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Color is a phenotypic trait of utmost importance, particularly in birds, which are known for their diverse color signals and color-producing mechanisms including pigment-based colors, light scattering from nanostructured feather tissues and combinations thereof. Bright iridescent plumage colors of hummingbirds are caused by light scattering by an organized array of flattened, pigment organelles, containing air-filled vesicles, called melanosomes. These hollow platelets are organized in multilayer arrays that contain numerous sharp air/melanin refractive index interfaces, producing brilliant iridescent colors. Despite their ecological significance and potential for inspiration of new optical materials, how platelets form and spatially arrange in nanostructures in growing feathers remains unknown. Here, we tested the hypothesis that melanosome formation and organization occurs mostly through passive self-assembly processes by assembling a developmental time series of growing hummingbird feathers using optical and electron microscopy. We show that hummingbird platelets contain air bubbles or vesicles upon their formation in pigment-producing cells, melanocytes. When melanosomes are transferred to neighboring keratinocytes (the cells shaping barbule structure) they drastically expand in size; and variation in this enlargement appears to be driven by physical constraints caused by the placement of the melanosomes within the barbule plate and their proximity to other melanosomes. As the barbule elongates and narrows, polymerizing feather corneous beta-protein orients melanosomes unilaterally, forcing them into a stacked configuration. These results reveal potentially novel forces driving the self-assembly of the nanostructures producing some of the brightest colors in nature.

Jellies are typically considered difficult organisms to raise in the lab by many scientists. This is due to their requirements for constant water current and the absence of corners. In the wild, jellies such as moon jellies (Aurelia aurita) rarely encounter habitats outside of the open ocean where they are part of the plankton, so they are not adapted to navigate obstacles or get out of small spaces such as the corners of aquaria. In order to conduct an experiment utilizing live moon jellies to assess their utility in bioremediation of oil spills, we designed and built 4 pseudo-kreisel aquaria to house our jellies using a limited budget and many readily-available materials. Here, we present the methods used to construct these aquaria inexpensively (important for undergraduate research!) and evidence of their effectiveness in long-term housing of live jellies so that other researchers interested in jelly research can construct similar housing. Briefly, we removed the corners from 10 gallon aquaria and also provided for continuous circular water currents by adding quarter pieces of the sides of 5 gallon buckets attached via silicon sealant. Current was provided by spray bars that provided even water flow in all areas of the aquaria, driven by pumps in the external sump and filtration systems. We built the sump/filtration systems using 5-gallon buckets containing bio-balls and filter floss. Water was delivered to the sumps via PVC overflow plumbed into the aquaria via a bulkhead set into the glass at the desired water level. The overflows were covered with a small piece of fine screen and directly behind the spray bars in order to prevent jellies from becoming stuck as water leaves the system for filtration. Results of husbandry including survival and indicators of jelly health such as pulsing rate and holes in their bells over approximately 3 months will be presented.

Since the discovery of red fluorescence in fish, much effort has been invested to elucidate its potential functions, one of them being signaling. This implies that the combination of red fluorescence and reflection should generate a visible contrast against the background. Here, we present in vivo iris radiance measurements of Tripterygion delaisi under natural light conditions at 5 and 20 m depth. We also measured substrate radiance of shaded and exposed foraging sites at those depths. To assess the visual contrast of the red iris against these substrates, we used the receptor noise model for chromatic contrasts and Michelson contrast for achromatic calculations. At 20 m depth, T. delaisi iris radiance generated strong achromatic contrasts against substrate radiance, regardless of exposure, and despite substrate fluorescence. Given that downwelling light above 600 nm is negligible at this depth, we can attribute this effect to iris fluorescence. Contrasts were weaker in 5 m. Yet, the pooled radiance caused by red reflection and fluorescence still exceeded substrate radiance for all substrates under shaded conditions and all but Jania rubens and Padina pavonia under exposed conditions. Due to the negative effects of anesthesia on iris fluorescence, these estimates are conservative. We conclude that the requirements to create visual brightness contrasts are fulfilled for a wide range of conditions in the natural environment of T. delaisi.

Active sensing using light, or active photolocation, is only known from deep sea and nocturnal fish with chemiluminescent ‘search’ lights. Bright irides in diurnal fish species have recently been proposed as a potential analogue. Here, we contribute to this discussion by testing whether iris radiance is actively modulated. The focus is on behaviourally controlled iris reflections, called ‘ocular sparks’. The triplefin Tripterygion delaisi can alternate between red and blue ocular sparks, allowing us to test the prediction that spark frequency and hue depend on background hue and prey presence. In a first experiment, we found that blue ocular sparks were significantly more often ‘on’ against red backgrounds, and red ocular sparks against blue backgrounds, particularly when copepods were present. A second experiment tested whether hungry fish showed more ocular sparks, which was not the case. However, background hue once more resulted in a significant differential use of ocular sparks. We conclude that iris radiance through ocular sparks in T. delaisi is not a side effect of eye movement, but adaptively modulated in response to the context under which prey are detected. We discuss the possible alternative functions of ocular sparks, including an as yet speculative role in active photolocation.

Since the discovery of red fluorescence in fish, much effort has been made to elucidate its potential contribution to vision. However, whatever that function might be, it always implies that the combination of red fluorescence and reflectance of the red iris is sufficient to generate a visual contrast. Here, we presentin vivoiris radiance measurements ofT. delaisiunder natural light fields at 5 and 20 m depth. We also took substrate radiance measurements of shaded and exposed foraging sites at those depths. To assess the visual contrast that can be generated by the red iris, we then calculated iris brightness in the 600-650 nm “red” waveband relative to substrate radiance. At 20 m depth,T. delaisiiris radiance substantially exceeded substrate radiance in the red waveband, regardless of exposure, and despite substrate fluorescence. Given that downwelling light in the 600-650 nm range is negligible at this depth, we can attribute this effect to iris fluorescence. As expected, contrasts were much weaker in 5 m – despite the added contribution of iris reflectance, but we identified specific substrates and conditions under which the pooled radiance caused by red reflectance and fluorescence still exceeded substrate radiance in the same waveband. Due to the negative effect of anesthesia on iris fluorescence these estimates are conservative. We conclude that the requirements to create visual brightness contrasts are fulfilled for a wide range of conditions in the natural environment ofT. delaisi.

Since the discovery of red fluorescence in fish, much effort has been invested to elucidate its potential functions, one of them being signaling. This implies that the combination of red fluorescence and reflection should generate a visible contrast against the background. Here, we present in vivo iris radiance measurements of Tripterygion delaisi under natural light conditions at 5 and 20 m depth. We also measured substrate radiance of shaded and exposed foraging sites at those depths. To assess the visual contrast of the red iris against these substrates, we used the receptor noise model for chromatic contrasts and Michelson contrast for achromatic calculations. At 20 m depth, T. delaisi iris radiance generated strong achromatic contrasts against substrate radiance, regardless of exposure, and despite substrate fluorescence. Given that downwelling light above 600 nm is negligible at this depth, we can attribute this effect to iris fluorescence. Contrasts were weaker in 5 m. Yet, the pooled radiance caused by red reflection and fluorescence still exceeded substrate radiance for all substrates under shaded conditions and all but Jania rubens and Padina pavonia under exposed conditions. Due to the negative effects of anesthesia on iris fluorescence, these estimates are conservative. We conclude that the requirements to create visual brightness contrasts are fulfilled for a wide range of conditions in the natural environment of T. delaisi.