Visual adaptation and retinal characterization of the Garganey (Anas querquedula): Histological and scanning electron microscope observations

Abstract

The present study was designed to provide a complete morphological description of the eye of the migratory Garganey duck (Anas querquedula) and its visual adaptation with the different surrounding environmental conditions during its migration journeys using a stereomicroscope, scanning electron microscope (SEM), and light microscope. The current work depends on six adult Garganey ducks that were captured from the area near and on the shores of Edku city. The obtained results revealed that the eye of the migratory Garganey duck has the features of both diurnal and nocturnal birds. The histological examination reveals that the pigmented epithelium of the retina has long prolongations filled with melanin. The cone is the dominant photoreceptor, but simple rods are present. The inner nuclear and ganglion cell layers are thick. SEM examination shows that the arrangement of the collagen fibrils on the external surface was reticular in shape. The radial folds present as pledged structures on the pigmented epithelium covered with circular structures. The main lens body has flat with hexagonal outlines fibers. The edges and surfaces of these hexagonal fibers were studded with protrusions or elevations (balls) and depressions (sockets). The sockets and balls were either rounded or ellipsoid in shape. The balls were more on the edges and the sockets on the surface. In conclusion, our findings indicated a higher degree of functional adaptation between the morphological structure of the eye and the surrounding environmental conditions.

Gross, ultrastructural, and histological characterizations of pecten oculi of the glossy ibis (Plegadis falcinellus): New insights into its scanning electron microscope–energy dispersive X‐ray analysis

“…Most anatomical researchers have focused their attention in recent decades on the anatomical features of the eye, particularly its retina, and its adaptations to aid the occurrence of vital functions such as feeding, reproduction, and lifestyle, which are primarily dependent on environmental conditions (Bassuoni et al, 2021). However, recently, most anatomical researchers began focusing on investigating the pecten oculi due to its participation in a most important function in the avian visual system and its relation to the feeding and migratory style, such as; the reduction of the intra‐ocular glow, adjustment of the intraocular pressure and optic fluid, blood‐barrier, the retina vascular nutritional supply, light absorption, avian's directions assurance, eye warming in the cold condition, and the stabilization of the vitreous body (Rodriguez‐Peralta, 1968; Seaman & Himelfarb, 1963).…”

“…The anatomical adaptation of the eye to different ecological statuses has long been a mystery to anatomical researchers (El‐Bakary & Abumandour, 2017; Nur et al, 2019), especially for the avian eye (Bassuoni et al, 2021). Functionally, the eye participates in the performance of multiple critical operations such as escaping from predatory birds or animals, searching for satisfactory feeding particles, and reproduction (Aboelnour et al, 2020).…”

“…Functionally, the eye participates in the performance of multiple critical operations such as escaping from predatory birds or animals, searching for satisfactory feeding particles, and reproduction (Aboelnour et al, 2020). The ophthalmic researchers concentrated fundamentally on describing the microscopic characteristics of the eye layers, particularly the retinal layer, and its modifications with the changeable ecological statuses to acclimate to the various essential operations such as the feeding mechanism, get‐away from the predatory species, migration mechanism, and reproduction (Bassuoni et al, 2021; El‐Bakary & Abumandour, 2017).…”

Ultrastructural characterizations of the pecten oculi of the common ostrich (Struthio camelus): New insight to scanning electron microscope–energy dispersive X‐ray analysis

“…Various microscopic studies were depicting the avian eye and its adaptation to environmental conditions such as; flying, feeding, and breeding behavior (Bassuoni, Abumandour, El‐Mansi, & Hanafy, 2021). The pecten oculi is described as an intra‐ocular structure that presents just in the avian eye which extended from the retina toward the lens close to the optic nerve entrance (Abumandour, Bassuoni, & Hanafy, 2021; Alan, Onuk, Alan, & Kabak, 2020; Ince, Onuk, Kabak, Alan, & Kabak, 2017; Smith, Smith, & Braekevelt, 1996).…”

“…The pecten oculi is not observed in any vertebrate species aside from the avian (Abumandour et al, 2021; Bassuoni et al, 2021; El‐Bakary & Abumandour, 2017; Ince et al, 2017; Yilmaz et al, 2017; Yilmaz et al, 2021). The primary endeavor to depict the anatomical features of the pecten oculi was happened by Sillman (1973).…”