PROTEIN FINGERPRINTING: A NEW TECHNIQUE REVEALS EXTENSIVE CONSPECIFIC BROOD PARASITISM

Abstract

Conspecific brood parasitism occurs in many birds and some insects, fishes, and amphibians. Here, we develop and test a novel molecular technique for ecological analysis, protein fingerprinting (PF), based on isoelectric focusing electrophoresis (IEF) in immobilized pH gradients. It is applied here to albumen from birds' eggs and permits accurate identification of eggs laid by different females. This technique greatly clarifies female alternative reproductive tactics and laying patterns in brood-parasitic Common Goldeneye ducks Bucephala clangula. A small, nondestructive sample of albumen is taken through a hole drilled through the eggshell, which is then sealed with superglue, preserving egg hatchability. IEF yields a rich pattern of albumen bands with extensive variation among females. Observation and video recording of egg-laying by 21 color-marked females showed that they had unique band patterns, which were fully repeatable within and between years. Brood parasitism occurred in two-thirds (13 of 19) of the video-recorded nests of color-ringed females, with up to five parasitic females per nest. Of 234 eggs, 36% were laid by females other than the incubating host. These results suggest that intraspecific brood parasitism is more common and important than suggested by earlier studies using traditional methods. Protein fingerprinting yields individual resolution similar to that of a DNA multilocus fingerprinting probe, and has several advantages. The albumen band pattern represents only the laying female, not her mate(s), making it easy to determine the maternity of eggs, and to identify a parasite that spreads her eggs among a number of nests. Albumen can be sampled as soon as the egg is laid, before predation or other losses occur, maximizing sample size and minimizing bias. Protein fingerprinting is relatively inexpensive and easy. It is also useful for several purposes other than maternity determination, such as relatedness estimation for categories of individuals.