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Roger S. Seymour - One of the best experts on this subject based on the ideXlab platform.
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A review of the energetics of pollination biology
Journal of Comparative Physiology B, 2013Co-Authors: Kimberly P. Mccallum, Freya O. Mcdougall, Roger S. SeymourAbstract:Pollination biology is often associated with mutualistic interactions between plants and their animal pollen vectors, with energy rewards as the foundation for co-evolution. Energy is supplied as food (often nectar from flowers) or as heat (in sun-tracking or thermogenic plants). The requirements of pollinators for these resources depend on many factors, including the costs of living, locomotion, thermoregulation and behaviour, all of which are influenced by body size. These requirements are modified by the availability of energy offered by plants and environmental conditions. Endothermic insects, birds and bats are very effective, because they move faster and are more independent of environmental temperatures, than are ectothermic insects, but they are energetically costly for the plant. The body size of endothermic pollinators appears to be influenced by opposing requirements of the animals and plants. Large body size is advantageous for endotherms to retain heat. However, plants select for small body size of endotherms, as energy costs of larger size are not matched by increases in flight speed. If high energy costs of Endothermy cannot be met, birds and mammals employ daily torpor, and large insects reduce the frequency of facultative Endothermy. Energy uptake can be limited by the time required to absorb the energy or eliminate the excess water that comes with it. It can also be influenced by variations in climate that determine temperature and flowering season.
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Endothermy of dynastine scarab beetles cyclocephala colasi associated with pollination biology of a thermogenic arum lily philodendron solimoesense
The Journal of Experimental Biology, 2009Co-Authors: Roger S. Seymour, Craig R White, Marc GibernauAbstract:SUMMARY Cyclocephala colasi beetles are facultative endotherms that spend most of their adult lives inside the inflorescences of Philodendron solimoesense , where ambient temperature ( T a ) averages about 28°C due to floral thermogenesis. Measurements of respiration within a range of T a showed that active beetles became spontaneously endothermic at T a below 28°C but were rarely endothermic above it. There was no evidence of Endothermy within the inflorescences, indicating that activities in the floral chamber can occur without the high energy expense of Endothermy. Bouts of Endothermy occurred at lower T a in respirometer chambers mainly in the evening, when the insects normally fly from one inflorescence to another, and during the night, when they normally eat and mate within the inflorescence. Patterns of Endothermy in individual episodes were studied in non-flying beetles with respirometry and infrared thermal imaging. Heat was generated in the thorax by oscillatory waves of respiration that were coupled with thoracic temperature ( T th ) increases. Stationary beetles could regulate T th at about 33°C independently of T a between 16 and 29°C. At T a =20°C, this represents a 116-fold increase in metabolic rate over resting, ectothermic values. Endothermy was clearly a requirement for flight, and beetles departing inflorescences warmed to about 30°C before take-off. During flight, T th was dependent on T a , decreasing from 37 to 28°C at T a of 37 to 20°C, respectively. The lowest T a at which flight could occur was about 20°C. Thermal conductance of stationary, endothermic beetles increased at higher metabolic rates, probably because of increased ventilatory heat loss.
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evidence for endothermic ancestors of crocodiles at the stem of archosaur evolution
Physiological and Biochemical Zoology, 2004Co-Authors: Roger S. Seymour, Christina L Bennettstamper, Sonya D Johnston, David R Carrier, Gordon C. GriggAbstract:Physiological, anatomical, and developmental features of the crocodilian heart support the paleontological evidence that the ancestors of living crocodilians were active and endothermic, but the lineage reverted to ectothermy when it invaded the aquatic, ambush predator niche. In endotherms, there is a functional nexus between high metabolic rates, high blood flow rates, and complete separation of high systemic blood pressure from low pulmonary blood pressure in a four-chambered heart. Ectotherms generally lack all of these characteristics, but crocodilians retain a four-chambered heart. However, crocodilians have a neurally controlled, pulmonary bypass shunt that is functional in diving. Shunting occurs outside of the heart and involves the left aortic arch that originates from the right ventricle, the foramen of Panizza between the left and right aortic arches, and the cog-tooth valve at the base of the pulmonary artery. Developmental studies show that all of these uniquely crocodilian features are secondarily derived, indicating a shift from the complete separation of blood flow of endotherms to the controlled shunting of ectotherms. We present other evidence for Endothermy in stem archosaurs and suggest that some dinosaurs may have inherited the trait.
Frank Seebacher - One of the best experts on this subject based on the ideXlab platform.
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Is Endothermy an Evolutionary By-Product?
