Spontaneous abortion as a response to reproductive conflict in the banded mongoose.

When breeding females compete for limited resources, the intensity of this reproductive conflict can determine whether the fitness benefits of current reproductive effort exceed the potential costs to survival and future fertility. In group-living species, reproductive competition can occur through post-natal competition among the offspring of co-breeding females. Spontaneous abortion could be a response to such competition, allowing females to curtail reproductive expenditure on offspring that are unlikely to survive and to conserve resources for future breeding opportunities. We tested this hypothesis using long-term data on banded mongooses, Mungos mungo, in which multiple females within a group give birth synchronously to a communal litter that is cared for by other group members. As predicted, abortions were more likely during dry periods when food is scarce, and in breeding attempts with more intense reproductive competition. Within breeding events, younger, lighter females carrying smaller fetuses were more likely to abort, particularly those that were also of lower rank. Our results suggest that abortion may be a means by which disadvantaged females conserve resources for future breeding attempts in more benign conditions, and highlight that female reproductive competition may be resolved long before the production of offspring.

Elevated glucocorticoid concentrations during gestation predict reduced reproductive success in subordinate female banded mongooses.

Dominant females in social species have been hypothesized to reduce the reproductive success of their subordinates by inducing elevated circulating glucocorticoid (GC) concentrations. However, this 'stress-related suppression' hypothesis has received little support in cooperatively breeding species, despite evident reproductive skews among females. We tested this hypothesis in the banded mongoose (Mungos mungo), a cooperative mammal in which multiple females conceive and carry to term in each communal breeding attempt. As predicted, lower ranked females had lower reproductive success, even among females that carried to term. While there were no rank-related differences in faecal glucocorticoid (fGC) concentrations prior to gestation or in the first trimester, lower ranked females had significantly higher fGC concentrations than higher ranked females in the second and third trimesters. Finally, females with higher fGC concentrations during the third trimester lost a greater proportion of their gestated young prior to their emergence from the burrow. Together, our results are consistent with a role for rank-related maternal stress in generating reproductive skew among females in this cooperative breeder. While studies of reproductive skew frequently consider the possibility that rank-related stress reduces the conception rates of subordinates, our findings highlight the possibility of detrimental effects on reproductive outcomes even after pregnancies have become established.

Bone loss in a new rodent model combining spinal cord injury and cast immobilization.

OBJECTIVES: Characterize bone loss in our newly developed severe contusion spinal cord injury (SCI) plus hindlimb immobilization (IMM) model and determine the influence of muscle contractility on skeletal integrity after SCI. METHODS: Female Sprague-Dawley rats were randomized to: (a) intact controls, (b) severe contusion SCI euthanized at Day 7 (SCI-7) or (c) Day 21 (SCI-21), (d) 14 days IMM-alone, (e) SCI+IMM, or (f) SCI+IMM plus 14 days body weight supported treadmill exercise (SCI+IMM+TM). RESULTS: SCI-7 and SCI-21 exhibited a >20% reduction in cancellous volumetric bone mineral density (vBMD) in the hindlimbs (p⋜0.01), characterized by reductions in cancellous bone volume (cBV/TV%), trabecular number (Tb.N), and trabecular thickness. IMM-alone induced no observable bone loss. SCI+IMM exacerbated cancellous vBMD deficits with values being >45% below Controls (p⋜0.01) resulting from reduced cBV/TV% and Tb.N. SCI+IMM also produced the greatest cortical bone loss with distal femoral cortical area and cortical thickness being 14-28% below Controls (p⋜0.01) and bone strength being 37% below Controls (p⋜0.01). SCI+IMM+TM partially alleviated bone deficits, but values remained below Controls. CONCLUSIONS: Residual and/or facilitated muscle contractility ameliorate bone decrements after severe SCI. Our novel SCI+IMM model represents a clinically-relevant means of assessing strategies to prevent SCI-induced skeletal deficits.

The evolution of democratic peace in animal societies.

A major goal in evolutionary biology is to elucidate common principles that drive human and other animal societies to adopt either a warlike or peaceful nature. One proposed explanation for the variation in aggression between human societies is the democratic peace hypothesis. According to this theory, autocracies are more warlike than democracies because autocratic leaders can pursue fights for private gain. However, autocratic and democratic decision-making processes are not unique to humans and are widely observed across a diverse range of non-human animal societies. We use evolutionary game theory to evaluate whether the logic of democratic peace may apply across taxa; specifically adapting the classic Hawk-Dove model to consider conflict decisions made by groups rather than individuals. We find support for the democratic peace hypothesis without mechanisms involving complex human institutions and discuss how these findings might be relevant to non-human animal societies. We suggest that the degree to which collective decisions are shared may explain variation in the intensity of intergroup conflict in nature.

