Natural selection promotes the conservation of linkage of co-expressed genes

Although there is increasing evidence that eukaryotic gene order is not always random, there is no evidence that putatively favourable gene arrangements are preserved by selection more than expected by chance. In yeast (Saccharomyces cerevisiae), for example, co-expressed genes tend to be linked, but whether such gene pairs tend to remain linked more often than expected under null neutral expectations is not known. We show using gene pairs in the S. cerevisiae–Candida albicans comparison that highly co-expressed gene pairs are conserved as pairs at about twice the average rate. However, co-expressed genes also tend to be in close physical proximity and, as expected from a null neutral model, genes (be they co-expressed or not) that are physically close together tend to be retained more often. This physical proximity, however, only accounts for a small proportion of the enhanced degree of conservation of co-expressed gene pairs. These results demonstrate that purely neutralist models of gene order evolution are not realistic.     

Gall-inducing insects provide insights into plant systematic relationships

Field surveys of cynipid gall-inducer occurrences on Quercus species were conducted in Florida, North Carolina, and Pennsylvania, USA. All cynipids demonstrated strong host species and organ fidelity. One result of this specialization is effective niche partitioning among cynipids. The host-association patterns of these specialist herbivores should reflect similarities among oaks, thus we clustered oak species according to their cynipid distributions. Cynipids distinguished small differences among their hosts. A dendrogram of oak species based on cynipid distributions was largely congruent with botanical arrangernents. Cynipid occurrences offer information helpful to resolving some aspects of oak systematics. Collaborative efforts between taxonomic botanists and entomologists will be useful in resolving a variety of plant and insect systematic problems.     

Sequence Analysis of the Mitochondrial Genome of Sarcophyton glaucum: Conserved Gene Order Among Octocorals

The nucleotide sequence for an 11,715-bp segment of the mitochondrial genome of the octocoral Sarcophyton glaucum is presented, completing the analysis of the entire genome for this anthozoan member of the phylum Cnidaria. The genome contained the same 13 protein-coding and 2 ribosomal RNA genes as in other animals. However, it also included an unusual mismatch repair gene homologue reported previously and codes for only a single tRNA gene. Intermediate in length compared to two other cnidarians (17,443 and 18,911 bp), this organellar genome contained the smallest amount of noncoding DNA (428, compared to 1283 and 781 nt, respectively), making it the most compact one found for the phylum to date. The mitochondrial genes of S. glaucum exhibited an identical arrangement to that found in another octocoral, Renilla kolikeri, with five protein-coding genes in the same order as has been found in insect and vertebrate mitochondrial genomes. Although gene order appears to be highly conserved among octocorals, compared to the hexacoral, Metridium senile, few similarities were found. Like other metazoan mitochondrial genomes, the A + T composition was elevated and a general bias against codons ending in G or C was observed. However, an exception to this was the infrequent use of TGA compared to TGG to code for tryptophan. This divergent codon bias is unusual but appears to be a conserved feature among two rather distantly related anthozoans. Received: 27 January 1998 / Accepted: 25 May 1998     

Chloroplast DNA characters, phylogeny, and classification of Lathyrus (Fabaceae)

Mapped cpDNA restriction site characters were analyzed cladistically and the resulting phylogenetic hypotheses were used to test monophyly and relationships of the infrageneric classification of Lathyrus (Fabaceae) proposed by Kupicha (1983, Notes from the Royal Botanic Garden Edinburgh 41: 209-244). The validity of previously proposed classification systems and questions presented by these classification schemes were explored. Two cpDNA regions, rpoC (rpoC1, its intron, part of rpoC2, and their intergenic spacer) and IR- (psbA, trnH-GUG, part of ndhF, and their intergenic spacers), were analyzed for 42 Lathyrus and two Vicia species. PCR (polymerase chain reaction) amplified rpoC and IR- products digested with 31 and 27 restriction endonucleases, respectively, resulted in 109 potentially informative characters. The strict consensus tree suggests that several of Kupicha's sections may be combined in order to constitute clades. The widespread section Orobus and the South American section Notolathyrus should be combined. Section Lathyrus, characterized by a twisted style, should either include sections Orobon and Orobastrum or be redefined as three sections, one of which is characterized by a 100 base pair deletion in the IR- region. Finally, a weighted parsimony analysis positions sections Clymenum (excluding L. gloeospermus) and Nissolia, both with phyllodic leaves, as sister sections. The affiliation of Lathyrus gloeospermus (section Clymenum) remains problematic.     

