Data collection

All offspring of inbred and control males were photographed on both sides at 14 weeks. At this age male colour patterns had developed. Males were photographed at the same age as coloration continues to develop through time (Endler, 1987). Fhotography was done under standard lighting conditions with a

Kodak 18% reflectance grey background. Each guppy was placed in a small plastic spectrophotometer cuvette which had optically clear sides. Anaesthetic was not used as it alters colour patterns (Reynolds et al. 1993, Endler 1978). Each fish was confined for a maximum o f thirty seconds before release, and all fish were removed fi'om their tanks for the same total amount o f time to

standardise the effect of stress on the appearance o f pigments (which are partially under voluntary control). Some melanic areas can be maximised for display and minimised when threatened, or on a pale background - (personal observation; Brooks & Caithness 1995b) and can vary dramatically over a time scale of minutes (Baerends et a l 1955). Being confined and photographed is a relatively stressful experience and all males would show their minimum melanic area. Therefore the time taken with this procedure was standardised for all fish.

These images were transferred to a Macintosh computer using a black and white CCD camera. Lengths and areas were measured using NIH Image. The resolution power of this system was limited by the pixel dimension o f the screen (average fish dimensions 547x210 pixels). Boundaries o f colour areas were visible on the captured black and white images. Where contrast was poor the boundaries were pinpointed using the original colour photograph.

Several morphological characters and secondary sexual characters were measured in each male guppy. Morphological characters measured were (Fig. 2.1): total length, body length, maximum depth, total area (including the tail fin), body area (excluding the tail fin), dorsal fin area, caudal fin area and gonopodial length. One paired morphological trait was measured, the length o f ten dorsal scales (on left and right sides). The measurement o f male colour pattern was broken down into pigment groups: carotenoid (orange), melanin (black) and iridescent (purple, green, yellow, blue and silver). The total area o f the pigment groups on each side o f the body was estimated. The boundaries between different iridescent colours were too faint to allow each colour area to be measured

visible from both sides and thus can not be considered as paired characters. In addition, fins (especially tails) were not always fully spread in photographs (c.f. Reynolds et al. 1993) as is typical o f non-displaying males. Besides, previous results have shown that tail colours yield similar results to body colours (Reynolds et a l 1993). Every measurement was done twice to estimate

measurement error. In addition the number and position of spots on each body side was recorded. Spot position was measured by the distance from the x.y centre o f the spot area to both the tip of the nose and vertically to the top o f the fish. A group of older males (photographed at >5 months) were measured in the same way.

More primitive colour analysis was employed for earlier experiments (see chapters 5 and 6). A grid composed of 1mm square units was used to measure body area and pigment areas for males used in the preliminary trials on display and female choice.

2.7 References

Baerends, G.P., Brouwer, R. & Waterbolk, H.T. 1955. Ethological studies on

Lebistes reticulatus (Peters). Behaviour 8:249-334.

Brooks, R. & Caithness, N. 1995b. Manipulating a seemingly non-preferred male ornament reveals a role in female choice. Proc. R. Soc. Lond. B., 261, 7-10.

Endler, J.A. 1978. A predator’s view of animal colour patterns. Evol. Biol. 11: 319-364.

Endler, J.A. 1983. Natural and sexual selection on colour patterns in poeciliid fishes. Environ. Biol. Fish 9: 173-190.

Endler, J.A. 1987. Predation, light intensity and courtship behaviour in Poecilia reticulata (Pisces:Poecilidae). Anim. Behav., 35,1376-1385.

Endler, J.A. 1991. Variation in the appearance of guppy color patterns to guppies and their predators under different visual conditions. Vision. Res. 31(3): 587-608.

Fajen, A. and Breden, F. 1992. Mitochondrial DNA sequence variation among natural populations of the Trinidad guppy, Poecilia reticulata. Evolution, 46, 1457-1465.

Gilliam, J.F., Fraser, D.F. & Alkins-Koo, M.A. 1993. Structure o f a tropical stream fish community: a role for biotic interactions. Ecology 74 (6): 1856-1870.

Houde, A. E. 1988a. Genetic difference in female choice between two guppy populations. Anim. Behav., 36, 510-516.

Houde, A. E. 1988b. The effects o f female choice and male-male competition on the mating success of male guppies. Anim. Behav., 36, 888-896.

Houde, A. E. 1992. Sex-linked heritability o f a sexually selected character in a natural population o f Poecilia reticulata (Pisces: Poecilidae) (guppies). Heredity, 69, 229-235.

Houde, A. E. and Endler, J. A. 1990. Correlated evolution o f female mating preferences and male colour patterns in the guppy Poecilia reticulata. Science, 248, 1405-1408.

Kodric-Brown, A. 1989. Dietary carotenoids and male mating success in the guppy: an environmental component to female choice. Behav. Ecol. Sociobiol., 25,393-401.

Liley, N.R. & Seghers, B.H. 1975. Factors affecting the morphology and behaviour of guppies in Trinidad. In: Function and evolution in behaviour. Eds Baerends, Beer & Manning. Clarendon Press, Oxford. Pp 92-118.

Magurran, A.E. & Seghers, B.H. 1990. Risk sensitive courtship in the guppy {Poecilia reticulata). Behaviour 112: 194-201.

Magurran, A.E. & Seghers, B.H. 1991. Variation in schooling and aggression amongst guppy {Poecilia reticulata) populations in Trinidad. Behaviour 118: 214-234.

Nicoletto, P. F. 1995. Offspring quality and female choice in the guppy, Poecilia reticulata. Anim. Behav., 49, 377-387.

Reynolds, J. D., Gross, M. R., and Coombs, M. J. 1993. Environmental conditions and male morphology determine alternative mating behaviour in Trinidadian guppies. Anim. Behav., 45, 145-152.

Rosen & Bailey 1963 Rosen, D.E. & Bailey, R.M. 1963. The poeciliid fishes (Cyprinodontiformes), their structure, zoogeography, and systematics. Bull. Amer. Mus. Nat. Hist. 126, 5-176.

Seghers, B.H. 1974. Schooling behaviour in the guppy {Poecilia reticulata)’, an evolutionary response to predation. Evolution 28: 486-489.

S ta n d ard m o rp h o lo g ical m easu rem en ts o f a m ale guppy

dorsal fin area 10 dorsal scales m ax im um d e p th b ody area g o n o po d i u m length standard length t o t a l length