Sex chromosomes, sex ratios and sex gaps in longevity in plants.

In animals, males and females can display markedly different longevity (also called sex gaps in longevity, SGL). Sex chromosomes contribute to establishing these SGLs. X-hemizygosity and toxicity of the Y chromosomes are two mechanisms that have been suggested to reduce male longevity (Z-hemizygosity and W toxicity in females in ZW systems). In plants, SGLs are known to exist, but the role of sex chromosomes remains to be established. Here, by using adult sex ratio as a proxy for measuring SGLs, we explored the relationship between sex chromosomes and SGLs across 43 plant species. Based on the knowledge accumulated in animals, we specifically asked whether: (i) species with XY systems tend to have female-biased sex ratios (reduced male longevity) and species with ZW ones tend to have male-biased sex ratios (reduced female longevity); and (ii) this pattern was stronger in heteromorphic systems compared to homomorphic ones. Our results tend to support these predictions although we lack statistical power because of a small number of ZW systems and the absence of any heteromorphic ZW system in the dataset. We discuss the implications of these findings, which we hope will stimulate further research on sex differences in lifespan and ageing across plants. This article is part of the theme issue 'Sex determination and sex chromosome evolution in land plants'.

Does body growth impair immune function in a large herbivore?

According to the principle of allocation, trade-offs are inevitable when resources allocated to one biological function are no longer available for other functions. Growth, and to a lesser extent, immunity are energetically costly functions that may compete with allocation to reproductive success and survival. However, whether high allocation to growth impairs immune system development during the growing period or immune system performance during adulthood is currently unknown in wild mammals. Using three roe deer (Capreolus capreolus) populations experiencing contrasting environmental conditions, we tested for potential costs of growth on immune phenotype over both the short-term (during growth), and the long-term (during adulthood) over the course of an individuals' life. We investigated potential costs on a set of 12 immune traits that reflect both innate and adaptive responses, and compared them between sexes and populations. Although fast growth tended to be associated with low levels of some humoral traits (globulins) during the growing period and some cellular immune traits (i.e. eosinophil and neutrophil counts) during adulthood, evidence for a trade-off between growth and other immune components was limited. Unexpectedly, no detectable growth costs on immunity were found in females from the population experiencing the least favourable environment. We discuss our findings in the light of the complex interplay between resource allocation strategies among reproduction, maintenance and immunity, in relation to local environmental conditions experienced by roe deer.

Immunosenescence patterns differ between populations but not between sexes in a long-lived mammal.

In animals, physiological mechanisms underlying reproductive and actuarial senescence remain poorly understood. Immunosenescence, the decline in the ability to display an efficient immune response with increasing age, is likely to influence both reproductive and actuarial senescence through increased risk of disease. Evidence for such a link has been reported from laboratory animal models but has been poorly investigated in the wild, where variation in resource acquisitions usually drives life-history trade-offs. We investigated immunosenescence patterns over 7 years in both sexes of two contrasting roe deer populations (Capreolus capreolus). We first measured twelve immune markers to obtain a thorough identification of innate and adaptive components of immunity and assessed, from the same individuals, the age-dependent variation observed in parasitic infections. Although the level of innate traits was maintained at old age, the functional innate immune traits declined with increasing age in one of two populations. In both populations, the production of inflammatory markers increased with advancing age. Finally, the adaptive response declined in late adulthood. The increasing parasite burden with age we reported suggests the effective existence of immunosenescence. Age-specific patterns differed between populations but not between sexes, which indicate that habitat quality could shape age-dependent immune phenotype in the wild.

Evolutionary allometry reveals a shift in selection pressure on male horn size.

How selection pressures acting within species interact with developmental constraints to shape macro-evolutionary patterns of species divergence is still poorly understood. In particular, whether or not sexual selection affects evolutionary allometry, the increase in trait size with body size across species, of secondary sexual characters, remains largely unknown. In this context, bovid horn size is an especially relevant trait to study because horns are present in both sexes, but the intensity of sexual selection acting on them is expected to vary both among species and between sexes. Using a unique data set of sex-specific horn size and body mass including 91 species of bovids, we compared the evolutionary allometry between horn size and body mass between sexes while accounting for both the intensity of sexual selection and phylogenetic relationship among species. We found a nonlinear evolutionary allometry where the allometric slope decreased with increasing species body mass. This pattern, much more pronounced in males than in females, suggests either that horn size is limited by some constraints in the largest bovids or is no longer the direct target of sexual selection in very large species.

Haematological parameters do senesce in the wild: evidence from different populations of a long-lived mammal.

Increasing evidence of senescence has been reported from long-term studies of wild populations. However, most studies have focused on life-history traits like survival, reproduction or body mass, generally from a single intensively monitored population. However, variation in the intensity of senescence across populations, and to a lesser extent between sexes, is still poorly understood. In addition, the pattern of age-specific changes in haematological parameters remains virtually unknown to date for any population of vertebrate living in the wild. Using repeated blood samples collected from known-aged (2-15 years of age) roe deer (Capreolus capreolus) from two populations facing highly different environmental conditions, we filled the gap. In particular, we investigated age-specific changes in haematocrit, albumin and creatinine. We reported clear evidence of senescence in all haematological parameters. Moreover, senescence patterns differed between sexes and populations. The rate of senescence was higher in males than in females for haematocrit with no site difference. On the other hand, the rate of senescence in creatinine was higher at Trois Fontaines than at Chizé with no sex difference. Our findings provide a first demonstration of age-specific declines in haematological parameters in wild populations of large herbivores and show that the process of senescence in vertebrates is not restricted to body mass or fitness components. We also demonstrate that the senescence pattern of haematological parameters is context dependent and varies both between sexes and according to environmental conditions.

