Diet, sex, and death in field crickets

Senescence is shaped by age-dependent trade-offs between fitness components. Because males and females invest different resources in reproduction, the trade-offs behind age-dependent reproductive effort should be resolved differently in the sexes. In this study, we assess the effects of diet (high carbohydrate and low protein vs. equal carbohydrate and protein) and mating (once mated vs. virgin) on lifespan and age-dependent mortality in male and female field crickets (Teleogryllus commodus), and on male calling effort. Females always had higher actuarial ageing rates than males, and we found a clear lifespan cost of mating in females. Mated males, however, lived longer than virgin males, possibly because virgins call more than mated males. The fastest age-dependent increases in mortality were among mated males on the high-carbohydrate diet. Males on a high-carbohydrate diet showed a faster increase in calling effort earlier in life, and a more pronounced pattern of senescence once they reached this peak than did males on a diet with equal amounts of protein and carbohydrates. Our results provide evidence that the cost of mating in this cricket species is both diet and sex-dependent, and that the underlying causes of sex differences in life-history traits such as lifespan and senescence can be complex.     

Individualism in plant populations: using stochastic differential equations to model individual neighbourhood-dependent plant growth

We study individual plant growth and size hierarchy formation in an experimental population of Arabidopsis thaliana, within an integrated analysis that explicitly accounts for size-dependent growth, size- and space-dependent competition, and environmental stochasticity. It is shown that a Gompertz-type stochastic differential equation (SDE) model, involving asymmetric competition kernels and a stochastic term which decreases with the logarithm of plant weight, efficiently describes individual plant growth, competition, and variability in the studied population. The model is evaluated within a Bayesian framework and compared to its deterministic counterpart, and to several simplified stochastic models, using distributional validation. We show that stochasticity is an important determinant of size hierarchy and that SDE models outperform the deterministic model if and only if structural components of competition (asymmetry; size- and space-dependence) are accounted for. Implications of these results are discussed in the context of plant ecology and in more general modelling situations.     

Growth and age determination of the tropical Australian cubozoan Chiropsalmus sp.

Chiropsalmus sp. medusae collected in this study ranged from 3 to 71 mm diagonal bell width and displayed growth best described by the following equation size (mm) = 74.9 × exp (−exp(0.041 (time since metamorphosis (day) −35.6674))). Growth rates of up to 7 mm week⁻¹ increase in diagonal bell width are theoretically possible, with animals able to reach sexual maturity in approximately 70 days. Correlation of the number of rings on the statoliths with the predicted age of the individual from the field produced a relationship that indicates the growth rings are laid down daily and as such could be used to infer age of the medusae. Over the 1998–1999 season, there were four influxes of juvenile cohorts, each occurring approximately 14 days after a major rainfall event.     

Estimating hominid life history: the critical interbirth interval

Unlike any great apes, humans have expanded into a wide variety of habitats during the course of evolution, beginning with the transition by australopithecines from forest to savanna habitation. Novel environments are likely to have imposed hominids a demographic challenge due to such factors as higher predation risk and scarcer food resources. In fact, recent studies have found a paucity of older relative to younger adults in hominid fossil remains, indicating considerably high adult mortality in australopithecines, early Homo, and Neanderthals. It is not clear to date why only human ancestors among all hominoid species could survive in these harsh environments. In this paper, we explore the possibility that hominids had shorter interbirth intervals to enhance fertility than the extant apes. To infer interbirth intervals in fossil hominids, we introduce the notion of the critical interbirth interval, or the threshold length of birth spacing above which a population is expected to go to extinction. We develop a new method to obtain the critical interbirth intervals of hominids based on the observed ratios of older adults to all adults in fossil samples. Our analysis suggests that the critical interbirth intervals of australopithecines, early Homo, and Neanderthals are significantly shorter than the observed interbirth intervals of extant great apes. We also discuss possible factors that may have caused the evolutionary divergence of hominid life history traits from those of great apes.     

