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Schou MF, Cornwallis CK. Adaptation to fluctuating temperatures across life stages in endotherms. Trends Ecol Evol 2024:S0169-5347(24)00123-X. [PMID: 38902165 DOI: 10.1016/j.tree.2024.05.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Revised: 05/16/2024] [Accepted: 05/24/2024] [Indexed: 06/22/2024]
Abstract
Accelerating rates of climate change have intensified research on thermal adaptation. Increasing temperature fluctuations, a prominent feature of climate change, means that the persistence of many species depends on both heat and cold tolerance across the entire life cycle. In endotherms, research has focused on specific life stages, with changes in thermoregulation across life rarely being examined. Consequently, there is a need to (i) analyse how heat and cold tolerance mechanisms coevolve, and (ii) test whether antagonistic effects between heat and cold tolerance across different life stages limit thermal adaptation. Information on genes influencing heat and cold tolerance and how they are expressed through life will enable more accurate modelling of species vulnerabilities to future climatic volatility.
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Affiliation(s)
- Mads F Schou
- Department of Biology, Aarhus University, 8000 Aarhus, Denmark.
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2
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Domínguez-Guerrero SF, Esquerré D, Burress ED, Maciel-Mata CA, Alencar LRV, Muñoz MM. Viviparity imparts a macroevolutionary signature of ecological opportunity in the body size of female Liolaemus lizards. Nat Commun 2024; 15:4966. [PMID: 38862522 PMCID: PMC11167029 DOI: 10.1038/s41467-024-49464-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 06/05/2024] [Indexed: 06/13/2024] Open
Abstract
Viviparity evolved ~115 times across squamate reptiles, facilitating the colonization of cold habitats, where oviparous species are scarce or absent. Whether the ecological opportunity furnished by such colonization reconfigures phenotypic diversity and accelerates evolution is unclear. We investigated the association between viviparity and patterns and rates of body size evolution in female Liolaemus lizards, the most species-rich tetrapod genus from temperate regions. Here, we discover that viviparous species evolve ~20% larger optimal body sizes than their oviparous relatives, but exhibit similar rates of body size evolution. Through a causal modeling approach, we find that viviparity indirectly influences body size evolution through shifts in thermal environment. Accordingly, the colonization of cold habitats favors larger body sizes in viviparous species, reconfiguring body size diversity in Liolaemus. The catalyzing influence of viviparity on phenotypic evolution arises because it unlocks access to otherwise inaccessible sources of ecological opportunity, an outcome potentially repeated across the tree of life.
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Affiliation(s)
| | - Damien Esquerré
- School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, NSW, 2522, Australia
| | - Edward D Burress
- Department of Ecology and Evolutionary Biology, Yale University, 06511, New Haven, CT, USA
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, 35487, USA
| | - Carlos A Maciel-Mata
- Predio Intensivo de Manejo de Vida Silvestre X-Plora Reptilia, 43350, Metztitlán, Hidalgo, México
| | - Laura R V Alencar
- Department of Ecology and Evolutionary Biology, Yale University, 06511, New Haven, CT, USA
| | - Martha M Muñoz
- Department of Ecology and Evolutionary Biology, Yale University, 06511, New Haven, CT, USA
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3
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Xu M, Wang G, Liu P, He Z, He K, Cheng Z, Wang Z, Chen W, Li Z, Zhang L. Age structure and body size of two Tibetan toad ( Bufo tibetanus) populations from different elevations in China. Ecol Evol 2024; 14:e11559. [PMID: 38863720 PMCID: PMC11165260 DOI: 10.1002/ece3.11559] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 05/21/2024] [Accepted: 05/28/2024] [Indexed: 06/13/2024] Open
Abstract
Understanding how age and body size vary across elevations can provide insights into the evolution of life-history traits in animals. In the present study, we compared the demographic (using skeletochronology) and morphological traits of the Tibetan toad (Bufo tibetanus) between two populations from different elevational habitats (2650 vs. 3930 m). We found that (1) the mean age and body size of females were significantly greater than those of males in both populations; (2) both sexes of toads from the higher elevation tended to be significantly older in age and larger in body size; (3) there was a significant positive relationship between age and body size within each sex of the toad at both elevations; and (4) growth rates varied between the two populations, with the higher rate observed in the lower-elevation population. Our results suggested that factors other than age, such as elevation-associated temperature, influence the observed differences in body size between the two populations. Future research at a broader range of elevations should focus on these factors and evaluate their influence on animal growth patterns.
