Slow Recovery from Inbreeding Depression Generated by the Complex Genetic Architecture of Segregating Deleterious Mutations

The deleterious effects of inbreeding have been of extreme importance to evolutionary biology, but it has been difficult to characterize the complex interactions between genetic constraints and selection that lead to fitness loss and recovery after inbreeding. Haploid organisms and selfing organisms like the nematode Caenorhabditis elegans are capable of rapid recovery from the fixation of novel deleterious mutation; however, the potential for recovery and genomic consequences of inbreeding in diploid, outcrossing organisms are not well understood. We sought to answer two questions: 1) Can a diploid, outcrossing population recover from inbreeding via standing genetic variation and new mutation? and 2) How does allelic diversity change during recovery? We inbred C. remanei, an outcrossing relative of C. elegans, through brother-sister mating for 30 generations followed by recovery at large population size. Inbreeding reduced fitness but, surprisingly, recovery from inbreeding at large populations sizes generated only very moderate fitness recovery after 300 generations. We found that 65% of ancestral single nucleotide polymorphisms (SNPs) were fixed in the inbred population, far fewer than the theoretical expectation of ∼99%. Under recovery, 36 SNPs across 30 genes involved in alimentary, muscular, nervous, and reproductive systems changed reproducibly across replicates, indicating that strong selection for fitness recovery does exist. Our results indicate that recovery from inbreeding depression via standing genetic variation and mutation is likely to be constrained by the large number of segregating deleterious variants present in natural populations, limiting the capacity for recovery of small populations.     

Proline Accumulation in Leaves of Periploca sepium via Both Biosynthesis Up-Regulation and Transport during Recovery from Severe Drought

Drought resistance and recovery ability are two important requisites for plant adaptation to drought environments. Proline (Pro) metabolism has been a major concern in plant drought tolerance. However, roles of Pro metabolism in plant recovery ability from severe drought stress are largely unexplored. Periploca sepium Bunge has gained increasing attention for its adaptation to dry environments. Here, we investigated Pro metabolism in different tissues of P. sepium seedlings in the course of drought stress and recovery. We found that leaf Pro metabolism response during post-drought recovery was dependant on drought severity. Pro biosynthesis was down-regulated during recovery from -0.4 MPa but increased continually and notably during recovery from -1.0 MPa. Significant correlation between Pro concentration and Δ1-pyrroline-5-carboxylate synthetase activity indicates that Glutamate pathway is the predominant synthesis route during both drought and re-watering periods. Ornithine δ-aminotransferase activity was up-regulated significantly only during recovery from −1.0 MPa, suggesting positive contribution of ornithine pathway to improving plant recovery capacity from severe drought. In addition to up-regulation of biosynthesis, Pro transport from stems and roots also contributed to high Pro accumulation in leaves and new buds during recovery from −1.0 MPa, as indicated by the combined analysis of Pro concentration and its biosynthesis in stems, roots and new buds. Except its known roles as energy, carbon and nitrogen sources for plant rapid recovery, significant positive correlation between Pro concentration and total antioxidant activity indicates that Pro accumulation can also promote plant damage repair ability by up-regulating antioxidant activity during recovery from severe drought stress.     

Rapid recovery from K current inactivation on membrane hyperpolarization in molluscan neurons

Recovery from K current inactivation was studied in molluscan neurons using two-microelectrode and internal perfusion voltage clamps. Experiments were designed to study the voltage-dependent delayed outward current (IK) without contamination from other K currents. The amount of recovery from inactivation and the rate of recovery increase dramatically when the membrane potential is made more negative. The time course of recovery at the resting potential, -40 mV, is well fit by a single exponential with a time constant of 24.5 s (n = 7). At more negative voltages, the time course is best fit by the sum of two exponentials with time constants at -90 mV of 1.7 and 9.8 s (n = 7). In unclamped cells, a short hyperpolarization can cause rapid recovery from inactivation that results in a shortening of the action potential duration. We conclude that there are two inactivated states of the channel and that the time constants for recovery from both states are voltage dependent. The results are discussed in terms of the multistate model for K channel gating that was developed by R. N. Aldrich (1981, Biophys. J., 36:519-532).     