Trends in ecology & evolution, 2020Co-Authors: Frank SeebacherAbstract:Endothermy alters the energetic relationships between organisms and their environment and thereby influences fundamental niches. Endothermy is closely tied to energy metabolism. Regulation of energy balance is indispensable for all life and regulatory pathways increase in complexity from bacteria to vertebrates. Increasing complexity of metabolic networks also increase the probability for endothermic phenotypes to appear. Adaptive arguments are problematic epistemologically because the regulatory mechanisms enabling Endothermy have not evolved for the 'purpose' of Endothermy and the utility of current traits is likely to have changed over evolutionary time. It is most parsimonious to view Endothermy as the evolutionary by-product of energy balance regulation rather than as an adaptation and interpret its evolution in the context of metabolic networks.
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The evolution of Endothermy is explained by thyroid hormone- mediated responses to cold in early vertebrates
Journal of Experimental Biology, 2014Co-Authors: Alexander G. Little, Frank SeebacherAbstract:The evolution of Endothermy is one of the most intriguing and consistently debated topics in vertebrate biology, but the proximate mechanisms that mediated its evolution are unknown. Here, we suggest that the function of thyroid hormone in regulating physiological processes in response to cold is key to understanding the evolution of Endothermy. We argue that the capacity of early chordates to produce thyroid hormone internally was the first step in this evolutionary process. Selection could then act on the capacity of thyroid hormone to regulate metabolism, muscle force production and cardiac performance to maintain their function against the negative thermodynamic effects of decreasing temperature. Thyroid-mediated cold acclimation would have been the principal selective advantage. The actions of thyroid hormone during cold acclimation in zebrafish are very similar to its role during endothermic thermogenesis. The thyroid-mediated increases in metabolism and locomotor performance in ectotherms eventually resulted in sufficient heat production to affect body temperature. From this point onwards, increased body temperature per se could be of selective advantage and reinforce thyroid-induced increases in physiological rates. Selection for increased body temperature would promote those mechanisms that maximise heat production, such as increased Na + /K + -ATPase activity, futile cycling by SERCA, and mitochondrial uncoupling, all of which are regulated by thyroid hormone. The specific end point of this broader evolutionary process would be endothermic thermoregulation. However, considering the evolution of Endothermy in isolation is misleading because the selective advantages that drove the evolutionary process were independent from Endothermy. In other words, without the selective advantages of thyroid-mediated cold acclimation in fish, there would be no endotherms.
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Dinosaur body temperatures: the occurrence of Endothermy and ectothermy
Paleobiology, 2003Co-Authors: Frank SeebacherAbstract:Despite numerous studies, the thermal physiology of dinosaurs remains unresolved. Thus, perhaps the commonly asked question whether dinosaurs were ectotherms or endotherms is inappropriate, and it is more constructive to ask which dinosaurs were likely to have been en- dothermic and which ones ectothermic. Field data from crocodiles over a large size range show that body temperature fluctuations decrease with increasing body mass, and that average daily body temperatures increase with increasing mass. A biophysical model, the biological relevance of which was tested against field data, was used to predict body temperatures of dinosaurs. However, rather than predicting thermal relations of a hypothetical dinosaur, the model considered correct paleogeographical distribution and climate to predict the thermal relations of a large number of dinosaurs known from the fossil record ( .700). Many dinosaurs could have had ''high'' ($308C) and stable (daily amplitude #28C) body temperatures without metabolic heat production even in winter, so it is unlikely that selection pressure would have favored the evolution of elevated resting metabolic rates in those species. Recent evidence of ontogenetic growth rates indicates that even the juveniles of large species (3000-4000 kg) could have had biologically functional body temper- ature ranges during early development. Smaller dinosaurs (,100 kg) at mid to high latitudes (.458) could not have had high and stable body temperatures without metabolic heat production. How- ever, elevated metabolic rates were unlikely to have provided selective advantage in the absence of some form of insulation, so probably insulation was present before Endothermy evolved, or else it coevolved with elevated metabolic rates. Superimposing these findings onto a phylogeny of the Dinosauria suggests that Endothermy most likely evolved among the Coelurosauria and, to a lesser extent, among the Hypsilophodontidae, but not among the Stegosauridae, Nodosauridae, Anky- losauridae, Hadrosauridae, Ceratopsidae, Prosauropoda, and Sauropoda.
Barry G. Lovegrove - One of the best experts on this subject based on the ideXlab platform.
