Hybridization occurs when either two genetically different species mate (interspecific hybridization), or when there is interbreeding between "genetically divergent individuals from the same species" (intraspecific hybridization). The hybrid offspring may or may not be fertile, although interspecific hybridization tends to yield sterile offspring whereas intraspecific hybridization tends to yield fertile offspring.[1] However, the offspring that are fertile may continue to breed enabling the establishment of this hybrid species with half of its genes from each parent species; or the hybrid offspring may breed with parent populations which can impact the genetic frequency of the parent species' population.[2] This back-crossing of alleles between a hybrid and a parent species is known as intogression, and it increases the genetic diversity of the parent species.[1]


A Zebroid

Photo by Raidarmax. An interspecific hybridization of a zebra and a donkey

In nature, hybridization does occur if two species have overlapping ranges, however Intraspecific hybridization is more common than interspecific hybridization.[1] More recently human disturbances and accelerated environmental changes have allowed more hybridization of species to occur. This can be detrimental to biodiversity in that some hybrid species may cause the parent's population to exhibit the traits found in the hybrid species (hybrid swarm). Hybrid species also utilize the same resources as their parent species which can limit its availability; this becomes an issue if a parent is a threatened or endangered species that the resources are being taken away from by the hybrid species.[2]


Photo by Mike Cline. Cutthroat-Rainbow hybrid trout

In many cases the hybridization between native and exotic species can have offspring with lower fitness levels. This is known as hybrid depression and it is because the genes that have been evolving in the parent populationof the native species may suddenly be broken apart and hybridized with the matching gene from the exotic parent, which has not evolved to synchronized with the environment the species has been introduced into.[4]

  1. 1.0 1.1 1.2 Wittler, G.H. n.d. taken from
  2. 2.0 2.1 UW-Madison, Peery Wildlife Ecology & Conservation lab. taken from
  4. Muhlfeld, C. C., et al. 2014. Invasive hybridization in a threatened species is accelerated by climate change.doi:10.1038/nclimate2252. Taken from