammals, suggesting that the phenotypic effects of these mutations depend on epistatic interaction with other positions. The evolutionary analysis of the β-adrenoreceptors delivers new insights about the diversity of these receptors in vertebrates, the evolution of the expression patterns and a comparative perspective regarding the polymorphisms that in humans are linked to pathological conditions.

New discoveries of tetrapods (ichthyostegid‐like and whatcheeriid‐like) in the Famennian (Late Devonian) localities of Strud and Becco (Belgium)

AbstractThe origin of tetrapods is one of the key events in vertebrate history. The oldest tetrapod body fossils are Late Devonian (Frasnian–Famennian) in age, most of them consisting of rare isolated bone elements. Here we describe tetrapod remains from two Famennian localities from Belgium: Strud, in the Province of Namur, and Becco, in the Province of Liège. The newly collected material consists of an isolated complete postorbital, fragments of two maxillae, and one putative partial cleithrum, all from Strud, and an almost complete maxilla from Becco. The two incomplete maxillae and cleithrum from Strud, together with the lower jaw previously recorded from this site, closely resemble the genusIchthyostega, initially described from East Greenland. The postorbital from Strud and the maxilla from Becco do not resemble the genusIchthyostega. They show several derived anatomical characters allowing their tentative assignment to a whatcheeriid‐grade group. The new tetrapod records show that there are at least two tetrapod taxa in Belgium and almost certainly two different tetrapod taxa at Strud. This locality joins the group of Devonian tetrapod‐bearing localities yielding more than one tetrapod taxon, confirming that environments favourable to early tetrapod life were often colonized by several tetrapod taxa.

Placoderm Assemblage from the Tetrapod-Bearing Locality of Strud (Belgium, Upper Famennian) Provides Evidence for a Fish Nursery.

The placoderm fauna of the upper Famennian tetrapod-bearing locality of Strud, Belgium, includes the antiarch Grossilepis rikiki, the arthrodire groenlandaspidid Turrisaspis strudensis and the phyllolepidid Phyllolepis undulata. Based on morphological and morphometric evidence, the placoderm specimens from Strud are predominantly recognised as immature specimens and this locality as representing a placoderm nursery. The Strud depositional environment corresponds to a channel in an alluvial plain, and the presence of a nursery in such environment could have provided nutrients and protection to the placoderm offspring. This represents one of the earliest pieces of evidence for this sort of habitat partitioning in vertebrate history, with adults living more distantly from the nursery and using the nursery only to spawn or give live birth.

Evolutionary history of the reprimo tumor suppressor gene family in vertebrates with a description of a new reprimo gene lineage

Genes related to human diseases should be natural targets for evolutionary studies, since they could provide clues regarding the genetic bases of pathologies and potential treatments. Here we studied the evolution of the reprimo gene family, a group of tumor-suppressor genes that are implicated in p53-mediated cell cycle arrest. These genes, especially the reprimo duplicate located on human chromosome 2, have been associated with epigenetic modifications correlated with transcriptional silencing and cancer progression. We demonstrate the presence of a third reprimo lineage that, together with the reprimo and reprimo-like genes, appears to have been differentially retained during the evolutionary history of vertebrates. We present evidence that these reprimo lineages originated early in vertebrate evolution and expanded as a result of the two rounds of whole genome duplications that occurred in the last common ancestor of vertebrates. The reprimo gene has been lost in birds, and the third reprimo gene lineage has been retained in only a few distantly related species, such as coelacanth and gar. Expression analyses revealed that the reprimo paralogs are mainly expressed in the nervous system. Different vertebrate lineages have retained different reprimo paralogs, and even in species that have retained multiple copies, only one of them is heavily expressed.

Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development.

Some of the greatest transformations in vertebrate history involve developmental and evolutionary origins of avian flight. Flight is the most power-demanding mode of locomotion, and volant adult birds have many anatomical features that presumably help meet these demands. However, juvenile birds, like the first winged dinosaurs, lack many hallmarks of advanced flight capacity. Instead of large wings they have small “protowings”, and instead of robust, interlocking forelimb skeletons their limbs are more gracile and their joints less constrained. Such traits are often thought to preclude extinct theropods from powered flight, yet young birds with similarly rudimentary anatomies flap-run up slopes and even briefly fly, thereby challenging longstanding ideas on skeletal and feather function in the theropod-avian lineage. Though skeletons and feathers are the common link between extinct and extant theropods and figure prominently in discussions on flight performance (extant birds) and flight origins (extinct theropods), skeletal inter-workings are hidden from view and their functional relationship with aerodynamically active wings is not known. For the first time, we use X-ray Reconstruction of Moving Morphology to visualize skeletal movement in developing birds, and explore how development of the avian flight apparatus corresponds with ontogenetic trajectories in skeletal kinematics, aerodynamic performance, and the locomotor transition from pre-flight flapping behaviors to full flight capacity. Our findings reveal that developing chukars (Alectoris chukar) with rudimentary flight apparatuses acquire an “avian” flight stroke early in ontogeny, initially by using their wings and legs cooperatively and, as they acquire flight capacity, counteracting ontogenetic increases in aerodynamic output with greater skeletal channelization. In conjunction with previous work, juvenile birds thereby demonstrate that the initial function of developing wings is to enhance leg performance, and that aerodynamically active, flapping wings might better be viewed as adaptations or exaptations for enhancing leg performance.

