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When your hypothesis is rejected, breathe in and out: you still have a result!

My experience with turtle physiology.

By Tábata Cordeiro

English edit by Lidia Paes Leme and Carla Elliff

My passion for sea turtles began in 2003, when my family moved from Rio de Janeiro to Salvador and I got to know the Tamar Project. Years later, I started my degree, in biology, of course! Now I had to find a way to study these charming and intriguing animals.

I started an internship at the Animal Physiology Laboratory (LAFISA/UFBA) in 2008. The day I went to talk to my future supervisor, Prof. Dr. Wilfried Klein, I told him that I was interested in working with turtles. That's how I started working with the morphology and physiology of breathing in these animals. This topic was my advisor's line of research and I was very interested in it. I remember that, in a conversation with another professor at the university, when I mentioned that I had started this internship, he joked that he had nothing new to know about chelonians. I felt challenged. And since I like being challenged, I decided to persist!

During my undergraduate studies, I learned that sea turtles are part of a group of animals known as Testudines, Testudinata or Chelonia, which also includes turtles (terrestrial animals) and terrapins (animals that inhabit freshwater environments). This is why we often see the name chelonians used to refer to them. Chelonians, animals that belong to the reptile class, are easy to recognize due to the group's slightly different anatomy. Testudines have a body surrounded by a shell, dorsally called a carapace (fused to the ribs and spine) and ventrally called a plastron (fused to the clavicles and interclavicle).

However, I had to postpone my dream of working with sea turtles. The species that occur in Brazil are considered vulnerable or endangered and, for this reason, are not allowed to be manipulated in the laboratory and this would be my working environment. I began my studies on the respiration of chelonians during my master's degree, investigating general aspects of ventilation and the metabolic rate in two freshwater species.

Bimodal breathing

Let me just provide a brief explanation of the subject of my work! Ventilation can be described as the movement of air or water in and out of structures specialized in the transport and exchange of oxygen and carbon dioxide between the animal and the external environment, such as the lungs. The amount of oxygen absorbed by each organism will determine its metabolic rate, i.e. the amount of energy consumed.

Chelonians are animals that perform intermittent ventilation, i.e. they alternate ventilatory moments, an expiration followed by an inspiration, with non-ventilatory moments, apnea. This characteristic has implications for the metabolic rate of this group of animals. Chelonians have been shown to have a metabolic rate that can be much lower when compared to mammals of a corresponding size. Ok, brief explanation done! 

Returning to my work, I noticed that one of the species I investigated, Phrynops geoffroanus, had a very low metabolic rate compared to other reptiles, due to the low level of oxygen it consumes. Based on this result, I proposed a PhD project to investigate behavioral, morphological and physiological issues associated with bimodal respiration in P. geoffroanus. Bimodal respiration can be defined as the ability of an animal to carry out gas exchange through both air and water.

The cute P. geoffroanus  (Source: Tábata Cordeiro with CC SA-BY 4.0 license).

Assuming that P. geoffroanus has one of the lowest metabolic rates among chelonians, what are the behavioral, morphological and physiological implications of this observed parameter? Thus, the central question of the study was "Does P. geoffroanus carry out gas exchange through structures other than lungs? In other words, does it perform bimodal respiration? If so, which structures are responsible for these exchanges?"

Spoiler: the interesting thing, at the end of this process, is that my working hypothesis was rejected. The results of my doctorate did not indicate that the species performs bimodal respiration! Or, alternatively, these exchanges are not proportionally adequate to maintain the species' basic metabolic needs. Thus, P. geoffroanus obtains oxygen primarily through its lungs. But let's see how I got there.


Working with chelonians involved overcoming MANY challenges. The first was how to get access to these animals: do field collections and organize the whole structure around this work, or get access to these animals through partnerships with a zoo and chase down all the possible and impossible documentation? I chose the second option and I can say that I learned a lot in terms of interpersonal relationships and dealing with bureaucratic issues. The second challenge concerns keeping the animals in an artificial environment. When the animals are in our care, we need to know how to keep them healthy: housing, feeding, air and water temperature, keeping an eye out for any changes in behavior. It is essential to have the contact details of a wildlife veterinarian to answer any questions.

In addition to the challenges of working with chelonians, there are the difficulties of working as a researcher (and in Brazil). I've had to give up being close to people I love because I've moved cities to do my master's and doctorate, and the adaptation phase of these changes involves issues that go beyond studying and doing experiments. It's very difficult to reconcile professional and private life when you're immersed in a project in which you put so much energy.

Almost everything changed between writing the project and carrying out the work! I made and broke partnerships, added and removed proposals from the project, I had to learn new techniques, such as handling different drugs to achieve analgesia and anesthesia in chelonians, surgical practices for cannulating blood vessels to collect material for blood analysis, biochemical and morphological analysis techniques, among others. I made some adaptations due to lack of equipment or time. 

To come to the conclusion that P. geoffroanus does not have bimodal breathing, I carried out behavioral, morphological and physiological analyses, testing the hypothesis that structures such as the skin, the buccopharyngeal cavity (popularly known simply as the mouth) and/or the cloacal pouches (structures attached to the cloaca, present only in some aquatic species of chelonians) would be responsible for gas exchange between the aquatic environment and the animals. In the end, contrary to what was expected, I observed that there were no behavioral changes when different areas of the animals' bodies were isolated from the aquatic environment; the morphological analyses were not very indicative of the presence of characteristics that could classify these structures as gas exchange sites (such as the small diffusion distance) and the biochemical results of the physiological experiments showed no differences when the animals were exposed to aquatic environments with either a higher or a lower oxygen concentration.

Based on these results, some hypotheses were raised: 1) P. geoffroanus may show tolerance to hypoxia and anoxia. This hypothesis was raised by Hsia and collaborators (2013), who argue that tolerance to hypoxia and anoxia is a characteristic that dates back to the Triassic and Jurassic, when aquatic chelonian lineages of that time were exposed to hypoxic and anoxic aquatic environments, due to the high density of vegetation and high biological oxidative demand, and the low atmospheric oxygen content, which was supposedly around 15%; 2) P. geoffroanus would be able to decrease energy consumption, hypometabolism. The researchers Hochachka and Lutz (2001) pointed out that this characteristic may be an important mechanism for maintaining the life of these animals, without the need to travel to the surface to perform aerial gas exchange so frequently. 

All this experience and learning has made me realize what places I want to occupy in my professional career. I want to continue working in research and teaching, bringing science closer to society. I want to share knowledge and values, and tell children and young people, regardless of gender, race or class, that they can study, choose what they want to be, produce and share knowledge.

Tábata discusses the results of her work at a scientific event (Source: Tábata Cordeiro with CC SA-BY 4.0 license).



Hsia C. C.; Schmitz, A.; Lambertz, M.; Perry, S. F.; Maina, J. N. (2013). Evolution of air breathing: Oxygen homeostasis and the transitions from water to land and sky. Comprehensive Physiology, 3, 849–915. DOI: 10.1002/cphy.c120003  

Hochachka, P. W.; Lutz, P. L. (2001). Mechanism, origin, and evolution of anoxia tolerance in

animals. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 130, 435–459. DOI:


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