Coevolution of pierid butterflies and their cruciferous foodplants

Summary The suitability of several Cruciferae species for the survival and development of the larvae of Anthocharis cardamines, which are seed and flower predators, was investigated. Large differences, consistent in time and space, were observed between the survival of sub-populations on different hostplants. Foodplants influenced A. cardamines survival and development by allelochemical and mechanical defences, which may also weaken a larva against pathogen attack. Oviposition by females appeared surprisingly maladaptive however with proportionately most eggs being laid on the hostplants yielding poorest larval survival, in opposition to previous expectations of coevolutionary theory. The evolutionary consequences of butterfly predation for Cruciferae are discussed, and juxtaposed to the needs of pollination.     

On the empirical choice of the time window for restricted mean survival time

The t-year mean survival or restricted mean survival time (RMST) has been used as an appealing summary of the survival distribution within a time window [0, t]. RMST is the patient's life expectancy until time t and can be estimated nonparametrically by the area under the Kaplan-Meier curve up to t. In a comparative study, the difference or ratio of two RMSTs has been utilized to quantify the between-group-difference as a clinically interpretable alternative summary to the hazard ratio. The choice of the time window [0, t] may be prespecified at the design stage of the study based on clinical considerations. On the other hand, after the survival data have been collected, the choice of time point t could be data-dependent. The standard inferential procedures for the corresponding RMST, which is also data-dependent, ignore this subtle yet important issue. In this paper, we clarify how to make inference about a random “parameter.” Moreover, we demonstrate that under a rather mild condition on the censoring distribution, one can make inference about the RMST up to t, where t is less than or even equal to the largest follow-up time (either observed or censored) in the study. This finding reduces the subjectivity of the choice of t empirically. The proposal is illustrated with the survival data from a primary biliary cirrhosis study, and its finite sample properties are investigated via an extensive simulation study.     

On the survival of populations in a heterogeneous and variable environment

Summary The survival time of small and isolated populations will often be relatively low, by which the survival of species living in such a way will depend on powers of dispersal sufficiently high to result in a rate of population foundings that about compensates the rate of population extinctions. The survival time of composite populations uninterruptedly inhabiting large and heterogeneous areas, highly depends on the extent to which the numbers fluctuate unequally in the different subpopulations. The importance of this spreading of the risk of extinction over differently fluctuating subpopulations is demonstrated by comparing over 19 years the fluctuation patterns of the composite populations of two carabid species, Pterostichus versicolor with unequally fluctuating subpopulations, and Calathus melanocephalus with subpopulations fluctuating in parallel, both uninterruptedly occupying the same large heath area. The conclusions from the field data are checked by simulating the fluctuation patterns of these populations, and thus directly estimating survival times. It thus appeared that the former species can be expected to survive more than ten times better than the latter (other things staying the same). These simulations could also be used to study the possible influence of various density restricting processes in populations already fluctuating according to some pattern. As could be expected, the survival time of a population, which shows a tendency towards an upward trend in numbers, will be favoured by some kind of density restriction, but the degree to which these restrictions are density-dependent appeared to be immaterial. Density reductions that are about adequate on the average need even not occur at high densities only, if only the chance of occurrence at very low densities is low. The density-level at which a population is generally fluctuating appeared to be less important for survival than the fluctuation pattern itself, except for very low density levels, of course. The different ways in which deterministic and stochastic processes may interact and thus determine the fluctuations of population numbers are discussed. It is concluded that some stochastic processes will operate everywhere and will thus necessarily result in density fluctuations; such an omnipresence is much less imperative, however, for density-dependent processes, by which population models should primarily be stochastic models. However, if density-dependent processes are added to model populations, that are already fluctuating stochastically the effects are taken up into the general, stochastic fluctuation pattern, without altering it fundamentally.Communication No. 228 of the Biological Station WijsterDedicated to Professor Michael Evenari     

Rapid identification and detection of intracellular survival testing of mycobacterium smegmatis mc²155 that contains eis gene from mycobacterium tuberculosis by flow cytometry

