Genetic diversity in an ant-dispersed chenopod Sclerolaena diacantha

Abstract Sclerolaena diacantha is a common and widespread, short-lived chenopod of arid Australia. The diaspore contains a food mass attractive to ants and, at sites where the ant Rhytidoponera sp B is common, thousands of diaspores accumulate on the nest mounds. Bagged plants set seed, showing that it is self-compatible. Population genetic variation was investigated at two levels: within and between sites, and within and between seed banks accumulated on the ant nests. Electrophoretic analysis of adult plants for 17 loci at 12 sites revealed nine polymorphic loci, but within sites only 6–18% of the loci were polymorphic. The values for mean gene diversity (He = 0.042) and total genetic diversity, (H_T= 0.088) were lower than those recorded for most other plant species. The mean fixation index of 0.52 indicated a mixed mating system with about 70% selfing. Most of the genetic diversity was distributed within sites (Dst = 0.008) and the mean value of 0.094 for GST indicated low levels of genetic differentiation. Electrophoretic analysis of seeds from 12 ant mounds at two sites showed that genetic differentiation was three times greater between seed banks than between the sites. However, collectively the genetic diversity stored within ant mounds was similar to the total diversity within the sites. It appears that restricted ant-dispersal and moderate inbreeding may create a local population structure that is undetected when sampling at a larger scale. Since investigations of genetic patterns on a very local scale are just beginning, there is much to learn about the evolutionary and genetic consequences of different seed flow patterns.     

The Arcoidea (Mollusca: Bivalvia): a review of the current phenetic-based systematics

The diversity and adaptive radiations of modern Arcoidea, here considered to contain the families Arcidae, Noetiidae, Cucullaeidae, and Glycymerididae, are reviewed. Most fall into either epibyssate or endobyssate life habits with only the Glycymerididae living as free burrowers. The phenetic characters of the families within the Arcoida are reviewed and the families are shown to be supported by very few synapomorphic characters. Homoplasy is shown to be widespread and is illustrated in a series of discussions on the ligament, epibyssate–endobyssate radiations, and possible parallelism within genera, and in a review of arcoid anatomical characters. Previously published molecular data are reviewed and these support the inclusion of the Glycymerididae in the Arcoidea. They also indicate, however, that polyphyly is probably widespread at the subfamily level.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 148 , 237–251.     

Partitioning of river metabolism identifies phytoplankton as a major contributor in the regulated Murray River (Australia)

1. River metabolism was measured over an annual cycle at three sites distributed along a 1000 km length of the lowland Murray River, Australia. 2. Whole system metabolism was measured using water column changes in dissolved oxygen concentrations while planktonic and benthic metabolism were partitioned using light‐dark bottles and benthic chambers. 3. Annual gross primary production (GPP) ranged from 775 to 1126 g O₂ m^?2 year^?1 which in comparison with rivers of similar physical characteristics is moderately productive. 4. Community respiration (CR) ranged from 872 to 1284 g O₂ m^?2 year^?1 so that annual net ecosystem production (NEP) was near zero, suggesting photosynthesis and respiration were balanced and that allochthonous organic carbon played a minor role in fuelling metabolism. 5. Planktonic rates of gross photosynthesis and respiration were similar to those of the total channel, indicating that plankton were responsible for much of the observed metabolism. 6. Respiration rates correlated with phytoplankton standing crop (estimated as the sum of GPP plus the chlorophyll concentration in carbon units), yielding a specific respiration rate of ?1.1 g O₂ g C^?1 day^?1. The respiration rate was equivalent to 19% of the maximum rate of phytoplankton photosynthesis, which is typical of diatoms. 7. The daily GPP per unit phytoplankton biomass correlated with the mean irradiance of the water column giving a constant carbon specific photon fixation rate of 0.35 gO₂ g Chl a^?1 day^?1 per μmole photons m^?2 s^?1 (ca. 0.08 per mole photons m^?2 on a carbon basis) indicating that light availability determined daily primary production. 8. Annual phytoplankton net production (NP) estimates at two sites indicated 25 and 36 g C m^?2 year^?1 were available to support riverine food webs, equivalent to 6% and 11% of annual GPP. 9. Metabolised organic carbon was predominantly derived from phytoplankton and was fully utilised, suggesting that food‐web production was restricted by the energy supply.     

Predictable and unpredictable spawning events: in situ behavioural data from free-spawning coral reef invertebrates

Summary

We describe the spawning behaviour and some aspects of spawning periodicity in a diverse group of marine invertebrates, principally echinoderms, but including sponges, anthozoans, molluscs, and polychaetes. Our observations were made both opportunistically and on a systematic basis between 1978 and 1992 on the central and northern Great Barrier Reef. Spawning was predictable in some of the species observed, for example Bohadschia argus, Euapta godeffroyi, and Stichopus variegatus (Holothuroidea), which exhibited regular lunar and diel periodicity. Others, such as Holothuria coluber, Actinopyga lecanora, and Bohadschia graffei (Holothuroidea), Acanthaster planei (Asteroidea), Hyotissa hyotis and Arca spp. (Bivalvia) exhibited no clear lunar or diel periodicity in spawning behaviour. Mass heterospecific spawnings which involved several species, often from different phyla, were commonly observed. The species participating were usually those with unpredictable spawning patterns and while the species involved were diverse there were also occasions when spawning involved species from the same genera. Fertilization rates were measured in situ for the predictable spawner Bohadschia argus and were found to vary between 0–96% depending on the circumstances of the spawnings. Fertilization rates for the unpredictable spawners showed similar variability; Holothuria coluber and Actinopyga lecanora ranged from 9–83%.     

