Life History Variation in Female Gambusia hubbsi

Gambusia hubbsi populations occur in a variety of fresh and brackish-water habitats on Andros, Bahamas. These include shallow water sites (tidal creeks, lakes, roadside ditches), and blueholes (vertical solution caves). In some blueholes G. hubbsi is the only species present, in others it co-occurs with other species, principal among these is a predator, Eleotris pisonis. By contrast to blueholes, shallow water sites have highly variable temperature and depth. In addition, they are frequented by avian piscivores and may be occasionally occupied by piscivores such as Eleotris. We sampled 10 shallow water sites, 14 blueholes where Eleotris is absent and 12 blueholes where Eleotris co-occurs with G. hubbsi. We measured and compared variation in female body size, fecundity, and reproductive investment among these three habitats. The observed patterns of life history variation are only partially in accord with expectations from theory regarding the effects of predation and seasonality on life history variation. Samples from populations that colonized a series of man-made trenches (Well Fields), a set of introductions into that habitat, and changes in life history traits of lab-raised females from three blueholes, suggest that the observed pattern of life history variation in other habitats also reflects differences in food availability among habitats, and imperfectly reflects the potential phenotypic variability of this species.     

蝶类的生命周期——从卵到成虫

简要介绍了蝶类与蛾类的区别以及蝶类生命周期的分期,即卵期、幼虫期、蛹期、成虫期和休眠期,并比较详细地介绍了蝶类的卵、幼虫、蛹和成虫的形态、生态和生物学特性。     

Intrapopulation Genome Size Variation in D. melanogaster Reflects Life History Variation and Plasticity

We determined female genome sizes using flow cytometry for 211 Drosophila melanogaster sequenced inbred strains from the Drosophila Genetic Reference Panel, and found significant conspecific and intrapopulation variation in genome size. We also compared several life history traits for 25 lines with large and 25 lines with small genomes in three thermal environments, and found that genome size as well as genome size by temperature interactions significantly correlated with survival to pupation and adulthood, time to pupation, female pupal mass, and female eclosion rates. Genome size accounted for up to 23% of the variation in developmental phenotypes, but the contribution of genome size to variation in life history traits was plastic and varied according to the thermal environment. Expression data implicate differences in metabolism that correspond to genome size variation. These results indicate that significant genome size variation exists within D. melanogaster and this variation may impact the evolutionary ecology of the species. Genome size variation accounts for a significant portion of life history variation in an environmentally dependent manner, suggesting that potential fitness effects associated with genome size variation also depend on environmental conditions.     

Life History Dependent Behavioural Variation in Water Striders,Aquarius remigis

We investigated behavioural consequences of life history states in Aquarius (Gerris) remigis, a hemipteran surface predator and scavenger of small North American streams. A repeated-measures field study comparing reproductive and non-reproductive first summer generation females and males during the same time in summer showed that non-reproductive males and females, which were foraging to survive the winter, behaved essentially alike, often being territorial. In contrast, reproductives of both sexes were more mobile than non-reproductives, reproductive males being much more mobile than reproductive females, always in search of and attacking potential mates. This resulted in reproductive males showing litde territoriality and having lower foraging success than all other categories, while reproductive females had higher foraging success than non-reproductive females or males, thus likely increasing their fecundity. Many behavioural variables did not change with time. Exceptions were a decrease in the mating activity of reproductives of both sexes, the number of mating attempts, mobility, and the stride rate of reproductive males, and an increase in overall foraging activity of all individuals. This indicates that the behaviour of reproductive males converged towards that of non-reproductive males as the season progressed. Individuals were assigned to either state post-hoc according to whether they had been seen mating at least once during the study period (July and August). Females were further tested to ascertain if they laid eggs. These results support the hypothesis that diapause and reproductive state to some degree predetermine behaviour, thus constraining behavioural flexibility. Attributing behavioural variation to various proximate causes can be central to the interpretation of alternative strategies and tactics.     

