Green algae to land plants: An evolutionary transition

Studies focused upon the evolutionary transition from ancestral green algae to the earliest land plants are important from a range of ecological, molecular and evolutionary perspectives. A substantial suite of ultrastructural, biochemical and molecular data supports the concept that land plants (embryophytes) are monophyletically derived from an ancestral charophycean alga. However, the details of phylogenetic branching patterns linking extant charophytes and seedless embryophytes are currently unclear. Moreover, the fossil record has so far been mute regarding the algae-land plant transition. Nevertheless, an accurate reflection of major evolutionary events in the history of the earliest land plants can be obtained by comparative paleontological-neontological studies, and comparative molecular, cellular and developmental investigations of extant charophytes and bryophytes. This review focuses upon research progress toward understanding three clade-specific adaptations that were important in the successful colonization of land by plants: the histogenetic apical meristem, the matrotrophic embryo, and decay-resistant cell wall polymers.     

Horizontal gene transfer between bacteria and animals

Horizontal gene transfer is increasingly described between bacteria and animals. Such transfers that are vertically inherited have the potential to influence the evolution of animals. One classic example is the transfer of DNA from mitochondria and chloroplasts to the nucleus after the acquisition of these organelles by eukaryotes. Even today, many of the described instances of bacteria-to-animal transfer occur as part of intimate relationships such as those of endosymbionts and their invertebrate hosts, particularly insects and nematodes, while numerous transfers are also found in asexual animals. Both of these observations are consistent with modern evolutionary theory, in particular the serial endosymbiotic theory and Muller's ratchet. Although it is tempting to suggest that these particular lifestyles promote horizontal gene transfer, it is difficult to ascertain given the nonrandom sampling of animal genome sequencing projects and the lack of a systematic analysis of animal genomes for such transfers.     

Mechanisms of madness: evolutionary psychiatry without evolutionary psychology

Delusions are currently characterised as false beliefs produced by incorrect inference about external reality (DSM IV). This inferential conception has proved hard to link to explanations pitched at the level of neurobiology and neuroanatomy. This paper provides that link via a neurocomputational theory, based on evolutionary considerations, of the role of the prefrontal cortex in regulating offline cognition. When pathologically neuromodulated the prefrontal cortex produces hypersalient experiences which monopolise offline cognition. The result is characteristic psychotic experiences and patterns of thought. This bottom-up account uses neural network theory to integrate recent theories of the role of dopamine in delusion with the insights of inferential accounts. It also provides a general model for evolutionary psychiatry which avoids theoretical problems imported from evolutionary psychology.     

Bacteriocins: ecological and evolutionary significance

Bacteriocins are compounds that are produced by bacteria and are antagonistic to other bacteria. Although they have been known for many years, recent interest in these compounds has increased because of their potential use as natural food preservatives. Although most of this research has been directed at the molecular level, a clearer picture of the ecological role played by bacteriocins in natural environments is beginning to emerge. In addition, the importance and practical implications of evolutionary aspects of bacteriocins and bacteriocin resistance are now being assessed.     

Mechanisms of, and barriers to, horizontal gene transfer between bacteria

Bacteria evolve rapidly not only by mutation and rapid multiplication, but also by transfer of DNA, which can result in strains with beneficial mutations from more than one parent. Transformation involves the release of naked DNA followed by uptake and recombination. Homologous recombination and DNA-repair processes normally limit this to DNA from similar bacteria. However, if a gene moves onto a broad-host-range plasmid it might be able to spread without the need for recombination. There are barriers to both these processes but they reduce, rather than prevent, gene acquisition.     

