Trait differences between and within ranges of an invasive legume species

Novel ecological interactions can drive natural selection in non-native species and trait evolution may increase the likelihood of invasion. We can gain insight into the potential role of evolution in invasion success by comparing traits of successful individuals in the invasive range with the traits of individuals from the native range in order to determine which traits are most likely to allow species to overcome barriers to invasion. Here we used Medicago polymorpha , a non-native legume species from the Mediterranean that has invaded six continents around the world, to quantify differences in life history traits among genotypes collected from the native and invasive range and grown in a common greenhouse environment. We found significant differences in fruit and seed production and biomass allocation between invasive and native range genotypes. Invasive genotypes had greater fecundity, but invested more energy into belowground growth relative to native genotypes. Beyond the variation between ranges, we found additional variation among genotypes within each range in flowering phenology, total biomass, biomass allocation, and fecundity. We found non-linear relationships between some traits and fitness that were much stronger for plants from the invasive range. These trait differences between ranges suggest that stabilizing selection on biomass, resource allocation, and flowering phenology imposed during or after introduction of this species may increase invasion success.

Of mutualism and migration: will interactions with novel ericoid mycorrhizal communities help or hinder northward Rhododendron range shifts?

Rapid climate change imperils many small-ranged endemic species as the climate envelopes of their native ranges shift poleward. In addition to abiotic changes, biotic interactions are expected to play a critical role in plant species’ responses. Below-ground interactions are of particular interest given increasing evidence of microbial effects on plant performance and the prevalence of mycorrhizal mutualisms. We used greenhouse mesocosm experiments to investigate how natural northward migration/assisted colonization of Rhododendron catawbiense, a small-ranged endemic eastern U.S. shrub, might be influenced by novel below-ground biotic interactions from soils north of its native range, particularly with ericoid mycorrhizal fungi (ERM). We compared germination, leaf size, survival, and ERM colonization rates of endemic R. catawbiense and widespread R. maximum when sown on different soil inoculum treatments: a sterilized control; a non-ERM biotic control; ERM communities from northern R. maximum populations; and ERM communities collected from the native range of R. catawbiense. Germination rates for both species when inoculated with congeners' novel soils were significantly higher than when inoculated with conspecific soils, or non-mycorrhizal controls. Mortality rates were unaffected by treatment, suggesting that the unexpected reciprocal effect of each species’ increased establishment in association with heterospecific ERM could have lasting demographic effects. Our results suggest that seedling establishment of R. catawbiense in northern regions outside its native range could be facilitated by the presence of extant congeners like R. maximum and their associated soil microbiota. These findings have direct relevance to the potential for successful poleward migration or future assisted colonization efforts.

Long distance homing in the cane toad (Rhinella marina) in its native range

Many animals exhibit complex navigation over different scales and environments. Navigation studies in amphibians have largely focused on species with life histories that require accurate spatial movements, such as territorial poison frogs and migratory pond-breeding amphibians that show fidelity to mating sites. However, other amphibian species have remained relatively understudied, leaving open the possibility that well-developed navigational abilities are widespread. Here, we measured short-term space use in non-territorial, non-migratory cane toads (Rhinella marina) in their native range in French Guiana. After establishing site fidelity, we tested their ability to return home following translocations of 500 and 1000 meters. Toads were able to travel in straight trajectories back to home areas, suggesting navigational abilities similar to those observed in amphibians with more complex spatial behavior. These observations break with the current paradigm of amphibian navigation and suggest that navigational abilities may be widely shared among amphibians.

Enriched root bacterial microbiome in invaded vs native ranges of the model grass allotetraploid Brachypodium hybridum

Invasive species can shift the composition of key soil microbial groups, thus creating novel soil microbial communities. To better understand the biological drivers of invasion, we studied plant-microbial interactions in species of the Brachypodium distachyon complex, a model system for functional genomic studies of temperate grasses and bioenergy crops. While Brachypodium hybridum invasion in California is in an incipient stage, threatening natural and agricultural systems, its diploid progenitor species B. distachyon is not invasive in California. We investigated the root, soil, and rhizosphere bacterial composition of Brachypodium hybridum in both its native and invaded range, and of B. distachyon in the native range. We used high-throughput, amplicon sequencing to evaluate if the bacteria associated with these plants differ, and whether biotic controls may be driving B. hybridum invasion. Bacterial community composition of B. hybridum differed based on provenance (native or invaded range) for root, rhizosphere, and bulk soils, as did the abundance of dominant bacterial taxa. Bacteroidetes, Cyanobacteria and Bacillus spp. (species) were significantly more abundant in B. hybridum roots from the invaded range, whereas Proteobacteria, Firmicutes, Erwinia and Pseudomonas were more abundant in the native range roots. Brachypodium hybridum forms novel biotic interactions with a diverse suite of rhizosphere microbes from the invaded range, which may not exert a similar influence within its native range, ostensibly contributing to B. hybridum’s invasiveness. These associated plant microbiomes could inform future management approaches for B. hybridum in its invaded range and could be key to understanding, predicting, and preventing future plant invasions.

