Variation in behavioural response to oxygen stress by egg-tending males of parapatric fluvial and lacustrine populations of a landlocked goby

The behavioural response of egg-tending males from parapatric fluvial and lacustrine populations of a landlocked goby Rhinogobius sp. (the orange form) to oxygen stress was compared in laboratory experiments. The natural spawning locations of these populations (rapids of tributary rivers and lakeshore of Lake Biwa, respectively) differ in dissolved oxygen concentration and its variability. Males of both populations spent a longer period of time in fanning behaviour under low dissolved oxygen conditions (4·5–5·0 mg l⁻¹), where >90% of eggs without paternal care died before reaching eyed stage, relative to fully saturated dissolved oxygen conditions (8·0–8·5 mg l⁻¹). Lacustrine males, who occasionally encounter oxygen stress (<2 mg l⁻¹) in their natural habitat, fanned eggs for a longer time period than fluvial males. The time difference in fanning behaviour between the two oxygen conditions was greater for lacustrine than fluvial males. Survival rate in the lower oxygen condition was higher for eggs tended by lacustrine males than those tended by fluvial males, probably due to this difference in fanning activity. These results showed that the response to oxygen stress differs between the two populations and, moreover, as both populations behaved adaptively in responding to the reduction in dissolved oxygen, contiguous habitats may have distinct natural selective pressures. It is suggested that regulation of egg fanning activity is strongly favoured by natural selection in unpredictable environments.     

Variation in native pollinators in the absence of honeybees: implications for reproductive success of an Australian generalist-pollinated herb Trachymene incisa (Apiaceae)

Most plants are generalist in terms of pollination, with the potential for significant spatial and temporal variation in their pollinators. Few studies have investigated how variable pollinators are in a generalist pollination system or how this variation affects plant reproduction. We investigated the degree of variation in pollinators and resulting reproductive success among populations of a widespread generalist-pollinated herb, Trachymene incisa (Apiaceae). The European honeybee was unexpectedly absent from the pollinator assemblages, providing the unique opportunity to study the native Australian pollinators. Insect visitation rates and the taxonomic composition of the pollinator assemblage varied significantly across populations, indicating that populations of T. incisa are not equally serviced and are not equally generalist. This highlights that sampling one population would not characterize the extent of species generalization. There was no positive correlation between insect visitation rate and reproductive success, with the Agnes Banks population receiving the highest visitation rate but producing the lowest reproductive output, and the Myall Lakes population receiving the lowest visitation rate and producing the highest seedling emergence. This study shows that variation in pollinators can have measurable effects on populations of generalist-pollinated plants, therefore there is potential for large-scale change in all plant–pollinator interactions.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 479–490.     

Markedly discordant mitochondrial DNA and allozyme phylogenies of tube-nosed fruit bats, Nyctimene, at the Australian–Oriental biogeographical interface

Australo-Papuan tube-nosed fruit bats of the genus Nyctimene reach their most westerly distribution on the island archipelagos of eastern Indonesia. A recent morphological examination indicates three species occur on Moluccan islands. Both allozyme electrophoresis and mitochondrial DNA (mtDNA) sequencing reveal there are only two species present, Nyctimene cephalotes and Nyctimene albiventer , but there is considerable disparity between the results obtained from the two genetic data sets. Allozyme data indicate N. albiventer occurs on Wokam, which sits on the Australian continental shelf and was joined to Australo-Papua during the last glacial maximum, and N. cephalotes on the other Moluccan islands, all of which are off the continental shelf. Divergence of these two species is dated at approximately 1.5 Mya. By contrast, the mtDNA gene tree shows two deep clades, one containing all specimens from Wokam and Yamdena, and the second all the specimens from the other islands. This especially marked incongruence between the two genetic data sets is ascribed to either a single introgression event of N. albiventer mtDNA into N. cephalotes on Yamdena at around 100 000 ya or lineage sorting of very old mtDNA lineages that coalesce a rather long time before the speciation event. These results highlight that caution should be exercised when relying on mtDNA as barcodes in species taxonomy. The continental-associated N. albiventer on Wokam has higher levels of allozyme heterozygosity and mtDNA nucleotide diversity than the N. cephalotes populations occurring on the more remote islands, indicating that this colonizing species has experienced bottlenecks and/or a low effective population size since speciation.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 589–602.     