Hearing in Plethodontid Salamanders: A Review

The ability to detect airborne sound using a pressure-transducing tympanic ear has evolved several times over the course of vertebrate history, suggesting that hearing is an advantageous modality and an informative model for sensory evolution. Amphibian hearing is especially interesting because these animals must negotiate water to land transitions. Salamanders are good animal models for the study of hearing, not only because they have a wide range of ear morphologies, but also because they have evolved extratympanic pathways for sound and vibration transmission. Here we suggest that sufficient extratympanic hearing in salamanders and reduced reliance on vocal communication has relaxed selection on the auditory system and allowed for the structural diversity of the salamander ear. Unique among salamanders is the family Plethodontidae, which is not only the most speciose and ecologically diverse family of salamanders, but also possesses a highly derived ear with great inter-specific variation. In this revi...

Developmental basis of phenotypic integration in two Lake Malawi cichlids.

BackgroundCichlid fishes from the Rift Lakes of East Africa have undergone the most spectacular adaptive radiations in vertebrate history. Eco-morphological adaptations in lakes Victoria, Malawi and Tanganyika have resulted in a vast array of skull shapes and sizes, yet primary axes of morphological variation are conserved in all three radiations, prominently including the size of the preorbital region of the skull. This conserved pattern suggests that development may constrain the trajectories of cichlid head morphological evolution.ResultsHere, we (1) present a comparative analysis of adult head morphology in two sand-dweller cichlids from Lake Malawi with preorbital size differences representative of the main axis of variation among the three lakes and (2) analyze the ontogeny of shape and size differences by focusing on known developmental modules throughout the head. We find that (1) developmental differences between the two species correlate with known developmental modules; (2) differences in embryonic cartilage development result in phenotypically integrated changes among all bones derived from a single cartilage, while differences in dermal bone development tend to influence isolated regions within a bone; and lastly (3) species-specific morphologies appear in the embryo as subtle differences, which become progressively amplified throughout ontogeny. We propose that this amplification takes place at skeletal growth zones, the locations and shapes of which are patterned during embryogenesis.ConclusionsThis study is the most anatomically comprehensive analysis of the developmental differences underlying cichlid skull evolution in the Rift Lakes of East Africa. The scale of our analysis reveals previously unnoticed correlations between developmental modules and patterns of phenotypic integration. We propose that the primary axes of morphological variation among East African cichlid adaptive radiations are constrained by the hierarchical modularity of the teleost head skeleton.

Post-Gondwana Africa and the vertebrate history of the Angolan Atlantic Coast

The separation of Africa from South America and the growth of the South Atlantic are recorded in rocks exposed along the coast of Angola. Tectonic processes that led to the formation of Africa as a continent also controlled sedimentary basins that preserve fossils. The vertebrate fossil record in Angola extends from the Triassic to the Holocene and includes crocodylomorph, dinosaur, and mammaliamorph footprints, but more extensively, bones of fishes, turtles, plesiosaurs, mosasaurs, crocodiles, and cetaceans. Pterosaurs, dinosaurs, and land mammals are rare in Angola. The northward drift of Africa through latitudinal climatic zones provides a method for comparing predicted paleoenvironmental conditions among localities in Angola, and also allows comparison among desert and upwelling areas in Africa, South America, and Australia. South America has shown the least northward drift and its Atacama Desert is the oldest coastal desert among the three continents. Africa’s northward drift caused the displacement of the coastal desert to the south as the continent moved north. Australia drifted from far southerly latitudes and entered the climatic arid zone in the Miocene, more recently than South America or Africa, but in addition, a combination of its drift, continental outline, a downwelling eastern boundary current, the Pacific Ocean to Indian Ocean throughflow, and monsoon influence, make Australia unique.

Evolution, Regulation, and Function of N-terminal Variable Region of Troponin T: Modulation of Muscle Contractility and Beyond.