Regulation of Kv4.3 closed state inactivation and recovery by extracellular potassium and intracellular KChIP2b

Mechanisms underlying Kv4 channel inactivation and recovery are presently unclear, although there is general consensus that the basic characteristics of these processes are not consistent with Shaker (Kv1) N- and P/C-type mechanisms. Kv4 channels also differ from Shaker in that they can undergo significant inactivation from pre-activated closed-states (closed-state inactivation, CSI), and that inactivation and recovery kinetics can be regulated by intracellular KChIP2 isoforms. To gain insight into the mechanisms regulating Kv4.3 CSI and recovery, we have analyzed the effects of increasing [K(+)](o) from 2 mM to 98 mM in the absence and in the presence of KChIP2b, the major KChIP2 isoform expressed in the mammalian ventricle. In the absence of KChIP2b, high [K(+)](o) promoted Kv4.3 inactivated closed-states and significantly slowed the kinetics of recovery from both macroscopic and closed-state inactivation. Coexpression of KChIP2b in 2 mM [K(+)](o) promoted non-inactivated closed-states and accelerated the kinetics of recovery from both macroscopic and CSI. In high [K(+)](o), KChIP2b eliminated or significantly reduced the slowing effects on recovery. Attenuation of CSI by the S4 charge-deletion mutant R302A, which produced significant stabilization of non-inactivated closed-states, effectively eliminated the opposing effects of high [K(+)](o) and KChIP2b on macroscopic recovery kinetics, confirming that these results were due to alterations of CSI. Elevated [K(+)](o) therefore slows Kv4.3 recovery by stabilizing inactivated closed-states, while KChIP2b accelerates recovery by destabilizing inactivated closed-states. Our results challenge underlying assumptions of presently popular Kv4 gating models and suggest that Kv4.3 possesses novel allosteric mechanisms, which are absent in Shaker, for coupling interactions between intracellular KChIP2b binding motifs and extracellular K(+)-sensitive regulatory sites.     

Recovery of Pisum root meristems after mitotic-inhibitory treatments with 3H-thymidine. Inhibition of cell-cycle progression by unincorporated 3H-thymidine.

Primary root meristems of Pisum sativum recover form a 3H-thymidine-induced reduction in mitotic activity once the roots are no longer exposed to exogenous 3H-thymidine. Cells arrested in G2 during 3H-thymidine treatment apparently do not divide for at least 16 hours after treatment, whereas cells remaining in G1 and S do divide and thereby account for recovery. Recovery occurs only when meristems are no longer exposed to exogenous (i.e. unincorporated) 3H-thymidine, suggesting that cytoplasmic irradiation from unincorporated 3H-thymidine prevents cellular recovery from 3H-thymidine-induced inhibition of cell progression through the mitotic cycle. Concentrations of 14C-thymidine which result in cytoplasmic irradiation nearly equivalent to that achieved with 3H-thymidine, but much lower levels of nuclear irradiation, also prevent recovery from 3H-thymidine-induced inhibition of mitotic activity, but do not alone produced such inhibition. These results support the contention that cytoplasmic irradiation prevents recovery from the effects of nuclear irradiation. Unincorporated 3H-thymidine also prevents recovery from sucrose deprivation in stationary phase G2 cells which have not incorporated 3H-thymidine into nuclear DNA.     

Fast inactivation of Nav current in rat adrenal chromaffin cells involves two independent inactivation pathways

Voltage-dependent sodium (Nav) current in adrenal chromaffin cells (CCs) is rapidly inactivating and tetrodotoxin (TTX)–sensitive. The fractional availability of CC Nav current has been implicated in regulation of action potential (AP) frequency and the occurrence of slow-wave burst firing. Here, through recordings of Nav current in rat CCs, primarily in adrenal medullary slices, we describe unique inactivation properties of CC Nav inactivation that help define AP firing rates in CCs. The key feature of CC Nav current is that recovery from inactivation, even following brief (5 ms) inactivation steps, exhibits two exponential components of similar amplitude. Various paired pulse protocols show that entry into the fast and slower recovery processes result from largely independent competing inactivation pathways, each of which occurs with similar onset times at depolarizing potentials. Over voltages from −120 to −80 mV, faster recovery varies from ∼3 to 30 ms, while slower recovery varies from ∼50 to 400 ms. With strong depolarization (above −10 mV), the relative entry into slow or fast recovery pathways is similar and independent of voltage. Trains of short depolarizations favor recovery from fast recovery pathways and result in cumulative increases in the slow recovery fraction. Dual-pathway fast inactivation, by promoting use-dependent accumulation in slow recovery pathways, dynamically regulates Nav availability. Consistent with this finding, repetitive AP clamp waveforms at 1–10 Hz frequencies reduce Nav availability 80–90%, depending on holding potential. These results indicate that there are two distinct pathways of fast inactivation, one leading to conventional fast recovery and the other to slower recovery, which together are well-suited to mediate use-dependent changes in Nav availability.     

