Combined effects of night-time temperature and allelochemicals on performance of a generalist insect herbivore

To assess the pattern of temperature influencing the effect of allelochemicals on growth of insect herbivores and to examine the potential effect of warmer nights due to global warming, we examined the simultaneous effects of allelochemicals and warmer night-time temperatures on an insect herbivore (Spodoptera exigua; Lepidoptera: Noctuidae). Dietary chlorogenic acid, rutin and tomatine levels reflected those occurring naturally in the leaves of tomato, a hostplant of this herbivore. We compared the effects of four thermal regimes having a daytime temperature of 26 °C , with the night-time temperature increased from 14 to 26 °C by increments of 4 °C . The effect of a particular allelochemical on developmental rate was similar among the four thermal regimes. Chlorogenic acid and tomatine each reduced final larval weight, but there was no effect of night-time temperature. In contrast, rutin had no effect on final weight, whereas final weight declined with increasing night-time temperature. Night-time temperature did not influence amount eaten. Larvae ate less when chlorogenic acid or tomatine was in the diet. For each allelochemical, there were no allelochemical by thermal regime interactions. In addition, we compared the effects of allelochemicals and the thermal regime of 26:14 °C and constant 20 °C , which was the average temperature of the 26:14 °C regime. Developmental rate was lower at the constant 20 °C regime, chlorogenic acid and tomatine each depressed developmental rate, and there were no allelochemical by thermal regime interactions. Thus, regardless of the specific allelochemical or amount, the pattern of response at the fluctuating regime was similar to that at the constant temperature. In contrast, comparison of the thermal regime of 26:22 °C and constant 24 °C , which was the average temperature of the 26:22 °C regime, showed several allelochemical by thermal regime interactions. At the 26:22 °C regime, developmental rate was disproportionatly higher at the maximal rutin concentration compared to that at constant 24 °C . At the constant 24 °C , final larval mass was disproportionately lower at the moderate tomatine concentration compared to that at the 26:22 °C regime. Because these results differ from that of other studies examining another species, it appears that the response to incremental changes in night-time temperature will reflect the allelochemicals and insect species tested. The contrast between the constant 24 °C and 26:22 °C regimes indicates that even small fluctuations (±2 °C ) in temperature over 24 h can yield differences in the response to an allelochemical.     

DIEL PHASING OF THE CELL-CYCLE IN THE FLORIDA RED TIDE DINOFLAGELLATE, GYMNODINIUM BREVE

The diel cycle is a key regulator of the cell-cycle in many dinoflagellates, but the mechanisms by which the diel cycle entrains the cell-cycle remain poorly understood. In this study, we describe diel phasing of the cell-cycle in the Florida red tide dinoflagellate Gymnodinium breve Davis, determine the diel cue which serves to entrain the cell-cycle, and provide evidence for the presence of cyclin-dependent kinase (CDK), a cell-cycle regulator which may be responsive to this cue. Four laboratory isolates from the West Coast of Florida were compared. When grown on a 16:8 h LD cycle, all isolates displayed phased cell division, with the S-phase beginning 6–8 h into the light phase, and mitosis following 12–14 h later, as determined by flow cytometry. A naturally occurring bloom of G. breve, studied over one diel cycle, displayed diel cell-cycle phasing similar to that in the laboratory cultures, with the S-phase beginning during daylight and the peak of mitosis occurring approximately 4 h after sunset. In the laboratory cultures, the dark/light "dawn" transition was found to provide the diel cue which serves to entrain the G. breve cell-cycle, whereas the light/ dark "dusk" transition did not appear to be involved. Evidence for the presence of CDK in G. breve was obtained using two approaches: (1) identification of a 34-kDa protein, immunoreactive to an antibody against a conserved amino acid sequence (α-PSTAIR) unique to the CDK protein family and (2) inhibition of the cell-cycle by olomoucine, a selective CDK inhibitor. Together, these results provide the basis from which one can begin addressing mechanisms by which the diel cycle regulates the cell-cycle in G. breve.     

CHROMOSOME NUMBERS AND PHYLOGENY IN MELAMPODIUM (COMPOSITAE)

The haplord chromosome numbers of n = 9, 10, 11, 12, 18, 20, 23, 25 ± 1, 27, 30, and 33 have been reported by various authors from 26 of the 37 recognized species of Melampodium. A chromosomal survey of 375 plants from 275 different populations suggests that the recorded numbers are stable within the genus and that infraspecific euploidy and aneuploidy are uncommon. These chromosome numbers can be arranged numerically, with morphological and limited cytogenetic substantiation, into four euploid series of x2 = 9, 10, 11, and 12. Of these four groups of species, the x = 10 series is the largest and morphologically most diverse. This consideration, along with additional evidence from the morphology of sterile disc ovaries, suggests that x = 10 is the ancestral chromosomal base in Melampodium. A comparison of morphological and cytological data from the closely related genera, Acanthospermum and Lecocarpus, indicates that the latter are probably on a common base of x = 11. Present day distributional patterns of all three genera support the hypothesis that x = 10 is the ancestral base for the entire complex.     

