The complexity of mass extinction

The Possible Earliest Allopolyploidization in Tracheophytes Revealed by Phylotranscriptomics and Morphology of Selaginellaceae

Selaginellaceae, originated in the Carboniferous and survived the Permian-Triassic mass extinction, is the largest family of lycophyte, which is sister to other tracheophytes. It stands out from tracheophytes by exhibiting extraordinary habitat diversity and lacking polyploidization. The organelle genome-based phylogenies confirmed the monophyly of Selaginella, with six or seven subgenera grouped into two superclades, but the phylogenetic positions of the enigmatic Selaginella sanguinolenta clade remained problematic. Here, we conducted a phylogenomic study on Selaginellaceae utilizing large-scale nuclear gene data from RNA-seq to elucidate the phylogeny and explore the causes of the phylogenetic incongruence of the S. sanguinolenta clade. Our phylogenetic analyses resolved three different positions of the S. sanguinolenta clade, which were supported by the sorted three nuclear gene sets, respectively. The results from the gene flow test, species network inference, and plastome-based phylogeny congruently suggested a probable hybrid origin of the S. sanguinolenta clade involving each common ancestor of the two superclades in Selaginellaceae. The hybrid hypothesis is corroborated by the evidence from rhizophore morphology and spore micromorphology. The chromosome observation and Ks distributions further suggested hybridization accompanied by polyploidization. Divergence time estimation based on independent datasets from nuclear gene sets and plastid genome data congruently inferred that allopolyploidization occurred in the Early Triassic. To our best knowledge, the allopolyploidization in the Mesozoic reported here represents the earliest record of tracheophytes. Our study revealed a unique triad of phylogenetic positions for a hybrid-originated group with comprehensive evidence and proposed a hypothesis for retaining both parental alleles through gene conversion.

Selaginella and 400 million years of separation

Selaginella (spikemoss) is an enigma in the plant kingdom. Although a fascination to botanists at the turn of the twentieth century, members of this genus are unremarkable in appearance, never flower, and are of no agronomic value. However, members of this genus are relicts from ancient times, and one has to marvel at how this genus has survived virtually unchanged in appearance for hundreds of millions of years. In light of the recent completion of the Selaginella moellendorffii genome sequence, this review is intended to survey what is known about Selaginella, with a special emphasis on recent inquiries into its unique biology and importance in understanding the early evolution of vascular plants.

Disharmony between society and environmental carrying capacity: a historical review, with an emphasis on China

Nature can survive without humans, but humans cannot survive without nature. Despite a clear understanding of this dependency, humans continue to exist in disharmony with nature, and our current environmental and human dilemmas reflect old problems with a long history. Societies have historically experienced many transitions from harmony between nature and society to a crisis of disharmony, followed by a subsequent transition from crisis to harmony. Such ecological crises arise when society no longer practices sustainable consumption of resources within the limits imposed by the environmental carrying capacity. Over the long term, the growth in human desires has always exceeded the growth in the environmental carrying capacity. Science, technology, and social institutions must all be improved to resolve the ecological crises that arise from this imbalance. This paper discusses how increasing understanding of the problem by the public and by decision makers is the key to minimizing the undesirable impacts of the coming bottleneck for sustainable development. Furthermore, we emphasize how this awareness must be translated into fundamental political and economic changes.