Divergent genetic and epigenetic post-zygotic isolation mechanisms in Mus and Peromyscus

Interspecific hybridization in the rodent genera Peromyscus and Mus results in abnormal placentation. In the Peromyscus interspecies hybrids, abnormal allelic interaction between an X-linked locus and the imprinted paternally expressed Peg3 locus was shown to cause the placental defects. In addition, loss-of-imprinting (LOI) of Peg3 was positively correlated with increased placental size. As in extreme cases this placental dysplasia constitutes a post-zygotic barrier against interspecies hybridization, this finding was the first direct proof that imprinted genes may be important in speciation and thus in evolution. In the Mus interspecies hybrids, a strong role of an X-linked locus in placental dysplasia has also been detected. However, here we show by backcross and allele specific expression analyses that neither LOI of Peg3 nor abnormal interactions between Peg3 and an X-linked locus are involved in generating placental dysplasia in Mus hybrids, although the placental phenotypes observed in the two genera seem to be identical. In contrast to this, another dysgenesis effect common to Peromyscus and Mus hybrids, altered foetal growth, is caused at least in part by the same X-chromosomal regions in both genera. These findings first underline the strong involvement of the X-chromosome in the genetics of speciation. Secondly, they indicate that disruption of epigenetic states, such as LOI, at specific loci may be involved in hybrid dysgenesis effects in one group, but not in another. Thus, we conclude that even in closely related groups divergent molecular mechanisms may be involved in the production of phenotypically similar post-zygotic barriers against hybridization.     

Detection of Pairwise Residue Proximity by Covariation Analysis for 3D-Structure Prediction of G-Protein-Coupled Receptors

G-protein-coupled receptor (GPCR) is one of the most important targets for medicines. Homology modeling based on the crystal structure of bovine rhodopsin is currently the most frequently used method for GPCR targeted drug design. Information about residue-residue contacts and the structural specificity in the subfamily is essential for constructing more precise 3D structures, to distinguish the structural differences between the template and targets. In this study, we adopted the covariation analysis to extract information about residue-residue interactions from the amino acid sequence. In the opsin family, a large number of adjacent covarying residue pairs were detected. The detected residue pairs have a strong tendency to gather in some regions important for the structure and function. These results suggest that the covariation analysis is practically utilized to detect adjacent residue pairs and also to apply for predicting functional sites. Analyses of other GPCR subfamilies, olfactory receptor and chemokine receptor families, demonstrated that some adjacent covarying residue pairs were common. Thus, the covariation analysis has possibilities in the substantial improvement of the 3D-structure modeling of GPCRs and in the detection of functional sites such as the ligand-binding sites.     

Causes of covariation of phenotypic traits among populations

Morphological and life-history traits often vary among populations of a species. Traits generally do not vary independently, but show patterns of covariation that can arise from genetic and environmental influences on phenotype. Covariance of traits may arise at an among-population level when genetically influenced traits diverge among populations in a correlated manner. Genetic correlations caused by pleiotropy and/or gene linkage can cause traits to evolve together, but among-population covariance can also arise among traits that are not genetically correlated. For example, “selective covariance” can arise when natural selection directly causes correlated change in a suite of traits. Similarly, mutation, migration, and drift may also sometimes cause correlated genetic changes among populations. Because covariation of traits among populations can arise by several different processes, the evolution of suites of traits must be interpreted with great caution. We discuss the sources of among-population covariance and illustrate one approach to identifying the sources' using data on floral traits of Dalechampia scandens (Euphorbiaceae).     

Covariation of morphological characters in the Triassic ammonoid Czekanowskites rieberi

The Triassic ammonoid Czekanowskites rieberi displays a covariation of morphological charac ters, which is rather common in ammonoids. Its morphological spectrum ranges from laterally compressed, involute, weakly ribbed forms to depressed, semiinvolute, strongly ribbed forms. In order to study this covariation, fifteen axially cut specimens have been analyzed by means of image analysis, which allows us to obtain the ontogenetic record of radii, area and perimeter of the individual whorl cross-sections. A logarithmic model of growth has been applied. Our data indicate that, owing to the covariation, the radii from the origin to the venter and to the umbil ical seam of a given whorl section vary inversely in order to maintain the relative position of the center of gravity of the whorl cross-section both throughout the ontogeny of single specimens and within the population. This influences hydrostatic parameters, such as the position of the center of mass and the orientation and stability of the shell. Since the ontogenetic record of the angular length of the body chamber is not known, we have calculated those hydrostatic varia bles using two mutually exclusive assumptions: (1) the angular length of the body chamber was constant throughout ontogeny and (2) the volume of the body chamber grew monotonically with the revolution angle. Fluctuations of the three hydrostatic variables were always less important in the first assumption. In any case, the spectrum of, for example, theoretical orien tations is comparable to those observed in the species of present-day Nautilus. The range of adult body-chamber length observed in C. rieberi is much narrower than the theoretical adult body-chamber length calculated under the second assumption which indicates that a certain control over this parameter existed in the natural population, probably in order to maintain a narrow range in orientation and stability. The excess or deficit in soft-body weight was probably compensated by inverse variations in shell-wall weight. The main conclusion is that, despite the extreme morphological variability, hydrostatic and, possibly, hydrodynamic properties of the population remained within narrow limits.     

