Wolfgang Engelmann: Passionate Researcher,Teacher,and Artist (26 February 1934 to 1 July 2023)

On 1 July 2023, our highly esteemed friend, colleague, and academic teacher Wolfgang Engelmann died unexpectedly in his 90th year. He researched and taught at the Institute of Biology I at the University of Tübingen, Germany, for 40 years and was one of the pioneers of modern chronobiology, inspired by the three “fathers of the biological clock,” Erwin Bünning, Colin Pittendrigh, and Jürgen Aschoff. The University of Tübingen had produced several world-renowned scientists over many decades, and Wolfgang Engelmann’s energetic and enthusiastic commitment made chronobiology a hot topic at the university. Wolfgang was not only a unique researcher but also a talented draftsman and painter. Painting allowed him to take a break from administrative tasks and forget about all the things that were going wrong on our planet and weighing him down.

Wolfgang was born in Weimar (Germany) on 26 February 1934, the second of five siblings. From 1944 to 1950, he attended the boarding and elite school Schulpforta near Naumburg in Germany. There, he suffered greatly under the strict control of the Nazi government, which was replaced in 1945/46 by the no less totalitarian leadership of the Soviet military administration. In 1950, when all students were to be forced to join the Free Democratic Youth (the state youth organization of the German Democratic Republic), he and a friend made an arduous escape in deep snow to the West on Boxing Day, 1 year before their high school graduation. Wolfgang found a new home in Hamburg, where he scraped by working as a longshoreman at the Port of Hamburg and other physically demanding jobs, made up for the “Abitur” (the German high school degree) he had been denied in Schulpforta, and began studying natural sciences at the University of Hamburg. This time of hunger and deprivation left a decisive mark on him. Wolfgang remained frugal and modest until the end of his life. He usually put himself in the back seat and supported other people to the best of his ability, not only students but also refugees and victims of various disasters. One example of his frugality and intrepidness was a trip to Naples in Italy in the 1950s. He hitchhiked with 80 Deutsch Mark in his pocket and returned with 40 Deutsch Mark after 10 days, even though he had to purchase new sneakers because they were stolen when he slept on a wall in the port of Naples.

In 1956, he moved to the University of Tübingen to continue studying natural sciences and received his doctorate in 1960 with Erwin Bünning for a technically challenging thesis on the relationship between photoperiodism and circadian rhythms in the plants Kalanchoe blossfeldiana and Ipomoea coccinea. By recording the opening and closing movements of Kalanchoe petals under the same illumination conditions that he used in parallel for photoperiodic floral induction in Kalanchoe plants, he was able to demonstrate unequivocally that the circadian clock was involved in the photoperiodic responses of this plant, whereas an hourglass appeared to be involved in Ipomoea (Bünning and Engelmann, 1960; Engelmann, 1960). From November 1961 to March 1963, Wolfgang joined David Shappirio at the University of Michigan in Ann Arbor, United States, as a Thyssen Foundation fellow, for his first postdoctoral period. There, he did research on the dipteran Chironomus tentans and demonstrated the photoperiodic control of the larval diapause in this insect. This work led to a well-received publication in Nature, in which his last name was misspelled as Englemann and Shappirio (1965).

Left: Wolfgang Engelmann in 1981 during drawing (photo: Charlotte Helfrich-Förster). Right: A scene in Canterbury, United Kingdom, painted by him during a scientific meeting (photo: Carl Johnson).

Back in Tübingen, Wolfgang was appointed scientific assistant at the Institute of Biology in October 1963 and remained dedicated to research on circadian rhythms and photoperiodic responses in plants and insects. At this time, he also met his future wife Sigrun Hörr. They married in 1965, and a year later, their son Dirk was born. For Wolfgang’s second postdoc, the small family moved to Princeton for a year, where he spent a scientifically fulfilling and productive time with Colin Pittendrigh investigating eclosion rhythms of Drosophila pseudoobscura, phase response curves, and the point of singularity. “Pitt” quickly recognized Wolfgang’s talents and made him an offer to join him as a research associate at Stanford University, to which Pitt had received an appointment as a full professor. A devastating fire in the home of Wolfgang’s family in Princeton, which they barely survived, put a question mark over their plans to stay in the United States. With a heavy heart, Wolfgang decided to comply with his family’s wishes and returned to Germany. Their daughter Lerke was born there in 1968. He worked as a research assistant, from 1974 on as a lecturer, and was appointed as a professor of Biology at the University of Tübingen in 1979. He cooperated with scientists all over the world, most notably with Anders Johnsson (Norway), Maroli Chandrashekaran and Vijay Sharma (India), Robert Lewis (New Zealand), Bronislaw Cymborowski (Poland), and many others.

