Life and career

Klaus Kalmring was born as the eldest of three brothers in Erfurt, Thuringia. He attended high school in Erfurt, but due to the turmoil at the end of World War II, he had to leave school without graduation at age 14. His parents were farmers and gardeners. Most likely they nourished their son’s interest in the natural world. Since his childhood, he also had a passion for geography and loved to spend hours studying maps and atlases. His talent was not overlooked, however, and he was accepted into the prestigious “Institut für Lehrerbildung” (teacher training) in Weimar (1951–1953). He passed the final examinations with excellent grades and could now be employed as a teacher for Russian language and Russian history. From 1953 to 1955 Klaus Kalmring taught both subjects in the central school in Unterpörlitz near Ilmenau, Thuringia, then in East Germany. In 1955 he relocated to Gelnhausen, then West Germany, to join his parents and worked as an assistant educator for youth in the children’s sanatorium in Weilmünster/Taunus from July to December. He also enrolled again in a high school, the Goethe-Gymnasium in Frankfurt am Main, where he attended evening classes and graduated in 1959. Immediately thereafter he started his studies in geography, biology and chemistry at the Johann-Wolfgang-Goethe-University in Frankfurt am Main. It was during an excursion in 1963 that he first met his wife-to-be, Elke Bremm. Two years later they were married. To finance his studies, Klaus Kalmring took up a position as a teacher for biology and geography at a private high school in Königshofen/Taunus until 1966, when he cancelled his contract to focus on his studies (Fig. 1). The school’s letter of reference explicitly acknowledges his extraordinary enthusiasm for his subject and for motivating and supporting the students—qualities, which he maintained throughout his life.

Fig. 1
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Portrait of Klaus Kalmring from his “Studienbuch” at the Johann Wolfgang Goethe-University Frankfurt am Main, 1959

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In 1969 Klaus Kalmring received his doctoral degree (Dr. phil. nat.) with a dissertation on the neurophysiology of muscles in cats, supervised by Prof. Rolf Hassler at the Max Planck Institute for Brain Research in Frankfurt am Main and supported by a research scholarship of the Max Planck Society. In 1969, Klaus Kalmring relocated to Bochum, where he joined the group of Prof. Johann Schwartzkopff, soon became junior (1971) and in 1976 senior assistant. He dedicated his years in Bochum to the study of the “Afferent auditory system in the ventral nerve cord in Locusta migratoria”, for which he received his habilitation and venia legendi in 1975. In July 1978, Klaus Kalmring was appointed professor of neurophysiology at the Philipps-Universität Marburg. Here, he built a large and innovative team which included not only biologists, but also experts with different backgrounds like physics, who all brought their special expertise to the study of the auditory and vibratory sensory system of bush crickets. The vibrant atmosphere, the spirit of scientific curiosity and hard, but rewarding work were characteristics of the Kalmring lab and will be remembered fondly by all, who had the opportunity to visit (Fig. 2). Those were indeed many: students, doctoral students, post-docs, colleagues from all over the world, especially Slovenia, the United Kingdom, Russia, Australia, India and China. As a result of one of his collaborative efforts, Klaus Kalmring was appointed guest professor at Shandong Teachers University, China, in 1995 (Fig. 3).

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Always full of energy—Klaus Kalmring on a lab excursion to Bavaria (~1989)

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Fig. 3
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Klaus Kalmring with colleagues from Shandong Teachers University, China, 1995. All photographs are the private property of E. Bremm-Kalmring, Marburg

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Klaus Kalmring was both inspired by what he was doing and inspiring to others around him. His group was in fact like a family to him. He had extraordinary amounts of energy and a very good sense of humor. His good sense of humor together with the high quality of his lectures and excellently organized courses attracted many students. He loved going out into the field, collecting bush crickets on sometimes long road trips to Southern Germany, Slovenia, Austria, France and Spain, for which he recruited students and family alike. These trips were always combined with visits to geological and/or cultural points of interest. Klaus Kalmring enjoyed lively discussions, even—or particularly—when they were controversial and was not afraid to speak out against authorities and influential colleagues, even if it meant risk.

He was aware that he had been lucky in his life, and he was happy to share and to support others, regardless of whether they were able to return his favors. He expected others to work hard when striving for knowledge and lived up to these postulates himself. Besides administrative work and teaching, he always found time for doing electrophysiological experiments himself until his retirement. All these attributes gained him the respect of students and colleagues. He used to claim that he had “the most beautiful profession in the world“, a unique opportunity to live his greatest passions: research and teaching.

Klaus Kalmring was saddened when he came up for mandatory retirement in 1996, and thereafter dedicated his energy to voluntary work on the board of a home for the elderly, and to his interest in architecture. He will be remembered as an excellent scientist and dedicated teacher and also as an extraordinary human being with a very broad knowledge. He touched the lives of many, and in many ways. The scientific life and career of Klaus Kalmring were honored during the 1st Symposium on Biotremology in San Michele, Italy, September 5–7, 2016.

