Apistogramma cacatuoides : typical adult wild male without any red markings on the unpaired fi ns, collected in the vicinity of Iquitós, Peru. 

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... Neotropical cichlid Apistogramma cacatuoides Hoedeman, 1951 is a highly polychromatic species. The species’ range is basically restricted to the River Ucayali basin in the northern half of Cis-Andean Peru and neighbouring Brazil, downriver to the Amazon drainage near Tefé ( Kullander , 1986; Römer , 2000, 2006). In the laboratory wild fi sh of different origins as well as domestic strains of variable colour are available. Hohl (2010a & b) presents background data on the origin of various aquarium-hobby colour morphs of A. cacatuoides . In mate-choice experiments wild-caught females from the río Algodón (150 km to the north of Iquitos) prefer inconspicuous males of their own morph with high statistical con fi dence instead of conspicuous males of a red-coloured aquarium strain (Römer & Beisenherz, 2005). This contradicts the widespread assump- tion of a general preference for mates with exagger- ated traits as signals ( Darwin, 1871; Bischoff et al ., 1985; Bradbury & Andersson, 1987; Andersson, 1994; Houde, 1997). On the other hand, phylogenetic studies of different animal taxa indicate that secondary sexual characteristics can be lost due to environmental, social, and random factors (reviewed by Wiens, 2001). Hence mate-choice preference for conspicuous traits in different fi sh species may decrease ( Forsgren, 1992; Endler & Houde , 1995; Godin & Briggs, 1996), reverse ( Johnson & Basolo, 2003), or even disap- pear ( Kingston et al ., 2003) so that mating happens at random (Berglund, 1993; Breden & Stoner, 1987) and thus deviate from theoretical expectations. The availability of wild specimens of different origin and coloration as well as of domestic strains of- fers an opportunity to monitor the way in which female A. cacatuoides choose their mates. The importance of colour in communication within and between the sexes of Apistogramma species has been demonstrated by Römer (2000) and Rodrigues et al . (2009). Beisenherz & Römer (2005) provide data supporting the in fl uence of colour in inter- and intraspeci fi c mate choice. Ready et al . (2006) examined the speci fi c status of allopatric Apistogramma populations with a similar habitus but differences in coloration. Allopatric populations may practise assortative mating by colour and thus may have to be seen as different distinct biological species ( Ready et al ., 2006). We will test on A. cacatuoides whether a preference for inconspicuously-coloured males con fi rms this general concept or is simply a matter of geographical variation. The dwarf cichlid Apistogramma cacatuoides was used for our standardised dichotomous mate-choice experiments. A detailed description of the cichlid genus Apistogramma and the investigated species A. cacatuoides has been given elsewhere ( Kullander, 1980; Römer, 2000, 2006). Females and males of A. cacatuoides are sexually dimorphic and dichromatic. Adult males are signi fi cantly larger than females. Additionally they have longer lappets in the dorsal fi n and a lyrate caudal fi n (Fig. 1). Courting and breeding female Apistogramma show a yellowish body with contrasting black markings (Fig. 2). The diagrams show the correlation between female preference for red-coloured males (red) and the propor- tion of wild males with red-coloured ornamentation on the caudal fi n. A. cacatuoides prefer richly structured areas with scattered driftwood and branches and a thick leaf layer where they can hide and establish their breeding territories (see Römer , 2000). Females of most Apistogramma species attach their eggs to the up- per interior surface of cave-like shelters and perform most of the brood care (for further information see Römer , 2000). In experiments for intraspeci fi c mate choice, wild- caught males and their fi rst and second generation (F 1 , F 2 ) descendants from random spawns with wild-caught females were tested against males from a red-coloured aquarium strain ( fi g. 3). Males of this captive strain are much more colourful than wild males and exhibit large red or yellow dots or speckles on their dorsal and caudal fi ns (Fig. in Römer , 2000, p. 118). We used wild-stock A. cacatuoides from different importations and locations, obtained by commercial collectors from four different collecting sites. Wild stock I originated from the río Algodón (150 km to the north of Iquitos) (Römer & Beisenherz, 2005). Two further wild stocks were collected near Iquitos: wild stock II de- rived from the río Itaya 20 km northwest of Iquitos, and wild stock III from the río Nanay 3.6 km south -west of Iquitos; specimens of wild stock IV were captured in small tributaries of the río Huallaga about 500 km west of Iquitos. All fi sh were kept in the laboratory in water with matching parameters. Temperature, pH, and water hard ness were measured electronically. The water was puri fi ed by fi ltration and regular weekly water changes. All fi sh were fed ad libitum with Artemia nauplii . In mate-choice experiments females of A. cacatuoides were offered two males as potential reproductive partners in experimental tanks (60 × 30 × 30 cm) which were divided into three unequal subunits by two separating glass dividers siliconed in at the left- and right-hand ends (compare Beisenherz et al ., 2006; Römer & Beisenherz , 2005). Any in fl uence of scent on fi sh behaviour during the experiments could thus be excluded. Our experimental set-ups also excluded acoustic information to a certain extent, as permanent external and internal noise was generated by air blow- ers and bubbling water. We therefore postulate that acoustic information, which may be of importance in mate choice in cichlid fi shes ( Slabbekoorn et al ., 2010), probably had no decisive in fl uence on the experimental results. One female was placed in the larger, central compartment of each aquarium (27 litres, 30 × 30 × 30 cm), and a male in each of the smaller lateral compartments (13.5 litres, 15 × 30 × 30 cm). Two plastic canisters (the type used for photographic fi lms, without lid) 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. To exclude habituation or general preference by females for a particular end of a tank during the experiments, males of wild stocks and the domestic strain were randomly placed into the left- or right-hand compartments of the experimental tanks. To exclude size preferences (here taken as total length) as a choice- modifying factor, only males of similar size were offered to a female. Females were randomly placed in the larger, central compartments of the experimental aquaria at least one day after males had been placed in the smaller lateral compartments. Displaying males were visible to females in the adjacent tank compartments. Females chose a male by spawning with him; this provides irrefutable evidence of their mate-choice behaviour (for detailed description see Beisenherz & Römer ( 2006)). During the experiments all but two females laid their eggs in one of the “caves” next to the glass pane close to one of the displaying males. Therefore a choice was considered made as soon as a female had spawned close to one of the available males. The two exceptions split their clutches between the two caves adjacent to each of the available males. After spawning, females were transferred from the experimental tanks to other aquaria where they were kept for several days before being retested with different males. 67 females of wild stock I, 44 of wild stock II, 34 of wild stock III, and 13 of wild stock IV were tested in mate-choice experiments. The females chose between males of their own population and males of the red aquarium strain. In addition, 74 females of the red aquarium strain were tested using males of their own strain and wild stock I. Differences in preferences between wild-stock and aquarium-stock females, as well as between the wild populations, were tested using Chi-Square and Fisher ́s exact tests. ...