21 research outputs found
Mechanisms of Assortative Mating in Speciation with Gene Flow: Connecting Theory and Empirical Research
The large body of theory on speciation with gene flow has brought to light fundamental differences in the effects of two types of mating rules on speciation: preference/trait rules, in which divergence in both (female) preferences and (male) mating traits is necessary for assortment, and matching rules, in which individuals mate with like individuals on the basis of the presence of traits or alleles that they have in common. These rules can emerge from a variety of behavioral or other mechanisms in ways that are not always obvious. We discuss the theoretical properties of both types of rules and explain why speciation is generally thought to be more likely under matching rather than preference/trait rules. We furthermore discuss whether specific assortative mating mechanisms fall under a preference/trait or matching rule, present empirical evidence for these mechanisms, and propose empirical tests that could distinguish between them. The synthesis of the theoretical literature on these assortative mating rules with empirical studies of the mechanisms by which they act can provide important insights into the occurrence of speciation with gene flow. Finally, by providing a clear framework we hope to inspire greater alignment in the ways that both theoreticians and empiricists study mating rules and how these rules affect speciation through maintaining or eroding barriers to gene flow among closely related species or populations
A robust new metric of phenotypic distance to estimate and compare multiple trait differences among populations
Whereas a rich literature exists for estimating population genetic divergence, metrics of phenotypic trait divergence are lacking, particularly for comparing multiple traits among three or more populations. Here, we review and analyze via simulation Hedgesâ g, a widely used parametric estimate of effect size. Our analyses indicate that g is sensitive to a combination of unequal trait variances and unequal sample sizes among populations and to changes in the scale of measurement. We then go on to derive and explain a new, non-parametric distance measure, âÎpâ, which is calculated based upon a joint cumulative distribution function (CDF) from all populations under study. More precisely, distances are measured in terms of the percentiles in this CDF at which each populationâs median lies. Îp combines many desirable features of other distance metrics into a single metric; namely, compared to other metrics, p is relatively insensitive to unequal variances and sample sizes among the populations sampled. Furthermore, a key feature of Îpâand our main motivation for developing itâis that it easily accommodates simultaneous comparisons of any number of traits across any number of populations. To exemplify its utility, we employ Îp to address a question related to the role of sexual selection in speciation: are sexual signals more divergent than ecological traits in closely related taxa? Using traits of known function in closely related populations, we show that traits predictive of reproductive performance are, indeed, more divergent and more sexually dimorphic than traits related to ecological adaptation
Importance of axon-glial interactions for the normal postnatal development of the mouse peripheral nervous system
The mouse nervous system undergoes a vast remodelling of synaptic connections
postnatally, resulting in a reduced number of innervating axons to target cells within
the first few weeks of life. This extensive loss of connections is known as synapse
elimination and it plays a critical role in sculpting and refining neural connectivity
throughout the nervous system, resulting in a finely tuned and well-synchronised
network of innervation. This process has been well characterised at the mouse
neuromuscular junction (NMJ), where synapse elimination takes place postnatally in
all skeletal muscles. It has been well studied for the reasons that it is easily accessible
for live imaging and post-mortem experimental analysis. Studies utilising this
synapse to uncover regulators of synapse elimination have mainly focused on the
importance of glial cell lysosomal activity, nerve conduction and target-derived
growth factor supply. It is clear that non-axonal cell types play key roles in the
success of developmental axon retraction at the NMJ, however the role of glial cells
in the regulation of this process has not been fully explored, as lysosomal activity is
thought of as a consequence of axon pruning rather than a molecular driver.
Previous studies have shown that signals emanating from myelinating glial cells can
modulate neurofilament composition and transport within the underlying axons. We
know that these changes in neurofilament composition and transport are underway
during developmental synapse elimination at the NMJ, so it seems logical to predict
that myelinating glial cells may play a role in the regulation of axonal pruning.
Myelinating glial cells are found along the entire length of lower motor neurons and
form physical interactions with the underlying axons at regions known as paranodes.
