title: Visual acuity trade-offs and microhabitat-driven adaptation of searching behaviour in psyllids (Hemiptera: Psylloidea: Aphalaridae).
abstract: Insects have evolved morphological and physiological adaptations in response to selection pressures inherent to their ecology. Consequently, visual performance and acuity often significantly vary between different insect species. Whilst psychophysics has allowed for the accurate determination of visual acuity for some Lepidoptera and Hymenoptera, very little is known about other insect taxa that cannot be trained to positively respond to a given stimulus. In this study, we demonstrate that prior knowledge of insect colour preferences can be used to facilitate acuity testing. We focused on four psyllid species (Hemiptera: Psylloidea: Aphalaridae), namely Ctenarytaina eucalypti, Ctenarytaina bipartita, Anoeconeossa bundoorensis and Glycaspis brimblecombei, that differ in their colour preferences and utilization of different host-plant modules (e.g. apical buds, stems, leaf lamellae) and tested their visual acuity in a modified Y-maze adapted to suit psyllid searching behaviour. Our study revealed that psyllids have visual acuity ranging from 6.3 to 8.7 deg. Morphological measurements for different species showed a close match between inter-ommatidial angles and behaviourally determined visual angles (between 5.5 and 6.6 deg) suggesting detection of colour stimuli at the single ommatidium level. Whilst our data support isometric scaling of psyllids' eyes for C. eucalypti, C. bipartita and G. brimblecombei, a morphological trade-off between light sensitivity and spatial resolution was found in A. bundoorensis. Overall, species whose microhabitat preferences require more movement between modules appear to possess superior visual acuity. The psyllid searching behaviours that we describe with the help of tracking software depict species-specific strategies that presumably evolved to optimize searching for food and oviposition sites.
authors.affiliation: Department of Ecology, Environment and Evolution, La Trobe University, Melbourne, VIC 3086, Australia kfarnier@students.latrobe.edu.au.
authors.forename: Kevin
authors.initials: K
authors.lastname: Farnier
authors.affiliation: School of Media and Communication, RMIT, Melbourne, VIC 3001, Australia.
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Dyer
authors.affiliation: Australian Centre for Evolutionary Biology and Biodiversity, School of Biological Sciences, University of Adelaide, Adelaide, SA 5005, Australia.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Taylor
authors.affiliation: Department of Ecology, Environment and Evolution, La Trobe University, Melbourne, VIC 3086, Australia.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Peters
authors.affiliation: Department of Ecology, Environment and Evolution, La Trobe University, Melbourne, VIC 3086, Australia.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Steinbauer
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001070:Appetitive Behavior; D017753:Ecosystem; D005260:Female; D006430:Hemiptera / Q000502:physiology*; D008297:Male; D035261:Plant Components, Aerial; D013045:Species Specificity; D014792:Visual Acuity
keywords: Eye parameter; Foliage; Inter-ommatidial angle; Visual angle