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Abstract Detail

Paleobotanical Section

Benca, Jeffrey [1], Stromberg, Caroline [2], Huttenlocker, Adam [3].

Testing climatic influences on leaf shape across the vascular plant tree of life.

Leaf margin-based climatic proxies have played a pivotal role in inferring mean annual temperature (MAT) and precipitation (MAP) in the fossil record. However, because these methods are based on woody dicotyledonous angiosperms, their use has been limited to the late Mesozoic and Cenozoic. Furthermore, the phylogenetic independence of leaf-margin climatic proxies has recently been called into question. If the core assumption of this approach— leaf shape responds in a predictable manner to climatic parameters irrespective of phylogenetic history— has adaptive basis, then lineages outside the crown angiosperms should show similar climate-induced morphological responses. Ferns and lycopsids provide the only living out-groups suitable to test this hypothesis. Specifically, both of these lineages evolved leaves independently of the lignophytes, have great breadth in growth form and ecological preference, substantially longer fossil records than seed plants, and yet still have sufficient extant diversity to work with. To test phylogenetic independence across crown vascular plants, four temperate lycophyte and fern taxa with toothed leaf margins (Lycopodiaceae: Lycopodiella alopecuroides, L. appressa, Lycopodium clavatum, and Polypodiaceae: Polystichum munitum), were grown for five months under 15°C and 25°C treatments in a growth chamber. Additionally, we studied four tropical fern species (Cibotiaceae: Cibotium glaucum, C. menziesii; and Polypodiaceae: Asplenium normale, A. polyodon) across a rainforest elevation transect spanning 800m, 5.2C° MAT, and 1,007 mm/yr MAP gradients on the slopes of Mauna Kea, Hawai’i. Using Digital Leaf Physiognomy Approach (DiLP), we applied four angiosperm-based leaf-climatic parameters to pinnules of ferns and microphylls of lycophytes: 1) Shape Factor, 2) Standardized Tooth Count, 3) Feret-Diameter Ratio, and 4) Tooth-Area Ratio. These measurements were compared within species in both growth chamber trials and across different elevations in the field. While statistically significant differences were detected in several of the measurements in both the field and growth chamber experiments, neither the extant ferns nor lycophytes that we studied displayed predictable changes in leaf margin state similar to those shown experimentally in angiosperms. Based on these observations, we suggest that climatic influences on leaf margin shape are not phylogenetically independent across the vascular plant clade. Furthermore, fossil plant groups that fall outside of the angiosperm lineage may not be suitable for leaf physiognomy-based climate analysis.

Broader Impacts:

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1 - University of California, Berkeley, Department of Integrative Biology, 2033 Valley Life Sciences Building #3140, Berkeley, CA, 94720, USA
2 - University of Washington, Department of Paleobotany, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195-1800, USA
3 - University of Washington, Biology, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195-1800, USA

leaf physiognomy

Presentation Type: Oral Paper:Papers for Sections
Session: 3
Location: Melrose/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 11:30 AM
Number: 3013
Abstract ID:358
Candidate for Awards:Maynard F. Moseley Award

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