Sympatric Speciation

Sympatric speciation is the formation of a new species from a population in the same geographical area, without any physical barrier. 'Sympatric' means 'same homeland'. The groups could meet, but something stops them interbreeding, so gene flow still stops.Sympatric speciation can happen in several ways:1. Ecological (habitat) isolation: groups in the same area use different habitats or food sources, such as different host plants, and so rarely meet at breeding time.2. Temporal isolation: a group starts to breed or flower at a different time, for example because of a change in soil or food source.3. Behavioural isolation: groups develop different courtship behaviour or mate preferences, so females choose only males of their own type (sexual selection).4. Polyploidy: common in plants. An error in meiosis produces gametes with extra sets of chromosomes, or two species hybridise and the hybrid doubles its chromosome number. The polyploid offspring cannot produce fertile offspring with the parent population, because their chromosomes do not pair properly in meiosis. A new species can arise in a single generation. Many crop plants, including bread wheat, are polyploids.Once the groups are reproductively isolated, the same processes as in allopatric speciation follow: different mutations, different selection pressures and genetic drift act on each gene pool, and the groups diverge.Sympatric speciation was once thought to be rare, but several well-studied examples, including Howea palms, apple maggot flies and cichlid fish, show that it does happen.