RESUMEN
In animal communication, functionally referential alarm calls elicit the same behavioral responses as their referents, despite their typically distinct bioacoustic traits. Yet the auditory forebrain in at least one songbird species, the black-capped chickadee Poecile atricapillus, responds similarly to threat calls and their referent predatory owl calls, as assessed by immediate early gene responses in the secondary auditory forebrain nuclei. Whether and where in the brain such perceptual and cognitive equivalence is processed remains to be understood in most other avian systems. Here, we studied the functional neurogenomic (non-) equivalence of acoustic threat stimuli perception by the red-winged blackbird Agelaius phoeniceus in response to the actual calls of the obligate brood parasitic brown-headed cowbird Molothrus ater and the referential anti-parasitic alarm calls of the yellow warbler Setophaga petechia, upon which the blackbird is known to eavesdrop. Using RNA-sequencing from neural tissue in the auditory lobule (primary and secondary auditory nuclei combined), in contrast to previous findings, we found significant differences in the gene expression profiles of both an immediate early gene, ZENK (egr-1), and other song-system relevant gene-products in blackbirds responding to cowbird vs. warbler calls. In turn, direct cues of threats (including conspecific intruder calls and nest-predator calls) elicited higher ZENK and other differential gene expression patterns compared to harmless heterospecific calls. These patterns are consistent with a perceptual non-equivalence in the auditory forebrain of adult male red-winged blackbirds in response to referential calls and the calls of their referents.
Asunto(s)
Passeriformes , Pájaros Cantores , Animales , Masculino , Vocalización Animal/fisiología , Pájaros Cantores/fisiología , Prosencéfalo/fisiología , Transcriptoma , Percepción Auditiva/fisiologíaRESUMEN
Communication between parents and dependent offspring is critical not only during provisioning, but also in antipredator contexts. In altricial birds, a top cause of reproductive failure is nest predation, and alarm calls both by parents and chicks can serve to alert others and increase the likelihood of offspring escaping predation. Understanding the factors that determine the strength of parental antipredator responses to different nestling alarm calls can provide insight into parent-offspring recognition. The prothonotary warbler (Protonotaria citrea), a host of the obligate brood parasite, the brown-headed cowbird (Molothrus ater), never rejects cowbird young and raises the parasite together with its own offspring. To determine whether warbler parents learn cowbird nestling alarm calls, we presented experimentally parasitized or non-parasitized parents with playbacks of conspecific warbler, parasitic cowbird, and a harmless heterospecific control, eastern bluebird (Sialis sialis), nestling alarm calls. We recorded the latency to respond and the number of chips given by members of the resident warbler pair. We found that parents were most likely to respond to warbler nestling alarm calls, least likely to respond to bluebird calls, with a statistically intermediate likelihood of responding to cowbird calls. Critically, current and past parasitism status did not affect the likelihood of response to any playback or the number of chips given, however, currently parasitized parents had greater response latencies to playbacks than non-parasitized parents. These results suggest that warbler parents do not learn cowbird alarm calls from breeding experiences and, in turn, that cowbirds may employ a generalized, bet-hedging alarm call.
Asunto(s)
Interacciones Huésped-Parásitos , Passeriformes , Pájaros Cantores , Animales , Comportamiento de Nidificación , Conducta PredatoriaRESUMEN
Species recognition is an essential behavioral outcome of social discrimination, flocking, mobbing, mating, and/or parental care. In songbirds, auditory species recognition cues are processed through specialized forebrain circuits dedicated to acoustic discrimination. Here we addressed the direction of behavioral and neural metrics of zebra finches' (Taeniopygia guttata) responses to acoustic cues of unfamiliar conspecifics vs. heterospecifics. Behaviorally, vocal response rates were greater for conspecific male zebra finch songs over heterospecific Pin-tailed Whydah (Vidua macroura) songs, which paralleled greater multiunit spike rates in the auditory forebrain in response to the same type of conspecific over heterospecific auditory stimuli. In contrast, forebrain activation levels were reversed to species-specific song playbacks during two functional magnetic resonance imaging experiments: we detected consistently greater responses to whydah songs over finch songs and did so independently of whether subjects had been co-housed or not with heterospecifics. These results imply that the directionality of behavioral and neural response selectivity metrics are not always consistent and appear to be experience-independent in this set of stimulus-and-subject experimental paradigms.
