LIFE-CYCLE EVOLUTION AS RESPONSE TO DIVERSE LAKE HABITATS IN PALEOZOIC AMPHIBIANS

The evolution of life cycles forms the subject of numerous studies on extant organisms, but is rarely documented in the fossil record. Here, I analyze patterns of development in time-averaged samples of late Carboniferous and early Permian amphibians, and compare them to paleoecological patterns derived from the same deposits located within a large sedimentary basin (Saar-Nahe, Germany). In 300-297 million years (myr) old Sclerocephalus haeuseri (1–1.7 m), adult size, morphology, and the course of ontogeny varied with respect to the habitats in which the species existed. These differences are best exemplified by ontogenetic trajectories, which reveal a full range of modifications correlating with environmental parameters (lake properties, food resources, competitors). In a 2- to 3-myr-long interval, six different lake habitats were inhabited by this species, which responded to changes by modification of growth rate, adult size, developmental sequence, skeletal features, prey preference, and relative degree of terrestriality.     

The importance of listening: juvenile allocation shifts in response to acoustic cues of the social environment

The social environment has a strong effect on the strength and direction of sexual selection. Juveniles, however, often have social cues that signal the current competitive environment which may provide cues of future competitive challenges. Here we demonstrate that juvenile crickets (Teleogryllus commodus) use the calls of surrounding adult males as a cue of the quality and density of rivals/mates they are likely to encounter. We reared hatchling crickets in six acoustic environments that varied in the density and quality of calls and demonstrate that individuals modified their development rate, phenotype and behaviour at maturity. Males matured more rapidly at a smaller size and called more when reared in a low competition environment. In contrast, males delayed maturity to grow larger when faced with an increased density of high-quality males. Females matured more rapidly when reared in a high density of high-quality males and allocated proportionately more resources towards egg production. A second experiment limiting nutrient availability demonstrates sex-specific allocation shifts in the last stadium when cues are most reliable. Our results demonstrate that the social environment significantly affects allocation strategies and phenotypes, highlighting the importance of juvenile experience and competitive context when examining fitness and selection.     

Evolution and plasticity of anuran larval development in response to desiccation. A comparative analysis

Anurans breed in a variety of aquatic habitats with contrasting levels of desiccation risk, which may result in selection for faster development during larval stages. Previous studies suggest that species in ephemeral ponds reduce their developmental times to minimize desiccation risks, although it is not clear how variation in desiccation risk affects developmental strategies in different species. Employing a comparative phylogenetic approach including data from published and unpublished studies encompassing 62 observations across 30 species, we tested if species breeding in ephemeral ponds (High risk) develop faster than those from permanent ponds (Low risk) and/or show increased developmental plasticity in response to drying conditions. Our analyses support shorter developmental times in High risk, primarily by decreasing body mass at metamorphosis. Plasticity in developmental times was small and did not differ between groups. However, accelerated development in High risk species generally resulted in reduced sizes at metamorphosis, while some Low risk species were able compensate this effect by increasing mean growth rates. Taken together, our results suggest that plastic responses in species breeding in ephemeral ponds are constrained by a general trade-off between development and growth rates.     

Flexibility in reproductive timing in human females: integrating ultimate and proximate explanations

From an ultimate perspective, the age of onset of female reproduction should be sensitive to variation in mortality rates, and variation in the productivity of non-reproductive activities. In accordance with this prediction, most of the cross-national variation in women's age at first birth can be explained by differences in female life expectancies and incomes. The within-country variation in England shows a similar pattern: women have children younger in neighbourhoods where the expectation of healthy life is shorter and incomes are lower. I consider the proximate mechanisms likely to be involved in producing locally appropriate reproductive decisions. There is evidence suggesting that developmental induction, social learning and contextual evocation may all play a role.     

Genetic variation in pathogen-induced early hatching of toad embryos

Accelerated hatching is one of few defences available to embryos, and is effective against many egg-stage risks. We present the first analysis of genetic variation in hatching plasticity, examining premature hatching of American toad embryos in response to pathogenic water moulds. We reared eggs from half- and full-sib families in the presence and absence of water mould. Hatching age and hatchling size showed low cross-environment genetic correlations, suggesting that early-induced hatching can evolve largely independently of spontaneous hatching. We found less phenotypic and additive genetic variation for early-induced hatching than spontaneous hatching, and a stronger correlation between egg and induced hatchling sizes. Directional selection by the pathogen may have eroded variation in early-induced hatching, pushing it against the constraint of hatching gland development. Later hatching has a second, muscular component. This pattern of variation may characterize defences based on developmental transitions, although other inducible defences show more variation in induced phenotypes.     

中国省级火电供应生命周期清单分析

应用生命周期评价方法,建立了我国各省区的火电供应生命周期清单。清单分析结果表明,我国各省区单位火电供应的生命周期清单之间,及与全国单位火电供应的生命周期清单之间均存在一定差异,以总能源投入和全球变暖潜值为例进行了分析。在全球变暖潜值方面,我国单位火电供应的平均值为1.05kg/k Wh。云南等15个省区的单位火电全球变暖潜值与全国平均水平相差±10%以上。如果基于全国单位火电供应的平均全球变暖潜值计算各省火电总量全球变暖潜值,与基于各省单位火电全球变暖潜值计算的结果相比,也存在一定的差距。15个省区与基于全国平均值计算的结果相差±10%以上,表明了核算各省区火电清单的必要性。中国省级火电供应生命周期清单为省区级别的材料、产品、产业等生命周期评价提供数据支撑,也为各省区电力节能减排提供了理论基础。     

Early-life conditions and age at first pregnancy in British women

There is growing evidence that the reproductive schedules of female mammals can be affected by conditions experienced during early development, with low parental investment leading to accelerated life-history strategies in the offspring. In humans, the relationships between early-life conditions and timing of puberty are well studied, but much less attention has been paid to reproductive behaviour. Here, we investigate associations between early-life conditions and age at first pregnancy (AFP) in a large, longitudinally studied cohort of British women (n = 4553). Low birthweight for gestational age, short duration of breastfeeding, separation from mother in childhood, frequent family residential moves and lack of paternal involvement are all independently associated with earlier first pregnancy. Apart from that of birthweight, the effects are robust to adjustment for family socioeconomic position (SEP) and the cohort member's mother's age at her birth. The association between childhood SEP and AFP is partially mediated by early-life conditions, and the association between early-life conditions and AFP is partially mediated by emotional and behavioural problems in childhood. The overall relationship between early-life adversities and AFP appears to be approximately additive.