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IN MEMORIAM
Harlan Lewis (1919-2008)
Arthur C. Gibson1
1Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, U.S.A., 90095-1606 E-mail: agibson@biology.ucla.edu.
Harlan Lewis, a pioneer on the genetics of plant speciation, died on December 12, 2008 at his home in Southern California, one month shy of his 90th birthday.
Starting in the mid-1930s, Julian Huxley, Theodosius Dobzhansky, Ernst Mayr, and G. Ledyard Stebbins refashioned the field of speciation as “The Modern Synthesis.” They did so by applying the principles of genetics to Darwin’s hypotheses, largely accepting allopatric speciation, a process in which disjunct populations differentiated from one another given appropriate conditions and then maintained their distinctiveness if they eventually came back into contact. For most groups of animals, allopatric speciation was considered a sufficient explanation for the origin of all species; it was often reinforced by behavioral, ecological, developmental, or genetic incompatibility mechanisms.
An earnest effort was made to apply the same concepts to speciation in plants, but here the picture was more complex as a result of hybridization, aneuploidy, polyploidy, and local genetic barriers (barriers within morphologically defined species), in addition to spatial separation. Edgar Anderson developed the concept of “introgressive hybridization,” whereby the genes from one distinct species or race entered another following hybridization, and interpreted a great deal of the variation he observed in that light. Mayr’s concept of the “biological species,” neatly defined units separated by genetic barriers with no internal barriers, proved ultimately not to apply well to plants because of all the special phenomena just mentioned, and because experimental hybridization was simple enough to show where and how the “biological species concept” failed. On the other hand, chromosomes, which varied through aneuploidy, polyploidy, and internal reassortment, proved to be especially valuable as indicators of evolutionary processes. Harlan Lewis was a leader in the movement to understand the cytogenetics of natural populations and species and the processes by which they diverged. He and his students provided many examples that caused the textbooks to be rewritten.
Harlan Lewis was born on January 8, 1919, in Redlands, California, and graduated in 1937 from Redlands High School, before attending San Bernardino Valley College (A.A. 1939) and then transferring to UCLA in 1939, on the day Hitler invaded Poland. Starting at age ten, Harlan was an enthusiastic plant collector; at UCLA he connected immediately with Carl Epling, world authority on mints (Lamiaceae), who had by that time, under the influence of Dobzhansky, become fascinated with mechanisms of speciation in the fly genus Drosophila, which was providing a treasure trove of information on species and speciation for animals. Lewis and Epling (1940) published a paper together while Harlan was an undergraduate. Harlan continued with Epling for graduate research on the mint genus Trichostema (M.A. 1942; Lewis, 1945) and doctoral research on sources of variability in three California species of Delphinium (Ranunculaceae; Lewis et al., 1951; Epling and Lewis, 1952; Lewis and Epling, 1954). By conducting very detailed reconnaissance of delphinium populations in central California. Through field and greenhouse studies, Harlan determined that diploid and autotetraploid races of the Delphinium species, which were virtually identical morphologically, lived in neighboring colonies in which chromosome number differences were permanently maintained with no ecological or habitat differences and without involving the kind of differentiation that might have led them to be treated as distinct species.
During the war years, Harlan Lewis was able to continue his plant studies by also working at Cal Tech on a project concerned with camouflaging oil tanks with native plants, a strategy that became unnecessary after the Battle of Midway. While in Pasadena, he interacted with their famous faculty and even published a paper with Frits Went on the germination of California native plants (1945). Fortunately for science, although Harlan was a member of the 44th infantry division and served briefly in post-Hitler Europe, he convinced the army that they would not need him for post-war service in Japan, and in 1946 he was able to complete his dissertation, the first UCLA Ph.D. in botany, and then joint the departmental faculty as a member.
Ledyard Stebbins, then becoming a giant in evolutionary biology, was a member of his doctoral committee. After he defended his dissertation in May, 1946, Harlan drove Stebbins through the nearby Santa Monica Mountains to discuss ideas for systematic research on annual plants. Annual plants could be grown, maintained, and manipulated much more easily than the perennial delphiniums. Stebbins suggested that a fertile topic would be Clarkia (Onagraceae), a genus that is now automatically associated with Harlan Lewis. He had reviewed papers by the Scandanavian geneticists Håkansson and Hiorth that showed the rich variation in chromosome number in these plants and ease with which they could be used for experimental purposes.
