Atomically dispersed Mn-N_(x) catalysts derived from Mn-hexamine coordination frameworks for oxygen reduction reaction

Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal-nitrogen-carbon catalysts for oxygen reduction reaction(ORR).Although rarely studied,Mn-N-C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis.Here,we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets(MnNCS)from an Mn-hexamine coordination framework.The atomically dispersed Mn-N_(4) sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure.The optimized MnNCS displayed an excellent ORR performance in half-cells(0.89 V vs.reversible hydrogen electrode(RHE)in base and 0.76 V vs.RHE in acid in half-wave potential)and Zn-air batteries(233 mW cm^(−2)in peak power density),along with significantly enhanced stability.Density functional theory calculations further corroborated that the Mn-N_(4)-C(12)site has favorable adsorption of*OH as the rate-determining step.These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.

Inverse of Rensch’s Rule of Allometry for Sexual Size Dimorphism in Bufo andrewsi

Difference in body size between males and females(sexual size dimorphism:SSD)and its variation are a common phenomenon in animal kingdom.Rensch’s rule predicts that the degree of SSD variation increases with the enlarged mean body size when males are larger than females and decreases when females are larger than males.Here,whether the patterns of variations in SSD in the Andrew’s toad(Bufo andrewsi)follow Rensch’s rule was tested using unpublished data from 14 populations and published data from 17 populations.Results show the reduced major axis regression of log10(male size)on log10(female size)across all populations displayed a significant hyperallometric relationship,which was consistent with inverse Rensch’s rule(the degree of SSD increased with enlarged mean body size).SSD could also be explained by sexual age difference(SAD)due to a positive SSD–SAD relationship among all populations.The findings suggest that the occurrence of inverse Rensch’s rule in B.andrewsi is likely to be a result of fecundity selection on increased reproductive investments in larger females.

Evidence for Expensive Tissue Hypothesis in the Asian Common Toad(Duttaphrynus melanostictus)

Dear Editor,Phenotypic plasticity of an organism by modifying morphological and physiological traits responding to diverse environments is widely recognized across animal taxa(Muñoz-Muñoz et al.,2021;Donihue et al.,2021;Giacomini et al.,2022;Zamora-Camacho et al.,2022;Jiang et al.,2022;Chen et al.,2023).The brain,as a critical phenotypic trait,displays a significant variation in size among different species(Striedter,2006).

Microhabitat Segregation of Parapatric Frogs in the Qinling Mountains

Coexistence mechanisms for species with similar ecological traits and overlapping geographic distributions are basic questions in ecology and evolutionary biology. Specific habitat requirements often limit distribution range as well as facilitate partitioning resource utilization in ecological similar species. Understanding niche segregation and differences in microhabitat utilization can contribute to identifying coexistence mechanisms between parapatric species. Feirana quadranus and F. taihangnica are two closely related frog species with parapatric geographic ranges and an elongated contact zone within the Qinling Mountains, which is an important watershed for East Asia. Here, we analysed the difference in microhabitat utilization between the two frog species and explored the key ecological factors that induced their microhabitat differentiation based on quadrats sampled in the contact zone. Our comparison of twenty environmental variables showed that both species used microhabitats with alkalescent warm water and gentle slope conditions. The principal component analysis indicated that climate-related variables, vegetation conditions, and river width were the important factors for microhabitat utilization of these species. These findings contribute to our understanding on the coexistence mechanisms of these two related and parapatric Asian mountain frog species. This study can also be helpful for identifying target habitats to conduct conservation actions and management strategies effectively in the face of environmental changes.

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.

Asymmetry of Testes in Guenther's Frog,Hylarana guentheri(Anuar:Ranidae)

Testes size in most animals commonly shows directional asymmetry. In birds, the left testis mass is usually larger than the right one, but the reports on the testes asymmetry in anurans are very few. Moller （1994） hypothesized that the right testis serves a compensatory role and increases in size when the left one is defective, and further suggested that testes asymmetry may be a reliable indicator of individual body condition. In this paper, we tested the compensation hypothesis in the Guenther＇s frog, Hylarana guentheri. From 60 sampled males, we found that there was a significant directional asymmetry in testes mass, with the left testis size being significantly correlated with relative testes asymmetry, providing evidence that the right testis had a compensatory function. However, testes mass and asymmetry were not correlated with body condition. Hence, we found no evidence that testes asymmetry in the Guenther＇s frog reflected male condition, and male age was also not related to testes mass or asymmetry.