Wolfgang’s numerous contacts with scientists and students have always “colored” the house in Hagelloch where his family lived. The many fruitful visits of scientists and student groups to this house over the years should be highlighted. The scientific discussions were always lively, but just as important were laughter, humor, music, and vibrant conversation. Sigrun and Wolfgang provided warm hospitality and generous meals—both of which will be gratefully remembered by the Tübingen students as well as the visiting scholars and students from all over the world.

In his research in Tübingen, Wolfgang was able to demonstrate the existence of endogenous clocks and characterize their properties in more than 20 different organisms, ranging from unicellulars to plants and animals. His work was not restricted to circadian rhythms, but he also studied ultradian and seasonal rhythms (Engelmann and Antkowiak, 1998; Schuster and Engelmann, 1997; Johnsson et al., 2012). In addition, he conducted experiments on himself to unravel the human circadian clock. Wolfgang was one of the first subjects to spend a month in complete isolation in Jürgen Aschoff’s bunker at Erling-Andechs to record the free-running activity rhythms of humans. He remained in regular contact with Aschoff and often visited Erling-Andechs with his own students. Wolfgang also investigated free-running human activity rhythms under constant light during the Arctic summer (Johnsson et al., 1979a). In July 1982, several members of the group made a 3-week excursion to northern Lapland to test the effects of extremely long days on locomotor activity and body temperature rhythms. The conditions were essentially continuous light (LL), but the intensity of the light did vary over 24 h. Wolfgang carried a measuring device weighing about 1 kg for continuous recording of his core body temperature using a continuously inserted rectal thermometer (all analog with printer), in addition to the backpack weighing about 20 kg with provisions, tent, and everything needed for survival during the 3 weeks.

It was impressive to see Wolfgang’s body temperature increasing to over 39 °C when climbing the hills and falling below 36 °C during the rather short sleeping periods. We all slept only briefly under the light in the arctic summer, but it was too late in the summer for our activity rhythms to free run. Obviously, the daily fluctuations in environmental light intensity were strong enough to synchronize our clocks to the 24-h environmental rhythms.

Wolfgang recorded his body temperature during a 3-week excursion in Northern Lapland together with some members of his group (photo: Charlotte Helfrich-Förster).

One of the many foci of Wolfgang’s research was to elucidate the effect of lithium and other substances on circadian clocks in many organisms, including humans. Lithium has been used to treat bipolar disorders and major depression in human patients for decades. Wolfgang found that lithium slowed the circadian clocks of most plants and animals (Engelmann, 1972, 2014; Hofmann et al., 1978; Delius et al., 1984; Rauch et al., 1986; Schmid and Engelmann, 1987; Smietanko and Engelmann, 1989). Because some human patients had short period lengths of certain rhythmic parameters that became out of phase with the rhythm of body temperature during depression (Pflug et al., 1982), Wolfgang tested the hypothesis that lithium (and other antidepressants) has a beneficial effect on depression by prolonging the period of short-period rhythms and normalizing the phase relationship of all rhythms, a hypothesis that proved to be correct (Eckhardt et al., 1983; Pflug and Engelmann, 1987). Together with his long-time collaboration partner Anders Johnsson (biophysicist at the Norwegian University of Science and Technology, Trondheim) and Burkhard Pflug (1939-2009; psychiatrist at Frankfurt University Hospital), he investigated the effect of lithium on healthy human volunteers during the Arctic summer in Spitsbergen under free-running conditions. They found that lithium indeed slowed down the speed of the human endogenous clock (Johnsson et al., 1979b, 1980, 1983). A detailed report about this adventurous experiment can be found in Engelmann (2010).