Caregiver's cognitive traits are associated with pup fitness in a cooperatively breeding mammal.

Studies across diverse taxa have revealed the importance of early life environment and parenting on characteristics later in life. While some have shown how early life experiences can impact cognitive abilities, very few have turned this around and looked at how the cognitive skills of parents or other carers during early life affect the fitness of young. In this study, we investigate how the characteristics of carers may affect proxies of fitness of pups in the cooperatively breeding banded mongoose (Mungos mungo). We gave adult mongooses a spatial memory test and compared the results to the success of the pups those individuals cared for. Our results show a tradeoff between speed and accuracy in the spatial memory task, with those individuals which were faster to move between cups in the test arena making more erroneous re-visits to cups that they had already checked for food. Furthermore, the accuracy of their carer predicted future survival, but not weight gain of the pups and the effect was contrary to expected, with pups that were cared for by less accurate individuals being more likely to survive to adulthood. Our research also provides evidence that while younger carers were less accurate during the test, the age of the carer did not have an impact on the chance of raising young that live to sexual maturity. Our findings suggest that banded mongoose carers' cognitive traits have fitness consequences for the young they care for, affecting the chance that these young live to maturity.

The social formation of fitness: lifetime consequences of prenatal nutrition and postnatal care in a wild mammal population.

Research in medicine and evolutionary biology suggests that the sequencing of parental investment has a crucial impact on offspring life history and health. Here, we take advantage of the synchronous birth system of wild banded mongooses to test experimentally the lifetime consequences to offspring of receiving extra investment prenatally versus postnatally. We provided extra food to half of the breeding females in each group during pregnancy, leaving the other half as matched controls. This manipulation resulted in two categories of experimental offspring in synchronously born litters: (i) 'prenatal boost' offspring whose mothers had been fed during pregnancy, and (ii) 'postnatal boost' offspring whose mothers were not fed during pregnancy but who received extra alloparental care in the postnatal period. Prenatal boost offspring lived substantially longer as adults, but postnatal boost offspring had higher lifetime reproductive success (LRS) and higher glucocorticoid levels across the lifespan. Both types of experimental offspring had higher LRS than offspring from unmanipulated litters. We found no difference between the two experimental categories of offspring in adult weight, age at first reproduction, oxidative stress or telomere lengths. These findings are rare experimental evidence that prenatal and postnatal investments have distinct effects in moulding individual life history and fitness in wild mammals. This article is part of the theme issue 'Evolutionary ecology of inequality'.

Characterization of genes with a putative key role in the parasitic lifestyle of the nematode Strongyloides ratti.

Parasitic nematodes are significant pathogens of humans and other animals. The molecular and genetic basis of animal parasitism is not yet fully understood. Strongyloides spp. are a genus of gastrointestinal nematodes of which species infect approximately 100­200 million people worldwide. S. ratti is a natural parasite of the rat, and a useful and amenable laboratory model. Previous EST and microarray analyses of the S. ratti life cycle have identified genes whose expression was specific, or biased, to the parasitic adult stage, suggesting that they may play a key role in parasitism in this species. Here we have further investigated the expression of these genes (by RT-PCR) throughout the S. ratti life-cycle. We produced recombinant proteins in vitro for a subset of these genes, which were used in Western blot analyses to investigate the distribution of the gene products among different stages of the S. ratti life cycle. We tested the efficacy of these recombinant proteins as anti-S. ratti vaccines. One of the proteins was detected in the excretory/secretory products of the parasitic stages.

Leaders of war: modelling the evolution of conflict among heterogeneous groups.

