Ultrastructural studies of the pecten oculi of the Garganey (Anas querquedula, Linnaeus 1758) and the Eurasian common moorhen (Gallinula chloropus chloropus, Linnaeus 1758)

Abstract

The present study represents the first attempts to give a full anatomical comparison of the vascular pigmented pectin oculi of the diurnal activity Anas querquedula and Gallinula chloropus chloropus. For achievement of this work, 10 mature birds from each species were examined under stereo‐ and electron microscope. The pecten oculi of A. querquedula is triangular fan‐like, while in Gallinula c. thin like‐fold. In both examined birds, the pecten oculi located postero‐anteriorly intraocular just adjacent to optic nerve disc and attached to the retina by its base, while the free apex projected into vitreous body. A. querquedula had 14–15 pleats, while Gallinula c. chloropus had 22–24 pleats. In A. querquedula, all pecten pleats connected to each other apically by a connecting bridge. The pecten oculi was plicated type in A. querquedula, but folded type in Gallinula c. chloropus. In A. querquedula, the external surface of the pleats head carried 8–10 transverse ridges, in addition to the external and lateral surface of the pleat body carried numerous round prominences that indicated the presence of numerous afferent and efferent vessels. In both examined birds, there is a retinal elevated fold situated parallel to the slightly elevated basal fold which is clear and thicker in A. querquedula than in Gallinula c. chloropus. In Gallinula c. chloropus, the transverse section shows that the pleats had numerous afferent and efferent vessels capillaries. Statistical analysis comparing the relative measurements of the pecten oculi in the two examined birds showed that there was a significant difference.

Pecten oculi of kestrel (Falco tinnunculus rupicolaeformes) and little owl (Athene noctua glaux): Scanning electron microscopy and histology with unique insights into SEM–EDX elemental analysis

“…Additionally, the pecteneal apex differs slightly between different species of birds. In this study, the free pecteneal apex was fused with one another, forming a free apical bridge that was directed towards the gelatinous vitreous body and ciliary body, similar to what was seen in a variety of diurnal birds, such as the migratory Garganey, budgerigar, black kite, chicken, white stork, Baladi ducks, common buzzard, seagulls, northern bald ibis, and migratory European wild quail (Abumandour et al, 2021;Abumandour et al, 2022;Alan et al, 2020;Gültiken et al, 2012;Ince et al, 2017;Kiama et al, 1994;Micali et al, 2012;Moselhy & El-Hady, 2019;Onuk, Tutuncu, et al, 2013;Puzzolo et al, 1985;Yilmaz et al, 2021), while the free pecteneal apex…”

“…These coiled surfaces provide a large surface area for efficient nutrient exchange between the blood capillaries and the retina; additionally, this specialized structure helps to maintain the health and functionality of the non-vascular retina by ensuring a constant supply of nutrients. Moreover, high SEM magnification showed that the pecteneal pleat's outer surface is covered by a thin smooth vitreopecteneal limiting membrane separating the pleat's outer surface from the gelatinous vitreous body, similar to that observed in many avian species (Abumandour et al, 2021;Abumandour et al, 2022;Elghoul et al, 2022;Kandyle et al, 2022;Uehara et al, 1996).…”

“…was not fused to one another and were separated in the meantime that was seen in some diurnal birds, including the migratory Eurasian moorhen and Glossy ibis (Abumandour et al, 2021;Kandyle et al, 2022). This unique fusion of the free pecteneal apexes creates a structural support system that enhances stability and provides a strong connection between the gelatinous vitreous body and ciliary body; additionally, this apical bridge may play a crucial role in maintaining the overall shape and integrity of the eye.…”

“…The visual (diurnal or nocturnal) active clock hours with the different feeding lifestyles were related to the morphological, ultrastructural appearance and composition of the intra‐ocular pecten oculi as they appeared in the diurnal avian species. These findings suggest that the pecten oculi may play a crucial role in facilitating visual activity and feeding behavior in diurnal avian species, such as the omnivorous birds like the Garganey, Eurasian moorhen, common loon, and duck (Abumandour et al, 2021; Braekevelt, 1986; Scala et al, 2002); the carnivorous birds like the great horned owl (Braekevelt, 1994; Kiama et al, 1994; Rahman et al, 2010), red‐tailed hawk (Braekevelt, 1991b), common buzzard (Gültiken et al, 2012), seagull (Ince et al, 2017), black kite (Kiama et al, 1994), stork (Onuk, Tutuncu, Alan, Kabak, & Gezer, 2013), and sparrow hawk (Rajab, 2012); and the herbivorous birds like the budgerigar, quail, emu, ostrich, and sparrow (Braekevelt, 1998; Elghoul et al, 2022; Micali et al, 2012; Orhan et al, 2011; Rajab, 2012). But nocturnal birds were represented mainly by carnivorous birds such as the nighthawk (Braekevelt, 1984), common barn owl (Yilmaz et al, 2017), barred owl (Smith et al, 1996), and yellow‐legged gulls (Segovia et al, 2020).…”

“…Similar observations were made of the fan‐like pecten oculi in the diurnal visual active carnivorous black kite (Kiama et al, 1994) and accordion‐like pecten oculi in the diurnal visual active carnivorous white stork (Onuk, Tutuncu, et al, 2013) and the diurnal visual active herbivorous turkey's native Gerze chicken (Alan et al, 2020). Moreover, there were other shapes of the pecten oculi in other different feeding habits of avian species, including the most famous quadrilateral pecten oculi shape in most diurnal visual active avian species of different feeding habits, such as the migratory omnivorous Eurasian moorhens and carnivorous Glossy ibis (Abumandour et al, 2021; Kandyle et al, 2022). However, the comb‐like pecten oculi was observed in diurnal omnivorous Baladi ducks (Moselhy & El‐Hady, 2019); the trapezoid‐like pecten oculi was observed in diurnal birds such as the migratory European wild quail, herbivorous quail, carnivorous jungle crow, and northern bald ibis (Abumandour et al, 2022; Pourlis, 2013; Rahman et al, 2010; Yilmaz et al, 2021); the shell‐like pecten oculi was observed in the herbivorous quail (Orhan et al, 2011); the snail‐like pecten oculi was observed in the seagull (Onuk, Tutuncue, et al, 2013); the folded pecten oculi was seen in the common ostrich (Elghoul et al, 2022).…”