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A phenology of the evolution of Endothermy in birds and mammals
Biological reviews of the Cambridge Philosophical Society, 2016Co-Authors: Barry G. LovegroveAbstract:Recent palaeontological data and novel physiological hypotheses now allow a timescaled reconstruction of the evolution of Endothermy in birds and mammals. A three-phase iterative model describing how Endothermy evolved from Permian ectothermic ancestors is presented. In Phase One I propose that the elevation of Endothermy - increased metabolism and body temperature (Tb ) - complemented large-body-size homeothermy during the Permian and Triassic in response to the fitness benefits of enhanced embryo development (parental care) and the activity demands of conquering dry land. I propose that Phase Two commenced in the Late Triassic and Jurassic and was marked by extreme body-size miniaturization, the evolution of enhanced body insulation (fur and feathers), increased brain size, thermoregulatory control, and increased ecomorphological diversity. I suggest that Phase Three occurred during the Cretaceous and Cenozoic and involved endothermic pulses associated with the evolution of muscle-powered flapping flight in birds, terrestrial cursoriality in mammals, and climate adaptation in response to Late Cenozoic cooling in both birds and mammals. Although the triphasic model argues for an iterative evolution of Endothermy in pulses throughout the Mesozoic and Cenozoic, it is also argued that Endothermy was potentially abandoned at any time that a bird or mammal did not rely upon its thermal benefits for parental care or breeding success. The abandonment would have taken the form of either hibernation or daily torpor as observed in extant endotherms. Thus torpor and hibernation are argued to be as ancient as the origins of Endothermy itself, a plesiomorphic characteristic observed today in many small birds and mammals.
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increased homeothermy during reproduction in a basal placental mammal
The Journal of Experimental Biology, 2014Co-Authors: Danielle L Levesque, Barry G. LovegroveAbstract:Homeothermic Endothermy, the maintenance of a high and stable body temperature (Tb) using heat produced by elevated metabolism, is energetically expensive. There is increasing evidence that the earliest endotherms were heterotherms that, rather than maintaining strict homeothermy, allowed Tb to fluctuate with large variations between active and rest-phase Tb. The high level of homeothermy observed in modern mammals is therefore likely to have evolved from an ancestral heterothermic state. One of the hypotheses for the evolution of Endothermy is that homeothermy allows for greater energetic output during reproduction (parental care model). We tested this hypothesis by measuring metabolic rates over a range of ambient temperatures in both reproductive and non-reproductive greater hedgehog tenrecs (Setifer setosus), a physiologically primitive mammal from Madagascar. Tenrecs have some of the lowest metabolic rates and highest levels of Tb variability of any mammal and are therefore good models of the ancestral eutherian state. During pregnancy and lactation, there was an increase in metabolism and Tb below the thermoneutral zone, accompanied by a decrease in Tb variability. The lower critical limit of the thermoneutral zone was estimated at ~25°C. However, whereas increases in resting metabolism were substantial below 20°C (up to 150% higher during reproduction), daytime rest-phase ambient temperatures at the study site rarely reached equivalent low levels. Thus, S. setosus provide an example for how relatively low-cost increases in homeothermy could have led to substantial increases in fitness by allowing for the faster production of young. The mechanisms necessary for increases in thermogenesis during reproduction would have further benefited the development of homeothermy in mammals.
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the evolution of Endothermy in cenozoic mammals a plesiomorphic apomorphic continuum
Biological Reviews, 2012Co-Authors: Barry G. LovegroveAbstract:The evolution of Endothermy in birds and mammals was one of the most important events in the evolution of the vertebrates. Past tests of hypotheses on the evolution of Endothermy in mammals have relied largely on analyses of the relationship between basal and maximum metabolic rate, and artificial selection experiments. I argue that components of existing hypotheses, as well as new hypotheses, can be tested using an alternative macrophysiological modeling approach by examining the development of Endothermy during the Cenozoic. Recent mammals display a 10°C range in body temperature which is sufficiently large to identify the selective forces that have driven the development of Endothermy from a plesiomorphic (ancestral) Cretaceous or Jurassic condition. A model is presented (the Plesiomorphic-Apomorphic Endothermy Model, PAE Model) which proposes that heterothermy, i.e. bouts of normothermy (constant body temperature) interspersed with adaptive heterothermy (e.g. daily torpor and/or hibernation), was the ancestral condition from which apomorphic (derived), rigid homeothermy evolved. All terrestrial mammal lineages are examined for existing data to test the model, as well as for missing data that could be used to test the model. With the exception of Scandentia and Dermoptera, about which little is known, all mammalian orders that include small-sized mammals (<500 g), have species which are heterothermic and display characteristics of Endothermy which fall somewhere along a plesiomorphic-apomorphic continuum. Orders which do not have heterothermic representatives (Cetartiodactyla, Perissodactyla, Pholidota, and Lagomorpha) are comprised of medium- to large-sized mammals that have either lost the capacity for heterothermy, or in which heterothermy has yet to be measured. Mammalian heterothermy seems to be plesiomorphic and probably evolved once in the mammalian lineage. Several categories of Endothermy are identified (protoEndothermy, plesioEndothermy, apoEndothermy, basoEndothermy, mesoEndothermy, supraEndothermy, and reversed mesoEndothermy) to describe the evolution of Endothermy during the Cenozoic. The PAE Model should facilitate the testing of hypotheses using a range of macrophysiological methods (e.g. the comparative method and the reconstruction of ancestral states).