Asunto(s)
Percepción Auditiva/fisiología , Señales (Psicología) , Pinzones/fisiología , Prosencéfalo/fisiología , Reconocimiento en Psicología/fisiología , Vocalización Animal/fisiología , Estimulación Acústica , Animales , Electrofisiología , Imagen por Resonancia Magnética , Masculino , Especificidad de la EspecieRESUMEN
Early exposure to salient cues can critically shape the development of social behaviors. For example, both oscine birds and humans can hear and learn to recognize familiar sounds in ovo and in utero and recognize them following hatching and birth, respectively. Here we demonstrate that different chronic acoustic playbacks alter genome-wide methylation of the auditory forebrain in late-stage zebra finch (Taeniopygia guttata) embryos. Within the same subjects, immediate early gene activation in response to acute con- or heterospecific song exposure is negatively correlated with methylation extent in response to repeated daily prior exposure to the same type of stimuli. Specifically, we report less relative global methylation following playbacks of conspecific songs and more methylation following playbacks of distantly-related heterospecific songs. These findings offer a neuroepigenomic mechanism for the ontogenetic impacts of early acoustic experiences in songbirds.
Asunto(s)
Estimulación Acústica/métodos , Percepción Auditiva/fisiología , Metilación de ADN/fisiología , Efectos Tardíos de la Exposición Prenatal/metabolismo , Prosencéfalo/metabolismo , Vocalización Animal/fisiología , Animales , Femenino , Pinzones , Masculino , Embarazo , Efectos Tardíos de la Exposición Prenatal/genéticaRESUMEN
Avian obligate brood parasitism, a reproductive strategy where a parasite lays its egg into the nest of another species, imposes significant fitness costs upon host parents and their offspring. To combat brood parasitism, many host species recognize and reject foreign eggs (rejecters), but others are accepters that raise the parasitic progeny. Some accepter hosts may be unable to grasp or pierce parasitic eggs even if they recognize them as foreign eggs in the clutch, whereas other accepters may not have evolved the cognitive skillsets to recognize dissimilar eggs in the nest. Here we assessed the endocrine responses of an accepter host species to model parasitic eggs to address these two alternatives. We experimentally parasitized nests of a locally common host of the brood-parasitic brown-headed cowbird (Molothrus ater), the prothonotary warbler (Protonotaria citrea; a cowbird-egg accepter), with a mimetic or non-mimetic model cowbird-sized egg. Our goal was to determine whether they perceived the non-mimetic egg as a greater stressor by measuring circulating corticosterone levels. We added eggs to nests during the incubation stage and obtained blood plasma samples from females on the nest 2 h later, using females with unmanipulated clutches as controls. Incubating females showed no differences in baseline plasma corticosterone levels between our different treatments. We conclude that exposure to foreign eggs does not activate the hypothalamic-pituitary-adrenal axis of prothonotary warbler hosts in this experimental paradigm.
Asunto(s)
Parásitos , Passeriformes , Animales , Femenino , Glucocorticoides , Sistema Hipotálamo-Hipofisario , Comportamiento de Nidificación , Óvulo , Sistema Hipófiso-SuprarrenalRESUMEN
Hosts of avian brood parasites may reduce or forego the costs of caring for foreign young by rejecting parasitic eggs from the nest. Yet, many host species accept parasitic eggs and, even among rejecter species, some individuals go on to incubate and hatch them. The factors explaining the variation in egg rejection between species have received much theoretical and empirical attention, but the causes of intraspecific variation in different individuals' propensity for accepting parasitic eggs are less well understood. Here we tested the maternal investment hypothesis, which predicts that hosts with costlier clutches will be more likely to reject parasitic eggs from their nest. We studied variation in the egg rejection responses of American robins (Turdus migratorius), a robust egg-rejecter host of the brood parasitic brown-headed cowbird (Molothrus ater), to 3D-printed cowbird-sized eggs which were painted dark blue, a color known to induce variable and repeatable egg rejection responses in individual robins. Costlier clutch investment was estimated by earlier laying date, larger clutch size, heavier unincubated yolk mass, and variable yolk steroid hormone concentrations. There was no statistical support for most of our predictions. However, we detected more concentrated and greater overall amount of deoxycorticosterone deposited in egg yolks of rejecters relative to acceptors, although this accounted for no more than 14% of variance in the data. Future work should test experimentally the potential physiological linkage between maternal egg yolk steroid investment and egg rejection propensity in this and other host species of avian brood parasites.