At the paranode, Neurofascin155 (Nfasc155: expressed by the myelinating glial cell)
interacts with a Caspr/contactin complex (expressed by the axon). This site has been
proposed as a likely site for axon-glial signalling due to the close apposition of the
cell membranes.
The main focus of this PhD project was to study the potential role of myelinating
glial cells in the success of synapse elimination at the NMJ, using a mouse model of
paranodal disruption (Nfasc155-/-). Chapters 3 and 4 show the results of this work.
This work has revealed a novel role for glia in the modulation of synapse elimination
at the mouse neuromuscular junction, mediated by Nfasc155 in the myelinating
Schwann cell. Synapse elimination was profoundly delayed in Nfasc155-/- mice and
was found to be associated with a non-canonical role for Nfasc155, as synapse
elimination occurred normally in mice lacking the axonal paranodal protein Caspr.
Loss of Nfasc155 was sufficient to disrupt axonal proteins contributing to
cytoskeletal organisation and trafficking pathways in peripheral nerve of Nfasc155-/-
mice and lower levels of neurofilament light (NF-L) protein in maturing motor axon
terminals. Synapse elimination was delayed in mice lacking NF-L, suggesting that
Nfasc155 influences neuronal remodelling, at least in part, by modifying cytoskeletal
dynamics in motor neurons. This work provides the first clear evidence for
myelinating Schwann cells acting as drivers of synapse elimination, with Nfasc155
playing a critical role in glial cell-mediated postnatal sculpting of neuronal
connectivity in the peripheral nervous system. A small section of the results within this thesis are devoted to the study of axon-glial
interactions in a mouse model of childhood motor neuron disease, otherwise known
as spinal muscular atrophy (SMA). In SMA, there are reduced levels of the
ubiquitously expressed survival motor neuron (SMN) protein. The NMJ is a
particularly vulnerable target in SMA, manifesting as a breakdown of neuromuscular
connectivity and progressive motor impairment. Recent studies have begun to shed
light on the role of non-neuronal cell types in the onset and progression of the
disease, presenting SMA as a multi-system disease rather than a purely neuronal
disorder. Recent evidence has highlighted that myelinating glial cells are
significantly affected in a mouse model of SMA, manifesting as an impaired ability
to produce key myelin proteins, resulting in deficient myelination. The final results
chapter of this thesis (Chapter 5) is focussed on further exploring the effects that loss
of SMN has in Schwann cells including their interactions with underlying axons.
This work reveals a disruption to axon-glial interaction, shown by a delay in the
development of paranodes, supporting the idea that non-neuronal cell types are also
affected in SMA.
The results within this thesis reveal a novel role for a glial cell protein, Nfasc155, in
the modulation of synapse elimination at the NMJ. Mechanistic insight in to
Nfasc155âs role in this process is also uncovered and likely involves axonal
cytoskeletal transport systems and the filamentous protein NF-L, which have not
previously been implicated in the process of synapse elimination. This work
highlights an important role for axon-glial interactions during normal postnatal
development of the mouse NMJ. This work also highlights a role for axon-glial
interactions in disease states of the NMJ. Using a mouse model of SMA, axon-glial
interaction was assessed with the finding of a delay in paranodal maturation due to
loss of SMN
I Keep my Problems to Myself: Negative Social Network Orientation, Social Resources, and Health-Related Quality of Life in Cancer Survivors
BACKGROUND: Cancer survivors treated with hematopoietic stem cell transplant rely on their social network for successful recovery. However, some survivors have negative attitudes about using social resources (negative social network orientation) that are critical for their recovery. PURPOSE: We examined the association between survivorsâ social network orientation and health-related quality of life (HRQoL) and whether it was mediated by social resources (network size, perceived support, and negative and positive support-related social exchanges). METHODS: In a longitudinal study, 255 survivors completed validated measures of social network orientation, HRQoL, and social resources. Hypotheses were tested using path analysis. RESULTS: More negative social network orientation predicted worse HRQoL (p < .001). This association was partially mediated by lower perceived support and more negative social exchanges. CONCLUSIONS: Survivors with negative social network orientation may have poorer HRQoL in part due to deficits in several key social resources. Findings highlight a subgroup at risk for poor transplant outcomes and can guide intervention development
