amphibian visual ecology symposium...amphibian visual ecology symposium 16 & 17 april 2015...
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AMPHIBIAN VISUAL ECOLOGY SYMPOSIUM
16 & 17 April 2015 Synpunkten Biology building B – 3rd floor
Sponsored by
PROGRAM
Thursday 16-‐April
13.30 | Symposium opening
13.30-‐15.30 | Session I: Nocturnal environments and constraints on colour vision
Almut Kelber: Nocturnal colour vision: Adaptations and limits
Jochen Smolka: Essential properties of visual environments from an animal's point of view
Daniel Pessoa: Influence of luminosity on visual performance and colour discrimination
15.30-‐16.00 | Coffee break
16.00-‐17.30 | Session II: Current progress in the study of colour vision thresholds in
anurans
Carola Yovanovich: Behavioural evidence of scotopic colour vision in amphibians
Sanna Koskela: Measuring the absolute sensitivity of frog color discrimination using phototactic behavior
Friday 17-‐April
09.30-‐11.30 | Session III: Ecological and evolutionary aspects of Amphibian vision
Julián Faivovich: Amphibian diversity and the evolution of diurnal habits
Taran Grant: Amphibian diversity and vision
Bibiana Rojas: Differences in detectability and behaviour among dyeing poison frogs (Dendrobates tinctorius) bearing different colour patterns
11.30 | Round table: Coffee & open discussions
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ABSTRACTS
Nocturnal colour vision -‐ adaptations and limits
Almut Kelber
Vision Group | Lund University | Sweden
When night falls, colours fade away, and with less than a half moon, humans are left colour-‐blind. Our visual system, instead of comparing signals from our three cones types, sums signals from large pools of rods to be able and still make sense of the visual scene. Most vertebrates, and probably many other animals, also turn colour-‐blind in dim light. Some animals, however, including large moths, geckos, and rare nocturnal bees, are still able to see colours under these dim-‐light conditions. I will discuss the adaptations that make this possible, and the limits of colour vision in dim light.
Essential properties of visual environments from an animal's point of view
Jochen Smolka & Dan-‐Eric Nilsson
Vision Group | Lund University | Sweden
Different animal species are adapted to live in different habitats. These adaptations include the eyes and visual system, which are tailored by evolution to extract useful information from the visual environment. Differences between the visual systems of different animal species can thus be expected to depend much on the different habitats they evolved in. To assess these relationships, we need standards for measuring and characterising visual environments. The current trend of environmental analysis with multispectral imaging generates huge amounts of data for any single scene, but it is not obvious how relevant scene characteristics should be extracted. Here, we instead use a calibrated RGB camera with a 180° fish-‐eye lens. By taking many exposures from different locations in an environment, we can sample characteristic features of the environment.
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A large set of images is then used for extracting essential features such as the average luminance gradient, its variation and total span in 3-‐4 spectral bands. In five sectors along the vertical, we also characterise the luminance and colour contrast at high (1°) and low (10°) spatial frequencies. Initial trials reveal surprisingly consistent features for different natural and man-‐made environments.
Influence of luminosity on visual performance and color discrimination
Daniel Marques de Almeida Pessoa
Laboratory of Sensory Ecology | Federal University of Rio Grande do Norte | Brazil
The number of photoreceptor classes found in the retina usually correlate with the dimensionality of color vision. A greater number of photoreceptor types, exhibiting different spectral sensitivities, will allow a higher number of comparisons, improving color discrimination. Although the majority of mammal species studied to date have been diagnosed as carrying dichromacy, also found in human colorblindness, behavioral experiments have shown that monkeys with three types of cones show trichromacy, as do humans with normal color vision. However, several phenomena have been shown to influence human color perception in response to changes in light intensities, stimuli eccentricity and stimuli size. Indeed, psychophysical studies have shown that human monocromats and dichromats may improve color discrimination under lower light levels, and have established that rod-‐cone interaction can influence our color perception. Rod-‐cone interaction is apparently not restricted to humans and also has been described in non-‐human primates. Here I will discuss how luminosity might influence mammalian color discrimination, presenting data on feeding behavior of bats and primates.
Behavioural evidence of scotopic colour vision in amphibians
Carola Yovanovich & Almut Kelber
Vision Group | Lund University | Sweden
The existence of two different spectral kinds of rods in anurans has long ago raised the question of whether these animals could use them for seeing colour at night, even at light levels that are too low to allow for reliable cones signals and cone-‐based colour
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discrimination. However, no confirmation of this ability has been reported in behavioural tests with a proper control of achromatic cues. We are tackling this question by testing colour vision at photopic, mesopic and scotopic light levels using two European anurans as model species. We use a two-‐choice test, in which the animals are shown moving, prey-‐sized stimuli, one green and one blue in each trial; snapping at the green stimulus is rewarded with a real prey item. Several combinations of blue and green shades varying in intensities, contrasts and position are used to exclude achromatic cues and ensure that the choice is based solely on colour. I will discuss our findings regarding behavioural performance of frogs and toads, the relevance of chromatic and achromatic cues, the thresholds for colour discrimination and how to complement this study with other behavioural and morphological approaches to elucidate the relevance of nocturnal colour vision in amphibians.
