Large-brained birds lay smaller but heavier clutches

The brain is among the most energetically costly organs in vertebrates,and thus trade-offs have been hypothesized to exert constraints on brain size evolution.The energy trade-off hypothesis(ETH) predicts that reducing the energy consumption of reproduction or other costly tissues should compensate for the cost of a large brain.Egg production in birds requires a large proportion of the total energy budget,and a clutch mass in some bird species can outweigh the body mass of the female.To date,this hypothesis has mainly been tested in mammals and ectothermic animals such as anurans and fishes.We collated data on adult brain size,body mass and eggproduction traits such as clutch size,egg mass and annual broods from published studies,and conducted a phylogenetic comparative test of the interplay between egg-production investment and brain size evolution across bird species.After controlling for phylogenetic relationships and body size,we find a negative correlation between brain size and clutch size across 1395 species,which favored ETH.However,when egg mass was integrated in models,positive associations were detected between brain size and mass of eggs(via egg mass,clutch mass and annual total egg mass).Our results suggest that brain size trades off against egg-production only via certain aspects(e.g.,clutch size).By contrast,a positive relationship between brain size and total egg reproduction(e.g.,clutch mass and annual total egg mass) implied increased total energy budget outweighing energy allocation across bird species.Our study shows that there is no general energy trade-off between brain size and eggreproduction investment,and suggests that brain size evolution follows mixed strategies across bird species.

A Review for Life-history Traits Variation in Frogs Especially for Anurans in China

Environmental variation can promote differentiation in life-history traits in species of anurans. Increased environmental stress usually results in larger age at sexual maturity, older mean age, longer longevity, slower growth, larger body size, and a shift in reproductive allocation from offspring quantity to quality, and a stronger trade-off between offspring size and number. However, previous studies have suggested that there are inconsistent geographical variations in life-history traits among anuran species in China. Hence, we here review the intraspecific patterns and differences in life-history traits（i.e., egg size, clutch size, testes size, sperm length, age at sexual maturity, longevity, body size and sexual size dimorphism） among different populations within species along geographical gradients for anurans in China in recent years. We also provide future directions for studying difference in sperm performance between longer and shorter sperm within a species through transplant experiments and the relationships between metabolic rate and brain size and life-history.

Different strategies in biomass allocation across elevation in two Gentiana plants on the Yunnan-Guizhou Plateau, China

Patterns of biomass allocation among organs in plants are important because they influence many growth processes.The Yunnan-Guizhou Plateau(YGP)is considered to be one of the most sensitive areas in China to climate changes,but we know little about how current climatic gradients on the plateau influence plant biomass allocation.Gentiana rigescens and G.rhodantha,on the YGP,are important species because they are used in traditional Chinese medicines.We therefore analyzed the biomass allocation patterns of the two species across an elevation gradient(1000–2810 m a.s.l.)on the YGP to understand and predict the impact of climate change on these plant species.We found that the total biomass,reproductive biomass,vegetative biomass,aboveground biomass,and belowground biomass in G.rigescens were all significantly larger than those in G.rhodantha(p<0.05).However,for both species the aboveground biomass was nearly isometrically related to belowground biomass,regardless of elevation,mean annual temperature(MAT)ranging from 8.4℃t to 18.8℃t,and mean annual precipitation(MAP)ranging from 681 to 1327 mm,while the reproductive biomass was allometrically related to vegetative biomass.Intriguingly,there was a significant positive relationship(p<0.05)between the slope of the allometric scaling of reproductive and vegetative biomass and elevation among G.rigescens populations,i.e.plants growing at high elevationsallocate proportionately more biomass to reproduction at larger sizes and less at smaller sizes than plants growing at lower elevations.However,for G.rhodantha the reproductive allocation was negatively correlated with latitude.The results suggested different strategies in reproductive allocation in the two Gentiana plants on the YGP.Further studies are needed to investigate other environmental factors,such as nutrients and light,and genetic factors,in order to understand the trend of reproductive allometry along the environmental gradients.Our study has implications for the management and conservation practices of the two Gentiana species.

Age,growth and reproduction of Sarcocheilichthys nigripinnis from the Qingyi Stream in the Huangshan Mountains

Identifying the life-history strategies of fish and their associations with the surrounding environment is the basic foundation in the conservation and sustainable utilization of fish species.We examined the age,growth,and reproduction of Sarcocheilichthys nigripinnis using 352 specimens collected monthly from May 2009 to April 2010 in the Qingyi Stream.We found the sex ratio of this study population was 0.58:1(female:male),significantly different from expected 1:1.Females and males both comprised four age groups.The annuli on the scales were formed during February and March.No obvious between-sex difference was observed in length-weight and length-scale-radius relationships.The total length in back-calculation significantly increased with age for both sexes,but did not differ significantly at each age between the two sexes.An inflection point was observed in the growth curves given by the von Bertalanffy growth function for total weight.At this inflection point,fish were 3.95 years.Both sexes reach their 50%sex maturity at age 2,when females and males were 94.7 mm and 103.0 mm total length.The temporal pattern of the gonado-somatic index corresponded to a spawning period that occurred from April through July.The non-synchronicity of egg diameter in each mature ovary during the breeding period suggested these fish may be batch spawners.The absolute fecundity increased significantly with total length and weight,whereas no significant correlation was observed between the relative fecundity and body size.

