Physical map and gene organization of the mitochondrial genome from the unicellular green alga Platymonas (Tetraselmis) subcordiformis (Prasinophyceae)

the entire mitochondrial genome (mt genome) of the unicellular green alga Platymonas subcordiformis (synonym Tetraselmis subcordiformis; Prasinophyceae) was cloned and a physical map for the four restriction enzymes Hind III, Eco RI, Bgl II and Xba I was constructed. The mt genome of P. subcordiformis is a 42.8 kb circular molecule, coding for at least 23 genes. Hybridization and sequence analysis revealed the presence of a ca. 1.5 kb inverted repeat on the mt genome of P. subcordiformis. Phylogenetic analyses based on sequences of several coxI genes were carried out. Our data indicate that mitochondria from P. subcordiformis and from land plants form a natural, monophyletic group.     

Aspects of the phylogeny of Platyhelminthes based on 18S ribosomal DNA and protonephridial ultrastructure

DNA studies of 23 taxa (20 platyhelminths, 1 nemertean, Homo and Artemia) and electron-microscopic studies of the protonephridia of many platyhelminths (supported by some additional ultrastructural data) have led to the following conclusions: the Neodermata are monophyletic; Temnocephalida and Dalyelliida form one clade and are not the primitive sister group of the Neodermata; Gyrocotylidea, Amphilinidea and Eucestoda form one monophylum; Pterastericolidae and Umagillidae are dalyelliids and not the sister group of the Neodermata; and Proseriata are unlikely to be closely related with the Tricladida. A large taxon consisting of the Proseriata and some other turbellarians may represent the sister group of the Neodermata.     

Sequence analysis of the complete mitochondrial DNA molecule of the hedgehog,Erinaceus europaeus,and the phylogenetic position of the Lipotyphla

The sequence of the mitochondrial DNA (mtDNA) molecule of the European hedgehog (Erinaceus europaeus) was determined. The length of the sequence presented is 17,442 nucleotides (nt). The molecule is thus the largest eutherian mtDNA molecule so far reported. The organization of the molecule conforms with that of other eutherians, but the control region of the molecule is exceptionally long, 1,988 nt, due to the presence of repeated motifs at two different positions in the 3 part of the control region. The length of the control region is not absolute due to pronounced heteroplasmy caused by variable numbers of the motif TACGCA in one of the repetitive regions. The sequence presented includes 46 repeats of this type. The other repeated region is composed of different AT-rich repeats. This region was identical among four clones studied. Comparison of mitochondrial peptide-coding genes identified a separate position of the hedgehog among several mammalian orders. The concatenated protein sequence of the 13 peptide-coding genes was used in a phylogenetic study using the opossum as outgroup. The position of the hedgehog sequence was basal among the other eutherian sequences included: human, rat, mouse, cow, blue whale, harbor seal, and horse. The analysis did not resolve the relationship among carnivores, perissodactyls, and artiodactyls/cetaceans, suggesting a closer relationship among these orders than acknowledged by classical approaches. Correspondence to: U. Arnason     

The complete nucleotide sequence of the mitochondrial DNA genome of the rainbow trout,Oncorhynchus mykiss

The complete nucleotide sequence of the mitochondrial DNA of the rainbow trout, Onchorynchus mykiss, has been determined. The total length of the molecule is 16,660 bp. The rainbow trout mitochondrial DNA has the same organization described in eutherian mammals, the clawed frog (Xenopus laevis), and the two fish species, Oriental stream loach (Crossotoma lacustre) and carp (Cyprinus carpio). Alignment and comparison of the deduced amino acid sequences of the 13 proteins encoded by rainbow trout and other vertebrate mitochondrial genomes allowed us to estimate that COI is the most conserved mitochondrial subunit (amino acid identity ranging from 85.6% to 94.8%) whereas ATPase 8 is the most variable one (amino acid identity ranging from 30.8% to 70.4%). Putative secondary structures for the 22 tRNAs found in the molecule are given along with an extensive comparison of tRNA sequences among representative species of each major group of vertebrates. In this sense, an unusual cloverleaf structure for the tRNA^Ser(AGY) is proposed. A stem-loop structure inferred for the origin of the L-strand replication (O_L) and the presence of a large polycytidine tract in the O_L loop is described. The existence of this stretch instead of the usual T-rich sequence reported so far in mammal mtDNAs is explained in terms of a less-strict template dependence of the RNA primase involved in the initiation of L-strand replication. Correspondence to: J.M. Bautista     