Of the nearly four dozen species of Clarkia, all but two are restricted to summer-dry, mediterranean-type climate areas of California. With so many similar, variable, and confusing species, the genus appeared to Stebbins, and to Harlan Lewis, as one that might have experienced rapid evolutionary radiation and in which speciation might still be proceeding rapidly (Lewis, 1953a, 1953b; Lewis and Raven, 1958). The taxonomy of Clarkia (including Godetia and Eucharidium, segregate genera that were recognized before Lewis’s studies) was confusing, with the boundaries between species not clearly defined. Having selected Clarkia for detailed study, in June, 1946, Harlan and his botanical wife Margaret began fixing root tips and collecting seeds of central California’s clarkias for chromosome number determination and experimental study. At UCLA team Lewis and Lewis sterilized beds and established breeding populations of these annuals in an experimental garden. The next year Harlan Lewis was awarded a one-year postdoctoral fellowship, spent at the John Innes Horticultural Institution at Merton Park near London. Conducting cytogenetic studies on these plants under the sponsorship of Kenneth Mather, Lewis (1949) published in the 1948 John Innes annual report his first chromosome counts of Clarkia.
It was through a combination of cytogenetics with detailed ecological studies, that Harlan Lewis would make his mark on understanding speciation processes, much as Theodosius Dobzhansky had done earlier for Drosophila. Returning from England in 1948, the young assistant professor soon began to work with his graduate students to sort out the rich evolutionary history of Clarkia.
Clarkia exhibits a wide range of chromosome numbers (n=5-12, 14, 17, 18, 26; original basic chromosome number, x=7), indicating a complexity that is undetectable by studying morphology alone. As Harlan Lewis and his graduate students teased out the reproductively isolated taxa, new species were recognized, and the full extent of reticulate evolution in the genus, involving many instances of polyploidy, aneuploidy, and race formation, became apparent. As one example, in one dibasic polyploidy series, a species with a diploid chromosome number of 2n=16 ´ a species with 2n=18 gave rise following chromosome doubling in the hybrid to Clarkia davyi, 2n=34, an allotetraploid, which subsequently hybridized with diploid C. speciosa, 2n=18, resulting with chromosome doubling in the origin of Clarkia prostrata 2n=52, a hexaploid. “floating” rings of chromosomes resulting from translocations were a common feature of the cytology of naturally occurring plants of Clarkia, as were supernumerary chromosomes, apparently associated with the origin of stable aneuploidy populations. In his first classic paper on evolution in clarkias, Lewis (1951) showed his commitment to intense sampling of natural populations. He documented a remarkable range of supernumerary chromosomes in Clarkia elegans sampled along 12 kilometers of a highway, with the extra chromosomes preserved through generations with no detectable genetic effect.
The first paper by Harlan Lewis that excited the scientific community was one explaining the origin of a species that he discovered in 1947, spotted by him while botanizing along winding Highway 49, then a dirt road, in Maricopa County in the foothills of the Sierra Nevada (Lewis and Roberts, 1956). The unusual populations grew on a north-facing talus slope above the Merced River. He later named these populations Clarkia lingulata (2n= 18), a species still known from only two populations, each about 100 m2 in size and just three kilometers apart, growing within sight of populations of C. biloba subsp. australis (2n=16), from which they originated by gaining an extra pair of chromosomes with two long arms. These duplicated chromosomes in C. lingulata made the two entities completely isolated genetically. Lewis and graduate student Peggy Roberts demonstrated that interspecific hybrids were difficult to obtain, and that the hybrid offspring were essentially sterile when selfed or backcrossed. Lewis had discovered a speciation event soon after it had occurred. This case demonstrated one role that genetic mistakes can play in the origin of species, especially in a rapidly evolving genus.