Mycobacterium tuberculosis is a facultative intracellular pathogen that has evolved the ability to survive and multiply within human macrophages. The enhanced intracellular survival (eis) gene (Rv2416c) from M. tuberculosis has been identified as a potential factor that can enhance the intracellular survival of Mycobacterium smegmatis in the macrophage cell line. However, the time requirements for intracellular survival testing of Mycobacterium using classical methodologies are still too long. In this study, we used M. smegmatis mc²155 that contains eis to develop and study a rapid method to test intracellular survival using flow cytometry. We demonstrated the success of this technique, which required only a few hours. This assay is rapid, accurate, and reproducible, and it would be valuable for the rapid detection of intracellular survival of mycobacteria.     

Survival of the African white‐backed vulture Gyps africanus in north‐eastern South Africa

Old World vultures are in decline across their entire range. Although critical for the formulation of effective conservation measures, neither survival nor movement patterns of African vultures are adequately known. This paper presents survival and movement data on the African white‐backed vultures (Gyps africanus) from South Africa. Survival estimates were modelled on resightings of tagged vultures. Birds were captured en masse and resighted between November 2005 and December 2010. A total of 93 adult and subadult birds were fitted with uniquely numbered patagial tags, which were resighted 3707 times(mean of 39.8 resightings per bird). The programme MARK was used to estimate survival. The best model was one where survival and recaptures varied only with time (e.g. year). However, owing to the fading (illegibility) of tags in later years, the relationship with time is probably spurious. The second best model was one where survival and recaptures varied with age and time. Annual survival estimates increased from 85.2% in second‐year birds to 99.9% in adults. This corresponds well with the survival of two other Gyps vultures that have been studied to date and underscores the point that additional mortality of adults in these long‐lived species will result in rapid population declines.     

Heat shock proteins mediate trade‐offs between early‐life reproduction and late survival in Drosophila melanogaster

Ageing and the resulting increased likelihood mortality are the inescapable fate of organisms because selection pressures on genes that exert their function late in life is weak, promoting the evolution of genes that enhance early‐life reproductive performance at the same time as sacrificing late survival. Heat shock proteins (HSP) are known to buffer various environmental stresses and are also involved in protein homeostasis and longevity. The characteristics of genes for HSPs (hsp) imply that they affect various life‐history traits, which in turn affect longevity; however, little is known about the effects of hsp genes on life‐history traits and their interaction with longevity. In the present study, the effects of hsp genes on multiple fitness traits, such as locomotor activity, total fecundity, early fecundity and survival time, are investigated in Drosophila melanogaster Meigen using RNA interference (RNAi). In egg‐laying females, RNAi knockdown of six hsp genes (hsp22, hsp23, hsp67Ba, hsp67Bb, hsp67Bc and hsp27‐like) does not shorten survival but rather increases it. Knockdown of five of those genes on an individual basis reduces early‐life reproduction, suggesting that several hsp genes mediate the trade‐off between early reproduction and late survival. The data indicate a positive effect of hsp genes on early reproduction and also negative effects on survival time, supporting the antagonistic pleiotropic effects predicted by the optimality theory of ageing.     

Accelerated failure time (AFT) modeling for the development and survival of Russian wheat aphid, <Emphasis Type="Italic">Diuraphis noxia</Emphasis> (Mordvilko)

Accelerated failure time model (AFT) and Cox’s proportional hazards model (PHM) are considered the two most significant models in survival analysis, which has become a de facto standard for biomedical data analysis and modeling. AFT not only plays an extremely significant role in survival analysis but also finds extensive applications in engineering reliability. Survival analysis studies a special type of random variables: time-to-event (also known as failure time, lifetime or survival time) random variables. Examples of time-to-event random variables include survival times of patients in a clinical trial and failure times of machine components. Since molting and death times of insect individuals are also perfect examples of time-to-event random variables, we argue that survival analysis including AFT modeling is ideal for analyzing insect development and survival data, and further for building dynamic models of insect development and survival. Here we demonstrate such an application with data collected by observing stage-to-stage development and survival of 1,800 Russian wheat aphids (RWA), Diuraphis noxia, reared in laboratory growth chambers arranged in 25 treatments (each with 72 individuals). The main advantages of survival analysis, including the unified modeling of survival and development as well as handling of information censoring, are also discussed.     

