BRAINCAKENatural Selection in Oysters
Oysters provide a clear, recent example of natural selection caused by disease, acting as a selection pressure.
In 1957 a parasitic disease called MSX, caused by the single-celled parasite Haplosporidium nelsoni, appeared among eastern oysters (Crassostrea virginica) in Delaware Bay on the east coast of the USA. It killed the large majority of the oysters in the bay within a few years.
The oyster population was not identical. Because of existing genetic variation, a small number of oysters had alleles that gave them some resistance to the parasite. The events that followed match the steps of natural selection:
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Key terms in this lesson
- selection pressure
- An environmental factor that affects the chance of survival and reproduction of organisms with a particular allele or characteristic.
More in Natural Selection
- Grayling Butterflies
- Fungal Carnivores
- The Same Species in Different Environments
- Natural Selection
- Natural Selection in Moths
- Reproductive Success
- Directional Selection
- Antibiotics
All 29 lessons in Natural Selection · All Edexcel AS-level Biology topics