A Molecular Genetic Approach to Understanding the Evolution of Immunoglobulin Gene Structure and Diversity

Immune function in higher vertebrates is mediated primarilyby multimeric glycoproteins found in the serum and on the surfacesof lymphoid cells. These molecules possess common structuralfeatures suggesting that they belong to a supergene family whichmay have originated from a common ancestral gene. Some multigenicmembers of the supergene family undergo unique forms of chromosomalrearrangement during somatic development. We have identifiedimmunoglobulin heavy chainvariable region (V_H) homologs in speciesrepresenting critical points in the vertebrate radiation, examinedtheir nucleotide sequences and found high degrees of organizationalhomology as well as localized regions of extended nucleotide(and amino acid) sequence identity with mammalian V_H genes.The unexpected high degree of nucleotide sequence identity suggeststhat within this multigene family, selection may be operatingat both the DNA and polypeptide levels.Using several differentapproaches, the V_H gene families in lower vertebrates have beenshown to be remarkably complex, discounting the possibilitythat a reduced number of germline genes accounts for the apparentlyrestricted natureof lower vertebrate immune responses. The lowervertebrate germline V_H genes possess prototypic recombinationsignal sequences, implicated in the somatic reorganization ofmammalian immunoglobulin variable region genes, and segmentalreorganizationresembling that seen in mammals has been observed in an elasmobranch.The detection of a recombination element flanked by short, directrepeats within the intervening sequence of one reptilian V_Hgene suggests that these sequences may be mobile, perhaps functioningoutside of the immunoglobulin loci in other developmental processes.The complex nature of the variable region gene families andtheir capacity to undergo structural change during somatic developmentsuggest that unique genetic mechanisms may govern their evolutionarystabilization and diversification.     

Temperature Effects on Maturity Periods in Tetrahymena pyriformis Syngen 1*

Cells of Tetrahymena pyriformis syngen 1 grown at 30 C after conjugation achieve sexual maturity more quickly than do cells grown at 19 C, whether time is measured in numbers of cell divisions or in terms of absolute time. This result is achieved regardless of the temperature at which conjugation and nuclear reorganization occur. These observations differ from those of other workers investigating Paramecium, and suggest that the long term “chronometer” is more tightly coupled to cell division in Paramecium multimicronucleatum and Paramecium caudatum than in Tetrahymena pyriformis.     

Effects of parasitization of Trichoplusia ni by Chelonus sp.

ABSTRACT. Parasitization of Trichoplusia ni (Huebner) (Lepidoptera: Noctuidae) by Chelonus sp. (Hymenoptera: Braconidae), an egg-larval parasitoid, leads to precocious cocoon spinning of the host in the fourth (penultimate) stadium followed by parasitoid emergence from the prepupa. We have investigated the mechanism by which Chelonus sp. disrupts host development. The developing larva and fluids injected by the adult female separately from the egg, are not the source of these effects, but it remains a possibility that the teratocytes, originating from the trophamnion of the parasitoid egg, are responsible. The titre of the juvenile hormone esterase activity in the haemolymph of the parasitized fourth instar host is similar to that in the initial period of the final instar of normal T. ni, but lacks the postwandering peak of activity. The increased JHE activity leads to a reduced JH titre early in the fourth stadia. This indicates that disruption of host development occurs within 12h after apolysis to the fourth stadium, if not before. Anti-juvenile hormone activity is not detected in extracts of parasitized T. ni. The morphological and behavioural changes associated with precocious development of the T. ni host are prevented by applications of juvenile hormone I, juvenile hormone II and the juvenoid, Ro 10–3108, but not juvenile hormone III and the juvenoid R 20458. However, these applications fail to prevent the onset of juvenile hormone esterase activity, another marker of precocious development. These observations indicate that simple anti-juvenile hormone activity may not be the mechanism of disruption of host development. Development of the parasitoid is disrupted by application of Ro 10–3108 and juvenile hormones I, II and III, but timing of eclosion is only affected by application of juvenile hormone I, juvenile hormone II and Ro 10–3108. This observation may indicate a discrimination by the parasitoid between its own juvenile hormone III and the host's juvenile hormone II.     

Do wild dogs exclude foxes? Evidence for competition from dietary and spatial overlaps

Abstract The management of wild canids (wild dogs/dingoes and foxes) presents a conservation dilemma for land managers across Australia. These canids are predators of wildlife and domestic stock but dingoes are considered native and anecdotal reports suggest that they may suppress foxes such that dingo/dog conservation may have a net benefit to wildlife. This study examines dietary and spatial interactions between wild dogs and foxes in the Greater Blue Mountains region of NSW to address the possibility of suppression through competitive exclusion by dogs on foxes. Predator diets were compared using faecal analysis as well as an analysis of 19 dietary studies from similar forest habitats in eastern Australia. Spatial relationships were examined using data from an extensive canid control programme. Diets of wild dogs and foxes showed a high degree of overlap in species taken, indicating potential for competition. But there was also evidence of resource partitioning with the size and arboreality of mammalian prey differing between the two predators. Wild dogs and foxes responded to different landscape‐scale variation in the physical environment, but there was no clear evidence of large‐scale differences in their distribution. At the fine scale there was a negative association between these predators that indicated possible temporal avoidance or localized habitat shifts. Therefore, there is evidence for dietary competition and fine‐scale exclusion, but no support for landscape‐scale exclusion of foxes by wild dogs in the Blue Mountains.     