Regulation of Kv4.3 Closed-State Inactivation and Recovery by Extracellular Potassium and Intracellular KChIP2b

Mechanisms underlying Kv4 channel inactivation and recovery are presently unclear, although there is general consensus that the basic characteristics of these processes are not consistent with Shaker (Kv1) N- and P/C-type mechanisms. Kv4 channels also differ from Shaker in that they can undergo significant inactivation from pre-activated closed-states (closed-state inactivation, CSI), and that inactivation and recovery kinetics can be regulated by intracellular KChIP2 isoforms. To gain insight into the mechanisms regulating Kv4.3 CSI and recovery, we have analyzed the effects of increasing [K+]o from 2 mM to 98mM in the absence and in the presence of KChIP2b, the major KChIP2 isoform expressed in the mammalian ventricle. In the absence of KChIP2b, high [K+]o promoted Kv4.3 inactivated closed-states and significantly slowed the kinetics of recovery from both macroscopic and closed-state inactivation. Coexpression of KChIP2b in 2 mM [K+]o promoted non-inactivated closed-states and accelerated the kinetics of recovery from both macroscopic and CSI. In high [K+]o, KChIP2b eliminated or significantly reduced the slowing effects on recovery. Attenuation of CSI by the S4 charge-deletion mutant R302A, which produced significant stabilization of non-inactivated closed-states, effectively eliminated the opposing effects of high [K+]o and KChiP2b on macroscopic recovery kinetics, confirming that these results were due to alterations of CSI. Elevated [K+]o therefore slows Kv4.3 recovery by stabilizing inactivated closed-states, while KChIP2b accelerates recovery by destabilizing inactivated closed-states. Our results challenge underlying assumptions of presently popular Kv4 gating models and suggest that Kv4.3 possesses novel allosteric mechanisms, which are absent in Shaker, for coupling interactions between intracellular KChIP2b binding motifs and extracellular K+-sensitive regulatory sites.     

Radiosensitivity of Mammalian Cells: III. Effect of Suboptimal Growth Temperatures on Recovery from Radiation-Induced Division Delay

We investigated the effect of suboptimal growth temperatures on recovery from radiation-induced division delay in Chinese hamster cells. It was found that no recovery occurred during the time that either log-phase or synchronized populations were incubated at 4°C and that injury sustained at low dose rates was cumulative over a period of 6.2 hr at low temperature. Postirradiation conditions influencing recovery from the induced division delay period are different from those affecting survival, suggesting that biochemical damage leading to division delay may be different from that leading to cell death.     

Immunoregulation of passively induced allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) can be readily induced passively by transfer of lymphocytes from neuroantigen immunized rats to naive recipients. This passively induced disease runs an acute, monophasic, self-limiting course, much the same as is usually seen in actively induced diseases. Here we examine the mechanisms regulating passive EAE. We report that splenectomy, thymectomy, and increasing age of recipients, manipulations which have been reported to influence recovery from actively induced EAE, have no effect on passively induced disease. EAE effector cells are not inactivated when transferred into recipients that have been actively sensitized and are beginning their recovery from clinical signs; this being a time when recovery associated suppressor cells are thought to be present. Finally, in the absence of suppressor T cells in both the recipient and in the transfer cell population, recovery from passive EAE still occurs. We conclude that suppressor T cells play no role in regulating passively induced EAE.     

A trapped intracellular cation modulates K+ channel recovery from slow inactivation

Upon depolarization, many voltage-gated potassium channels undergo a time-dependent decrease in conductance known as inactivation. Both entry of channels into an inactivated state and recovery from this state govern cellular excitability. In this study, we show that recovery from slow inactivation is regulated by intracellular permeant cations. When inactivated channels are hyperpolarized, closure of the activation gate traps a cation between the activation and inactivation gates. The identity of the trapped cation determines the rate of recovery, and the ability of cations to promote recovery follows the rank order K+ > NH4+ > Rb+ > Cs+ > Na+, TMA. The striking similarity between this rank order and that for single channel conductance suggests that these two processes share a common feature. We propose that the rate of recovery from slow inactivation is determined by the ability of entrapped cations to move into a binding site in the channel's selectivity filter, and refilling of this site is required for recovery.     

