Comparative analysis of the molecular starvation response of Southern Ocean copepods.

Large lipid-storing copepods dominate mesozooplankton biomass in the polar oceans and form a critical link between primary production and higher trophic levels. The ecological success of these species depends on their ability to survive periods of food deprivation in a highly seasonal environment, but the molecular changes that mediate starvation tolerance in these taxa are unknown. We conducted starvation experiments for two dominant Southern Ocean copepods, Calanoides acutus and Calanus propinquus, allowing us to compare the molecular starvation response between species. These species differ in life history, diet and metabolic traits, and expressed overlapping but distinct transcriptomic responses to starvation. Most starvation-response genes were species-specific, but we identified a conserved core set of starvation-response genes related to RNA and protein metabolism. We used phylotranscriptomics to place these results in the context of copepod evolution and found that starvation-response genes are under strong purifying selection at the sequence level and stabilizing selection at the expression level, consistent with their role in mediating essential biological functions. Selection on starvation-response genes was especially strong in our focal lipid-storing lineage relative to other copepod taxa, underscoring the significance of starvation tolerance for these species. We also found that certain key lipid enzymes (elongases and desaturases) have experienced diversification and positive selection in lipid-storing lineages, reflecting the unique lipid storage needs of these animals. Our results shed light on the molecular adaptations of high-latitude zooplankton to variable food conditions and suggest that starvation-response genes are under particularly strong sequence and expression constraints.

A perspective on neuroethology: what the past teaches us about the future of neuroethology.

For 100 years, the Journal of Comparative Physiology-A has significantly supported research in the field of neuroethology. The celebration of the journal's centennial is a great time point to appreciate the recent progress in neuroethology and to discuss possible avenues of the field. Animal behavior is the main source of inspiration for neuroethologists. This is illustrated by the huge diversity of investigated behaviors and species. To explain behavior at a mechanistic level, neuroethologists combine neuroscientific approaches with sophisticated behavioral analysis. The rapid technological progress in neuroscience makes neuroethology a highly dynamic and exciting field of research. To summarize the recent scientific progress in neuroethology, I went through all abstracts of the last six International Congresses for Neuroethology (ICNs 2010-2022) and categorized them based on the sensory modalities, experimental model species, and research topics. This highlights the diversity of neuroethology and gives us a perspective on the field's scientific future. At the end, I highlight three research topics that may, among others, influence the future of neuroethology. I hope that sharing my roots may inspire other scientists to follow neuroethological approaches.

Centennial issue.

The Journal of Comparative Physiology A, also known as JCPA, was founded by Karl von Frisch and Alfred Kühn in 1924, then under its German title Zeitschrift für vergleichende Physiologie. During the 100 years of its history, it became the leading international journal in comparative physiology and its daughter discipline, neuroethology. As such, it had a major impact on the development of these disciplines. In celebration of this achievement and the nearly 10,000 articles that appeared during the last 100 years, this Centennial Issue is published. Its authors reflect on the history of JCPA and the early pioneers, including women scientists, of comparative physiology; share the impact that the Journal had on their careers; discuss the benefit of the enormous taxonomic diversity of model systems used in studies published in JCPA; contrast this philosophy with the strategy of a limited number of standard biomedical model systems; review popular and trending research topics covered in JCPA; and, by interrogating the past, take a peek into the future of neuroethology.

One hundred years of excellence: the top one hundred authors of the Journal of Comparative Physiology A.

The Journal of Comparative Physiology A is the premier peer-reviewed scientific journal in comparative physiology, in particular sensory physiology, neurophysiology, and neuroethology. Founded in 1924 by Karl von Frisch and Alfred Kühn, it celebrates its 100th anniversary in 2024. During these 100 years, many of the landmark achievements in these disciplines were published in this journal. To commemorate these accomplishments, we have compiled a list of the Top 100 Authors over these 100 years, representing approximately 1% of all its authors. To select these individuals, three performance criteria were applied: number of publications, total number of citations attracted by these articles, and mean citation rate of the papers published by each author. The resulting list of the Top 100 Authors provides a fascinating insight into the history of the disciplines covered by the Journal of Comparative Physiology A and into the academic careers of many of their leading representatives.