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Affiliation(s)
- Mengshuang Xu
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Gege Wang
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Putong Liu
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Zhuolin He
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Kaiqin He
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Zhiqiang Cheng
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Ziqi Wang
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
| | - Wei Chen
- School of Resources and Environmental EngineeringAnhui UniversityHefeiAnhuiChina
| | - Zhibing Li
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
- The Observation and Research Field Station of Taihang Mountain Forest Ecosystems of Henan Province, Puyang Field Scientific Observation and Research Station for Yellow River Wetland Ecosystem and Research Center for ecological management and protection of the Yellow River BasinHenanChina
| | - Lixia Zhang
- Department of Ecology, College of Life SciencesHenan Normal UniversityXinxiangHenanChina
- The Observation and Research Field Station of Taihang Mountain Forest Ecosystems of Henan Province, Puyang Field Scientific Observation and Research Station for Yellow River Wetland Ecosystem and Research Center for ecological management and protection of the Yellow River BasinHenanChina
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Hay EM, McGee MD, White CR, Chown SL. Body size shapes song in honeyeaters. Proc Biol Sci 2024; 291:20240339. [PMID: 38654649 PMCID: PMC11040244 DOI: 10.1098/rspb.2024.0339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2024] [Accepted: 03/22/2024] [Indexed: 04/26/2024] Open
Abstract
Birdsongs are among the most distinctive animal signals. Their evolution is thought to be shaped simultaneously by habitat structure and by the constraints of morphology. Habitat structure affects song transmission and detectability, thus influencing song (the acoustic adaptation hypothesis), while body size and beak size and shape necessarily constrain song characteristics (the morphological constraint hypothesis). Yet, support for the acoustic adaptation and morphological constraint hypotheses remains equivocal, and their simultaneous examination is infrequent. Using a phenotypically diverse Australasian bird clade, the honeyeaters (Aves: Meliphagidae), we compile a dataset consisting of song, environmental, and morphological variables for 163 species and jointly examine predictions of these two hypotheses. Overall, we find that body size constrains song frequency and pace in honeyeaters. Although habitat type and environmental temperature influence aspects of song, that influence is indirect, likely via effects of environmental variation on body size, with some evidence that elevation constrains the evolution of song peak frequency. Our results demonstrate that morphology has an overwhelming influence on birdsong, in support of the morphological constraint hypothesis, with the environment playing a secondary role generally via body size rather than habitat structure. These results suggest that changing body size (a consequence of both global effects such as climate change and local effects such as habitat transformation) will substantially influence the nature of birdsong.
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Affiliation(s)
- Eleanor M. Hay
- School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
| | - Matthew D. McGee
- School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
| | - Craig R. White
- School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
| | - Steven L. Chown
- School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
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Names GR, Grindstaff JL, Westneat DF, Heidinger BJ. Climate change and its effects on body size and shape: the role of endocrine mechanisms. Philos Trans R Soc Lond B Biol Sci 2024; 379:20220509. [PMID: 38310941 PMCID: PMC10838645 DOI: 10.1098/rstb.2022.0509] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 11/21/2023] [Indexed: 02/06/2024] Open
Abstract
In many organisms, rapidly changing environmental conditions are inducing dramatic shifts in diverse phenotypic traits with consequences for fitness and population viability. However, the mechanisms that underlie these responses remain poorly understood. Endocrine signalling systems often influence suites of traits and are sensitive to changes in environmental conditions; they are thus ideal candidates for uncovering both plastic and evolved consequences of climate change. Here, we use body size and shape, a set of integrated traits predicted to shift in response to rising temperatures with effects on fitness, and insulin-like growth factor-1 as a case study to explore these ideas. We review what is known about changes in body size and shape in response to rising temperatures and then illustrate why endocrine signalling systems are likely to be critical in mediating these effects. Lastly, we discuss research approaches that will advance understanding of the processes that underlie rapid responses to climate change and the role endocrine systems will have. Knowledge of the mechanisms involved in phenotypic responses to climate change will be essential for predicting both the ecological and the long-term evolutionary consequences of a warming climate. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.
