title: Retinal temporal resolution and contrast sensitivity in the parasitic lampreyMordacia mordaxand its non-parasitic derivativeMordacia praecox.
abstract: Lampreys and hagfishes are the sole extant representatives of the early agnathan (jawless) vertebrates. We compared retinal function of fully metamorphosed, immatureMordacia mordax(which are about to commence parasitic feeding) with those of sexually mature individuals of its non-parasitic derivativeMpraecoxWe focused on elucidating the retinal adaptations to dim-light environments in these nocturnally active lampreys, using electroretinography to determine the temporal resolution (flicker fusion frequency, FFF) and temporal contrast sensitivity of enucleated eyecups at different temperatures and light intensities. FFF was significantly affected by temperature and light intensity. Critical flicker fusion frequency (cFFF, the highest FFF recorded) ofM. praecoxandM. mordaxincreased from 15.1 and 21.8 Hz at 9°C to 31.1 and 36.9 Hz at 24°C, respectively. Contrast sensitivity of both species increased by an order of magnitude between 9 and 24°C, but remained comparatively constant across all light intensities. Although FFF values forMordaciaspp. are relatively low, retinal responses showed a particularly high contrast sensitivity of 625 inM. praecoxand 710 inM. mordaxat 24°C. This suggests selective pressures favour low temporal resolution and high contrast sensitivity in both species, thereby enhancing the capture of photons and increasing sensitivity in their light-limited environments. FFF indicated all retinal photoreceptors exhibit the same temporal response. Although the slow response kinetics (i.e. low FFF) and saturation of the response at bright light intensities characterise the photoreceptors of both species as rod-like, it is unusual for such a photoreceptor to be functional under scotopic and photopic conditions.
authors.affiliation: School of Biological Sciences (M092), The University of Western Australia, Crawley, WA 6009, Australia rachaelwarrington@hotmail.com.|UWA Oceans Institute, The University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Rachael E
authors.identifier: 0000-0002-3871-5197
authors.initials: RE
authors.lastname: Warrington
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Hart
authors.affiliation: Centre for Fish, Fisheries and Aquatic Ecosystems Research, School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA 6150, Australia.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Potter
authors.affiliation: School of Biological Sciences (M092), The University of Western Australia, Crawley, WA 6009, Australia.|UWA Oceans Institute, The University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Collin
authors.affiliation: School of Biological Sciences (M092), The University of Western Australia, Crawley, WA 6009, Australia.|UWA Oceans Institute, The University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Jan M
authors.initials: JM
authors.lastname: Hemmi
mesh_terms: D000818:Animals; D015350:Contrast Sensitivity; D005260:Female; D005425:Flicker Fusion; D007798:Lampreys / Q000502:physiology*; D008027:Light; D012160:Retina / Q000502:physiology; D014785:Vision, Ocular
keywords: Dim-light vision; Electroretinography; Flicker fusion frequency; Retinal adaptations