Life History of Learning: Performance Curves of Honeybees in the Wild

Learning is probably a major contributor to fitness in most animals yet it has not been well integrated into life history research. To quantify the role of learning in shaping lifetime patterns of performance, we must measure learning in natural settings as well as in controlled experimental conditions. As a part of a long‐term project measuring the relative contributions of learning, physiology, and effort to observed patterns of lifetime performance, I quantified the foraging success of worker honeybees in the wild. Bees exhibited a four‐fold increase in the net rate of food delivery to the colony over their first 4 d as foragers. The major contributors to that pattern were decreases in departure weights and increases in arrival weights. Combined with previous research, this study suggests that learning is the major contributor to the observed increases in lifetime performance, whereas age‐specific changes in physiology and effort have a significant though lesser role.     

Genetic Variation for Life History Sensitivity to Seasonal Warming in Arabidopsis thaliana

Climate change has altered life history events in many plant species; however, little is known about genetic variation underlying seasonal thermal response. In this study, we simulated current and three future warming climates and measured flowering time across a globally diverse set of Arabidopsis thaliana accessions. We found that increased diurnal and seasonal temperature (1°–3°) decreased flowering time in two fall cohorts. The early fall cohort was unique in that both rapid cycling and overwintering life history strategies were revealed; the proportion of rapid cycling plants increased by 3–7% for each 1° temperature increase. We performed genome-wide association studies (GWAS) to identify the underlying genetic basis of thermal sensitivity. GWAS identified five main-effect quantitative trait loci (QTL) controlling flowering time and another five QTL with thermal sensitivity. Candidate genes include known flowering loci; a cochaperone that interacts with heat-shock protein 90; and a flowering hormone, gibberellic acid, a biosynthetic enzyme. The identified genetic architecture allowed accurate prediction of flowering phenotypes (R² > 0.95) that has application for genomic selection of adaptive genotypes for future environments. This work may serve as a reference for breeding and conservation genetic studies under changing environments.     

The Rate-Size Trade-Off Structures Intraspecific Variation in Daphnia ambigua Life History Parameters

The identification of trade-offs is necessary for understanding the evolution and maintenance of diversity. Here we employ the supply-demand (SD) body size optimization model to predict a trade-off between asymptotic body size and growth rate. We use the SD model to quantitatively predict the slope of the relationship between asymptotic body size and growth rate under high and low food regimes and then test the predictions against observations for Daphnia ambigua. Close quantitative agreement between observed and predicted slopes at both food levels lends support to the model and confirms that a ‘rate-size’ trade-off structures life history variation in this population. In contrast to classic life history expectations, growth and reproduction were positively correlated after controlling for the rate-size trade-off. We included 12 Daphnia clones in our study, but clone identity explained only some of the variation in life history traits. We also tested the hypothesis that growth rate would be positively related to intergenic spacer length (i.e. the growth rate hypothesis) across clones, but we found that clones with intermediate intergenic spacer lengths had larger asymptotic sizes and slower growth rates. Our results strongly support a resource-based optimization of body size following the SD model. Furthermore, because some resource allocation decisions necessarily precede others, understanding interdependent life history traits may require a more nested approach.     

Increased Extinction Potential of Insular Fish Populations with Reduced Life History Variation and Low Genetic Diversity

Theoretical work has shown that reduced phenotypic heterogeneity leads to population instability and can increase extinction potential, yet few examples exist of natural populations that illustrate how varying levels expressed diversity may influence population persistence, particularly during periods of stochastic environmental fluctuation. In this study, we assess levels of expressed variation and genetic diversity among demographically independent populations of tidewater goby (Eucyclogobius newberryi), show that reductions in both factors typically coincide, and describe how low levels of diversity contribute to the extinction risk of these isolated populations. We illustrate that, for this annual species, continuous reproduction is a safeguard against reproductive failure by any one population segment, as natural, stochastically driven salinity increases frequently result in high mortality among juvenile individuals. Several study populations deviated from the natural pattern of year-round reproduction typical for the species, rendering those with severely truncated reproductive periods vulnerable to extinction in the event of environmental fluctuation. In contrast, demographically diverse populations are more likely to persist through such periods through the continuous presence of adults with broader physiological tolerance to abrupt salinity changes. Notably, we found a significant correlation between genetic diversity and demographic variation in the study populations, which could be the result of population stressors that restrict both of these diversity measures simultaneously, or suggestive of a causative relationship between these population characteristics. These findings demonstrate the importance of biocomplexity at the population level, and assert that the maintenance of diversity contributes to population resilience and conservation of this endangered species.     