Influence of mass transfer limitations on determination of the half saturation constant for hydrogen uptake in a mixed-culture CH(4)-producing enrichment

There is strong evidence in the literature supporting the existence of significant mass transfer limitations on the kinetics of exogenous H(2) consumption by methanogens. The half saturation constant for H (2) uptake by a mixed-culture, CH(4) producing enrichment was measured using an experimental protocol that avoided internal mass transfer limitations. The value obtained was two orders of magnitude smaller than any other previously reported. A mathematical model for acetogenic syntrophic associations was developed to check the capacity of H(2) as electron transporter between syntrophic partners. It was found that H(2) diffusion could account for the rate of transport of electrons between the syntrophic microorganisms and that formate is not a necessary intermediate. The possibility that formate may be an intermediate in this system was not ruled out. A Monod-type kinetic equation was modified to include the observed H(2) threshold effect. This modified equation was used to predict the CH(4)-production rate in a batch-fed digester. The results show that the external and internal H(2) pools are kinetically coupled. (c) 1992 John Wiley & Sons, Inc.     

Phenetic relationships among varanid lizards based upon comparative electrophoretic data and karyotypic analyses

Comparative electrophoretic phenotypes of 18 of the 32 species of the lizard genus Varanus have been determined for four proteins. The animals studied were representative of species from Africa, Israel, Southeast Asia and Australia. Malate dehydrogenase (A₂) exhibited a single phenotype throughout. Lactate dehydrogenase (B₄) showed four distinctive electrophoretic forms which grouped the various subgenera as follows: (1) Polydaedalus, Empagusia (African); (2) Psammosaurus (Israel); (3) three species of Varanus, V. gouldii, V. spenceri, V. mertensi (Australian); (4) Dendrovaranus, Indovaranus (Southeast Asian), other Varanus species, Odatria (Australian). Electrophoretic and previously reported karyotypic data were used to interpret the phylogenetic relationships as well as the mode and direction of evolution of these animals. In particular, the results questioned the reality of the subgenus Varanus as a taxonomic unit, since four distinct karyotypic forms and two LDH-B₄ phenotypes were observed for these animals, of which one belongs to another subgenus. Serum albumin and carbonic anhydrase phenotypes were of little use in deciding phenotypic groupings.     

微生物对昆虫行为的影响研究进展

在漫长的进化过程中,微生物与昆虫形成了多种形式的互作关系。微生物的广泛分布为与昆虫接触并影响昆虫的行为提供了背景条件。为了深入探究微生物影响昆虫行为的现象和机制,本文综述了微生物影响昆虫行为方面的研究进展。微生物通过产生可被昆虫识别的化学信号物质、参与昆虫或寄主植物信息化合物的合成等方式可影响昆虫对其寄主的定位和选择。在对昆虫种内和种间关系的研究中也发现微生物起着非常重要的作用。通过改变昆虫性信息素等方式,微生物还能影响到昆虫的繁殖行为;除此之外,微生物合成或参与合成的信息化合物还可以影响昆虫的社会性和聚集等行为。根据当前对微生物影响昆虫行为方面的研究现状,我们建议可进一步研究：(1)微生物影响昆虫行为的过程中,影响昆虫行为的信息化合物是如何产生的？(2)微生物在影响昆虫行为的过程中是否涉及更多的物种间互作？(3)对于一些在特定时期可影响昆虫行为的共生微生物来说,宿主昆虫是如何获得并维持这些微生物的？     

微生物种间直接电子传递研究进展

一直以来氢气和甲酸被认为是微生物间电子传递的中间电子传递体。近年来的研究发现,微生物之间可以通过种间直接电子传递(DIET)来替代氢气/甲酸传递。DIET作为一种新发现的微生物间电子传递途径,其电子传递效率要高于传统的种间氢气/甲酸传递。DIET这一新发现改变了微生物互营生长代谢必须依赖氢气或甲酸等电子载体的传统认识,为今后研究微生物互营现象打开了新视角。虽然DIET研究取得了很大进展,但是目前对能够进行DIET的微生物种类、DIET机制及影响DIET的因素尚缺乏深入研究。本文首先概述了能形成DIET的微生物,然后重点分析了能够进行DIET的电子供体微生物胞外电子传递的机制和电子受体微生物直接利用胞外电子的分子机制,最后阐述了导电材料对DIET的影响,并提出了DIET今后的研究方向,旨在为DIET研究提供参考。