Working with C. lingulata and other narrow endemics related to widespread (and presumably ancestral) progenitors, Lewis noticed that derived species of Clarkia tend to be restricted to drier sites, where they occur as peripheral populations at the edge of the distribution of the parent species. In 1955, Lewis planted mixtures of C. biloba and C. lingulata in four locations and studied them over four generations under natural conditions. In these experimental populations, C. biloba was typically the better competitor¾except at the driest site. This pattern led Lewis (Lewis and Roberts, 1956) to propose a mode of speciation that he called catastrophic selection (Lewis, 1962), in which peripheral populations, under greater stress than those located at more favorable situations near the center of their ranges, experience extinction or near extinction. If that population recovers, the few surviving individuals are apt to have a distinctive set of characteristics, by chance alone, and can rapidly evolve as a deviant daughter species with unique features. Sometimes catastrophic selection is interpreted as a version of quantum speciation, but experts recognize that genetic mistakes may be important mechanisms for isolating populations and rapid speciation. It was very satisfying to Harlan Lewis that, years later, his general speciation model and specific explanation for the origin of C. lingulata was supported by molecular studies showing few allelic differences from parental C. biloba and reduced heterozygosity in the daughter species (Gottlieb, 1974).
Harlan Lewis ran a very active laboratory with many graduate students from 1947 for about 15 years. His students worked together, often on Clarkia, all emphasizing cytogenetics in their studies. Common facilities and a sense of exciting discovery drove them forward to a number of exciting discoveries about the nature of speciation. With his close colleague Henry J. Thompson, Harlan and their studies scoured the mountains, valleys, and deserts of Southern California, eager to study the plants biosystematically and creating an outstanding learning environment in the process.
As a central product of these years, Harlan and Margaret Lewis (1955) published a comprehensive monograph of Clarkia, which helped greatly to clarify the phylogeny of that genus. That same year Harlan was named an AAAS Fellow and received a Guggenheim Fellowship to continue his groundbreaking studies, and he had become an active player in key evolution, systematic, and genetic organizations. Carl Epling in 1955 honored him by naming a mint from Ecuador Harlanlewisia murex.
While a professor in botany and then also dean of life sciences (1962-81), Harlan Lewis had an important impact on evolutionary biology by producing a number of outstanding graduate students who continued to expand our knowledge of speciation, cytogenetics, and systematic botany. Lewis continuously was recognized for his research and leadership in the field, including being elected president of the Pacific Division of the Botanical Society of America (1959), Society for the Study of Evolution (1961), American Society of Plant Taxonomists (1969), International Organization of Plant Biosystematics (1969-75), and American Society of Naturalists (1971). He served on numerous editorial boards, for Evolution was an associate editor (1952-54) and editor (1972-75), and for The American Naturalist he was an associate editor (1966-67). He was also named a fellow of the California Academy of Sciences.
Throughout his academic career, Harlan Lewis showed a keen interest in ornamental horticulture, combining his energy with that of his colleague Mildred Mathias at UCLA in informing others about the names and characteristics of the cultivated flora of Southern California. He co-taught a number of undergraduate and graduate courses with Professor Mathias. Harlan served as president of Southern California Horticultural Society, and maintained an outstanding living collection of unusual plant species at his home, which he proudly showed to the many distinguished visitors.
Harlan Lewis retired from UCLA in 1982 but continued to remain active in studying plants. Since retirement, he authored treatments of Clarkia and Gayophytum (Onagraceae) and Trichostema (Lamiaceae) for the various editions of The Jepson Manual and the upcoming volume in Flora of North America. In 1984 the Botanical Society of America convened a symposium in his honor on “Molecular Evidence and Plant Phylogeny,” and the 1991 volume of Madroño was dedicated to Harlan Lewis for his contributions to California botany. Harlan Lewis took great joy in describing a new species of Trichostema in 2006. He will be remembered by many in the local area as a prominent member of the Rotary Club. And as a distinguished professor emeritus, he was instrumental in improving services for the emeriti at UCLA, and was named 2006 Emeritus Professor of the Year.
Those who knew Harlan Lewis recognized an individual who worked diligently to meld the fields of systematics, genetics, and evolution, with a strong interest in defining the nature of species in the context of ecology. He had a quick, analytical mind and attacked research projects with creative and analytical approaches that were cutting edge for his time. To the UCLA students, he continued to teach biology while serving as dean.To his graduate students he gave expert guidance, always willing to impart his knowledge, and encouraged freedom to ask the most interesting questions. On top of that, Harlan Lewis was always invested personally in any paper that he published, any research experiment performed, and in excellence in science overall.