Scientific legacy

Klaus Kalmring became attracted to the processing of auditory information by different Orthopteran species as simple invertebrate examples for intraspecific auditory communication. He favored invertebrate species over mammalian species because of their relative simplicity for a physiological approach and for ethical reasons. The most important aspect of his group’s research work was its integrative character, ranging from bioacoustics, electrophysiology, and neuroanatomy to behavior and ecology and including the application of a large spectrum of methods. One particular achievement was the development of equipment like precision amplifiers, apparatus needed for digital recording and playback techniques as well as versatile software with the support of highly motivated physicists. This development of technology was instrumental for many studies involving highly resolved sound recording, signal manipulation, single cell recording and others. Back then many of these techniques still were in an experimental stage, like the use of glass microelectrodes for single cell recordings, multi-unit recordings, the use of tracers for cell labeling or simply the use of computers.

To find out functional commonalities as well as species-specific adaptations for the reception and recognition of conspecific signals, Klaus Kalmring turned to comparative neuroethological studies of auditory/vibratory information processing in a wide range of Orthopteran species, especially in Tettigoniidae. He was among the first to describe the convergence of auditory and vibratory information in ventral nerve cord interneurons of acridids and tettigoniids (Čokl et al. 1977; Kalmring and Kühne 1980). His investigations on the tonotopic organization of receptor cells and afferent projections in the ventral cord of locusts and bush crickets (e.g., Kalmring et al. 1993) are still the basis for today’s research on transduction mechanisms. He measured the tuning curves of individual auditory receptors in combination with the application of tracing techniques to establish the auditory threshold curves that are commonly tuned to conspecific song frequency parameters. Thereby, he identified a species-specific range of relatively low numbers of auditory receptors (~23 up to 50 scolopidial cells in the crista acoustica close to the tympanum) in tettigoniids (see Table 1), yet broad-banded hearing up to the ultrasonic range (>40 kHz). Morphological and physiological investigations on non-auditory but homologous organs complemented the investigations in Ensifera (Jeram et al. 1995). All these data are still important for concepts and hypotheses developed in regard to the evolution of auditory sense organs in insects. In addition, amplification functions of the acoustic trachea were identified and shown to enhance the sensitivity in the low frequency range as evolutionary adaptations in some species. Physiological and anatomical investigations revealed neuronal plasticity in the auditory system of insects, which was not self-evident by that time (Lakes et al. 1990). Studies on the elytral sound production identified a broad song spectrum range up to the ultrasonic range (Keuper et al. 1988). High temporal resolution of song features revealed individual sound impulses when the plectrum strikes along the teeth of the file (pars stridens) of the wings during sound production and age-related wear lowers this tooth impact rate (Stiedl et al. 1991). Thereby, the concept of synchronized activity of ensemble populations of neurons for parallel stimulus processing (that could not be explained by single response properties) emerged (Rössler et al. 1990, 2006). Female bush crickets demonstrated behavioral (phonotactic) discrimination between songs composed of song syllables with different sound impulse rates (Stiedl et al. 1991). These naturally occurring differences in sound impulse rates within syllables were not reflected in the temporal action potential discharge patterns of individual auditory receptor neurons, but they resulted in distinct patterns of synchronization in the ensemble activities of auditory receptor neurons. This discovery was made years before the concept of synchronized activation was described and globally accepted in olfactory information processing. Behavioral (phono- and vibrotactic) experiments addressed the importance of auditory and vibratory communication signals as an important basis for the survival of species for mate localization (Stiedl and Kalmring 1989). Finally, ecological studies on the distribution patterns of individuals in the habitat suggested that oviposition sites influence larval distribution, whereas adult males show clumped distribution due to auditory interaction. Main research findings from different Orthopteran species are highlighted in Table 1.

Table 1 Taxonomy and systematics of the Orthoptera species studied by Klaus Kalmring and his group and the main results of their experiments on auditory signals (A), behavior (B), ecology (E), morphology (M), neuroanatomy (N) and electrophysiology (P)
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The bibliography of Klaus Kalmring lists 85 publications in total (see supplementary information) from 1967 to 2006. However, the output of his group is even larger, because he did not insist on honorary authorships as head of the group. The publication of the book Acoustic and Vibrational Communication in Insects, co-edited with Norbert Elsner in 1985 and based on two symposia held at the 17th International Congress of Entomology in Hamburg, is a milestone in the developing field of what we now call ‘biotremology’. The comprehensive analysis of the “auditory–vibratory sensory system” in bush crickets (reviewed by Rössler et al. 2006) is Klaus Kalmring’s scientific legacy.