Whole-body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians

First published: 10 December 2021The whole-body (tachymetabolic) endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. That assumption is consistent with current acceptance that the non-shivering thermogenesis (NST) component of regulatory body heat originates differently in each group: from skeletal muscle in birds and from brown adipose tissue (BAT) in mammals. However, BAT is absent in monotremes, marsupials, and many eutherians, all whole-body endotherms. Indeed, recent research implies that BAT-driven NST originated more recently and that the biochemical processes driving muscle NST in birds, many modern mammals and the ancestors of both may be similar, deriving from controlled 'slippage' of Ca2+ from the sarcoplasmic reticulum Ca2+ -ATPase (SERCA) in skeletal muscle, similar to a process seen in some fishes. This similarity prompted our realisation that the capacity for whole-body endothermy could even have pre-dated the divergence of Amniota into Synapsida and Sauropsida, leading us to hypothesise the homology of whole-body endothermy in birds and mammals, in contrast to the current assumption of their independent (convergent) evolution. To explore the extent of similarity between muscle NST in mammals and birds we undertook a detailed review of these processes and their control in each group. We found considerable but not complete similarity between them: in extant mammals the 'slippage' is controlled by the protein sarcolipin (SLN), in birds the SLN is slightly different structurally and its role in NST is not yet proved. However, considering the multi-millions of years since the separation of synapsids and diapsids, we consider that the similarity between NST production in birds and mammals is consistent with their whole-body endothermy being homologous. If so, we should expect to find evidence for it much earlier and more widespread among extinct amniotes than is currently recognised. Accordingly, we conducted an extensive survey of the palaeontological literature using established proxies. Fossil bone histology reveals evidence of sustained rapid growth rates indicating tachymetabolism. Large body size and erect stature indicate high systemic arterial blood pressures and four-chambered hearts, characteristic of tachymetabolism. Large nutrient foramina in long bones are indicative of high bone perfusion for rapid somatic growth and for repair of microfractures caused by intense locomotion. Obligate bipedality appeared early and only in whole-body endotherms. Isotopic profiles of fossil material indicate endothermic levels of body temperature. These proxies led us to compelling evidence for the widespread occurrence of whole-body endothermy among numerous extinct synapsids and sauropsids, and very early in each clade's family tree. These results are consistent with and support our hypothesis that tachymetabolic endothermy is plesiomorphic in Amniota. A hypothetical structure for the heart of the earliest endothermic amniotes is proposed. We conclude that there is strong evidence for whole-body endothermy being ancient and widespread among amniotes and that the similarity of biochemical processes driving muscle NST in extant birds and mammals strengthens the case for its plesiomorphy.Gordon Grigg, Julia Nowack, José Eduardo Pereira Wilken Bicudo, Naresh Chandra Bal, Holly N. Woodward and Roger S. Seymou

AbeTx1 is a novel sea anemone toxin with a dual mechanism of action on Shaker-type K+ channels activation

Voltage-gated potassium (KV) channels regulate diverse physiological processes and are an important target for developing novel therapeutic approaches. Sea anemone (Cnidaria, Anthozoa) venoms comprise a highly complex mixture of peptide toxins with diverse and selective pharmacology on KV channels. From the nematocysts of the sea anemone Actinia bermudensis, a peptide that we named AbeTx1 was purified and functionally characterized on 12 different subtypes of KV channels (KV1.1–KV1.6; KV2.1; KV3.1; KV4.2; KV4.3; KV11.1; and, Shaker IR), and three voltage-gated sodium channel isoforms (NaV1.2, NaV1.4, and BgNaV). AbeTx1 was selective for Shaker-related K+ channels and is capable of inhibiting K+ currents, not only by blocking the K+ current of KV1.2 subtype, but by altering the energetics of activation of KV1.1 and KV1.6. Moreover, experiments using six synthetic alanine point-mutated analogs further showed that a ring of basic amino acids acts as a multipoint interaction for the binding of the toxin to the channel. The AbeTx1 primary sequence is composed of 17 amino acids with a high proportion of lysines and arginines, including two disulfide bridges (Cys1–Cys4 and Cys2–Cys3), and it is devoid of aromatic or aliphatic amino acids. Secondary structure analysis reveals that AbeTx1 has a highly flexible, random-coil-like conformation, but with a tendency of structuring in the beta sheet. Its overall structure is similar to open-ended cyclic peptides found on the scorpion κ-KTx toxins family, cone snail venoms, and antimicrobial peptides

