Automated Charting of the Visual Space of Housefly Compound Eyes

Summary

The protocol here describes the measurement of the spatial organization of the visual axes of housefly eyes, mapped by an automatic device, using the pseudopupil phenomenon and the pupil mechanism of the photoreceptor cells.

Abstract

This paper describes the automatic measurement of the spatial organization of the visual axes of insect compound eyes, which consist of several thousands of visual units called ommatidia. Each ommatidium samples the optical information from a small solid angle, with an approximate Gaussian-distributed sensitivity (half-width on the order of 1˚) centered around a visual axis. Together, the ommatidia gather the visual information from a nearly panoramic field of view. The spatial distribution of the visual axes thus determines the eye's spatial resolution. Knowledge of the optical organization of a compound eye and its visual acuity is crucial for quantitative studies of neural processing of the visual information. Here we present an automated procedure for mapping a compound eye's visual axes, using an intrinsic, in vivo optical phenomenon, the pseudopupil, and the pupil mechanism of the photoreceptor cells. We outline the optomechanical setup for scanning insect eyes and use experimental results obtained from a housefly, Musca domestica, to illustrate the steps in the measurement procedure.

Introduction

The compactness of insect visual systems and the agility of their owners, demonstrating highly developed visual information processing, have intrigued people from both scientific and non-scientific backgrounds. Insect compound eyes have been recognized as powerful optical devices enabling acute and versatile visual capacities^1,2. Flies, for instance, are well-known for their fast responses to moving objects, and bees are famous for possessing color vision and polarization vision².

The compound eyes of arthropods consist of numerous anatomically similar units,....

Protocol

The protocol is in accordance with the University's insect care guidelines.

1. Preparation of a housefly,  Musca domestica

1. Collect the fly from the laboratory-reared population. Place the fly in the brass holder (Figure 1).
   1. Cut 6 mm from the upper part of the restraining tube (see Table of Materials). The new upper part of the tube has an external diameter of 4 mm and an internal diameter of 2.5 mm (Figure 1A). Place the live fly inside the tube, seal the tube with cotton to prevent damaging the fly, a....

Results

Animals and optical stimulation
Experiments are performed on houseflies (Musca domestica) obtained from a culture maintained by the Department of Evolutionary Genetics at the University of Groningen. Before the measurements, a fly is immobilized by gluing it with a low-melting-point wax in a well-fitting tube. The fly is subsequently mounted on the stage of a motorized goniometer. The center of the two rotary stages coincides with the focal point of a microscopic setup²⁴

Discussion

The spatial distribution of the visual axes of housefly eyes can be charted using the pseudopupil phenomenon of compound eyes and the reflection changes caused by the light-dependent pupil mechanism. Therefore, an investigated fly is mounted in a goniometric system, which allows inspection of the local facet pattern with a microscope setup equipped with a digital camera, all under computer control. Image analysis yields eye maps. An essential difficulty encountered is that without careful positioning of the eye at the be.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Digital Camera	PointGrey	BFLY-U3-23S6C-C	Acquision of amplified images and digital communication with PC
High power star LED	Velleman	LH3WW	Light source for observation and imaging the compound eye
Holder for the investigated fly	University of Groningen		Different designs were manufactured by the university workshop
Linear motor	ELERO	ELERO Junior 1, version C	Actuates the upper microscope up and down. (Load 300N, Stroke speed 15mm/s, nominal current 1.2A)
Low temperature melting wax	various		The low-temperature melting point wax serves to immobilize the fly and fix it to the holder
Microscope	Zeiss		Any alternative microscope brand will do; the preferred objective is a 5x
Motor and LED Controller	University of Groningen	Z-o1	Designed and built by the University of Groningen and based on Arduino and Adafruit technologies.
Motorized Stage	Standa (Vilnius, Lithuania)	8MT175-50XYZ-8MR191-28	A 6 axis motorized stage modified to have 5 degrees of freedom.
Optical components	LINUS		Several diagrams and lenses forming an epi-illumination system (see Stavenga, Journal of Experimental Biology 205, 1077-1085, 2002)
PC running MATLAB	University of Groningen		The PC is able to process the images of the PointGrey camera, control the LED intensity, and send control commants to the motor cotrollers of the system
Power Supply (36V, 3.34A)	Standa (Vilnius, Lithuania)	PUP120-17	Dedicated power supply for the STANDA motor controllers
Soldering iron	various		Used for melting the wax
Stepper and DC Motor Controller	Standa (Vilnius, Lithuania)	8SMC4-USB-B9-B9	Dedicated controllers for the STANDA motorized stage capable of communicating with MATLAB
Finntip-61	Finnpipette Ky, Helsinki	FINNTIP-61, 200-1000μL	PIPETTE TIPS FOR FINNPIPETTES, 400/BOX. It is used to restrain the fly
Carving Pen Shaping/Thread Burning Tool	Max Wax		The tip of the carving pen is designed to transfer wax to the head of fly
MATLAB	Mathworks, Natick, MA, USA	main program plus Image Acquisition, Image Analysis, and Instrument Control toolboxes.	Programming language used to implement the algorithms