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The evolutionary history of cnidarian life cycles has been debated since the 1880s, with different hypotheses favored even by current textbooks. Contributing to the disagreement is the fact that the systematic relationships of the four cnidarian classes have received relatively little examination using modern systematic methods. Here we present analyses of class-level relationships based on 18S ribosomal DNA (rDNA) sequence, mitochondrial 16S rDNA sequence, mitochondrial genome structure, and morphological characters. DNA sequences were aligned using a repeatable parsimony-based approach incorporating a range of alignment parameters. Analyses of individual data sets and of all data combined are unanimous in grouping the classes possessing a medusa stage, leaving the holobenthic Anthozoa basal within the phylum.

Sequence divergence in the internal transcribed spacer region 1 (ITS-1) of the ribosomal DNA locus was assessed in subspecies of the coastal North American tiger beetle, Cicindela dorsalis. The spacer region was amplified using the polymerase chain reaction and cloned for sequencing. Of a total of 50 clones obtained from 12 specimens, 42 clones were different in at least one nucleotide position. In a parsimony analysis of these sequences, the main phylogenetic distinction was found to separate sequences from the Gulf of Mexico and the Atlantic Ocean. Within these two assemblages phylogenetic resolution was low, and the variation within individuals was almost as high as the variation within the entire lineage. The pattern of sequence variation suggests the existence of two forms of the ITS-1 that are maintained on different chromosomes. Polymorphisms of limited geographical distribution could be detected, and 41 additional clones were partly sequenced, to assess the geographic distribution of these polymorphisms in more detail. In a population aggregation analysis, the geographic pattern of ITS-1 distribution was basically congruent with that obtained in earlier studies from mitochondrial DNA in the same C. dorsalis populations.

Portions of the 12S and 16S mitochondrial ribosomal genes for 16 species representing nine tribes in the mammal family Bovidae were compared with six previously published orthologous sequences. Phylogenetic analysis of variable nucleotide positions under different constraints and weighting schemes revealed no robust groupings among tribes. Consensus trees support previous hypotheses of monophyly for four clades, including the traditional subfamily Bovinae. However, the basal diversification of bovid tribes, which was largely unresolved by morphological, immunodiffusion, allozyme, and protein sequence data, remains unresolved with the addition of DNA sequence data. The intractability of this systematic problem is consistent with a rapid radiation of the major bovid groups. Several analyses of our data show that monophyly of the Bovidae, which was weakly supported by previous morphological and molecular work, is questionable.

The origins and times of divergence of the speciose Hawaiian Drosophilidae are examined using mtDNA sequences. The Hawaiian Drosophilidae are resolved as the sister group to the subgenus Drosophila. No one member of the subgenus Drosophila could be determined to be more closely related to the Hawaiian Drosophilidae than could any other. This result suggests that the Hawaiian Drosophilidae arose before the diversification of the subgenus Drosophila and after the divergence of the subgenus Sophophora. In light of fossil evidence, this phylogenetic scenario suggests that the Hawaiian Drosophilidae lineages are no younger than 30 Myr.

Drosophila differens, endemic to Molokai, Drosophila planitibia of Maui, and Drosophila silvestris and Drosophila heteroneura from the island of Hawaii are chromosomally homosequential species that presumably have colonized the newer islands of the Hawaiian archipelago by sequential founder events. We have examined the phylogenetic relationships of these four species by using mitochondrial DNA restriction site data for 23 enzymes. Both distance and character-state analyses indicate that a sequential or monotonic branching relationship exists for mtDNA restriction site data from the four species. The mtDNA data suggest that the maternal lineage that gave rise to D. differens is ancestral to the D. planitibia maternal lineage, which in turn shares the most recent common ancestor with the D. silvestris and D. heteroneura maternal lineages [with Drosophila hemipeza (Oahu) and Drosophila neopicta (Molokai and Maui) as outside references]. We also discuss the phylogenetic implications of the mtDNA data in comparison with other sources of phylogenetic data. We conclude that hybridization of the species in this group has been an important factor in the evolution of the nuclear genomes. Because of small population sizes and mating asymmetries, it is possible that the nuclear genetic distance of species that are physically capable of hybridizing (e.g., on the same island or island complex) is depressed. Consequently the mtDNA genetic distance appears to be more sensitive in establishing the sequence of evolutionary events responsible for the present distribution and population structure of these species.

We used the polymerase chain reaction (PCR) to amplify, clone, and sequence 10 engrailedhomeodomains from 8 species in the five major molluscan classes, including the serially organized chiton (Polyplacophora) lineage. The Drosophila melanogastergene engrailed(en) is one of several genes involved in embyonic segment polarity determination. Studies of engrailedsequence and expression in molluscs are of interest due to questions regarding the evolution and homology of segmentation in these taxa. Nucleotide and deduced amino acid sequence comparisons reflect evolutionary conservation within helices of the enhomeodomain and ancient divergences in the region 3′ to the homeodomain.

rDNA nontranscribed spacer (NTS) lengths of Drosophila mercatorum have been measured in individuals from several geographic regions. Individuals from the different geographic subpopulations share some length fragments but are in general distinct. The length differences, both within and between individuals, arise from different copy numbers of a 250-bp repeating unit that is localized to one part of the NTS. In addition to the length differences caused by the 250-bp repeat, there is a Y chromosome (male)-specific length variant elsewhere in the NTS that is approximately 70 bp shorter than the NTS fragment from the X chromosome. Sexual dimorphism seems to be present in all Drosophila. Also, D. mercatorum has fewer NTS length variants per individual than does D. melanogaster while possessing comparable levels of restriction-site polymorphism. The mechanisms that may cause this pattern of variation are selection, gene conversion, and unequal recombination.

The subfamily Serrasalminae (Characidae, Teleostei) is an endemic Neotropical group of fishes distributed along the Amazon, Paraná-Paraguay and Orinoco Basins. The pacu (Piaractus mesopotamicus) is found in all major rivers that comprise the Pantanal of Mato Grosso. In order to investigate population genetic structure within the group, an enriched microsatellite library was constructed. Eight polymorphic were loci screened, with an average of 6.5 alleles per locus. Five loci exhibited greater than 60% heterozygosity. Additionally, a high level of cross-species amplification was obtained.