Narrow water barriers prevent multiple colonizations and limit gene flow among California Channel Island wild buckwheats (Eriogonum: Polygonaceae)

Abstract

The relative roles of chance colonization and subsequent gene flow in the development of insular endemic biotas have been extensively studied in remote oceanic archipelagos, but are less well characterized on nearshore island systems. The current study investigated patterns of colonization and divergence between and within two wild buckwheat species (Polygonaceae), Eriogonum arborescens and E. giganteum, endemic to the California Channel Islands to determine whether geographical isolation is driving diversification. Using plastid and nuclear sequence data and microsatellite allele frequencies, we determined that gene flow in these Eriogonum spp. is restricted by isolation. The data suggest that successful colonization of and gene flow among the islands are infrequent. Colonization appears to have followed a stepping-stone model that is consistent with a north-to-south pattern across the islands. This colonization pattern coupled with relatively little post-colonization inter-island gene flow, particularly among southern islands, has generated a pattern of more divergent lineages on the isolated southern islands. These results run counter to the general expectation that all islands close to a continental source should receive a high level of gene flow. Finally, management recommendations focused on protecting the lineages from loss of private alleles and the erosion of the remaining genetic diversity are offered.

Genetic Differentiation and Relationship among Castanopsis chinensis, C. qiongbeiensis, and C. glabrifolia (Fagaceae) as Revealed by Nuclear SSR Markers

“…The repeated emergence of the land bridge between mainland China and Hainan Island provided opportunities for the plant to disperse from mainland China to Hainan Island (Nm = 0.6443-0.6449). The result was consistent with the study of Quercus pacifica [41] and Eriogonum arborescens [43] in California Channel Islands, where historical gene flow attenuated the population differentiation caused by strait isolation. On the contrary, the genetic differentiation would be high if the historical gene flow was very low (Nm = 0.000-0.004), for example, Amentotaxus argotaenia on Taiwan island [44] and Nigella species in eastern Aegean [45].…”

Near‐shore island lizard fauna shaped by a combination of human‐mediated and natural dispersal

“…This pattern of differentiation between the Northern and Southern Channel Islands is consistent with other studies (e.g. Funk et al, 2016; Hofman et al, 2015; Riley et al, 2016) and highlights how the these two geologically distinct groups of islands are largely independent with respect to broad patterns of diversification.…”

Phylogeography and genetic structure of endemic Acmispon argophyllus and A. dendroideus (Fabaceae) across the California Channel Islands

“…For species that are not known to have been widely used by Native Americans and do not have obvious properties for high mobility, it is more difficult to make inferences about their means of dispersal and gene flow. For the Channel Islands, studies have more often suggested gene flow from north to south (Ramirez and Beckwitt, 1995; Chatzimanolis et al, 2010; Riley et al, 2016). By contrast, our analyses suggest that gene flow in A. dendroideus has occurred from Santa Catalina northward.…”