Egyedek közti variáció az antiparazitikus tojás-diszkriminációban: az anyai befektetés hipotézis tesztelése Kivonat A költésparazita madárfajok gazdái csökkenthetik vagy megszüntethetik az idegen fióka nevelésének költségeit úgy, hogy eltávolítják a fészekbol a paraziták tojásait. Ennek ellenére több gazdafaj is elfogadja a parazita tojásokat, sot az elutasító gazdafajok körében is akadnak olyan egyedek, amelyek elfogadják és kikeltik az idegen tojást. Bár az eddigi elméleti és kísérleti kutatások nagy hangsúlyt fektettek a különbözo gazdafajok közti, költésparazita tojások diszkriminacióját befolyásoló tényezok feltárására, a parazita tojások elfogadásának gazdafajon belüli varianciája kevésbé tisztázott. Jelen kutatásunkban az anyai befektetés hipotézisét vizsgáltuk, melynek értelmében azok az egyedek, amelyek több energiát fektetnek fészekaljukba, nagyobb valószínuséggel távolítják el a költésparazita tojásait a fészekbol. A vándorrigónak (Turdus migratorius) a parazita tojást elutasító viselkedését vizsgáltuk meg a költésparazita barnafeju gulyajáró (Molothrus ater) tojásához hasonló méretu, de sötétkék színu, 3 D nyomtatóval készített mutojásokat használva. A költési periódusban korábban letojt, több tojásból álló, nagyobb inkubálatlan tömegu és változatos szteroid hormonkoncentrácijú sárga szíku tojásokkal rendelkezo fészekaljakat tekintettük a magasabb anyai befektetésu fészekaljaknak. Feltevéseink nagyrészét statisztikai eredményeink nem támasztották alá. Mindezek ellenére, a parazita tojásokat elfogadó egyedekéhez képest, az idegen tojást elutasító egyedek tojásai sárga szíkanyagában nagyobb koncentrációban és mennyiségben volt jelen a dezoxikortikoszteron, bár ez az adatainkra jellemzo varianciának csupán 14%-át magyarázta. További kísérletes vizsgálatok szükségesek ahhoz, hogy feltárhassuk az esetleges fiziológiás kapcsolatot az anyai tojas szteroid hormone befektetés és a parazita tojások elutasításának gyakorisága között ennél a gazdafajnál, és más költésparazita gazdáknál egyaránt. Translated kindly by Attila Marton, Debrecen University.
RESUMEN
Obligate avian brood parasites lay their eggs in nests of other host species, which assume all the costs of parental care for the foreign eggs and chicks. The most common defensive response to parasitism is the rejection of foreign eggs by hosts. Different cognitive mechanisms and decision-making rules may guide both egg recognition and rejection behaviors. Classical optimization models generally assume that decisions are based on the absolute properties of the options (i.e., absolute valuation). Increasing evidence shows instead that hosts' rejection decisions also depend on the context in which options are presented (i.e., context-dependent valuation). Here we study whether the chalk-browed mockingbird's (Mimus saturninus) rejection of parasitic shiny cowbird (Molothrus bonariensis) eggs is a fixed behavior or varies with the context of the clutch. We tested three possible context-dependent mechanisms: (1) range effect, (2) habituation to variation, and (3) sensitization to variation. We found that mockingbird rejection of parasitic eggs does not change according to the characteristics of the other eggs in the nest. Thus, rejection decisions may exclusively depend on the objective characteristics of the eggs, meaning that the threshold of acceptance or rejection of a foreign egg is context-independent in this system.