Acknowledgments. Thanks to Dr. Peter H. Raven, a graduate student and protégé of Harlan Lewis, for his helpful comments on the manuscript.
Literature Cited
Epling, C. and H. Lewis. 1952. Increase of the adaptive range of the genus Delphinium. Evolution 6: 253-267.
Gottlieb, L.D. 1974. Genetic confirmation of the origin of Clarkia lingulata. Evolution 28: 244-250.
Lewis, H. 1947. Leaf variation in Delphinium variegatum. Bulletin of the Torrey Botanical Club 74: 57-59.
Lewis, H. 1949. Chromosome numbers in Clarkia and Godetia. John Innes Horicultural Institution Annual Report 1948: 19.
Lewis, H. 1951. The origin of supernumerary chromosomes in natural populations of Clarkia elegans. Evolution 5: 142-157.
Lewis, H. 1953a. The mechanism of evolution in the genus Clarkia. Evolution 7: 1-20.
Lewis, H. 1953b. Chromosome phylogeny and habitat preference of Clarkia. Evolution 7: 102-109.
Lewis, H. 1962. Catastrophic selection as a factor in speciation. Evolution 16: 257-271.
Lewis, H. and C. Epling. 1940. Three species pairs from Southern and Lower California. American Midland Naturalist 24: 743-749.
Lewis, H. and C. Epling. 1954. A taxonomic study of Californian delphiniums. Brittonia 8: 1-22.
Lewis, H., C. Epling, G.A.L. Mehlquist, and C.G. Wyckoff. 1951. Chromosome numbers of Californian delphiniums and their geographical occurrence. Annals of the Missouri Botanical Garden 38: 101-117.
Lewis, H. and M.E. Lewis. 1955. The genus Clarkia. University of California Publications in Botany 20: 241-392.
Lewis, H. and P.H. Raven. 1958. Rapid evolution of Clarkia. Evolution 12: 319-336.
Lewis, H. and M.R. Roberts. 1956. The origin of Clarkia lingulata. Evolution 10: 126-138.
Lewis, H. and F.W. Went. 1945. Plant growth under controlled conditions. IV. Response of California annuals to photoperiod and temperature. American Journal of Botany 32: 1-12.
Dr. Rogers McVaugh passed away September 24, 2009. Obituaries for Rogers can be found in the Chapel Hill News, in the University Gazette, and the University of Michigan herbarium site. [Posted 7 October 2009]
Botanist Dr. Elizabeth Neese passed away on August 8, 2008 from apparent heart failure at the age of 73. She had been a member of the American Society of Plant Taxonomists since 1980. She was well known and respected in the botanical community for her expertise on desert and alpine plants of the American West, as well as for her photography of Rocky Mountain wildflowers. She held a Master's in botany from the University of Minnesota and a Ph.D in botany from Brigham Young University. She is survived by four children and three grandchildren. She will be dearly missed. [Posted 20 May 2009]
Dr. Raymond Carl Jackson passed away April 7, 2008. See his memorium here.
CARROLL EMORY WOOD, JR., 88, of Boston, formerly of Roanoke and Salem, VA, passed away peacefully on March 15, 2009. at his Boston home. Professor of Biology at Harvard University and Curator of the Arnold Arboretum, Carroll was a mentor to many botanists and students at Harvard, the University of North Carolina, and the University of Michigan Biological Station. A specialist in the flora of the Southeastern U.S., he initiated, supervised and edited “The Generic Flora of the Southeastern United States”, to which he continued to contribute long after his retirement from Harvard. He was admired by his many friends and colleagues for his compassion, commitment and unfailing sense of humor. A resident of Boston’s South End for almost 50 years, Carroll was beloved by neighbors and friends for his gentle nature and horticultural guidance. A memorial “Celebration of Carroll” will be held Sunday, April 26, 2009, from 3-5 pm, at United South End Settlements, 566 Columbus Avenue, Boston.
Dr. John Reeder, famed agrostologist, passed away peacefully at his home in Tucson, Arizona, on the evening of February 8, 2009. He was born in Charlotte, Michigan on July 29, 1914. He grew up on a farm there, and first went to the University at Corvallis Oregon. It was here he met Charlotte Goodding, whose father, Leslie Goodding, later became a well known botanist in southern Arizona.
