322 research outputs found
SpeciationâbyâDepth on Coral Reefs: Sympatric Divergence with Gene Flow or Cryptic Transient Isolation?
The distributions of many sister species in the sea overlap geographically but are partitioned along depth gradients. The genetic changes leading to depth segregation may evolve in geographic isolation as a prerequisite to coexistence or may emerge during primary divergence leading to new species. These alternatives can now be distinguished via the power endowed by the thousands of scorable loci provided by secondâgeneration sequence data. Here, we revisit the case of two depthâsegregated, genetically isolated ecotypes of the nominal Caribbean candelabrum coral Eunicea flexuosa. Previous analyses based on a handful of markers could not distinguish between models of genetic exchange after a period of isolation (consistent with secondary contact) and divergence with gene flow (consistent with primary divergence). Analyses of the history of isolation, genetic exchange and population size based on 15,640 new SNP markers derived from RNAseq data best support models where divergence began 800K BP and include epochs of divergence with gene flow, but with an intermediate period of transient isolation. Results also supported the previous conclusion that recent exchange between the ecotypes occurs asymmetrically from the Shallow lineage to the Deep. Parallel analyses of data from two other corals with depthâsegregated populations (Agaricia fragilis and Pocillopora damicornis) suggest divergence leading to depthâsegregated populations may begin with a period of symmetric exchange, but that an epoch of population isolation precedes more complete isolation marked by asymmetric introgression. Thus, while divergenceâwithâgene flow may account for much of the differentiation that separates closely related, depthâsegregated species, it remains to be seen whether any critical steps in the speciation process only occur when populations are isolated
Algebraic totality, towards completeness
Finiteness spaces constitute a categorical model of Linear Logic (LL) whose
objects can be seen as linearly topologised spaces, (a class of topological
vector spaces introduced by Lefschetz in 1942) and morphisms as continuous
linear maps. First, we recall definitions of finiteness spaces and describe
their basic properties deduced from the general theory of linearly topologised
spaces. Then we give an interpretation of LL based on linear algebra. Second,
thanks to separation properties, we can introduce an algebraic notion of
totality candidate in the framework of linearly topologised spaces: a totality
candidate is a closed affine subspace which does not contain 0. We show that
finiteness spaces with totality candidates constitute a model of classical LL.
Finally, we give a barycentric simply typed lambda-calculus, with booleans
and a conditional operator, which can be interpreted in this
model. We prove completeness at type for
every n by an algebraic method
Cryptic temporal changes in stock composition explain the decline of a flounder (<i>Platichthys</i> spp.) assemblage
Unobserved diversity, such as undetected genetic structure or the presence of cryptic species, is of concern for the conservation and management of global biodiversity in the face of threatening anthropogenic processes. For instance, unobserved diversity can lead to overestimation of maximum sustainable yields and therefore to overharvesting of the more vulnerable stock components within unrecognized mixedâstock fisheries. We used DNA from archival (otolith) samples to reconstruct the temporal (1976â2011) genetic makeup of two mixedâstock flounder fisheries in the Ă
land Sea (AS) and the Gulf of Finland (GoF). Both fisheries have hitherto been managed as a single stock of European flounders (Platichthys flesus), but were recently revealed to target two closely related species: the pelagicâspawning P. flesus and the newly described, demersalâspawning P. solemdali. While the AS and GoF fisheries were assumed to consist exclusively of P. solemdali, P. flesus dominated the GoF flounder assemblage (87% of total) in 1983, had disappeared (0%) by 1993, and remained in low proportions (10%â11%) thereafter. In the AS, P. solemdali dominated throughout the sampling period (>70%), and P. flesus remained in very low proportions after 1983. The disappearance of P. flesus from the GoF coincides in time with a dramatic (~60%) decline in commercial landings and worsening environmental conditions in P. flesusâ northernmost spawning ground, the Eastern Gotland Basin, in the preceding 4â6 years. These results are compatible with the hypothesis that P. flesus in the GoF is a sink population relying on larval subsidies from southern spawning grounds and the cause of their disappearance is a cessation of larval supply. Our results highlight the importance of uncovering unobserved genetic diversity and studying spatiotemporal changes in the relative contribution of different stock components, as well as the underlying environmental causes, to manage marine resources in the age of rapid anthropogenic change
The deindustrialisation/tertiarisation hypothesis reconsidered: a subsystem application to the OECD7
The diffusion of outsourcing, both national and international, and
vertical FDIs among manufacturing firms, along with the higher integra-
tion of business services in manufacturing, has recently led to question
the empirical evidence supporting the Deindustrialisation/Tertiarisation
(DT) hypothesis. Rather than a \real" phenomenon, it has been argued,
DT would be an \apparent" one, mainly due to the reorganization of
production across national and sectoral boundaries.
The empirical studies that have dealt with the topic so far have
not been able to effectively rule out such possibility, because of two
main limitations: the sectoral level of the analysis and/or the national
focus. In order to overcome them, the paper carries out an appreciative
investigation of the actual extent of the DT occurred in the OECD
area over the '80s and the '90s by moving from a sector to a subsystem
perspective, thus retaining both direct and indirect relations, and by
referring to a \pseudo-World" of 7 OECD countries, thus taking into
account the \global" dimension of the phenomenon.
The results strongly support the DT hypothesis: although the weight
of business sector services in the manufacturing subsystem increased,
acting as a counterbalancing tendency to the manufacturing decline,
subsystem shares significantly decreased, thus confirming DT as a more
fundamental trend of modern economies
Outsourcing and structural change: shifting firm and sectoral boundaries
The paper aims at investigating the structural change implications of
outsourcing. In trying to bridge the organizational/industrial and the
sectoral/structural analysis of outsourcing, it discusses the rational and
the methodological pros and cons of a âbatteryâ of outsourcing measurements
for structural change analysis. Their functioning is then illustrated
through a concise application of them to the OECD area over the â80s and
the early â90s. A combined used of them emerges as recommendable in
checking for the role of outsourcing with respect to that of other structural
change determinants
HLA-class I markers and multiple sclerosis susceptibility in the Italian population
Previous studies reported an association with multiple sclerosis (MS) of distinct HLA-class I markers, namely HLA-A*02, HLA-Cw*05 and MOG-142L. In this work, we tested the association with MS of A*02 and Cw*05 in 1273 Italian MS patients and 1075 matched controls, which were previously analyzed for MOG-142, and explored the relationship among these three markers in modulating MS risk. HLA-A*02 conferred a statistically robust MS protection (odds ratio, OR=0.61; 95% confidence intervals, CI=0.51â0.72, P<10â9), which was independent of DRB1*15 and of any other DRB1* allele and remained similar after accounting for the other two analyzed class I markers. Conversely, the protective effect we previously observed for MOG-142L was secondary to its linkage disequilibrium with A*02. Cw*05 was not associated considering the whole sample, but its presence significantly enhanced the protection in the HLA-A*02-positive group, independently of DRB1: the OR conferred by A*02 in Cw*05-positive individuals (0.22, 95% CI=0.13â0.38) was significantly lower than in Cw*05-negative individuals (0.69, 95% CI=0.58â0.83) with a significant (P=4.94 Ă 10â5) multiplicative interaction between the two markers. In the absence of A*02, Cw*05 behaved as a risk factor, particularly in combination with DRB1*03 (OR=3.89, P=0.0006), indicating that Cw*05 might be a marker of protective or risk haplotypes, respectively
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