The influence of local environment on the aging and mortality ofAedes aegypti (L.): Case study in Fortaleza‐CE,Brazil

It is generally assumed that the daily probability of survival of mosquitoes is independent of age. To test this assumption we have conducted a three‐year experimental fieldwork study (2005–2007) at Fortaleza‐CE in Brazil, determining daily survival rates of the dengue vector Aedes aegypti (L.). Survival rates of adult Ae. aegypti may be age‐dependent and the statistical analysis is a sensitive approach for comparing patterns of mosquito survival. The mosquito survival data were better fit by a Weibull survival function than by the more traditionally used Gompertz or logistic survival functions. Gompertz, Weibull, or logistic survival functions often fit the survival, and the tails of the survival curves usually appear to fall between the values predicted by the three functions. We corroborate that the mortality of Ae. aegypti in semi‐natural conditions may no more be considered as a constant phenomenon during the life of adult mosquitoes but varies according to the age and environmental conditions under a tropical climate. This study estimates the variability in the survival rate of Ae. aegypti and environmental factors that are related to such variability. The statistical analysis shows that the fitting ability, concerning the hazard function, was in decreasing order: Seasonal Cox, the three‐parameter Gompertz, and the three‐parameter Weibull, that was similar to the three‐parameter logistic. The advantage of using the Cox model is that it is convenient for exploring the relationship between survival and several explanatory variables. The Cox model has the advantage of preserving the variable in its original quantitative form and of using a maximum of information. The survival analyses indicate that mosquito mortality is both age‐ and environment‐dependent.     

GOMPERTZ Model with Heredity in Random Environment

In this paper we investigate the GOMPERTZ model in a randomly varying environment after incorporating the aspect of heredity. Exact expressions for the first two moments of the logarithm of population size are obtained. Special case of the dichotomic MARKOV process being a white noise process is considered. The stability of the system is also discussed.     

Reproductive effort accelerates actuarial senescence in wild birds: an experimental study

Optimality theories of ageing predict that the balance between reproductive effort and somatic maintenance determines the rate of ageing. Laboratory studies find that increased reproductive effort shortens lifespan, but through increased short‐term mortality rather than ageing. In contrast, high fecundity in early life is associated with accelerated senescence in free‐living vertebrates, but these studies are non‐experimental. We performed lifelong brood size manipulation in free‐living jackdaws. Actuarial senescence – the increase in mortality rate with age – was threefold higher in birds rearing enlarged‐ compared to reduced broods, confirming a key prediction of the optimality theory of ageing. Our findings contrast with the results of single‐year brood size manipulation studies carried out in many species, in which there was no overall discernible manipulation effect on mortality. We suggest that our and previous findings are in agreement with predictions based on the reliability theory of ageing and propose further tests of this proposition.     

A general framework for modeling population abundance data

Time-series data resulting from surveying wild animals are often described using state-space population dynamics models, in particular with Gompertz, Beverton-Holt, or Moran-Ricker latent processes. We show how hidden Markov model methodology provides a flexible framework for fitting a wide range of models to such data. This general approach makes it possible to model abundance on the natural or log scale, include multiple observations at each sampling occasion and compare alternative models using information criteria. It also easily accommodates unequal sampling time intervals, should that possibility occur, and allows testing for density dependence using the bootstrap. The paper is illustrated by replicated time series of red kangaroo abundances, and a univariate time series of ibex counts which are an order of magnitude larger. In the analyses carried out, we fit different latent process and observation models using the hidden Markov framework. Results are robust with regard to the necessary discretization of the state variable. We find no effective difference between the three latent models of the paper in terms of maximized likelihood value for the two applications presented, and also others analyzed. Simulations suggest that ecological time series are not sufficiently informative to distinguish between alternative latent processes for modeling population survey data when data do not indicate strong density dependence.     

Temporal patterns of growth in larval cohorts of the Japanese sardine Sardinops melanostictus in a coastal nursery area

