Hybridization in the Island Endemic, Catalina Mahogany

Abstract

Allozyme data, combined with traditional morphological and anatomical data, were used to evaluate the genetic status of the island endemic, Cercocarpus traskiae (Catalina mahogany). Comprising only seven adult plants and close to 70 seedlings, C. traskiae is confined to Wild Boar Gully on the southwest side of Santa Catalina Island in Los Angeles County, California Electrophoretic examination of 22 enzyme loci revealed that all but two of the seven adult C. traskiae trees were unique allozymically. Furthermore four of the seven C. traskiae individuals were morphologically and/or anatomically intermediate between “true”C. traskiae and the more abundant Cercocarpus species on Santa Catalina, C. betuloides var, blancheae. Further electrophoretic analyses revealed that two of these four individuals possessed an additive “hybrid” enzyme phenotype indicating that these individuals were hybrid. Twenty‐five of the seedlings were also assayed but none of the seedlings displayed hybrid enzyme phenotypes. Given the evidence for hybridization described herein, we make two suggestions to enhance the long‐term preservation of C. traskiae. First, it may be desirable to eliminate the single C. betuloides var.: blancheae individual in Wild Boar Gully. Second, we suggest that established cuttings of true C. traskiae be transplanted to areas on Santa Catalina where the probability of hybridization is minimal Our data further demonstrate that accurate taxonomic identification and an understanding of population genetic structure are necessary for the enlightened management of small relict populations or island endemics.

Allozyme variation and structure of the Canarian endemic palm tree Phoenix canariensis (Arecaceae): implications for conservation

“…Also, morphologically intermediate individuals may be hybrid progeny corresponding to F 2 or later generations that have lost P. dactylifera alleles by backcrossing to pure P. canariensis. As most gene flow occurs between the hybrid and a single parent (P. canariensis), the segregating generations will be mostly advanced generation backcrosses and have multilocus associations typical of the most compatible parent (P. canariensis), as suggested earlier (Rieseberg et al, 1989;Arnold et al, 1991;Nason et al, 1992;Rieseberg and Ellstrand, 1993). In addition, selection against recombinants should be intense in hybrid zones; therefore, the surviving individuals would be those that retained the ecological traits of one parent, such as backcrosses (Anderson, 1998).…”

“…They have also been used successfully to characterise and differentiate close by related species, ecological varieties or natural and artificial hybrids (Rieseberg et al, 1989;Booij et al, 1995;Bendiab et al, 1998;Elisiário et al, 1999). Therefore, they could provide valuable insights into the genetic problems posed by the Canarian endemic P. canariensis.…”

Genetics of species re-introductions: Applications of genetic analysis

“…Employing enzyme gel electrophoresis it was possible to conclude that seven unique genotypes were present, two of these apparently hybrids between C. traskiae and its common sympatric congener C. betuloides ssp. blanchae (Rieseberg et al, 1989). The threat of genetic swamping of the extremely small C. traskiae gene pool was thus implicated.…”

Hybrid Zone Dynamics and Species Replacement Between Orconectes Crayfishes in a Northern Wisconsin Lake

“…Hybridization thus hastens the elimination of gene flow between populations, providing final closure to the speciation process. At the other extreme, hybridizing populations can fuse (Brochman 1984;Rieseberg et al 1989;Rieseberg and Gerber 1995). This mixing can occur to varying degrees, ranging from the formation of a hybrid swarm (Avise et al 1984;Roche and Roche 1991;Childs et al 1996;Williams et al 1996) to the complete genetic assimilation or replacement of one group by another (Rhymer and Simberloff 1996).…”