Genetic and ontogenetic variation in an endangered tree structures dependent arthropod and fungal communities.

Plant genetic and ontogenetic variation can significantly impact dependent fungal and arthropod communities. However, little is known of the relative importance of these extended genetic and ontogenetic effects within a species. Using a common garden trial, we compared the dependent arthropod and fungal community on 222 progeny from two highly differentiated populations of the endangered heteroblastic tree species, Eucalyptus morrisbyi. We assessed arthropod and fungal communities on both juvenile and adult foliage. The community variation was related to previous levels of marsupial browsing, as well as the variation in the physicochemical properties of leaves using near-infrared spectroscopy. We found highly significant differences in community composition, abundance and diversity parameters between eucalypt source populations in the common garden, and these were comparable to differences between the distinctive juvenile and adult foliage. The physicochemical properties assessed accounted for a significant percentage of the community variation but did not explain fully the community differences between populations and foliage types. Similarly, while differences in population susceptibility to a major marsupial herbivore may result in diffuse genetic effects on the dependent community, this still did not account for the large genetic-based differences in dependent communities between populations. Our results emphasize the importance of maintaining the populations of this rare species as separate management units, as not only are the populations highly genetically structured, this variation may alter the trajectory of biotic colonization of conservation plantings.

Comparison of contemporary mating patterns in continuous and fragmented Eucalyptus globulus native forests.

While habitat fragmentation is a central issue in forest conservation studies in the face of broad-scale anthropogenic changes to the environment, its effects on contemporary mating patterns remain controversial. This is partly because of the inherent variation in mating patterns which may exist within species and the fact that few studies have replication at the landscape level. To study the effect of forest fragmentation on contemporary mating patterns, including effective pollen dispersal, we compared four native populations of the Australian forest tree, Eucalyptus globulus. We used six microsatellite markers to genotype 1289 open-pollinated offspring from paired fragmented and continuous populations on the island of Tasmania and in Victoria on mainland Australia. The mating patterns in the two continuous populations were similar, despite large differences in population density. In contrast, the two fragmented populations were variable and idiosyncratic in their mating patterns, particularly in their pollen dispersal kernels. The continuous populations showed relatively high outcrossing rates (86-89%) and low correlated paternity (0.03-0.06) compared with the fragmented populations (65-79% and 0.12-0.20 respectively). A greater proportion of trees contributed to reproduction in the fragmented (de/d>or= 0.5) compared with the continuous populations (de/d = 0.03-0.04). Despite significant inbreeding in the offspring of the fragmented populations, there was little evidence of loss of genetic diversity. It is argued that enhanced medium- and long-distance dispersal in fragmented landscapes may act to partly buffer the remnant populations from the negative effects of inbreeding and drift.

A geographic mosaic of genetic variation within a foundation tree species and its community-level consequences.

Knowledge of the manner in which genetic variation within a tree species affects associated communities and ecosystem processes across its entire range is important for understanding how geographic mosaics of genetic interactions might develop and support different communities. While numerous studies have investigated the community and ecosystem consequences of genetic variation at the hybrid cross type or genotype level within a species, none has investigated the community-level effects of intraspecific genetic variation across the geographic range of a widespread species. This is the scale at which geographic mosaics of coevolution are hypothesized to exist. Studies at this level are particularly important for foundation tree species, which typically support numerous microbial, fungal, plant, and animal communities. We studied genetic variation across eight geographical races of the forest tree Eucalyptus globulus representing its natural distribution across southeastern Australia. The study was conducted in a 15-year-old common garden trial based on families derived from single-tree open-pollinated seed collections from the wild. Neutral molecular genetic variation within E. globulus was also assessed and compared with genetic divergence in the phenotypic and community traits. Three major findings emerged. First, we found significant genetically based, hierarchical variation in associated communities corresponding to geographical races of E. globulus and families within races. Second, divergence in foliar communities at the racial level was associated with genetically based divergence in specific leaf morphological and chemical traits that have known defensive functions. Third, significant positive correlations between canopy community dissimilarity and both neutral molecular genetic and leaf quantitative genetic dissimilarity at the race level supported a genetic similarity rule. Our results argue that genetic variation within foundation tree species has the potential to be a significant driver of the geographical mosaics of variation typical of forest communities, which could have important ecological and evolutionary implications.

Biodiversity consequences of genetic variation in bark characteristics within a foundation tree species.

The developing field of community genetics has the potential to broaden the contribution of genetics to conservation biology by demonstrating that genetic variation within foundation plant species can act to structure associated communities of microorganisms, invertebrates, and vertebrates. We assessed the biodiversity consequences of natural patterns of intraspecific genetic variation within the widely distributed Australian forest tree, Eucalyptus globulus. We assessed genetic variation among geographic races of E. globulus (i.e., provenances, seed zones) in the characteristics of tree-trunk bark in a 17-year-old common garden and the associated response of a dependent macroarthropod community. In total, 180 macroarthropod taxa were identified following a collection from 100 trees of five races. We found substantial genetically based variation within E. globulus in the quantity and type of decorticating bark. In the community of organisms associated with this bark, significant variation existed among trees of different races in composition, and there was a two-fold difference in species richness (7-14 species) and abundance (22-55 individuals) among races. This community variation was tightly linked with genetically based variation in bark, with 60% of variation in community composition driven by bark characteristics. No detectable correlation was found, however, with neutral molecular markers. These community-level effects of tree genetics are expected to extend to higher trophic levels because of the extensive use of tree trunks as foraging zones by birds and marsupials. Our results demonstrate the potential biodiversity benefits that may be gained through conservation of intraspecific genetic variation within broadly distributed foundation species. The opportunities for enhancing biodiversity values of forestry and restoration plantings are also highlighted because such planted forests are increasingly becoming the dominant forest type in many areas of the world.