War, in human and animal societies, can be extremely costly but can also offer significant benefits to the victorious group. We might expect groups to go into battle when the potential benefits of victory (V) outweigh the costs of escalated conflict (C); however, V and C are unlikely to be distributed evenly in heterogeneous groups. For example, some leaders who make the decision to go to war may monopolize the benefits at little cost to themselves ('exploitative' leaders). By contrast, other leaders may willingly pay increased costs, above and beyond their share of V ('heroic' leaders). We investigated conflict initiation and conflict participation in an ecological model where single-leader-multiple-follower groups came into conflict over natural resources. We found that small group size, low migration rate and frequent interaction between groups increased intergroup competition and the evolution of 'exploitative' leadership, while converse patterns favoured increased intragroup competition and the emergence of 'heroic' leaders. We also found evidence of an alternative leader/follower 'shared effort' outcome. Parameters that favoured high contributing 'heroic' leaders, and low contributing followers, facilitated transitions to more peaceful outcomes. We outline and discuss the key testable predictions of our model for empiricists studying intergroup conflict in humans and animals. This article is part of the theme issue 'Intergroup conflict across taxa'.

A veil of ignorance can promote fairness in a mammal society.

Rawls argued that fairness in human societies can be achieved if decisions about the distribution of societal rewards are made from behind a veil of ignorance, which obscures the personal gains that result. Whether ignorance promotes fairness in animal societies, that is, the distribution of resources to reduce inequality, is unknown. Here we show experimentally that cooperatively breeding banded mongooses, acting from behind a veil of ignorance over kinship, allocate postnatal care in a way that reduces inequality among offspring, in the manner predicted by a Rawlsian model of cooperation. In this society synchronized reproduction leaves adults in a group ignorant of the individual parentage of their communal young. We provisioned half of the mothers in each mongoose group during pregnancy, leaving the other half as matched controls, thus increasing inequality among mothers and increasing the amount of variation in offspring birth weight in communal litters. After birth, fed mothers provided extra care to the offspring of unfed mothers, not their own young, which levelled up initial size inequalities among the offspring and equalized their survival to adulthood. Our findings suggest that a classic idea of moral philosophy also applies to the evolution of cooperation in biological systems.

Two hypotheses to explain why RNA interference does not work in animal parasitic nematodes.

RNA interference (RNAi) has been used extensively in model organisms such as Caenorhabditis elegans. Methods developed for RNAi in C. elegans have also been used in parasitic nematodes. However, RNAi in parasitic nematodes has been unsuccessful or has had limited success. Studies of genes essential for RNAi in C. elegans and of RNAi in Caenorhabditis spp. other than C. elegans suggest two complementary, and testable, hypotheses for the limited success of RNAi in animal parasitic nematodes. These are: (i) that the external supply of double stranded RNA (dsRNA) to parasitic nematodes is inappropriate to achieve RNAi and (ii) that parasitic nematodes are functionally defective in genes required to initiate RNAi from externally supplied dsRNA.

TGF-beta and the evolution of nematode parasitism.

The many similarities between arrested dauer larvae of free-living nematodes and infective L3 of parasitic nematodes has led to suggestions that they are analogous lifecycle stages. The control of the formation of dauer larvae in Caenorhabditis elegans is well understood, with a TGF-beta-superfamily growth factor playing a central role. Recent analyses of the expression of homologous TGF-beta genes in parasitic nematodes has allowed this analogy to be tested; but the results so far do not support it. Rather, the results imply that in the evolution of animal parasitism, parasitic nematodes have taken signalling pathways and molecules from their free-living ancestors and used them in different ways in the evolution of their parasitic lifestyles.

Temperature is a cue for gene expression in the post-infective L3 of the parasitic nematode Brugia pahangi.

The temporal expression pattern of two genes, Bp-cdd and Bp-S3, was studied at defined points throughout the life cycle of Brugia pahangi. Both mRNAs were up-regulated to coincide with the transition of the L3 from the vector to the mammalian host. Bp-cdd was expressed almost exclusively in the post-infective (p.i.) L3 and L4 stages of the life cycle while Bp-S3 was also expressed in adult worms, but at a much lower level than in the larval stages. Immunogold labelling with an antiserum raised to the recombinant Bp-CDD localised the native antigen to the hypodermis in the p.i. L3 and L4. Specific labelling was not detected in the adult worm. The expression of both mRNAs could be triggered by exposure of the vector-derived L3 to a simple mammalian culture system. Analysis of the factors, which induced expression suggested that the temperature shift which accompanies the transition from mosquito to mammal was the most important cue for expression of both genes.

Alteration in rate modulation of reflexes to lumbar motoneurons after midthoracic spinal cord injury in the rat. I. Contusion injury.

