Number and distribution of neurons in the retinal ganglion cell layer in relation to foraging behaviors of tyrant flycatchers

Abstract

The tyrant flycatchers represent a monophyletic radiation of predominantly insectivorous passerine birds that exhibit a plethora of stereotyped prey capture techniques. However, little is known about their retinal organization. Using retinal wholemounts, we estimated the total number and topography of neurons in the ganglion cell layer in the generalist yellow-bellied elaenia (Elaenia flavogaster) and the up-hover-gleaner mouse-colored tyrannulet (Phaeomyias murina) with the optical fractionator method. The mean estimated total number of neurons in the ganglion cell layer was 4,152,416 +/- 189,310 in E. flavogaster and 2,965,132 +/- 354,359 in P. murina. Topographic maps of isocounting lines revealed a similar distribution for both species: a central fovea and a temporal area surrounded by a poorly defined horizontal streak. In addition, both species had increased numbers of giant ganglion cells in the dorsotemporal retina forming an area giganto cellularis. In E. flavogaster, these giant ganglion cells were also distributed across the nasal and ventral retinal peripheries, which is in agreement with the generalist habits of this species. However, in P. murina these cells were rarely seen along the nasal and ventral peripheries, possibly reflecting a lesser need to perceive movement because this species captures stationary insects resting on foliage. Thus, we suggest that the retinas of the tyrant flycatchers in the present study show a general common pattern of neuron distribution in the ganglion cell layer irrespective of their foraging habits. We also suggest that the distribution of giant ganglion cells is indicative of the visual requirements of the species.

Spatial resolving power and spectral sensitivity of the saltwater crocodile, Crocodylus porosus, and the freshwater crocodile, Crocodylus johnstoni

“…The optical fractionator probe (West et al, 1991) modified for the retina (Coimbra et al, 2009) was used to sample the retinal ganglion cell layer with a ×60 NA 1.35 oil immersion lens. Briefly, a counting grid was superimposed on the digitised outline of the retina, giving a sampling location for each grid point within the outline.…”

“…The shape and position of retinal regions of high ganglion cell density have been correlated with the visual environment and lifestyle of many animal groups, including reptiles, birds and mammals (Hughes, 1977;Barbour et al, 2002;Coimbra et al, 2009). Both saltwater and freshwater crocodiles spend a significant proportion of their time waiting for the right time to ambush prey in a 'minimum exposure' posture with only the eyes and nostrils protruding above the water's surface.…”

Disruptive colouration in reef fish: does matching the background reduce predation risk?

“…Retinas from each fish were extracted and fixed in 4% paraformaldehyde immediately using standard methods (Coimbra et al, 2012;Coimbra et al, 2009;Ullmann et al, 2012). For optimal photoreceptor viewing and counting, all retinas required bleaching to remove the densely pigmented retinal pigment epithelium (RPE) that covered large parts of the retina.…”

“…Photoreceptors were counted using the Optical Fractionator workflow within the software StereoInvestigator (v11.03; MBF Bioscience) following standard methods to count retinal cells in whole-mounted fish retinas (Coimbra et al, 2012;Coimbra et al, 2009;de Busserolles et al, 2014b). Topographical maps were produced using a script in R developed in previously published work, with the Gaussian Kernel Smoother method that utilises Spatstat (Baddeley and Turner, 2004;Garza-Gisholt et al, 2014).…”

Morphology, Characterization and Distribution of Retinal Photoreceptors in the South American (Lepidosiren paradoxa) and Spotted African (Protopterus dolloi) Lungfishes

“…The topographic distribution of the oil droplet containing photoreceptor in P. dolloi was assessed using the modified optical fractionator technique detailed in Coimbra et al (2009). Using StereoInvestigator software (Microbrightfield Inc., USA) on a Windows 7 PC connected to a compound microscope (Olympus BX50) equipped with a motorized stage (MAC200, Ludle Electronic Products, USA) and digital video camera (MicroFIRE, OPTRONICS), the outline of the retinal wholemount was digitized using a x4 objective (NA 0.13).…”