Altitudinal Variation in Digestive Tract Lengh in Feirana quadranus

Selective pressures favor variation in organ size in response to environmental changes and evolutionary process. In particular, changes in environmental temperature and rainfall at different altitudes often affect food resources, thereby mediating energy intake and allocation. The digestive tract provided a functional relationship between energy intake and allocation, of which gut morphology was associated with diet changes and food quality under different environments. Here we studied altitudinal variation in the digestive tract across four Feirana quadranus populations and tested the hypothesis that relative size of digestive tract should increase with increasing altitude. The results showed that although significant variation in length of the digestive tract was observed in females among populations, altitudinal variation in relative length of digestive tract or gut was non-significant. In addition, the digestive tract length was not correlated with temperature and precipitation across the four populations. Our findings suggest that individuals living in low-temperature and-precipitation populations at high altitudes did not display longer digestive tract than high temperature and precipitation populations at low altitudes, possibly because of small populations or sample sizes.

Trophic Niche Shifts in Mountain Feirana Frogs under Human-mediated Habitat Transformations

Urbanization can induce environmental changes, disturbing habitat transformation process, and resulting in niche shift of species and local extinctions. Amphibians have experienced worldwide population declines, with ha bitat loss acting as one of the most disruptive causes. How amphibian species response to changing habitats could be reflected in their utilization and assimilation of resources. Using stable isotopes, we explored trophic niche variation between natural and transformed habitats for three closely related frog species in the genus Feirana(F. quadranus, F. taihangnica and F. kangxianensis). Our results indicated that the δ~(13)C value was negatively correlated with body size(snout-vent length) and the δ~(15)N value increased along with the ontogenetic process. The δ~(13)C values were significantly different among habitat types, and the variation of δ~(15)N values was relatively limited in different disturbed gradients. Urban groups displayed broader trophic niche width than both rural and natural groups. When species in sympatry, their resource utilization and trophic niche overlap probability were more similar in rural habitats than their natural counterparts. Our findings would be conducive to understand trophic niche and function variation in amphibians during the urbanization process, allowing for effective predictions of ecological consequences of habitat transformation. This study can also provide insight into conservation strategies for mountain amphibians in the Anthropocene.

Ecological and Geographical Reasons for the Variation of Digestive Tract Length in Anurans

Changes of environmental conditions can shape organs size evolution in animal kingdoms. In particular, environmental changes lead to difference in food resources between different habitats, thereby affecting individual’s energy intake and allocation. The digestive theory states that animals consuming food with low contents of digestible materials should result in increasing gut length. In this study, to test the hypothesis of digestive theory, we studied ecological and geographical reasons for variation in digestive tract length among 35 species of anurans distributing in different altitude and latitude. The results showed that ecological type significantly affected digestive tract length among species, with aquatic and terrestrial species having longer digestive tract than arboreal ones. Latitude was positively correlated with digestive tract length. However, altitude, as well as monthly mean temperature and precipitation, did not correlate with digestive tract length among species. Our findings suggest that aquatic and terrestrial species might forage less digestible materials than arboreal species, thereby displaying relatively longer digestive tract than arboreal species.

No Evidence for Significant Effect of Body Size and Age on Male Mating Success in the Spot-legged Treefrog

In anurans, body size and age of individuals generally affect male mating success. To test whether body size and age have effects on male mating success in the foam-nesting treefrog Polypedates megacephalus, a species widely distributed in China, we analyzed differences in body size and age between mated and unmated males for three populations using a Generalized Linear Mixed Model（GLMM）. The results showed that mated males did not exhibit larger body size and older age than unmated males, suggesting that large and/or old male individuals did not have greater mating success than small and/or young males. Moreover, we also found a non-significant size-assortative mating pattern for all populations. Our findings suggest that body size and age of the foam-nesting treefrog do not affect male mating success.

The Effects of Prey Items Diversity and Digestible Materials in Stomach on Digestive Tract Length in Hylarana guentheri

Difference in environmental condition shapes variation in digestive tract length in evolutionary process.In particular,environmental difference results in variation in food resource among different habitats,and thereby affecting energy intake and energy allocation.The digestive theory predicts that animals foraging high indigestible materials of stomach contents can promote the increased gut dimensions.Here,we studied variation in digestive tract and gut length across six Hylarana guentheri populations at different altitudes and latitudes to test the prediction of the digestive theory.We found that altitude and latitude did not affect variation in relative size of digestive tract and gut among populations.We also found that relative size of digestive tract and gut did not be correlated with diversity of prey items,but negatively correlated with proportion of digestible materials.Our findings suggest that individuals foraging less digestible materials display relatively longer digestive tract than individuals foraging more digestible materials.

No Evidence for the Compensation Hypothesis in the Swelled Vent Frog(Feirana quadranus)

The compensation hypothesis predicts that if the left testis is defective e.g.due to developmental stress,the increased right testis serves a compensatory role,and thereby displaying testes asymmetry which can be a reliable indicator of male body condition.Here,to test the prediction of the compensation hypothesis,we analyzed difference in size between left testis and right testis and the relationship between testes asymmetry and male body condition in the swelled vent frog(Feirana quadranus).We found that the left testis was larger than right testis,displaying a significant directional asymmetry in testes size.Although testes mass was correlated with body condition,testes asymmetry was not correlated with body condition,which cannot provide evidence that the right testis had a compensatory function.Our findings suggest no evidence for the compensation hypothesis in this species due to lacking the compensatory function in right testis.

