Evolution of insect-plant relationships: chemical constraints, coadaptation, and concordance of insect/plant traits

Co-adaptations, co-evolution, and co-speciation between herbivores and their host plants have been topics of interest for several decades. Difficulties in deciphering these relationships as well as physiological, biochemical, and ecological adaptations of herbivorous insects themselves are discussed here in relation to biotic and abiotic environmental factors that create temporal as well as spatial mosaics of genetic variation. Hybridization was shown in swallowtail butterflies (Papilio) (Lepidoptera: Papilionidae) to produce some trait concordance, but mostly independent geographic trait clines (physiological, biochemical, and morphological). Strong and extensive genetic introgression of Liriodendron tulipifera detoxification abilities was documented northward across the hybrid zone, presumably as a result of regional climate warming only during the last 3–4 years. These and other genetic novelties produced by hybridization may be important in speciation processes, and they also emphasize the difficulties identifying appropriate taxonomic classifications for discussing any species concept. Host plant detoxification abilities (as `key innovations') are shown capable of rapid movement between different polyphagous herbivore species independently of the host plant availability and well beyond the insect species geographical range distribution. Part of the difficulty associated with ecologically categorizing herbivore species and identifying affiliated adaptations for host plant use may be related to independent movement of various `species-diagnostic' traits. Climate-driven local selection regimes could help generate the dynamic variation observed for co-adapted, co-evolved, or non-adapted genotypes, and may produce the confusing and changing patterns of geographic mosaics seen within and among closely related herbivores. Experimental analyses of several factors that could explain the asymmetrical shapes of trait clines across the hybrid zone for tiger swallowtail butterflies are discussed.     

IS THE POPULATION SIZE OF A SPECIES RELEVANT TO ITS EVOLUTION?

Abstract This paper examines aspects of genetic draft, the stochastic force induced by substitutions at one locus on the dynamics of a closely linked locus. Of particular interest is the role of population size on genetic draft. Remarkably, the rate of substitution of weakly selected advantageous mutations decreases with increasing population size, whereas that for deleterious mutations increases with population size. This dependency on population size is the opposite of that for genetic drift. Moreover, these rates are only weakly dependent on population size, again contrary to the strong dependency of drift‐based dynamics. Four models of the strongly selected loci responsible for genetic draft are examined. Three of these exhibit a very weak dependency on population size, which implies that their induced effects will also be weakly dependent on population size. Together, these results suggest that population size and binomial sampling may not be relevant to a species' evolution. If this is the case, then a number of evolutionary conundrums are resolved.     

Integrating genetic and environmental forces that shape the evolution of geographic variation in a marine snail

Temporal and spatial patterns of phenotypic variation have traditionally been thought to reflect genetic differentiation produced by natural selection. Recently, however, there has been growing interest in how natural selection may shape the genetics of phenotypic plasticity to produce patterns of geographic variation and phenotypic evolution. Because the covariance between genetic and environmental influences can modulate the expression of phenotypic variation, a complete understanding of geographic variation requires determining whether these influences covary in the same (cogradient variation) or in opposing (countergradient variation) directions. We focus on marine snails from rocky intertidal shores as an ideal system to explore how genetic and plastic influences contribute to geographic and historical patterns of phenotypic variation. Phenotypic plasticity in response to predator cues, wave action, and water temperature appear to exert a strong influence on small and large-scale morphological variation in marine snails. In particular, plasticity in snail shell thickness: (i) may contribute to phenotypic evolution, (ii) appears to have evolved across small and large spatial scales, and (iii) may be driven by life history trade-offs tied to architectural constraints imposed by the shell. The plasticity exhibited by these snails represents an important adaptive strategy to the pronounced heterogeneity of the intertidal zone and undoubtedly has played a key role in their evolution.     

Effects of food quality on growth and biochemical composition of a calanoid copepod,Argyrodiaptomus furcatus,and its importance as a natural food source for larvae of two tropical fishes

Growth, reproduction and biochemical composition were analyzed for the copepod Argyrodiaptomus furcatus fed on the alga Ankistrodesmus gracilis grown in different media. The ingestion of this copepod by larvae of two species of tropical fishes was also evaluated. The mean peak density of the copepod population was 1369 individuals l^–1 for all four diets used, and the highest was 1387 individuals l^–1 on diet ARV (algae + ration + vitamins). A small copepod, A. furcatus tends to have a short life span. The smallest females did not attain maturity in the shortest time on all diets used. Food quality may play a major role in the dynamics of the biochemical composition of this copepod. Argyrodiaptomus furcatus was a more important food item for larvae of tambaqui (Colossoma macropomum) than of pacu (Piaractus mesopotamicus). However, it made up a large part of the gut contents of larvae of both species.     