Quick methods for evaluating survival of age-characterizable long-lived territorial birds

Survival is a key life-history trait in animals. However, most methods of survival estimation require substantial human and economic investment in the long term, particularly in species occurring in low densities, the case of most endangered species. An alternative to traditional recapture (CR) methods is estimation of adult survival based indirectly on either age ratios (AGR) or turnover rates (TOR) in territorial species. These 2 methods are applicable to bird species in which recruited individuals enter into the breeding population whilst still exhibiting the external traits that distinguish those animals from experienced adults. The main advantages of these methods are that survival can be easily estimated for all monitored individuals after just 1 or 2 breeding seasons and that disturbance to the species is minimized. The main constraints of indirect methods are that the assumptions are more restrictive than in CR methods, and survival estimates, although comparable between sites and years, may be biased. We used data from a long-term monitoring survey of 2 populations of the endangered Bonelli's eagle (Aquila fasciata), one in Catalonia (NE Spain) and the other in Provence and Languedoc-Roussillon (SE France). We evaluated survival estimates using the AGR and TOR methods and compared them with CR methods and provide suitable corrections for refining survival estimates based on indirect methods. In Catalonia (2002–2008), survival was estimated at 0.84 by CR methods (SE = 0.047; n = 25 radio tagged eagles), at 0.86 by the corrected AGR method (SE = 0.011; n = 558 bird * year), and at 0.86 by the corrected TOR method (SE = 0.022; n = 547 bird * year). In France (1999–2008), survival was estimated at 0.88 by CR methods (SE = 0.040; n = 45 darvic banded eagles), at 0.87 by the corrected AGR method (SE = 0.015; n = 443 bird * year), and at 0.87 by the corrected TOR method (SE = 0.015; n = 438 bird * year). All analyses suggest that females survive better than males and that individuals from the French population survive better than individuals from the Catalan population. We conclude that indirect methods, which should not be regarded as a substitute of CR methods, will allow wildlife managers and researchers to estimate accurately adult survival in a territorial species over a short period of time and to monitor survival across populations over large geographic ranges and over time. © 2011 The Wildlife Society.     

Time matching between grooming partners: Do methodological distinctions between short versus long‐term reciprocation matter?

Primatologists have long focused on grooming exchanges to examine aspects of social relationships, co‐operation, and social cognition. One particular interest is the extent to which reciprocating grooming partners time match, and the time frame over which they do so. Conclusions about time matching vary across species. Generally, researchers focus on the duration of pauses between grooming episodes that involve a switch in partner roles and choose a cut‐off point to distinguish short from longer‐term reciprocation. Problematically, researchers have made inconsistent choices about cut‐offs. Such methodological variations are potentially concerning, as it is unclear whether inconsistent conclusions about short‐term time matching are attributable to species/ecological differences, or are due in part to methodological inconsistency. We ask whether various criteria for separating short versus long‐term reciprocation influence conclusions about short‐term time matching using data from free‐ranging rhesus ( Macaca mulatta) and captive‐crested macaques ( Macaca nigra). We compare several commonly used cut‐offs to ones generated by the currently preferred approach—survival analysis. Crested macaques displayed a mild degree of time matching regardless of the cutoff used. For rhesus macaques, whereas most cut‐offs yielded similar degrees of time matching as the one derived from survival analysis, very short ones significantly underestimated both the degree of time matching and the influence of rank distance on time matching. Although researchers may have some flexibility in their choice of cut‐offs, we suggest that they employ caution by using survival analysis when possible, and when not possible, by avoiding very short time windows.     