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Affiliation(s)
- Gabrielle R. Names
- Department of Biological Sciences, North Dakota State University, 1340 Bolley Drive, Fargo, ND 58102, USA
- Biology Department, California Lutheran University, 60 West Olsen Road, Thousand Oaks, CA 91360, USA
| | | | - David F. Westneat
- Department of Biology, University of Kentucky, 101 Morgan Building, Lexington, KY 40506, USA
| | - Britt J. Heidinger
- Department of Biological Sciences, North Dakota State University, 1340 Bolley Drive, Fargo, ND 58102, USA
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McQueen A, Barnaby R, Symonds MRE, Tattersall GJ. Birds are better at regulating heat loss through their legs than their bills: implications for body shape evolution in response to climate. Biol Lett 2023; 19:20230373. [PMID: 37990562 PMCID: PMC10663788 DOI: 10.1098/rsbl.2023.0373] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 11/01/2023] [Indexed: 11/23/2023] Open
Abstract
Endotherms use their appendages-such as legs, tails, ears and bills-for thermoregulation by controlling blood flow to near-surface blood vessels, conserving heat when it is cold, and dissipating heat in hot conditions. Larger appendages allow greater heat dissipation, and appendage sizes vary latitudinally according to Allen's rule. However, little is known about the relative importance of different appendages for thermoregulation. We investigate physiological control of heat loss via bird bills and legs using infrared thermography of wild birds. Our results demonstrate that birds are less able to regulate heat loss via their bills than their legs. In cold conditions, birds lower their leg surface temperature to below that of their plumage surface, retaining heat at their core. In warm conditions, birds increase their leg surface temperature to above that of their plumage surface, expelling heat. By contrast, bill surface temperature remains approximately 2°C warmer than the plumage surface, indicating consistent heat loss under almost all conditions. Poorer physiological control of heat loss via bird bills likely entails stronger selection for shorter bills in cold climates. This could explain why bird bills show stronger latitudinal size clines than bird legs, with implications for predicting shape-shifting responses to climate change.
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Affiliation(s)
- Alexandra McQueen
- Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, VIC 3125, Australia
| | - Ryan Barnaby
- Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, VIC 3125, Australia
| | - Matthew R. E. Symonds
- Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Burwood, VIC 3125, Australia
| | - Glenn J. Tattersall
- Department of Biological Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario, Canada L2S 3A1
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Tabh JKR, Nord A. Temperature-dependent Developmental Plasticity and Its Effects on Allen's and Bergmann's Rules in Endotherms. Integr Comp Biol 2023; 63:758-771. [PMID: 37160342 PMCID: PMC10503470 DOI: 10.1093/icb/icad026] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 05/02/2023] [Accepted: 05/04/2023] [Indexed: 05/11/2023] Open
Abstract
Ecogeographical rules, describing common trends in animal form across space and time, have provided key insights into the primary factors driving species diversity on our planet. Among the most well-known ecogeographical rules are Bergmann's rule and Allen's rule, with each correlating ambient temperature to the size and shape of endotherms within a species. In recent years, these two rules have attracted renewed research attention, largely with the goal of understanding how they emerge (e.g., via natural selection or phenotypic plasticity) and, thus, whether they may emerge quickly enough to aid adaptations to a warming world. Yet despite this attention, the precise proximate and ultimate drivers of Bergmann's and Allen's rules remain unresolved. In this conceptual paper, we articulate novel and classic hypotheses for understanding whether and how plastic responses to developmental temperatures might contributed to each rule. Next, we compare over a century of empirical literature surrounding Bergmann's and Allen's rules against our hypotheses to uncover likely avenues by which developmental plasticity might drive temperature-phenotype correlations. Across birds and mammals, studies strongly support developmental plasticity as a driver of Bergmann's and Allen's rules, particularly with regards to Allen's rule. However, plastic contributions toward each rule appear largely non-linear and dependent upon: (1) efficiency of energy use (Bergmann's rule) and (2) thermal advantages (Allen's rule) at given ambient temperatures. These findings suggest that, among endotherms, rapid changes in body shape and size will continue to co-occur with our changing climate, but generalizing the direction of responses across populations is likely naive.
