A comparison of the population genetic structure of parasitic Viscum album from two landscapes differing in degree of fragmentation

Abstract

Parasite populations do not necessarily conform to expected patterns of genetic diversity and structure. Parasitic plants may be more vulnerable to the negative consequences of landscape fragmentation because of their specialized life history strategies and dependence on host plants, which are themselves susceptible to genetic erosion and reduced fitness following habitat change. We used AFLP genetic markers to investigate the effects of habitat fragmentation on genetic diversity and structure within and among populations of hemiparasitic Viscum album. Comparing populations from two landscapes differing in the amount of forest fragmentation allowed us to directly quantify habitat fragmentation effects. Populations from both landscapes exhibited significant isolation-by-distance and sex ratios biased towards females. The less severely fragmented landscape had larger and less isolated populations, resulting in lower levels of population genetic structure (F(ST) = 0.05 vs. 0.09) and inbreeding (F(IS) = 0.13 vs. 0.27). Genetic differentiation between host-tree subpopulations was also higher in the more fragmented landscape. We found no significant differences in within-population gene diversity, percentage of polymorphic loci, or molecular variance between the two regions, nor did we find relationships between genetic diversity measures and germination success. Our results indicate that increasing habitat fragmentation negatively affects population genetic structure and levels of inbreeding in V. album, with the degree of isolation among populations exerting a stronger influence than forest patch size

Gene flow and inter-sterility between allopatric and sympatric populations of Heterobasidion abietinum and H. parviporum in Europe

“…Similar patterns have been obtained when studying host fragmentation in the case of other tree pathogenic organisms, i.e. the hemi‐parasitic plant ( Viscum album L.) (Stanton et al. 2009).…”

The roles of history and ecology in chloroplast phylogeographic patterns of the bird‐dispersed plant parasite Phoradendron californicum (Viscaceae) in the Sonoran Desert

“…Mistletoes are key species in ecosystems (Watson, 2001); thus, most attention has focused on their ecological attributes (e.g., Martínez del Rio et al, 1996; Aukema, 2004; Watson, 2009). However, genetic structure and phylogenetic studies suggest that both ecological and historical processes can also influence mistletoes divergence at multiple scales through processes like postglacial dispersal from Pleistocene refugia (Amico and Nickrent, 2009), formation of host races (Glazner et al, 1988; Overton, 1997; Jerome and Ford, 2002; Zuber and Widmer, 2009), and landscape fragmentation (Stanton et al, 2009). Given the evidence of divergence along the Baja California Peninsula across several taxa according to the above‐mentioned literature and more recent studies (Smith et al, 2012; Garrick et al, 2013; Mantooth et al, 2013; Trujano‐Alvarez and Alvarez‐Castaneda, 2013; Dolby et al, unpublished manuscript), and considering the challenge of understanding how multiple biotic and abiotic factors might have influenced divergence in desert mistletoe, we investigated the extent to which historical, ecological, and geographic drivers can explain the observed patterns of intraspecific divergence.…”

Hybridization and differential introgression associated with environmental shifts in a mistletoe species complex

“…Accordingly, the most accepted explanation of mistletoe diversification is that of ‘host-race formation’ 12 , 34 – 36 , where genetic differentiation, and eventually host-race formation, is acquired through isolation-by-distance or by ecological adaptation following the ‘invasion’ of a different host species (‘host-switching’ hypothesis 12 ). In addition, the geographic structuring of genetic variation in some mistletoe species has been explained as the result of past climate changes 31 , 32 , 37 , 38 , landscape fragmentation 39 , emergence of biogeographic barriers 30 – 32 , 38 , and by the parasites’ own climatic niche preferences 40 , 41 .…”