Leslie D. Gottlieb

Leslie David Gottlieb (1936–2012) was a United States biologist described by the Botanical Society of America as "one of the most influential plant evolutionary biologists over the past several decades". He was employed at the University of California, Davis for 34 years, and published widely. In addition to his primary work in plant genetics, Gottlieb was an advocate for rare and endangered plant conservation.

Education

Following a Bachelor of Arts degree in English from Cornell University in 1957, Gottlieb's career began at Oregon State University in the Botany and Plant Pathology Department. He earned a master's degree in December 1965 with major professor Dr. Kenton Chambers and wrote a thesis on hybridization between species of manzanita (''Arctostaphylos'') trees in southwestern Oregon. His PhD at the University of Michigan 1969 examined patterns of diversity and mechanisms of speciation in '' Stephanomeria''. He was a faculty member of the Department of Genetics at the University of California, Davis from 1970 until 2004.

Research

Gottlieb researched a broad array of subjects including plant systematics, plant speciation (Quantum Speciation), polyploidy, gene duplication, biochemical evolution of isozymes and molecular genetics, and published more than 120 research papers and received a number of awards including a John Simon Guggenheim Fellowship (1975) and Fellowship of the American Association for the Advancement of Science (1985). In 1993 he was named Alumni Association Fellow of Oregon State University. In 1965 he earned his master's degree and wrote a thesis on hybridization between species of manzanita in southwestern Oregon.

Quantum speciation

Gottlieb was occupied with new species formation via " quantum speciation" throughout his career. As defined by Verne Grant, and cited by Gottlieb in his 2003 summary of the subject in plants "we can define quantum speciation as the budding off of a new and very different daughter species from a semi-isolated peripheral population of the ancestral species in a cross-fertilizing organism...as compared with geographical speciation, which is a gradual and conservative process, quantum speciation is rapid and radical in its phenotypic or genotypic effects or both." Grant thought that it would be accompanied by inbreeding in the founder population. Therefore, "quantum speciation" would be related to, if not identical with, in Gottlieb's use of the term, sympatric speciation. In fact Gottlieb's first publication on "sympatric speciation" in ''Stephanomeria','' published in 1971, was summarised by him in the above 2003 paper on "quantum speciation." Gottlieb did not believe that sympatric speciation required disruptive selection to form a reproductive isolating barrier, as defined by Grant, and in fact Gottlieb stated that requiring disruptive selection was "unnecessarily restrictive" in identifying cases of sympatric speciation.

In terminology used by Gottlieb, "progenitor species " would be the parental or "ancestral" species and the newly formed daughter species was "derived."

In his first study of progenitor-derivative pairs of species, Gottlieb examined the diploid, geographically limited, self-pollinating derived species '' Stephanomeria malheurensis'' with the diploid, geographically widespread obligate outcrossing ancestral species ''Stephanomeria exicua ssp. coronaria.'' In this case the reproductive isolating barrier was probably a change from outcrossing to selfing, and was maintained by this and a high degree of inter-specific sterility with ssp. ''coronaria'' as a result of chromosomal structural differences. Using what was then the most modern molecular technique, starch gel electrophoresis, to determine the genetics of populations Gottlieb found that ''S. malheurensis'' had a subset of the genetic variability of ssp. ''coronaria''. This, as well as its geographical close proximity, led Gottlieb to propose that ''S. malhurensis'' was a product of "quantum speciation." Additionally, ''S. malheurensis'' was found to be much less adapted to the local habitat than ssp. ''coronaria'' (hence the name malhurensis, which in French, "Malheur" means unhappiness or misfortune), indicating that it was probably not formed by disruptive selection.

In his second study of progenitor-derivative pairs of species, Gottlieb looked at the putative progenitor diploid ''Clarkia rubicunda'' and its hypothesized derivative, diploid ''C. franciscana''. In 1958, Lews and Raven hypothesized that ''C. franciscana'', which was highly self-pollinating and geographically limited, was derived from the outcrossing and more widespread ''C. rubicunda'' by large chromosomal structural rearrangements. Lewis and Raven hypothesized that ''C. franciscana'' had rapidly speciated from ''C. rubicunda'' by a mechanism Harlan Lewis called "catastrophic selection." As with ''Stephanomeria'', Gottlieb hypothesized that if ''C. franciscana'' was a derived species by "rapid speciation," then the derived species should have a genetic compliment that is similar to its progenitor, "i.e., possess few novel alleles." In fact, Gottlieb found that ''C. franciscana'' was genetically distinct from ''C. rubicunda''; it did not, as expected, have a subset of the genes found in ''C. rubicunda.'' A subsequent analysis published in 1992 on another population of ''C. franciscana'', unknown to Gottlieb 20 years earlier, led to similar conclusions. Importantly Gottlieb ended his 1973 study of ''C. franciscana'' by stating: "To strengthen phylogenetic analyses of rapid speciation, the criterion is proposed that a species accepted as having had a rapid and recent origin by chromosomal reorganization be substantially similar to its progenitor upon electrophoretic examination." In this context Gottlieb equated "electrophoretic examination" with genetic examination by the use of isozymes. And, using this criterion, Gottlieb was not able to conclude that ''C. franciscana'' was derived from its putative progenitor ''C. rubicunda'', as hypothesized by Lewis and Raven in 1958.

