The future of invasive African grasses in South America under climate change

Phylogenomic analysis reveals five independently evolved African forage grass clades in the genus Urochloa

BACKGROUND AND AIMS

The grass genus Urochloa (Brachiaria) sensu lato includes forage crops that are important for beef and dairy industries in tropical and sub-tropical Africa, South America and Oceania/Australia. Economically important species include U. brizantha, U. decumbens, U. humidicola, U. mutica, U. arrecta, U. trichopus, U. mosambicensis and Megathyrsus maximus, all native to the African continent. Perennial growth habits, large, fast growing palatable leaves, intra- and interspecific morphological variability, apomictic reproductive systems and frequent polyploidy are widely shared within the genus. The combination of these traits probably favoured the selection for forage domestication and weediness, but trait emergence across Urochloa cannot be modelled, as a robust phylogenetic assessment of the genus has not been conducted. We aim to produce a phylogeny for Urochloa that includes all important forage species, and identify their closest wild relatives (crop wild relatives). Finally, we will use our phylogeny and available trait data to infer the ancestral states of important forage traits across Urochloa s.l. and model the evolution of forage syndromes across the genus.

METHODS

Using a target enrichment sequencing approach (Angiosperm 353), we inferred a species-level phylogeny for Urochloa s.l., encompassing 54 species (~40 % of the genus) and outgroups. Phylogenies were inferred using a multispecies coalescent model and maximum likelihood method. We determined the phylogenetic placement of agriculturally important species and identified their closest wild relatives, or crop wild relatives, based on well-supported monophyly. Further, we mapped key traits associated with Urochloa forage crops to the species tree and estimated ancestral states for forage traits along branch lengths for continuous traits and at ancestral nodes in discrete traits.

KEY RESULTS

Agricultural species belong to five independent clades, including U. brizantha and U. decumbens lying in a previously defined species complex. Crop wild relatives were identified for these clades supporting previous sub-generic groupings in Urochloa based on morphology. Using ancestral trait estimation models, we find that five morphological traits that correlate with forage potential (perennial growth habits, culm height, leaf size, a winged rachis and large seeds) independently evolved in forage clades.

CONCLUSIONS

Urochloa s.l. is a highly diverse genus that contains numerous species with agricultural potential, including crop wild relatives that are currently underexploited. All forage species and their crop wild relatives naturally occur on the African continent and their conservation across their native distributions is essential. Genomic and phenotypic diversity in forage clade species and their wild relatives need to be better assessed both to develop conservation strategies and to exploit the diversity in the genus for improved sustainability in Urochloa cultivar production.

Vascular Plant Species Inventory of Mexico's Revillagigedo National Park: Awareness of Alien Invaders as a Sine Qua Non Prerequisite for Island Conservation

The Revillagigedo Archipelago, located in the Eastern Pacific Ocean, stands out for its unique biological richness and endemism. These islands remained uninhabited until the second half of the twentieth century, allowing a better conservation status than on other oceanic islands. However, the continuous introduction of potentially invasive alien plant species, and the lack of adequate control or eradication actions, jeopardize the conservation and restoration of these islands' fragile ecosystems. We present the most complete vascular plant species inventory and an updated list of alien plant species of the Revillagigedo Archipelago, which was compiled through an extensive review of national and international plant collections and other sources. Our 272 species list includes 106 alien plant species (39.3%; 104 in Socorro, and 16 in Clarion): 67 (24.8%) are naturalized, 14 (5.2%) are casual aliens, and 25 (9.3%) subsist under cultivation. The documented alien species belong to 73 families. Annual and perennial herbs are the prevailing life forms in the alien flora, while naturalized species are primarily native to North America. The number of introduced species has increased significantly since the islands became inhabited. Many of the recently introduced species pose a major invasion risk like on other islands of the world.

Characterizing the Spatial Distribution of Eragrostis Curvula (Weeping Lovegrass) in New Jersey (United States of America) Using Logistic Regression

The increasing spread of invasive plants has become a critical driver of global environmental change. Once established, invasive species are often impossible to eradicate. Therefore, predicting the spread has become a key element in fighting invasive species. In this study, we examined the efficiency of a logistic regression model as a tool to identify the spatial occurrence of an invasive plant species. We used Eragrostis curvula (Weeping Lovegrass) as the dependent variable. The independent variables included temperature, precipitation, soil types, and the road network. We randomly selected 68 georeferenced points to test the goodness of fit of the logistic regression model to predict the presence of E. curvula. We validated the model by selecting an additional 68 random points. Results showed that the probability to successfully predict the presence of E. Curvula was 82.35%. The overall predictive accuracy of the model for the presence or absence of E. Curvula was 80.88%. Additional tests including the Chi-square test, the Hosmer–Lemeshow (HL) test, and the area under the curve (AUC) values, all indicated that the model was the best fit. Our results showed that E. curvula was associated with the identified variables. This study suggests that the logistic regression model can be a useful tool in the identification of invasive species in New Jersey.