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Kealohanuiopuna M. Kinney Gregory P. Asner Susan Cordell Oliver A. Chadwick Katherine Heckman Sara Hotchkiss Marjeta Jeraj Ty Kennedy-Bowdoin David E. Knapp Erin J. Questad Jarrod M. Thaxton Frank Trusdell James R. Kellner 《PloS one》2015,10(6)
We used measurements from airborne imaging spectroscopy and LiDAR to quantify the biophysical structure and composition of vegetation on a dryland substrate age gradient in Hawaii. Both vertical stature and species composition changed during primary succession, and reveal a progressive increase in vertical stature on younger substrates followed by a collapse on Pleistocene-aged flows. Tall-stature Metrosideros polymorpha woodlands dominated on the youngest substrates (hundreds of years), and were replaced by the tall-stature endemic tree species Myoporum sandwicense and Sophora chrysophylla on intermediate-aged flows (thousands of years). The oldest substrates (tens of thousands of years) were dominated by the short-stature native shrub Dodonaea viscosa and endemic grass Eragrostis atropioides. We excavated 18 macroscopic charcoal fragments from Pleistocene-aged substrates. Mean radiocarbon age was 2,002 years and ranged from < 200 to 7,730. Genus identities from four fragments indicate that Osteomeles spp. or M. polymorpha once occupied the Pleistocene-aged substrates, but neither of these species is found there today. These findings indicate the existence of fires before humans are known to have occupied the Hawaiian archipelago, and demonstrate that a collapse in vertical stature is prevalent on the oldest substrates. This work contributes to our understanding of prehistoric fires in shaping the trajectory of primary succession in Hawaiian drylands. 相似文献
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Edgar Knapp 《Planta》1930,12(3):354-361
Ohne ZusammenfassungMit 1 Textabbildung 相似文献
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Retinoic acid-induced transformation of reticulate scales to feather-like structures (Dhouailly and Hardy, '78) provides a useful model to study biochemical differentiation in avian skin. In this study, immunofluorescent analysis of reticulate scale-feathers (RSFs) indicates that they contain beta keratin in feather barbs and, thus, are true feathers, biochemically. Epidermal cells that would otherwise produce only alpha keratin in reticulate scales are induced to reorganize and differentiate into barb ridge cells that accumulate feather beta keratins. The mechanism for these dramatic morphological and biosynthetic responses to retinoic acid is unknown. 相似文献
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Teresa Sadras Mickaël Martin Kohei Kume Mark E. Robinson Supraja Saravanakumar Gal Lenz Zhengshan Chen Joo Y. Song Tanya Siddiqi Laura Oksa Anne Marie Knapp Jevon Cutler Kadriye Nehir Cosgun Lars Klemm Veronika Ecker Janet Winchester Dana Ghergus Pauline Soulas-Sprauel Markus Müschen 《Molecular cell》2021,81(10):2094-2111.e9
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Leslie A. Knapp 《Evolutionary anthropology》2005,14(1):28-37
The major histocompatibility complex (MHC) contains the most diverse genes known in vertebrates. These genes encode cell‐surface molecules that play a central role in controlling immunological activity and, as a consequence, in tissue rejection, autoimmunity, and immune responses to infectious diseases. In vertebrates, there are many different MHC genes, most with many alleles. This is true for all primates studied thus far. Multiple loci and alleles allow for an increased peptide‐binding repertoire; their variety has a profound impact on an organism's ability to battle constantly evolving pathogens. The argument that infectious disease is a driving force for MHC variability is supported by observations that most of the allelic variation centers on the amino acid residues that directly interact with foreign peptides. However, while MHC diversity could be maintained through heterozygote advantage, frequency‐dependent selection, or both, the direct evidence that natural selection enhances diversity is limited. Indeed, it is not wholly clear whether selection operates only with respect to disease resistance or if behavioral and biological mechanisms also contribute to the extreme variation that has been observed for many species. Furthermore, reproductive behavior and biology may also help to maintain genetic variability at MHC loci. 相似文献