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Affiliation(s)
- Joshua K R Tabh
- Lund University, Department of Biology, Section for Evolutionary Ecology, Sölvegatan 37, SE-223 62, Sweden
| | - Andreas Nord
- Lund University, Department of Biology, Section for Evolutionary Ecology, Sölvegatan 37, SE-223 62, Sweden
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Liu P, Lou Y, Yao J, Wang L, Møller AP, Sun Y. Variation in bill surface area is associated with local climatic factors across populations of the plain laughingthrush. Ecol Evol 2023; 13:e10535. [PMID: 37780534 PMCID: PMC10534077 DOI: 10.1002/ece3.10535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Revised: 05/31/2023] [Accepted: 09/01/2023] [Indexed: 10/03/2023] Open
Abstract
Recent studies have found that avian bill and tarsus morphology may have evolved in response to climatic conditions, and these organs play important roles in thermoregulation and water retention in extreme environments. Here, we examined whether bill surface area and tarsus length were associated with climatic conditions in the plain laughingthrush, Garrulax davidi, which mainly occurs in north China and occupies several climatic zones from east to west. We measured bill surface area and tarsus length in 321 adults from 11 populations, almost encompassing all habitat types of the species. We analyzed the relationships among these morphological traits and local climatic factors. Bill surface area was positively correlated with maximum temperature, indicating that bill surface area tended to be larger in hotter environments. Furthermore, we found a negative relationship among bill surface area and winter precipitation, indicating that bill surface area tended to be larger in arid areas. However, we did not find any relationships between tarsus length and climatic factors. These results suggest that local climates may shape the evolution of bill morphology divergence, and summer seems to be the critical season for thermoregulation in this temperate zone passerine.
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Affiliation(s)
- Pengfei Liu
- School of Life Science and TechnologyLongdong UniversityQingyangChina
| | - Yingqiang Lou
- Key Laboratory of Animal Ecology and Conservation BiologyInstitute of Zoology, Chinese Academy of ScienceBeijingChina
| | - Jingxiao Yao
- School of Life Science and TechnologyLongdong UniversityQingyangChina
| | - Linghui Wang
- School of Life Science and TechnologyLongdong UniversityQingyangChina
| | - Anders Pape Møller
- Ecologie Systématique Evolution, Université Paris–Sud, CNRS, AgroParisTechUniversité Paris–SaclayOrsay CedexFrance
| | - Yuehua Sun
- Key Laboratory of Animal Ecology and Conservation BiologyInstitute of Zoology, Chinese Academy of ScienceBeijingChina
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Liu J, Chai Z, Wang H, Ivanov A, Kubelka V, Freckleton R, Zhang Z, Székely T. Egg characteristics vary longitudinally in Arctic shorebirds. iScience 2023; 26:106928. [PMID: 37305692 PMCID: PMC10250164 DOI: 10.1016/j.isci.2023.106928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Revised: 04/16/2023] [Accepted: 05/16/2023] [Indexed: 06/13/2023] Open
Abstract
Arctic environments are changing rapidly and if we are to understand the resilience of species to future changes, we need to investigate alterations in their life histories. Egg size and egg shape are key life-history traits, reflecting parental investment as well as influencing future reproductive success. Here we focus on egg characteristics in two Arctic shorebirds, the Dunlin (Calidris alpina) and the Temminck's stint (Calidris temminckii). Using egg photos that encompass their full breeding ranges, we show that egg characteristics exhibit significant longitudinal variations, and the variation in the monogamous species (Dunlin) is significantly greater than the polygamous species (Temminck's stint). Our finding is consistent with the recent "disperse-to-mate" hypothesis which asserts that polygamous species disperse further to find mates than monogamous species, and by doing so they create panmictic populations. Taken together, Arctic shorebirds offer excellent opportunities to understand evolutionary patterns in life history traits.
