Aim  To examine the different uses and perceptions of introduced Australian acacias (wattles; Acacia subgenus Phyllodineae) by rural households and communities. Location  Eighteen landscape‐scale case studies around the world, in Vietnam, India, Réunion, Madagascar, South Africa, Congo, Niger, Ethiopia, Israel, France, Portugal, Brazil, Chile, Dominican Republic and Hawai‘i. Methods  Qualitative comparison of case studies, based on questionnaire sent to network of acacia researchers. Information based on individual knowledge of local experts, published and unpublished sources. Results  We propose a conceptual model to explain current uses and perceptions of introduced acacias. It highlights historically and geographically contingent processes, including economic development, environmental discourses, political context, and local or regional needs. Four main groupings of case studies were united by similar patterns: (1) poor communities benefiting from targeted agroforestry projects; (2) places where residents, generally poor, take advantage of a valuable resource already present in their landscape via plantation and/or invasion; (3) regions of small and mid‐scale tree farmers participating in the forestry industry; and (4) a number of high‐income communities dealing with the legacies of former or niche use of introduced acacia in a context of increased concern over biodiversity and ecosystem services. Main conclusions  Economic conditions play a key role shaping acacia use. Poorer communities rely strongly on acacias (often in, or escaped from, formal plantations) for household needs and, sometimes, for income. Middle‐income regions more typically host private farm investments in acacia woodlots for commercialization. Efforts at control of invasive acacias must take care to not adversely impact poor dependent communities.

The neighbourhood model apportions offspring of individual mother plants to self-fertilization, outcrossing to males within a circumscribed area around the mother plant (the neighbourhood), and outcrossing to males outside the neighbourhood. Formerly the model was applied only to haploid pollen gametes in the offspring of conifers, but is extended so that it can be used with genotypic data from diploid offspring of both angiosperms and gymnosperms. In addition, it is shown that the mating parameters can be estimated without independent estimates of allele frequencies in the pollen pools outside the neighbourhood; thus the model might be applied effectively to natural populations exposed to unknown external pollen sources. Parameters of the neighbourhood mating model were estimated for a 10-year-old seed orchard population of the insect-pollinated tree, Eucalyptus regnans, in southeast Australia, which contained a mixture of two geographical provenances (Victoria and Tasmania). The mating patterns revealed were complex. Crosses between trees of the same provenance occurred three times more often than crosses between trees of different provenances. Levels of self-fertilization and patterns of mating within neighbourhoods were influenced by provenance origin, crop fecundity and orchard position (central vs. edge) of mother trees. Gene dispersal, however, was extensive, with approximately 50% of effective pollen gametes coming from males more than 40 m away from mother trees (average distance between neighbouring trees was 7.4 m). Thus, insect pollinators are efficient promoters of cross-fertilization in this orchard, with the result that the effective number of males mating with each female is large.

A database of herbarium specimens of Eucalyptus, together with published and unpublished literature, was searched for records of natural or manipulated interspecific hybrids. The database was also used in conjunction with the informal classification of Pryor and Johnson to generate a list of all pairwise combinations of species within each subgenus, indexed according to tazionomic affinity and degree of coincidence of geographic distribution. The frequency of recorded interspecific hybrids in relation to the total numbers of species pairs in each index category provided a basis for exploration of patterns of hybridisation within the genus.The different subgenera are reproductively isolated under both natural and manipulated conditions.Within subgenera, current geographic distribution is a major determinant of natural hybridisation, The frequency of natural hybridisation in general reflects the hierarchy of taxonomic affinities, although important exceptions were noted in Monomlyptus and CorymQia, and there is considerable variation in rates of inter and intrasectional hybridisation within Sympt?yomyrtus. T a m m m i c revision may be indicated in such cases. Across the genus, natural hybridisation is a rather restricted phenomenon. Only 15% of combinations expected on geographic/taxonomic grounds have been recorded, and 37% of 'these are known from only a single herbarium record.Most records of manipulated hybrids derive from the wmmercidy important subgenus Symphyomyrtus. Combinations between geographically isolated species are Frequent and successfd crosses have been made between species in different sections, although a n increased frequency of viability problems was noted in some cases. l[mplications for tree breeding are discussed.

Aim  This study reports on the contribution of the Australian Tree Seed Centre (ATSC) to the international dissemination of Australian acacias. It also describes the current uses and the scale of economic benefits derived from planting Australian acacias, and speculates about possible future trends in usage. This information is crucial for the evaluation of overall human‐mediated transfers of Australian acacias as a global experiment in biogeography. Location  Australia and Global. Methods  ATSC databases were used to determine which taxa were sent to which regions of the world and in what numbers. Location, scale and value of uses of the most important species were described from a review of published and grey literature, and we drew on our collective experience to speculate about future trends. Results  The ATSC despatched samples of 322 taxa (or roughly a third of Acacia species native to Australia) between 1980 and 2010 to 149 countries. Plantations in SE Asia and South Africa supplying the pulp and paper industry cover an area of over 2 M ha and produce pulp worth around $US4.3B p.a. In SE Asia, pulpwood species also provide logs for an expanding industry based on solid wood product. Tannin is produced from Acacia mearnsii in South Africa and Brazil. A suite of multi‐purpose species helps meeting the demand for food, fodder, fuelwood, poles and site amelioration in dry zone regions of Africa and elsewhere and are widely incorporated into agro‐forestry systems. Acacia saligna is the most widely planted non‐timber species with around 600,000 ha established worldwide. Many acacia species also have horticultural uses particularly in Europe. Main conclusions  The ATSC has been the major agent for systematic exploration and worldwide dissemination of Australian acacias over the past 30 years, but seed from local and regional sources of exploited species will dominate future movements. The scale of production from currently planted species will expand to meet the demands of population growth, using improved varieties. Plantations for energy and carbon sequestration might become increasingly widespread.

