Assays to Detect UV-reflecting Structures and Determine their Importance in Mate Preference using the Sailfin Molly Poecilia latipinna

Summary

This protocol outlines the use of spectrophotometry to detect ultraviolet-reflecting structures on organisms (in this example, the sailfin molly Poecilia latipinna) and describes dichotomous choice tests for fish that allow inferences to be made on the role of ultraviolet cues during mate selection.

Abstract

Many organisms use cues and signals beyond human sensitivity during social interactions. It is important to take into account how organisms perceive their worlds when trying to understand their behavior and ecology. Sensitivity to the ultraviolet spectrum (UV; 300 - 400 nm) is found across multiple genera of birds, fish, reptiles, amphibians, and even mammals. This protocol describes a technique for examining organisms for the presence of UV-reflecting structures and a method for testing whether these cues are used as social signals in the context of mate choice. A spectrophotometer is used to detect the presence of UV reflectance and variation in reflective intensity between individuals and sexes. An example of this technique is presented in which a dichotomous mate choice test exposes sexually receptive individuals to opposite sex individuals whose visual appearance can be manipulated by filters that either transmit full spectrum or block UV wavelengths. This system allowed for the determination that female, but not male, sailfin mollies (Poecilia latipinna) were using UV markings as part of their mating decisions. These types of studies serve to expand our knowledge of the range of organisms that utilize UV and provide insight into how UV plays a role in their lives.

Introduction

Understanding the cues and signals used in animal social interactions allows us to comprehend the phenotypic variation both within and among species. This variation plays an important role in evolutionary processes such as population divergence, sexual selection, and speciation. Often, however, researchers are limited to exploring the cues most obvious to human sensory systems, especially those within the visual or auditory realms. Use of spectrophotometry, however, allows us to expand our investigations beyond the human visible spectrum and into wavelengths that may be important in social interactions in other species.

In particular, the s....

Protocol

All experiments were conducted with the approval of Ohio Wesleyan University's Institutional Animal Care and Use Committee.

1. Recording UV Reflectance of Fish using a Spectrophotometer

1. Calibrate a spectrophotometer and light source with a known white standard over the range of wavelengths to be measured according the recommendations of the instrument or software.
2. Anesthetize fish by placing in a 0.5% solution of ethyl 3-aminobenzoate methane sulfonic acid salt (MS-222) buffered with an equal quantity of sodium bicarbonate until fish becomes unresponsive. Once unresponsive, immediately place the fish on a black, non-reflective background. ....

Results

Figures 1 and 2 show the mating preference aquarium set up and UV measurement sites for our experiments.

Measuring UV reflectance allowed for the determination that P. latipinna do possess UV characteristics, especially along the sides of their bodies (Figure 3), in addition to individual variation in these traits. Once UV traits were found, testing revealed that female.......

Discussion

Spectrophotometry was successful in identifying UV markings on P. latipinna. Both sexes of P. latipinna possess UV markings along their sides. In addition, some males had UV markings on their dorsal fins, traits previously found to be important in female mating preferences⁷.

We recommend using UV spectrophotometry as a mechanism to detect the presence of UV markings. Further testing could determine its role in social interactions, including mating preference (as de.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Spectrophotometer, P1000	Ocean Optics		newer models are availabe
DT 1000 xenon UV light source	Ocean Optics		newer models are availabe
Ocean Optics Overture Software	Ocean Optics		newer software is available
R200-Angle-UV bifurcated fiber-optic probe (Guided Wave)	Ocean Optics		newer models are availabe
Certified reflectance standard, white	labsphere
75.7 L Aquarium, divided	Experimental Builder
Full Spectrum Bulb	Nature's Sunlight
UV blocking sheet	GAM UV Sheet