Retinal ganglion cell topography and spatial resolving power in African megachiropterans: Influence of roosting microhabitat and foraging.
Megachiropteran bats (megabats) show remarkable diversity in microhabitat occupation and trophic specializations, but information on how vision relates to their behavioral ecology is scarce. Using stereology and retinal wholemounts, we measured the topographic distribution of retinal ganglion cells and determined the spatial resolution of eight African megachiropterans with distinct roosting and feeding ecologies. We found that species roosting in open microhabitats have a pronounced streak of high retinal ganglion cell density, whereas those favoring more enclosed microhabitats have a less pronounced streak (or its absence in Hypsignathus monstrosus). An exception is the cave-dwelling Rousettus aegyptiacus, which has a pronounced horizontal streak that potentially correlates with its occurrence in more open environments during foraging. In all species, we found a temporal area with maximum retinal ganglion cell density (∼5,000-7,000 cells/mm2) that affords enhanced resolution in the frontal visual field. Our estimates of spatial resolution based on peak retinal ganglion cell density and eye size (∼6-12 mm in axial length) range between ∼2 and 4 cycles/degree. Species that occur in more enclosed microhabitats and feed on plant material have lower spatial resolution (∼2 cycles/degree) compared with those that roost in open and semiopen areas (∼3-3.8 cycles/degree). We suggest that the larger eye and concomitant higher spatial resolution (∼4 cycles/degree) in H. monstrosus may have facilitated the carnivorous aspect of its diet. In conclusion, variations in the topographic organization and magnitude of retinal ganglion density reflect the specific ecological needs to detect food/predators and the structural complexity of the environments. J. Comp. Neurol. 525:186-203, 2017. © 2016 Wiley Periodicals, Inc.
School of Anatomical Sciences, University of the Witwatersrand, Parktown, 2193, Johannesburg, South Africa.|The Oceans Institute, The University of Western Australia, Crawley, Western Australia, 6009, Australia.|School of Animal Biology, The University of Western Australia, Crawley, Western Australia, 6009, Australia.
João Paulo
JP
Coimbra
Queensland Brain Institute, The University of Queensland, Santa Lucia, Queensland, 4072, Australia.
John D
JD
Pettigrew
Faculty of Sciences, University of Kisangani, B.P. 1232, Kisangani, Democratic Republic of the Congo.
Consolate
C
Kaswera-Kyamakya
Faculty of Sciences, University of Kisangani, B.P. 1232, Kisangani, Democratic Republic of the Congo.|Department of African Zoology, Royal Museum for Central Africa, B-3080, Tervuren, Belgium.|Laboratory of Histology and Neuropathology, Free University of Brussells, B-1070, Brussels, Belgium.|Department of Anthropology, University of Arkansas, Fayetteville, Arkansas, 72701.
Emmanuel
E
Gilissen
The Oceans Institute, The University of Western Australia, Crawley, Western Australia, 6009, Australia.|School of Animal Biology, The University of Western Australia, Crawley, Western Australia, 6009, Australia.
Shaun P
SP
Collin
School of Anatomical Sciences, University of the Witwatersrand, Parktown, 2193, Johannesburg, South Africa.
Paul R
PR
Manger
D000349:Africa; D000818:Animals; D002452:Cell Count; D002685:Chiroptera / Q000033:anatomy & histology* / Q000502:physiology; D017753:Ecosystem; D005247:Feeding Behavior / Q000502:physiology; D009425:Nesting Behavior / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000502:physiology; D013045:Species Specificity; D014794:Visual Fields / Q000502:physiology
RRID: SciRes_000114; RRID: SciRes_000116; megabats; megachiropterans; retinal ganglion cells; retinal topography; spatial resolving power; stereology; visual ecology