Asunto(s)
Toma de Decisiones , Comportamiento de Nidificación/fisiología , Óvulo , Passeriformes/fisiología , Animales , Cognición , Femenino , Interacciones Huésped-Parásitos , Masculino , Passeriformes/parasitologíaRESUMEN
Implantation of a duodenal-jejunal endoluminal bypass liner (DJBL) has shown to induce weight loss and to improve metabolic parameters. DJBL is a reversible endoduodenal sleeve mimicking duodenal bypass while lacking risks and limitations of bariatric surgery.Effects on metabolic control, body mass parameters, appetite regulation, glucose tolerance, organ health, and lipid profile were determined in 16 morbidly overweight patients with type 2 diabetes mellitus. In addition, relevant hormones (leptin, ghrelin, gastric inhibitory peptide, glucagon-like peptide, and insulin) were measured by enzyme-linked immunosorbent assay (ELISA) and chemiluminescent microparticle immunoassay (CMIA) at 0, 1, 32, and 52 weeks post-implant following a mixed meal tolerance test. Lipoprotein subclasses were analysed by proton nuclear magnetic resonance (1H NMR) spectrometry. DJBL provoked weight loss, a decrease in fat mass, and an improvement in insulin resistance and hepatic function in most but not all of the patients, but in the long term did not increase gut hormone fasting levels pointing to a combined effect of more than gut parameters alone. Lipidome analysis was done in 10 patients, allowing classification to responders and non-responders by reduction of sLDL-p subfraction; and to further analyse the atherogenic profile. Responders showed an overall more pronounced effect regarding improvement of HbA1c, BMI, and HOMA index.Implantation of a DJBL in obese type 2 diabetes patients does not per se lead to an improvement of the metabolic situation. Further analyses including larger cohorts have to be performed to identify responding patients, to better treat non-responders and to analyse the key effectors.
Asunto(s)
Adiposidad , Cirugía Bariátrica , Diabetes Mellitus Tipo 2/cirugía , Duodeno/cirugía , Yeyuno/cirugía , Obesidad Mórbida/fisiopatología , Adulto , Anciano , Glucemia/análisis , Estudios de Casos y Controles , Diabetes Mellitus Tipo 2/epidemiología , Diabetes Mellitus Tipo 2/metabolismo , Duodeno/metabolismo , Femenino , Estudios de Seguimiento , Polipéptido Inhibidor Gástrico/metabolismo , Glucagón/metabolismo , Péptido 1 Similar al Glucagón/metabolismo , Humanos , Insulina/metabolismo , Secreción de Insulina , Yeyuno/metabolismo , Masculino , Persona de Mediana Edad , Resultado del Tratamiento , Pérdida de PesoRESUMEN
BACKGROUND: Prader-Willi syndrome (PWS) is a genetic disorder characterized by morbid obesity resulting from insatiable appetite. Complications like diabetes mellitus or other cardiovascular diseases typically occur during lifetime. Lifestyle advice and education as well as limited caloric intake are the major concepts in assistance of PWS patients. METHODS: A 12.9-month follow-up study, which included 8 formerly genetically diagnosed PWS patients, was conducted. Physical and laboratory examinations were done at the beginning and at the end of the follow-up. Improved medical care and lifestyle advice were given. The participants lived in an assisted living environment with a fixed daily schedule and limited caloric intake. RESULTS: The group of patients consisted of manifest diabetics (n=6) as well as nondiabetics (n=2). Therapeutic concepts were simplified in 2 patients by switching from insulin to oral antidiabetics. The reduction in body weight was moderate, but attributable to a loss of fat mass. A significant reduction in blood cholesterol and triglyceride content was achieved along the observational period as well as a significant reduction of glycosylated hemoglobin (HbA1c) in the group of diabetic PWS patients. Systolic blood pressure improved during the study. CONCLUSION: A combination of an assisted living environment following conservative treatments as well as consistent patient care improved the daily and medical situation of PWS patients. Weight loss and, as a consequence, improvements in terms of metabolic condition and blood pressure were observed. A combination of medical and daily routine management should be established in PWS patients to improve their quality of life.
