Discussion 2: Interconnectedness of Life Discussion

BSC 1005: Color Variation in Guppies (Poecilia reticulata)

What selection pressure causes the variation in color pattern of male guppies?

Introduction. Guppies ( Poecilia reticulata) exhibit a complex color pattern polymorphism, in which males display a variety of colors and color patterns (Endler 1980). Guppies are native to the mountain forest streams of northeastern Venezuela, Margarita, Trinidad and Tobago (Endler 1978). Male color patterns are so different in these natural populations that no two males are alike. The color patterns consist of a mosaic of spots or patches varying in color, size, position and reflectivity (Figure 1). The patterns range from bright and conspicuous to more subtle and cryptic (inconspicuous). These patterns are controlled by genes on both the X and Y chromosome, and are only expressed in males.

Figure 1. Variation in guppy male color pattern (left and right columns). Center column shows females.

Photo: Kimberly Hughes

The Task. Use the data in the following tables to search for characteristics in the habitat and other selective pressures that might promote differences in male color pattern.

Table 2.1. Information About the Pools Where the Venezuelan Guppies Were Found

Characteristic	Pool
	1	2	3	4
Type	Deep (at a bend in the stream)	Deep (above a natural rock dam)	Shallow (at a bend in the stream)	Deep (above a 6 ft. waterfall)
Pool location (see Figure 2.3)	50 m upstream from the river	100 m upstream from the river	150 m upstream from the river	200 m upstream from the river
Turbidity of water (NTU)	Ranges between 27.50 and 36.25	Ranges between 8.75 and 27.50	Ranges between 3.00 and 8.75	Ranges between 3.00 and 8.75
Predatory fish in the pool (total)	28	15	6	0
Cichlids	12	0	0	0
Rivulus	6	10	6	0
Acara	10	4	0	0
Guppies found in the pool (total)	102	165	187	231
Bright males	5	50	76	108
Drab males	41	19	10	5
Bright females	0	0	0	0
Drab females	56	96	101	118

Note: Turbidity is the cloudiness or haziness of a !uid. Nephelometric turbidity unit (NTU) range in value from 0 (completely clear) to 50 (no light passes through the !uid).

Guppy Behavior and Female Preference Data Sheet

Overview: Guppy Mating System

· Prior to mating, males display to females using a sigmoid display. Females observe males then can select a male to mate with using a glide motion.

· There is very little male-male aggression.

Table 3. Factors Affecting Female Mate Preference

Factor	Effect on Female Preference
Orange spots	In general, when given a choice between males with dull, small orange spots or bright, big orange spots, females preferred to mate with males with big, bright orange spots.
Male boldness towards predators	When predators are present, male guppies may move toward them to inspect them. Females prefer males who move towards predators to inspect them (i.e. males who are more bold), because they may be more informed about the predators in their habitat.
Novelty	When given a choice between males they have interacted with before, and novel (new) males they have never seen, females chose to mate with novel males.

Table 4. Fema le Preference for Bright Males

Pool	Female Preference for Bright Males
1	2
2	4
3	7
4	9

(scale 1-10: 10 = very strong preference)

References: Breden & Stoner (1987); Houde & Endler (1990); Godin & Dugatkin (1996)