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The role of habitat gaps and oceanography on the biogeography and population genetics of rocky intertidal gastropods in the Bay of Biscay
No full textIn biogeography, patterns of species abundance, distribution, size, population genetics and morphology often do not follow simple latitudinal gradients – which are classically assumed in such “rules” as the abundant centre hypothesis and Bergmann’s rule. Rather, the biogeography of a species or groups of species are more likely to be associated with abiotic and biotic variables such as availability of suitable habitat, temperature, dispersal potential, and habitat specificity. However, previous biogeographic studies rarely go beyond simple pattern description, particularly for marine species. In this thesis, I find that regional patterns of abundance, distribution, size, morphology, and population genetics are often associated with regional and local differences in environmental and biotic variables, such as upwelling intensity, habitat availability, and intrinsic attributes of species ecology, such as their level of habitat specificity. For example, a lower availability of suitable habitat can result in a fragmented distribution and subsequently lower genetic connectivity for species dependent upon that habitat. Differing abundances and recruitment among localities may also affect intraspecific competition, so density-dependent interactions occur, resulting in smaller/larger individuals. This would not necessarily follow the classically assumed temperature-size rule of smaller individuals usually being found at higher temperatures. Within a species, differing growth rates and adaptations to environmental variables can result in local morphological variation.These biogeographic concepts are explored in depth using rocky intertidal species of the Bay of Biscay as a model system, which contains a 230 km habitat gap and regional variation in temperature unrelated to a latitudinal gradient. In Chapter 2, the almost complete mitochondrial genome of Steromphala umbilicalis is described in relation to other Vetigastropoda. By removing different genes, and using amino acid or nucleotide sequences, different phylogenies are generated. From this, it is proposed that selection mechanisms may be occurring. In Chapter 3, the population genetics of the congeners S. umbilicalis (habitat generalist) and S. pennanti (habitat specialist), are described over the sympatric portion of their range, using both a newly developed mitochondrial marker and microsatellites. By combining this information with abundance estimates, S. umbilicalis is shown to have a more continuous distribution and is more abundant, and therefore shows greater genetic connectivity than S. pennanti which has a more fragmented distribution and lower abundance. In Chapter 4, the abundances, size structures and distributions of S. umbilicalis, S. pennanti, Phorcus lineatus, Patella vulgata and Patella depressa are explored using multiple linear regression for environmental variables including sea surface temperature, air temperature, wave exposure, distance to the habitat gap, and adjacent rocky substrate. Sea temperature showed a positive relationship with P. depressa abundance and the opposite for P. vulgata. Subsequent density-dependent interactions in P. depressa resulted in smaller individuals being associated with higher abundance between localities, and between quadrats within localities for both Patella species. The habitat gap amplified the differences in abundance between the cool water region in northern France dominated by P. vulgata and the warm water Basque region dominated by P. depressa. In Chapter 5, the aspect ratio of S. umbilicalis is explored at the macroscale in relation to multiple environmental variables. Sea temperature shows the best relationship with aspect ratio, both with initial European data and an expanded dataset including museum specimens from the British Isles. Whilst the underlying mechanism is unclear, it may be linked to a decreased growth rate at higher temperature, resulting in a more pointed shell.This work throws new light on biogeographic patterns and processes, particularly regarding temperature around range centres. It has implications when considering the impacts of global warming, particularly in relation to rocky intertidal biogeography.<br/
Dataset: Bay of Biscay rocky intertidal
No full textThis dataset supports the thesis entitled "The role of habitat gaps and oceanography on the biogeography and population genetics of rocky intertidal gastropods in the Bay of Biscay". Appendix 7.5.
Quadrat information (Quadrats.xlsx) with abundance of species and Patella measurements within each quadrat. Steromphala pennanti measurements (G_pen.csv) and Steromphala umbilicalis measurements (S_umb_measurements.xlsx).</span
Testing the contribution of individual genes in mitochondrial genomes for assessing phylogenetic relationships in Vetigastropoda
No full textPhylogenetic analyses for molluscs frequently make use of the mitochondrial (mt) markers COX1, 12S and 16S, in part because of the availability of universal primers (e.g. Plazzi & Passamonti, 2010; Williams et al., 2010; Aktipis & Giribet, 2011; Plazzi et al., 2011; Wakabayashi et al., 2012). Recent phylogenetic studies have expanded on gene sampling, sequenced entire mt genomes and undertaken phylogenetic analyses using all protein-coding and rRNA genes for determining relationships within Mollusca, generally resulting in well-resolved trees with highly supported nodes (e.g. White et al., 2011; Williams, Foster & Littlewood, 2014; Uribe et al., 2015). However, several papers have pointed out that trees based purely on mtDNA can produce erroneous deep relationships between different molluscan taxa (Stöger & Schrödl, 2013; Bernt et al., 2013a). This is perhaps unsurprising, given that mtDNA generally evolves more quickly than the nuclear genome (Burton & Barreto, 2012), and deeper relationships may therefore be beyond the saturation point of mtDNA. However, with the recent development of next-generation sequencing, entire mt genomes can be sequenced rapidly and relatively cheaply. It is therefore important to determine the utility and reliability of the mt genome as a marker for phylogenetic analysis
Data from: Contrasting genetic structure of sympatric congeneric gastropods: do differences in habitat preference, abundance, and distribution matter?
No full textAim: The relationship of population genetics with the ecology and biogeography of species may be explored by comparing phenotypically similar but ecologically different congeners with overlapping ranges. We compared genetic differentiation between two congeneric rocky intertidal gastropods across a major portion of their sympatric range. We hypothesized that the habitat generalist with high abundance and continuous distribution would exhibit comparatively less genetic differentiation than the habitat specialist with low abundance and a fragmented distribution.
Location: Northeast Atlantic from the northwest Iberian Peninsula to southern British coastline.
Taxon: Gastropoda, Trochidae, Steromphala (formerly Gibbula)
Methods: Field surveys were conducted to assess presence/absence and abundance of Steromphala umbilicalis (generalist) and S. pennanti (specialist) at 23 localities along ~1800 km coastline. We isolated polymorphic microsatellite markers for both species (seven loci for S. umbilicalis and eight for S. pennanti) and used these to genotype 187 S. umbilicalis and 157 S. pennanti individuals. We used standard population genetic analyses to compare patterns of genetic differentiation between species in relation to the field surveys.
Results: Steromphala pennanti showed a more fragmented distribution, significantly lower abundance, and greater genetic differentiation than S. umbilicalis. One S. umbilicalis population towards the north of the range (southern Britain) was genetically distinct from all other sampled populations. Steromphala pennanti showed greater genetic differentiation between three southern localities, which may be attributable to its fragmented distribution and lower abundance because of limited availability of its preferred fucoid habitat in this region. We also suggest that oceanographic currents could be associated with regional genetic structure.
Main conclusions: The habitat generalist showed high local abundances, continuous distribution and low regional genetic differentiation across much of its range. We found the opposite pattern for the habitat specialist. Our study highlights the importance of considering ecological (e.g. abundance, habitat preferences) and abiotic variables (e.g. ocean currents and temperature) for understanding differences in genetic structure of sympatrically distributed congeners
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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