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Photoreceptor types and distributions in the retinae of insectivores

Published online by Cambridge University Press:  09 April 2001

LEO PEICHL
Affiliation:
Max-Planck-Institut für Hirnforschung, Deutschordenstr. 46, D-60528 Frankfurt a. M., Germany
HEINZ KÜNZLE
Affiliation:
Anatomische Anstalt der Universität München, Pettenkoferstr. 11, D-80336 München, Germany
PETER VOGEL
Affiliation:
Institut d'Écologie, Bâtiment de Biologie, Université de Lausanne, CH-1015 Lausanne, Switzerland

Abstract

The retinae of insectivores have been rarely studied, and their photoreceptor arrangements and expression patterns of visual pigments are largely unknown. We have determined the presence and distribution of cones in three species of shrews (common shrew Sorex araneus, greater white-toothed shrew Crocidura russula, dark forest shrew Crocidura poensis; Soricidae) and in the lesser hedgehog tenrec Echinops telfairi (Tenrecidae). Spectral cone types were identified and quantified in flattened whole retinae by antisera/antibodies recognizing the middle-to-long-wavelength-sensitive (M/L-)cone opsin and the short-wavelength-sensitive (S-)cone opsin, respectively. A combination of immunocytochemistry with conventional histology was used to assess rod densities and cone/rod ratios. In all four species the rods dominate at densities of about 230,000–260,000/mm2. M/L- and S-cones are present, comprising between 2% of the photoreceptors in the nocturnal Echinops telfairi and 13% in Sorex araneus that has equal diurnal and nocturnal activity phases. This suggests dichromatic color vision like in many other mammals. A striking feature in all four species are dramatically higher S-cone proportions in ventral than in dorsal retina (0.5% vs. 2.5–12% in Sorex, 5–15% vs. 30–45% in Crocidura poensis, 3–12% vs. 20–50% in Crocidura russula, 10–30% vs. 40–70% in Echinops). The functional and comparative aspects of these structural findings are discussed.

Type
Research Article
Copyright
2000 Cambridge University Press

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