Rucete ✏ Campbell Biology In a Nutshell
Unit 4 MECHANISMS OF EVOLUTION — Concept 24.4 Speciation Can Occur Rapidly or Slowly and Can Result from Changes in Few or Many Genes
Speciation—the formation of new species—can occur at varying speeds, from rapid bursts to gradual transformations over millions of years. Additionally, speciation may result from genetic changes in just a few genes or involve many genetic differences.
The Time Course of Speciation
Speciation patterns observed in the fossil record show two distinct tempos:
Punctuated Equilibria:
Species remain relatively unchanged (stasis) for long periods, punctuated by rapid bursts of evolutionary change.
Example: Marine invertebrate species appear suddenly in the fossil record, changing little thereafter.
Gradual Speciation:
Species evolve gradually, showing continuous and slow morphological change over extended periods.
Speciation Rates
Rapid speciation can occur within just a few generations when populations diverge significantly due to strong selective pressures.
Example: Hybrid sunflower species (Helianthus anomalus) rapidly evolved from parent species due to natural selection in new habitats.
Speciation intervals vary greatly, ranging from thousands to millions of years. On average, speciation intervals are approximately 6.5 million years, indicating no fixed "speciation clock."
Studying the Genetics of Speciation
Speciation can be influenced by changes in just a few genes or numerous genetic differences:
Single-gene changes can create reproductive barriers. Example: Shell-coiling direction in Japanese snails prevents mating between individuals.
Pollinator preference in monkey flowers (Mimulus cardinalis and M. lewisii) influenced by changes at a single genetic locus, affecting reproductive isolation significantly.
Complex speciation can involve multiple genes. Example: Hybrid sterility in fruit flies involves gene interactions across multiple loci.
From Speciation to Macroevolution
Speciation events accumulate over time, contributing to broader evolutionary patterns (macroevolution).
Over many generations, small differences accumulate, leading to significant evolutionary changes, such as whales evolving from terrestrial ancestors.
Evolutionary history consists of repeated cycles of speciation and extinction, shaping life's diversity.
In a Nutshell
Speciation can be rapid or gradual and involve simple or complex genetic mechanisms. Fossil evidence and genetic studies reveal diverse patterns and processes by which new species form, underscoring speciation’s complexity and variability.