Can the Dynamic Colouration and Patterning of Bluelined Goatfish (Mullidae; Upeneichthys lineatus) Be Perceived by Conspecifics?

Analysing biological colour patterns from digital images: An introduction to the current toolbox

Understanding the numerous roles that colouration serves in the natural world has remained a central focus in many evolutionary and ecological studies. However, to accurately characterise and then compare colours or patterns among individuals or species has been historically challenging. In recent years, there have been a myriad of new resources developed that allow researchers to characterise biological colours and patterns, specifically from digital imagery. However, each resource has its own strengths and weaknesses, answers a specific question and requires a detailed understanding of how it functions to be used properly. These nuances can make navigating this emerging field rather difficult. Herein, we evaluate several new techniques for analysing biological colouration, with a specific focus on digital images. First, we introduce fundamental background knowledge about light and perception to be considered when designing and implementing a study of colouration. We then show how numerous modifications can be made to images to ensure consistent formatting prior to analysis. After, we describe many of the new image analysis approaches and their respective functions, highlighting the type of research questions that they can address. We demonstrate how these various techniques can be brought together to examine novel research questions and test specific hypotheses. Finally, we outline potential future directions in colour pattern studies. Our goal is to provide a starting point and pathway for researchers wanting to study biological colour patterns from digital imagery.

A fish can change its stripes: investigating the role of body colour and pattern in the bluelined goatfish

Bluelined goatfish (Upeneichthys lineatus) rapidly change their body colour from a white horizontally banded pattern to a seemingly more conspicuous vertically banded red pattern, often when foraging. Given the apparent conspicuousness of the pattern to a range of observers, it seems unlikely that this colour change is used for camouflage and instead may be used for communication/signalling. Goatfish often drive multispecies associations, and it is possible that goatfish use this colour change as a foraging success signal to facilitate cooperation, increase food acquisition, and reduce predation risk through a 'safety in numbers' strategy. Using a novel approach, we deployed 3D model goatfish in different colour morphs-white without bands, white with black vertical bands, and white with red vertical bands-to determine whether the red colouration is an important component of the signal or if it is only the vertical banding pattern, regardless of colour, that fish respond to as an indicator of foraging success. Use of remote underwater video allowed us to obtain information without the influence of human observers on the communities and behaviours of other fish in response to these different colours exhibited by goatfish. We found that conspecifics were more abundant around the black- and red-banded model fish when compared with the white models. Conspecifics were also more likely to forage around the models than to pass or show attraction, but this was unaffected by model colour. No difference in the abundance and behaviour of associated heterospecifics around the different models was observed, perhaps due to the static nature of the models. Some species did, however, spend more time around the red- and black-banded fish, which suggests the change in colour may indicate benefits in addition to food resources. Overall, the results suggest that the body colour/pattern of U. lineatus is likely a signalling tool but further work is required to explore the benefits to both conspecifics and heterospecifics and to further determine the behavioural functions of rapid colour change in U. lineatus.

Dynamic colour change as a signalling tool in bluelined goatfish (Upeneicthtys lineatus)

Many animal species can rapidly change their body colouration and patterning, but often the ecological drivers of such changes are unknown. Here, we explored dynamic colour change in the bluelined goatfish, Upeneichthys lineatus, a temperate marine teleost species. Upeneichthus lineatus can change in a matter of seconds, from a uniform white colour to display prominent, vertical, dark red stripes. Initial observations suggested that rapid colour change in U. lineatus was associated with feeding and may act as a signal to both conspecifics and heterospecifics that are frequently observed to follow feeding goatfish. Field observations of the colour and behaviour of individual U. lineatus were collected to (1) document the repertoire of behaviours that U. lineatus displays and categorise associated colour patterns; (2) quantify the speed of dynamic colour change; (3) establish the context in which U. lineatus changes colour and pattern; and (4) test whether the behaviour of follower fishes is influenced by colour patterning or specific behaviours of the focal goatfish. We found that U. lineatus changed colouration from white to the red banded pattern in less than 10 s. The key driver of rapid colour change in U. lineatus was feeding, particularly when the fish fed with its head buried in sediment. Conspecific followers were most likely to be white in colour and adopt searching behaviour, regardless of the focal fish colour or behaviour. Other species of follower fish spent significantly more time following U. lineatus that were displaying dark red stripes when searching or eating, implying the red stripes may be an interspecific signalling mechanism. Our findings indicate that rapid colour change in teleost fish may be used for social communication and may provide U. lineatus with increased protection from predation when feeding via a safety-in-numbers approach.