Historical contingency and the origin of tropical-temperate niche transitions in the grass family (Poaceae)
Jill Preston1 & Siri Fjellheim2
1The University of Vermont; 2Norwegian University of Life Sciences. Jill.Preston@uvm.edu
Biotic and abiotic factors interact to restrict the distribution of taxonomic groups between specific boundaries that comprise their ecological niche. Whereas a large part of a taxon’s ability to penetrate these boundaries will be dictated by local selection pressures and novel ecological opportunities, niche evolution will also be constrained internally through the inheritance of adaptive, neutral, or even maladaptive ancestral trait complexes and their underlying mechanisms.
Flowering plants evolved when the Earth was largely tropical. However, although the majority of species have remained in the tropics, there are multiple examples of evolutionary shifts into both northern and southern temperate regions. Using the grass family (Poaceae) as a model, we aim to pinpoint key traits that have facilitated tropical-temperate boundary crossings, and assess the degree to which such transitions have been facilitated by changes in lineage-specific versus deeply conserved developmental modules. Our data so far support a combination of these forces at play in the evolution of flowering time and cold acclimation, and highlight the importance of phylogenetic history in shaping the evolutionary potential of taxa to cross major ecological boundaries.
Key words: grasses, low temperature adaptations, Pooideae, temperate regions, vernalization.
Funded by: National Science Foundation, Norway Research Council, United States Department of Agriculture - HATCH
Grasses and grasslands of Madagascar
Maria Vorontsova1, Guillaume Besnard2, Caroline Lehmann3 & Vololoniaina Jeannoda4
1Royal Botanic Gardens, Kew; 2Laboratoire Evolution & Diversité Biologique (EDB, UMR 5174), CNRS/IRD/Université Toulouse III; 3University of Edinburgh; 4Département de Biologie et Ecologie Végétales, University of Antananarivo. m.vorontsova@kew.org
Anthropogenic destruction has long been blamed for 65% of Madagascar’s land area being covered by grassland and savanna. Over the last six years, via new collections of Malagasy grasses and taxonomic work, we have found that an estimated 217 of Madagascar’s 541 grass species are endemic, a level of endemicity consistent with other subtropical islands. Madagascar contains 70 endemic grass lineages that colonised Madagascar primarily from Africa, with a mean age of 3.5 million years; 50% of grass dispersals were C4 lineages pre-adapted to open canopy habitats. The High Plateau is home to a diverse grass flora, where a grass checklist of the Itremo Protected Area found 20% of grass species restricted to the High Plateau. Grass community composition suggests Tapia woodlands, historically perceived as degraded forest, are a savanna and that the grass and tree functional traits of this ecosystem diverge from gallery forests. Phylogenetic diversity within grassy ecosystems decreases with strong physical disturbance, such as grazing, indicating ecosystem dynamics typical of natural assemblages. Madagascar is home to an ancient and diverse grass flora, with local species assemblages functioning similarly to savanna ecosystems of Africa, indicating that pre-human Madagascar was home to tropical grasslands and savannas.
Key words: Africa, evolution, Madagascar, Poaceae, savanna.
Funded by: GBIF BID; British Ecological Society; UK SynTax award scheme supported by BBSRC and NERC; National Geographic Society; Bentham-Moxon Trust; Kew Madagascar Conservation Centre; Madagascar National Parks; Direction Générale des Forêts; Parc Botanique et Zoologique de Tsimbazaza
Wind pollination and evolution of the grass flower Lynn G. Clark1 & Phillip C. Klahs1
1Iowa State University. lgclark@iastate.edu
Imagine the remarkable and seemingly random journey a pollen grain must travel to accomplish pollination in anemophilous plants. Grasses, the most diverse wind-pollinated family of seed plants, have evolved a wide array of spikelet morphologies that apparently uniformly rely on anemophily.
We explore the critical junction of flower form and function by constructing virtual models of grass spikelets (the flower with associated bracts) for computational fluid dynamic simulations to understand the aerodynamics of anemophily and investigate to what extent spikelet morphology has been shaped by it. Do variations in spikelet morphology (particularly compression, presence or absence of awns, and stigma position at anthesis) affect pollination? Do these variations correlate to ecological niche? Our preliminary results indicate that two species of Festuca (one from forests, one from prairies) differ in airflow patterns around the spikelet, with the forest species creating faster wind speeds around the stigmas relative to the prairie species. Additionally, spikelets with well-developed glumes and awns funnel passing air through different regions relative to the same spikelet without those structures. This research increases our understanding of the macroevolutionary history of grass spikelet morphology and may be applied to studies of wind pollination in other angiosperms.