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Affiliation(s)
- Jin Liu
- Key Laboratory for Biodiversity Science and Ecological Engineering, College of Life Sciences, Beijing Normal University, Beijing 100875, China
- Institute of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China
| | - Ziwen Chai
- Key Laboratory for Biodiversity Science and Ecological Engineering, College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Hui Wang
- Key Laboratory for Biodiversity Science and Ecological Engineering, College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Anton Ivanov
- Timiryazev State Biological Museum, Malaya Grusinskaya, 15, Moscow 123242, Russia
- All-Russian Research Institute for Environmental Protection (ARRIEP), 36 km MKAD, Moscow 117628, Russia
| | - Vojtěch Kubelka
- Department of Zoology and Centre for Polar Ecology, Faculty of Science, University of South Bohemia, Branišovská 1760, České Budejovice 37005, Czech Republic
| | - Robert Freckleton
- Ecology and Evolutionary Biology, School of Biosciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK
| | - Zhengwang Zhang
- Key Laboratory for Biodiversity Science and Ecological Engineering, College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Tamás Székely
- Department of Evolutionary Zoology and Human Biology, Faculty of Science, University of Debrecen, Egyetem tér 1, Debrecen, Hungary
- Milner Centre for Evolution, University of Bath, Claverton Down, Bath BA2 7AY, UK
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Chaves JN, Tattersall GJ, Andrade DV. Energetic costs of bill heat exchange demonstrate contributions to thermoregulation at high temperatures in toco toucans (Ramphastos toco). J Exp Biol 2023; 226:286952. [PMID: 36752123 DOI: 10.1242/jeb.245268] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Accepted: 01/31/2023] [Indexed: 02/09/2023]
Abstract
Body temperature regulation under changes in ambient temperature involves adjustments in heat production and heat exchange rates between the animal and the environment. One mechanism involves the modulation of the surface temperature of specific areas of the body through vasomotor adjustment. In homeotherms, this thermoregulatory adjustment is essential for the maintenance of body temperature over a moderate temperature range, known as the thermal neutral zone (TNZ). The bill of the toco toucan (Ramphastos toco) has been described as a highly efficient thermal window and hypothesized to assist in the thermal homeostasis of this bird. Herein, we directly evaluated the contribution of heat exchange through the bill of the toco toucan and role of the bill in the delimitation of the TNZ. To do this, we measured metabolic rate (MR), via oxygen consumption, over a range of ambient temperatures from 0 to 35°C. MR measurements were made in birds with the bill intact and with the bill insulated. The limits of the TNZ did not differ between treatments, ranging from 10.8 to 25.0°C. The MR differed among treatments only at elevated temperatures (30 and 35°C), reaching 0.92±0.11 ml O2 g-1 h-1 (mean±s.d.) for the intact group and 1.13±0.13 ml O2 g-1 h-1 for the insulated group. These results indicate that although heat dissipation through the bill does not contribute significantly to widening of the TNZ, it may well be critically important in assisting body temperature regulation at higher temperatures extending above the upper limit of the TNZ.
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Affiliation(s)
- Jussara N Chaves
- Departamento de Biodiversidade, Instituto de Biociências, Universidade Estadual Paulista, 13506-900 Rio Claro, São Paulo, Brazil
| | - Glenn J Tattersall
- Department of Biological Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada
| | - Denis V Andrade
- Departamento de Biodiversidade, Instituto de Biociências, Universidade Estadual Paulista, 13506-900 Rio Claro, São Paulo, Brazil
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Allometry reveals trade-offs between Bergmann's and Allen's rules, and different avian adaptive strategies for thermoregulation. Nat Commun 2023; 14:1101. [PMID: 36843121 PMCID: PMC9968716 DOI: 10.1038/s41467-023-36676-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Accepted: 02/10/2023] [Indexed: 02/28/2023] Open
Abstract
Animals tend to decrease in body size (Bergmann's rule) and elongate appendages (Allen's rule) in warm climates. However, it is unknown whether these patterns depend on each other or constitute independent responses to the thermal environment. Here, based on a global phylogenetic comparative analysis across 99.7% of the world's bird species, we show that the way in which the relative length of unfeathered appendages co-varies with temperature depends on body size and vice versa. First, the larger the body, the greater the increase in beak length with temperature. Second, the temperature-based increase in tarsus length is apparent only in larger birds, whereas in smaller birds, tarsus length decreases with temperature. Third, body size and the length of beak and tarsus interact with each other to predict the species' environmental temperature. These findings suggest that the animals' body size and shape are products of an evolutionary compromise that reflects distinct alternative thermoregulatory adaptations.
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