Transesophageal echocardiography of cardiac function in Nile crocodiles - A novel tool for assessing complex hemodynamic patterns.

BACKGROUND: The crocodilian heart is unique among reptiles with its four-chambered structure and complete intracardiac separation of pulmonary and systemic blood flows and pressures. Crocodiles have retained two aortic arches; one from each ventricle, that communicate via Foramen of Panizza, immediately distally from the aortic valves. Moreover, crocodiles can regulate vascular resistance in the pulmonary portion of the right ventricular outflow tract (RVOT). These unique features allow for a complex regulation of shunting between the pulmonary and systemic circulations. Studies on crocodile shunting have predominantly been based on invasive measurements, but here we report on the use of echocardiography. METHODS: Experiments were performed on seven pentobarbital anaesthetized juvenile Nile crocodiles (length and mass of 192 ± 13 cm and 26 ± 5 kg, respectively). Echocardiographic imaging was performed using a transesophageal (TEE) approach. All images were EKG-gated. RESULTS: We obtain excellent views of cardiac structures and central vasculature through the esophagus. Standard imaging planes were defined for both long- and short axis views of the left ventricle and truncus arteriosus. For the RV, only a short axis view could be obtained. Color Doppler was used to visualize flow. Pulsed waved Doppler for measuring flow profiles across the atrioventricular valves, in the two RVOTs and the left ventricular outflow tract. Shunting across the Foramen of Panizza could be visualized and gated to the EKG. CONCLUSION: TEE can be used to image the unique features of the crocodile heart and allow for in-vivo imaging of the complex shunting hemodynamics, including timing of cardiac shunts.

Reporting guidelines for terrestrial respirometry: Building openness, transparency of metabolic rate and evaporative water loss data.

Respirometry is an important tool for understanding whole-animal energy and water balance in relation to the environment. Consequently, the growing number of studies using respirometry over the last decade warrants reliable reporting and data sharing for effective dissemination and research synthesis. We provide a checklist guideline on five key sections to facilitate the transparency, reproducibility, and replicability of respirometry studies: 1) materials, set up, plumbing, 2) subject conditions/maintenance, 3) measurement conditions, 4) data processing, and 5) data reporting and statistics, each with explanations and example studies. Transparency in reporting and data availability has benefits on multiple fronts. Authors can use this checklist to design and report on their study, and reviewers and editors can use the checklist to assess the reporting quality of the manuscripts they review. Improved standards for reporting will enhance the value of primary studies and will greatly facilitate the ability to carry out higher quality research syntheses to address ecological and evolutionary theories.

Commentary: The microbial dependence continuum: Towards a comparative physiology approach to understand host reliance on microbes.

Comparative physiologists often compare physiological traits across organisms to understand the selective pressures influencing their evolution in different environments. Traditionally focused on the organisms themselves, comparative physiology has more recently incorporated studies of the microbiome-the communities of microbes living in and on animals that influence host physiology. In this commentary, we describe the utility of applying a comparative framework to study the microbiome, particularly in understanding how hosts vary in their dependence on microbial communities for physiological function, a concept we term the "microbial dependence continuum". This hypothesis suggests that hosts exist on a spectrum ranging from high to low reliance on their microbiota. Certain physiological traits may be highly dependent on microbes for proper function in some species but microbially independent in others. Comparative physiology can elucidate the selective pressures driving species along this continuum. Here, we discuss the microbial dependence continuum in detail and how comparative physiology can be useful to study it. Then, we discuss two example traits, herbivory and flight, where comparative physiology has helped reveal the selective pressures influencing host dependence on microbial communities. Lastly, we discuss useful experimental approaches for studying the microbial dependence continuum in a comparative physiology context.

Primary Cell Culture as a Model System for Evolutionary Molecular Physiology.