This study investigated the regulation of reflex excitability in normal and midthoracic contusion-injured animals. Recent observations revealed that rate depression, a rate-modulatory process that decreases reflex excitability, was significantly decreased following experimental midthoracic contusion injury. The present experiments were performed to extend those studies and to determine if posttetanic potentiation (PTP), a rate-modulatory process that increases reflex excitability, also was altered in lumbar monosynaptic reflexes (MSRs) following midthoracic contusion injury. In normal animals, a mean PTP of 160% of the pretetanus control was observed at 30 sec following tetanus of the tibial MSR. The decay of the PTP in normal animals followed a rapid initial, then a more gradual pattern, before returning to pretetanus values by 5 min posttetanus. Following midthoracic contusion injury, the maximal (unpotentiated) MSRs were significantly increased in amplitude, whereas the percent potentiation of the PTP of the tibial MSRs was significantly decreased. PTP decay in postcontusion animals was significantly more gradual than observed in normal animals and followed a single decay process. Further analysis of rate depression of tibial MSRs in normal animals revealed that the attenuation pattern produced by stimulation within the lower range of test frequencies was different from that produced by stimulation at the higher test frequencies. Following contusion, rate depression of tibial MSRs was significantly reduced at all test frequencies. These physiological changes in the stretch reflex neural pathway are discussed relative to the development of spasticity.

Neural tissue transplantation and CNS trauma: anatomical and functional repair of the injured spinal cord.

Neural tissue transplantation has become recognized widely as a powerful experimental tool for studying structure-function relationships, development, plasticity, and capacities for regeneration in the adult CNS. In addition, this area of investigation has generated considerable interest in approaches that might be applicable to a variety of catastrophic neurological disorders. In this regard, attention has been given to neural tissue grafting as a potential therapeutic strategy in various forms of neurodegenerative disease. More recently, however, other investigations have begun to focus on the possible application of peripheral and central neural tissue transplants for promoting repair in forms of CNS trauma. This review highlights various neural transplantation approaches that have been explored primarily in the context of injury to the adult CNS, with emphasis on spinal cord injury. An overview is presented of the evolution of this area of research in terms of emerging biological perspectives, technological advances, and experimental modelling. Discussion centers on progress that has been made and a variety of theoretical and practical issues that remain to be resolved.

Feasibility and safety of neural tissue transplantation in patients with syringomyelia.

Transplantation of fetal spinal cord (FSC) tissue has demonstrated significant potential in animal models for achieving partial anatomical and functional restoration following spinal cord injury (SCI). To determine whether this strategy can eventually be translated to humans with SCI, a pilot safety and feasibility study was initiated in patients with progressive posttraumatic syringomyelia (PPTS). A total of eight patients with PPTS have been enrolled to date, and this report presents findings for the first two patients through 18 months postoperative. The study design included detailed assessments of each subject at multiple pre- and postoperative time points. Outcome data were then compared with each subject's own baseline. The surgical protocol included detethering, cyst drainage, and implantation of 6-9-week postconception human FSC tissue. Immunosuppression with cyclosporine was initiated a few days prior to surgery and continued for 6 months postoperatively. Key outcome measures included: serial magnetic resonance imaging (MRI) exams, standardized measures of neurological impairment and functional disability, detailed pain assessment, and extensive neurophysiological testing. Through 18 months, the first two patients have been stable neurologically and the MRIs have shown evidence of solid tissue at the graft sites, without evidence of donor tissue overgrowth. Although it is still too soon to draw any firm conclusions, the findings from the initial two patients in this study suggest that intraspinal grafting of human FSC tissue is both feasible and safe.

Neurophysiological assessment of the feasibility and safety of neural tissue transplantation in patients with syringomyelia.

