Peak Density, Size and Regional Distribution of Ganglion Cells in the Retina of the Fur Seal <i>Callorhinus ursinus</i>

Abstract

The total number, size, topographic distribution and peak density of ganglion cells were studied in retinal wholemounts of the fur seal, Callorhinus ursinus. The cell distribution showed a distinct zone of high ganglion cell density. It was located in the temporal retinal quadrant, near the horizontal meridian, 10–12 mm (25–31°) from the optic disk. The peak cell density in this zone was 812–1332 cells/mm² (mean 1053 cells/mm²), i.e. 125–205 cells/deg² (mean 162 cells/deg²). These data predict a retinal resolution of 5.6.–7.1 cycle/deg. The ganglion cell soma size ranged from 10 to 50 µm. Cell size histograms were bimodal in shape with modes below and above 30 µn.

Ganglion Cell Distribution and Retinal Resolution in the Florida Manatee, Trichechus Manatus Latirostris

“…This estimate is comparable to the underwater visual acuity found in the behavioral investigation in Florida manatees Trichechus manatus latirostris (Bauer et al, 2003), which reported for one subject, in freshwater at 1-m distance, a minimum angle of resolution of 24 0 , and in saltwater, a best resolution of 21 0 (nb: a second subject was found to have a much poorer resolution of 56 0 ). The data indicate that the retinal resolution and visual acuity of the Florida manatee are markedly lower than that reported in whales and dolphins (9 0 -14 0 by Mass and Supin, 1995, 1999, 2002 and in pinnipeds (3 0 -8 0 by Mass and Supin, 1992, 2010Hanke et al, 2009). It is, however, slightly higher than that in the Amazon river dolphin (40 0 -45 0 by Mass and Supin, 1989).…”

“…Many cetaceans, such as the common dolphin Delphinus delphis (Dral, 1983), bottlenose dolphin Tursiops truncatus (Dral, 1977;Mass and Supin, 1995), harbor porpoise Phocoena phocoena (Mass and Supin, 1986), Chinese river dolphin Lipotes vexillifer (Gao and Zhou, 1987), gray whale Eschrichtius gibbosus ), Dall's porpoise, and Minke whale Balaenoptera acutorostrata (Murayama et al, 1992(Murayama et al, , 1995, have two spots of high cell density, one in the nasal and the other in the temporal retinal quadrants. In pinnipeds, a high cell density area occurs as either a discrete spot (the northern fur seal, Mass and Supin, 1992; the Weddel seal, Welsch et al, 2001) or a streak (the walrus, Mass, 1992) or a combination of both (the sea otter Enhydra lutris, Mass and Supin, 2000; the harbor seal, Hanke et al, 2009; the Caspian Seal, Mass and Supin, 2010). All these patterns are different from that found in the manatee.…”

Adaptive features of aquatic mammals' eye

“…Eye anatomy in pinnipeds, despite notable difference from cetaceans, has some common features reflecting adaptation to underwater vision (Fig. 3A,B) (Jamieson and Fisher, 1972;Mass, 1992;Mass and Supin, 1992. In particular, a characteristic feature is an almost spherical or slightly elliptical lens.…”

“…7A-D). In the northern fur seal (Callorhinus ursinus), ganglion cells are mostly of 14 to 28 mm with the largest cells up to 50 mm (Mass and Supin, 1992); in the Steller sea lion (Eumetopias jubatus), the majority of cells are 10 to 25 mm with some cells are as large as 37 mm (Mass and Supin, 2005); in the harp seal (Pagophilus groenlandicus), typical cells are 20 to 30 mm with some cells were as large as 60 mm (Nagy and Ronald, 1970;Mass and Supin, 2003). Giant ganglion cells were noticed also in the retina of the harbor seal (Phoca vitulina) (Jamieson and Fisher, 1971).…”

“…Those authors studied transverse retinal sections. Later topographic mapping of ganglion cells in retinal whole-mounts, however, revealed high-density areas in five pinniped species belonging to different families, including Odobenidae: the walrus (Odobenus rosmarus) (Mass, 1992), Otariidae: northern fur seal (Callorhinus ursinus) (Mass and Supin, 1992) and Steller sea lion (Eumetopias jubatus) (Mass and Supin, 2005), and Phocidae: harp seal (Pagophilus groenlandicus) (Mass and Supin, 2003) and Weddell seal (Leptonychotes weddellii) (Welsch et al, 2001). Figure 10 presents typical examples of high-and low-density areas in a whole-mount of the harp seal's retina (Mass and Supin, 2003).…”