Recognizing detachment-mode seafloor spreading in the deep geological past.

Large-offset oceanic detachment faults are a characteristic of slow- and ultraslow-spreading ridges, leading to the formation of oceanic core complexes (OCCs) that expose upper mantle and lower crustal rocks on the seafloor. The lithospheric extension accommodated by these structures is now recognized as a fundamentally distinct “detachment-mode” of seafloor spreading compared to classical magmatic accretion. Here we demonstrate a paleomagnetic methodology that allows unequivocal recognition of detachment-mode seafloor spreading in ancient ophiolites and apply this to a potential Jurassic detachment fault system in the Mirdita ophiolite (Albania). We show that footwall and hanging wall blocks either side of an inferred detachment have significantly different magnetizations that can only be explained by relative rotation during seafloor spreading. The style of rotation is shown to be identical to rolling hinge footwall rotation documented recently in OCCs in the Atlantic, confirming that detachment-mode spreading operated at least as far back as the Jurassic

Effects of pesticide mixtures on host-pathogen dynamics of the amphibian chytrid fungus

Anthropogenic and natural stressors often interact to affect organisms. Amphibian populations are undergoing unprecedented declines and extinctions with pesticides and emerging infectious diseases implicated as causal factors. Although these factors often cooccur, their effects on amphibians are usually examined in isolation. We hypothesized that exposure of larval and metamorphic amphibians to ecologically relevant concentrations of pesticide mixtures would increase their post-metamorphic susceptibility to the fungus Batra-chochytrium dendrobatidis (Bd), a pathogen that has contributed to amphibian population declines worldwide. We exposed five anuran species (Pacific treefrog, Pseudacris regilla; spring peeper, Pseudacris crucifer; Cascades frog, Rana cascadae; northern leopard frog, Lithobates pipiens; and western toad, Anaxyrus boreas) from three families to mixtures of four common insecticides (chlorpyrifos, carbaryl, permethrin, and endosulfan) or herbicides (glyphosate, acetochlor, atrazine, and 2,4-D) or a control treatment, either as tadpoles or as newly metamorphic individuals (metamorphs). Subsequently, we exposed animals to Bd or a control inoculate after metamorphosis and compared survival and Bd load. Bd exposure significantly increased mortality in Pacific treefrogs, spring peepers, and western toads, but not in Cascades frogs or northern leopard frogs. However, the effects of pesticide exposure on mortality were negligible, regardless of the timing of exposure. Bd load varied considerably across species; Pacific treefrogs, spring peepers, and western toads had the highest loads, whereas Cascades frogs and northern leopard frogs had the lowest loads. The influence of pesticide exposure on Bd load depended on the amphibian species, timing of pesticide exposure, and the particular pesticide treatment. Our results suggest that exposure to realistic pesticide concentrations has minimal effects on Bd-induced mortality, but can alter Bd load. This result could have broad implications for risk assessment of amphibians; the outcome of exposure to multiple stressors may be unpredictable and can differ between species and life stages

Variation in styles of rifting in the Gulf of California

Author Posting. © Nature Publishing Group, 2007. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 448 (2007): 466-469, doi:10.1038/nature06035.The rifting of continental lithosphere is a fundamental solid-earth process that leads to the formation of rifted continental margins and ocean basins. Understanding of this process comes from observations of the geometry of rifted margins and the magmatism resulting from rifting, which inform us about the strength of the lithosphere, the state of the underlying mantle, and the transition from rifting to seafloor spreading. Here we describe results from the PESCADOR seismic experiment in the southern Gulf of California and present the first crustal-scale images across conjugate margins of multiple segments within a single rift that has reached the stage of oceanic spreading. A surprisingly large variation in rifting style and magmatism is observed between these segments, from wide rifting with minor syn-rift magmatism to narrow rifting in magmatically robust segments. These differences encompass much of the variation observed across nearly all other non-end-member continental margins. The characteristics of magmatic endmember margins are typically explained in terms of mantle temperature. Our explanations for the variation in the Gulf of California, in contrast, invoke mantle depletion to account for wide, magma-poor rifting and mantle fertility and possibly the influence of sediments to account for robust rift and post-rift magmatism in the Gulf of California. These factors may vary laterally over small distances in regions that have transitioned from convergence to extension, as is the case for the Gulf of California and many other rifts.This work was funded by a grant from the U.S. NSF-MARGINS program

