Mäthger Lydia M.

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Mäthger
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Lydia M.
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  • Article
    Pupil dilation and constriction in the skate Leucoraja erinacea in a simulated natural light field
    (The Company of Biologists, 2022-02-14) Mäthger, Lydia M. ; Bok, Michael J. ; Liebich, Jan ; Sicius, Lucia ; Nilsson, Dan-Eric
    The skate Leucoraja erinacea has an elaborately shaped pupil, whose characteristics and functions have received little attention. The goal of our study was to investigate the pupil response in relation to natural ambient light intensities. First, we took a recently developed sensory–ecological approach, which gave us a tool for creating a controlled light environment for behavioural work: during a field survey, we collected a series of calibrated natural habitat images from the perspective of the skates' eyes. From these images, we derived a vertical illumination profile using custom-written software for quantification of the environmental light field (ELF). After collecting and analysing these natural light field data, we created an illumination set-up in the laboratory, which closely simulated the natural vertical light gradient that skates experience in the wild and tested the light responsiveness – in particular the extent of dilation – of the skate pupil to controlled changes in this simulated light field. Additionally, we measured pupillary dilation and constriction speeds. Our results confirm that the skate pupil changes from nearly circular under low light to a series of small triangular apertures under bright light. A linear regression analysis showed a trend towards smaller skates having a smaller dynamic range of pupil area (dilation versus constriction ratio around 4-fold), and larger skates showing larger ranges (around 10- to 20-fold). Dilation took longer than constriction (between 30 and 45 min for dilation; less than 20 min for constriction), and there was considerable individual variation in dilation/constriction time. We discuss our findings in terms of the visual ecology of L. erinacea and consider the importance of accurately simulating natural light fields in the laboratory.
  • Article
    Elaborate pupils in skates may help camouflage the eye
    (Company of Biologists, 2019-01-21) Youn, Sean ; Okinaka, Corey ; Mäthger, Lydia M.
    The skate Leucoraja erinacea is a bottom-dweller that buries into the substrate with its eyes protruding, revealing elaborately shaped pupils. It has been suggested that such pupil shapes may camouflage the eye, yet this has never been tested. Here, we asked whether skate pupils dilate or constrict depending on background spatial frequency. In experiment 1, the skates' pupillary response to three artificial checkerboards of different spatial frequencies was recorded. Results showed that pupils did not change in response to spatial frequency. In experiment 2, in which skates buried into three natural substrates of different spatial frequencies, such that their eyes protruded, pupils showed a subtle but statistically significant response to changes in substrate spatial frequency. Although light intensity is the primary factor determining pupil dilation, our results show that pupils also change depending on the spatial frequency of natural substrates, which suggests that pupils may aid in camouflaging the eye.