Understory upheaval: factors influencing Japanese stiltgrass invasion in forestlands of Tennessee, United States

Importance of Anthropogenic Determinants of Tubastraea coccinea Invasion in the Northern Gulf of Mexico

Tubastraea coccinea is an invasive coral that has had ecological, economic, and social impacts in the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico (GoM). Tubastraea coccinea is considered a major threat to marine biodiversity, whose occurrence in its non-native range has been associated with artificial structures such as oil/gas platforms and shipwrecks. A recent species distribution model identified important determinants of T. coccinea invasion in the northern GoM and projected its potential range expansion. However, the potential effects of anthropogenic factors were not considered. We used boosted regression trees to develop a species distribution model investigating the importance of oil/gas platforms and shipping fairways as determinants of T. coccinea invasion in the northern GoM. Our results indicate that maximum salinity, distance to platform, minimum nitrate, and mean pH were the first to fourth most influential variables, contributing 31.9%, 23.5%, 22.8%, and 21.8%, respectively, to the model. These findings highlight the importance of considering the effects of anthropogenic factors such as oil/gas platforms as potential determinants of range expansion by invasive corals. Such consideration is imperative when installing new platforms and when decommissioning retired platforms.

Nodding behavior observed in Japanese stiltgrass, Microstegium vimineum , seedlings from time-lapse observations

Invasive species are the second main cause of biodiversity loss because of their exceptional ability to supplant native species by creating major upheavals in ecosystems. Inexpensive and prevalent time-lapse photography provides an exciting opportunity to better understand the aggressive behavior of invasive species including how they invade and conquer new territory. One of the most pervasive invasive species in the Eastern United States is Japanese stiltgrass, Microstegium vimineum (Trin.) A. Campus, which originated from Southeast Asia. Previous research has examined the conditions that enable Japanese stiltgrass to become invasive, but nothing is known regarding root and shoot behavior. Here time-lapse was used to examine Japanese stiltgrass seedlings, early in their development, as a first step to observe its behavior. Our results demonstrate that Japanese stiltgrass shoots appear to drop or collapse and then resurrect back to an upright stature - sometimes the same plant exhibits this behavior multiple times. We have shown, in addition, that emergent stilt root growth rate increases with increased root length. This and similar kinds of analyses may provide insight into how Japanese stiltgrass thrives aggressively in a non-native environment with the goal of developing better methods of controlling this noxious weed.

Chromosome Level Genome Assembly and Annotation of Highly Invasive Japanese Stiltgrass (Microstegium vimineum)

The invasive Japanese stiltgrass (Microstegium vimineum) affects a wide range of ecosystems and threatens biodiversity across the eastern USA. However, the mechanisms underlying rapid adaptation, plasticity, and epigenetics in the invasive range are largely unknown. We present a chromosome-level assembly for M. vimineum to investigate genome dynamics, evolution, adaptation, and the genomics of phenotypic plasticity. We generated a 1.12-Gb genome with scaffold N50 length of 53.44 Mb respectively, taking a de novo assembly approach that combined PacBio and Dovetail Genomics Omni-C sequencing. The assembly contains 23 pseudochromosomes, representing 99.96% of the genome. BUSCO assessment indicated that 80.3% of Poales gene groups are present in the assembly. The genome is predicted to contain 39,604 protein-coding genes, of which 26,288 are functionally annotated. Furthermore, 66.68% of the genome is repetitive, of which unclassified (35.63%) and long-terminal repeat (LTR) retrotransposons (26.90%) are predominant. Similar to other grasses, Gypsy (41.07%) and Copia (32%) are the most abundant LTR-retrotransposon families. The majority of LTR-retrotransposons are derived from a significant expansion in the past 1-2 Myr, suggesting the presence of relatively young LTR-retrotransposon lineages. We find corroborating evidence from Ks plots for a stiltgrass-specific duplication event, distinct from the more ancient grass-specific duplication event. The assembly and annotation of M. vimineum will serve as an essential genomic resource facilitating studies of the invasion process, the history and consequences of polyploidy in grasses, and provides a crucial tool for natural resource managers.