Plant genetic diversity in the Canary Islands: a conservation perspective

Abstract

The Canary Islands are an Atlantic volcanic archipelago with a rich flora of ∼570 endemic species. The endemics represent ∼40% of the native flora of the islands, and ∼20% of the endemics are in the E (endangered) category of the International Union for Conservation of Nature. A review of allozyme variation in 69 endemic species belonging to 18 genera and eight families is presented. The average species-level genetic diversity (H(T)) at allozyme loci is 0.186, which is twice as high as the mean reported for endemics of Pacific archipelagos. Possible factors contributing to this higher diversity are discussed, but the reasons remain obscure. An average of 28% of the allozyme diversity within species resides among populations, indicating a high level of interpopulational differentiation. Studies of reproductive biology indicate that many of the endemic species are outcrossers. The high total diversity within species, the relatively high differentiation among populations, and the outcrossing breeding systems have implications for species conservation. Decreased population sizes in outcrossing species would promote biparental inbreeding and increase inbreeding depression. The relatively high proportion of allozyme diversity among populations indicates that the most effective strategy for preserving genetic variation in species is to conserve as many populations as possible. The genetic diversity in many Canary Island endemics is endangered by: (1) overgrazing by introduced animals, such as barbary sheep, goats, mouflons, rabbits, and sheep; (2) interspecific hybridization following habitat disturbance or planting of endemics along roadsides or in public gardens; (3) competition with alien plant species; and (4) decline of population size because of urban development and farming.

Human-induced hybridization among congeneric endemic plants on Tenerife, Canary Islands

“…The human-disturbed areas are colonized by P. cruenta 9 P. echinata hybrids from Teno to N central Tenerife and P. cruenta 9 P. tussilaginis hybrids from N central Tenerife to Anaga. On Tenerife, it has previously been shown that road sides provide a suitable habitat for a hybrid swarm consisting of five different Argyranthemum species (Brochmann 1984;Francisco-Ortega et al 2000). However, for Argyranthemum it is not clear whether the hybrids manage to expand from the road verges into the surrounding habitat .…”

“…On the one hand, natural habitats are increasingly being fragmented, which negatively affects the population viability of many species (e.g., Young and Clarke 2000;Oostermeijer et al 2003). On the other hand, natural barriers that originally played an important role in speciation processes are being broken down by the creation of infrastructure (roads, waterways), so that previously isolated sister species can hybridize after establishing secondary contact (Rhymer and Simberloff 1996;Francisco-Ortega et al 2000). There are several examples of such anthropogenic hybridization.…”

“…Introduction of non-native species, habitat destruction through deforestation and development of human infrastructure are all well known to have a major impact on native island biodiversity (Whittaker and Fernández-Palacios 2007). Because of their often recent evolutionary origin, island endemics tend to hybridize easily despite morphological and ecological differences (Baldwin et al 1998;Francisco-Ortega et al 2000;Fjellheim et al 2009). Postzygotic barriers are typically weak (Carlquist and Cole 1974;Levin et al 1996), and hybrids are often fertile so that introgression can readily occur.…”

“…Due to the specific geographical histories of the oceanic archipelagos, island endemics are often highly specialized and have extremely narrow geographic distributions (Baldwin et al 1998;Francisco-Ortega et al 2000;Emerson 2002). Unfortunately, a high proportion of these species is threatened or has already gone extinct because of anthropogenic activities.…”

Fungal diversity in the rhizosphere of endemic plant species of Tenerife (Canary Islands): relationship to vegetation zones and environmental factors

“…Tenerife has a well-investigated flora: the endemics represent approximately 40% of the native flora, though 20% are meanwhile in the endangered category of the International Union for Conservation of Nature (Francisco-Ortega et al, 2000). Adaptive radiation into diverse habitats and genetic drift are often considered to be important factors producing such an extensive speciation (Baldwin et al, 1998).…”