The feasibility and safety of a procedure involving fetal spinal cord tissue transplantation in patients with syringomyelia was assessed using a neurophysiological protocol designed to quantitate peripheral nerve function, spinal cord reflex excitability, and spinal cord conduction pathways essential for somatosensory evoked potentials. We report here data obtained before and for 18 months following the transplantation procedure performed on the first two patients in this study. The neurophysiological assessment protocols included measures of cortical and spinal cord evoked potentials, H-reflex excitability, and peripheral nerve conduction. Prior to the procedure, both patients had significant deficits on some of the neurophysiological measures, for example, lower extremity cortical evoked potentials. However, robust measures of intact pathways, such as upper extremity cortical evoked potentials, were also observed preoperatively in both patients. Thus, it was anticipated that conduction in these intact pathways could be at risk either from complications from the transplantation procedure and/or from continued expansion of the syrinx. Following the transplantation procedure, no negative changes were observed in any of the neurophysiological measures in either patient. In addition, patient 1 showed a decrease in the rate potentiation of tibial H-reflexes on the right side and an increase in the response probability of left tibial H-reflexes. The results of this postoperative longitudinal assessment provide a first-level demonstration of the safety of the intraspinal neural tissue transplantation procedure. However, the consideration of safety is currently limited to the grafting procedure itself, since the long-term fates of the donor tissue in these two patients remain to be shown more definitively.

Velocity-dependent ankle torque in the normal rat.

We evaluated the velocity-dependent ankle torque and associated activity of the ankle extensor muscle stretch reflexes in normal rats. A 287% increase in velocity-dependent ankle torque was observed at the highest velocity tested compared with the lowest velocity. Low velocity torques were minimally altered during general anesthesia that depressed EMG activity by up to 90%. However, velocity-dependent torque during higher velocity ankle rotations (306-612 degrees s-1 correlated with parallel increases in EMG magnitude recorded from the triceps surae muscles. General anesthesia (pentobarbital) abolished 61% of the velocity-dependent ankle torque at 612 degrees s-1. We conclude that ankle torque and ankle extensor muscle activity display velocity enhancement over a broad range. These observations indicate that protocols designed to assess ankle torque in the rat should use instrumentation to produce a broad range of velocities up to at least 600 degrees s-1.

Respiratory-related cortical potentials evoked by inspiratory occlusion in humans.

It has long been recognized that humans can perceive respiratory loads. There have been several studies on the detection and psychophysical quantification of mechanical load perception. This investigation was designed to record cortical sensory neurogenic activity related to inspiratory mechanical loading in humans. Inspiration was periodically occluded in human subjects while the electroencephalographic (EEG) activity in the somatosensory region of the cerebral cortex was recorded. The onset of inspiratory mouth pressure (Pm) was used to initiate signal averaging of the EEG signals. Cortical evoked potentials elicited by inspiratory occlusions were observed when C3 and C alpha were referenced to CZ. This evoked potential was not observed with the control (unoccluded) breaths. There was considerable subject variability in the peak latencies that was related to the differences in the inspiratory drive, as measured by occlusion pressure (P0.1). The results of this study demonstrate that neurogenic activity can be recorded in the somatosensory region of the cortex that is related to inspiratory occlusions. The peak latencies are longer than analogous somatosensory evoked potentials elicited by stimulation of the hand and foot. It is hypothesized that a portion of this latency difference is related to the time required for the subject to generate sufficient inspiratory force to activate the afferents mediating the cortical response.

Activation of spinal cord interneurons which process inputs from the femoral-saphenous vein.

Recordings were made from single spinal cord interneurons which could be activated by electrical stimulation of afferents terminating in the wall of the femoral-saphenous vein. Interneurons were either excited or both excited and inhibited by venous afferent stimulation. Most of the venous afferent-driven interneurons could also be driven by electrical activation of A-alpha beta muscle and cutaneous afferents. Stimulation of several different muscle nerves drove single interneurons.

Patterns of cortical projection to hindlimb muscle motoneurone pools.

This study was undertaken to examine the organization of the hindlimb area of the motor cortex. Two specific questions were posed. The first was: are the cortical neurones which control the excitability of a given motoneurone pool localized in a small zone of corjex or are they diffuse? The second question was: does microstimulation in the hindlimb area of the motor cortex activate spinal motoneurones in a reciprocal fashion, i.e., is cortically elicited facilitation of a muscle accompanied by inhibition of the antagonist? Intracortical microstimulation was used to condition monosynaptic reflexes of the cat hindlimb to study the organization of a cortical projection to lumbar motoneurone pools. Cortical neurones which produced facilitation or inhibition of a given monosynaptic reflex were localized within a small zone of the cortex. Facilitatory and inhibitory effective zones were found to have similar shape and size. Intracortical microstimulation elicited facilitation or inhibition of individual monosynaptic reflexes without eliciting reciprocal effects on the antagonists. The pyramidal tract was shown to play an important role in the mediation of cortically elicited facilitation as well as inhibition of the monosynaptic reflexes in the lumbar cord.