Recent findings of sequence convergence in the Prestin gene among some bats and cetaceans suggest that parallel adaptations for high-frequency hearing have taken place during the evolution of echolocation. To determine if this gene is an exception, or instead similar processes have occurred in other hearing genes, we have examined Tmc1 and Pjvk, both of which are associated with non-syndromic hearing loss in mammals. These genes were amplified and sequenced from a number of mammalian species, including echolocating and non-echolocating bats and whales, and were analysed together with published sequences. Sections of both genes showed phylogenetic signals that conflicted with accepted species relationships, with coding regions uniting laryngeal echolocating bats in a monophyletic clade. Bayesian estimates of posterior probabilities of convergent and divergent substitutions provided more direct evidence of sequence convergence between the two groups of laryngeal echolocating bats as well as between echolocating bats and dolphins. We found strong evidence of positive selection acting on some echolocating bat species and echolocating cetaceans, contrasting with purifying selection on non-echolocating bats. Signatures of sequence convergence and molecular adaptation in two additional hearing genes suggest that the acquisition of high-frequency hearing has involved multiple loci.

Many sea urchins can detect light on their body surface and some species are reported to possess image-resolving vision. Here, we measure the spatial resolution of vision in the long-spined sea urchin , using two different visual responses: a taxis towards dark objects and an alarm response of spine-pointing towards looming stimuli. For the taxis response we used visual stimuli, which were isoluminant to the background, to discriminate spatial vision from phototaxis. Individual animals were placed in the centre of a cylindrical arena under bright down-welling light, with stimuli of varying angular width placed on the arena wall at alternating directions from the centre. We tracked the direction of movement of individual animals in relation to the stimuli to determine whether the animals oriented towards the stimulus. We found that responds by taxis towards isoluminant stimuli with a spatial resolution in the range of 29-69 deg. This corresponds to a theoretical acceptance angle of 38-89 deg, assuming a contrast threshold of 10%. The visual acuity of the alarm response of was tested by exposing animals to different sized dark looming and appearing stimuli on a monitor. We found that displays a spine-pointing response to appearing black circles of 13-25 deg angular width, corresponding to an acceptance angle of 60-116 deg, assuming the same contrast threshold as above.

Onychophorans, also known as velvet worms, possess a pair of simple lateral eyes, and are a key lineage with regard to the evolution of vision. They resemble ancient Cambrian forms, and are closely related to arthropods, which boast an unrivalled diversity of eye designs. Nonetheless, the visual capabilities of onychophorans have not been well explored. Here, we assessed the spatial resolution of the onychophoran using behavioural experiments, three-dimensional reconstruction, anatomical and optical examinations, and modelling. Exploiting their spontaneous attraction towards dark objects, we found that can resolve stimuli that have the same average luminance as the background. Depending on the assumed contrast sensitivity of the animals, we estimate the spatial resolution to be in the range 15-40 deg. This results from an arrangement where the cornea and lens project the image largely behind the retina. The peculiar ellipsoid shape of the eye in combination with the asymmetric position and tilted orientation of the lens may improve spatial resolution in the forward direction. Nonetheless, the unordered network of interdigitating photoreceptors, which fills the whole eye chamber, precludes high-acuity vision. Our findings suggest that adult specimens of cannot spot or visually identify prey or conspecifics beyond a few centimetres from the eye, but the coarse spatial resolution that the animals exhibited in our experiments is likely to be sufficient to find shelter and suitable microhabitats from further away. To our knowledge, this is the first evidence of resolving vision in an onychophoran.

Highlights d Ophiocoma wendtii orients to visual stimuli during the day, but not at night d O. pumila has a similar photoreceptor system but does not orient to visual stimuli d Both species express multiple opsins, including at least two r-opsins d Chromatophores screen photoreceptors in light-adapted O. wendtii, enabling vision

Hereditary deafness affects 0.1% of individuals globally and is considered as one of the most debilitating diseases of man. Despite recent advances, the molecular basis of normal auditory function is not fully understood and little is known about the contribution of single-nucleotide variations to the disease. Using crossspecies comparisons of 11 'deafness' genes (Myo15, Ush1 g, Strc, Tecta, Tectb, Otog, Col11a2, Gjb2, Cldn14, Kcnq4, Pou3f4) across 69 evolutionary and ecologically divergent mammals, we elucidated whether there was evidence for: (i) adaptive evolution acting on these genes across mammals with similar hearing capabilities; and, (ii) regions of long-term evolutionary conservation within which we predict disease-associated mutations should occur. We find evidence of adaptive evolution acting on the eutherian mammals in Myo15, Otog and Tecta. Examination of selection pressures in Tecta and Pou3f4 across a taxonomic sample that included a wide representation of auditory specialists, the bats, did not uncover any evidence for a role in echolocation. We generated 'conservation indices' based on selection estimates at nucleotide sites and found that known disease mutations fall within sites of high evolutionary conservation. We suggest that methods such as this, derived from estimates of evolutionary conservation using phylogenetically divergent taxa, will help to differentiate between deleterious and benign mutations.

A degree-of-polarization threshold for orientation behaviour is 15 reported for nocturnal dung beetle Escarabaeus satyrus in the context 16 of measurements showing changes in the degree of polarization of 17 skylight with lunar phase. 18 Abstract 19For polarized light to inform behaviour, the typical range of degrees of 20 polarization observable in the animal's natural environment must be 21 above the threshold for detection and interpretation. Here we present 22 the first investigation of the degree of linear polarization threshold for 23 orientation behaviour in a nocturnal species, with specific reference to 24 the range of degrees of polarization measured in the night sky. An 25 effect of lunar phase on the degree of polarization of skylight was 26 found, with smaller illuminated fractions of the moon's surface 27 corresponding to lower degrees of polarization in the night sky. We 28 found that South African dung beetle Escarabaeus satyrus 29 (Boheman, 1860) can orient to polarized light for a range of 30 degrees of polarization similar to that observed in diurnal insects, 31 reaching a lower threshold between 0.04 and 0.32, possibly as low as 32 2 0.11. For degrees of polarization lower than 0.23, as measured on a 33 crescent moon night, orientation performance was considerably 34 weaker than that observed for completely linearly-polarized stimuli, 35 but was nonetheless stronger than in the absence of polarized light. 36

How well can a bird discriminate between two red berries on a green background? The absolute threshold of colour discrimination is set by photoreceptor noise, but animals do not perform at this threshold; their performance can depend on additional factors. In humans and zebra finches, discrimination thresholds for colour stimuli depend on background colour, and thus the adaptive state of the visual system. We have tested how well chickens can discriminate shades of orange or green presented on orange or green backgrounds. Chickens discriminated slightly smaller colour differences between two stimuli presented on a similarly coloured background, compared to a background of very different colour. The slope of the psychometric function is steeper when stimulus and background colours are similar but shallower when they differ markedly, indicating that background colour affects the certainty with which the animals discriminate the colours. The effect we find for chickens is smaller than that shown for zebra finches. We modelled the response to stimuli using Bayesian and maximum likelihood estimation (MLE) and implemented the psychometric function to estimate the effect size. We found that the result is independent of the psychophysical method used to evaluate the effect of experimental conditions on choice performance.

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