Depression recovery from the primary care patient's perspective: 'hear it in my voice and see it in my eyes'

Purpose This paper aims to contribute to the discussion about the concept of recovery from depression from the patient perspective.Methods A structured, computer-assisted telephone interview of 576 participants from the Australian diamond cohort study who were asked, at the one year follow-up, how they would know if someone had recovered from depression. The responses were thematically analysed using a modified grounded-theory approach.Results Participants found the question challenging on a number of levels, relating to the definition of recovery, the subjective nature of getting better from depression, pessimism about the possibility of recovery and concerns that people hide how they really feel. Participants reported observation and human interaction as crucial to deciding if recovery had occurred. This led to three broad groups of indicators for recovery: a person's actions, their appearance and their thoughts and feelings.Conclusions Australian primary care patients with depressive symptoms report using observation and human interaction when trying to decide if someone is getting better from depression, leading to a broad range of indicators of recovery that include, but are not limited to, the traditional symptom-based definitions of depression remission. This data suggests that patients have a rich variety of ways of describing recovery, supporting a call for more patient-centred approaches to setting goals for depression recovery in the primary care setting.     

Recovery of supraspinal control of stepping via indirect propriospinal relay connections after spinal cord injury

Spinal cord injuries (SCIs) in humans and experimental animals are often associated with varying degrees of spontaneous functional recovery during the first months after injury. Such recovery is widely attributed to axons spared from injury that descend from the brain and bypass incomplete lesions, but its mechanisms are uncertain. To investigate the neural basis of spontaneous recovery, we used kinematic, physiological and anatomical analyses to evaluate mice with various combinations of spatially and temporally separated lateral hemisections with or without the excitotoxic ablation of intrinsic spinal cord neurons. We show that propriospinal relay connections that bypass one or more injury sites are able to mediate spontaneous functional recovery and supraspinal control of stepping, even when there has been essentially total and irreversible interruption of long descending supraspinal pathways in mice. Our findings show that pronounced functional recovery can occur after severe SCI without the maintenance or regeneration of direct projections from the brain past the lesion and can be mediated by the reorganization of descending and propriospinal connections. Targeting interventions toward augmenting the remodeling of relay connections may provide new therapeutic strategies to bypass lesions and restore function after SCI and in other conditions such as stroke and multiple sclerosis.     

Protecting endangered species: do the main legislative tools work?

It is critical to assess the effectiveness of the tools used to protect endangered species. The main tools enabled under the U.S. Endangered Species Act (ESA) to promote species recovery are funding, recovery plan development and critical habitat designation. Earlier studies sometimes found that statistically significant effects of these tools could be detected, but they have not answered the question of whether the effects were large enough to be biologically meaningful. Here, we ask: how much does the recovery status of ESA-listed species improve with the application of these tools? We used species' staus reports to Congress from 1988 to 2006 to quantify two measures of recovery for 1179 species. We related these to the amount of federal funding, years with a recovery plan, years with critical habitat designation, the amount of peer-reviewed scientific information, and time listed. We found that change in recovery status of listed species was, at best, only very weakly related to any of these tools. Recovery was positively related to the number of years listed, years with a recovery plan, and funding, however, these tools combined explain <13% of the variation in recovery status among species. Earlier studies that reported significant effects of these tools did not focus on effect sizes; however, they are in fact similarly small. One must conclude either that these tools are not very effective in promoting species' recovery, or (as we suspect) that species recovery data are so poor that it is impossible to tell whether the tools are effective or not. It is critically important to assess the effectiveness of tools used to promote species recovery; it is therefore also critically important to obtain population status data that are adequate to that task.     

The end and the beginning: recoveries from mass extinctions

The evolutionary consequences of mass extinctions depend as much on the processes of survival and recovery following these biotic crises as on the patterns of extinction themselves. Paleontologists are currently documenting biotic recoveries from six major mass extinctions and several smaller biotic crises. Although the immediate responses are remarkably similar after each event, with low-diversity assemblages dominated by widespread, eurytopic species, the recovery response in the long-term is more varied. Lineages that survive the extinction can lack the resilience for recovery, whereas others vanish from the fossil record seemingly to return from the dead after several million years.     