The Influence of Diurnal Temperature Variation on Degree-Day Accumulation and Insect Life History

Ectotherms, such as insects, experience non-constant temperatures in nature. Daily mean temperatures can be derived from the daily maximum and minimum temperatures. However, the converse is not true and environments with the same mean temperature can exhibit very different diurnal temperate ranges. Here we apply a degree-day model for development of the grape berry moth (Paralobesia viteana, a significant vineyard pest in the northeastern USA) to investigate how different diurnal temperature range conditions can influence degree-day accumulation and, hence, insect life history. We first consider changes in diurnal temperature range independent of changes in mean temperatures. We then investigate grape berry moth life history under potential climate change conditions, increasing mean temperature via variable patterns of change to diurnal temperature range. We predict that diurnal temperature range change can substantially alter insect life history. Altering diurnal temperature range independent of the mean temperature can affect development rate and voltinism, with the magnitude of the effects dependent on whether changes occur to the daily minimum temperature (Tmin), daily maximum temperature (Tmax), or both. Allowing for an increase in mean temperature produces more marked effects on life history but, again, the patterns and magnitude depend on the nature of the change to diurnal temperature range together with the starting conditions in the local environment. The study highlights the importance of characterizing the influence of diurnal temperature range in addition to mean temperature alone.     

生长素信号转导途径与植物胁迫反应相互作用的证据(英)

生长素影响植物多种生理过程 ,有报道显示生长素可能影响植物对逆境胁迫的反应。我们利用cDNA阵列技术鉴定拟南芥 (Arabidopsisthaliana (L .)Heynh .)的生长素应答基因 ,发现多个胁迫应答基因受生长素抑制 ,包括ArabidopsishomologofMEKkinase1(ATMEKK1) ,RelA/SpoThomolog 3(At_RSH3) ,Catalase 1(Cat1)和Ferritin 1(Fer1) ,说明生长素可调节胁迫应答基因的表达。此外 ,我们还证明吲哚乙酸 (IAA)合成途径中的腈水解酶基因nitrilase 1(NIT1)和nitrilase 2 (NIT2 )受盐胁迫诱导 ,提示在逆境条件下IAA的合成可能随之增加。我们利用生长素不敏感突变体研究生长素与逆境反应相互作用的信号转导 ,发现胁迫应答基因在野生型和生长素不敏感突变体auxinresistant2 (axr2 )中可被盐胁迫诱导 ,而在auxinresistant1_3(axr1_3)中则不被诱导 ,说明生长素与逆境胁迫反应的相互作用可能发生在泛素途径。     

生长素信号转导途径与植物胁迫反应相互作用的证据

生长素影响植物多种生理过程,有报道显示生长素可能影响植物对逆境胁迫的反应.我们利用cDNA阵列技术鉴定拟南芥(Arabidopsis thaliana (L.) Heynh.)的生长素应答基因,发现多个胁迫应答基因受生长素抑制,包括Arabidopsis homolog of MEK kinase1 (ATMEKK1),RelA/SpoT homolog 3 (At-RSH3),Catalase 1 (Cat1) 和Ferritin 1 (Fer1),说明生长素可调节胁迫应答基因的表达.此外,我们还证明吲哚乙酸(IAA)合成途径中的腈水解酶基因nitrilase 1 (NIT1) 和nitrilase 2 (NIT2) 受盐胁迫诱导,提示在逆境条件下IAA的合成可能随之增加.我们利用生长素不敏感突变体研究生长素与逆境反应相互作用的信号转导,发现胁迫应答基因在野生型和生长素不敏感突变体auxin resistant 2 (axr2) 中可被盐胁迫诱导,而在auxin resistant 1-3 (axr1-3)中则不被诱导,说明生长素与逆境胁迫反应的相互作用可能发生在泛素途径.     

