148 research outputs found
Evolution and stable isotopes in Placostylus species of the southwest Pacific : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology, Massey University, New Zealand
Human activities during the Holocene have induced a sixth biodiversity crisis and initiated
rapid changes in the climate. The anthropogenic pressures put on ecosystems can result in direct
or indirect environmental degradation, fragmentation and defaunation. Understanding local
patterns of wildlife population structure, species interactions and initial biodiversity are all
crucial to making well-informed decisions that leads to population sustainability and
conservation of global biodiversity.
This thesis is focused on the genus of giant land snail Placostylus and seeks to improve our
overall knowledge of the genus and its potential to store information about the local
environment (such as temperature and humidity) during shell formation. Placostylus is a genus
endemic to the southwest Pacific and the many species present a valuable opportunity to
integrate studies of ecology and environment at a scale relevant to current anthropogenic
climate change. The characteristics of Placostylus shells can be used to investigate extant and
extinct morphological variation within the genus, and their chemical composition can be used
to track the environmental conditions in which the snails lived. In parallel to shell analysis the
generation of genetic data can be used to infer phylogenetic relationships between distant taxa,
and at a fine-scale patterns of population structure allow us to infer gene flow and
differentiation. Understanding the extent to which shell shape and size is controlled by genetic
differences and how much phenotypic plasticity leads to differences is essential if we are to
correctly interpret the significant of phenotypic variation. For example, arid conditions can lead
to Placostylus snails maturing when much smaller in size. Potentially, intraspecific shell shape
and size variation and shell chemistry can all inform us about the local environmental
conditions that existed as snail shells were formed.
Three main axes are developed throughout the thesis. First the diversity of Placostylus and
extended species of the super-family Orthalicoidea are introduced using a phylogenetic
investigation. Evolutionary relationships are inferred from DNA sequences of mitochondrial
and nuclear genetic datasets. Second, morphological variation is examined in detail where two
Placostylus snail species are sympatric (the Isle of Pines, New Caledonia). The variation in
shell shape of taxa living and growing in the same environment must represent genetic
differences rather than phenotypic plasticity. However, genetic data from the Placostylus
species present on the Isle of Pines was needed when a third snail morphotype was discovered.
On the Isle of Pines giant land snails of the species P. fibratus are harvested for food, where
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they are sympatric with the vulnerable species P. porphyrostomus. Understanding local
population structure of both species and their interaction will inform management decisions for
both species. Third, the stable isotopic composition of extant Placostylus shells is analysed
from Placostylus shells from New Zealand and New Caledonia. This works has the aim to
establish a climate proxy system which through the analysis of fossil shells could inform us
about past environmental conditions. A protocol to sample high-resolution isotopic signatures
from Placostylus shells is developed and the stable isotopic composition of shells are examined
in light of the environmental variables of the snail collection locations
Suction duration and numbers of Araneae and Auchenorrhyncha collected in grassland when using an open-ended cylinder to define the sample area
Suction samplers are typically used with touch-down samples, where the nozzle is held stationary on the ground, or within an open-ended cylinder, where the nozzle is moved through the enclosed vegetation. With touch-down sampling, published estimates suggest that virtually all individuals and species of grassland invertebrate are captured within 3 s. Effects of suction duration on catch when sampling within a cylinder have rarely been investigated. Here, it was found that extrapolation from studies of touch-down sampling, based on the relative areas of the G-vac nozzle and the cylinder, can be used to guide minimum sampling durations for Auchenorrhyncha (leafhoppers and planthoppers) when using a G-vac. Additional time, however, may be necessary when sampling Araneae (spiders), probably because movement of the G-vac nozzle within the cylinder results in disturbance of the vegetation such that more specimens are made available to be captured than with touch-down sampling
Suction duration and numbers of Araneae and Auchenorrhyncha collected in grassland when using an open-ended cylinder to define the sample area
Suction samplers are typically used with touch-down samples, where the nozzle is held stationary on the ground, or within an open-ended cylinder, where the nozzle is moved through the enclosed vegetation. With touch-down sampling, published estimates suggest that virtually all individuals and species of grassland invertebrate are captured within 3 s. Effects of suction duration on catch when sampling within a cylinder have rarely been investigated. Here, it was found that extrapolation from studies of touch-down sampling, based on the relative areas of the G-vac nozzle and the cylinder, can be used to guide minimum sampling durations for Auchenorrhyncha (leafhoppers and planthoppers) when using a G-vac. Additional time, however, may be necessary when sampling Araneae (spiders), probably because movement of the G-vac nozzle within the cylinder results in disturbance of the vegetation such that more specimens are made available to be captured than with touch-down sampling
Suction samplers for grassland invertebrates: comparison of numbers caught using Vortisâ„¢and G-vac devices
1. The efficiency of Vortis TM and a modified garden leaf-blower/vacuum ‘G-vac’ sampler were compared by sampling invertebrates using standardised sample areas and suction times at three grassland sites. The G-vac caught more individuals of Araneae, Auchenorrhyncha, Thysanoptera and Hymenoptera than the Vortis. Numbers of Diptera did not differ between devices, but the VortisTM captured greater numbers of Coleoptera.
