Ectoparasitism as a possible cost of social life: a comparative analysis using Australian passerines (Passeriformes)

The hypothesis that cooperative breeding entails a cost in terms of transmission of ectoparasites was tested by a comparative analysis among sympatric Australian passerines. The general trend found using the allometry method and outgroup analysis indicates that contagious ectoparasites are not more common on cooperatively breeding than on non-cooperatively breeding hosts. Body weight, migratory patterns and relative abundance of hosts are factors far more important than cooperative breeding that affect the levels of ectoparasitism in the host genera studies. Ectoparasitism increases with host body weight and relative adundance, while sedentary host genera tended to show less hippoboscid fly diversity than migratory host genera. There is an interaction between breeding system and migratory pattern when relative density of contagious ectoparasites (i.e. mites, ticks and bird lice) is considered: the number of contagious ectoparasites per host is larger on cooperatively breeding host genera than on non-cooperatively breeding host genera among sedentary passerines, but the trend is reversed for migrant passerines.     

On the possible origin and evolution of the genetic code

The genetic code is examined for indications of possible preceding codes that existed during early evolution. Eight of the 20 amino acids are coded by ‘quartets’ of codons with four-fold degeneracy, and 16 such quartets can exist, so that an earlier code could have provided for 15 or 16 amino acids, rather than 20. If two-fold degeneracy is postulated for the first position of the codon, there could have been 10 amino acids in the code. It is speculated that these may have been phenylalanine, valine, proline, alanine, histidine, glutamine, glutamic acid, aspartic acid, cysteine and glycine. There is a notable deficiency of arginine in proteins, despite the fact that it has six codons. Simultaneously, there is more lysine in proteins than would be expected from its two codons, if the four bases in mRNA are equiprobable and are arranged randomly. It is speculated that arginine is an ‘intruder’ into the genetic code, and that it may have displaced another amino acid such as ornithine, or may even have displaced lysine from some of its previous codon assignments. As a result, natural selection has favored lysine against the fact that it has only two codons. The introduction of tRNA into protein synthesis may have been a cataclysmic and comparatively sudden event, since duplication of tRNA takes place readily, and point mutations could rapidly differentiate members of the family of duplicates from each. Two tRNAs for different amino acids may have a common ancestor that existed more recently than the separation of the prokaryotes and eukaryotes. This is shown by homology of twoE. coli tRNAs for glycine and valine, and two yeast tRNAs for arginine and lysine.     

The evolution of morphological diversity in continental assemblages of passerine birds

Understanding geographic variation in the species richness and lineage composition of regional biotas is a long‐standing goal in ecology. Why do some evolutionary lineages proliferate while others do not, and how do new colonists fit into an established fauna? Here, we analyze the morphological structure of assemblages of passerine birds in four biogeographic regions to examine the relative influence of colonization history and niche‐based processes on continental communities of passerine birds. Using morphological traits related to habitat choice, foraging technique, and movement, we quantify the morphological spaces occupied by different groups of passerine birds. We further quantify morphological overlap between groups by multivariate discriminant analysis and null model analyses of trait dispersion. Finally, we use subclade disparity through time to assess the temporal component of morphological evolution. We find mixed support for the prediction, based on priority, that first colonizers constrain subsequent colonizers. Indeed, our results show that the assembly of continental communities is idiosyncratic with regards to the diversification of new clades and the filling of morphospace.     

Evolutionary innovation in the vertebrate jaw: A derived morphology in anuran tadpoles and its possible developmental origin

The mouthparts of anuran tadpoles are highly derived compared to those of caecilians or salamanders. The suprarostral cartilages support the tadpole's upper beak; the infrarostral cartilages support the lower beak. Both supra- and infrarostral cartilages are absent in other vertebrates. These differences reflect the evolutionary origin of a derived feeding mode in anuran tadpoles. We suggest that these unique cartilages stem from the evolution of new articulations within preexisting cartilages, rather than novel cartilage condensations. We propose testing this hypothesis through a search for similarities in the development of the suprarostral and infrarostral cartilage articulations and of the primary jaw joint. In Xenopus, the gene zax is expressed in a region corresponding to the infrarostral cartilage. This gene is related to the bapx1-gene, which regulates jaw joint development. Further investigation of these genes, as well as other genes with joint-related functions, in anuran craniofacial development may provide a connection between the morphological diversity seen in the vertebrate head and the corresponding diversity in genetic regulatory processes. We believe that the evolution of larval jaws in anurans may shed light on the general evolutionary mechanisms of how new articulations, not only in the jaw region, could have arisen in the vertebrate skull.     