Dietary protein and carbohydrate affect feeding behavior and metabolic regulation in hummingbirds (Melanotrochilus fuscus) Las proteínas y carbohidratos dietarios afectan la conducta de alimentación y la regulación metabólica en picaflores (Melanotrochilus fuscus)

The objective of this work was to link hummingbird feeding behavior with metabolic regulation and in addition to assess whether dietary composition would affect entrance into torpor. Hummingbirds were fed a combination of diets with contrasting amounts of protein and carbohydrate. The diets were composed of the following: 2.4 % protein (P) - 12 % sucrose (S) and 0.8 % protein (P) - 36 % sucrose (S). The main findings showed that periods of feeding on each of the diets could be distinguished as separate bouts or feeding events. Hummingbirds presented to high protein-low carbohydrate diets (2.4P-12S) ingested a larger volume of diet, fed for longer (both around 1.7x) and increased the interval between feedings compared with hummingbirds fed diets 0.8P-36S. Physiological regulation between feeding events, on the other hand, was achieved through an increase in metabolic rate for low protein-high sugar diets (0.8P-36S). This response could probably be related to high sucrose assimilation rates through the digestive system of hummingbirds, a process already known to be very efficient in these birds. Additionally, there was a steeper decrease in oxygen consumption for hummingbirds fed diets 2.4P-12S during fasting and a suggestion of a higher torpor incidence in birds fed these dietsEl objetivo de este trabajo fue unir la conducta de alimentación de picaflores con su regulación metabólica y además determinar como la composición dietaria podría afectar la entrada en sopor. Los picaflores fueron alimentados con una combinación de dietas con cantidades contrastantes de proteínas y carbohidratos. La composición dietaria fue: 2,4 % proteína (P) - 12 % sacarosa (S) y 0.8 % proteína (P) - 36 % (sacarosa) (S). Se observó que para cada dieta, los períodos de alimentación se pueden distinguir como eventos separados de alimentación. Cuando se enfrentan a dietas de alta proteína-bajo carbohidratos (2,4P-12S), los picaflores ingieren grandes volúmenes de alimento, se alimentan por mayor tiempo (cerca de 1,7x) y aumentan el intervalo entre alimentación en comparación a los picaflores enfrentados a dietas 0,8P-36S. Por otra parte, la regulación fisiológica entre eventos de alimentación, se logró con un aumento en la tasa metabólica para las dietas de baja proteína-alta azúcar (0,8P-36S). Esta respuesta podría esta relacionada con una alta asimilación de sacarosa, un proceso conocido en picaflores. Además, existió un fuerte decremento en consumo de oxígeno en picaflores alimentados con 2,4P-12S durante ayuno, sugiriendo una alta incidencia de sopo

Further analysis of open-respirometry systems: an a-compartmental mechanistic approach

A system is said to be "instantaneous" when for a given constant input an equilibrium output is obtained after a while. In the meantime, the output is changing from its initial value towards the equilibrium one. This is the transient period of the system and transients are important features of open-respirometry systems. During transients, one cannot compute the input amplitude directly from the output. The existing models (e.g., first or second order dynamics) cannot account for many of the features observed in real open-respirometry systems, such as time lag. Also, these models do not explain what should be expected when a system is speeded up or slowed down. The purpose of the present study was to develop a mechanistic approach to the dynamics of open-respirometry systems, employing basic thermodynamic concepts. It is demonstrated that all the main relevant features of the output dynamics are due to and can be adequately explained by a distribution of apparent velocities within the set of molecules travelling along the system. The importance of the rate at which the molecules leave the sensor is explored for the first time. The study approaches the difference in calibrating a system with a continuous input and with a "unit impulse": the former truly reveals the dynamics of the system while the latter represents the first derivative (in time) of the former and, thus, cannot adequately be employed in the apparent time-constant determination. Also, we demonstrate why the apparent order of the output changes with volume or flow