GENETIC CONSTRAINTS ON MACROEVOLUTION: THE EVOLUTION OF HOST AFFILIATION IN THE LEAF BEETLE GENUS OPHRAELLA

We hypothesize that the evolution of an ecologically important character, the host associations of specialized phytophagous insects, has been influenced by limitations on genetic variation. Using as a historical framework a phylogenetic reconstruction of the history of host associations in the beetle genus Ophraella (Chrysomelidae), we have employed quantitative-genetic methods to screen four species for genetic variation in larval survival, oviposition (in one species only), and feeding responses to their congeners' host plants, in the Asteraceae. We here report results of studies of one species and evaluate the results from all four. Analysis of half-sib/full-sib families and of progenies of wild females of O. notulata, a specialist on Iva (Ambrosiinae), provided evidence of genetic variation in larval consumption of five of six test plants and in adult consumption of four of six. Larval mortality was complete on five plants; only on Ambrosia, a close relative of the natural host, was there appreciable, and genetically variable, survival. Oviposition on Ambrosia showed marginally significant evidence of genetic variation; a more distantly related plant elicited no oviposition at all. In compiling results from four Ophraella species, reported in this and two other papers, we found no evidence of genetic variation in 18 of 39 tests of feeding responses and 14 of 16 tests of larval survival on congeners' hosts. This result is consistent with the hypothesis that absence or paucity of genetic variation may constrain or at least bias the evolution of host associations. The lower incidence of genetic variation in survival than in feeding behavior may imply, according to recent models, that avoidance is a more common evolutionary response to novel plants than adaptation. The usually great disparity between mean performance on congeners' hosts and the species' natural hosts, and an almost complete lack of evidence for negative genetic correlations, argue against the likelihood that speciation has occurred by sympatric host shift. The presence versus apparent absence of genetic variation in consumption was correlated with the propinquity of relationship between the beetle species tested and the species that normally feeds on the test plant, suggesting that the history of host shifts in Ophraella has been guided in part by restrictions on genetic variation. It was also correlated with the propinquity of relationship between a test plant and the beetle's natural host. The contributions of plant relationships and insect relationships, themselves correlated in part, to the pattern of genetic variation, are not readily distinguishable, but together accord with phylogenetic evidence that these and other phytophagous insects adapt most readily to related plants. In this instance, therefore, the macroevolution of an ecologically important character appears to have been influenced by genetic constraints. We hypothesize that absence of the structural prerequisites for genetic variation in complex characters may affect genetic variation and the trajectory of evolution.     

Phylogeny and adaptive radiation within the Anomopoda: a preliminary exploration

The distinctness of the Anomopoda and the polyphyletic nature of the so-called Cladocera are emphasized.An attempt is made to reconstruct the ancestral anomopod, which probably lived in Palaeozoic times. This task is facilitated by the availability of detailed information on extant forms, which includes functional as well as purely morphological considerations and enables us to understand the means whereby complex mechanisms were transformed during evolution. Comparative studies on the ecology and habits of extant forms also throw light on the probable way of life of the ancestral anomopod.Adaptive radiation within the Anomopoda is briefly surveyed and an outline of the suggested phylogeny of the order is indicated.Institute of Environmental and Biological Sciences, University of Lancaster     

The phylogeny of lower Hymenoptera (Insecta), with a summary of the early evolutionary history of the order

