Biology subjects

Lloyd Evans, D.

Publications and source records attributed to Lloyd Evans, D..

5 recordsLinked to original sources

bioRxiv2020

On the Validity of the Saccharum Complex and the Saccharinae Subtribe: A Re-assessment

The Saccharum Complex represents an hypothetical collective of species that were supposedly responsible, through interbreeding, for the origins of sugarcane. Though recent phylogenetic studies have cast doubt on the veracity of this hypothesis, it has cast a long shadow over the taxonomics of the Andropogoneae and the Saccharinae subtribe. Though evidence suggests that Saccharum s.s. is comprised of only three true species, according to Kews GrassBase there are as many as 34 species in Saccharum s.l. Our recent work has shown that many of these species are millions of years divergent from Saccharum. As the Saccharum complex represents the species that sugarcane breeders attempt to introgress into sugarcane, and as the Saccharinae, in its current form, covers almst 12 million years of Andropogoneae evolution an update on the extents of the Taxonomic and customary groupings is much needed. Based on the latest sequence based phylogenies and the inclusion of traditional taxonomics we develop an integrated view of the Saccharinae + Saccharum complex species in the context of the major groupings within the Andropogoneae. We use this phylogeny to re-circumscribe the limits of both the Saccharinae subtribe and the Saccharum complex group of interbreeding species.

evolutionary biology↗

bioRxiv2020

Origins, History and Molecular Characterization ofCreole Cane

Since it was first introduced to Europe in 711 CE and planted in the Americas in 1506, a single type of cane dominated sugar production for 1100 years, until it was finally ousted by Tahitian cane c. 1790. This cane became known as Creolea[A][Z] and is present in the ancestry of many sugarcane hybrids, even today. Whether there was only a single variety of Creole cane or multiple varieties has been a matter of debate for decades. Creole cane remains relevant today, as a Creole cane from Jamaica is the currently chosen lecotype for Saccharum officinarum. In this study we identify 18 historical images of Creole cane, many not previously published. We employ image analyses to characterize the internodes and demonstrate evidence for only a single type of Creole in the new world. Chloroplasts and 45s ribosomal RNA sequences from the cultivar BH10/12 (known to have a Creole female parent) were determined that Java ribbon cane is the historical New World sugarcane known as Creole. We demonstrate that Creole cane is an hybrid and not a single species. Thus S. officinarum has no type specimen. We also sequence a ribbon cane (also known as Guinguam) that appeared in the Caribbean between 1790 and 1810 and demonstrate that this cane was a Sinense type from Java that links back to the work of Rumphinus (1660s).

genomics↗

bioRxiv2020

Assembly of 23 Plastid Genomes Provides the Chloroplast View on Miscanthus Origins

Despite its economic importance as a new biofuel resource, little work has been done on the large-scale phylogenetics of Miscanthus. Twenty-three complete Miscanthus chloroplasts were assembled and annotated. A phylogeny was performed with these assemblies, which shows the relationships between the main Miscanthus species and sub-species. The phylogeny demonstrates that there is no meaningful distinction between Miscanthus floridulus and Miscanthus transmorrisonensis as the accessions are not distinct. However, at the crown of the tree there is a clear distinction between M. sinensis malepartus and M. sinensis condensatus subspecies. The phylogeny reaveals that the female parent of Miscanthus xgiganteus is Miscanthus lutarioriparius rather than Miscanthus sacchariflorus. The phylogeny also shows a novel hybrid between Miscanthus oligostachyus and Miscanthus sinensis, a grouping to which Miscanthus sinensis var Purpurascens belongs. This hybrid form is named Miscanthus xoligostachyus.

evolutionary biology↗

bioRxiv2020

A Geophysical and Climatological Assessment of New Guinea -- Implications for the Origins of Saccharum

Any assessment of whether or not Saccharum species are native or introduced in New Guinea require an evolutionary (in a geological sense), geophysical and climatological assessment of the island. Like many of the land masses circling the Pacific (in the volcanically active region known as the ring of fire) New Guinea is geologically young, with the island in its modern form not pre-dating 2 Ma. Novel modelling of the 74 ka youngest Toba supereruption indicates a potential extinction level tsunami and loss of habitat. The late Pleistocene megafaunal mass extinction and the last glacial maximum (33-16 ka) are two global effects that would have significantly altered the flora on New Guinea; though the implications of these events on New Guinea have not previously been studied. Even if the genus Saccharum was established on the island during pre-historic times the consequences of Toba and other global climate change events means that it would have been eliminated from New Guinea and would have had to be re-introduced during the period of human colonization. Indeed, given the evolution of Saccharums immediate ancestors in Africa and Indochina it is most parsimonious to conclude that it was never native to New Guinea, but was introduced by humans relatively recently. Little work has been done on palaeotsunami evidence and ancient tsunami modelling in New Guinea. However, the recent recognition that the Aitape skull (dating to about 6 ka) may have been the victim of a tsunami (Goff et al. 2017) show that, in the past, tsunami have pen etrated significantly (about 10 km in this case) into the interior of the island to have a profound effect on biodiversity. This tsunami would have left the north coast of the island impoverished of plant life for several decades after.

paleontology↗

bioRxiv2020

Complete Chloroplast Genomes of Saccharum giganteum, Saccharum longisetosum, Cleistachne sorghoides, Sarga timorense, Narenga porphyrocoma and Tripsacum dactyloides. Comparisons with ITS phylogeny and Placement within Saccharum.

The first complete chloroplast and Internal Transcribed Sequence (ITS) cassette sequences for the species: Saccharum giganteum, Saccharum longisetosum, Cleistachne sorghoides, Saccharum narenga and Tripsacum dactyloides are presented. Corresponding sequences for a new isolate of Sarga timorense were assembled. Phylogenetic analyses place S. giganteum, S. longisetosum and S. narenga within the Saccharinae but distinct from Saccharum, whilst C. sorghoides emerges as a member of genus Sarga and Tripsacum datyloides as a member of the Tripsacinae. Comparison of chloroplast and ITS phylogenies reveal complex reticulate evolution within the Saccharinae, with S. giganteum, S. longisetosum and S. narenga, despite having the same base chromosome count (15) having different evolutionary origins; making them members of different genera and not members of genus Saccharum. The importance of reticulate evolution in the origins of Andropogoneae, particularly the Saccharinae and the unique positions of Saccharum and Miscanthus is discussed.

evolutionary biology↗