Measuring the absolute sensitivity of frog color discrimination using phototactic behavior
Sanna Koskela, Noora Nevala & Kristian Donner
Division of Physiology and Neuroscience | University of Helsinki | Finland
Unlike most vertebrates, amphibians have two spectrally distinct classes of rods for night vision: the "red" rods with peak sensitivity at 500 nm and "green" rods with peak sensitivity at 430 nm. Thus, these animals are potential dichromats in dim light. We have set up a behavioral test based on innate phototactic behavior to investigate whether the common frog (Rana temporaria) can distinguish two spectrally different stimuli at low light levels.
When put in a dark container, frogs interpret a light cue as an opening through which to escape and will jump towards it (Aho et al. 1993). In the current experiment, a frog can jump towards one of four equal sectors in the ceiling of a container, two of which are dark, while each of the two others holds a homogeneously lit circular window. The two windows, ”blue” and “non-‐blue”, both stimulate the red rods equally, but only the “blue” window provides significant stimulation of the green rods. As reported in the literature (Hailman & Jaeger 1974), we have found that the frogs show a consistent preference for the blue light stimulus (“blue response”). This preference holds even at light levels close to the absolute visual threshold, thus demonstrating that green rods do support scotopic color discrimination. By lowering the general light intensity, we have determined the absolute threshold for "blue" discrimination, quantitatively expressed as a minimum ratio of photoisomerizations in green vs. red rods.
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References:
Aho, AC, Donner, K, Reuter, T (1993) Retinal origins of the temperature effect on absolute visual sensitivity in frogs. J Physiol, 463:501–521.
Hailman, JP, Jaeger, RG (1974) Phototactic responses to spectrally dominant stimuli and use of colour vision by adult anuran amphibians: A comparative survey. Anim Behav, 22:757–795.
Amphibian diversity and the evolution of diurnal habits
Julián Faivovich
Herpetology Division | Argentine Museum of Natural Sciences | Argentina
In this presentation I will briefly introduce the state of the art of our knowledge on amphibian phylogenetic relationships. This will serve as a historical framework to discuss the origin of diurnal habits and the evolution of a few character systems related to vision during the evolutionary history of amphibians.
Amphibian diversity and vision
Taran Grant
Zoology Department | Sao Paulo University | Brazil
For a very long time, amphibians were considered little more than a footnote in the grand history of tetrapod diversification, even by amphibian specialists. For example, in a technical paper on the clasping organs of amphibians, Moodie (1908: 257) summarized that “The Amphibia on the whole have played but a small part in the history of animal life on earth. They have never become the dominant type in any age as did the fishes, reptiles and mammals. They have always, so to speak, filled in the corners, left by their more aggressive contemporaries. Their chief interest lies in that they were the ancestors of the higher forms of life.” That view of amphibians as a primitive, transitional grade between aquatic fishes and fully terrestrial "higher vertebrates" fit nicely with the narrative of the Modern Synthesis, and even now many biologists continue to see amphibians in that light. For this reason, many fundamental questions that have been studied in detail in other tetrapods have been all but ignored in amphibians. However, over the past 50 years or so, it has
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become clear that amphibians are a diverse and unique evolutionary lineage of more than 7000 extant species characterized by evolutionary novelties that make them fascinating in their own right. The role vision played in amphibian evolution is poorly understood. In this talk, I will draw attention to some of the diverse, vision-‐related questions that can be studied in amphibians, focusing on their distribution, communication, predation, and development.
Differences in detectability and behaviour among dyeing poison frogs (Dendrobates tinctorius) bearing different colour patterns
Bibiana Rojas
Centre of Excellence in Biological Interactions | University of Jyväskylä | Finland
The enormous color pattern variation in some aposematic species is paradoxical because the stabilising selection exerted by predators is expected to favour one signal rather tan several, especially within the same population. The mechanisms maintaining such unexpected variation are still poorly understood, although it has been suggested that both non adaptive (e.g. gene flow, drift) as well as adaptive processes (i.e. a trade-‐off between natural and sexual selection, a link between fitness-‐related traits and phenotype, spatio-‐temporal variation in selection pressures) may have a relevant role. We tested whether polymorphic warning signals, such as those observed in the dyeing poison frog (Dendrobates tinctorius) could be maintained as a result of differences in detectability and behaviour among the morphs. In order to do this we followed frogs in the wild and studied their movement trajectories; and also exposed paraffin wax models bearing different colour patterns to wild predators in a tropical rainforest in French Guiana. Additionally, we examined how easy it was for ‘human predators’ to find frog models of different morphs in two different light environments (closed forest and forest gap). We found that real frogs with elongated patterns moved in one direction and at higher speeds than frogs with interrupted patterns, suggesting a possible dazzle effect. In the experiment with wax models, ‘cryptic’ models were attacked more often than those resembling aposematic frogs, but the two aposematic morphs tested did not different in the rate at which predators attacked them. However, the detectability of different aposematic morphs seemed to depend both on predator experience and light environment. We suggest that behavioural differences, as well as differences in detectability among the morphs in specific light environments, may provide novel explanations for the maintenance of within-‐population variation in warning signals.