Electron transfer from cytochrome f to photosystem I in green algae

The time course of P700⁺ reduction and cytochrome f oxidation following a single-turnover flash excitation of photosystem I was measured under various conditions in different strains of green algae. P700⁺ was reduced with a half-time of 4 s. The rate of cytochrome f oxidation was found to depend widely on physiological factors. Reversible transitions are described from a slow-oxidation state (t _1/2=500 s) to a fast-oxidation state (t _1/2=80 s). The addition of ionophore strongly favours and stabilizes the fast-oxidation state. We suggest that these transitions reflect either reversible association between the cytochrome bf complex and the reaction center of photosystem I or changes in the mobility of oxidized plastocyanin. The transitions might be under the control of the membrane potential or the intracellular ATP content. The relation of these reversible transitions with the light state transitions, and their possible involvement in a switch from linear to cyclic electron transfer, are discussed.Abbreviations cyt cytochrome - DCHC dicyclohexyl-18-crown-6 - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DNP-INT dinitrophenylether of iodonitrothymol - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - LHC light harvesting complex - PC plastocyanin - PS I photosystem I     

Cooperation in animals: An evolutionary overview

Evolutionary biologists have grappled with the question of the emergenceand maintenance of cooperation since Darwin first listed animal cooperation asapotential problem for his theory of natural selection. Here I review four pathsthat have been delineated in the study of intra-specific cooperation amonganimals. These paths – kinship, reciprocity, byproduct mutualism andgroupselection – serve as a starting point for behavioral ecologistsinterestedstudying the initiation and maintenance of cooperation. After reviewing theempirical and theoretical underpinnings of these paths to cooperation, I touchupon some recent work that has attempted to examine (or reexamine) the role ofphylogeny, punishment and morality in the light of cooperative behavior.     

Hepatic gene transfer in animals using retroviruses containing the promoter from the gene for phosphoenolpyruvate carboxykinase

Two methods are described for directing the expression of genes to the livers of animals using retroviral vectors containing the predominantly liver-specific promoter from the gene for phosphoenolpyruvate carboxykinase (PEPCK)-linked to the structural gene for either amino 3'-glycosyl phosphotransferase (neo) or bovine growth hormone (bGH). Replication-incompetent retrovirus was used to infect the livers of fetal rats by intraperitoneal injection of animals in utero or to infect adult rats by direct injection into the portal vein after partial hepatectomy. The proviruses were integrated into the hepatic DNA, and the chimeric genes were expressed from the PEPCK promoter for as long as 8 months after infection. The expression of the PEPCK-bGH gene was regulated by diet and hormones in a manner similar to the regulation of the endogenous PEPCK gene in the liver. The potential of this method for targeting genes to the liver is discussed.     

Ancient horizontal gene transfer can benefit phylogenetic reconstruction

Although horizontal gene transfer (HGT) is usually considered a disruptive force in recovering organismal phylogeny, it creates important phylogenetic information. In the 'net of life', the recipient of an ancient gene transfer can be the ancestor of a lineage that inherits the transferred gene; thus, the transferred gene marks the recipient and its descendants as a monophyletic group. Ancient gene transfer events can also reveal the order of emergence of donor and recipient lineages. In addition, these ancient events can significantly shape the genetic systems of the recipients and can play a part in their long-term evolution. In this article, we discuss the recent progress in phylogenetic application of ancient HGTs and describe two examples of transfer events to the ancestor of red algae and green plants that support a common origin of these two groups. We also address the potential pitfalls of this application.     

