Large scale geographic clines of parasite damage to Populus tremula L.

Abstract

According to the geographic mosaic theory of coevolution (GMTC), clines of traits reflecting local co‐adaptation (including resistance genes) should be common between a host and its parasite and should persist across time. To test the GMTC‐assumption of persistent clinal patterns we compared the natural prevalence of two parasites on aspen Populus tremula trees: mining moths of the genus Phyllocnistis and leaf rust Melampsora spp. Damage data were collated from the Swedish National Forest Damage Inventory (2004–2006). In addition, occurrence of the parasites was scored in field conditions in two common gardens in the north and south of Sweden over five growing seasons (2004–2008), then related to biomass (stem height and diameter) and to concentrations of eleven leaf phenolics. Phyllocnistis mainly occurred in the northern garden, a distribution range which was confirmed by the countrywide inventory, although Phyllocnistis was more abundant on southern clones, providing evidence for possible local maladaptation. Melampsora occurred all over the country and in both gardens, but built up more quickly on northern clones, which suggests a centre of local clone maladaptation in the north. Stem growth also followed a clinal pattern as did the concentration of three phenolic compounds: benzoic acid, catechin and cinnamic acid. However, only benzoic acid was related to parasite presence: negatively to Phyllocnistis and positively to Melampsora and it could thus be a potential trait under selection. In conclusion, clines of Phyllocnistis were stronger and more persistent compared to Melampsora, which showed contrasting clines of varying strength. Our data thus support the assumption of the GMTC model that clines exist in the border between hot and cold spots and that they may be less persistent for parasites with an elevated gene flow, and/or for parasites which cover relatively larger hot spots surrounded by fewer cold spots.

Genetic Variation in Functional Traits Influences Arthropod Community Composition in Aspen (Populus tremula L.)

“…Earlier reports have identified heritability in community composition in Populus species but in smaller collections of genotypes than ours [33], [49]. Here we report heritability values for arthropod abundance, species richness and diversity (Shannon index), traits that differ between regional populations, suggesting that there is regional variation in resistance to canopy arthropods in accordance with our previous work on leaf-mining moths and leaf rust fungus [65].…”

“…This scoring took place in late August 2007 when among-tree differences in infection were highest and before autoinfection had spread to all trees [65]; at this time the scores in the field were poisson-distributed. All phenotyping on visual scales was repeated to ensure that scoring was consistent.…”

“…The Swedish Aspen Collection (SwAsp) was established in 2004 from the clonal propagation of 116 P. tremula trees collected from 12 regions across Sweden, spanning nearly ten degrees of latitude, and grown in two common gardens, one in northern and one in southern Sweden [17]. It is in this population that latitudinal genetic differentiation has been documented for several plant traits [16], [17], in addition to latitudinal trends of attack by rust fungus and leaf-mining insects that reflect countrywide forest survey data [65].…”

Both plant genotype and herbivory shape aspen endophyte communities

“…Due to their preference for salicinoid compounds, we hypothesised that these beetles would directly or indirectly interfere with the endophyte community in the foliar endosphere of P. tremula , which we initially expected to be associated with genotype (Albrectsen et al 2010a, b). Furthermore, we looked for evidence of competitive relationships between fungi of, respectively, plant and potential herbivore origin.…”

Geographic parthenogenesis and plant-enemy interactions in the common dandelion

“…Plant-pathogen interactions have been less studied than plant-herbivore interactions in a latitudinal context [24] and relatively little empirical evidence exists to support the idea that plant pathogen pressure is lower at higher latitudes. These studies have typically been performed either across small latitudinal ranges, spanning less than one [29] up to fifteen degrees latitude [30-32], or on wider geographic scales but focusing on microbial diversity in general rather than on pathogen pressure [33]. If a pattern of decreasing herbivory and pathogen pressure with increasing latitude is in fact absent then the biotic interactions hypothesis cannot be a general explanation for geographic parthenogenesis.…”