Hybridization

The ``hybrid policy''⁶proposed by the U.S. Fish & Wildlife Service in 1996 specifically notes that hybrids may be worthy of protection.

The Services believe the responsibility to conserve endangered and threatened species under the Act extends to those intercross progeny if (1) the progeny share the traits that characterize the taxon of the listed parent, and (2) the progeny more closely resemble the listed parent's taxon than an entity intermediate between it and the other known or suspected non-listed parental stock. The best biological information available, including morphometric, ecological, behavioral, genetic, phylogenetic, and/or biochemical data, can be used in this determination.

The questions involving identification and protection of hybrids are fundamentally in the domain of systematics

• What are the relationships of this presumed hybrid? Is it distinct from other taxa?

• Does it closely resemble a non-listed taxon?

In the end the question of whether to protect the product of becomes the question, ``Is this entity an evolutionarily significant unit?'' In that sense, hybrids pose no particular problem for endangered species protection. For example, the U.S. Fish and Wildlife determined

Recent evidence indicates that Lloyd's hedgehog cactus is not a distinct species but rather a hybrid or cross which is not evolving independently of its parental species. Therefore, E. lloydii no longer qualifies for protection under the Act.⁷

In that case a taxonomic decision led to delisting of a species. In another case taxonomic work confirmed that a species of hybrid origin was distinct and worthy of protection.

Heiser was able to produce hybrids between Pecos sunflower and both common sunflower and prairie sunflower, but these hybrids were of low fertility. These results support the validity of Pecos sunflower as a true species. In 1990, Rieseberg et al. published the results of molecular tests on the hypothesized hybrid origin of Pecos sunflower, using electrophoresis to test enzymes and restriction- fragment analysis to test ribosomal and chloroplast DNA. This work identified Pecos sunflower as a true species of ancient hybrid origin with the most likely hybrid parents being common sunflower and prairie sunflower.⁸

Hybridization can, however, threaten the persistence of endangered species. Of the eleven individuals of Catalina Island mountain mahogany that remained in the wild in 1995, five were hybrids [8].