To understand the evolution and basic mechanisms of circadian clocks, Wolfgang studied single-celled organisms as the supposedly simplest organisms on Earth (Kiefner et al., 1974; Engelmann, 1988; Kippert et al., 1990). Among these experiments, his research on the marine rhizopod Thalassomyxa australis is noteworthy. T. australis lives in rockpools in the tidal zones of the West coast of Australia and shows a pronounced circadian feeding rhythm that depends on the environmental temperature and the food organism (Silyn-Roberts et al., 1986; Landsbeck and Engelmann, 1991). In addition, the clock of T. australis needs several zeitgebers to be entrained to the 24-h rhythm: temperature cycles, light-dark cycles, and cyclical shaking that mimics the tides in its natural environment (Smietanko et al., 1988; Förster and Engelmann, 1988). Wolfgang speculated that T. australis may be an organism that is in an early evolutionary stage of circadian rhythms that still lack temperature compensation (Silyn-Roberts et al., 1986), an interesting idea that has not yet been thoroughly examined.

Another of Wolfgang’s interests was to unravel the formal properties of circadian clocks, by investigating the effects of light (Engelmann et al., 1973; Johnsson et al., 2006), electromagnetic fields (Engelmann et al., 1996; Sharma et al., 2014), and heavy water (Brenner and Engelmann, 1973; Maurer and Engelmann, 1974) on rhythms of plants and animals. In the case of light, he was able to stop the eclosion rhythm of D. pseudoobscura (Chandrashekaran and Engelmann, 1976) and the petal movement rhythm in K. blossfeldiana (Engelmann et al., 1978) with a light pulse of defined timing and strength—in other words, he reached the point of singularity that was predicted by Arthur Winfree (Engelmann and Witte, 2016). He tried hard to find the point of singularity also in the activity rhythms of individual Drosophila melanogaster flies, but without success, probably because the activity rhythm is controlled by a coupled population of clock neurons in the fly brain, as we know today.

Wolfgang was also the first to show that light can synchronize the endogenous clocks of eyeless Drosophila mutants (sine oculis), first for their eclosion rhythms (Engelmann and Honegger, 1966) and later for their activity rhythms (Helfrich and Engelmann, 1983). This research was evidence of an extraretinal photoreceptor that was found years later in the form of the blue light pigment cryptochrome. This work was only possible because of Wolfgang’s excellent skills in developing innovative methods for recording and analyzing all kinds of rhythms, methods that he made available to the scientific community (Engelmann, 2004). For example, he was the first to develop an automatic recording system using infrared light barriers for activity rhythms in flies (Engelmann and Mack, 1978).

By continuing a research focus in the former Bünning lab, Wolfgang maintained an interest in rhythmic leaf movements. He recorded the ultradian and circadian leaf movements of many different plants. Again, he was the first to show that Arabidopsis thaliana, an important model in plant science, also moves its leaves up and down in a circadian rhythm during the growth phase (Engelmann et al., 1992). To this end, he and a graduate student developed an experimental apparatus that allowed them to record leaf movements in three-dimensional space. He continued these and other recordings of leaf and petal movements in retirement in the basement of his home in Hagelloch, resulting in many illustrative time-lapse movies (see below).

Wolfgang was a charismatic teacher who captivated many students. His internships were legendary because he was the only teacher in the biological faculty in Tübingen who did not make any prefabricated experiments, but let the students choose their internship project themselves. During the first days of the internship, the students were presented with the diverse projects of the working group and could choose which one they wanted to pursue during the next 3 weeks. Each student worked on a different project, with massive support from the staff and sometimes the institute workshop. Each project had an open-ended outcome. Sometimes all that was left at the end of the internship was the experimental setup, but it was not uncommon for the internship experiments to form the basis of later diploma or doctoral theses. In any case, the students learned what science is and what good scientific practice looks like. It was remarkable that Wolfgang always treated the students as equals. He took them as seriously as his colleagues and was always enthusiastic about their ideas and results. A scientific liveliness and creativity existed in the working group that we later rarely experienced in our own scientific lives. The results of all members as well as the current literature were openly and critically discussed in the working group seminars, and new working hypotheses were established. A question frequently asked by Wolfgang was, “How could we test this?”