Identifying “vital attributes” for assessing disturbance–recovery potential of seafloor communities

Despite a long history of disturbance–recovery research, we still lack a generalizable understanding of the attributes that drive community recovery potential in seafloor ecosystems. Marine soft‐sediment ecosystems encompass a range of heterogeneity from simple low‐diversity habitats with limited biogenic structure, to species‐rich systems with complex biogenic habitat structure. These differences in biological heterogeneity are a product of natural conditions and disturbance regimes. To search for unifying attributes, we explore whether a set of simple traits can characterize community disturbance–recovery potential using seafloor patch‐disturbance experiments conducted in two different soft‐sediment landscapes. The two landscapes represent two ends of a spectrum of landscape biotic heterogeneity in order to consider multi‐scale disturbance–recovery processes. We consider traits at different levels of biological organization, from the biological traits of individual species, to the traits of species at the landscape scale associated with their occurrence across the landscape and their ability to be dominant. We show that in a biotically heterogeneous landscape (Kawau Bay, New Zealand), seafloor community recovery is stochastic, there is high species turnover, and the landscape‐scale traits are good predictors of recovery. In contrast, in a biotically homogeneous landscape (Baltic Sea), the options for recovery are constrained, the recovery pathway is thus more deterministic and the scale of recovery traits important for determining recovery switches to the individual species biological traits within the disturbed patch. Our results imply that these simple, yet sophisticated, traits can be effectively used to characterize community recovery potential and highlight the role of landscapes in providing resilience to patch‐scale disturbances.     

Biological Recover y from Lake Acidification: Zooplankton Communities as a Model of Patterns and Processes

Knowledge of the recovery of aquatic communities from lake acidification is limited. Data from studies of crustacean zooplankton communities, however, do reveal some of the major mechanisms important in the biological recovery process. Important influences on recovery include factors related to habitat quality and the ability of organisms to colonize. During recovery, existing species and colonists from internal and external sources interact to form a new community. The relative roles of internal and external influences remain poorly understood. Four general community types can be identified as possible outcomes of the recovery process: the original community, a normal alternate community, a community limited by dispersal, and a community limited by biological resistance. Empirical data indicate that, given suitable water quality, about a decade is sufficient to permit substantial recovery of zooplankton communities if there are no severe physical or biological barriers to restructuring.     

Recovery of a northern New England salt marsh plant community from winter icing

High latitude salt marsh plant communities are frequently exposed to conspicuous winter ice disturbances, which trigger secondary succession. In this paper, we document the recovery of a northern New England salt marsh from a severe winter icing event in 1998. Ice disturbances that killed plants but that left the underlying peat intact recovered rapidly. However, ice damage that killed plants and removed the underlying peat, led to areas of physiologically harsh edaphic conditions, specifically waterlogged and anoxic soils that limited plant recolonization. A transplant experiment revealed that only the most stress-tolerant plants were capable of invading the most stressful portions of ice disturbances. A second experiment that artificially dried disturbance patches accelerated patch recovery. These data suggest that recovery from intense ice disturbance is dependent on stress-tolerant plants invading edaphically harsh disturbances, eventually facilitating the recolonization of the community. This process likely takes longer than a decade for full recovery to occur in the areas where both plants and the peat base are removed.     

A rapid form of activity-dependent recovery from short-term synaptic depression in the intensity pathway of the auditory brainstem

Short-term synaptic plasticity acts as a time- and firing rate-dependent filter that mediates the transmission of information across synapses. In the avian auditory brainstem, specific forms of plasticity are expressed at different terminals of the same auditory nerve fibers and contribute to the divergence of acoustic timing and intensity information. To identify key differences in the plasticity properties, we made patch-clamp recordings from neurons in the cochlear nucleus responsible for intensity coding, nucleus angularis, and measured the time course of the recovery of excitatory postsynaptic currents following short-term synaptic depression. These synaptic responses showed a very rapid recovery, following a bi-exponential time course with a fast time constant of ~40 ms and a dependence on the presynaptic activity levels, resulting in a crossing over of the recovery trajectories following high-rate versus low-rate stimulation trains. We also show that the recorded recovery in the intensity pathway differs from similar recordings in the timing pathway, specifically the cochlear nucleus magnocellularis, in two ways: (1) a fast recovery that was not due to recovery from postsynaptic receptor desensitization and (2) a recovery trajectory that was characterized by a non-monotonic bump that may be due in part to facilitation mechanisms more prevalent in the intensity pathway. We tested whether a previously proposed model of synaptic transmission based on vesicle depletion and sequential steps of vesicle replenishment could account for the recovery responses, and found it was insufficient, suggesting an activity-dependent feedback mechanism is present. We propose that the rapid recovery following depression allows improved coding of natural auditory signals that often consist of sound bursts separated by short gaps.