LOSS OF NUPTIAL COLOR IN THREESPINE STICKLEBACKS (GASTEROSTEUS ACULEATUS)

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Conspicuous nuptial coloration in Gasterosteus aculeatus (threespine stickleback) has been observed to decrease in western North America.
• This color loss is often attributed to increased predation or convergent threat displays.

Purpose of the Study:

• To investigate the variation in red nuptial color expression across 66 populations of threespine stickleback in the Queen Charlotte Archipelago.
• To test hypotheses linking nuptial-color loss to predation rates and water spectral properties.

Main Methods:

• Examined 66 populations of Gasterosteus aculeatus for red nuptial color expression.
• Assessed the correlation between color loss and the presence of vertebrate predators.
• Analyzed the relationship between nuptial-color expression and water spectral properties, specifically relative transmission at 400 nm.

Main Results:

• Extensive variation in red nuptial color was found; 31 populations lacked red throats, while five showed major red expression.
• No correlation was observed between nuptial-color loss and the presence or absence of vertebrate predators.
• Greatest red pigment expression occurred in clear water habitats, while color loss was prevalent in stained waters, supporting the water spectra hypothesis.

Conclusions:

• Water spectral properties, particularly water clarity and spectral composition, are strongly associated with the loss of red nuptial color in threespine sticklebacks.
• Predation rates do not appear to be a primary driver of nuptial-color loss in the studied populations.
• New hypotheses suggest signal-masking in spectrally restricted habitats and dietary carotenoid deficiencies may explain the observed patterns.