When visits came from international colleagues, which was not uncommon given Wolfgang’s reputation, the whole group sat together in a circle, and he introduced each individual and his research project to the guest. Whether state examination candidate, diploma candidate, or doctoral student, all were integrated into the international research discussion. Wolfgang also usually took the whole group with him to symposia (we usually camped together at the closest campground). This way we got to know the scientific world at an early stage and were able to establish international contacts. So, it is not surprising that many of Wolfgang’s mentees became scientists themselves and some of them attained professorships. Probably his most famous mentee was Maroli Krishnayya Chandrashekaran (1937-2009), also called Shekhar, who came to Tübingen to be a postdoc of Erwin Bünning. Shekhar and Wolfgang developed an especially close friendship. They worked together for many years. Shekhar later founded chronobiology in India and is regarded as the first “Indian chronobiologist.” Shekhar visited Wolfgang frequently after his return to India to collaborate, and in return, Wolfgang spent research time in Shekhar’s lab. Wolfgang also organized an international Symposium at the University of Madurai (India) in December 1978, after Shekhar became the chair of Biology there. Through Wolfgang’s former PhD student Sang-Zin Han, who until recently held a professorship in Seoul, chronobiology reached South Korea, and through his former doctoral student Rolf Dorka, new chronobiological concepts entered the Anthroposophical Society. Barbara Helm, who now studies the timing of bird migration at the Swiss Ornithological Institute, had a fruitful working time as a diploma student with Wolfgang in Tübingen, and Hans-Willi Honegger, Gottfried Wiedenmann, Bernd Antkowiak, and the author of this article who did their PhDs with him have also become successful scientists.

Wolfgang was also heavily involved in the international teaching of chronobiology. He taught at several European Erasmus summer schools on chronobiology, and in 2000, after his retirement, he worked as a visiting lecturer at the Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR) in Bangalore, India. There he interacted not only with students and faculty members but also with villagers in the rural area, even though he did not speak the local language.

Left: Wolfgang interacting with students at the Erasmus Summer School in Groningen in 1991. Right: Wolfgang with Shekhar at the Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR) in Bangalore in 2000.

Wolfgang maintained his passion for science until the last minute of his life. He maintained lifelong intensive scientific contacts all over the world and followed with great interest the latest publications on endogenous clocks. He often asked his colleagues by e-mail for pdf files of articles and was always enthusiastic about new findings.

In a review on Shekhar’s book “Time in the living world,” Wolfgang wrote (Engelmann, 2011):

Scientists are a privileged group of people: They can choose a topic of their own and do research on it. Furthermore, they can discuss their work with co-scientists and publish the results, thus contributing to the ever increasing knowledge of mankind. Their teaching usually attracts students to join them in their quest to “find out” the mysteries of nature. Often this research is of no immediate use for the society, but might well prove to be beneficial in the future. A country investing in science and scientists might not be rewarded immediately by the results, but the increase in knowledge and understanding will pay off in the long run . . .

Scientists and their work are supported by the public. It should therefore be an obligation on the part of scientists to tell people what they do.

Wolfgang took the obligation to inform the public about science very seriously. Especially after his retirement in 1999, he devoted more time to writing online articles and books about biological rhythms, which are available to everyone under the Tübingen University Library’s publication system, TOBIAS.lib at: https://tobias-lib.uni-tuebingen.de/xmlui/browse?type=author&value=Engelmann%2C+Wolfgang

On that website, one can find 77 works by Wolfgang, including time-lapse videos of leaf and petal movements of various plants and on the eclosion of flies. Furthermore, there are several books written for the scientific lay audience on topics such as “Bio-Calendar—The Year in the Life of Plants and Animals,” “Flower Clocks, Time-Memory and Time-Forgetting,” “Rhythms of Life—An Introduction based on Selected Topics and Examples,” “Clocks that go by the Moon—Influence of the Moon on the Earth and its Living Creatures,” and many others.

Wolfgang worked continuously on updating and completing his work. He died on the way to a lecture series for Linux users in Tübingen, whose text typesetting system LaTeX he used to write his online texts and on which he constantly updated his knowledge. Unfortunately, the last articles he wrote will remain unfinished.

We have lost not only our outstanding teacher and passionate researcher but also a dear friend and colleague. Our thoughts and sympathy go out to his wife, his two children, and the eight grandchildren, for whom we cannot fill the sudden void with words.

Charlotte Helfrich-Förster¹ Department of Neurobiology and Genetics Theodor-Boveri Institute, Biocenter, University of Würzburg, Würzburg, Germany e-mail: [e-mail]