# The Geographical Variation of Colour Change in the Arabian Killifish (Aphaniops dispar Sensu Lato) From Freshwater and Marine Ecosystems

## TL;DR

This study explores how the Arabian killifish changes color in different environments, finding that marine populations are more adaptable than freshwater ones.

## Contribution

The study provides new insights into geographical variation in color change across multiple populations of a single species.

## Key findings

- All populations darkened similarly on black backgrounds, but lightening was less effective, especially in one freshwater population.
- Marine populations showed greater chromatic color change responses compared to freshwater populations.
- Environmental and evolutionary factors may explain differences in color change abilities among populations.

## Abstract

Widely distributed animals may exhibit substantial plastic physiological, morphological and behavioural responses to environmental changes. One such extraordinary form of plasticity is colour change, which varies substantially among most taxonomic groups. Most studies on colour change have focused on a single population, which has left a gap in our knowledge of colour change variation between populations. Examining colour change variation across populations of a taxon can shed light on how it evolves. Colour plasticity is influenced by spatial and temporal contextual variables, including visual habitat heterogeneity, predator diversity and their interaction. Using the Arabian killifish (Aphaniops dispar sensu lato) as a model, we examined the geographical variation of colour change in two freshwater and two marine populations from the west of Saudi Arabia, separated by vicariant and distance barriers and that differed in habitat visual characteristics and potentially in predator diversity. We used digital photography and visual modelling to investigate the ability of individuals in each of the populations to change colour when presented with achromatic (black and white) and chromatic (beige, brown and green) backgrounds. When presented with a black background, we found that individuals in all populations were capable of becoming darker at varying rates, but in a similar manner. Becoming lighter was more challenging, with individuals from all populations changing less on white than on black backgrounds and with one freshwater population exhibiting almost no response. However, there were complex interpopulation differences in chromatic responses, with marine populations exhibiting generally greater responses to the given backgrounds than freshwater populations. Here, we discuss the evolutionary and ecological factors possibly underlying these variations and their repercussions.

Animals that live in a wide range of environments possess plastic traits such as colour change, but most research has only looked at this within single populations. In this study, we tested four populations of the Arabian killifish from marine and freshwater ecosystems, examining how well they change colour against different backgrounds. The study found differences in the ability to change colour between populations, with marine populations generally showing more colour‐changing responses than freshwater ones; the study highlights how environmental and evolutionary pressures may shape colour change among populations.