The evolution of the Indian Ocean parrots (Psittaciformes): extinction, adaptive radiation and eustacy

Parrots are among the most recognisable and widely distributed of all bird groups occupying major parts of the tropics. The evolution of the genera that are found in and around the Indian Ocean region is particularly interesting as they show a high degree of heterogeneity in distribution and levels of speciation. Here we present a molecular phylogenetic analysis of Indian Ocean parrots, identifying the possible geological and geographical factors that influenced their evolution. We hypothesise that the Indian Ocean islands acted as stepping stones in the radiation of the Old-World parrots, and that sea-level changes may have been an important determinant of current distributions and differences in speciation. A multi-locus phylogeny showing the evolutionary relationships among genera highlights the interesting position of the monotypic Psittrichas, which shares a common ancestor with the geographically distant Coracopsis. An extensive species-level molecular phylogeny indicates a complex pattern of radiation including evidence for colonisation of Africa, Asia and the Indian Ocean islands from Australasia via multiple routes, and of island populations ‘seeding’ continents. Moreover, comparison of estimated divergence dates and sea-level changes points to the latter as a factor in parrot speciation. This is the first study to include the extinct parrot taxa, Mascarinus mascarinus and Psittacula wardi which, respectively, appear closely related to Coracopsis nigra and Psittacula eupatria.     

The evolution of embryogeny in seed plants and the developmental origin and early history of endosperm

For almost a century, the formation of endosperm from a second and distinctive fertilization event has been viewed as a unique feature of flowering plants. However, until recently, the evolutionary origin of this unique embryo-nourishing entity remained a mystery. Based upon comparative developmental analysis of reproduction among basal angiosperms and their closest extant relatives, the Gnetales (Ephedra, Gnetum, and Welwitschia), it is possible to construct an explicit hypothesis of the events that led to the evolutionary establishment of double fertilization and endosperm. The formulation of this historical record is derived entirely from and dependent upon the determination of reproductive features that are likely to have characterized the common ancestors of angiosperms and Gnetales. Current evidence is most congruent with the concept that a process of double fertilization first evolved in a common ancestor of the Gnetales and angiosperms. Initially, however, the second fertilization product was diploid and yielded a supernumerary embryo. Subsequent to the divergence of the angiosperm lineage from its closest relatives (which include the Gnetales), modification of the development of the supernumerary embryo (derived from the second fertilization event) led to the establishment of an embryo-nourishing endosperm. Comparative analysis of patterns of embryogeny within Gnetales and angiosperms establishes that embryo development in the ancestors of flowering plants (with a rudimentary process of double fertilization) was ab initio cellular, and not free nuclear, as had previously been assumed. Thus, it is likely that the earliest flowering plants displayed an ab initio cellular pattern of endosperm development, whose expression was inherited from that of the supernumerary embryo of the ancestors of flowering plants.     

On the phylogenetic position of the scrub-birds (Passeriformes: Menurae: Atrichornithidae) of Australia

Evolutionary relationships of the scrub-birds Atrichornis were investigated using complete sequences of the recombination-activating gene RAG-1 and the proto-oncogene c-mos for two individuals of the noisy scrub-bird Atrichornis clamosus. Phylogenetic analysis revealed that Atrichornis was sister to the genus Menura (the lyrebirds) and that these two genera (the Menurae) were sister to the rest of the oscine passerines. A sister relationship between Atrichornis and Menura supports the traditional view, based on morphology and DNA hybridization, that these taxa are closely related. Similarly, a sister relationship with the remaining oscine passerines agrees with the morphological distinctiveness of Atrichornis and Menura, although this result contradicts conclusions based on DNA hybridization studies. Although Atrichornis is very well known morphologically, previous conclusions regarding its relationships were hampered by a lack of comparative knowledge of other passerines, making concurrence of the sequence data of particular significance.     