Altitudinal Variation in Digestive Tract Length in Yunnan Pond Frog (Pelophylax pleuraden)

The digestive tract plays an important role in digestion and the acquisition of food energy. Understanding the impact of abiotic environments on digestive tract morphology is especially important for evolution of digestive tract across different environments. Here, we investigated altitudinal variation in digestive tract length in the Yunnan Pond Frog （Pelophylaxpleuraden） across five populations ranging from 1413 m to 1935 m a.s.1, in Ningnan County, Sichuan province in western China. Frogs were collected during the breeding season, from 1-5 June 2012. Our results revealed that females had longer digestive tract and relative digestive tract （i.e. digestive tract length / body size） lengths in com- parison to males, on average, but the differences between them decreased with increasing altitude. Digestive tract and relative digestive tract lengths increased with increasing altitude suggesting that a higher proportion of indigestible ma- terials may be consumed at high-altitude sites and result in a relative increase in digestive tract dimensions.

Age Structure of Two Species of Odorous Frogs(Odorrana margaretae and Odorrana grahami)

Variation in age structure and body size benefits are identified to understand the evolution of life history.Here,we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Odorrana grahami)by using skeletochronology.The ages at sexual maturity of O.grahami and O.margaretae in both sexes were 1 and 2 years,respectively.For both sexes,the maximum age observed in O.margaretae was six years.For O.grahami,the maximum age observed in males and females were 4 and 5 years,respectively.Males and females did not differ in mean age in the two species.The average body size of both species considerably differed between sexes,with females being larger than males.The body size of females was also larger than that of males when the effect of age was removed.We also found positive correlations between body size and age within each sex in O.margaretae,but only for female in O.grahami.The female-biased sexual size dimorphism of the two species suggested that fecundity selection for larger female size may increase the reproductive output.

Effects of Life Histories on Genome Size Variation in Squamata

Genome size changes significantly among taxonomic levels,and this variation is often related to the patterns shaped by the phylogeny,life histories and ecological factors.However,there are mixed evidences on the main factors affecting molecular evolution in animals.In this study,we used phylogenetic comparative analysis to investigate the evolutionary rate of genome size and the relationships between genome size and life histories(i.e.,hatchling mass,clutch size,clutches per year,age at sexual maturity,lifespan and body mass)among 199 squamata species.Our results showed that the evolutionary rate of genome size in Lacertilia was significantly faster than Serpentes.Moreover,we also found that larger species showed larger hatchling mass,more clutches per year and clutch size and longer lifespan.However,genome size was negatively associated with clutch size and clutches per year,but not associated with body mass we looked at.The findings suggest that larger species do not possess the evolution of large genomes in squamata.

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.

Chemical defense mediates population density-driven on anuran brain size evolution

Dear Editor,The evolutionary arms race between predator and prey is a strong selective force for producing a wide array of defense strategies in animals,including strong limbs,body armor,poisonousness,mimicry,or crypsis(Bednekoff,2006).

Large-brained birds display lower extra-pair paternity

Extra-pair paternity(EPP)benefits to improve the reproductive success via extra-pair fertilizations without the costs of parental care in males and through improved offspring quality with additional food and parental care in females among species of birds.Variations in the EPP appear to link to behavioral and ecological factors and sexual selection.According to the“relationship intelligence hypothesis”,the cognitive abilities of the birds play an important role in maintaining long-term relationships.Here,we undertook thefirst comparative test of the relationships between extra-pair paternity and brain size,testis size,and life histories among 315 species of birds using phylogenetically controlled comparative analyses and path analysis.After controlling for the effects of shared ancestry and body mass,the frequency of EPP was negatively correlated with relative brain size,but positively with testis size across species of birds.However,the frequency of EPP was not linked to life-history traits(e.g.incubation period,fledging period,clutch size,egg mass,and longevity).Ourfindings suggest that large-brained birds associated with enhanced cognitive abilities are more inclined to maintain long-term stable relationships with their mates and to mutualism with them than to increase the frequency of EPP.

Anuran brain size predicts food availability-driven population density

Dear Editor,The population density of organisms often varies widely among species in natural environments, and this variation is associated with body size and energy requirements(White et al., 2007). For example, large-bodied species usually require large areas to meet energetic requirements, which can provide species with more food abundance and lower population density. An earlier study has proposed that the energetic requirements are also related to brain size in animals(Mink et al., 1981).