Decrease in social cohesion in a colonial seabird under a perturbation regime.

Social interactions, through influence on behavioural processes, can play an important role in populations' resilience (i.e. ability to cope with perturbations). However little is known about the effects of perturbations on the strength of social cohesion in wild populations. Long-term associations between individuals may reflect the existence of social cohesion for seizing the evolutionary advantages of social living. We explore the existence of social cohesion and its dynamics under perturbations by analysing long-term social associations, in a colonial seabird, the Audouin's gull Larus audouinii, living in a site experiencing a shift to a perturbed regime. Our goals were namely (1) to uncover the occurrence of long-term social ties (i.e. associations) between individuals and (2) to examine whether the perturbation regime affected this form of social cohesion. We analysed a dataset of more than 3500 individuals from 25 years of monitoring by means of contingency tables and within the Social Network Analysis framework. We showed that associations between individuals are not only due to philopatry or random gregariousness but that there are social ties between individuals over the years. Furthermore, social cohesion decreased under the perturbation regime. We sustain that perturbations may lead not only to changes in individuals' behaviour and fitness but also to a change in populations' social cohesion. The consequences of decreasing social cohesion are still not well understood, but they can be critical for the population dynamics of social species.

Morfometría y variantes anatómicas del tronco celíaco en población mexicana / Morphometry and anatomical variants of the celiac trunk in Mexican population

RESUMEN: Las variantes anatómicas del tronco celíaco (TC) son relevantes en el ámbito quirúrgico e intervencionista. Existen diferentes estudios a nivel mundial que han demostrado las variaciones que puede presentar el TC tanto en longitud como en estructura; dichos estudios han sido realizados predominantemente en población asiática y europea. Por lo anterior, realizamos un estudio que caracterizó esta estructura y que sea referente para la población mexicana. Se analizó una muestra de 50 especímenes cadavéricos humanos embalsamados de origen mexicano. El promedio de longitud del TC a su primera rama fue de 12,44 mm; de su origen a la segunda rama fue de 17,07 mm; y hasta la tercera fue de 19,15 mm. En la muestra de estudio se encontraron variantes en el 20 % de los especímenes, de éstos el 14 % presentaron variantes morfométricas en cuanto a longitud y 6 % en estructura. Respecto a las variantes morfométricas, destacó la presencia de un TC de 3 mm de longitud. En cuanto a las variantes morfológicas dos individuos presentaron un tronco gastro-esplénico con tronco hepato-mesentérico; y el tercero un tronco bifurcado hepato-gástrico con la arteria esplénica naciendo de la arteria hepática común. Éste último no reportado en la literatura.

SUMMARY: Anatomical variants in the celiac trunk (CT) are important in surgical and interventional fields. Studies worldwide have demonstrated length and structure variations in the celiac trunk. These studies have predominantly been carried out in Asian and European population. Therefore, we considered it necessary to realize a study to describe this structure and serve as a reference in the Mexican population. A sample of 50 human cadaveric specimens of Mexican origin was analyzed. The average length of the celiac trunk from its origin to its first branch was 12.44 mm, to the second branch was 17.07 mm, and to the third branch was 19.15 mm. In the studied sample, variants were found in 20 % of the specimens, 14 % of these presented morphometric variations in terms of length, and 6 % in terms of structure. In reference to the morphometric variants, the presence of one 3 mm length CT was noteworthy. Morphological variants were found in two specimens presenting a gastro-splenic trunk with a hepatomesenteric trunk, and a third specimen with hepatogastric bifurcated trunk, with the splenic artery originating from the common hepatic artery was observed. No reports were found in the literature concerning the latter.

Disentangling the role of seed bank and dispersal in plant metapopulation dynamics using patch occupancy surveys.

