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Tropical Biology

Arthan, Watchara [1], Dunning, Luke [2], Besnard, Guillaume [3], Lehmann, Caroline E.R. [4], Kellogg, Elizabeth [5], Hackel, Jan [6], Mitchley, Jonathan [7], Vorontsova, Maria [6].

Evolution of lineages, niches, and traits in the dominant savanna grasses Heteropogon and Themeda (Panicoideae-Andropogoneae).

Closely related C4 grass genera Heteropogon and Themeda are common to dominant components of many grasslands and savannas across the tropics. Previous studies suggested a close relationship between the two genera, but full phylogenetic investigations had not been performed. Biogeographically and ecologically,species of Heteropogon and Themeda vary from the rare and locally endemic to the cosmopolitan and well-known: H. contortus and T. triandra are two of the world’s most common grasses. We hypothesized that climate, habitat, and functional traits shaped the modern macroecological patterns observed. We performed phylogenomic reconstructions to understand evolutionary history and ecological niche evolution. Occurrence records, bioclimatic data, habitat classification, and functional trait data were compiled. Niche analyses were performed to compare niche occupancy among species, and trait differences were statistically tested. Phylogenic trees were then integrated with the bioclimatic, habitat, and functional trait data to investigate how environmental niches and traits evolved to shape the distributions of Heteropogon and Themeda. Phylogenetic analyses demonstrated that Heteropogon and Themeda are not monophyletic. Heteropogon melanocarpus and H. ritchiei were nested within the Themeda clade in both plastome and nuclear trees. Themeda arundinacea and T. villosa formed a lineage separate from other Themeda species. Discordant positions of H. triticeus between the plastome and nuclear trees suggests that hybridization may have been involved in the evolutionary process. We found that temperature and precipitation seasonality, mean annual precipitation, and precipitation of driest quarter were significant factors in the species distributions in bioclimatic space. These variables separated the species by habitats and functional traits into clear savanna and wetland groups. Savanna occupancy and adaptations are likely to have been ancestral to the Heteropogon-Themeda clade. Evolutionary shifts into wetland environments occured at least twice. We propose that the functional traits and bioclimatic niche occupancy evolved as adaptations to savanna and then wetland environments. Wetland species exhibit greater plant height and longer leaf blades than the savanna species. Habitat is also associated with awn morphology: straight awns present in wetland species were likely reduced from the geniculate awns observed in the savanna species, potentially linked to fire and the amount of precipitation. We describe and analyse complex ecological characteristics, evolutionary history and relationships of the Heteropogon-Themeda group for the first time, with a view to better understand and predict the ecology and dynamics of tropical savanna environments.

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1 - Royal Botanic Gardens, Kew, Department of Plant and Fungal Biology, Kew, Richmond, Surrey, TW9 3AE, UK
2 - University of Sheffield, Department of Animal and Plant Sciences, Western Bank, Sheffield , S10 2TN, UK
3 - CNRS, Université Paul Sabatier, Laboratoire Évolution & Diversité Biologique (EDB), 118 Route de Narbonne, Toulouse , 31062, France
4 - Royal Botanic Garden Edinburgh, Tropical Diversity, Edinburgh, EH3 5LR, UK
5 - Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO, 63132, United States
6 - Royal Botanic Gardens, Kew, Department of Plant and Fungal Biology, Kew, Richmonnd, Surrey, TW9 3AE, UK
7 - University of Reading, School of Biological Sciences, Whiteknights, Reading, Berkshire , RG6 6AH, UK

niche evolution
C4  grasses
functional traits
Bioclimatic niche
Trait evolution.

Presentation Type: Oral Paper
Session: TB, Tropical Biology
Location: Virtual/Virtual
Date: Monday, July 19th, 2021
Time: 1:15 PM(EDT)
Number: TB004
Abstract ID:754
Candidate for Awards:None

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