Retinal asymmetry in birds

AbstractVertebrate sensory systems are generally based on bilaterally symmetrical sense organs. It is evident, nevertheless, that birds preferentially use either their left or right eye for viewing novel or familiar stimuli [1], and perform visual discrimination tasks under monocular viewing conditions better with one eye than with the other [2,3]. Because of the nearly complete contralateral decussation of the optic nerves in birds [4], it has been assumed that this division of labour is due solely to cerebral hemispheric specialisation, generated as a result of uneven photostimulation of the eyes of the developing embryo during the last three or four days before hatching [5,6]. Here, however, we present evidence that in the European starling, Sturnus vulgaris, even the retinae are morphologically asymmetrical in terms of photoreceptor distribution. This is the first evidence for such asymmetry in any bird and suggests that retinal photoreceptor composition should be assessed during studies involving the lateralisation of visually mediated behaviours

Visual pigments, cone oil droplets, ocular media and predicted spectral sensitivity in the domestic turkey (Meleagris gallopavo)

AbstractA microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris gallopavo) revealed the presence of five different types of vitamin A1-based visual pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive visual pigment (wavelength of maximum absorbance, λmax, 504 nm). Four different types of single cone contained visual pigment maximally sensitive to wavelengths in either the long (LWS, λmax 564 nm), medium (MWS, λmax 505 nm), short (SWS, λmax 460 nm) or violet (VS, λmax 420 nm) spectral ranges. The LWS, MWS and SWS single cones contained pigmented oil droplets with cut-off wavelengths (λcut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone visual pigment. The principal member contained an oil droplet with a λcut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spectral transmission of the ocular media, suggest that turkeys have considerable sensitivity to wavelengths in the ultraviolet-A (UV-A, 315–400 nm) spectral range. This has implications for both the visual ecology of wild birds and the welfare of intensively farmed individuals

Can't tell the caterpillars from the trees: countershading enhances survival in a woodland

Perception of the body's outline and three-dimensional shape arises from visual cues such as shading, contour, perspective and texture. When a uniformly coloured prey animal is illuminated from above by sunlight, a shadow may be cast on the body, generating a brightness contrast between the dorsal and ventral surfaces. For animals such as caterpillars, which live among flat leaves, a difference in reflectance over the body surface may degrade the degree of background matching and provide cues to shape from shading. This may make otherwise cryptic prey more conspicuous to visually hunting predators. Cryptically coloured prey are expected to match their substrate in colour, pattern and texture ( though disruptive patterning is an exception), but they may also abolish self-shadowing and therefore either reduce shape cues or maintain their degree of background matching through countershading: a gradation of pigment on the body of an animal so that the surface closest to illumination is darker. In this study, we report the results from a series of field experiments where artificial prey resembling lepidopteran larvae were presented on the upper surfaces of beech tree branches so that they could be viewed by free-living birds. We demonstrate that countershading is superior to uniform coloration in terms of reducing attack by free-living predators. This result persisted even when we fixed prey to the underside of branches, simulating the resting position of many tree-living caterpillars. Our experiments provide the first demonstration, in an ecologically valid visual context, that shadowing on bodies (such as lepidopteran larvae) provides cues that visually hunting predators use to detect potential prey species, and that countershading counterbalances shadowing to enhance cryptic protection

Ecological constraints on breeding system evolution: The influence of habitat on brood desertion in Kentish plover

PubMedID: 169030631. One of the fundamental insights of behavioural ecology is that resources influence breeding systems. For instance, when food resources are plenty, one parent is able to care for the young on its own, so that the other parent can desert and became polygamous. We investigated this hypothesis in the context of classical polyandry when females may have several mates within a single breeding season, and parental duties are carried out largely by the male. 2. We studied a precocial wader, the Kentish plover Charadrius alexandrinus, that exhibits variable brood care such that the chicks may be raised by both parents, only by the female or, more often, only by the male. The timing of female desertion varies: some females desert their brood at hatching of the eggs and lay a clutch for a new mate, whereas other females stay with their brood until the chicks fledge. Kentish plovers are excellent organisms with which to study breeding system evolution, as some of their close relatives exhibit classical polyandry (Eurasian dotterel Eudromias morinellus, mountain plover Charadrius montanus), whereas others are polygynous (northern lapwing Vanellus vanellus). 3. Kentish plovers raised their broods in two habitats in our study site in southern Turkey: saltmarsh and lakeshore. Food intake was higher on the lakeshore than in the saltmarsh as judged from feeding behaviour of chicks and adults. As the season proceeded and the saltmarsh dried out, the broods moved toward the lakeshore. 4. As the density of plovers increased on lakeshore, the parents spent more time defending their young, and female parents stayed with their brood longer on the lakeshore. 5. We conclude that the influence of food abundance on breeding systems is more complex than currently anticipated. Abundant food resources appear to have profound implications on spatial distribution of broods, and the social interactions between broods constrain female desertion and polyandry. © 2006 2006 British Ecological Society

Improving bioscience research reporting: the ARRIVE guidelines for reporting animal research

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Congruence of phenotypic and genetic variation at the subspecific level in a Neotropical passerine

The increasing availability of molecular phylogenies has highlighted the issue that genotypic and phenotypic patterns of variation are not always congruent, particularly below the species level. This has led to an ongoing discussion on the validity of the subspecies category and on the use of molecular data to help revise traditional classifications based on phenotypic data. We compared patterns of spatial diversification in genotype and phenotype in the Blue-black Grosbeak Cyanocompsa cyanoides, a Neotropical songbird with four recognised subspecies. Variation in phenotype and genotype are partially congruent among the four subspecies. The more genetically divergent subspecies C. c. rothschildii is strongly differentiated from the other subspecies in meristic characters, plumage colo uration and song . W e suggest that this taxon be accorded full species status as C. rothschildii. Regarding the remaining diversity within C. cyanoides, both phenotypic and genetic markers suggests that it could be divided into two subgroups, but the boundaries of genetic lineages do not coincide with those of subspecies defined using phenotypic data. Lack of complete congruence between phenotypic and molecular markers may be expected, since they are subject to different evolutionary processes. The discordance could also be due to a methodological problem, as subspecies ? geographic boundaries were defined on the basis of phenotypic descriptions that were not systematically evaluated. We consider the subspecies to be an informative taxonomic entity , but note that many current subspecific designations for diverse species need extensive reassessment.Fil: García, Natalia Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Barreira, Ana Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Lavinia Oblanca, Pablo Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Tubaro, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin