Zoofysiologi - Forskningsprofil

Forskningsprofil

Crocodiles can eat very large meals and we study the physiological changes associated with digestion. Crocodilian haemoglobin is unique because of a specific and potent effect of bicarbo-nate on its oxygen binding and we are studying the ontogenetic development of this character.

Our field is comparative physiology - the study of how animals survive and thrive under different environmental conditions. We thus wish to understand the molecular, cellular, organ and organismal adaptations of invertebrate and vertebrate animals. While cellular and molecular approaches reveal the mechanisms of adaptations, their functional benefits must be documented at the organismal level. As an example, we study molecular aspects of haemoglobin function along with red blood cellular and cardio-respiratory functions and the mechanisms of whole-organism gas exchange. Other studies concern gas and metabolite exchange between fetal and maternal stages of viviparous animals. This research has, among others, documented how a single amino acid substitution that creates one additional salt bridge within the haemoglobin molecule correlates with the ability of the bar-headed goose to cross the Himalayas and to fly at altitudes 3 km higher than those tolerated by related species. Further studies to be mentioned include heart muscle function under different conditions. We also study what different animals sense, how they integrate sensory input and how they react to given stimuli. Especially the sensory organs of the lateral line and inner ear have our interest. Our findings are always interpreted in an evolutionary context.

Pompeii worm (Alvinella pompejana) lives at Pacific hydrothermal vents; it can survive water of 80°C and is the most heat tolerant animal on earth. African lungfish (Protopterus amphibius) that estivates in dried mud survives year-long droughts through striking adaptations..

Based on the desire to know how and why the animals work like they do, we evaluate the functional importance of a given trait, explain the proximate causes for the particular responses and seek to trace mechanistic explanations. We follow an integrative approach necessitated by frequent perceptions that organismal function is more than the "sum of its parts", and by the facts that organ, cellular and molecular functions interact in a non-linear fashion, and fundamental aspects regarding the interplay of different processes remain poorly understood.

The nose of the sperm whale
The marine iguana from Galapagos is able to perform deep dives.

Our research is aimed at understanding fundamental mechanisms and therefore is basic to applied sciences such as ecotoxicology and aquaculture. Furthermore, some of the animals we study are "model-organisms" for clinically-oriented studies minded at disease treatment. Our research is often conducted under controlled laboratory conditions, but increasingly includes field-based experiments. Thus, biosonar function is being described in field studies conducted on animals as divergent as 2 gram bats and 50 ton sperm whales. Similarly, we are developing methods for long-term recording of heart rate and body temperature in reptiles in natural surroundings.

Andean frogs (Telmatobius culeus, with oversized respiratory skin, and T. peruvianus ) show exciting adaptations to the hypoxic conditions that prevail at altitude (4300 m). These adaptations are studied in Aarhus.
Bar-Headed goose (Anser indicus) can fly over the Himalayas; its high blood oxygen affinity can be ascribed to a single amino acid exchange in the hemoglobin.

Our approach to zoophysiology exploits on the "August Krogh principle" which states that a given mechanism can best be understood by studies of particular species that exhibit distinct adaptations. As examples, we investigate the digestive physiology of snakes that can eat more than their own body weight, the cardiovascular physiology of turtles that can survive for more than half a year without oxygen, haemoglobins from fish living in oxygen-poor Amazon waters, frogs that live at 4000 m elevation in the Andes mountains, and worms that thrive at volcanoes at the bottom of the Pacific Ocean. We use "site-directed" mutagenesis to understand physiological consequences of specific amino acid substitutions in haemoglobin and study its interactions with red cell membranes and the roles of a number of peptides that control digestive and cardiovascular functions. At the organismal level we employ computer-based systems for collection and calculation of large amounts of data obtained by simultaneous measurement of different variables in chronically instrumented animals. We are developing satellite-based techniques for monitoring biosonar function and diving behaviour in whales. Furthermore, we extensively rely on mathematical models and computations to describe physiological functions and to pose specific hypotheses that can be tested experimentally. This approach has been particularly important to develop our understanding of gas exchange at the organismal level.

Rüppels griffon (Gyps rueppelli) that was struck by a commercial airplane at 11,300 meters altitude over West Africa. Studies from our laboratory show that tis species possesses unique hemoglobin components with high oxygen-binding potential (compared to other birds) (7). Vertebrate hemoglobin consists of 2 alphachains (light and dark blue) and 2 betachains (yellow and green). Each of these can bind one oxygen molecule at the (red) heme groups.
(C. Ho & coworkers).