John was married to Charlotte in 1941 in Corvallis, Oregon. She was working in the Herbarium there. He later joined the Armed Forces near the beginning of World War II. He was stationed in New Guinea, where he collected grasses to send back to the US Herbarium. Among his collections was Melinus repens, which was then thought to be a native of New Guinea for a time. John was on one of the few small Malaria Units, made up of a dozen or so people, whose mission was Malaria Control among the troops. “Jungle Rot,” a fungal infection, became a problem for people stationed it this wet and warm place, and many people, including John, were hospitalized because of it. He spent 6 months in Fawn General Hospital, after which he was reunited with Charlotte and spent the summer at his folks’ farm in Michigan. John was accepted at Harvard, and he attended classes there, living on the GI bill payment and simultaneously held a job at Jamaica Plain Herbarium, which boasted a fine library. He received his PhD. and worked at Yale the next 20 years, teaching Dendrology and Plant Taxonomy through the Forestry Graduate School. John and Charlotte left Yale in 1968 to go to Rocky Mountain Herbarium at Laramie, Wyoming, studying grasses in his retirement. Later they moved to Tombstone,Arizona, for three years. Tombstone proved to be too far from a major herbarium, and they moved to Tucson in 1983, to the house John and Charlotte lived in until his death. John and Charlotte were both very active in their older years, supplying the Herbarium with a bent toward grasses and provided ARIZ with one of the best, and best curated grass collections, in the world.
In the words of one of our most active and productive botanists associated with ARIZ, Dr. Richard Felger states “Grasses seemed like such a mystery that I never thought I could effectively deal with them. But that was to change. John and Charlotte patiently pointed out my mistakes in identifications and where the existing keys had problems. They demystified grasses for me –what a privilege to get a start from the world experts. They patiently pointed out subtleties, and are always available to help. In 1987 John and I went on a field trip to northern Sonora. In the mountains west of Cananea he scrambled up a rocky slope and re-discovered the long-lost Bouteloua eludens in Mexico. I will never forget how he whooped and yelled: "Eludens Hill," 27.0 km E of Cananea on Mex Hwy 2, 1524 m, rocky south-facing slope with numerous grasses and forbes. What a privilege that we have a world-class collection of grasses at ARIZ – due to the devotion of Charlotte and John Reeder. Just last week I saw John patiently showing a student how to identify some grasses. Their friendship and professionalism and enthusiasm have helped shape my career.”
Charlotte plans to continue her study of grasses at ARIZ, identifying and publishing works on grasses.
John Tucker
Marking the end of an era at UC Davis, Professor emeritus and past Herbarium Director Dr. John Tucker passed away on July 5, 2008 due to complications of a stroke suffered two weeks earlier. John was an oak expert. He wrote the key and descriptions for the oak family treatment for the 1991 Jepson Manual, and at the age of 92, he finished a new version of that treatment this past spring for the upcoming Jepson Manual revision. Many people benefited from John's expertise and sent him oak samples in letters or brought oaks to the herbarium for him to identify. He was generous with his time and always glad to look at any oak from anywhere.
John credited Maunsell Van Rensselaer, Director of the Santa Barbara Botanic Garden during its early years, with encouraging his interest in botany. John had long had an interest in trees, and he obtained a botanical assistant position at the garden after coursework at Santa Barbara State College and the University of Idaho — a position he returned to during summer vacations until 1942. John had thought that he might earn a degree in forestry, but Van Rensselaer noted John's careful horticultural, botanical, and plant collecting skills and encouraged him to get a degree in botany instead. With that advice, John continued on to UC Berkeley, where he earned a bachelor's degree and a doctorate, both in botany, in 1940 and 1950, respectively.
His collection notebooks from his senior year at UCB in 1940 already emphasized oaks, with long entries describing the appearance of each one. He was sometimes frustrated in his attempts to gather more information while out in the field with Ledyard Stebbins, his genetics teacher. On one excursion in San Luis Obispo County west of Santa Margarita, he commented "Stebbins and Walters were so intent in their chase after peonies that I didn't have time to stop and collect or get more dope on [the hybrid blue oaks that held his interest]."
