Abstract Detail

Development and Structure

Neupert, Deannah [1], Baker, Robert (Rob) [2], Moore, Rich [3], Bauer, Jonathan [4].

The evolution of structural novelty: A morphological analysis of development in Mimulus and its implications for plant architecture and reproduction.

The evolution of structural novelty can be difficult to study because transitional forms are often extinct. Consequently, determining how existing structures are modified to create new structures with novel functions is challenging. Here, we propose Mimulus gemmiparus as a potential system for understanding evolutionary novelty due to a vegetative reproductive structure found only on this species. Within the genus Mimulus, two vertically serial axillary meristems are typically initiated in each leaf axil. The primary axillary meristem usually varies between becoming a branch or a flower while the secondary, subtending axillary meristem may also develop into a (typically proleptic) branch or flower. In contrast, the secondary axillary meristem in M. gemmiparus expands into a vegetative propagule, which then arrests and is ensheathed by the subtending leaf petiole, resulting in a novel structure: the aerial bulbil. The bulbil will detach and develop into a functional individual and is a mechanism of asexual reproduction. To visualize the evolutionary divergence of whole plant and axillary meristem development in M. gemmiparus, I compared the growth of M. gemmiparus to two sympatric sister taxa, M. guttatus, and M. floribundus. Throughout ontogeny, I measured height, node development, and bulbil development and model the growth of the plants using a Function-Valued Trait (FVT) approach to determine how plant development has been modified to accommodate the novel reproductive structure in M. gemmiparus. Many populations of M. gemmiparus modeled using height as an FVT have a faster developmental rate as compared to M. guttatus and M. floribundus suggesting prioritization of stem elongation but have a slower rate when using node development as an FVT suggesting a prioritization of axillary meristem development. I then imaged development of axillary meristems over time within each species using scanning electron microscopy to create a cross-species comparative developmental series capturing axillary meristem fate and outgrowth. In M. gemmiparus, the primary and secondary axillary meristems initiate and develop faster than the primary and secondary axillary meristems in serially homologous nodes of M. guttatus and M. floribundus. At the second epigeal node in M. gemmiparus, the secondary axillary meristem is fully developed and ensheathed prior to the differentiation of the secondary axillary meristems in M. guttatus and M. floribundus. Our timeseries shows distinctions between the development within the nodes of Mimulus species, but it also shows the co-option of the leaves and branches to form a novel structure, the bulbil. We show that in M. gemmiparus, growth rates of axillary meristems have been increased to support growth of a novel reproductive structure, formed from modified leaves and meristems that, in related species, would be used to form branches. This demonstrates that existing structures can be radically altered to fill an entirely new function.

1 - Miami University, Biology Department, 212 Pearson Hall, 700 E. High St, Oxford, OH, 45056, USA
2 - National Park Service, Inventory And Monitoring Division, 1201 Oakridge Drive, Suite 150, Fort Collins, CO, 80525, United States
3 - Miami University, Biology Department, 212 Pearson Hall, 700 E. High St., Oxford, OH, 45056, United States
4 - Miami University, Biology Department, 212 Pearson Hall, 700 E. High St, Oxford, OH, 45056, United States

Structural novelty
Function-valued traits
Scanning electron microscopy.

Presentation Type: Poster
Number: PDS008
Abstract ID:450
Candidate for Awards:Developmental and Structural Section best poster,Developmental and Structural Section Graduate Student Registration Award

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