Gallaher, Timothy , Adams, Dean , Sherratt, Emma , Attigala, Lakshmi , Klahs, Phillip , Wysocki, Bill , Burke, Sean , Duvall, Mel , Clark, Lynn .
The evolution of leaf shape in the grass family (Poaceae).
Grasses have adapted to a remarkable breadth of habitats. They are best known from open grasslands and croplands which today cover over 40% of the Earth’s terrestrial surface; however, the family also has members, including the oldest extant lineages, which are found in deeply shaded forest understories or more open woodlands. Some grasses have adapted to areas characterized by hot and arid conditions while others are able to tolerate subfreezing temperatures. In a series of studies we investigated the role of the grass leaf as an adaptive macroevolutionary structure. We used geometric morphometrics to evaluate the evolution of leaf shape as well as other characters such as leaf thickness and the presence of pseudopetioles over a new time-calibrated plastome-based phylogeny of the family. We used ancestral state reconstructions and rate of change analyses to evaluate correlations between characters, climate/habitat and photosynthetic pathway. Grasses likely originated in the forest understory over 100 MYA with broad pseudopetiolate leaves. Linear leaves evolved several times in the family beginning in the Paleocene. Several key shifts in the rate of change of leaf shape were identified. These character shifts are associated with the occupation of open habitats and greater numbers of species in the Pooideae, Chloridoideae and Andropogoneae. Likewise re-adaptation to shaded conditions involves a regain of wider leaves and pseudopetioles, as seen in the Panicoideae. These patterns strongly suggest functional constraints on leaf shape in both shady and open habitats. Further work is needed to understand the mechanisms that act upon the meristems within the developing leaf and how these interact to produce the overall structure of the organ, as well as to assess homology of the leaf blade and associated structures (e.g., pseudopetioles, collar, auricles, leaf intercalary meristems) across the family.
1 - Iowa State University, EEOB, 251 Bessey Hall, Ames, IA, 50011, USA
2 - Iowa State University, EEOB, 2220 Osborn Dr., Room 251 Bessey Hall, Ames, IA, 50011, United States
3 - The Australian National University, Division of Evolution, Ecology & Genetics, Research School of Biology, 116 Daley Road, Acton, ACT, 2601, Australia
4 - Iowa State University, Ecology Evolution and Organismal Biology, 2200 Osborn Dr. , Room 251 Bessey , Ames, IA, 50011-4009, USA
5 - Iowa State University, Ecology and Evolutionary Biology, 2200 Osborn Dr., 251 Bessey Hall, Ames, IA, 50011-4009, USA
6 - Northern Illinois University, Department Of Biological Sciences, 1425 W. Lincoln Hwy, DeKalb, IL, 60115, United States
7 - Northern Illinois University, Department of Biological Sciences, 1425 W. Lincoln Hwy, DeKalb, IL, 60115, USA
8 - Iowa State University, 2220 Osborn Dr., Room 251 Bessey Hall, Ames, IA, 50011-4009, United States
Presentation Type: Oral Paper
Candidate for Awards:None