Staminodes: Their morphological and evolutionary significance

Different approaches to circumscribe staminodial structures in the angiosperms are reviewed. The need for a morphological distinction between “true staminodes” (derived from stamens or homologous to stamens) and “pseudostaminodes” (nonhomologous to stamens) is emphasized. In phylogenetic studies the term “staminode” is often used uncritically, without knowledge of the true homology of these structures. Staminodes are either whole organs (outer tiers or whorls, namely petals, intermediate tiers, or organs within a tier), or partial organs. This article aims to discuss the shortcomings of the past and current approach of staminodes and proposes definitions of staminode types for use as characters in phylogenetic analyses. Staminodial structures should be classified according to their position and function in the flower. Both aspects are intricately linked and make the identification of staminodes sometimes problematic. Shifts in time (heterochrony) and space (heterotopy or homeosis) make that a regressing organ either aborts completely or becomes remodeled into something new. Petals are included in the definition of staminodes as they combine function and heterotopy. A hierarchical ordering of staminodial types is given and discussed. Three interdependent but possibly complementary functions are attached to the occurrence of staminodes: an attractive, nutritional, and structural function. The importance of staminodes for the evolution of the androecium and flower is demonstrated. The difficulty in unmasking pseudostaminodes, comprising receptacular disks, is demonstrated. The value and shortcomings of molecular-based interpretations of staminodes are discussed. It is shown that the decision to recognize a staminode from receptacular emergences often relies on unstable grounds and remains largely dependent on the acceptance of a given phylogenetic background.     

Mechanisms of sperm-egg interactions emerging from gene-manipulated animals

Sperm-egg interactions have been studied for many years using biochemical approaches such as the employment of antibodies and ligands that interact with sperm or with eggs and their vestments. As a result, various factors that participate in fertilization have emerged. However, when animals were genetically manipulated to examine the roles of those factors, most of them were found, to our surprise, to be "not essential". Of course, all biological systems contain redundancies and compensatory mechanisms, but at least some factors were found to be "essential" after gene disruption. As a whole, the explanations of sperm-egg interactions require significant modification from the gene manipulation point of view. In this review, information about sperm-egg interactions obtained from genetically manipulated animals is mainly revisited in order to propose a new vision.     

Reconstructing evolution: gene transfer from plastids to the nucleus

During evolution, the genomes of eukaryotic cells have undergone major restructuring to meet the new regulatory challenges associated with compartmentalization of the genetic material in the nucleus and the organelles acquired by endosymbiosis (mitochondria and plastids). Restructuring involved the loss of dispensable or redundant genes and the massive translocation of genes from the ancestral organelles to the nucleus. Genomics and bioinformatic data suggest that the process of DNA transfer from organelles to the nucleus still continues, providing raw material for evolutionary tinkering in the nuclear genome. Recent reconstruction of these events in the laboratory has provided a unique tool to observe genome evolution in real time and to study the molecular mechanisms by which plastid genes are converted into functional nuclear genes. Here, we summarize current knowledge about plastid-to-nuclear gene transfer in the context of genome evolution and discuss new insights gained from experiments that recapitulate endosymbiotic gene transfer in the laboratory.     

Interstrain gene transfer in Chlamydia trachomatis in vitro: mechanism and significance

The high frequency of between-strain genetic recombinants of Chlamydia trachomatis among isolates obtained from human sexually transmitted infections suggests that lateral gene transfer (LGT) is an important means by which C. trachomatis generates variants that have enhanced relative fitness. A mechanism for LGT in C. trachomatis has not been described, and investigation of this phenomenon by experimentation has been hampered by the obligate intracellular development of this pathogen. We describe here experiments that readily detected LGT between strains of C. trachomatis in vitro. Host cells were simultaneously infected with an ofloxacin-resistant (Ofx^r) mutant of a serovar L1 strain (L1:Ofx^r-1) and a rifampin-resistant (Rif^r) mutant of a serovar D strain (D:Rif^r-1). Development occurred in the absence of antibiotics, and the progeny were subjected to selection for Ofx^r Rif^r recombinants. The parental strains differed at many polymorphic nucleotide sites, and DNA sequencing was used to map genetic crossovers and to determine the parental sources of DNA segments in 14 recombinants. Depending on the assumed DNA donor, the estimated minimal length of the transferred DNA was ≥123 kb in one recombinant but was ≥336 to ≥790 kb in all other recombinants. Such trans-DNA lengths have been associated only with conjugation in known microbial LGT systems, but natural DNA transformation remains a conceivable mechanism. LGT studies can now be performed with diverse combinations of C. trachomatis strains, and they could have evolutionary interest and yield useful recombinants for functional analysis of allelic differences between strains.