Paternity analysis can be used to estimate mean effective pollen dispersal (micro(d)) by sampling offspring from a mother plant and assaying each for a large number of allozyme loci. The male in the population with the highest likelihood of paternity, based entirely on the degree of genetic relationship with the offspring (transition probability) or combined with information on probability of mating with the mother plant, is inferred as the pollen parent. Computer simulations show that the mean distance between inferred males and mother plants (d) reliably estimates micro(d) in defined circumstances. If male mating success decreases with distance from the mother plant, paternity inference based entirely on transition probabilities results in d values that are upwardly biased, perhaps considerably. More reliable estimates can be obtained in this situation when prior information on the general form of the relationship between mating success and distance between mates (the distance function) is used, along with transition probabilities, to infer paternity. However, this procedure is valid only when the general form of the distance function can be reliably assumed. Computer simulations also show that the bootstrap method can be used to closely approximate the SE of .

The genetic architecture of hybrid fitness characters can provide valuable insights into the nature and evolution of postzygotic reproductive barriers in diverged species. We determined the genome-wide distribution of barriers to introgression in an F 1 hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and E. globulus (Labill.). Two interspecific backcross families (N ϭ 186) were used to construct comparative, single-tree, genetic linkage maps of an F 1 hybrid individual and two backcross parents. A total of 1354 testcross AFLP marker loci were evaluated in the three parental maps and a substantial proportion (27.7% average) exhibited transmission ratio distortion (␣ ϭ 0.05). The distorted markers were located in distinct regions of the parental maps and marker alleles within each region were all biased toward either of the two parental species. We used a Bayesian approach to estimate the position and effect of transmission ratio distorting loci (TRDLs) in the distorted regions of each parental linkage map. The relative viability of TRDL alleles ranged from 0.20 to 0.72. Contrary to expectation, heterospecific (donor) alleles of TRDLs were favored as often as recurrent alleles in both backcrosses, suggesting that positive and negative heterospecific interactions affect introgression rates in this wide interspecific pedigree.T HE nature of postzygotic reproductive barriers is suppressing recombination and thereby extending the a fundamental question in evolutionary genetics.effects of linked isolation genes . The More than 60 years after it was proposed that postzygotic sizes of chromosomal segments over which gene flow is barriers may be by-products of genetic differentiation restricted may therefore be determined by the comamong diverging species (Dobzhansky 1937; Muller bined effect of isolation genes and recombination mod-1942), the mechanisms involved in postzygotic isolation ifiers in hybrid genomes (Rieseberg and Burke 2001). remain unknown for many groups of organisms, includThe prevailing view emerging from studies of postzying most plant species. Two general mechanisms are gotic barriers in plants and animals is that postzygotic thought to underlie postzygotic isolation. Deleterious isolation is caused mostly by extensive negative epistatic interactions between heterospecific genes may lead to interactions in hybrid genomes (Burke and Arnold hybrid sterility and hybrid inviability, while chromo-2001). Simple two-locus incompatibilities such as those somal rearrangements in the parental species may result described by the Dobzhansky-Muller model predict the in abnormal meiotic products in their hybrids with negaestablishment of a postzygotic barrier when a gene from tive effects on hybrid fertility (Burke and Arnold one species interacts negatively within the hybrid ge-2001). Both of these mechanisms have been shown to netic background with a gene from another species reduce gene flow in hybrids of plant species (Rieseberg (Dobzhansky 1937; Muller 1942 tance of compl...

Comparative genetic mapping in interspecific pedigrees presents a powerful approach to study genetic differentiation, genome evolution and reproductive isolation in diverging species. We used this approach for genetic analysis of an F(1) hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and Eucalyptus globulus (Labill.). This wide interspecific cross is characterized by hybrid inviability and hybrid abnormality. Approximately 20% of loci in the genome of the F(1) hybrid are expected to be hemizygous due to a difference in genome size between E. grandis (640 Mbp) and E. globulus (530 Mbp). We investigated the extent of colinearity between the two genomes and the distribution of hemizygous loci in the F(1) hybrid using high-throughput, semi-automated AFLP marker analysis. Two pseudo-backcross families (backcrosses of an F(1) individual to non-parental individuals of the parental species) were each genotyped with more than 800 AFLP markers. This allowed construction of de novo comparative genetic linkage maps of the F(1) hybrid and the two backcross parents. All shared AFLP marker loci in the three single-tree parental maps were found to be colinear and little evidence was found for gross chromosomal rearrangements. Our results suggest that hemizygous AFLP loci are dispersed throughout the E. grandis chromosomes of the F(1) hybrid.

Acacia mangium and A. auriculiformis flowered between February and May, producing mature pods between October and April. The flowers of both species were similar in structure and showed weak protogyny and variable levels of andromonoecy. Male flowers either lacked pistils completely or had small sterile pistils. Controlled hand pollination resulted in pollen tubes in the pistil and penetration of the ovules following self and cross intraspecific and interspecific pollination. The cross A. auriculiformis × A. mangium was more successful than the reciprocal, but fertile seed was produced following interspecific pollination in both directions and all seedlings were shown to be hybrid by isozyme analysis of parents and seedlings. There were relatively few insect visitors to the flowering branches, but the same suite of insects was observed foraging for pollen on both species. Native bees belonging to the Halictidae carried most polyads on their hairy bodies and may act as pollinating agents. There appeared to be no major fertility barriers to interspecific hybridisation between Acacia mangium and A. auriculiformis, and hybrids could occur spontaneously via synchronous flowering and common insect visitors.