Systematic relationships in the white-rayed species of Melampodium (Compositae)

The white-rayed species complex ofMelampodium has been treated by various authors as containing one, two, or three species. A re-evaluation of the taxa in this complex by use of Chromatographic profiles of methanolic leaf extracts from numerous populations over the range of the group has revealed three distinct patterns which, along with morphological and ecological data, provide support for the recognition of three species within the group. Distributional analysis of previously and newly reported chromosome counts of 157 plants in 99 populations shows tetraploid races ofn = 20 in bothM. leucanthum var.leucanthum andM. cinereum var.cinereum to be located primarily in central and south central Texas but locally intermixed with diploid races. Interpretation of morphology, meiotic configurations, and chemical profiles confirms that these cytotypes are autopolyploid in origin and should not be given formal recognition. All data are used to interpret evolutionary relationships, and it is believed thatM. leucanthum var.argopkyllum may closely resemble the progenitor of the entire complex.     

A Simplified Bacterial Spore Stain

A simplification of the Schaeffer-Fulton spore stain for bacteria is presented. It is shown that omission of the heating step during staining with malachite green resulted in spore stains as good as when the heat was applied. The simplified procedure involves (1) heat fixation of the smear by 20 passages through the flame, (2) staining with saturated aqueous malachite green for 10 minutes, (3) rinsing, and (4) counterstaining with 0.25% aqueous safranin for 15 seconds. The omission of the heating step in staining has obvious advantages, particularly in the classroom.     

Reproductive biology of Lactoris fernandeziana (Lactoridaceae)

Lactoris fernandeziana, monotypic in its family, is endemic to the cloud forests of Robinson Crusoe Island. Although there has been considerable study of the relationships of Lactoris, as a rare species and as a putative primitive paleoherb, little is known of its reproductive biology. Knowledge of the latter is essential for effective conservation programs. The species is gynomonoecious. The overall proportion of flowers is ∼1 female:1 hermaphrodite. The inconspicuous semipendulous green flowers, usually in mixed-gender inflorescences, do not produce rewards. Hermaphrodite flowers are herkogamous and protogynous. Pollen grains are shed from the extrorse anthers in permanent dry tetrads. There is a mean of 12879 tetrads per hermaphrodite flower. Both flower types bear an average of ∼18 ovules. The P/O (pollen/ovule) ratios imply facultative or obligate xenogamy, but hand pollinations show that Lactoris is self-compatible. No floral visitors were ever observed, but stigmata of open-pollinated flowers bore tetrads, and 64% of such styles had pollen tubes. Flowers enclosed in large mesh (1 mm) bags bore similar numbers of tetrads and pollen tubes. Thus, we conclude that Lactoris is anemophilous, a syndrome perhaps reflected by the P/O ratio. Low genetic diversity (isozymes and DNA) supports selfing and implies limited distance wind pollen dispersal. The small size of the island, the ± 1000 extant Lactoris plants, coupled with anemophily, self-compatibility, and pendant flower position, have yielded a geitonogamous system with high seed set and low genetic diversity. If inbreeding depression is expressed, it is in seed germination and seedling vigor, for Lactoris is very difficult to cultivate. For this species, effective conservation practices need to focus on habitat preservation and promotion of outcrossing.     

Application of electrospray ionization mass spectrometry for studying human immunodeficiency virus protein complexes

Mass spectrometry (MS) with electrospray ionization (ESI) has shown utility for studying noncovalent protein complexes, as it offers advantages in sensitivity, speed, and mass accuracy. The stoichiometry of the binding partners can be easily deduced from the molecular weight measurement. In many examples of protein complexes, the gas phase-based measurement is consistent with the expected solution phase binding characteristics. This quality suggests the utility of ESI-MS for investigating solution phase molecular interactions. Complexes composed of proteins from the human immunodeficiency virus (HIV) have been studied using ESI-MS. Multiply charged protein dimers from HIV integrase catalytic core (F185K) and HIV protease have been observed. Furthermore, the ternary complex between HIV protease dimer and inhibitor pepstatin A was studied as a function of solution pH. Zinc binding to zinc finger-containing nucleocapsid protein (NCp7) and the NCp7-psi RNA 1:1 stoichiometry complex was also studied by ESI-MS. No protein-RNA complex was observed in the absence of zinc, consistent with the role of the zinc finger motifs for RNA binding. Proteins Suppl. 2:28–37, 1998. © 1998 Wiley-Liss, Inc.     