In plants, the presence of a seed bank challenges the application of classical metapopulation models to aboveground presence surveys; ignoring seed bank leads to overestimated extinction and colonization rates. In this article, we explore the possibility to detect seed bank using hidden Markov models in the analysis of aboveground patch occupancy surveys of an annual plant with limited dispersal. Patch occupancy data were generated by simulation under two metapopulation sizes (N = 200 and N = 1,000 patches) and different metapopulation scenarios, each scenario being a combination of the presence/absence of a 1-yr seed bank and the presence/absence of limited dispersal in a circular 1-dimension configuration of patches. In addition, because local conditions often vary among patches in natural metapopulations, we simulated patch occupancy data with heterogeneous germination rate and patch disturbance. Seed bank is not observable from aboveground patch occupancy surveys, hence hidden Markov models were designed to account for uncertainty in patch occupancy. We explored their ability to retrieve the correct scenario. For 10 yr surveys and metapopulation sizes of N = 200 or 1,000 patches, the correct metapopulation scenario was detected at a rate close to 100%, whatever the underlying scenario considered. For smaller, more realistic, survey duration, the length for a reliable detection of the correct scenario depends on the metapopulation size: 3 yr for N = 1,000 and 6 yr for N = 200 are enough. Our method remained powerful to disentangle seed bank from dispersal in the presence of patch heterogeneity affecting either seed germination or patch extinction. Our work shows that seed bank and limited dispersal generate different signatures on aboveground patch occupancy surveys. Therefore, our method provides a powerful tool to infer metapopulation dynamics in a wide range of species with an undetectable life form.

Consecutive cohort effects driven by density-dependence and climate influence early-life survival in a long-lived bird.

Conditions during early life, including maternal cohort effects, can influence the future fitness of individuals. This may be particularly true for long-distance migrating birds, because, apart from conditions experienced by cohorts during rearing, conditions during early life in regions far from breeding grounds may also influence their population dynamics. Very little is known about the fitness consequences of those conditions experienced by juveniles after independence, especially in wild populations and for long-lived birds. We used multi-event capture-recapture-recovery models and a unique 26-year dataset for the Audouin's gull (Larus audouinii) to assess for the first time whether survival was influenced by early conditions, both during the rearing period (i.e. a maternal cohort effect potentially affected by density dependence) and the first winter (i.e. a cohort effect driven by climate when birds disperse to wintering grounds). Our results show that juvenile survival was highly sensitive to early-life conditions and that survival decreased with stronger density dependence and harsh climate. The two consecutive cohort effects were of similar magnitude and they may represent a selection filter. Thus, early-life conditions had a strong impact on survival, and neglecting this complexity may hinder our understanding on how populations of long-lived animals fluctuate and respond to perturbations.

Disruptive viability selection on a black plumage trait associated with dominance.

Traits used in communication, such as colour signals, are expected to have positive consequences for reproductive success, but their associations with survival are little understood. Previous studies have mainly investigated linear relationships between signals and survival, but both hump-shaped and U-shaped relationships can also be predicted, depending on the main costs involved in trait expression. Furthermore, few studies have taken the plasticity of signals into account in viability selection analyses. The relationship between signal expression and survival is of particular interest in melanin-based traits, because their main costs are still debated. Here, we first determined the main factors explaining variability in a melanin-based trait linked to dominance: the bib size of a colonial bird, the sociable weaver Philetairus socius. We then used these analyses to obtain a measure representative of the individual mean expression of bib size. Finally, we used capture-recapture models to study how survival varied in relation to bib size. Variation in bib size was strongly affected by year and moderately affected by age, body condition and colony size. In addition, individuals bearing small and large bibs had higher survival than those with intermediate bibs, and this U-shaped relationship between survival and bib size appeared to be more pronounced in some years than others. These results constitute a rare example of disruptive viability selection, and point towards the potential importance of social costs incurred by the dominance signalling function of badges of status.

Assessing the impact of climate variation on survival in vertebrate populations.