Identifiability analysis and improvement of a tree water flow and storage model

A recently published tree water flow and storage model (RCGro) for simulating water transport dynamics in trees and related stem diameter variations was improved in order to better describe a data set gathered under mild drought stress conditions. Model improvements were carried out based on the results of a mathematical identifiability analysis. This analysis provided important information with respect to the balance between model complexity and data availability. Using the identifiability analysis results, we were able to (1) highlight weaknesses of the model; (2) obtain information on how the model could be reduced in some places, to improve its identifiability properties, and extended in others, to enhance model performance; (3) identify which measurements are necessary to optimally calibrate the model. The resulting improved model was less complex (contained less unidentifiable parameters), had better dynamic properties and was able to better describe the stress data set.     

RecJ, ExoI and RecG are required for genome maintenance but not for generation of genetic diversity by repeat-mediated phase variation in Haemophilus influenzae

High levels of genetic diversity are generated in Haemophilus influenzae populations through DNA repeat-mediated phase variation and recombination with DNA fragments acquired by uptake from the external milieu. Conversely, multiple pathways for maintenance of the genome sequence are encoded in H. influenzae genomes. In Escherichia coli, mutations in single-stranded-DNA exonucleases destabilise tandem DNA repeats whilst inactivation of recG can stabilise repeat tracts. These enzymes also have varying effects on recombination. Deletion mutations were constructed in H. influenzae genes encoding homologs of ExoI, RecJ and RecG whilst ExoVII was refractory to mutation. Inactivation of RecJ and RecG, but not ExoI, increased sensitivity to irradiation with ultraviolet light. An increase in spontaneous mutation rate was not observed in single mutants but only when both RecJ and ExoI were mutated. None of the single- or double-mutations increased or decreased the rates of slippage in tetranucleotide repeat tracts. Furthermore, the exonuclease mutants did not exhibit significant defects in horizontal gene transfer. We conclude that RecJ, ExoI and RecG are required for maintenance of the H. influenzae genome but none of these enzymes influence the generation of genetic diversity through mutations in the tetranucleotide repeat tracts of this species.     

Structure and function of bordered pits: new discoveries and impacts on whole-plant hydraulic function

Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and tracheids) that are essential components in the water-transport system of higher plants. The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem. Averaged across a wide range of species, pits account for > 50% of total xylem hydraulic resistance, indicating that they are an important factor in the overall hydraulic efficiency of plants. The structure of pits varies dramatically across species, with large differences evident in the porosity and thickness of pit membranes. Because greater porosity reduces hydraulic resistance but increases vulnerability to embolism, differences in pit structure are expected to correlate with trade-offs between efficiency and safety of water transport. However, trade-offs in hydraulic function are influenced both by pit-level differences in structure (e.g. average porosity of pit membranes) and by tissue-level changes in conduit allometry (average length, diameter) and the total surface area of pit membranes that connects vessels. In this review we address the impact of variation in pit structure on water transport in plants from the level of individual pits to the whole plant.     