Troponin T (TnT) is the tropomyosin-binding and thin filament-anchoring subunit of the troponin complex in skeletal and cardiac muscles. At the center of the sarcomeric thin filament regulatory system of striated muscles, TnT plays an essential role in transducing Ca(2+) signals in the regulation of contraction. Having emerged predating the history of vertebrates, TnT has gone through more than 500 million years of evolution that resulted in three muscle-type-specific isoforms and numerous alternative RNA splicing variants. The N-terminal region of TnT is a hypervariable structure responsible for the differences among the TnT isoforms and splice forms. This focused review summarizes our current knowledge of the molecular evolution of the N-terminal variable region and its role in the structure and function of TnT. In addition to the physiologic and pathophysiologic significances in modifying the contractility of skeletal and cardiac muscles during development and in adaptation to stress and disease conditions, the hyperplasticity of the N-terminal region of TnT demonstrates an informative example for the evolution of protein three-dimensional structure and provides insights into the molecular evolution and functional potential of proteins.

Estrogen Receptor β Activation Rapidly Modulates Male Sexual Motivation through the Transactivation of Metabotropic Glutamate Receptor 1a

In addition to the transcriptional activity of their liganded nuclear receptors, estrogens, such as estradiol (E2), modulate cell functions, and consequently physiology and behavior, within minutes through membrane-initiated events. The membrane-associated receptors (mERs) underlying the acute effects of estrogens on behavior have mostly been documented in females where active estrogens are thought to be of ovarian origin. We determined here, by acute intracerebroventricular injections of specific agonists and antagonists, the type(s) of mERs that modulate rapid effects of brain-derived estrogens on sexual motivation in male Japanese quail. Brain aromatase blockade acutely inhibited sexual motivation. Diarylpropionitrile (DPN), an estrogen receptor β (ERβ)-specific agonist, and to a lesser extent 17α-estradiol, possibly acting through ER-X, prevented this effect. In contrast, drugs targeting ERα (PPT and MPP), GPR30 (G1 and G15), and the Gq-mER (STX) did not affect sexual motivation. The mGluR1a antagonist LY367385 significantly inhibited sexual motivation but mGluR2/3 and mGluR5 antagonists were ineffective. LY367385 also blocked the behavioral restoration induced by E2 or DPN, providing functional evidence that ERβ interacts with metabotropic glutamate receptor 1a (mGluR1a) signaling to acutely regulate male sexual motivation. Together these results show that ERβ plays a key role in sexual behavior regulation and the recently uncovered cooperation between mERs and mGluRs is functional in males where it mediates the acute effects of estrogens produced centrally in response to social stimuli. The presence of an ER-mGluR interaction in birds suggests that this mechanism emerged relatively early in vertebrate history and is well conserved. Significance statement: The membrane-associated receptors underlying the acute effects of estrogens on behavior have mostly been documented in females, where active estrogens are thought to be of ovarian origin. Using acute intracerebroventricular injections of specific agonists and antagonists following blockade of brain aromatase, we show here that brain-derived estrogens acutely facilitate male sexual motivation through the activation of estrogen receptor β interacting with the metabotropic glutamate receptor 1a. This behavioral effect occurring within minutes provides a mechanistic explanation of how an estrogen receptor not intrinsically coupled to intracellular effectors can signal from the membrane to govern behavior in a very rapid fashion. It suggests that different subtypes of estrogen receptors could regulate the motivation versus performance aspects of behavior.

Instantaneous reproductive isolation in polyploid treefrogs: Mechanisms and consequences

Speciation by polyploidy—duplication of chromosome sets—commonly occurs in plants and happened twice in the early evolutionary history of vertebrates. The gray treefrog (Hyla versicolor) is a recently evolved tetraploid species found in the eastern United States, where it often occurs with a cryptic diploid species (Hyla chrysoscelis). Assortative mating by ploidy is favored by selection because of triploid hybrid sterility and is based solely on selective phonotaxis of females to the species (ploidy)-specific calls of males. The tetraploid species has arisen multiple times independently; the calls and preferences of frogs in these lineages are nearly the same. Autotriploids of the diploid species created in the laboratory show parallel shifts in both the key call-properties of males and female preferences in the direction of the wild-type tetraploid species. These shifts are probably caused by changes in cell size (larger in tetraploids) and number (fewer in tetraploids) rather than the difference in gene dosage. The magnitude of changes expected in autotetraploids would be sufficient for instant pre-mating isolation of diploids and recently derived tetraploids, hence promoting instantaneous speciation, which would then be reinforced by selection against the production of infertile hybrids.