Large-scale environmental correlates of forest tree distributions in Catalonia (NE Spain)

Aim To explore the environmental correlates of tree species distributions in Catalonia according to the chorological status of the species. Location The study area is the region of Catalonia, in north‐eastern Spain. Methods We used presence‐absence data for 24 species, sampled in random plots distributed throughout forests of Catalonia. A climate model for the Catalonia region provided environmental variables. We used classification tree analysis to explore the environmental correlates of the realized niches of tree species. The predictive accuracy of the models was assessed using the ROC curve approach. Potential distribution maps of tree species were generated for the whole Catalonia region. Results Models were ranked from low to high accuracy for the 24 species. Differences in accuracy among species were related to the chorological status of species. Zonal species, or species at the core of their range (Mediterranean and Sub‐Mediterranean species), were generally well predicted, while extrazonal species, or species at the edge of their range, were predicted only moderately well. Mediterranean species distributions showed good correlations with extreme temperatures and annual precipitation. Main conclusions The above trends confirmed the difficulty of identifying the realized niche of species at the edges of their ranges. In contrast, Mediterranean and Sub‐Mediterranean species, which were at the core of their range, were well‐predicted, confirming the importance of extremes of temperature and annual precipitation as effective surrogates for variables having more direct physiological roles in limiting the ability of plants to survive and grow. Maps of potential tree distributions allowed us to define suitable habitats and to highlight areas where species have been planted outside their natural distribution.     

Revision of the amphipod (Crustacea) family Stegocephalidae

The amphipod (Crustacea) family Stegocephalidae Dana, 1852 is revised, and the results of a phylogenetic analysis of the family are presented. The morphological information, obtained mainly through direct examination of the species, has been transformed into 200 characters. 91 stegocephalid species (91% of all recognized species) are included in the analysis, in addition to six outgroup taxa. Based upon this analysis, the family is divided into five subfamilies and 26 genera. Four new subfamilies (Andaniexinae, Andaniopsinae, Bathystegocephalinae & Parandaniinae) and ten new genera (Alania, Austrocephaloides, Austrophippsia, Bouscephalus, Gordania, Medi-terexis, Pseudo, Schellenbergia, Stegonomadia & Stegomorphia) are erected. Five genera are put into synonymy (Andaniella with Andaniopsis; Phippsiella and Stegocephalopsis with Stegocephalus; Stegophippsiella with Stego-cephalina; Euandania with Parandania).     

SUMMER HOME RANGE AND HABITAT SELECTION OF HARBOR SEAL (PHOCA VITULINA) PUPS

We studied the summer home range and habitat selection of harbor seal pups tracked using VHF radio telemetry along the coast of central Norway in 1997 and 1998. Median fixed kernel home range of six pups tracked in 1998 was 10.4 km² and the median core area was 1.2 km². One particular deep basin (>100 m deep) was highly selected, and extensively used by four of the pups, probably for feeding. An area adjacent to the deep basin also was selected, probably for haul outs. One pup spent most of the time in inshore, kelp forest areas. Shallow areas without kelp forest and exposed land were used least frequently, possibly because they did not provide suitable areas for feeding and to haul out. The seals hauled out more during calm wind and low tide than during rough wind and high tide. Seals seemed to haul out on intertidal rocks associated with islands, and alternated between several haul-out sites. We found no pattern in haul-out activity associated with age, time of day, air/sea temperature, cloud cover, or rainfall. In 1997, seven pups were tracked manually. These data were associated with methodological limitations, and they were used only to illustrate that these seals stayed mainly within the shallow, inshore, kelp forest area, indicating a possible difference in habitat use between years.     

Habitat light, colour variation, and ultraviolet reflectance in the Grand Cayman anole, Anolis conspersus

Data from a diversity of sources are consistent with the hypothesis that the Grand Cayman anole, Anolis conspersus, is descended directly from Anolis grahami of Jamaica. Although the two species have remained morphologically similar, coloration in A. conspersus has changed considerably from that of its ancestor. The most dramatic difference is seen in dewlap colour, where A. conspersus has evolved a blue and highly UV-reflective dewlap from the ancestral orange-and-yellow colour state. In addition, variation in normal (non-metachrosis) dorsum coloration in A. grahami populations is limited to shades of green (olive, emerald, teal), whereas in A. conspersus dorsum coloration varies from green to blue and to brown. This increased colour variation occurs despite Grand Cayman being a small, relatively featureless island only 35 km in length. Results of this study suggest that ambient light differences associated with precipitation-related vegetation structure may have played an important role in the evolution of A. conspersus body colour variation. Evidence is presented to show how geological, ecological, and physiological factors could have interacted to select for a short wavelength-reflective dewlap from a long wavelength-reflective precursor following the colonization of Grand Cayman from Jamaica by A. grahami between 2 and 3 Mya.