Primary cell culture is a powerful model system to address fundamental questions about organismal physiology at the cellular level, especially for species that are difficult, or impossible, to study under natural or semi-natural conditions. Due to their ease of use, primary fibroblast cultures are the dominant model system, but studies using both somatic and germ cells are also common. Using these models, genome evolution and phylogenetic relationships, the molecular and biochemical basis of differential longevities among species, and the physiological consequences of life history evolution have been studied in depth. With the advent of new technologies such as gene editing and the generation of induced pluripotent stem cells (iPSC), the field of molecular evolutionary physiology will continue to expand using both descriptive and experimental approaches.

Differential acclimation kinetics of the two forms of type IV chromatic acclimaters occurring in marine Synechococcus cyanobacteria.

Synechococcus, the second most abundant marine phytoplanktonic organism, displays the widest variety of pigment content of all marine oxyphototrophs, explaining its ability to colonize all spectral niches occurring in the upper lit layer of oceans. Seven Synechococcus pigment types (PTs) have been described so far based on the phycobiliprotein composition and chromophorylation of their light-harvesting complexes, called phycobilisomes. The most elaborate and abundant PT (3d) in the open ocean consists of cells capable of type IV chromatic acclimation (CA4), i.e., to reversibly modify the ratio of the blue light-absorbing phycourobilin (PUB) to the green light-absorbing phycoerythrobilin (PEB) in phycobilisome rods to match the ambient light color. Two genetically distinct types of chromatic acclimaters, so-called PTs 3dA and 3dB, occur at similar global abundance in the ocean, but the precise physiological differences between these two types and the reasons for their complementary niche partitioning in the field remain obscure. Here, photoacclimation experiments in different mixes of blue and green light of representatives of these two PTs demonstrated that they differ by the ratio of blue-to-green light required to trigger the CA4 process. Furthermore, shift experiments between 100% blue and 100% green light, and vice-versa, revealed significant discrepancies between the acclimation pace of the two types of chromatic acclimaters. This study provides novel insights into the finely tuned adaptation mechanisms used by Synechococcus cells to colonize the whole underwater light field.

A library of electrophysiological responses in plants - a model of transversal education and open science.

Electrophysiology in plants is understudied, and, moreover, an ideal model for student inclusion at all levels of education. Here, we report on an investigation in open science, whereby scientists worked with high school students, faculty, and undergraduates from Chile, Germany, Serbia, South Korea, and the USA. The students recorded the electrophysiological signals of >15 plant species in response to a flame or tactile stimulus applied to the leaves. We observed that approximately 60% of the plants studied showed an electrophysiological response, with a delay of ~ 3-6 s after stimulus presentation. In preliminary conduction velocity experiments, we verified that observed signals are indeed biological in origin, with information transmission speeds of ~ 2-9 mm/s. Such easily replicable experiments can serve to include more investigators and students in contributing to our understanding of plant electrophysiology.

Leukocyte Concentrations Are Isometric in Reptiles Unlike in Endotherms.

AbstractHow do large and small reptiles defend against infections, given the consequences of body mass for physiology and disease transmission? Functionally equivalent mammalian and avian granulocytes increased disproportionately with body mass (i.e., scaled hypermetrically), such that large organisms had higher concentrations than expected by a prediction of proportional protection across sizes. However, as these scaling relationships were derived from endothermic animals, they do not necessarily inform the scaling of leukocyte concentration for ectothermic reptiles that have a different physiology and evolutionary history. Here, we asked whether and how lymphocyte and heterophil concentrations relate to body mass among more than 120 reptile species. We compared these relationships to those found in birds and mammals and to existing scaling frameworks (i.e., protecton, complexity, rate of metabolism, or safety factor hypotheses). Both lymphocyte and heterophil concentrations scaled almost isometrically among reptiles. In contrast, functionally equivalent granulocytes scaled hypermetrically and lymphocytes scaled isometrically in birds and mammals. Life history traits were also poor predictors of variation in reptilian heterophil and lymphocyte concentrations. Our results provide insight into differences in immune protection in birds and mammals relative to that in reptiles through a comparative lens. The shape of scaling relationships differs, which should be considered when modeling disease dynamics among these groups.