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Endler's Guppies – Natural and Sexual Selection on Colour Spots

BiologyEvolutionAges 17–18Virtual lab

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Use with my class

Set the predators and the strength of female preference in a guppy pool and follow the number and length of the males' colour spots over the generations. Graphs separate what predators remove from what females favour. Then rerun John Endler's 1980 experiments: ten greenhouse ponds and the transfer of 200 guppies to a stream above a waterfall.

Lesson: Natural and sexual selection: predation, female choice and the colour spots of male guppies (Endler's experiments)

What it shows

Male guppies carry colour spots that attract females but also attract predators. John Endler tested this balance in 1980 with ten greenhouse ponds and a transfer between Trinidad streams. In this lab you set the predators and the strength of female preference and watch spot number and length change over the generations. A graph shows the push from each kind of selection. The genetics are simplified, and the selection strengths were fitted to bring the runs close to Endler's means. He did not measure them.

How to use

On Pool, choose the predators, female preference and gravel, then press Run or Next generation. Press Record data to add a row to the table. On Ponds, press Run to follow ten ponds from month 0 to month 20; the two censuses fill the table. On Stream, press Introduce 200 guppies and follow them for 15 generations. Tick Show Endler's means to compare, then answer the self-check question on each tab.

Parameters you can change

  • Experiment Pool, Ponds, Stream
  • Predators in the pool None, Rivulus, Pike cichlid
  • Number of predators 1–12
  • Female preference for colourful males 0–200 %
  • Gravel Fine, Coarse
  • Random seed (0 = a new run each time) 0–9999

Questions to explore

  1. On Pool, with no predators, how do spots per male change at 100% and at 0% female preference, and why?
  2. On Ponds, which spots account for most of the difference between C and R ponds at Census II?
  3. On Pool, with one pike cichlid, what happens to the natural and sexual selection lines once spot number stops changing?

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