The impact of the ongoing rapid climate change on natural systems is a major issue for human societies. An important challenge for ecologists is to identify the climatic factors that drive temporal variation in demographic parameters, and, ultimately, the dynamics of natural populations. The analysis of long-term monitoring data at the individual scale is often the only available approach to estimate reliably demographic parameters of vertebrate populations. We review statistical procedures used in these analyses to study links between climatic factors and survival variation in vertebrate populations. We evaluated the efficiency of various statistical procedures from an analysis of survival in a population of white stork, Ciconia ciconia, a simulation study and a critical review of 78 papers published in the ecological literature. We identified six potential methodological problems: (i) the use of statistical models that are not well-suited to the analysis of long-term monitoring data collected at the individual scale; (ii) low ratios of number of statistical units to number of candidate climatic covariates; (iii) collinearity among candidate climatic covariates; (iv) the use of statistics, to assess statistical support for climatic covariates effects, that deal poorly with unexplained variation in survival; (v) spurious detection of effects due to the co-occurrence of trends in survival and the climatic covariate time series; and (vi) assessment of the magnitude of climatic effects on survival using measures that cannot be compared across case studies. The critical review of the ecological literature revealed that five of these six methodological problems were often poorly tackled. As a consequence we concluded that many of these studies generated hypotheses but only few provided solid evidence for impacts of climatic factors on survival or reliable measures of the magnitude of such impacts. We provide practical advice to solve efficiently most of the methodological problems identified. The only frequent issue that still lacks a straightforward solution was the low ratio of the number of statistical units to the number of candidate climatic covariates. In the perspective of increasing this ratio and therefore of producing more robust analyses of the links between climate and demography, we suggest leads to improve the procedures for designing field protocols and selecting a set of candidate climatic covariates. Finally, we present recent statistical methods with potential interest for assessing the impact of climatic factors on demographic parameters.

Stabilizing natural selection on the early expression of a secondary sexual trait in a passerine bird.

Natural selection is a central tenet of evolutionary theory, yet the estimation of the direction and intensity of selection remains problematic. Here, we assess the strength of selection on the early expression of a secondary sexual ornament, bill colour, in male European blackbirds (Turdus merula) using 5 years of capture-mark-recapture (CMR) data. The best-fitting model consisted of a quadratic relationship between survival rate and bill colour, indicating stabilizing natural selection on the early expression of a secondary sexual trait. There was no evidence for sexual selection acting on bill colour in the first year. We suggest that the consideration of early selection and the adoption of refined statistical methods may reveal patterns of selection in the wild that have, as yet, remained undetected.

Environment-dependent inbreeding depression in a hermaphroditic freshwater snail.

Inbreeding depression was simultaneously studied under contrasted environments, laboratory and natural conditions, using individuals originating from 14 families of the freshwater snail Physa acuta. Both survival and growth of juveniles showed inbreeding depression under laboratory conditions. The same fitness components were monitored with mature snails either kept under laboratory conditions or released at a natural site and analysed using capture-mark-recapture models. Genetic composition of both samples was similar. Inbreeding depression on survival was highest in the laboratory while strong outbreeding depression was revealed in the field. Thus inbreeding depression may not be always higher under natural conditions, at the opposite of what is commonly assumed. We suggest that inbreeding depression is dependent on metabolic requirements imposed by the environment. Other evidences showing that inbreeding depression is environment-dependent are reviewed. We conclude that genetic models should include both genetic and environmental variance in inbreeding depression for studying mating system evolution.

Threshold concentrations of endothelin-1: the effects on contractions induced by 5-hydroxytryptamine in isolated rat cerebral and mesenteric arteries.

This study compares the effects of threshold concentrations of endothelin-1 in isolated rat basilar arteries with those in mesenteric arterial branches and investigates the mechanisms of inhibitory and potentiating endothelin-1-effects. In basilar arteries, endothelin-1 reduces the contractions induced by 5-hydroxytryptamine (5-HT), by the thromboxane A2 agonist U46619, and by vasopressin. The inhibitory effect of endothelin-1 on the contraction induced by 5-HT is abolished by deendothelialization, by the endothelin ET(B) receptor antagonist RES 701-1, by indomethacin, or by glibenclamide. In mesenteric arteries, endothelin-1 potentiates the contractile effects of 5-HT, U46619, and vasopressin. The potentiation of the contractile effect induced by 5-HT is only somewhat modified by deendothelialization, but abolished by the thromboxane A2 receptor antagonists GR32191 and ridogrel. U46619 potentiates the 5-HT-effect in mesenteric arteries. Thus, though the contractile endothelin ET(A) receptors were not blocked, threshold concentrations of endothelin-1 inhibited contractile effects in the rat basilar artery via activation of endothelial ET(B) receptors. Prostaglandins and ATP-sensitive K+ channels are involved in this inhibitory action. In contrast, endothelin-1 potentiates contractile actions in mesenteric arteries via the release of endogeneous thromboxane A2 from non-endothelial cells. The study points out the completely different role of the endothelium in combined effects of endothelin-1 between cerebral and mesenteric arteries.

