page_title: Evidence for speciation by reinforcement
section_title: Insects
hierarchical_section_title: Evidence for speciation by reinforcement / Evidence from nature / Insects
caption_attribution_description: English: Distribution of the species of the genus Magicicada in the U.S. Green = 17-year cicadas; M. septendecim Red = 13-year cicadas; M. tredecim Blue = M. neotredecim Yellow = sympatric overlap of M. neotredecim with M. tredecim[1]
context_page_description: Reinforcement is a process within speciation where natural selection increases the reproductive isolation between two populations of species by reducing the production of hybrids. Evidence for speciation by reinforcement has been gathered since the 1990s, and along with data from comparative studies and laboratory experiments, has overcome many of the objections to the theory. Differences in behavior or biology that inhibit formation of hybrid zygotes are termed prezygotic isolation. Reinforcement can be shown to be occurring by measuring the strength of prezygotic isolation in a sympatric population in comparison to an allopatric population of the same species. Comparative studies of this allow for determining large-scale patterns in nature across various taxa. Mating patterns in hybrid zones can also be used to detect reinforcement. Reproductive character displacement is seen as a result of reinforcement, so many of the cases in nature express this pattern in sympatry. Reinforcement's prevalence is unknown, but the patterns of reproductive character displacement are found across numerous taxa, and is considered to be a common occurrence in nature.
context_section_description: Ethological isolation has been observed between some mosquito species in the Southeast Asian Aedes albopictus group, suggesting—from laboratory experiments of mating trials—that selection against hybrids is occurring, in the presence of reproductive character displacement.
  Female mate discrimination is increased with intermediate migration rates between allopatric populations of Timema cristinae (genus Timema) compared to high rates of migration (where gene flow impedes selection) or low rates (where selection is not strong enough).
  Where the ranges of the cicada species Magicicada tredecim and M. neotredecim overlap (where they are sympatric), the pitch of M. neotredecim male calling songs is roughly 1.7 kHz compared to 1.1 kHz for those of M. tredecim, with corresponding female song pitch preference differences. In allopatric M. neotredecim populations, the mating call pitch is 1.3–1.5 kHz. The biogeography of the cicadas suggests that M. neotredecim originated after the retreat of the last glacial advance in North America.
  The song differences of Laupala crickets on the Hawaiian Islands appear to exhibit patterns consistent with character displacement in sympatric populations. A similar pattern exists with Allonemobius fasciatus and A. socius, species of ground crickets in eastern North America.
  Males in sympatric populations of the damselflies Calopteryx maculata and C. aequabilis are able to discriminate between females of different species better than those in allopatric populations; with females of C. aequabilis in sympatric populations exhibiting lighter wing colors compared to allopatric females—an illustration of reproductive character displacement.
  Fifteen species of sympatrically distributed Agrodiaetus butterflies with pronounced differences in wing color pattern likely arose as a result of speciation by reinforcement. Phylogenetic patterns indicate the differences arose in allopatry and were reinforced when the distributions came into secondary contact.
caption: Distribution of the periodical cicadas in the U.S. The yellow area corresponds to the sympatric overlap of Magicicada neotredecim (blue) with Magicicada tredecim (red)
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