Tuebingen, January 24, 2014. Guppies have been popular among aquarium hobbyists for a long time due to their beautiful colours. These diversely coloured fish have also attracted the attention of biologists from the Max Planck Institute for Developmental Biology in Tübingen, Germany, and the Bioscience and Biotechnology Centre of Nagoya University in Japan. In their recent scientific work, the team around the Ph.D. student Verena Kottler, Professor Christine Dreyer and Professor Detlef Weigel focussed on the structure of the colourful pattern of male guppies. The Journal PLOS One is publishing the scientific article on Wednesday.
While guppy females are camouflaged by an inconspicuous reticulate pattern, guppy males are highly colourful, displaying iridescent, orange, and black spots and stripes. Many studies have investigated the animals’ behaviour and interactions with their environment. Previous studies found that guppy females prefer males with high amounts of orange and iridescent pigments.
Verena Kottler and her team asked how different pigment cell types are organised within the male ornaments, which makes it possible to further understand the genetics that underlies these colours. “We know a lot about the behaviour and ecology of the guppy, but the underlying genetic factors haven’t been investigated much so far,” states Kottler. The research team investigated the pigment cell distribution within the spots and fins of male wild-type guppies from three genetically divergent strains called Cumaná, Quare6, and Maculatus. Cumaná guppies are derived from a wild population in Venezuela. Quare6 guppies are descendants of fish from the Quare River on Trinidad, and Maculatus guppies have been bred in captivity by researchers and hobby breeders. The scientists focused on the central orange and central black spots near the gonopodium, as these two spots are present in all three strains despite their considerably different male ornaments.
The research team identified three different pigment cell types in the skin of male guppies and their experiments revealed that at least two of the three types of pigment cells contribute to each of the investigated ornamental traits. This suggests that complex interactions between different pigment cell types are necessary to form the ornamental pattern of guppy males. Also, the study demonstrated that two layers of pigment cell types, one in the dermis and the other in the hypodermis, are responsible for the colour pattern of the fish. Notably, the researchers found that the pigment cell distribution within the central orange and black spots of Cumaná, Quare6, and Maculatus males are very similar, despite Cumaná and Quare6 guppies being derived from geographically distant populations that may have been separated for almost a million years. This suggests that the pigment cell distribution within these spots is indeed conserved within the guppy and might be controlled by conserved genetic factors.