Insular biogeography and population genetics of dwarf mistletoe (Arceuthobium americanum) in the Central Rocky Mountains

Abstract

Abstract. Lodgepole pine dwarf mistletoe (Arceuthobium americanum), an aggressive parasite of lodgepole pine (Pinus contorta subsp. latifolia), is limited, in the Central Rocky Mountains, to montane host "islands." We sought to quantify the effect of the insularity and life history of A. americanum on its population genetic structure by considering three questions: (1) Do apparent limits to A. americanum pollen and seed dispersal affect gene flow at small spatial scales? (2) Are patterns of genetic diversity on montane "islands" and "mainlands" consistent with the predictions of island biogeographic theory? (3) What is the origin and genetic relationship of "island" and "mainland" populations of A. americanum within the Central Rocky Mountain study area? We used seven A. americanum microsatellite markers developed specifically for the project to genotype 241 individuals from six populations (four "island" and two "mainland" locations) at the western edge of the Central Rocky Mountains, Idaho, USA. All loci were unlinked and polymorphic with a range of 4-24 alleles per locus. To consider gene flow, we performed spatial analyses and compared F-statistics from our data to those from a wide range of species and functional groups. We tested the predictions of biogeographic theory by quantifying associations of genetic diversity with "island" area and isolation from "mainland" populations. To consider the genetic relationships of "island" and "mainland" regions, we applied agglomerative and Bayesian hierarchical classifications to datasets, and objectively identified the optimal numbers of clusters in these analyses. We found that F IS values in A. americanum were similar to those reported for dispersal-limited species with similar life-history characteristics, and F ST values were similar to those reported for plants with animal-facilitated seed dispersal. As predicted by biogeographic theory, island allelic richness was positively correlated with geographic size of the population and negatively correlated with distance from mainland populations. Average linkage (UPGMA) classifications and Bayesian cluster analyses both identified two groupings of island populations radiating from the mainland populations. Our results are likely to be of interest to foresters managing dwarf mistletoe infections, particularly in the Central Rocky Mountains, and to ecologists and geneticists working with insular population distributions.

Island biogeography theory explains the genetic diversity of a fragmented rock ptarmigan (Lagopus muta) population

“…A relationship between genetic diversity and island area has been documented in several studies (Hänfling et al, ; Knaepkens, Bervoets, Verheyen, & Eens, ; Sato et al, ; Wang et al, ; White & Searle, ), but to our knowledge, only two have been conducted in montane landscapes (Epps et al, ; Hill et al, ). Our results showed that H n.b.…”

“…Several studies have found a significant relationship between distance to the mainland and genetic diversity (Francisco et al, ; García‐Verdugo et al, ; Hill et al, ; Yamada & Maki, ). Similarly, we found a significant relationship between H o and distance to the mainland.…”

“…Furthermore, a significant relationship between genetic diversity and island area (Frankham, ; Hill, Loxterman, & Aho, ; Sato et al, ; Wang et al, ), and between genetic diversity and distance to the mainland (Francisco et al, ; García‐Verdugo et al, ; Yamada & Maki, ) has also been found. While several studies have examined the relationship between island area, distance to the mainland and genetic diversity, to our knowledge only Hill et al () and Mcglaughlin et al () explicitly tested for the equilibrium model of island biogeography.…”

“…Several studies have for a number of different taxa found that genetic diversity was lower on islands compared to the mainland (Băncilă & Arntzen, ; Frankham, ; Mcglaughlin et al, ; Wang et al, ), and that it can be related to some of the predictions of the equilibrium model of island biogeography (Francisco, Santiago, Mizusawa, Oldroyd, & Arias, ; García‐Verdugo et al, ; Hurston et al, ; Mcglaughlin et al, ; Sato et al, ; Wang et al, ; Yamada & Maki, ). Furthermore, a significant relationship between genetic diversity and island area (Frankham, ; Hill, Loxterman, & Aho, ; Sato et al, ; Wang et al, ), and between genetic diversity and distance to the mainland (Francisco et al, ; García‐Verdugo et al, ; Yamada & Maki, ) has also been found. While several studies have examined the relationship between island area, distance to the mainland and genetic diversity, to our knowledge only Hill et al () and Mcglaughlin et al () explicitly tested for the equilibrium model of island biogeography.…”

“…Of the many studies investigating the relationship between genetic diversity and the different parameters of the island biogeography theory, few have been conducted on population living on the continent (e.g., mountain islands, forest islands or lakes; Hänfling & Brandl, ; Hänfling, Hellemans, Volckaert, & Carvalho, ), and to our knowledge only two have been conducted on mountain islands (Epps, Palsboll, Wehausen, Roderick, & McCullough, ; Hill et al, ). For continental populations, an island can be described as a patch of suitable habitat surrounded by unsuitable matrix habitat (Haila, ).…”