A cladistic analysis of the lower Hymenoptera, including all the ‘symphytan’ families and the apocritan families Stephanidae, Megalyridae, Trigonalyidae, Ibaliidae, Vespidae and Gasteruptiidae, has been undertaken. A total of 98 characters were scored for 21 taxa. Twenty equally parsimonious minimum-length trees were obtained. The phylogenetic status of the Xyelidae is uncertain: they might be monophyletic. or the Xyelinae might be the sistergroup of the rest of the Hymenoptera. The non-xyelid Hymenoptera are probably monophyletic; the phylogeny Tenthredinoidea + (Megalodontoidea + (Cephidae + (Anaxyelidea + (Siricidae + (Xiphydriidae + (Orussidae + Apocrita)))))) is proposed for this clade. The Blasticotomidae are probably the sistergroup of all othe Tenthredinoidea, but tenthredinoid phylogeny is otherwise uncertain. Substantial homoplasy occurs within the ‘siricoid’ families, making the relative positions of the Anaxyelidae and Siricidae uncertain. The Stephanidae might be the sistergroup of the rest of the Apocrita; the phylogeny of the remaining apocritan taxa included is insufficiently elucidated. The phylogeny proposed here supports the hypothesis that the appearance of parasitism in the Hymenoptera took place in the common ancestor of Orussidae + Apocrita, the host of which was probably wood boring insect larvae. The exact larval mode of feeding of the ancestral hymenopteran cannot be determined due ot the diversity of lifestyles in the basal lineages of the order.     

Phylogenetic characterization of ineffective Frankia in Alnus glutinosa (L.) Gaertn. nodules from wetland soil inoculants

Ineffective Frankia endophytes were retrieved from various wet soils by using Alnus glutinosa clones as trapping plants. No pure cultures could be isolated from these ineffective nodules. Therefore, the phylogenetic position of these endophytes was determined by sequence analysis of cloned PCR products of bacterial 16S rDNA, derived from nodules. The results showed that all nodule endophytes belong to a hitherto undescribed cluster of the Frankia phylogenetic tree. The position of these uncultured ineffective Frankia nodule endophytes is different from that of the ineffective Frankia isolates derived from A. glutinosa nodules, even when originating from the same geographical location. This suggests a bias in current isolation techniques.     

Species-independent, geographical structuring of chloroplast DNA haplotypes in a montane herb Ipomopsis (Polemoniaceae)

Two hypotheses have been proposed to explain the occurrence of hybrid zones between red-flowered Ipomopsis aggregata and white-flowered I. tenuituba . Either local adaptation to hummingbird and hawkmoth pollinators has given rise to sympatric (or parapatric) divergence of flower colour and morphology (primary intergradation at hybrid zones), or alternatively two previously allopatric species are coming into contact at several geographical areas of secondary intergradation. We examined restriction site patterns in nuclear DNA (nrDNA), chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) from populations of I. aggregata and I. tenuituba representing seven zones of sympatry. No variation was detected in a 350-bp fragment of mtDNA and uninformative levels of variation were observed for nrDNA. We detected 22 potentially informative restriction site polymorphisms in cpDNA, all of which united geographical areas containing populations of both species. We detected no informative species-specific markers. Studies of other species (e.g. oaks) have detected similar species-independent geographical structure of cpDNA. However, in these cases secondary interegradation could be inferred from species-specific nuclear alleles. The pattern in Ipomopsis is consistent with both primary intergradation (independent speciation in each area of sympatry) or secondary intergradation involving complete cytoplasmic replacement. Thus, additional data are needed to explain the origin of hybrid zones in Ipomopsis .     

缘蝽科族级单元系统发育关系支序分析(半翅目:异翅亚目:缘蝽总科)

在已有比较形态学研究基础上,本文选择了15个特征方面（外生殖器为主）的74个新征,以支序分析方法探讨了缘蝽科族（或亚科）的系统发育关系。结果表明棒缘蝽亚科、希缘蝽族、沟缘蝽族较为原始,与其余类群差异较大,缘蝽科的范围值得进一步研究;除Chariesterini外的缘蝽亚科是高等的缘蝽类群;Chariesterini似应从缘蝽亚科中独立出来;狭义巨缘蝽族以及萧的鼻缘蝽族、梭缘蝽族、昧缘蝽族、曼缘蝽族成立;拟黛缘蝽属、副黛缘蝽属、华黛缘蝽属、异黛缘蝽属应从”黛缘蝽族”中分别独立出来成立新族,即拟黛缘蝽族、副黛缘蝽族、华黛缘蝽族和异黛缘蝽族,以使原有的黛缘蝽族成为自然类群。