Distribution of Oriental and German cockroaches, Blatta orientalis and Blattella germanica (Dictyoptera), in the United Kingdom

Results are presented of a survey carried out by Rentokil Ltd on the distribution of the Oriental cockroach Blatta orientalis L. and the German cockroach Blattella germanica L. in the United Kingdom. The known ranges of both species are increased considerably by the findings of the survey, with several new vice-county records for Scotland (including the Western Isles), England and Wales. The frequency at which Blatta orientalis was observed in outdoor habitats may indicate that this species sometimes spreads to new areas without human assistance.     

Production of benthic macroinvertebrate communities along a southern Appalachian river continuum

1. Annual production was estimated for macroinvertebrate communities of principle habitats along a first- to seventh-order river continuum in the southern Appalachian Mountains (U.S.A.). Annual production was relatively low in depositional habitats, pebble/gravel substrata, and on cobble devoid of plant biomass (mosses and hydrophytes). Production was greater in bedrock habitats and greatest on hydrophyte-covered cobble, with estimates reaching 364 g AFDM (ash-free dry mass)m^–2 yr^–1 in a sixth-order river reach. Annual production in depositional habitats was correlated to standing crops of benthic organic material (BOM) in low-order stream reaches but not in higher-order reaches, indicating differences in BOM availability with stream size. In cobble, pebble/gravel and bedrock habitats production was significantly correlated to standing crops of aquatic plants, which can stabilize substrata and enhance access of collector-filtering invertebrates to entrained food resources. 2. By accounting for proportional availability of habitats along the continuum, estimates of total production ranged from 5 to 154 g AFDM m^–2 yr^–1, and increased significantly with stream size. Annual production estimated for sixth- and seventh-order reaches of the continuum were amongst the highest reported thus far for lotic systems. Organization of the benthic community along the continuum, based on production estimates for individual functional feeding-groups, generally supported predictions of the River Continuum Concept (RCC): shredder contributions were greatest in low-order reaches and declined downstream; scraper percentages were greatest in the middle of the continuum; collector-filterer contributions increased with increasing stream size. Longitudinal trends for collector-gatherers and predators did not support RCC predictions; these groups appeared to be influenced by localized changes in habitat availability and occurrence of vertebrate predators along the continuum.     

Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply

We investigated the effect of CO₂ concentration and soilnutrient availability during growth on the subsequent decomposition andnitrogen (N) release from litter of four annual grasses that differ inresource requirements and native habitat. Vulpia microstachys isa native grass found on California serpentine soils, whereas Avenafatua, Bromus hordaceus, and Lolium multiflorum areintroduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO₂ altered litter C:N ratio,decomposition, and N release, but the direction and magnitude of thechanges differed among plant species and nutrient treatments. ElevatedCO₂ had relatively modest effects on C:N ratio of litter,increasing this ratio in Lolium roots (and shoots at high nutrients),but decreasing C:N ratio in Avena shoots. Growth of plants underelevated CO₂ decreased the decomposition rate of Vulpialitter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO₂ on N loss fromlitter also differed among species, with Vulpia litter from high-CO₂ plants releasing N more slowly than ambient-CO₂litter, whereas growth under elevated CO₂ caused increased Nloss from Avena litter. CO₂ effects on N release in Lolium and Bromus depended on the nutrient regime in whichplants were grown. There was no overall relationship between litter C:Nratio and decomposition rate or N release across species and treatments.Based on our study and the literature, we conclude that the effects ofelevated CO₂ on decomposition and N release from litter arehighly species-specific. These results do not support the hypothesis thatCO₂ effects on litter quality consistently lead to decreasednutrient availability in nutrient-limited ecosystems exposed to elevatedCO₂.     

Out of Africa: molecular phylogenetics and biogeography of Wolffiella (Lemnaceae)

The monophyletic genus Wolffiella (Lemnaceae) comprises 10 species divided taxonomically into three sections. Relative to other genera of Lemnaceae, Wolffiella has a restricted range, with species distributed in warm temperate to tropical areas of Africa and the Americas, with only one species occurring in both areas. Sequence data from coding (rbcL and matK) and non‐coding (trnK and rpl16 introns) regions of cpDNA were analyzed phylogenetically to resolve relationships within Wolffiella, and these results were compared to earlier allozyme and morphological studies. Allozymes, cpDNA and morphology all supported the recognition of three sections. Relationships among species were similar in most respects between the allozyme and cpDNA trees, as well as among the different plastid partitions. In Wolffiella, both non‐synonymous and synonymous substitutions were greater in matK than in rbcL, as observed in other taxa. The synonymous substitution rate in matK was similar to the substitution rate of the non‐coding regions. All partitions, including coding regions, exhibited some homoplasy. Biogeographical reconstructions from a combination of cpDNA partitions indicated that Wolffiella originated in Africa with early movement to and radiation in the Americas. The one species found in both Africa and the Americas, W. welwitschii, likely originated in the Americas and subsequently dispersed to Africa. Using the SOWH test, the cpDNA data could reject two alternative biogeographical hypotheses suggested from analyses of morphological and allozyme data. The present distribution of Wolffiella can be explained by two major dispersal events and this contrasts with the more complex species distributions in other Lemnaceae genera. Limited dispersal in Wolffiella relative to other Lemnaceae genera may be due to more recent origins of species, lower dispersibility and poorer colonizing ability. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79 , 565–576.