Updated assessment of hatchery‐reared pallid sturgeon (Forbes & Richardson, 1905) survival in the lower Missouri River

As pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905), natural reproduction and recruitment remains very minimal in the lower Missouri River from Gavins Point Dam (river kilometer [rkm] 1305.2) to the confluence with the Mississippi River (rkm 0.0), hatchery supplementation and river‐wide monitoring efforts have continued. Annual survival estimates of hatchery‐reared pallid sturgeon stocked in the lower Missouri River were previously estimated during 1994–2008. Low recapture rates prior to 2006 limited the data available to estimate survival, which resulted in considerable uncertainty for the estimate of annual survival of age‐1 fish. Therefore, the objective was to provide more precise estimates of annual survival of pallid sturgeon using five additional years of stocking and sampling. The Cormack‐Jolly‐Seber model structure provided in program MARK was used to estimate the age‐specific survival estimates. Over 135 000 hatchery‐reared pallid sturgeon were released during 1994–2011 and recaptured at a rate of 1.9%, whereby estimates for the annual survival of age‐0 (Ø = 0.048) and >age‐1 (Ø = 0.931) were similar to those previously reported, but the age‐1 (Ø = 0.403) survival estimate was 52% lower. Post hoc analysis using time‐specific survival estimates indicated lower survival for age‐1 fish post‐2003 year classes, relative to the pre‐2002 year classes. An analysis confirms that hatchery‐reared pallid sturgeon continue to survive in the wild. However, low survival during the first 2 years of life is a management concern as efforts are aimed at maximizing genetic diversity and population growth. A follow‐up analysis also demonstrated the variability of capture rates and survival over time, which reinforces the need to continue to monitor and evaluate mark‐recapture data. The mark‐recapture efforts have provided demographic parameter estimates that remain a critical component for species recovery as these data are incorporated into population models.     

One-step targeted maximum likelihood estimation for time-to-event outcomes

Researchers in observational survival analysis are interested in not only estimating survival curve nonparametrically but also having statistical inference for the parameter. We consider right-censored failure time data where we observe n independent and identically distributed observations of a vector random variable consisting of baseline covariates, a binary treatment at baseline, a survival time subject to right censoring, and the censoring indicator. We assume the baseline covariates are allowed to affect the treatment and censoring so that an estimator that ignores covariate information would be inconsistent. The goal is to use these data to estimate the counterfactual average survival curve of the population if all subjects are assigned the same treatment at baseline. Existing observational survival analysis methods do not result in monotone survival curve estimators, which is undesirable and may lose efficiency by not constraining the shape of the estimator using the prior knowledge of the estimand. In this paper, we present a one-step Targeted Maximum Likelihood Estimator (TMLE) for estimating the counterfactual average survival curve. We show that this new TMLE can be executed via recursion in small local updates. We demonstrate the finite sample performance of this one-step TMLE in simulations and an application to a monoclonal gammopathy data.     

Effects of increasing root carbon investment on the mortality and resprouting of Haloxylon ammodendron seedlings under drought

• Tree mortality induced by drought is one of the most complex processes in ecology. Although two mechanisms associated with water and carbon balance are proposed to explain tree mortality, outstanding problems still exist.
• Here, in order to test how the root system benefits survival and resprouting of Haloxylon ammodendron seedlings, we examined the various water‐ and carbon‐related physiological indicators (shoot water potential, photosynthesis, dark respiration, hydraulic conductance and non‐structural carbohydrates [NSC]) of H. ammodendron seedlings, which were grown in drought and control conditions throughout a grow season in greenhouse.
• The survival time of the seedling root system (died 70 days after drought) doubled the survival time of the shoot (died at 35 days). Difference in survival time between shoot and root resulted from sustained root respiration supported by increased NSC in roots under drought. Furthermore, investment into the root contributed to resprouting following drought. Based on these results, a death criterion is proposed for this species. The time sequence of major events indicated that drought shifted carbon allocation between shoot and root and altered the flux among different sinks (growth, respiration or storage). The interaction of water and carbon processes determined death or survival of droughted H. ammodendron seedlings.
• These findings revealed that the ‘root protection’ strategy is critical in determining survival and resprouting of this species, and provided insights into the effects of carbon and water dynamics on tree mortality.