The allometry between secondary sexual traits and body size is nonlinear among cervids.

Allometric relationships between sexually selected traits and body size have been extensively studied in recent decades. While sexually selected traits generally display positive allometry, a few recent reports have suggested that allometric relationships are not always linear. In male cervids, having both long antlers and large size provides benefits in terms of increased mating success. However, such attributes are costly to grow and maintain, and these costs might constrain antler length from increasing at the same rate as body mass in larger species if the quantity of energy that males can extract from their environment is limiting. We tested for possible nonlinearity in the relationship between antler size and body mass (on a log-log scale) among 31 cervids and found clear deviation from linearity in the allometry of antler length. Antler length increased linearly until a male body mass threshold at approximately 110 kg. Beyond this threshold, antler length did not change with increasing mass. We discuss this evidence of nonlinear allometry in the light of life-history theory and stress the importance of testing for nonlinearity when studying allometric relationships.

New fission fragment distributions and r-process origin of the rare-earth elements.

Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A≳140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of 110≲A≲170 nuclei. Here, we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant A≃278 mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations, we show that this specific FFD leads to a production of the A≃165 rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of r nuclei with A≳140.

Sperm competition roles and ejaculate investment in a promiscuous mammal.

Theoretical models of sperm competition predict how males should allocate sperm and seminal fluid components to ejaculates according to their mating role (dominant vs. subordinate). Here, we present a detailed analysis of ejaculate expenditure according to male roles in the bank vole (Myodes glareolus). Sperm competition occurs regularly in this species, and dominant males typically achieve higher fertilization success than subordinates. Contrary to theoretical predictions, we found that dominant male bank voles invest more sperm per ejaculate than subordinates, both absolutely and relative to body and testes mass. The testes of dominant males were also absolutely (although not relatively) larger than those of subordinates. However, we found no evidence that subordinate males compensate for lower sperm numbers per ejaculate by increasing ejaculation frequency or sperm velocity. Similarly, we found no evidence for differential investment in copulatory plug size according to male roles in sperm competition, although dominant males had significantly larger seminal vesicles (both absolutely and relative to body mass) compared with subordinates. We conclude that sperm competition roles can have significant but unexpected influences on ejaculate investment in mammals with clearly defined differences in male social status.

Sperm competition and brain size evolution in mammals.

The 'expensive tissue hypothesis' predicts a size trade-off between the brain and other energetically costly organs. A specific version of this hypothesis, the 'expensive sexual tissue hypothesis', argues that selection for larger testes under sperm competition constrains brain size evolution. We show here that there is no general evolutionary trade-off between brain and testis mass in mammals. The predicted negative relationship between these traits is not found for rodents, ungulates, primates, carnivores, or across combined mammalian orders, and neither does total brain mass vary according to the level of sperm competition as determined by mating system classifications. Although we are able to confirm previous reports of a negative relationship between brain and testis mass in echolocating bats, our results suggest that mating system may be a better predictor of brain size in this group. We conclude that the expensive sexual tissue hypothesis accounts for little or none of the variance in brain size in mammals, and suggest that a broader framework is required to understand the costs of brain size evolution and how these are met.

[Value of interferon alpha determination in the diagnosis of meningoencephalitis presumed to be of viral origin]. / Intérêt du dosage de l'interféron alpha dans le diagnostic des méningo-encéphalites présumées virales.

Quantitative determination of alpha interferon (IFN) is used as an early marker in viral encephalitis. IFN is detected during 10 days following the onset of clinical symptoms. In 26 patients (11 children from 1 day to 6 year old and 15 adults from 17 to 70 year old) with central nervous system disorders (15 meningo-encephalitis, 5 meningitis, 1 myelitis, 1 polyradiculoneuritis, 1 dementia, 1 epilepsy and 2 other), alpha IFN is quantified using a cytopathic effect inhibition assay of VSV on MDBK cells. The mean value of alpha IFN is 80 UI/ml (range from 0 to 512 UI/ml). Virus involved are herpes virus in 38.5% of cases (10/26) and 66% of viral meningoencephalitis (8/12), H.I.V. in 3 cases, VZV in 2 and measles virus in 1 case. Viral aetiology is suspected in six other patients. The results show the importance of early determination of alpha IFN (immediately after the first symptoms and on the first admission to the hospital) in sera and cerebrospinal fluids (CSF) simultaneously with viral culture and antibody research. The presence of alpha IFN only in CSF and a higher titre of alpha IFN in CSF than in serum are important data to distinguish primitive acute necrotizing encephalitis from post eruptive or post infectious perivenous encephalitis. In herpes virus infections with specific treatment all the patients recover. However to prevent brain damage in survivors the treatment should be established as soon as possible.

[Benign paralysis of the 6th cranial nerve in children]. / La paralysie bénigne de la vie paire crânienne chez l'enfant.

Acquired sixth nerve palsies in infants and children that occur without fever primarily suggest a tumor or intracranial hypertension. In a few instances, the cause is benign and spontaneous recovery occurs although relapses are occasionally seen. We report seven episodes of benign sixth nerve palsy in four children aged 5 1/2 months to 8 1/2 years. An ENT infection was the precipitating factor in four of these seven episodes. Recovery consistently occurred within 4 days to 6 weeks. None of the children had residual oculomotor impairment. The various etiologic hypotheses put forward in the literature are discussed. No study provides a pathophysiologic explanation for these transient palsies.