Phytophthora cinnamomi in Shanghai and its possible origin

Camellia leaves were most effective for recoveringPhytophthora cinnamomi from soils followed by azalea leaves and cedar needles. A total of 131 isolates ofP. cinnamomi was obtained from soils and roots collected in Shanghai. Among them 125 were A¹ and 6 were A² type. There was little variation in morphological and physiological characteristics among 82 isolates tested. It is suggested that the fungus may have been a recent settler in Shanghai.     

Reconstruction of possible paths of the origin and morphological evolution of bacteriophages

The problem of the origin and evolution of viruses and, in particular, the origin and evolution of bacteriophages is of considerable interest. However, so far, this problem has not been solved with quantitative methods of molecular systematics. In the present study, an attempt to reconstruct the possible paths of appearance and evolution of bacteriophages based on their structural features and morphogenesis, as well as general characteristics of their life cycles and genome organization, was carried out. A scheme describing phylogeny of the main bacteriophage groups and evolution of their life cycles is suggested. Existence of two independently evaluating types of morphogenesis ("budding outward" and "budding inward") is postulated.     

Duplication of accelerated evolution and growth hormone gene in passerine birds

We report the discovery of a duplication of the growth hormone (GH) gene in a major group of birds, the passerines (Aves: Passeriformes). Phylogenetic analysis of 1.3-kb partial DNA sequences of GH genes for 24 species of passerines and numerous outgroups indicates that the duplication occurred in the ancestral lineage of extant passerines. Both duplicates and their open-reading frames are preserved throughout the passerine clade, and both duplicates are expressed in the zebra finch brain, suggesting that both are likely to be functional. The estimated rates of amino acid evolution are more than 10-fold higher in passerine GH genes than in those of their closest nonpasserine relatives. In addition, although the 84 codons sequenced are generally highly conserved for both passerines and nonpasserines, comparisons of the nonsynonymous/synonymous substitution ratios and the rate of predicted amino acid changes indicate that the 2 gene duplicates are evolving under different selective pressures and may be functionally divergent. The evidence of differential selection, coupled with the preservation of both gene copies in all major lineages since the origin of passerines, suggests that the duplication may be of adaptive significance, with possible implications for the explosive diversification of the passerine clade.     

Photoreceptor-like outer segments in the pineal organ of the lovebird,Uroloncha domestica (Aves: Passeriformes)

Summary In the pineal organ of the lovebird, Uroloncha domestica, bulbous, cup-shaped and elongated outer segments of photoreceptor-like pinealocytes are demonstrated by scanning electron microscopy. These scarce outer segments, 4–11 m in length, extend into the pineal lumen. The present structural observations speak in favor of photosensitive pinealocytes in the pineal organ of Uroloncha domestica. The relation of the photoreceptor-like pinealocytes to acetylcholinesterase-positive nerve cells and a nervous connection between the pineal and the brain indicate that the pineal organ of this passeriform species may be the site of neuroendocrine and photoreceptive functions.Supported by a fellowship from the Japan Society for the Promotion of Science to M. UeckSupported by a grant from the Ministry of Education of Japan to K. Wake and by a grant of the Deutsche Forschungsgemeinschaft to M. Ueck     

寄生虫的起源与进化

介绍了寄生虫的提前适应机制在寄生虫起源与进化中的重要作用,同时还推测了寄生虫可能的进化过程,并且阐述了寄生虫对寄生生活的适应对策以及对宿主行为的改变。     

The origin and evolution of the ribosome

Background  

The origin and early evolution of the active site of the ribosome can be elucidated through an analysis of the ribosomal proteins' taxonomic block structures and their RNA interactions. Comparison between the two subunits, exploiting the detailed three-dimensional structures of the bacterial and archaeal ribosomes, is especially informative.