Contractions induced by NO synthase inhibition in isolated rat basilar artery: role of the endothelium and endogenous vasoconstrictors.

Alterations of the endothelium may play a role in the generation of cerebral vasospasm. The objective of this study was to investigate the involvement of the endothelium and of endogenous endothelin (ET) on the NG-nitro-L-arginine (L-NOARG)-induced contractions in isolated rat basilar arteries. L-NOARG, NG-nitro-L-arginine methyl esther, and methylene blue, but not D-NOARG, induced concentration-dependent contractions and spontaneous vasomotion. The effect of L-NOARG was reversed by L-arginine and submaximally reduced in de-endothelialized arteries. The contractile effect of L-NOARG was completely suppressed by the ET-antagonists BQ 123 and Ro 46-2005 in a part of the basilar arteries. After washout of the respective antagonist, the L-NOARG-induced contraction started, but was not influenced by a second application of the antagonist. In another part of preparations the antagonists failed to influence the L-NOARG-induced contraction. Inconsistent suppressor effects were also observed after preincubation with ketanserin, Manning compound, losartan, or indomethacin. None of these antagonists reversed the established L-NOARG-induced contraction. Thus, endothelium-derived NO suppresses spontaneous contraction and vasomotion in rat basilar arteries. Endogenous ET, 5-HT, vasopressin, angiotensin or cyclooxygenase metabolites do not cause the contraction induced by inhibition of the NO synthase, but may act as 'trigger factors', that may play a role in rat models of cerebral vasospasm or infarction.

Interactions between vasoconstrictors in isolated human cerebral arteries.

This study investigates whether different endogeneous vasoconstrictors exert synergistic effects in isolated human cerebral arteries, because potentiation of contractile effects may play a role in the pathogenesis of cerebral vasospasm. Isolated human pial arteries obtained from macroscopically intact tissue during brain tumour operations were mounted onto a wire myograph. Concentration-response curves of 5-hydroxytryptamine (5-HT) were constructed in the absence and presence of threshold concentrations of the thromboxane A2 (TXA)-analog U46619, and endothelin-1 (ET-1). Threshold concentrations of U46619 markedly enhanced the maximum contractile effect of 5-HT. The response to 5-HT remained markedly increased even after washout of U46619. Threshold concentrations of ET-1 increased the maximum response to 5-HT, and markedly shifted the dose-response curve to the left. Even after washout of ET-1, the dose-response curve of 5-HT remained shifted to the left. The increase of the contractile effect of 5-HT in the presence of U46619 did not correlate with the relaxant action of the endothelium-dependent vasodilator carbachol. Thus, synergism between contractile substances such as 5-HT, U46619, or ET-1 is seen in human cerebral arteries, and responses to 5-HT are potentiated even after washout of ET-1 and U46619. The potentiation does not depend on the endothelial function. We conclude that synergistic responses between endogeneous vasoconstrictors such as 5-HT, TXA and ET-1 may be involved in the pathogenesis of cerebral vasospasm after subarachnoid haemorrhage.

Effects of potassium channel openers in isolated human cerebral arteries.

The objective of this study was to compare the relaxant effects of the K+ channel openers pinacidil and lemakalim in isolated human pial arteries with the effects of the dihydropyridines nifedipine and nimodipine and the prostacyclin analog iloprost. Relaxation was measured in vessels contracted by 40 mmol/L K+. In contrast to the potent and consistent relaxant effects of nifedipine, nimodipine, and iloprost, the potency of pinacidil and lemakalim proved to be highly variable and inversely correlated with the onset velocity of the preceding contractions of K+ as well as with the endothelium-dependent relaxation of carbachol. Thus, in contrast to dihydropyridines and iloprost, pinacidil and lemakalim selectively elicited potent relaxations in those arteries that exhibited signs of altered vascular wall functions.

The statistical analysis of survival in animal populations.

Estimating, comparing and modelling survival rates are central to population biology. However, there are many difficulties in measuring these rates in animal populations in the wild. The most relevant information is based on samples of marked individuals, i.e. capture-recapture data. In recent years, a number of new statistical approaches to the analysis of such data have been developed, permitting more sophisticated and precise measurement of survival rates.