Inter-individual variation in provisioning rate,prey size and number,and links to total prey biomass delivered to nestlings in the Collared Flycatcher(Ficedula albicollis)

Background:In bird species where offspring growth and survival rely on parents’food provisioning,parents can maximise their fitness by increasing the quantity and/or the quality of preys delivered to their offspring.Many studies have focused on inter-individual variation in feeding rate,yet this measure may not accurately reflect the total amount of food(i.e.energy)provided by parents if there is large variation in the quantity and quality of preys at each feeding.Here,we explored the relative role of individual(sex,age,body condition),breeding(hatching date,brood size)and environmental(temperature)factors on feeding rate,prey number,size and quality,and their contribution to total prey biomass delivered to the nestlings of 164 Collared Flycatcher(Ficedula albicollis)parents in 98 nests.Results:Preys delivered to the nest were mainly larvae(53.6%)and flying insects(45.6%).Feeding rate increased with brood size and age,and was higher in males than females.Mean prey number decreased,but mean prey size increased,as the season progressed and parents feeding their brood with primary larvae brought more preys per visit.Relationships between feeding rate,mean prey number and size remained when taking into account the provision-ing quality:parents brought either a large number of small prey or a small number of larger items,and the force of the trade-offs between feeding rate and mean prey number and size depended on the quality of the provisioning of the parents.Whatever the percentage of larvae among preys in the provisioning,the variance in total prey biomass was foremost explained by feeding rate(65.1%to 76.6%)compared to mean prey number(16.4%to 26%)and prey size(2.7%to 4%).Conclusions:Our study shows that variation in feeding rate,prey number,size,but not quality(i.e.percentage of lar-vae),were influenced by individual factors(sex and age)and breeding decisions(brood size and timing of breeding)and that,whatever the provisioning strategy adopted,feeding rate was the best proxy of the total biomass delivered to the nestlings.

Nest complexity correlates with larger brain size but smaller body mass across bird species

Amniotes differ substantially in absolute and relative brain size after controlling for allometry,and numerous hypotheses have been proposed to explain brain size evolution.Brain size is thought to correlate with processing capacity and the brain’s ability to support complex manipulation such as nest-building skills.The increased complexity of nest structure is supposed to be a measure of an ability to manipulate nesting material into the required shape.The degree of nest-structure complexity is also supposed to be associated with body mass,partly because small species lose heat faster and delicate and insulated nests are more crucial for temperature control of eggs during incubation by small birds.Here,we conducted comparative analyses to test these hypotheses by investigating whether the complexity of species-typical nest structure can be explained by brain size and body mass(a covariate also to control for allometric effects on brain size)across 1353 bird species from 147 families.Consistent with these hypotheses,our results revealed that avian brain size increases as the complexity of the nest structure increases after controlling for a significant effect of body size,and also that a negative relationship exists between nest complexity and body mass.

Latitudinal and seasonal variation in reproductive effort of the eastern fence lizard (Sceloporus undulatus)

Geographic variation in life-history traits among populations of wide-ranging species is influenced by both spa­tial and temporal aspects of the environment. Rarely, however, are the effects of both aspects examined concur­rently. We collected gravid female lizards (Sceloporus undulatus) from northern (Indiana), central (Mississippi) and southern (Florida) populations, spanning nearly the full latitudinal range of the species, to examine among-population differences in strategies of reproductive energy allocation. Adult females from the southern popula­tion were smaller, and produced fewer and smaller eggs in their first clutches than did females from the more northern populations. Southern females were more likely to produce a second clutch, and second clutches were smaller than first clutches for females from the 2 northern populations. Together these trends eliminated popu­lation differences in overall reproductive output after accounting for body size. The trend for greater reproduc­tive energy to be allocated to first clutches at higher latitudes, and to later clutches at lower latitudes is corrobo­rated by published data from field studies on multiple populations. Distributing reproductive effort by producing more clutches of smaller eggs may be an adaptive response to the long season available for egg incubation and lizard activity in sub-tropical southern environments. In contrast, allocating greater resources to early reproduc­tion may enhance maternal fitness in the relatively short activity seasons that characterize more northern sites.