2. Estimated air velocity within the collecting nozzle was greater for the G-vac and its mode of application resulted in greater disturbance of the grass sward than with the VortisTM. These differences may have contributed to the lar-
ger captures of certain taxa by the G-vac.
3. It is concluded that G-vacs can be applied with confidence as a credible alternative to the bespoke Vortis
TM, and particularly for taxa which are most frequently sampled using suction samplers
Interfertility of independently originated allopolyploid populations
The reduction in genetic diversity in polyploid lineages, formed from whole-genome duplication of a few individuals, can affect their long-term evolutionary potential. Because most polyploids originate multiple times, secondary contact and gene exchange among independently formed polyploids can create novel genetic combinations and reduce the severity of genetic bottlenecks. However, independently originated polyploids may be reproductively isolated from each other due to genetic and chromosomal differences predating the polyploidisation event, or evolving subsequently in the dynamic genomes of young polyploid populations. Here we conducted experimental crosses to investigate the phenotype and interfertility between two independently originated populations of the allopolyploid Mimulus peregrinus (Phrymaceae). We found that individuals from the two populations are phenotypically distinct, but that inter- and intrapopulation crosses are not statistically different. Interpopulation crosses produce viable and fertile offspring, although our results suggest the existence of partial reproductive barriers in the form of reduced pollen viability. We found no difference in pollen viability between F1 and F2 generations. In contrast, we detected a reduction in floral and vegetative size, and in the proportion of plants that flowered, between F1 and F2 generations for both intra- and interpopulation crosses. Together, our results indicate that populations of independent origin can partially exchange genes, producing variable offspring, and that the phenotype of M. peregrinus may be unstable in the early generations. Natural selection on genetically-based variation may be required for the evolution of more stable and fertile individuals of this nascent allopolyploid
La construction collaborative d'Ontoural et son utilisation sur différents terrains
International audienceL'ingénierie des EIAH fondée sur des ontologies est un sujet qui a déjà donné matière à de nombreuses publications, mais sa mise en pratique est encore rare et très récente. Le projet OURAL a eu pour objectifs de faire travailler ensemble plusieurs partenaires qui avaient à concevoir et développer des services pour la formation en ligne. Il a étudié pratiquement comment concevoir et partager des ontologies sur lesquelles fonder leur ingénierie. Cet article décrit les contextes expérimentaux choisis, rend compte de l'expérience originale d'une ontologie développée en commun et nommée Ontoural, et de son utilisation sur les différents terrains. Il la compare à des ontologies déjà disponibles qui couvrent tout ou partie du domaine modélisé et tire les leçons de cette construction dans un objectif de mise à disposition de bonnes pratiques
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The genetic basis of a social polymorphism in halictid bees
The emergence of eusociality represents a major evolutionary transition from solitary to group reproduction. The most commonly studied eusocial species, honey bees and ants, represent the behavioral extremes of social evolution but lack close relatives that are non-social. Unlike these species, the halictid bee Lasioglossum albipes produces both solitary and eusocial nests and this intraspecific variation has a genetic basis. Here, we identify genetic variants associated with this polymorphism, including one located in the intron of syntaxin 1a (syx1a), a gene that mediates synaptic vesicle release. We show that this variant can alter gene expression in a pattern consistent with differences between social and solitary bees. Surprisingly, syx1a and several other genes associated with sociality in L. albipes have also been implicated in autism spectrum disorder in humans. Thus, genes underlying behavioral variation in L. albipes may also shape social behaviors across a wide range of taxa, including humans
Telomere-to-Telomere Genome Sequences across a Single Genus Reveal Highly Variable Chromosome Rearrangement Rates but Absolute Stasis of Chromosome Number
Genome rearrangements in filamentous fungi are prevalent but little is known about the modalities of their evolution, in part because few complete genomes are available within a single genus. To address this, we have generated and compared 15 complete telomere-to-telomere genomes across the phylogeny of a single genus of filamentous fungi, Epichloë. We find that the striking distinction between gene-rich and repeat-rich regions previously reported for isolated species is ubiquitous across the Epichloë genus. We built a species phylogeny from single-copy gene orthologs to provide a comparative framing to study chromosome composition and structural change through evolutionary time. All Epichloë genomes have exactly seven nuclear chromosomes, but despite this conserved ploidy, analyses reveal low synteny and substantial rearrangement of gene content across the genus. These rearrangements are highly lineage-dependent, with most occurring over short evolutionary distances, with long periods of structural stasis. Quantification of chromosomal rearrangements shows they are uncorrelated with numbers of substitutions and evolutionary distances, suggesting that different modes of evolution are acting to create nucleotide and chromosome-scale changes
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