The Role of Morphological Biochemical Reciprocity in Early Land Plant Evolution

A morphological-biochemical reciprocity is used to constructa scenario for the evolution of the land and vascular planthabits. The optimal designs of autotrophs are shown to be limitedby their biosynthetic capacities, i.e., the morphological mannerin which surface area-dependent functions are maintained withincreasing size is primarily dictated by the availability ofspecific architectural polymers. The evolution of biosyntheticpathways (involving the detoxification-conversion of primarymetabolites into useful architectural polymers, e.g., cellulose,lignin) predates and allows for transitions from simple dichotomous-convolutedmorphologies to ‘tree-like’ erect plants. The reciprocitybetween morphology and biochemistry is seen to result in a stratifiedstability, i.e., optimal designs, parameterized by their biosyntheticcapacities, result in a hierarchy of stable forms, which undergotransitions when environmental factors alter. Finite element analyses of geometric forms, showing a size increasewith constant surface area-to-volume ratios, indicate simplelobed or convoluted structures are optimal designs for primitivenon-vascular plants, while physical parameters defining theoptimal design of erect plants indicate the necessity for differentialtissue density. Selective pressures favouring an erect plantposture (photosynthetic rates; reproduction) coupled with achemosynthetic ability to structurally reinforce specializedconductive cells is seen to result in the lignification of tracheid-likecells.     

The Role of Nitrogen Deposition in Widespread Plant Community Change Across Semi-natural Habitats

Experimental studies have shown that deposition of reactive nitrogen is an important driver of plant community change, however, most of these experiments are of short duration with unrealistic treatments, and conducted in regions with elevated ambient deposition. Studies of spatial gradients of pollution can complement experimental data and indicate whether the potential impacts demonstrated by experiments are actually occurring in the ‘real world’. However, targeted surveys exist for only a very few habitats and are not readily comparable. In a coordinated campaign, we determined the species richness and plant community composition of five widespread, semi-natural habitats across Great Britain in sites stratified along gradients of climate and pollution, and related these ecological parameters to major drivers of biodiversity, including climate, pollution deposition, and local edaphic factors. In every habitat, we found reduced species richness and changed species composition associated with higher nitrogen deposition, with remarkable consistency in relative species loss across ecosystem types. Whereas the diversity of mosses, lichens, forbs, and graminoids declines with N deposition in different habitats, the cover of graminoids generally increases. Considered alongside previous experimental studies and survey work, our results provide a compelling argument that nitrogen deposition is a widespread and pervasive threat to terrestrial ecosystems.     

Ribosomal Gene Magnification in Drosophila: A Chromosomal Change

The sex-linked mutant "bobbed" can undergo a rapid phenotypic reversion during a prescribed series of outcrosses. The experiments reported here distinguish between two general genetic models. The first is that the phenotypic change results from the changing genetic background brought about by the outcrosses. The second is that the phenotypic change results from an alteration of the X chromosome in the germ line. The data support the second model. It is shown that both the bobbed and reverted phenotypes segregate from the same female. In addition, the reverted phenotype maps in or near the proximal heterochromatin of the X chromosome, which is the standard map position of both bobbed and the nucleolus organizer.     

植物内生细菌对植物健康的作用

植物内生菌是一个多样性十分丰富的微生物类群,存在于没有外在感染症状的健康植物组织内,并与宿主植物协同进化.随着研究领域的不断拓宽和研究方法的不断更新,植物内生菌与植物健康的关系以及应用逐渐成为研究热点.本文主要综述了内生细菌的多样性、进入植物组织内的机制以及内生细菌的主要功能及应用,提出了现阶段内生菌研究存在的问题,并展望了内生菌研究的前景.     