External morphology of the short-beaked common dolphin, Delphinus delphis: growth, allometric relationships and sexual dimorphism

Growth, allometric relationships and sexual dimorphism are described from measurements of 105 male, 149 female and 38 unsexed specimens of short‐beaked common dolphin, Delphinus delphis, stranded along the Irish coastline (53.8% of the sample) or by‐caught in fisheries (46.2% of the sample), from 1990 to 2003. For each dolphin, 24 external body length measurements were recorded. Ages were determined for 183 dolphins by analysis of growth layer groups in the dentine. Males ranged in total body length (TBL) from 105 to 231 cm and females from 93 to 230 cm, with a maximum age of 25 years obtained for both sexes. Using a single Gompertz growth curve, asymptotic values obtained for TBL were 211.6 cm and 197.4 cm for males and females, respectively. Asymptotic lengths were attained at 11 years in males and 9 years in females. The gestation period was estimated to last approximately 11.5 months. Sexual size dimorphism (SSD) was evident, with males being significantly larger than females for 20 of the characters measured, and an SSD ratio of 1.06 was obtained. Sexual shape dimorphism was lacking, except for the presence of prominent postanal humps in mature males.     

Daily growth patterns and age‐at‐recruitment of the anchoveta Engraulis ringens as indicated by a multi‐annual analysis of otolith microstructure across developmental stages

The anchoveta (Engraulis ringens ) plays a key role in the ecology of the Humboldt Current System and is of major economic importance; however, many aspects of its early life history are still poorly understood. In this study, an analysis of daily age and length patterns was carried out using the sagittal otoliths from wild larvae (0–0.2 cm standard length, L _S), pre‐recruits (3–6 cm total length, L _T), recruits (7–12 cm L _T) and young adults (12–15 cm L _T). Additionally, variability in growth and age at recruitment (A _R) were evaluated for recruits caught in northern Chile in 1973, 1982, 2009, 2010, 2012, 2013, 2014 and 2015. The age–length relationship showed four allometric patterns that were well described by Laird‐Gompertz models. The absolute growth rates at the inflexion point (G _AR) were 0.56, 0.75, 1.22 and 1.16 mm d^?1 for larvae, pre‐recruits, recruits and young adults, respectively. At the interannual scale, G _AR values were always >1 mm d^?1 (mean ± S.D . 1.37 ± 0.21 mm d^?1; range 1.12–1.64 mm d^?1), irrespective of the season of hatching (i.e. winter v. spring); additionally, in most cases, G _AR values were reached before the second month of life (mean ± S.D . 50.47 ± 9.73 days) at c. 4 cm L _T (mean ± S.D . 4.22 ± 0.29 cm). Mean A _R was < 150 days (112 ± 29 days; range 75–149 days); in contrast, estimates of A _R were higher and growth rates were lower in 1973, 1983 and 2000. These results demonstrate very fast growth and early A _R of anchoveta in northern Chile, suggesting most fish are removed by the fisheries at very early ages. An evaluation of the implications of these results on stock assessment and management of this species is highly recommended.     

Modeling of biomass production by Spirulinaplatensis as function of phosphate concentrations and pH regimes

Batch cultivations were performed to evaluate the influence of phosphate concentrations (0.25, 0.5, 0.75, and 1.0 g L⁻¹) for pH regimes (9.5, 10.0, and 10.5) on the biomass production by Spirulina platensis. The best condition for cell growth (3.099 g L⁻¹) was found at 0.5 g L⁻¹ phosphate and pH value of 10.0. Cultivation time, phosphate, and pH caused to increase significantly (p < 0.01) in biomass production by S. platensis. Lag time was observed up to 4 h. After then, biomass production increased sharply (p < 0.01) from 0.020 g L⁻¹ to 2.063, 2.213, 1.532, and 0.797 g L⁻¹ at 0.25, 0.5, 0.75, and 1.0 g L⁻¹ phosphate values, respectively. Modified Gompertz model could be regarded as sufficient to describe the biomass production by S. platensis with high determination coefficients and low sum of square value indicated that. Biological parameters for biomass production were successfully predicted by modified Gompertz model.     

Estimation of non-linear growth models by linearization: a simulation study using a Gompertz function

A method based on Taylor series expansion for estimation of location parameters and variance components of non-linear mixed effects models was considered. An attractive property of the method is the opportunity for an easily implemented algorithm. Estimation of non-linear mixed effects models can be done by common methods for linear mixed effects models, and thus existing programs can be used after small modifications. The applicability of this algorithm in animal breeding was studied with simulation using a Gompertz function growth model in pigs. Two growth data sets were analyzed: a full set containing observations from the entire growing period, and a truncated time trajectory set containing animals slaughtered prematurely, which is common in pig breeding. The results from the 50 simulation replicates with full data set indicate that the linearization approach was capable of estimating the original parameters satisfactorily. However, estimation of the parameters related to adult weight becomes unstable in the case of a truncated data set.