Asunto(s)
Síndrome de Prader-Willi/terapia , Adulto , Presión Sanguínea , Índice de Masa Corporal , Peso Corporal , Grosor Intima-Media Carotídeo , Colesterol/sangre , Complicaciones de la Diabetes/sangre , Complicaciones de la Diabetes/terapia , Femenino , Estudios de Seguimiento , Prueba de Tolerancia a la Glucosa , Hemoglobina Glucada/metabolismo , Humanos , Hipoglucemiantes/uso terapéutico , Estilo de Vida , Masculino , Obesidad Mórbida/sangre , Obesidad Mórbida/terapia , Síndrome de Prader-Willi/sangre , Calidad de Vida , Sístole , Triglicéridos/sangre , Pérdida de Peso , Adulto JovenRESUMEN
The study of the evolution of sexual differences in behavioral and morphological displays requires analyses of the extent of sexual dimorphism across various sensory modalities. In the seabird family Sulidae, boobies show dramatic sexual dimorphism in their vocalizations, and gannet calls have also been suggested to be dimorphic to human observers. This study aimed to evaluate the presence of sexually dimorphic calls in the Australasian gannet (Morus serrator) through the first comprehensive description of its vocalizations recorded at two localities; Cape Kidnappers, where individuals were banded and sexed from DNA samples, and at the Muriwai gannetry, both on the North Island of New Zealand. Calls were first inspected using basic bioacoustic features to establish a library of call element types for general reference. Extensive multivariate tests, based on a dynamic time warping algorithm, subsequently revealed that no sexual differences could be detected in Australasian gannet calls. The analyses, however, indicated extensive and consistent vocal variation between individuals, particularly so in female gannets, which may serve to signal individual identity to conspecifics. This study generates predictions to identify whether differences in Australasian gannet vocalizations play perceptual and functional roles in the breeding and social biology of this long-lived biparental seabird species.
Asunto(s)
Algoritmos , Aves/fisiología , Individualidad , Procesamiento de Señales Asistido por Computador , Vocalización Animal , Animales , Femenino , Masculino , Cadenas de Markov , Análisis Multivariante , Nueva Zelanda , Caracteres Sexuales , Factores Sexuales , Espectrografía del Sonido , Factores de TiempoRESUMEN
In 1965, Hamilton and Orians (HO) hypothesized that the starting point for the evolution of obligate interspecific brood parasitism in birds was the facultative laying of physiologically committed eggs in neighbouring active nests of con- and heterospecifics, following predation of a bird's own nest during the laying stage. We tested this prediction of the HO hypothesis by using captive pairs of zebra finches (Taeniopygia guttata), a species with evidence for intraspecific parasitism both in the wild and in captivity. As predicted, in response to experimental nest removal, subjects laid eggs parasitically in simulated active conspecific nests above chance levels. Across subsequent trials, we detected both repeatability and directional change in laying patterns, with some subjects switching from parasitism to depositing eggs in the empty nest. Taken together, these results support the assumptions and predictions of the HO hypothesis, and indicate that the zebra finch is a potential model species for future behavioural and genetic studies in captive brood parasite research.
Asunto(s)
Evolución Biológica , Pinzones , Comportamiento de Nidificación , Animales , Femenino , Masculino , Oviparidad , Conducta PredatoriaRESUMEN
Hosts either tolerate avian brood parasitism or reject it by ejecting parasitic eggs, as seen in most rejecter hosts of common cuckoos, Cuculus canorus, or by abandoning parasitized clutches, as seen in most rejecter hosts of brown-headed cowbirds, Molothrus ater. What explains consistent variation between alternative rejection behaviours of hosts within the same species and across species when exposed to different types of parasites? Life history theory predicts that when parasites decrease the fitness of host offspring, but not the future reproductive success of host adults, optimal clutch size should decrease. Consistent with this prediction, evolutionarily old cowbird hosts, but not cuckoo hosts, have lower clutch sizes than related rarely- or newly parasitized species. We constructed a mathematical model to calculate the fitness payoffs of egg ejector vs. nest abandoner hosts to determine if various aspects of host life history traits and brood parasites' virulence on adult and young host fitness differentially influence the payoffs of alternative host defences. These calculations showed that in general egg ejection was a superior anti-parasite strategy to nest abandonment. Yet, increasing parasitism rates and increasing fitness values of hosts' eggs in both currently parasitized and future replacement nests led to switch points in fitness payoffs in favour of nest abandonment. Nonetheless, nest abandonment became selectively more favourable only at lower clutch sizes and only when hosts faced parasitism by a cowbird- rather than a cuckoo-type brood parasite. We suggest that, in addition to evolutionary lag and gape-size limitation, our estimated fitness differences based on life history trait variation provide new insights for the consistent differences observed in the anti-parasite rejection strategies between many cuckoo- and cowbird-hosts.