     

Survival ofMegasphaera elsdenii during starvation

Batch- and continuous-cultured cell suspensions of the anaerobic ruminal bacteriumMegasphaera elsdenii strain T-81 were subjected to total nutrient starvation, during which time changes in cell viability, cell composition, and endogenous fermentation acids were monitored. The populations exhibited poor survival capabilities with a 50% survival time of 9–13 h. The primary substrates used for endogenous metabolism appeared to be cellular RNA, carbohydrate, and possibly protein. The types and amounts of major fermentation acids (acetic, butyric, caproic) released from starving cells varied depending upon initial growth conditions and starvation time. The data suggest that growth conditions affect cell composition and have important roles in survival ofM. elsdenii.     

Effects of Lead Exposure,Flock Behavior,and Management Actions on the Survival of California Condors (Gymnogyps californianus)

Translocation is an increasingly important tool for managing endangered species, but factors influencing the survival of translocated individuals are not well understood. Here we examine intrinsic and extrinsic drivers of survival for critically endangered California condors (Gymnogyps californianus) whose wild population recovery is reliant upon releases of captively bred stock. We used known fate models and information-theoretic methods to compare the ability of hypothesized covariates, most of which serve as proxies for lead exposure risk, to predict survival rates of condors in California. Our best supported model included the following predictors of survival: age of the recovery program, precipitation, proportion of days observed feeding on proffered carcasses, maximum blood lead concentration over the preceding 18 months, and time since release. We found that as flocks have increased in size and age, condors are increasingly likely to range more widely and less likely to be observed feeding on proffered food, and these “wilder” behaviors were associated with lower survival. After accounting for these behaviors, we found a positive survival trend, which we attribute to ongoing improvements in management. Our findings illustrate that the survival of translocated animals, such as highly social California condors, is influenced by behaviors that change through time.

     

Captive killer whale (Orcinus orca) survival

Killer whales (Orcinus orca) were first placed into captivity in 1961 and are now found in theme parks around the world. Despite successful breeding of captive killer whales since 1985 there is growing concern for their welfare in captivity, which often includes claims of poor survival. We employed Kaplan‐Meier and Cox Proportional hazards models and annual survival rate analyses on 201 captive killer whales to discern how sex, facility (U.S. vs. foreign), captive‐born vs. wild‐captured, pre‐ vs. post‐1 January 1985, and animal age upon entering captivity affect survival. Overall median survival estimate was 6.1 yr, with no difference between male and female survival. Killer whales in U.S. facilities (12.0 yr) demonstrated a significantly higher median survival than those in foreign facilities (4.4 yr), as did whales entering captivity post‐1 January 1985 (11.8 yr) vs. those entering prior to 1 January 1985 (3.9 yr). Median survival for captive‐born (14.1 yr) was significantly higher than wild‐captured killer whales (5.5 yr), though the two failed to differ among the post‐1 January 1985 cohort. Facility location and pre‐ vs. post‐1 January 1985 were predictors of the hazard rate. Survival of captive killer whale cohorts has generally improved through time, although survival to age milestones are poor when compared to wild killer whales.     

Age‐specific survival and movement among major African Penguin Spheniscus demersus colonies

Reliable estimates of survival and dispersal are crucial to understanding population dynamics, but for seabirds, in which some individuals spend years away from land, mortality and emigration are often confounded. Multistate mark–recapture methods reduce bias by incorporating movement into the process of estimating survival. We used a multistate model to provide unbiased age‐specific survival and movement probabilities for the Endangered African Penguin Spheniscus demersus based on 5281 nestlings and 31 049 adults flipper‐banded and resighted in the Western Cape, South Africa, between 1994 and 2012. Adult survival was initially high (≥ 0.74) but declined after 2003–2004 coincident with a reduction in the availability of Sardine Sardinops sagax and Anchovy Engraulis encrasicolus on the west coast of South Africa. Juvenile survival was poorly estimated, but was lower and more variable than adult survival. Fidelity to the locality of origin varied over time, but was high in adults at Robben and Dassen islands (≥ 0.88) and above 0.55 for juvenile and immature Penguins at all localities. Movement occurred predominantly during 1994–2003 and was indicative of immigration to Robben and Dassen islands. Our results confirm that a prolonged period of adult mortality contributed to the observed decline in the African Penguin population and suggest a need for approaches operating over large spatial scales to ensure food security for marine top predators.     