Growth patterns of larval sardine Sardinops melanostictus were studied in a coastal nursery area, in southern Japan for four monthly hatch cohorts of larvae (November, December, January and February) for the 2003–2004 and 2004–2005 seasons. Laird–Gompertz models were fitted to each cohort using both total length (L_T)‐at‐age at capture and mean L_T‐at‐age data derived from backcalculations. In both approaches, the absolute daily growth rates (G_R) and absolute daily growth rates at the inflection point (G_XO) were estimated. In parallel, individual growth rates (G_I) were derived from backcalculated L_T (L_B). Growth showed the following general common patterns irrespective of hatch month, season and methods: (1) significant Laird–Gompertz fits, (2) asymptotic growth, (3) a decrease in G_R after the inflexion point, except for February for the 2003–2004 season that showed an apparent constant growth pattern, (4) six in eight cohorts showed G_XO ranging from 0·8 to 1·2 mm day^?1 and (5) a decreasing tendency of G_I from 1·75 to 0·24 mm day^?1, from first feeding through the first month of larval life. The contrasting pattern between the 2003–2004 and the 2004–2005 seasons were: (1) allometric v. logarithmic (ln) L_T and otolith radius relationships, (2) low G_XOv. high G_XO, (3) high G_Rv. low G_R when growth turned asymptotic, (4) low G_XOv. high G_XO when monthly hatch cohorts were combined and (5) L_B and G_I not differing among monthly hatch cohorts. The differences in growth patterns and growth rates between seasons seemed to be linked to the influx of warmer and oligotrophic waters of the Kuroshio Current that triggered an increase of 3° C in the coastal area for the 2003–2004 seasons. In the overall context, however, the high G_XO, within cohorts and seasons reported in the current study, suggests that either sea surface temperature (SST) or food availability, or both are in the optimal range of preferences for S. melanostictus larvae. Consequently, nearshore coastal areas seem to be playing an important role as a nursery area for the larval stage of this species.     

Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster

It has been suggested that mitochondrial DNA (mtDNA) may play an important role in aging. Yet, few empirical studies have tested this hypothesis, partly because the degree of sequence polymorphism in mtDNA is assumed to be low. However, low sequence variation may not necessarily translate into low phenotypic variation. Here, we report an experiment that tests whether there is within-population variation in cytoplasmic genes for female longevity and senescence. To achieve this, we randomly selected 25 "mitochondrial founders" from a single, panmictic population of Drosophila melanogaster and used these founders to generate distinct "mt" lines in which we controlled for the nuclear background by successive backcrossing. Potential confounding effects of cytoplasmically transmitted bacteria were eliminated by tetracycline treatment. The mt lines were then assayed for differences in longevity, Gompertz intercept (frailty), and demographic rate of change in mortality with age (rate-of-senescence) in females. We found significant cytoplasmic effects on all three variables. This provides evidence that genetic variation in cytoplasmic genes, presumably mtDNA, contributes to variation in female mortality and aging.     

Postcatastrophe Population Dynamics and Density Dependence of an Endemic Island Duck

ABSTRACT Laysan ducks (Anas laysanensis) are restricted to approximately 9 km² in the Northwestern Hawaiian Islands, USA. To evaluate the importance of density dependence for Laysan ducks, we conducted a Bayesian analysis to estimate the parameters of a Gompertz model and the magnitude of process variation and observation error based on the fluctuations in Laysan duck abundance on Laysan Island from 1994 to 2007. This model described a stationary distribution for the population at carrying capacity that fluctuates around a long-term mean of 456 ducks and is between 316 to 636 ducks 95% of the time. This range of expected variability can be used to identify changes in population size that warn of catastrophic events. Density-dependent population dynamics may explain the recovery of Laysan duck from catastrophic declines and allow managers to identify population monitoring thresholds.     

Morphogenesis in Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis> (Bong.) Carr.) bud cultures – tree maturation and explants from epicormic shoots

The adventitious bud forming ability of Sitka spruce (Picea sitchensis (Bong.) Carr.) buds in vitro was found to be dependent upon the age of tree from which the explants were taken. Bud formation declined exponentially with increasing tree age when 1.0 and 10 μM 6-benzylaminopurine (BA) were used to induce adventitious buds. When less BA was used (0.1 μM) bud production was much lower with all ages of tree and no mathematical relationship between declining bud production and tree age was found. By a tree age of 6 years bud-forming ability had declined severely. Even the few buds that developed on older tree tissues failed to elongate into shoots, became necrotic and eventually died, indicating that adventitious bud induction in this species is not a rejuvenative process. Callusing of bud explants also declined with increasing tree age when 0.1 μM BA was used whilst very little callusing occurred at the higher cytokinin concentrations (1.0 and 10 μM BA). Tissue necrosis in vitro increased with tree age, whilst the ability of BA to retard necrosis declined with increasing tree age. Buds from epicormic shoots, formed on the lower trunks of 20-year-old trees when these were exposed to light, were not significantly better at forming adventitious buds in vitro than buds taken from the lower branches of the crown.     

A stochastic gompertz model with hereditary effect

Summary In this paper we have studied a stochastic version of the Gompertz model for population growth of a single species after incorporating the aspect of heredity. Various statistical characteristics-the mean-value function, covariance-kernel, etc.-are evaluated for a delta-correlated process and their asymptotic values obtained. The effect of the hereditary kernel on the various statistics is discussed and it is found that it is to shift the distribution towards the origin.     

非线性增长模型的回归分析

本文对Logistic模型和Gompertz模型给出了计算参数值的迭代公式,并提出了一种确定迭代初始值的新方法．