Countryside Stewardship Scheme and Butterflies: A Study of Plant and Butterfly Species Richness

Butterfly and plant species richness were recorded from 1997 to 2000 on 2 and 6 m grass margins created at three farms in Essex which had entered the Countryside Stewardship Scheme (CSS) in October 1996. On both the 2 and 6 m margins there was a significant relationship between the length of hedgerow and the number of plant species observed on the margins, but the seed mixtures used may not have been ideal and natural regeneration should not have been used on the clay soils of Essex. Butterfly species richness was significantly greater on the 2 m margins than on the control sections, and was greater when a higher number of grass species were included in the original seed mixture. Plant species richness was greater on the 6 m margins when established by natural regeneration. CSS grass margins could be improved as butterfly habitats if they are linked to existing habitats such as hedgerows, are sown with a better range of native grasses and herbs and are managed in a way more conducive to wildlife. These changes to the policy of establishment of CSS margins could help combat habitat loss and fragmentation within the countryside.     

Evolutionary History and Novel Biotic Interactions Determine Plant Responses to Elevated CO2 and Nitrogen Fertilization

A major frontier in global change research is predicting how multiple agents of global change will alter plant productivity, a critical component of the carbon cycle. Recent research has shown that plant responses to climate change are phylogenetically conserved such that species within some lineages are more productive than those within other lineages in changing environments. However, it remains unclear how phylogenetic patterns in plant responses to changing abiotic conditions may be altered by another agent of global change, the introduction of non-native species. Using a system of 28 native Tasmanian Eucalyptus species belonging to two subgenera, Symphyomyrtus and Eucalyptus, we hypothesized that productivity responses to abiotic agents of global change (elevated CO₂ and increased soil N) are unique to lineages, but that novel interactions with a non-native species mediate these responses. We tested this hypothesis by examining productivity of 1) native species monocultures and 2) mixtures of native species with an introduced hardwood plantation species, Eucalyptus nitens, to experimentally manipulated soil N and atmospheric CO₂. Consistent with past research, we found that N limits productivity overall, especially in elevated CO₂ conditions. However, monocultures of species within the Symphyomyrtus subgenus showed the strongest response to N (gained 127% more total biomass) in elevated CO₂ conditions, whereas those within the Eucalyptus subgenus did not respond to N. Root:shoot ratio (an indicator of resource use) was on average greater in species pairs containing Symphyomyrtus species, suggesting that functional traits important for resource uptake are phylogenetically conserved and explaining the phylogenetic pattern in plant response to changing environmental conditions. Yet, native species mixtures with E. nitens exhibited responses to CO₂ and N that differed from those of monocultures, supporting our hypothesis and highlighting that both plant evolutionary history and introduced species will shape community productivity in a changing world.     

Stoichiometry of Energy Coupling by Proton-Translocating ATPases: A History of Variability

One of the central energy-coupling reactions in living systems is the intraconversion of ATP with a transmembrane proton gradient, carried out by proton-translocating F- and V-type ATPases/synthases. These reversible enzymes can hydrolyze ATP and pump protons, or can use the energy of a transmembrane proton gradient to synthesize ATP from ADP and inorganic phosphate. The stoichiometry of these processes (H⁺/ATP, or coupling ratio) has been studied in many systems for many years, with no universally agreed upon solution. Recent discoveries concerning the structure of the ATPases, their assembly and the stoichiometry of their numerous subunits, particularly the proton-carrying proteolipid (subunit c) of the F_O and V₀ sectors, have shed new light on this question and raise the possibility of variable coupling ratios modulated by variable proteolipid stoichiometries.