Abstract Detail

Anatomy and Morphology

Losada, Juan [1], Blanco-Moure, Nuria [2], Leslie, Andrew [3].

Anatomical changes and the evolution of dispersal mechanisms in the seed cones of the pine family.

The final fate of the complex seed cones of conifers is to disperse seeds, and this process is ultimately mediated by the morphology and anatomy of the cone scales. Although the same set of organs facilitates dispersal, specific dispersal mechanisms can vary widely among genera. In the family Pinaceae, two major mechanisms of scale-mediated seed release evolved during the approximately 150 million year evolutionary history of the crown group: cone scale flexure and cone scale shedding. The biomechanics of scale flexure are well understood, but the anatomical mechanisms of scale shedding and the underlying causes of its evolution have been understudied so far. In order to answer these questions, we studied approximately fifty species from the Pinaceae family, including representatives of all living genera. To assess whether the seed dispersal mechanisms were related to different reproductive biology or ecology, we asked whether there were any differences in the relative size of seeds and cones in scale flexers and scale shedders. To understand the specific mechanisms of scale shedding, analyzed the anatomy of the xylem in the scale bases, which ultimately controls whether scales flex or are shed. Finally, we compared these data with previously published fossils from the family to evaluate the ancestry of dispersal mechanisms in the family. We find broad differences in reproductive tissue allocation within Pinaceae, which are likely correlated with the evolution of the two seed dispersal mechanisms. Members of the abietoid clade exhibit a higher relative amount of seed tissue compared to members of the pinoid clade, and their cones have proportionally more seeds. Scale shedding appears to have evolved multiple times in abietoids with larger cones and larger seeds, suggesting that shedding is a more effective mechanism than flexing when dispersing large and tightly packed propagules. Pinoids have relatively less seed tissue even at large seed sizes and never evolve scale shedding. Anatomically, the abietoid genera that shed scales share a suite of traits: they all have relatively small cross sectional xylem area at the base of the scales and have thinner tracheid cell walls than do Pinaceae that use scale flexion. Xylem area in fossil Pinaceae from the Cretaceous, including likely early abietoids, largely matches that of modern-day scale flexers, suggesting that shedding has evolved multiple times. The evolution of dispersal mechanisms then appears to be related to relative tissue allocation in seed cones, and mediated by variation in tracheid and xylem anatomy.

1 - Brown University/ Arnold Arboretum of Harvard University, Ecology and Evolutionary Biology, 80 Waterman Street, Providence, RI, 02912, United States
2 - No, No, No , No, Boston, MA, 02131, United States
3 - Brown University, Box G-W, 80 Waterman Street, Providence, RI, 02912, United States

Keywords:
gymnosperms
conifers
seed cone
seed dispersal
functional anatomy.

Presentation Type: Oral Paper
Session: 6, Anatomy and Morphology I
Location: 113/Mayo Civic Center
Date: Monday, July 23rd, 2018
Time: 10:30 AM
Number: 6010
Abstract ID:120
Candidate for Awards:None