Phenotypic Plasticity of Leaf Shape along a Temperature Gradient in Acer rubrum

Both phenotypic plasticity and genetic determination can be important for understanding how plants respond to environmental change. However, little is known about the plastic response of leaf teeth and leaf dissection to temperature. This gap is critical because these leaf traits are commonly used to reconstruct paleoclimate from fossils, and such studies tacitly assume that traits measured from fossils reflect the environment at the time of their deposition, even during periods of rapid climate change. We measured leaf size and shape in Acer rubrum derived from four seed sources with a broad temperature range and grown for two years in two gardens with contrasting climates (Rhode Island and Florida). Leaves in the Rhode Island garden have more teeth and are more highly dissected than leaves in Florida from the same seed source. Plasticity in these variables accounts for at least 6–19 % of the total variance, while genetic differences among ecotypes probably account for at most 69–87 %. This study highlights the role of phenotypic plasticity in leaf-climate relationships. We suggest that variables related to tooth count and leaf dissection in A. rubrum can respond quickly to climate change, which increases confidence in paleoclimate methods that use these variables

Paleotemperature Proxies from Leaf Fossils Reinterpreted in Light of Evolutionary History

Present-day correlations between leaf physiognomic traits (shape and size) and climate are widely used to estimate paleoclimate using fossil floras. For example, leaf-margin analysis estimates paleotemperature using the modern relation of mean annual temperature (MAT) and the site-proportion of untoothed-leaf species (NT). This uniformitarian approach should provide accurate paleoclimate reconstructions under the core assumption that leaf-trait variation principally results from adaptive environmental convergence, and because variation is thus largely independent of phylogeny it should be constant through geologic time. Although much research acknowledges and investigates possible pitfalls in paleoclimate estimation based on leaf physiognomy, the core assumption has never been explicitly tested in a phylogenetic comparative framework. Combining an extant dataset of 21 leaf traits and temperature with a phylogenetic hypothesis for 569 species-site pairs at 17 sites, we found varying amounts of non-random phylogenetic signal in all traits. Phylogenetic vs. standard regressions generally support prevailing ideas that leaf-traits are adaptively responding to temperature, but wider confidence intervals, and shifts in slope and intercept, indicate an overall reduced ability to predict climate precisely due to the non-random phylogenetic signal. Notably, the modern-day relation of proportion of untoothed taxa with mean annual temperature (NT-MAT), central in paleotemperature inference, was greatly modified and reduced, indicating that the modern correlation primarily results from biogeographic history. Importantly, some tooth traits, such as number of teeth, had similar or steeper slopes after taking phylogeny into account, suggesting that leaf teeth display a pattern of exaptive evolution in higher latitudes. This study shows that the assumption of convergence required for precise, quantitative temperature estimates using present-day leaf traits is not supported by empirical evidence, and thus we have very low confidence in previously published, numerical paleotemperature estimates. However, interpreting qualitative changes in paleotemperature remains warranted, given certain conditions such as stratigraphically closely-spaced samples with floristic continuity

Molecular phylogenetics reveal multiple tertiary vicariance origins of the African rain forest trees

Background - Tropical rain forests are the most diverse terrestrial ecosystems on the planet. How this diversity evolved remains largely unexplained. In Africa, rain forests are situated in two geographically isolated regions: the West-Central Guineo-Congolian region and the coastal and montane regions of East Africa. These regions have strong floristic affinities with each other, suggesting a former connection via an Eocene pan-African rain forest. High levels of endemism observed in both regions have been hypothesized to be the result of either 1) a single break-up followed by a long isolation or 2) multiple fragmentation and reconnection since the Oligocene. To test these hypotheses the evolutionary history of endemic taxa within a rain forest restricted African lineage of the plant family Annonaceae was studied. Molecular phylogenies and divergence dates were estimated using a Bayesian relaxed uncorrelated molecular clock assumption accounting for both calibration and phylogenetic uncertainties. Results - Our results provide strong evidence that East African endemic lineages of Annonaceae have multiple origins dated to significantly different times spanning the Oligocene and Miocene epochs. Moreover, these successive origins (c. 33, 16 and 8 million years ¿ Myr) coincide with known periods of aridification and geological activity in Africa that would have recurrently isolated the Guineo-Congolian rain forest from the East African one. All East African taxa were found to have diversified prior to Pleistocene times. Conclusion - Molecular phylogenetic dating analyses of this large pan-African clade of Annonaceae unravels an interesting pattern of diversification for rain forest restricted trees co-occurring in West/Central and East African rain forests. Our results suggest that repeated reconnections between the West/Central and East African rain forest blocks allowed for biotic exchange while the break-ups induced speciation via vicariance, enhancing the levels of endemicity. These results provide an explanation for present day distribution patterns and origins of endemicity for African rain forest trees. Moreover, given the pre-Pleistocene origins of all the studied endemic East African genera and species, these results also offer important insights for setting conservation priorities in these highly diversified but threatene

Floral diversity during Plio-Pleistocene Siwalik sedimentation (Kimin Formation) in Arunachal Pradesh, India, and its palaeoclimatic significance

A morpho-taxonomic study of leaf remains from the upper part of the Siwalik succession of sediments (Kimin Formation; upper Pliocene to lower Pleistocene) of Papumpare district, Arunachal Pradesh, India, revealed 23 species representing 20 genera belonging to 15 angiosperm families. The recovered fossil leaves are comparable to modern Bambusa tulda Roxb. (Poaceae), Mangifera indica Linn., Dracontomelum mangiferum Blume (Anacardiaceae); Chonemorpha macrophylla G. Don (Apocynaceae); Pongamia pinnata (L) Pierre., Millettia pachycarpa Benth., Dalbergia rimosa Roxb., Millettia extensa (Fabaceae); Macaranga denticulate Muell. Arg., Croton caudatus Geisel. (Euphorbiaceae); Combretum decandrum Roxb. (Combretaceae); Dysoxylum procerum Hiern. (Meliaceae); Dipterocarpus sp. Gaertn.f. (Dipterocarpaceae); Actinodaphne angustifolia Nees., Actinodaphne obovata Blume., Lindera pulcherrima Benth., Litsea salicifolia Roxb. (Lauraceae); Calophyllum polyanthum Wall. (Clusiaceae); Knema glaucescens Hook.f. (Myristaceae); Canarium bengalense Roxb. (Burseraceae); Quercus lamellose Smith; Quercus semicarpifolia Smith (Fagaceae); and Berchemia floribunda Wall. (Rhamnaceae). Among these taxa, 11 species are recorded as new to the Neogene flora of India. Analysis of the floral assemblage with respect to the distribution pattern of modern equivalent taxa and the physiognomic characters of the fossil leaves, suggests that a tropical evergreen forest was growing in a warm humid climate in the region at the time of deposition. This is in contrast to modern tropical semi-evergreen forests that occupy the area. Values of mean annual temperature (MAT) of 29.3°C and mean annual precipitation (MAP) of 290 mm have been calculated using leaf-margin characters and fossil leaf size

Changes In Spruce Composition Following Burial In Lake-sediments For 10,000 Yr

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62582/1/287534a0.pd