Module 11: Speed of Speciation

Speciation is the process by which species develop. It is an evolutionary process of the formation of new and distinct species. The species evolve by genetic modification. The new species are reproductively isolated from the previous species, that is the new species cannot mate with the old species. In parapatric speciation there is no specific extrinsic barrier to gene flow. The population is continuous, but nonetheless, the population does not mate randomly. Individuals are more likely to mate with their geographic neighbors than with individuals in a different part of the population's range. In this mode, divergence may happen because of reduced gene flow within the population and varying selection pressures across the population's range. Allopatric speciation is speciation that happens when two populations of the same species become isolated from each other due to geographic changes. Sympatric speciation is speciation that occurs when two groups of the same species live in the same geographic location, but they evolve differently until they can no longer interbreed and are considered different species. The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid. For example, the sunflower Helianthus anomalus originated from the hybridization of two other sunflower species and quickly diverged into a new species. The abrupt changes in variability across the genome, even between very closely linked genes, implies that the sizes of the hitch-hiked fragments detected in this study were small; seemingly much smaller than in another sunflower hybrid species, H. paradoxus, where microsatellites several centimorgans from selected QTLs exhibited a significant reduction in variability. The reason for this difference is not clear, although H. anomalus appears to have a more ancient origin.