Assessing the Cost of Global Biodiversity and Conservation Knowledge
<div><p>Knowledge products comprise assessments of authoritative information supported by standards, governance, quality control, data, tools, and capacity building mechanisms. Considerable resources are dedicated to developing and maintaining knowledge products for biodiversity conservation, and they are widely used to inform policy and advise decision makers and practitioners. However, the financial cost of delivering this information is largely undocumented. We evaluated the costs and funding sources for developing and maintaining four global biodiversity and conservation knowledge products: The IUCN Red List of Threatened Species, the IUCN Red List of Ecosystems, Protected Planet, and the World Database of Key Biodiversity Areas. These are secondary data sets, built on primary data collected by extensive networks of expert contributors worldwide. We estimate that US116â204 million), plus 293 person-years of volunteer time (range: 278â308 person-years) valued at US12â16 million), were invested in these four knowledge products between 1979 and 2013. More than half of this financing was provided through philanthropy, and nearly three-quarters was spent on personnel costs. The estimated annual cost of maintaining data and platforms for three of these knowledge products (excluding the IUCN Red List of Ecosystems for which annual costs were not possible to estimate for 2013) is US6.2â6.7 million). We estimated that an additional US12 million. These costs are much lower than those to maintain many other, similarly important, global knowledge products. Ensuring that biodiversity and conservation knowledge products are sufficiently up to date, comprehensive and accurate is fundamental to inform decision-making for biodiversity conservation and sustainable development. Thus, the development and implementation of plans for sustainable long-term financing for them is critical.</p></div
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A multi-taxon analysis of European Red Lists reveals major threats to biodiversity.
Acknowledgements: The European Red List assessments have been compiled by numerous species experts, many of whom are affiliated with the IUCN Species Survival Commission and are listed as co-authors of the assessments on the IUCN Red List of Threatened Species. The views expressed in this publication do not necessarily reflect those of IUCN or those of the EC. The designation of geographical entities in this paper, and the presentation of the material, do not imply the expression of any opinion whatsoever on the part of IUCN or the EC concerning the legal status of any country, territory, or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries.Funder: European Commission; funder-id: http://dx.doi.org/10.13039/501100000780Funder: National Parks and Wildlife Service; funder-id: http://dx.doi.org/10.13039/100012733Funder: Republic of IrelandFunder: Ministry of Economic Affairs; funder-id: http://dx.doi.org/10.13039/501100004725Funder: Department of Nature & Biodiversity (Ministerie van Economische Zaken, Directie Natuur & Biodiversiteit), the NetherlandsFunder: Council of EuropeFunder: Office fĂ©dĂ©ral de lâenvironnement, SwitzerlandFunder: Swedish Environmental Protection Agency (Naturvardsverket), SwedenFunder: British Entomological Society, United KingdomFunder: Ministry of Sustainable Development and Infrastructure, Government of the Grand-DuchĂ© of LuxembourgFunder: Ministry of the Environment of the Czech RepublicFunder: ArtDatabanken from the Swedish University of Agricultural SciencesBiodiversity loss is a major global challenge and minimizing extinction rates is the goal of several multilateral environmental agreements. Policy decisions require comprehensive, spatially explicit information on species' distributions and threats. We present an analysis of the conservation status of 14,669 European terrestrial, freshwater and marine species (ca. 10% of the continental fauna and flora), including all vertebrates and selected groups of invertebrates and plants. Our results reveal that 19% of European species are threatened with extinction, with higher extinction risks for plants (27%) and invertebrates (24%) compared to vertebrates (18%). These numbers exceed recent IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services) assumptions of extinction risk. Changes in agricultural practices and associated habitat loss, overharvesting, pollution and development are major threats to biodiversity. Maintaining and restoring sustainable land and water use practices is crucial to minimize future biodiversity declines