Differences in seasonal survival suggest species‐specific reactions to climate change in two sympatric bat species

Long‐lived animals with a low annual reproductive output need a long time to recover from population crashes and are, thus, likely to face high extinction risk, if the current global environmental change will increase mortality rates. To aid conservation of those species, knowledge on the variability of mortality rates is essential. Unfortunately, however, individual‐based multiyear data sets that are required for that have only rarely been collected for free‐ranging long‐lived mammals. Here, we used a five‐year data set comprising activity data of 1,445 RFID‐tagged individuals of two long‐lived temperate zone bat species, Natterer's bats (Myotis nattereri) and Daubenton's bats (Myotis daubentonii), at their joint hibernaculum. Both species are listed as being of high conservation interest by the European Habitats Directive. Applying mixed‐effects logistic regression, we explored seasonal survival differences in these two species which differ in foraging strategy and phenology. In both species, survival over the first winter of an individual's life was much lower than survival over subsequent winters. Focussing on adults only, seasonal survival patterns were largely consistent with higher winter and lower summer survival but varied in its level across years in both species. Our analyses, furthermore, highlight the importance of species‐specific time periods for survival. Daubenton's bats showed a much stronger difference in survival between the two seasons than Natterer's bats. In one exceptional winter, the population of Natterer's bats crashed, while the survival of Daubenton's bats declined only moderately. While our results confirm the general seasonal survival pattern typical for hibernating mammals with higher winter than summer survival, they also show that this pattern can be reversed under particular conditions. Overall, our study points toward a high importance of specific time periods for population dynamics and suggests species‐, population‐, and age class‐specific responses to global climate change.     

Bayes Estimator of Survival Probability from Randomly Censored Observations with Weibull Distribution of Time to Death

This paper deals with Bayes estimation of survival probability when the data are randomly censored. Such a situation arises in case of a clinical trial which extends for a limited period T. A fixed number of patients (n) are observed whose times to death have identical Weibull distribution with parameters β and θ. The maximum times of observation for different patients are also independent uniform variables as the patients arrive randomly throughout the trial. For the joint prior distribution of (β, θ) as suggested by Sinha and Kale (1980, page 137) Bayes estimator of survival probability at time t (0<t<T) has been obtained. Considering squared error loss function it is the mean of the survival probability with respect to the posterior distribution of (β, θ). This estimator is then compared with the maximum likelihood estimator, by simulation, for various values of β, θ and censoring percentage. The proposed estimator is found to be better under certain conditions.     

Highly variable rates of survival to metamorphosis in wild boreal toads (Anaxyrus boreas boreas)

Life history theory suggests that long-lived, pond-breeding amphibians should have low and highly variable early life-stage survival rates, but this theoretical expectation is often untested and the causes of variation are usually unknown. We evaluated the impact of hydroperiod, presence of a pathogen (Batrachochytrium dendrobatidis [Bd]), presence of a potential predator (cutthroat trout Oncorhychus clarki stomias), and whether animals had been reintroduced into a site on survival of early life stages of boreal toads (Anaxyrus boreas boreas). We used a multistate mark-recapture framework to estimate survival of boreal toad embryos from egg to metamorphosis at four sites over 5 years. We found substantial spatial and temporal variation in survival to metamorphosis and documented some evidence that monthly tadpole survival was lower in sites with Bd, without trout, and at permanent sites. Our results support theories of amphibian life history, aid in the management of this species of conservation concern, and contribute to our knowledge of the ecology of the species. Additionally, we present methodology that allows practitioners to account for different lengths of time between sampling periods when estimating survival probabilities which is especially applicable to organisms with distinct biological stages.