Speciation – allopatric and sympatric (polyploidy), reproductive isolation and the species concept
BiologyEvolutionAges 17–18
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Sign in to playA population of mice is split in two by a geographic barrier (a river, a mountain range or the sea). The two sides have different soil colours, so natural selection pushes fur colour in opposite directions, alongside mutation and genetic drift. Track mean fur colour, genetic distance and the share of pairs still able to interbreed, then remove the barrier to test whether the populations still interbreed. Further screens show sympatric speciation by polyploidy, habitat or behavioural isolation; test the biological species concept with real crosses (a horse and a donkey give a sterile mule) alongside chromosome numbers and genome sizes; and follow an adaptive radiation from one ancestor on an archipelago.
Lesson: Speciation: allopatric and sympatric speciation, polyploidy, habitat and behavioural isolation, reproductive isolation, the biological species concept and adaptive radiation
What it shows
New species form when gene flow between populations stops. In allopatric speciation a geographic barrier splits a population, and selection, mutation and drift make the two parts diverge until they are reproductively isolated. In sympatric speciation this happens in one place: a plant that doubles its chromosomes (polyploidy) cannot produce fertile offspring with its parent species, and insects or fish that mate on their own host or choose mates of their own colour can split too. The biological species concept tests species by interbreeding, which works for a horse and a donkey but has limits, and one ancestor can radiate into many species on islands.
How to use
On the Allopatric screen choose River and press Run; when the status says two species, press Remove barrier and count the hybrids. On the Sympatric screen choose Polyploidy and watch tetraploids appear, then lower Self-pollination to see them fail; try Habitat and Behavioural isolation too. On the Species concept screen choose a cross such as Horse × donkey. On the Adaptive radiation screen press Run and watch one ancestor split into species with different beaks.
Parameters you can change
- Geographic barrier No barrier, River, Mountain range, Sea (rising water forms an island)
- Individuals per population 30–150
- Difference between the two environments 0–100 %
- Selection strength 0–10
- Mutation rate per locus per generation 1–10 ×10⁻⁴
- Genetic difference threshold for reproductive isolation 10–40 %
- Screen Allopatric speciation, Sympatric speciation, Biological species concept, Adaptive radiation
- Mechanism of sympatric speciation Polyploidy, Habitat isolation, Behavioural isolation
- Rate of unreduced gametes 0.5–10 %
- Rate of self-pollination 0–100 %
- Breeding advantage of tetraploids 0–50 %
- Strength of mate choice by colour 0–10
- Test cross Horse × donkey, Domestic horse × Przewalski's horse, Horse × zebra, Lion × tiger, Dog × grey wolf, Grey wolf × coyote, Evening primrose 2n × 4n, Evening primrose 4n × 4n, Primula floribunda × Primula verticillata, Indian muntjac × Reeves's muntjac
- Chance of hopping to another island per 10 000 years 0.5–10 %
Questions to explore
- Why can a tetraploid plant be a new species after only one generation, without any geographic barrier?
- Why is a mule sterile even though it is healthy, and what does that tell us about horses and donkeys?
- Why do wolves and coyotes show a limit of the biological species concept?