Pattern of the Divergence of Olfactory Receptor Genes during Tetrapod Evolution

The olfactory receptor (OR) multigene family is responsible for the sense of smell in vertebrate species. OR genes are scattered widely in our chromosomes and constitute one of the largest gene families in eutherian genomes. Some previous studies revealed that eutherian OR genes diverged mainly during early mammalian evolution. However, the exact period when, and the ecological reason why eutherian ORs strongly diverged has remained unclear. In this study, I performed a strict data mining effort for marsupial opossum OR sequences and bootstrap analyses to estimate the periods of chromosomal migrations and gene duplications of OR genes during tetrapod evolution. The results indicate that chromosomal migrations occurred mainly during early vertebrate evolution before the monotreme-placental split, and that gene duplications occurred mainly during early mammalian evolution between the bird-mammal split and marsupial-placental split, coinciding with the reduction of opsin genes in primitive mammals. It could be thought that the previous chromosomal dispersal allowed the OR genes to subsequently expand easily, and the nocturnal adaptation of early mammals might have triggered the OR gene expansion

Experiences With and Attitudes Toward Death and Dying Among Homeless Persons

BACKGROUND: Homeless persons face many barriers to health care, have few resources, and experience high death rates. They live lives of disenfranchisement and neglect. Few studies have explored their experiences and attitudes toward death and dying. Unfortunately, studies done in other populations may not apply to homeless persons. Exploring these experiences and attitudes may provide insight into life, health care, and end-of-life (EOL) concerns of this population. OBJECTIVE: To explore the experiences and attitudes toward death and dying among homeless persons. DESIGN: Qualitative study utilizing focus groups. PARTICIPANTS: Fifty-three homeless persons recruited from homeless service agencies. MEASUREMENTS: In-depth interviews, which were audiotaped and transcribed. RESULTS: We present seven themes, some of which are previously unreported. Homeless persons described many significant experiences with death and dying, and many participants suffered losses while very young. These encounters influenced participants’ attitudes toward risks and risky behavior: e.g., for some, these experiences provided justification for high-risk behaviors and influenced their behaviors while living on the streets. For others, they may be associated with their homelessness. Finally, these experiences informed their attitudes toward death and dying as well as EOL care; homeless persons believe that care will be poor at the EOL. CONCLUSIONS: Findings from this study have implications for addressing social services, health promotion, prevention, and EOL care for homeless persons, as well as for others who are poor and disenfranchised

The Cerebellum Link to Neuroticism: A Volumetric MRI Association Study in Healthy Volunteers

Prior research suggests an association between reduced cerebellar volumes and symptoms of depression and anxiety in patients with mood disorders. However, whether a smaller volume in itself reflects a neuroanatomical correlate for increased susceptibility to develop mood disorders remains unclear. The aim of the present study was to examine the relationship between cerebellar volume and neurotic personality traits in a non-clinical subject sample. 3T Structural magnetic resonance imaging scans were acquired, and trait depression and anxiety scales of the revised NEO personality inventory were assessed in thirty-eight healthy right-handed volunteers. Results showed that cerebellar volume corrected for total brain volume was inversely associated with depressive and anxiety-related personality traits. Cerebellar gray and white matter contributed equally to the observed associations. Our findings extend earlier clinical observations by showing that cerebellar volume covaries with neurotic personality traits in healthy volunteers. The results may point towards a possible role of the cerebellum in the vulnerability to experience negative affect. In conclusion, cerebellar volumes may constitute a clinico-neuroanatomical correlate for the development of depression- and anxiety-related symptoms

Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

Author Posting. © Macmillan Publishers, 2008. This is the author's version of the work. It is posted here by permission of Macmillan Publishers for personal use, not for redistribution. The definitive version was published in Nature 455 (2008): 790-794, doi:10.1038/nature07333.The formation of oceanic detachment faults is well established from inactive, corrugated fault planes exposed on seafloor formed along ridges spreading at less than 80 km/My1-4. These faults can accommodate extension for up to 1-3 Myrs5, and are associated with one of two contrasting modes of accretion operating along the northern Mid-Atlantic Ridge (MAR). The first is symmetrical accretion, dominated by magmatic processes with subsidiary high-angle faulting and formation of abyssal hills on both flanks. The second is asymmetrical accretion involving an active detachment fault6 along one ridge flank. An examination of ~2500 km of the MAR between 12.5 and 35°N reveals asymmetrical accretion along almost half of the ridge. Hydrothermal activity identified to date in the study region is closely associated with asymmetrical accretion, which also exhibits high-levels of near continuous hydroacoustically and teleseismically recorded seismicity. Enhanced seismicity is probably generated along detachment faults accommodating a sizeable proportion of the total plate separation. In contrast, symmetrical segments have lower levels of seismicity, which concentrates primarily at their ends. Basalts erupted along asymmetrical segments have compositions that are consistent with crystallization at higher pressures than basalts from symmetrical segments, and with lower extents of partial melting of the mantle. Both seismic and geochemical evidence indicate that the axial lithosphere is thicker and colder at asymmetrical sections of the ridge, either because associated hydrothermal circulation efficiently penetrates to greater depths, or because the rising mantle is cooler. We suggest that much of the variability in seafloor morphology, seismicity and basalt chemistry found along slow-spreading ridges can be thus attributed to the frequent involvement of detachments in oceanic lithospheric accretion.Supported by CNRS (JE), NSF (DKS, HS, JC, CL and SE), WHOI (JE, DKS, HS and JC), Harvard University (JE, CL and SE), Univ. of Leeds (JC), and MIT (JE)

Reproductive toxicity of seafood contaminants: Prospective comparisons of Swedish east and west coast fishermen's families

Cohorts comprising fishermen's families on the east coast of Sweden have been found to have a high consumption of contaminated fish as well as high body burdens of persistent organochlorine pollutants (POPs). Their west coast correspondents are socio-economically similar, but with considerably lower POP exposure since the fish caught on the west coast is far less contaminated. The rationale for this was that the cohorts residing on the east coast of Sweden have been found to have a high consumption of contaminated fish as well as high body burdens of POPs, whereas their west coast correspondents are socio-economically similar, but with considerably lower POP exposure since the fish caught on the west coast is far less contaminated. Among the reproductive outcomes investigated are included both male and female parameters, as well as couple fertility and effects on the fetus. A range of exposure measures, including both questionnaire assessments of fish consumption and biomarkers, have been used

The Winter Worries of Bats : Past and Present Perspectives on Winter Habitat and Management of Cave Hibernating Bats

Winter is a time of fascinating changes in biology for cave-hibernating bats, but it is also a time of vulnerability. Unsurprisingly, assessments of winter habitat for these mammals and how it can be managed have been a focus of many researchers involved with the North American Society for Bat Research over the last 50 years. Over this time, a paradigm shift has occurred in the way scientists think about factors driving selection of winter habitat, especially temperature. To illustrate this change, we review three hypotheses seeking to explain microclimate selection in cavernicolous bats. The first, which we call the “Colder is Better Hypothesis,” posits that bats should select cold microclimates that minimize energy expenditure. The “Hibernation Optimization Hypothesis” suggests that bats should select microclimates that reduce expression of torpor to balance energy conservation against non-energetic costs of hibernation. Finally, the “Thrifty Female Hypothesis” asserts that females should select colder microclimates than males to conserve energy for reproduction. We discuss these hypotheses and the shift from viewing hibernation as a phenomenon driven solely by the need to conserve energy in the context of hibernacula management in North America. We focus on both historical and recent conservation threats, most notably alteration of thermal regimes and the disease white-nose syndrome. We urge against returning to an over-simplified view of winter habitat selection in response to our current conservation challenges.Peer reviewe

Fault-controlled hydration of the upper mantle during continental rifting

Water and carbon are transferred from the ocean to the mantle in a process that alters mantle peridotite to create serpentinite and supports diverse ecosystems1. Serpentinized mantle rocks are found beneath the sea floor at slow- to ultraslow-spreading mid-ocean ridges1 and are thought to be present at about half the world’s rifted margins2, 3. Serpentinite is also inferred to exist in the downgoing plate at subduction zones4, where it may trigger arc magmatism or hydrate the deep Earth. Water is thought to reach the mantle via active faults3, 4. Here we show that serpentinization at the rifted continental margin offshore from western Spain was probably initiated when the whole crust cooled to become brittle and deformation was focused along large normal faults. We use seismic tomography to image the three-dimensional distribution of serpentinization in the mantle and find that the local volume of serpentinite beneath thinned, brittle crust is related to the amount of displacement along each fault. This implies that sea water reaches the mantle only when the faults are active. We estimate the fluid flux along the faults and find it is comparable to that inferred for mid-ocean ridge hydrothermal systems. We conclude that brittle processes in the crust may ultimately control the global flux of sea water into the Earth