The next progenitor-derived pair of species Gottlieb examined were diploid ''Clarkia biloba'' and diploid '' Clarkia lingulata''. ''C. biloba'' is geographically widespread, while ''C. lingulata'' is known from only two populations on the southern periphery of ''C. biloba''; both are highly outcrossing, and there is no evidence that ''C. lingulata'' is better adapted to its habitat than ''C. biloba.'' They differ from each other by chromosomal structural differences, and hybrids between them are sterile. Lewis and Roberts proposed in 1956 that ''C. lingulata'' arose from ''C. biloba'' rapidly and in close proximity; in 1962, Lewis coined the term "catastrophic selection" to define its mode of origin. Gottlieb using starch gel electrophoresis, determined that indeed ''C. lingulata'' had a high degree of genetic similarity to ''C. biloba'', with fewer alleles and reduced heterozygosity. Subsequent studies confirmed a sister species relationship using chloroplast DNA as well as nucleotide sequences of the gene phosphoglucose isomerase. Gottlieb stated that this species pair, too, arose from quantum speciation.

Similar work was done with species pairs in the genus '' Layia''. Here, the widespread progenitor was the diploid ''L. glandulosa'', while the more restricted was the diploid ''L. discoidea''. Both are obligate outcrossers, though the former has ray flowers while the latter only has disc flowers. Further, both are completely interfertile, while ''L. discoidea'' is restricted to serpentine habitats. As with the former species pairs, Gottlieb applied the electrophoretic test to these species and found that they had a very high genetic identity for the isozymes studied. Therefore, the Gottlieb and Ford concluded that these two species were related as progenitor and derivative. Gottlieb proposed that ''L. discoidea'' arose relatively recently from adaptation to serpentine soils, also as an example of quantum speciation.

In his 2003 review, Gottlieb summarized:

The general lesson from the review of these studies is that quantum speciation remains an important and useful concept that can be applied to a greater variety of situations than initially envisaged. The genetic and chromosomal changes need not be as radical as once supposed, and a new species may originate and persist even without novel adaptations.

Another species pair that Gottlieb studied involved ''Gaura longiflora'' and ''G. demareei''; both species are annuals, diploids, highly inter-fertile and obligate outcrossers. In this study Gottlieb demonstrated that ''G. demareei'' was genetically highly similar to ''Gaura longiflora.'' Although he did not use the words "quantum speciation" in this study, Gottlieb concluded that these species pairs represented, as with ''Clarkia'' and ''Stephanomeria'' above, that "speciation in annual plants that are obligately outcrossing can occur with minimal genetic differentiation and accords with previous results for self-pollinating species." And further, that "speciation in annual plants appears not to be consistent with the orthodox views of the process (e.g., Mayr, 1963), which propose that organisms acquire reproductive isolation as an important by-product of adapting to habitats different from that of the parental ones, that this process marks a substantial genetic reconstitution, and that it occurs gradually over long periods of time."

Polyploidy

Another subject that intrigued Gottlieb throughout his career was that of polyploidy. In a commemorative 2014 review, Soltis et al. refer to Gottlieb and Roose's 1976 paper on ''Tragopogon'' as a "classic" in the field. In Soltis et al.'s words: "This classic paper addressed the link between genotype and biochemical phenotype and documented enzyme additivity in allopolyploids. Perhaps more important than their model of additivity, however, was their demonstration of novelty at the biochemical level. Enzyme multiplicity—the production of novel enzyme forms in the allopolyploids—can provide an extensive array of polymorphism for a polyploid individual and may explain, for example, the expanded ranges of polyploids relative to their diploid progenitors."

Although Gottlieb was not the first to hypothesize that enzyme multiplicity from dimeric isozymes could benefit the adaptedness of polyploids, his work on glutamate oxaloacetate transaminase in 1973 on the allotetraploid ''Stephanomeria elata'' was amongst the earliest as well as the first in a wild plant. Their classic 1976 paper also demonstrated the utility of isozymes in sorting out a complicated systematics in ''Tragopogon'', the presence of fixed heterozygosity in its polyploids, as well as the occurrence of novel isozymes (multimers) in the ''Tragopogon'' allopolyploids.

Gottlieb's further studies on polyploidy were concerned with the fates of those genes that were duplicated by an allopolyploidization event. That is, he was interested to know if the homeologus genomes of allopolyploids were changed by being in the same nucleus—were there novel patterns of gene expression that may influence fitness; or, to quote Gottlieb in 1999 do "...polyploid species evolve differently than their diploid parents". To sort this out, Gottlieb maintained that one had to know if any differences one saw in the allopolyploid were indeed differences from polyploidization or were they a "legacy" of the diploid progenitors.