Novel patterns of historical isolation, dispersal, and secondary contact across Baja California in the Rosy Boa (Lichanura trivirgata)

Mitochondrial DNA (mtDNA) sequence variation was examined in 131 individuals of the Rosy Boa (Lichanura trivirgata) from across the species range in southwestern North America. Bayesian inference and nested clade phylogeographic analyses (NCPA) were used to estimate relationships and infer evolutionary processes. These patterns were evaluated as they relate to previously hypothesized vicariant events and new insights are provided into the biogeographic and evolutionary processes important in Baja California and surrounding North American deserts. Three major lineages (Lineages A, B, and C) are revealed with very little overlap. Lineage A and B are predominately separated along the Colorado River and are found primarily within California and Arizona (respectively), while Lineage C consists of disjunct groups distributed along the Baja California peninsula as well as south-central Arizona, southward along the coastal regions of Sonora, Mexico. Estimated divergence time points (using a Bayesian relaxed molecular clock) and geographic congruence with postulated vicariant events suggest early extensions of the Gulf of California and subsequent development of the Colorado River during the Late Miocene-Pliocene led to the formation of these mtDNA lineages. Our results also suggest that vicariance hypotheses alone do not fully explain patterns of genetic variation. Therefore, we highlight the importance of dispersal to explain these patterns and current distribution of populations. We also compare the mtDNA lineages with those based on morphological variation and evaluate their implications for taxonomy.     

Branch lengths, support, and congruence: testing the phylogenomic approach with 20 nuclear loci in snakes

Many authors have claimed that short branches in the Tree of Life will be very difficult to resolve with strong support, even with the large multilocus data sets now made possible by genomic resources. Short branches may be especially problematic because the underlying gene trees are expected to have discordant phylogenetic histories when the time between branching events is very short. Although there are many examples of short branches that are difficult to resolve, surprisingly, no empirical studies have systematically examined the relationships between branch lengths, branch support, and congruence among genes. Here, we examine these fundamental relationships quantitatively using a data set of 20 nuclear loci for 50 species of snakes (representing most traditionally recognized families). A combined maximum likelihood analysis of the 20 loci gives strong support for 69% of the nodes, but many remain weakly supported, with bootstrap values for 20% ranging from 21% to 66%. For the combined-data tree, we find significant correlations between the length of a branch, levels of bootstrap support, and the proportion of genes that are congruent with that branch in the separate analyses of each gene. We also find that strongly supported conflicts between gene trees over the resolution of individual branches are common (roughly 35% of clades), especially for shorter branches. Overall, our results support the hypothesis that short branches may be very difficult to confidently resolve, even with large, multilocus data sets. Nevertheless, our study provides strong support for many clades, including several that were controversial or poorly resolved in previous studies of snake phylogeny.     

Rooting and dating maples (Acer) with an uncorrelated-rates molecular clock: implications for north American/Asian disjunctions

Simulations suggest that molecular clock analyses can correctly identify the root of a tree even when the clock assumption is severely violated. Clock-based rooting of phylogenies may be particularly useful when outgroup rooting is problematic. Here, we explore relaxed-clock rooting in the Acer/Dipteronia clade of Sapindaceae, which comprises genera of highly uneven species richness and problematic mutual monophyly. Using an approach that does not presuppose rate autocorrelation between ancestral and descendant branches and hence does not require a rooted a priori topology, we analyzed data from up to seven chloroplast loci for some 50 ingroup species. For comparison, we used midpoint and outgroup rooting and dating methods that rely on rooted input trees, namely penalized likelihood, a Bayesian autocorrelated-rates model, and a strict clock. The chloroplast sequences used here reject a single global substitution rate, and the assumption of autocorrelated rates was also rejected. The root was placed between Acer and Dipteronia by all three rooting methods, albeit with low statistical support. Analyses of Acer diversification with a lineage-through-time plot and different survival models, although sensitive to missing data, suggest a gradual decrease in the average diversification rate. The nine North American species of Acer diverged from their nearest relatives at widely different times: eastern American Acer diverged in the Oligocene and Late Miocene; western American species in the Late Eocene and Mid Miocene; and the Acer core clade, including A. saccharum, dates to the Miocene. Recent diversification in North America is strikingly rare compared to diversification in eastern Asia.