species of iris from southern Louisiana has been studied by Arnold & Bennett (1993) regarding the increased fitness of hybrid variants. Fish Espinasa et al. found that introgression between a surface-dwelling members of Astroblepus and a troglomorphic species, Astroblepus pholeter, resulted in the development of previously lost traits in offspring, such as distinct eyes and optic nerves. Introgression line An introgression line (IL) is a crop species that contains genetic material artificially derived from a wild relative population through repeated backcrossing. An example of a collection of ILs (called an IL-Library) is the use of chromosome segments from Solanum pennellii (a wild species of tomato) that was introgressed into Solanum lycopersicum (the cultivated tomato). The lines of an IL-library usually cover the complete genome of the donor. Introgression lines allow the study of quantitative trait loci, but also the creation of new varieties by introducing exotic traits. Lineage fusion Lineage fusion is an extreme variant of introgression that results from the merging of two distinct species or populations. This eventually results in a single population that displaces or replaces the parental species in the region. Some lineage fusion occurs soon after two taxa diverge or speciate, especially if there are few reproductive barriers between lineages. It is not strictly necessary for the two lineages to be closely related, but rather have the ability to produce viable offspring. See also Chimera (genetics) Genetic engineering Genetic erosion Genetic pollution Transgene Transgenic plant References Further reading Décobert, O. (2017). Complément à l’inventaire des Carabini du Midi toulousain (Coleoptera, Carabidae) - Carnets natures, 2017, vol. 4 : 33-38 (ISSN 2427-6111) https://carnetsnatures.fr/volume4/carabidae-decobert.pdf ("Forbidden" - No Access 2015-04-06) Alternate Link: Patterns of Hybridization in Plants Classical genetics