Abstract Detail

Macroevolution

Kates, Heather [1], O'Meara, Brian [2], Folk, Ryan [3], Guralnick, Robert [4], Soltis, Douglas [5], Soltis, Pamela [6].

Using a 13,000-species phylogeny of the nitrogen-fixing clade to reconstruct the origins and evolution of a critical symbiosis.

One single clade contains all flowering plant lineages known to undergo nodule development with nitrogen-fixing bacterial symbionts. About half of the more than 30,000 species in the nitrogen-fixing clade are thought to form this symbiosis. These “nitrogen-fixing species” occur across 10 families in four orders (Rosales, Cucurbitales, Fagales, Fabales). A clear understanding of the evolutionary history of this critical symbiosis is needed to uncover the genetic basis of the nodulation trait and to ask how nitrogen-fixing symbioses within the nodulating clade contributed to the diversification of angiosperms.
Here we present an ancestral reconstruction of the nodulation state performed using hidden Markov models and the largest phylogenetic estimate yet for the nitrogen-fixing clade: a phylogeny of over 13,000 species inferred from 86 nuclear loci grafted into the 20,000-species rosid phylogeny reconstructed by Sun et al. (2020). Our results suggest that the ancestor of the nitrogen-fixing clade lacked nodulation but was predisposed to transition to nodulation. We identify this state as a predisposition because its rate of transition to the nodulating state is many orders of magnitude faster than that of non-nodulating lineages outside of the nitrogen-fixing clade, and we find that this “precursor” state is more likely to be lost than it is to lead to a gain of nodulation.

1 - University Of Florida, Florida Museum Of Natural History, Dickinson Hall, Gainesville, FL, 32611, United States
2 - University of Tennessee, Knoxville, TN, USA
3 - 295 E. Lee Blvd., P.O. Box GY, Mississippi State, MS, 39762, United States
4 - Florida Museum Of Natural History, 358 Dickinson Hall, University O, 358 Dickinson Hall, University Of Florida, Gainesville, FL, 32611, United States
5 - Boise State University, Snake River Plains Herbaria, , Boise, Idaho, 83725, USA
6 - University Of Florida, Florida Museum Of Natural History, PO Box 117800, Gainesville, FL, 32611, United States

Keywords:
rosids
nitrogen fixation
large phylogeny
Ancestral State reconstruction
hidden markov models.

Presentation Type: Oral Paper
Session: MACROIII, Macroevolution III
Location: Virtual/Virtual
Date: Friday, July 23rd, 2021
Time: 11:30 AM(EDT)
Number: MACROIII007
Abstract ID:963
Candidate for Awards:None