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perspectives of Endothermy revisited the endothermic temperature range
Journal of Thermal Biology, 1991Co-Authors: Barry G. Lovegrove, Gerhard Heldmaier, Thomas RufAbstract:Abstract 1. 1. Theoretical predictions and verifications from the literature of various body temperature patterns in small mammals indicate (a) labile core (abdominal) temperature regulation, (b) marked skin temperature regulation (direct and indirect evidence), and (c) evidence of extra-hypopthelamic setpoint temperatures. 2. 2. Adopting a concept of conductance and heat production optimization in terms of the range of Tas experienced daily or seasonally, the (a) low TRMRs of desert and arboreal endotherms, (b) high Tbs of birds, and (c) the absolute Tbs of all endotherms, are predirected are verified. 3. 3. Definitions of various critical Tbs are presented whicha llow a more analytical evaluation of species-specific Tbs and intra- and interspecific Tb comparisons. Two “endothermic temperature range” statistics are proposed which quantify the range of ambient temperatures over which an endotherm can remain potentially active.
Nicholas J Marra - One of the best experts on this subject based on the ideXlab platform.
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comparative transcriptomics of elasmobranchs and teleosts highlight important processes in adaptive immunity and regional Endothermy
BMC Genomics, 2017Co-Authors: Nicholas J Marra, Vincent P Richards, Angela M Early, Steve M Bogdanowicz, Paulina Pavinski D Bitar, Michael J Stanhope, Mahmood S ShivjiAbstract:Comparative genomic and/or transcriptomic analyses involving elasmobranchs remain limited, with genome level comparisons of the elasmobranch immune system to that of higher vertebrates, non-existent. This paper reports a comparative RNA-seq analysis of heart tissue from seven species, including four elasmobranchs and three teleosts, focusing on immunity, but concomitantly seeking to identify genetic similarities shared by the two lamnid sharks and the single billfish in our study, which could be linked to convergent evolution of regional Endothermy. Across seven species, we identified an average of 10,877 Swiss-Prot annotated genes from an average of 32,474 open reading frames within each species’ heart transcriptome. About half of these genes were shared between all species while the remainder included functional differences between our groups of interest (elasmobranch vs. teleost and endotherms vs. ectotherms) as revealed by Gene Ontology (GO) and selection analyses. A repeatedly represented functional category, in both the uniquely expressed elasmobranch genes (total of 259) and the elasmobranch GO enrichment results, involved antibody-mediated immunity, either in the recruitment of immune cells (Fc receptors) or in antigen presentation, including such terms as “antigen processing and presentation of exogenous peptide antigen via MHC class II”, and such genes as MHC class II, HLA-DPB1. Molecular adaptation analyses identified three genes in elasmobranchs with a history of positive selection, including legumain (LGMN), a gene with roles in both innate and adaptive immunity including producing antigens for presentation by MHC class II. Comparisons between the endothermic and ectothermic species revealed an enrichment of GO terms associated with cardiac muscle contraction in endotherms, with 19 genes expressed solely in endotherms, several of which have significant roles in lipid and fat metabolism. This collective comparative evidence provides the first multi-taxa transcriptomic-based perspective on differences between elasmobranchs and teleosts, and suggests various unique features associated with the adaptive immune system of elasmobranchs, pointing in particular to the potential importance of MHC Class II. This in turn suggests that expanded comparative work involving additional tissues, as well as genome sequencing of multiple elasmobranch species would be productive in elucidating the regulatory and genome architectural hallmarks of elasmobranchs.
John A. Ruben - One of the best experts on this subject based on the ideXlab platform.
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The evolution of Endothermy in terrestrial vertebrates: Who? When? Why?
Physiological and biochemical zoology : PBZ, 2004Co-Authors: Willem J. Hillenius, John A. RubenAbstract:Abstract Avian and mammalian Endothermy results from elevated rates of resting, or routine, metabolism and enables these animals to maintain high and stable body temperatures in the face of variable ambient temperatures. Endothermy is also associated with enhanced stamina and elevated capacity for aerobic metabolism during periods of prolonged activity. These attributes of birds and mammals have greatly contributed to their widespread distribution and ecological success. Unfortunately, since few anatomical/physiological attributes linked to Endothermy are preserved in fossils, the origin of Endothermy among the ancestors of mammals and birds has long remained obscure. Two recent approaches provide new insight into the metabolic physiology of extinct forms. One addresses chronic (resting) metabolic rates and emphasizes the presence of nasal respiratory turbinates in virtually all extant endotherms. These structures are associated with recovery of respiratory heat and moisture in animals with high resting m...