Newly discovered retinal structure may enhance vision for some birds

December 17, 2019

A newly discovered retinal structure in the eyes of certain kinds of songbirds might help the animals find and track insect prey more easily.

The foundation of avian vision rests on cells called cone and rod photoreceptors. Most birds have four cone photoreceptors for color vision, a fifth cone for non-color-related tasks, and a rod for night vision. Each cone photoreceptor cell contains a spherical structure called an "oil droplet," which filters light before it is converted to electrical signals by the visual pigments, enhancing color discrimination.

However, the researchers have discovered a never-before-seen type of cone structure in the retina of a group of small songbirds, called flycatchers. Instead of an oil droplet, it contains a high- energy-producing cellular structure called "megamitochondria" surrounded by hundreds of small, orange-colored droplets. The researchers named this novel cellular structure a megamitochondria-small oil droplet complex, or MMOD-complex.

The discovery, made at Purdue University, is detailed in a paper that appeared in the journal Scientific Reports, as part of a collaboration with the State University of New York at Plattsburgh, the University of Wisconsin-Madison, and the University of California, Davis.

The researchers studied this retinal structure using light microscopy, transmission electron microscopy and a technique called microspectrophotometry, which measures the wavelengths of light that these structures absorb the most. The MMOD-complex works as long-pass filters, letting light with wavelengths longer the 565 nanometers - or yellow, orange and red - pass through, and absorbing the shorter wavelengths of green, blue and violet.

Traditional cones were present throughout the retina of these flycatchers, and their density decreased moving away from the center toward the periphery. However, the MMOD-complex photoreceptors were present only in the central region of the retina, an arrangement that could help birds detect flying insects, said Esteban Fernandez-Juricic, a professor of biological sciences at Purdue.

"The retina of flycatchers, which are sit-and-wait predatory birds, evolved a novel cellular structure in a photoreceptor that may allow them to detect, track and capture fast-moving prey, like insects," he said.

The paper's lead author was Luke Tyrrell, a former Purdue doctoral student and now an assistant professor of biological science at SUNY Plattsburgh.

"This new cone organelle has not been reported before in this form in any other vertebrate retina and may allow these birds to see their world in a different way from other animals," Tyrrell said.

A complete listing of the paper's authors is available in the abstract, and the paper is available online here. The research was funded by the National Science Foundation. Future research will be aimed at establishing the function of this structure and assess the ability of flycatchers to catch prey under different ambient light conditions.
-end-
ABSTRACT

A novel cellular structure in the retina of insectivorous birds

Luke P. Tyrrell1*, Leandro B. C. Teixeira2, Richard R. Dubielzig2, Diana pita3, Patrice Baumhardt3, Bret A. Moore4 & Esteban Fernández-Juricic3

1SUNY Plattsburgh, Department of Biological Sciences, 101 Broad Street, Plattsburgh, NY, 12901, USA. 2University of Wisconsin-Madison, Department of Pathobiological Sciences, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI, 53706, USA. 3Purdue University, Department of Biological Sciences, 915 W State Street, West Lafayette, IN, 47904, USA. 4University of California-Davis, William R. Pritchard Veterinary Teaching Hospital, School of Veterinary Medicine, 1 Garrod Drive, Davis, CA, 95695, USA. *email: ltyrr002@plattsburgh.edu

The keen visual systems of birds have been relatively well-studied. the foundations of avian vision rest on their cone and rod photoreceptors. Most birds use four cone photoreceptor types for color vision, a fifth cone for achromatic tasks, and a rod for dim-light vision. The cones, along with their oil droplets, and rods are conserved across birds - with the exception of a few shifts in spectral sensitivity - despite taxonomic, behavioral and ecological differences. Here, however, we describe a novel photoreceptor organelle in a group of New World flycatchers (Empidonax spp.) in which the traditional oil droplet is replaced with a complex of electron-dense megamitochondria surrounded by hundreds of small, orange oil droplets. the photoreceptors with this organelle were unevenly distributed across the retina, being present in the central region (including in the fovea), but absent from the retinal periphery and the area temporalis of these insectivorous birds. of the many bird species with their photoreceptors characterized, only the two flycatchers described here (E. virescens and E. minimus) possess this unusual retinal structure. We discuss the potential functional significance of this unique sub-cellular structure, which might provide an additional visual channel for these small predatory songbirds.

Note to Journalists: The paper is available online at https://www.nature.com/articles/s41598-019-51774-w or by contacting Steve Tally at 765-494-9809, steve@purdue.edu.

Purdue University

Related Songbirds Articles from Brightsurf:

Songbirds reduce reproduction to help survive drought
New research from the University of Montana suggests tropical songbirds in both the Old and New Worlds reduce reproduction during severe droughts, and this - somewhat surprisingly -- may actually increase their survival rates.

Male songbirds can't survive on good looks alone, says a new study
Brightly colored male songbirds not only have to attract the female's eye, but also make sure their sperm can last the distance, according to new research.

Understanding why songbirds choose their homes
New research by University of Alberta biologists uses a new approach to modelling the populations of six species of songbirds in Canada's boreal forest -- and the results show that standard modeling methods may not be accurately capturing species distribution patterns.

Daddy daycare: Why some songbirds care for the wrong kids
Interspecific feeding -- when an adult of one species feeds the young of another -- is rare among songbirds, and scientists could only speculate on why it occurs, but now, Penn State researchers have new insight into this behavior.

Neonicotinoid insecticides cause rapid weight loss and travel delays in migrating songbirds
Songbirds exposed to imidacloprid, a widely used neonicotinoid insecticide, exhibit anorexic behavior, reduced body weight and delays in their migratory itinerary, according to a new study.

International scientists shed new light on demise of two extinct New Zealand songbirds
They may not have been seen for the past 50 and 110 years, but an international study into their extinction has provided answers to how the world lost New Zealand's South Island kokako and huia.

Scent brings all the songbirds to the yard
Lehigh University scientists found that not only can chickadees smell, but the males and females prefer the smell of their own species over the smell of the opposite species.

Scientists identify brain region that enables young songbirds to change their tune
In a scientific first, Columbia scientists have demonstrated how the brains of young songbirds become tuned to the songs they learn while growing up.

The case of the poisoned songbirds
Researchers from the California Department of Fish and Wildlife's Wildlife Investigations Laboratory present their results from a toxicological investigation into a mortality event involving songbirds in a new publication in Environmental Toxicology and Chemistry.

Baby tiger sharks eat songbirds
Tiger sharks have a reputation for being the 'garbage cans of the sea' -- they'll eat just about anything, from dolphins and sea turtles to rubber tires.

Read More: Songbirds News and Songbirds Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.