We assess phylogenetic patterns of hybridization in the speciose, ecologically and economically important genus Eucalyptus, in order to better understand the evolution of reproductive isolation. Eucalyptus globulus pollen was applied to 99 eucalypt species, mainly from the large commercially important subgenus, Symphyomyrtus. In the 64 species that produce seeds, hybrid compatibility was assessed at two stages, hybrid-production (at approximately 1 month) and hybrid-survival (at 9 months), and compared with phylogenies based on 8,350 genome-wide DArT (diversity arrays technology) markers. Model fitting was used to assess the relationship between compatibility and genetic distance, and whether or not the strength of incompatibility "snowballs" with divergence. There was a decline in compatibility with increasing genetic distance between species. Hybridization was common within two closely related clades (one including E. globulus), but rare between E. globulus and species in two phylogenetically distant clades. Of three alternative models tested (linear, slowdown, and snowball), we found consistent support for a snowball model, indicating that the strength of incompatibility accelerates relative to genetic distance. Although we can only speculate about the genetic basis of this pattern, it is consistent with a Dobzhansky-Muller-model prediction that incompatibilities should snowball with divergence due to negative epistasis. Different rates of compatibility decline in the hybrid-production and hybrid-survival measures suggest that early-acting postmating barriers developed first and are stronger than later-acting barriers. We estimated that complete reproductive isolation can take up to 21-31 My in Eucalyptus. Practical implications for hybrid eucalypt breeding and genetic risk assessment in Australia are discussed.

No abstract

Species distribution modeling is a widely used tool in many branches of ecology and evolution. Evaluations of the transferability of species distribution models—their ability to predict the distribution of species in independent data domains—are, however, rare. In this study, we contrast the transferability of a process‐based and a correlative species distribution model. Our case study uses 664 Australian eucalypt and acacia species. We estimate models for these species using data from their native Australia and then assess whether these models can predict the adventive range of these species. We find that the correlative model—MaxEnt—has a superior ability to describe the data in the training data domain (Australia) and that the process‐based model—TTR‐SDM—has a superior ability to predict the distribution of the study species outside of Australia. The implication of this analysis, that process‐based models may be more appropriate than correlative models when making projections outside of the domain of the training data, needs to be tested in other case studies.

Understanding how and why rates of evolutionary diversification vary is a key issue in evolutionary biology, ecology, and biogeography. Evolutionary rates are the net result of interacting processes summarized under concepts such as adaptive radiation and evolutionary stasis. Here, we review the central concepts in the evolutionary diversification literature and synthesize these into a simple, general framework for studying rates of diversification and quantifying their underlying dynamics, which can be applied across clades and regions, and across spatial and temporal scales. Our framework describes the diversification rate (d) as a function of the abiotic environment (a), the biotic environment (b), and clade‐specific phenotypes or traits (c); thus, d ~ a,b,c. We refer to the four components (a–d) and their interactions collectively as the “Evolutionary Arena.” We outline analytical approaches to this framework and present a case study on conifers, for which we parameterize the general model. We also discuss three conceptual examples: the Lupinus radiation in the Andes in the context of emerging ecological opportunity and fluctuating connectivity due to climatic oscillations; oceanic island radiations in the context of island formation and erosion; and biotically driven radiations of the Mediterranean orchid genus Ophrys. The results of the conifer case study are consistent with the long‐standing scenario that low competition and high rates of niche evolution promote diversification. The conceptual examples illustrate how using the synthetic Evolutionary Arena framework helps to identify and structure future directions for research on evolutionary radiations. In this way, the Evolutionary Arena framework promotes a more general understanding of variation in evolutionary rates by making quantitative results comparable between case studies, thereby allowing new syntheses of evolutionary and ecological processes to emerge.

Oligotrophic subtropical gyres are the largest continuous biomes on Earth and play a key role in global biogeochemical cycles. Microbial communities govern primary production and carbon cycling in the oligotrophic South Pacific Gyre, yet the ecological processes which underpin microbial biogeography in the region remain understudied. We investigated microbial biogeography and community assembly processes at three depths over a ~2,000-km the transect was longitudinal, so ran from 32°S, 170°W to 32°S, 152°W). Thus the latitude (32°S) was constant. Microbial communities in the surface waters (15 and 50 m) were remarkably similar across the transect, whilst communities at the deep chlorophyll maximum were distinct from the surface waters and displayed greater compositional heterogeneity. An ecological null model approach indicated that homogeneous selection was the dominant community assembly process in both the surface waters (100%) and at the deep chlorophyll maximum (91.81%), although variable selection (2.34%) and stochastic processes (5.85%) had a minor influence at the deep chlorophyll maximum. Homogeneous selection (76.69%77.90%), dispersal limitation (15.00%-20.05%) and variable selection (3.01%-7.11%) influenced community assembly between the surface waters and the deep chlorophyll maximum. Seawater density and temperature, which were correlated, were the most important environmental modulators of the balance between stochastic and deterministic assembly processes. Our findings demonstrate remarkable similarity in microbial community composition across longitudinal scales in the oligotrophic South Pacific Gyre, underpinned by strong environmental selection which overwhelms the influence of ecological drift. These data significantly advance our understanding of microbial community dynamics in the oligotrophic subtropical gyres which dominate the Earth's surface.

Nothofagus (southern beech) species form a major component of southern hemisphere forests, and in many regions are becoming an important focus for restoration efforts. However, restoration projects are predominantly carried out at small, local scales using a wide range of different techniques that have produced mixed results. In order to improve outcomes and develop general strategies for southern beech restoration, we review and compare data from previous trials to determine what techniques have been scientifically tested, identify the most effective methods, and pinpoint gaps in current practices. We assessed the effects of restoration techniques, applied in 91 trials from 22 publications across the southern hemisphere, on seedling survival and growth. Providing shelter improved both seedling survival and growth, controlling weeds improved survival, and protecting from herbivores improved seedling growth. Despite being one of the most commonly applied techniques, fertilizer application only marginally improved seedling survival and did not significantly influence seedling growth. Other techniques, such as increasing glasshouse container size or growth time or manipulating soil before planting, showed mixed results. Surprisingly, no trials examined the use of ectomycorrhizal fungal inoculum as a restoration technique. We discuss the outcomes of this review in the context of our current understanding of southern beech regeneration ecology, to inform future Nothofagus restoration practices and suggest where future research should be directed.

No abstract

There are two prominent and competing hypotheses that disagree about the effect of competition on diversification processes. The first, the bounded hypothesis, suggests that species diversity is limited (bounded) by competition between species for finite ecological niche space. The second, the unbounded hypothesis, proposes that innovations associated with evolution render competition unimportant over macroevolutionary timescales. Here we use phylogenetically structured niche modelling to show that processes consistent with both of these diversification models drive species accumulation in conifers. In agreement with the bounded hypothesis, niche competition constrained diversification, and in line with the unbounded hypothesis, niche evolution and partitioning promoted diversification. We then analyse niche traits to show that these diversification enhancing and inhibiting processes can occur simultaneously on different niche dimensions. Together these results suggest a new hypothesis for lineage diversification based on the multi-dimensional nature of ecological niches that can accommodate both bounded and unbounded evolutionary processes.