Asunto(s)
Aves/fisiología , Aves/parasitología , Interacciones Huésped-Parásitos , Comportamiento de Nidificación , Animales , Modelos Biológicos , Passeriformes/fisiología , Reproducción/fisiologíaRESUMEN
INTRODUCTION: Multiradicular nerve root compression, and long lasting radicular syndrome occur very often. They happen particularly on degenerative spine. Huge synovial cyst of the zygapophyseal joints may account for it, expand in the epidural area and cause radicular syndrome. EXEGESIS: Two cases of huge synovial cysts spreading into the spinal channel are reported here. Diagnostic and therapeutic modalities are discussed. On degenerative spine, facet joints osteoarthritis may result in synovial cysts. Physical examination findings are radicular syndrome. CONCLUSION: Huge synovial cysts may result in multiple nerve root compression syndrome, as reported in our two cases. Typically, there's no history of preceding trauma and symptoms appear progressively. Magnetic resonance imaging of the spine shows an intra-spinal round mass with typical signal intensity and capsular formation. Treatment consists either in facet joint steroid injection performed with radiologic guidance or in surgical excision.
Asunto(s)
Radiculopatía/etiología , Quiste Sinovial/complicaciones , Articulación Cigapofisaria , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , SíndromeRESUMEN
In most birds and mammals, young are raised in family groups. The phenotypes of nestmates and parents are thus reliable cues for recognition of conspecifics and kin. However, in some species, young develop alone, or in broods of mixed relatedness (e.g. because of multiple paternity or maternity), or among heterospecifics or unrelated conspecifics (brood parasites). Under these circumstances, the best referent (model) for discriminating close from distant kin and heterospecifics from conspecifics might be one's own self. This recognition process is known as self-referent phenotype matching. Here we review recent experimental evidence of self-referencing and suggest that behavioral neuroscience can provide new tools and insights into how it works (its proximate mechanistic and ontogenetic bases) and why it exists (its adaptive significance).
Asunto(s)
Encéfalo/fisiología , Comportamiento de Nidificación/fisiología , Conducta Sexual Animal/fisiología , Animales , Fenotipo , Especificidad de la EspecieRESUMEN
In clonal rat somatomammotroph cells (GH3/ B6) Ca2+ influx through voltage-dependent Ca2+ channels is important for regulating the Ca2+ concentration that mediates hormone secretion. To study the Ca2+ channel subtypes in GH3/B6 cells, Ca2+ channel currents were recorded with the whole-cell configuration of the patch-clamp technique using Ba2+ as the charge carrier. Forty-nine percent of the total Ba2+ current amplitude was mediated by a nifedipine-sensitive current (L-type). In addition, three other high-voltage-activated Ca2+ channel current components could be distinguished pharmacologically: 10 nM omega-agatoxin-IVA-sensitive current (22%; P-type), omega-conotoxin-MVIIC-sensitive current (18%; Q-type), and toxin-resistant current (24%). Since omega-conotoxin GVIA (2 microM) had no blocking effect, N-type Ca2+ channels are assumed not to be present in GH3/B6 cells. The T-type Ca2+ channel current was either absent or very small. Different pore-forming alpha1 subunits of Ca2+ channels were found to be expressed in GH3/B6 cells, which could be the molecular correlates of the different Ba2+ current subtypes: alpha1G of T-type, alpha1C, alpha1D and alpha1S of L-type, and alpha1A of P/Q-type current. In addition, transcripts for beta1, beta2 and beta3 subunits were detected. Blockage of L-type channels with 10 microM nifedipine or P/Q-type channels with 10 nM omega-agatoxin MVIIC + 200 nM omega-conotoxin blocked action potential firing in GH3/B6 cells and decreased basal prolactin secretion.
