Maximum and minimum metabolic rates in birds are flexible traits and such flexibility can be advantageous in variable climates.The climatic variability hypothesis(CVH)posits that more variable climates should result i...Maximum and minimum metabolic rates in birds are flexible traits and such flexibility can be advantageous in variable climates.The climatic variability hypothesis(CVH)posits that more variable climates should result in greater metabolic flexibility for geographically distinct populations.Whether the CVH applies to sympatric species occupying microclimates differing in variability is unknown.Microclimates of open habitats are likely more variable than those of sheltered habitats.If the CVH extends to microclimates,we expect birds from open habitats to show greater flexibility than those from sheltered habitats.To test this extension of the CVH,we compared seasonal variation in microclimates and metabolic rates for sympatric horned larks Eremophila alpestris,which occupy open habitats,and house sparrows Passer domesticus,which occupy sheltered habitats.We measured operative temperature(T_(e′) an integrative measure of the thermal environment),summit metabolic rate(M_(sum′) maximal cold-induced metabolic rate),and basal metabolic rate(BMR,minimal maintenance metabolic rate)in summer and winter.For both winter and summer,daily minimum Te was similar between open and sheltered habitats but maximum Te was higher for open habitats.Winter microclimates,however,were colder for open than for sheltered habitats after accounting for convective differences.Both species increased M_(sum) in winter,but seasonal M_(sum) flexibility was greater for larks(43%)than for sparrows(31%).Winter increases in BMR were 92.5% and 11% for larks and sparrows,respectively,with only the former attaining statistical significance.Moreover,species*season interactions in general linear models for whole-organism metabolic rates were significant for BMR and showed a similar,although not significant,pattern for M_(sum),with greater seasonal metabolic flexibility in horned larks than in house sparrows.These results suggest that extending the CVH to sympatric bird species occupying different microclimates may be valid.展开更多
Species distributed across wide elevational gradients are likely to experience local thermal adaptation and exhibit high thermal plasticity,as these gradients are characterised by steep environmental changes over shor...Species distributed across wide elevational gradients are likely to experience local thermal adaptation and exhibit high thermal plasticity,as these gradients are characterised by steep environmental changes over short geographic distances(i.e.,strong selection differentials).The prevalence of adaptive intraspecific variation in thermal tolerance with elevation remains unclear,however,particularly in freshwater taxa.We explored variation in upper and lower thermal limits and acclimation capacity among Iberian populations of adults of the widespread water beetle Agabus bipustulatus(Dytiscidae)across a 2000 m elevational gradient,from lowland to alpine areas.Since mean and extreme temperatures decline with elevation,we predicted that populations at higher elevations will show lower heat tolerance and higher cold tolerance than lowland ones.We also explored whether acclimation capacity is positively related with climatic variability across elevations.We found significant variation in thermal limits between populations of A.bipustulatus,but no evidence of local adaptation to different thermal conditions across the altitudinal gradient,as relationships between thermal limits and elevation or climatic variables were largely nonsignificant.Furthermore,plasticities of both upper and lower thermal limits were consistently low in all populations.These results suggest thermal niche conservatism in this species,likely due to gene flow counteracting the effects of divergent selection,or adaptations in other traits that buffer exposure to climate extremes.The limited adaptive potential and plasticity of thermal tolerance observed in A.bipustulatus suggest that even generalist species,distributed across wide environmental gradients,may have limited resilience to global warming.展开更多
文摘Maximum and minimum metabolic rates in birds are flexible traits and such flexibility can be advantageous in variable climates.The climatic variability hypothesis(CVH)posits that more variable climates should result in greater metabolic flexibility for geographically distinct populations.Whether the CVH applies to sympatric species occupying microclimates differing in variability is unknown.Microclimates of open habitats are likely more variable than those of sheltered habitats.If the CVH extends to microclimates,we expect birds from open habitats to show greater flexibility than those from sheltered habitats.To test this extension of the CVH,we compared seasonal variation in microclimates and metabolic rates for sympatric horned larks Eremophila alpestris,which occupy open habitats,and house sparrows Passer domesticus,which occupy sheltered habitats.We measured operative temperature(T_(e′) an integrative measure of the thermal environment),summit metabolic rate(M_(sum′) maximal cold-induced metabolic rate),and basal metabolic rate(BMR,minimal maintenance metabolic rate)in summer and winter.For both winter and summer,daily minimum Te was similar between open and sheltered habitats but maximum Te was higher for open habitats.Winter microclimates,however,were colder for open than for sheltered habitats after accounting for convective differences.Both species increased M_(sum) in winter,but seasonal M_(sum) flexibility was greater for larks(43%)than for sparrows(31%).Winter increases in BMR were 92.5% and 11% for larks and sparrows,respectively,with only the former attaining statistical significance.Moreover,species*season interactions in general linear models for whole-organism metabolic rates were significant for BMR and showed a similar,although not significant,pattern for M_(sum),with greater seasonal metabolic flexibility in horned larks than in house sparrows.These results suggest that extending the CVH to sympatric bird species occupying different microclimates may be valid.
基金supported by the R&D project id.PID2019-108895GB-I00funded by MCIN/AEI/10.13039/501100011033+3 种基金VI PPIT Universidad de Sevilla(IV.7 Ayuda Suplementaria a Grupos de Investigación por captación de fondos en las convocatorias de proyectos de investigación del Plan Estatal2020/1110)funded by a postdoctoral contract from the“Consejería de Economía,Conocimiento,Empresas y Universidad de la Junta de Andalucía-Fondo Social Europeo de Andalucía 2014-2020”(“Talento Doctores,PAIDI program”)funded by a postdoctoral contract from the“María Zambrano”program,by the Spanish“Ministerio de Universidades”(funded by European Union-NextGenerationEU)。
文摘Species distributed across wide elevational gradients are likely to experience local thermal adaptation and exhibit high thermal plasticity,as these gradients are characterised by steep environmental changes over short geographic distances(i.e.,strong selection differentials).The prevalence of adaptive intraspecific variation in thermal tolerance with elevation remains unclear,however,particularly in freshwater taxa.We explored variation in upper and lower thermal limits and acclimation capacity among Iberian populations of adults of the widespread water beetle Agabus bipustulatus(Dytiscidae)across a 2000 m elevational gradient,from lowland to alpine areas.Since mean and extreme temperatures decline with elevation,we predicted that populations at higher elevations will show lower heat tolerance and higher cold tolerance than lowland ones.We also explored whether acclimation capacity is positively related with climatic variability across elevations.We found significant variation in thermal limits between populations of A.bipustulatus,but no evidence of local adaptation to different thermal conditions across the altitudinal gradient,as relationships between thermal limits and elevation or climatic variables were largely nonsignificant.Furthermore,plasticities of both upper and lower thermal limits were consistently low in all populations.These results suggest thermal niche conservatism in this species,likely due to gene flow counteracting the effects of divergent selection,or adaptations in other traits that buffer exposure to climate extremes.The limited adaptive potential and plasticity of thermal tolerance observed in A.bipustulatus suggest that even generalist species,distributed across wide environmental gradients,may have limited resilience to global warming.