Key words: biomechanics, computational fluid dynamics, Poaceae, pollination, reproductive biology.
The Viking syndrome—why grasses are so successful Peter Linder1
1University of Zürich, Switzerland. peter.linder@systbot.uzh.ch
Poaceae is highly successful, occurring in (almost) all ecosystems and ecologically dominating many, and high species richness. The success of grasses may be due to their capacity to colonize, persist, and transform environments (the “Viking syndrome”). This results from combining effective long-distance dispersal, efficacious establishment biology, ecological flexibility, resilience to disturbance and the capacity to modify environments by changing the fire and mammalian herbivory regimes. We identify a diverse set of functional traits linked to dispersal, establishment and competitive abilities. These include unique features such as the spikelet, the awned lemma, the precocious embryo and large starch reserves. Other potentially important traits are wind pollination, widespread polyploidy, gametic self-incompatibility, C4 photosynthesis, frost tolerance, and a sympodial growth-form. Grasses have traits that facilitate frequent fire and tolerate grazing. We trace the accumulation of these traits since the late Cretaceous grass origin, and link these to the several phases in the grass success story: Cretaceous dinosaur fodder, to occasional late Palaeogene tropical grassland patches, to extensive Miocene C3 grasslands, to dramatic Pliocene expansion of tropical C4 savannas and grasslands, and finally Pleistocene C3 steppe grasslands.
Key words: dispersal, establishment biology, fire and grazing regimes, functional traits, Poaceae
Macrofossils, cuticles, and phytoliths: an update on the paleoecology and biogeography of the grasses
Timothy J. Gallaher1, María Laura Pipo2, Lynn G. Clark3, Ari Iglesias2 & Caroline A.E.
Strömberg4
1University of Washington, Biology Department, Iowa State University, EEOB; 2Instituto de Investigaciones en Biodiversidad y Medioambiente (CONICET-UNCO); 3Iowa State University, EEOB; 4University of Washington, Biology Department, Burke Museum of Natural History and Culture. tjgallaher@gmail.com
The timing of the origin and diversification of the grass family has become the subject of intense debate particularly with regards to the taxonomic placement of recently described grass phytoliths and cuticle from the Maastrichtian of India. Here, we report on new quantitative analyses of phytoliths from multiple sources and a newly discovered early-mid Campanian fossil grass cuticle from James Ross Island, Antarctica. Time calibrated phylogenetic analyses and ancestral area estimations using macrofossils, fossil cuticles and phytoliths support an Early Cretaceous Gondwanan origin of the Poaceae. Ancestral habitat estimations using extant taxa indicate that grasses first evolved in forest-associated habitats and may have occupied key positions in forest margins, allowing lineages to more readily evolve into either deep shade or open habitats. In the Late Cretaceous or Paleocene, the PACMAD and Pooideae moved from forest associated ecosystems to open habitats, more than 30 Ma before the spread of grass-dominated vegetation in the Oligocene-Miocene. Our temporal estimations also suggest that C4 photosynthesis evolved first in the Chloridoideae in the Eocene or Oligocene, approximately 15-20 Ma earlier than other C4
PACMAD lineages and long before the rise to dominance of C4 grasslands within the last 10 Ma.
Key words: ancestral state estimation, fossils, paleobotany, phylogenetics, Poaceae.
C4 grass species assemblages in savannas: a biogeographical approach Yanis Bouchenak-Khelladi1
1Institute of Systematic and Evolutionary Botany, University of Zürich. boucheny@tcd.ie
Modern savannas are species-rich biomes, which include many modern mammal lineages and are dominated by C4 grass (Poaceae) species. These systems are thought to have evolved by the late Miocene-early Pliocene and have spread worldwide 8 mya. However, the assembly of grass species seems to indicate massive grass intercontinental dispersal but its role in savanna species assemblies is unknown. To resolve the question of how the modern subfamily composition of the savannas in each disjunct region was assembled, we ask (i) on which continent did C4 clades evolve and (ii) whether dispersal from the area of origin accelerated with the ecological dominance of savannas.
We used the largest time-corrected species-level phylogenies of PACMAD grasses to optimize ancestral biogeographical areas using the Dispersal-Extinction-Cladogenesis model and computed relative dispersal rates for each clade through time. We show that dispersal rates for Andropogoneae increased by 8 mya, which coincided with an increase in the isotopic signal.
However, the major C4 clades started dispersing before the onset of savanna expansion in the middle Miocene. The presence of C4 clades by the early Miocene in Africa, Tropical Asia and Australasia suggests that local C4 patches were followed by intercontinental dispersal in the late Miocene.
Key words: biogeography, C4 grasses, intercontinental dispersals, Miocene, spread of savannas.