High variation in foliage and leaf litter chemistry among 45 tree species of a neotropical rainforest community

Distinct ecosystem level carbon : nitrogen : phosphorus (C : N : P) stoichiometries in forest foliage have been suggested to reflect ecosystem-scale selection for physiological strategies in plant nutrient use. Here, this hypothesis was explored in a nutrient-poor lowland rainforest in French Guiana. Variation in C, N and P concentrations was evaluated in leaf litter and foliage from neighbour trees of 45 different species, and the litter concentrations of major C fractions were also measured. Litter C ranged from 45.3 to 52.4%, litter N varied threefold (0.68-2.01%), and litter P varied seven-fold (0.009-0.062%) among species. Compared with foliage, mean litter N and P concentrations decreased by 30% and 65%, respectively. Accordingly, the range in mass-based N : P shifted from 14 to 55 in foliage to 26 to 105 in litter. Resorption proficiencies indicated maximum P withdrawal in most species, but with a substantial increase in variation in litter P compared with foliage. These data suggest that constrained ecosystem-level C : N : P ratios do not preclude the evolution of highly diversified strategies of nutrient use and conservation among tropical rainforest tree species. The resulting large variation in litter quality will influence stoichiometric constraints within the decomposer food web, with potentially far-ranging consequences on nutrient dynamics and plant-soil feedbacks.     

Patterns of clavicular bilateral asymmetry in relation to the humerus: variation among humans

Studies of directional asymmetry in the human upper limb have extensively examined bones of the arm, forearm, and hand, but have rarely considered the clavicle. Physiologically, the clavicle is an integrated element of the upper limb, transmitting loads to the axial skeleton and supporting the distal bones. However, clavicles develop in a manner that is unique among the bones of the upper limb. Previous studies have indicated that the clavicle has a right-biased asymmetry in diaphyseal breadth, as in humeri, radii, ulnae, and metacarpals, but unlike these other elements, a left-biased length asymmetry. Few studies have assessed how clavicular asymmetry relates to these other bones of the upper limb. Bilateral directional asymmetry of the clavicle is examined in relation to the humerus in a large, geographically diverse human sample, comparing lengths and diaphyseal breadths. Dimensions were converted into percentage directional (%DA) and absolute (%AA) asymmetries. Results indicate that humans have same-side %DA bias in the clavicles and humeri, and contralateral length %DA between these elements. Diaphyseal breadths in both clavicles and humeri are more asymmetric-both in direction and amount-than lengths. Differences in diaphyseal asymmetry are shown to relate to variation in physical activities among groups, but a relationship between activity and length asymmetry is not supported. This further supports previous research, which suggests different degrees of sensitivity to loading between diaphyseal breadths and maximum lengths of long bones. Differences in lateralized behavior and the potential effects of different bone development are examined as possible influences on the patterns observed among human groups.     

Differences of the porcine amelogenin X and Y chromosome genes (AMELX and AMELY) and their application for sex determination in pigs

Molecular sexing in wild and domestic animals has becoming an important issue in several fields including reproduction. X and Y chromosome-specific sequence differences of the amelogenin genes (AMELX and AMELY) have been described in different mammalian species and used for sex determination. We studied the possibility to use sequence variability between the porcine AMELX and AMELY genes for sex determination in pigs. Sequence analysis of about 400 bp of intron 3 of the porcine amelogenin genes showed the presence of a 9-10 bp deletion in AMELY gene compared to AMELX sequences. Moreover, one single nucleotide polymorphism (SNP) was detected for the AMELY sequence. Four other SNPs and 1 bp insertion differentiated three AMELX haplotypes indicating an unexpected quite high nucleotide diversity for a chromosome X region. Two sex determination assays targeting the 9-10 bp difference between AMELX and AMELY were developed. Assessment of the accuracy of the amelogenin assays to correctly sex individuals was tested on 329 pigs belonging to different breeds/lines. All analysed animals were correctly sexed with the new designed amelogenin tests. No amplification was obtained in human, cattle, goat, sheep, and horse genomic DNA. These assays can be used for sex diagnosis of small amounts of genomic DNA (20 pg) obtained from different sources including embryo biopsies, hair, meat, and other biological specimens. Thus, apart from the application in the reproduction field, these tests can be useful in several other sectors including forensics, archaeozoology, meat production, and processing as well as for quality control in sample identification.