Fungal Diversity in Multiple Post-harvest Aged Red Pine Stumps and Their Potential Influence on Heterobasidion Root Rot in Managed Stands Across Minnesota

Thinning operations that occur in managed red pine (Pinus resinosa) stands, create tree stumps that can serve as a habitat for fungi, especially Heterobasidion irregulare, the cause of a serious root disease. Different fungi can colonize stumps early and the community of fungi can change over time as initial fungal species become replaced. Samples were collected from both the native and non-native range of red pine from stumps that were cut at different time periods. Stumps that were harvested at 0–1, 2–3, 5–6, and 10–12 years before sampling were used to provide data on the diversity of fungi that colonize tree stumps and how these communities can change over time as well as how they influence colonization of H. irregulare. Traditional culturing methods and Illumina MiSeq sequencing were used to identify the fungi in the samples. Of particular interest was Phlebiopsis gigantea, which can colonize cut stumps and prevent H. irregulare from becoming established. Overall, P. gigantea was the most abundant fungus isolated and sequenced via Illumina MiSeq. Results show that Phlebiopsis gigantea was isolated from 90% of all stumps sampled for sites harvested within 3 years of sampling in the native range of red pine compared to 33% in the non-native range. For Illumina MiSeq, 5,940 total amplicon sequence variants (ASVs) were detected. P. gigantea represented 14% of the total reads and composed 19% of the reads in the native range and 8% in non-native range of red pine. Furthermore, P. gigantea represented 38% of the reads for stumps that were harvested within 3 years of sampling in the native range of red pine compared to 14% in the non-native range. These results help demonstrate that a higher amount of P. gigantea is present in the native range of red pine and could be acting as a native biological control agent. Additional fungi, including Resinicium bicolor, Hypochnicium cremicolor, Leptographium spp., and others identified at different cutting times are also discussed. Finally, different diversity indices revealed similar, but slightly higher diversity for southern sites via Shannon and Simpson Diversity indices. Beta diversity demonstrated a similar species composition in stumps harvested at different times with these stumps being grouped together based on harvesting years.

New Serbian records of the slug Tandonia kusceri (H. Wagner, 1931) (Gastropoda: Eupulmonata: Milacidae) suggest its continuous dispersal to the north

Tandonia kusceri (H. Wagner) is a terrestrial slug native to the Balkan Peninsula (S. Serbia, N. Macedonia, Bulgaria and Dobrudja region of Romania) and the European part of Turkey. In Serbia, it was known mostly from the southern regions. The northernmost locality (Palić settlement, near Subotica) reported here suggests that the slug’s distribution is nearly continuous from its native range until Slovakia. The new record was first recognised from the pictures posted on a Facebook group for insect identification in 2021. The identification was subsequently confirmed by anatomical examination. This further emphasises the importance of social media in monitoring the spread of invasive invertebrates.

Increased rates of dispersal of free-ranging cane toads (Rhinella marina) during their global invasion

Invasions often accelerate through time, as dispersal-enhancing traits accumulate at the expanding range edge. How does the dispersal behaviour of individual organisms shift to increase rates of population spread? We collate data from 44 radio-tracking studies (in total, of 650 animals) of cane toads (Rhinella marina) to quantify distances moved per day, and the frequency of displacement in their native range (French Guiana) and two invaded areas (Hawai’i and Australia). We show that toads in their native-range, Hawai’i and eastern Australia are relatively sedentary, while toads dispersing across tropical Australia increased their daily distances travelled from 20 to 200 m per day. That increase reflects an increasing propensity to change diurnal retreat sites every day, as well as to move further during each nocturnal displacement. Daily changes in retreat site evolved earlier than did changes in distances moved per night, indicating a breakdown in philopatry before other movement behaviours were optimised to maximise dispersal.

Profile of the in silico secretome of the palm dieback pathogen, a fungus that puts natural oases at risk

Understanding biotic changes that occur alongside climate change constitute a research priority of global significance. Here, we address a plant pathogen that poses a serious threat to life on natural oases, where climate change is already taking a toll and severely impacting human subsistence. Fusarium oxysporum f. sp. albedinis is a pathogen that causes dieback disease on date palms, a tree that provides several critical ecosystem services in natural oases; and consequently, of major importance in this vulnerable habitat. Here, we assess the current state of global pathogen spread, we annotate the genome of a sequenced pathogen strain isolated from the native range and we analyse its in silico secretome. The palm dieback pathogen secretes a large arsenal of effector candidates including a variety of toxins, a distinguished profile of secreted in xylem proteins (SIX) as well as an expanded protein family with an N-terminal conserved motif [SG]PC[KR]P that could be involved in interactions with host membranes. Using agrobiodiversity as a strategy to decrease pathogen infectivity, while providing short term resilient solutions, seems to be widely overcome by the pathogen. Hence, the urgent need for future mechanistic research on the palm dieback disease and a better understanding of pathogen genetic diversity.