Dissolved oxygen concentration and emergence of sea trout fry from natural redds in tributaries of the River Rhine

A total of 4289 sea trout Salmo trutta alevins swam up from six of eleven covered redds. They emerged only from those redds where the mean dissolved oxygen level was >6·9 mg l⁻¹ and the Sorting coe.cient, an indicator of intragravel void space, was <5. These results are discussed in relation to field studies using artificially buried salmonid eggs but also in relation to the ongoing programme for the reintroduction of Atlantic salmon in tributaries of the River Rhine.     

The Portuguese naturalist Correia da Serra (1751–1823) and his impact on early nineteenth-century botany

This paper focuses on the contributions to natural history, particularly in methods of plant classification of the Portuguese botanist, man of letters, diplomat, and Freemason Abbé José Correia da Serra (1751–1823), placing them in their national and international political and social contexts. Correia da Serra adopted the natural method of classification championed by the Frenchman Antoine-Laurent de Jussieu, and introduced refinements of his own that owe much to parallel developments in zoology. He endorsed the view that the classification of plants should be based on the establishment of affinities rather than of differences. The emphasis on affinities went hand in hand with the development of the concept of symmetry. This idea was introduced by Correia da Serra in systematics and was adopted and further developed by his friend, Augustin-Pyramus de Candolle. Correia da Serra also argued that Cryptogamia reproduce sexually, advocated extension of methods of comparative anatomy from zoology to botany, and applied them to the study of fruits. Correia da Serra was one among many of the estrangeirados, Portuguese``Europeanized' intellectuals who traveled extensively abroad in most cases to escape political or religious persecution at home. The estrangeirados were important contributors to 18th and 19th century European thinking. Most of the estrangeirados were pivotal in the introduction, dissemination and propagation of the new sciences in Portugal, but unlike most of his fellow estrangeirados, Correia da Serra was also an innovative man of science in his own right. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mechanism of tRNA Translocation on the Ribosome

During the translocation step of the elongation cycle of peptide synthesis two tRNAs together with the mRNA move synchronously and rapidly on the ribosome. Translocation is catalyzed by the elongation factor G (EF-G) and requires GTP hydrolysis. The fundamental biochemical features of the process were worked out in the 1970–80s, to a large part by A.S. Spirin and his colleagues. Recent results from pre-steady-state kinetic analysis and cryoelectron microscopy suggest that translocation is a multistep dynamic process that entails large-scale structural rearrangements of both ribosome and EF-G. Kinetic and thermodynamic data, together with the structural information on the conformational changes in the ribosome and EF-G, provide a detailed mechanistic model of translocation and suggest a mechanism of translocation catalysis by EF-G.     

酵母RNA聚合酶ⅡRpb2和Rpb3两亚基间相互作用位点的定位

为研究S .pombeRNApolⅡ各亚基间体内装配成复合体的机制 ,本文首次用酵母双杂交系统鉴定了Rpb2和Rpb3两亚基间体内相互作用的位点。首先将Rpb2的 4个片段克隆至Gal4BD表达载体pAS2上 ,构建BD Rpb2片段融合蛋白重组质粒 ;同时将Rpb3克隆至Gal4AD表达载体pGADGH上 ,构建AD Rpb3融合蛋白重组质粒。其次 ,将pGADGHRpb3分别与pAS2Rpb2各片段重组质粒共转化到受体酵母菌Y1 90感受态细胞内 ,筛选并鉴定β gal活性阳性 (β gal+)的共转化子。最后 ,将β gal+共转化子中的Rpb2片段进行序列分析并进行同源序列比较确定其在Rpb2中的位置。结果表明 ,Rpb2与Rpb3相互作用的位点位于Rpb2的 90 2～ 989aa肽段内     

Crossability of Brassica tournefortii and B. rapa, and morphology and cytology of their F1 hybrids

The crossability between Brassica tournefortii (TT, 2n = 20) and Brassica rapa (AA, 2n = 20) and the cytomorphology of their F₁ hybrids were studied. Hybrids between these two species were obtained only when B. tournefortii was involved as a female parent. The hybrid plants were intermediate for most of the morphological attributes and were found to be free from white rust under field conditions. The F₁ plants showed poor pollen fertility, although occasional seed set was achieved from open pollination. Self-pollination or backcrosses did not yield any seeds in these plants. The occurrence of chromosome association ranging from bivalents (0–7), trivalents (0–2) to a rare quadrivalent (0–1) in the dihaploid hybrids indicates pairing between the T and A genomes. The homoeologous pairing coupled with seed set in the F₁ plants offer an opportunity for interspecific gene transfers from B. tournefortii to B. rapa and vice-versa through interspecific hybridization. Received: 3 July 2000 / Accepted: 22 September 2000