His Ph.D., under the guidance of Herbert Mason, Ledyard Stebbins, and Adriance Foster, dealt with the evolution and relationships of scrub oak (Quercus dumosa) and related species, including hybridization between scrub oak and grey oak (Quercus turbinella), and the parentage of Alvord's oak (Quercus × alvordiana). On sabbatical leave in 1955-1956, John began to study variation in hybrid oak populations in the southern rocky mountain region, an extremely difficult task.
To say that John's studies of oak taxonomy were detailed is an understatement. During his numerous field expeditions, especially within California and the southwestern U.S., John described oak populations from an ecological, geological, historical, and taxonomic viewpoint. He collected flowers to look at chromosome counts, acorns to analyze their chemistry and viability, and seemingly endless population samples to look at leaf surfaces and architecture. Everything was documented with careful notes. He collected pollen and crossed oaks and then collected acorns to examine acorn viability and subsequent progeny — techniques more easily applied to annual plants rather than slow-growing trees like oaks. John's final collections were of Shreve's oak (Quercus parvula var. shrevei), a species whose characteristics and distribution had held his interest for more than a decade.
John did not have the luxury of focusing exclusively on research. While still a graduate student at UC Berkeley, he was hired as Director of what was then the UC Davis Botany Department Herbarium. At that time the herbarium housed 9,400 specimens in just six wooden cases. In 1951, he initiated an exchange program for trading extra specimens with other institutions, and under his leadership, the collection expanded dramatically. In the mid-1950s, the collection moved to a small temporary building with a metal roof, and John sweltered in the Davis summer heat. In 1961, it moved to a new home in Robbins Hall, a space that John designed. Upon his retirement in 1986, the Botany Department Herbarium was officially named the J. M. Tucker Herbarium to honor his 39 years as director. The J. M. Tucker Herbarium is now incorporated into the UC Davis Center for Plant Diversity herbarium which includes nearly 300,000 specimens from all over the world in a wonderful, new, temperature-controlled space for which John provided the lead gift.
In addition to directing the herbarium, John was hired to do plant identifications for UC Cooperative Extension, a task he did alone until 1953, when he hired June McCaskill to help him with that task. John also taught courses in general botany, plant taxonomy, and poisonous plants - courses which served hundreds of students per year. In his first two decades, he also had to collect all the plant material for his courses, something few UC professors still have to do. He was also very active on committees and took his committee service very seriously.
His exemplary service record is partly what led to John becoming Director of the UC Davis Arboretum for 12 years (at the same time as he was herbarium Director). This new administrative task was extremely time-consuming, basically another half-time job on top of his other duties. John took the task on, because he loved the Arboretum and had been involved with it since the early 1950s. In 1962, he established an oak grove near the western end of the Arboretum, planting acorns that he had collected from around the world. Today the Arboretum is home to 574 oak trees, including a number of native California oak species, and is recognized as a national resource.
During his career, John received numerous honors and awards, including a Guggenheim Fellowship in 1955. He was selected as a fellow of the American Association for the Advancement of Science and the California Academy of Sciences. He also was a member of the American Institute of Biological Sciences, American Society of Plant Taxonomists, Botanical Society of America, California Botanical Society, International Association for Plant Taxonomy, Sigma Xi honor society and Society for the Study of Evolution.
He was preceded in death by his wife of 46 years, the former Katrine June Petersen (June), son Chris, brother Robert, and sisters Viola, Valenzuela, and Helen. He is survived by his daughter, Carolyn Tucker, son, Peter Tucker, and grandson Carson Mack; sister Mary Kraft; and brothers Glenn Tucker, Ken Tucker and his wife Shirley, and Stanley Tucker and his wife Marion.
A memorial service in his honor is planned for 10 a.m. Saturday, Aug. 9, at the UC Davis University Club on Old Davis Road. The service will be followed by an informal luncheon. In lieu of flowers, the family requests that memorial donations be made to either the UC Davis Foundation Herbarium Endowment in support of the J. M. Tucker Herbarium or the UC Regents J. M. Tucker Endowment in Support of the Arboretum's oak collection. Donations may be sent to: Allison Chilcott, CAES Dean's Office, 150 Mrak Hall, One Shields Ave., UC Davis, Davis, CA 95616. — Ellen Dean, University of California, Davis. [Posted 23 July 2008]