Book Review: Chawla,H.S.: Introduction to Plant Biotechnology

Plant Cell, Tissue and Organ Culture (PCTOC) -     

Past Climate Change and Plant Evolution in Western North America: A Case Study in Rosaceae

Species in the ivesioid clade of Potentilla (Rosaceae) are endemic to western North America, an area that underwent widespread aridification during the global temperature decrease following the Mid-Miocene Climatic Optimum. Several morphological features interpreted as adaptations to drought are found in the clade, and many species occupy extremely dry habitats. Recent phylogenetic analyses have shown that the sister group of this clade is Potentilla section Rivales, a group with distinct moist habitat preferences. This has led to the hypothesis that the ivesioids (genera Ivesia, Horkelia and Horkeliella) diversified in response to the late Tertiary aridification of western North America. We used phyloclimatic modeling and a fossil-calibrated dated phylogeny of the family Rosaceae to investigate the evolution of the ivesioid clade. We have combined occurrence- and climate data from extant species, and used ancestral state reconstruction to model past climate preferences. These models have been projected into paleo-climatic scenarios in order to identify areas where the ivesioids may have occurred. Our analysis suggests a split between the ivesioids and Potentilla sect. Rivales around Late Oligocene/Early Miocene (∼23 million years ago, Ma), and that the ivesioids then diversified at a time when summer drought started to appear in the region. The clade is inferred to have originated on the western slopes of the Rocky Mountains from where a westward range expansion to the Sierra Nevada and the coast of California took place between ∼12-2 Ma. Our results support the idea that climatic changes in southwestern North America have played an important role in the evolution of the local flora, by means of in situ adaptation followed by diversification.     

The Evolution of Language: A Comparative Review

For many years the evolution of language has been seen as a disreputable topic, mired in fanciful “just so stories” about language origins. However, in the last decade a new synthesis of modern linguistics, cognitive neuroscience and neo-Darwinian evolutionary theory has begun to make important contributions to our understanding of the biology and evolution of language. I review some of this recent progress, focusing on the value of the comparative method, which uses data from animal species to draw inferences about language evolution. Discussing speech first, I show how data concerning a wide variety of species, from monkeys to birds, can increase our understanding of the anatomical and neural mechanisms underlying human spoken language, and how bird and whale song provide insights into the ultimate evolutionary function of language. I discuss the “descended larynx” of humans, a peculiar adaptation for speech that has received much attention in the past, which despite earlier claims is not uniquely human. Then I will turn to the neural mechanisms underlying spoken language, pointing out the difficulties animals apparently experience in perceiving hierarchical structure in sounds, and stressing the importance of vocal imitation in the evolution of a spoken language. Turning to ultimate function, I suggest that communication among kin (especially between parents and offspring) played a crucial but neglected role in driving language evolution. Finally, I briefly discuss phylogeny, discussing hypotheses that offer plausible routes to human language from a non-linguistic chimp-like ancestor. I conclude that comparative data from living animals will be key to developing a richer, more interdisciplinary understanding of our most distinctively human trait: language.     

Chromosomal Evolution and Patterns of Introgression in Helianthus

Knowledge of the nature and extent of karyotypic differences between species provides insight into the evolutionary history of the genomes in question and, in the case of closely related species, the potential for genetic exchange between taxa. We constructed high-density genetic maps of the silverleaf sunflower (Helianthus argophyllus) and Algodones Dune sunflower (H. niveus ssp. tephrodes) genomes and compared them to a consensus map of cultivated sunflower (H. annuus) to identify chromosomal rearrangements between species. The genetic maps of H. argophyllus and H. niveus ssp. tephrodes included 17 linkage groups each and spanned 1337 and 1478 cM, respectively. Comparative analyses revealed greater divergence between H. annuus and H. niveus ssp. tephrodes (13 inverted segments, 18 translocated segments) than between H. annuus and H. argophyllus (10 inverted segments, 8 translocated segments), consistent with their known phylogenetic relationships. Marker order was conserved across much of the genome, with 83 and 64% of the H. argophyllus and H. niveus ssp. tephrodes genomes, respectively, being syntenic with H. annuus. Population genomic analyses between H. annuus and H. argophyllus, which are sympatric across a portion of the natural range of H. annuus, revealed significantly elevated genetic structure in rearranged portions of the genome, indicating that such rearrangements are associated with restricted gene flow between these two species.