Asunto(s)
Canales de Calcio Tipo L/genética , Canales de Calcio Tipo L/metabolismo , Canales de Calcio Tipo N/genética , Canales de Calcio Tipo N/metabolismo , Adenohipófisis/citología , Animales , Bloqueadores de los Canales de Calcio/farmacología , Vacuna contra la Varicela/farmacocinética , Células Clonales , Cartilla de ADN , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Nifedipino/farmacología , Técnicas de Placa-Clamp , Adenohipófisis/metabolismo , Prolactina/metabolismo , Ratas , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , omega-Agatoxina IVA/farmacología , omega-Conotoxinas/farmacologíaRESUMEN
Many spiders, and in particular those in the genus Argiope, spin highly visible web decorations whose function and significance are the subject of spirited debate. In this work, we present data to address two of the competing hypotheses that fuel this controversy. In particular, we examine the relationship between the presence of web decorations and spider survivorship (predator-protection hypothesis) and the relationship between the presence of prey and spider decorating behavior (the prey-attraction hypothesis). Our laboratory studies reveal that the decorating behavior of the spider A. argentata has a genetic component but that the expression of decorating behavior tends to be elicited only when a spider is well fed. Furthermore, our field studies show that in the presence of abundant stingless bees, spider decorating behavior is induced. Nevertheless, our field surveys also suggest that spiders that decorate their webs show reduced survivorship. We propose that the high correlation between web decorating in the presence of stingless bees supports the hypothesis that A. argentata engage in decorating behavior when attracting or targeting specific prey types. However, we also propose that web decorations attract the predators of A. argentata because high-frequency decorators suffer lower survivorship than spiders that decorate moderately or rarely. These findings suggest that spider web decorating behavior is affected by conflicting selection pressures: the positive effect of prey attraction versus the negative effect of predator attraction. Due to the heritable component of decorating behavior, web decorating among A. argentata is likely to be particularly sensitive to the spider's local ecology as well as local patterns of gene flow.
Asunto(s)
Arañas/genética , Arañas/fisiología , Animales , Abejas , Conducta Animal , Evolución Biológica , Femenino , Masculino , Modelos Biológicos , Linaje , Polimorfismo Genético , Conducta Predatoria , Transducción de SeñalRESUMEN
Recognition of conspecifics is an essential precursor of sexual reproduction. Most mammals and birds learn salient features of their parents or siblings early in ontogeny and later recognize individuals whose phenotypes match the mental image (template) of relatives closely enough as conspecifics. However, the young of brood parasites are reared among heterospecifics, so social learning will yield inappropriate species recognition templates. Initially, it was inferred that conspecific recognition in brood parasites depended on genetically determined templates. More recently it was demonstrated that learning plays a critical role in the development of parasites' social preferences. Here we propose a mechanism that accommodates the interaction of learned and genetic components of recognition. We suggest that conspecific recognition is initiated when a young parasite encounters some unique species-specific signal or "password" (e.g. a vocalization, behaviour or other characteristic) that triggers learning of additional aspects of the password-giver's phenotype. We examined the possibility that nestlings of the obligately brood-parasitic brown-headed cowbird (Molothrus ater) could use a species-specific vocalization, the "chatter", as a password. We found that six-day-old nestlings responded (begged) significantly more frequently to playbacks of chatters than to other avian sounds and that two-month-old fledglings approached playbacks of chatters more quickly than vocalizations of heterospecifics. Free-living cowbird fledglings and adults also approached playbacks of chatters more often than control sounds. Passwords may be involved in the ontogeny of species recognition in brood parasites generally.
Asunto(s)
Pájaros Cantores , Vocalización Animal , Animales , Especificidad de la EspecieRESUMEN
Cowbirds exhibit extensive variation in their social, territorial, and reproductive behaviors. Nissl-stained brain sections of specimens from a previous study (J. C. Reboreda, N. S. Clayton, & A. Kacelnik, 1996) were used to study the gross anatomy of a song control nucleus in 3 South American cowbirds (bay-winged, Molothrus badius; shiny, M. bonariensis; and screaming, M. rufoaxillaris). Cowbird high vocal center (HVC) volumes were consistently higher in males than in females in all 3 species. The largest HVC size of females found in bay-winged cowbirds is consistent with observations that females of this species, but not of the other 2 species, occasionally sing. The extent of the sexual dimorphism of relative HVC size was highest for the sexually dichromatic and promiscuous shiny cowbirds and smaller for the monochromatic and monogamous bay-winged and screaming cowbirds, suggesting that selection pressures associated with morphological traits and social systems are reflected in brain architecture.