Just as in humans, beauty is in the eye of the beholder for female Cockatoo dwarf cichlids (Apistogramma cacatuoides).
A study by German scientists published in the most recent issue of the journal Vertebrate Zoology has found that females in different populations of the fish vary in their preferences for red colour in males.
Bernd Engelking, Uwe Römer and Wolfgang Beisenherz carried out a series of mate choice experiments in which female Cockatoo dwarf cichlids were offered two males as potential mates in experimental tanks.
The authors tested wild-caught males and their first- and second-generation descendants from random spawns with wild-caught females against males from a red-coloured aquarium strain.
The wild-caught fish used in the experiments came from four different collecting sites in Peru: (1) from the río Algodón (150 km north of Iquitos); (2) from the río Itaya 20 km northwest of Iquitos; (3) from the río Nanay 3.6 km southwest of Iquitos, and (4) from the small tributaries of the río Huallaga about 500 km west of Iquitos.
The authors unequally divided the experimental tanks into three using transparent partitions (one large central and two smaller lateral compartments), placing one male in each lateral compartment and one female in the central compartment. Two plastic canisters were placed in the female’s section of each experimental tank to act as caves, one close to each of the lateral compartments housing the males.
The authors recorded in which of the plastic "caves" the females had laid eggs, this serving as irrefutable evidence of mate choice.
The authors found that wild females preferred red-coloured males from 3–69% of the time, depending on the geographic origin of the females, and that the aquarium-strain females preferred their own bright-coloured males about 90% of the time. The females from the río Agodón were the least impressed by red colour, choosing their own drabber males 97% of the time, whereas those from the río Huallaga were the most impressed and chose their own drabber males only 31% of the time.
These results suggest that different strains and populations of the Cockatoo dwarf cichlid have different preferences for male colour. The authors demonstrate a clear geographical gradient in the distribution of males with coloured fin ornamentation and the strong preference of females for different forms of the males among the different populations may indicate the beginning of speciation within the Cockatoo dwarf cichlid.
For more information, see the paper: Engelking, B, U Römer and W Beisenherz (2010) Intraspecific colour preference in mate choice by female Apistogramma cacatuoides Hoedeman, 1951 (Teleostei: Perciformes: Cichlidae). Vertebrate Zoology 60, pp. 199–208.