Transketolase from Cyanophora paradoxa: In Vitro Import into Cyanelles and Pea Chloroplasts and a Complex History of a Gene Often, But Not Always, Transferred in the Context of Secondary Endosymbiosis

ABSTRACT. The glaucocystophyte Cyanophora paradoxa is an obligatorily photoautotrophic biflagellated protist containing cyanelles, peculiar plastids surrounded by a peptidoglycan layer between their inner and outer envelope membranes. Although the 136-kb cyanelle genome surpasses higher plant chloroplast genomes in coding capacity by about 50 protein genes, these primitive plastids still have to import >2,000 polypeptides across their unique organelle wall. One such protein is transketolase, an essential enzyme of the Calvin cycle. We report the sequence of the pre-transketolase cDNA from C. paradoxa and in vitro import experiments of precursor polypeptides into cyanelles and into pea chloroplasts. The transit sequence clearly indicates the localization of the gene product to cyanelles and is more similar to the transit sequences of the plant homologues than to transit sequences of other cyanelle precursor polypeptides with the exception of a cyanelle consensus sequence at the N-terminus. The mature sequence reveals conservation of the thiamine pyrophosphate binding site. A neighbor-net planar graph suggests that Cyanophora , higher plants, and the photosynthetic protist Euglena gracilis acquired their nuclear-encoded transketolase genes via endosymbiotic gene transfer from the cyanobacterial ancestor of plastids; in the case of Euglena probably entailing two transfers, once from the plastid in the green algal lineage and once again in the secondary endosymbiosis underlying the origin of Euglena's plastids. By contrast, transketolase genes in some eukaryotes with secondary plastids of red algal origin, such as Thalassiosira pseudonana , have retained the pre-existing transketolase gene germane to their secondary host.     

Regulation of growth response to water stress in the soybean primary root. I. Proteomic analysis reveals region‐specific regulation of phenylpropanoid metabolism and control of free iron in the elongation zone

In water‐stressed soybean primary roots, elongation was maintained at well‐watered rates in the apical 4 mm (region 1), but was progressively inhibited in the 4–8 mm region (region 2), which exhibits maximum elongation in well‐watered roots. These responses are similar to previous results for the maize primary root. To understand these responses in soybean, spatial profiles of soluble protein composition were analysed. Among the changes, the results indicate that region‐specific regulation of phenylpropanoid metabolism may contribute to the distinct growth responses in the different regions. Several enzymes related to isoflavonoid biosynthesis increased in abundance in region 1, correlating with a substantial increase of isoflavonoid content in this region which could contribute to growth maintenance via various potential mechanisms. In contrast, caffeoyl‐CoA O‐methyltransferase, which is involved in lignin synthesis, was highly up‐regulated in region 2. This response was associated with enhanced accumulation of lignin, which may be related to the inhibition of growth in this region. Several proteins that increased in abundance in both regions of water‐stressed roots were related to protection from oxidative damage. In particular, an increase in the abundance of ferritin proteins effectively sequestered more iron and prevented excess free iron in the elongation zone under water stress.     

Contribution of paddock trees to the conservation of terrestrial invertebrate biodiversity within grazed native pastures

Abstract: Paddock trees are a common feature in the agricultural landscapes of Australia. Recent studies have demonstrated the value of scattered paddock trees for soil fertility, native pasture plants and arboreal faunas; however, the degree to which scattered paddock trees contribute to the conservation of terrestrial invertebrate biodiversity within grazed landscapes remains unknown. We ask three questions: (i) Is there a difference between the terrestrial invertebrate assemblages found under paddock trees compared with surrounding grazed native pastures? (ii) Can gradients in soil and litter variables from the base of trees explain patterns in invertebrate assemblages? and (iii) Does the presence of scattered paddock trees have implications for the conservation of terrestrial invertebrate biodiversity within grazed native pastures? We used pitfall trapping and extraction from soil cores to sample the invertebrate assemblages under six New England Peppermint trees (Eucalyptus nova‐anglica Deane and Maiden) and compared them with assemblages sampled from the open paddock. Formicidae and Collembola univariate and multivariate data were analysed along with a range of soil and litter variables. We found (i) significant differences in the assemblages of invertebrates under trees compared with surrounding grazed pastures; (ii) that most soil and litter variables revealed gradients away from tree bases and these variables explained significant variation in invertebrate assemblages; and (iii) more native invertebrates and more species of invertebrates were found under trees compared with the surrounding pastures. We discuss the relationships between paddock trees, the ground and soil environments and the invertebrate communities that inhabit these environments, and conclude with a discussion of the future for paddock trees and the biota supported by them.