In 1980, Roose and Gottlieb showed that in the recent (less than 100 years old) allotetraploid ''Tragopogon miscellus'', the genes for alcohol dehydrogenase reflected their expression in the diploid parents—there was no gene silencing, changes in tissue expression, or other effect on the catalytic properties of the enzyme. In 1999, Ford and Gottlieb found that the tetraploid '' Clarkia gracilis'' expressed the same genes for cytosolic phosphoglucose isomerase as the diploid parents; in this case gene silencing was identified in ''C. gracilis'' but they concluded that it probably occurred in one of the diploid parents, which was extinct. This was not the case when Gottlieb and Ford looked at the recent allotetraploids ''Clarkia delicata'' and ''C. similis''. In ''C. similis'' a gene producing phosphoglucose isomerase (called PgiC2) was silenced after the polyploidization event, while in ''C. delicata'' it was polymorphic for a normal gene and a silenced gene. As the authors concluded PgiC2 in ''C. delicata'' "presents an example of a natural experiment in progress because the defective allele may yet be fixed or lost from the species." Further, Ford and Gottlieb postulated that silenced genes in polyploid plants could be repositories of silenced genes for "plant breeding, for example, to alter metabolism or development of cultivated relatives."

Gene duplication

Although Gottlieb did much pioneering work on gene duplication in polyploids, he also pioneered studying gene duplication in diploids. He conducted many studies on various genes in several species, summarizing his work up to 1982 in ''Clarkia'' and ''Stephanomeria'' with duplicated genes producing phosphoglucose isomerase (PGI), alcohol dehydrogenase (ADH), and triosephosphate isomerase (TPI). In that review, he reported that PGI in ''Clarkia'' was produced in both the cytosol and plastids by one or two nuclear genes controlling the cytosolic PGI and one nuclear gene controlling the plastid PGI. The cytosolic genes received the majority of his attention, which were found to be either single or duplicated. Further, the duplicated genes were hypothesized to have arisen by translocations rather than by un-equal crossing over. Gottlieb applied gene duplications in determining the phylogeny of "Clarkia", because "Duplications originating by chromosomal rearrangements have a high probability of being unique. Thus species with the PGI duplication presumably descended from a single references ancestor and can now be grouped into a monophyletic assemblage..." He conducted biochemical studies of the cytosolic PGIs in '' Clarkia xantiana'', and found that there was very little difference in PGI's produced by the duplicated genes. In this same review he reported on a "family" of duplicated genes in '' Stephanomeria exigua'' that controlled the production of ADH. Here Roose and Gottlieb found that several tightly linked genes were inherited as one unit, and that populations could be polymorphic for duplicated and non-duplicated genes. He reported in ''Stephanomeria exigua'' that TPI was produced by two nuclear genes that assorted independently, and that hybrid enzymes between the two loci were not found. In ''Clarkia'' species both cytosolic and plastid TPI are produced by duplicated genes, and that both loci have genetic variability.

Post 1982 Gottlieb continued to work on other enzyme systems produced by duplicated loci in different species. In ''Clarkia'' he reported that duplicated genes for 6-phosphogluconate dehydrogenase (6-PGD) occurred throughout the genus for both cytosolic and plastid 6-PGD. In homosporus ferns he found a duplicated gene for TPI, resulting in the only case of heterozygosity resulting from gene duplication in ferns—counter to previous theory. In Layia Gottlieb found that isocitrate dehydrognease (IDH) isozymes had one gene controlling plastid IDH and 2-3 duplicated genes controlling cytosolic IDH. In this same study with '' Layia'' he found that phosphoglucomutase (PGM) also had one gene controlling plastid PGM, and duplicated cytosolic genes. He also examined six additional genera in the Madieae, and, with ''Layia'' representing 7 of the 10 genera in this tribe of the Asteraceae. Since he found that the duplicated cytosolic PGM were found in all the genera, he postulated that the duplication may have been present at the formation of this tribe, and hypothesized that examining PGM in other tribes may help understand phylogenic relationships in the Asteraceae. Further, he asserted that the discovery of duplicated genes in the tribe Madinae, along with the work of others, supported the view that duplicated genes in flowering plants was widespread. Additionally, since all such duplicated genes were unlinked, he favored the view that duplications were the result of overlapping reciprocal translocations rather than by unequal crossing-over. Gottlieb also applied PGM isozymes to species in the genus ''Clarkia'', and found that some species had duplicated plastid PGM, others had duplicated cytosolic PGM, and that their phylogenetic distribution was consistent with earlier work on PGI.

By far the majority of Gottlieb's gene duplication work was done with PGI in ''Clarkia'', though he also compared the PGI from the bacteria ''Escherichia coli'' with ''Clarkia'', showing that the nuclear encoded chloroplast (plastid) isozyme of PGI from '' Clarkia xantiana'' when compared to ''Escherichia coli'' shared 87.6% of its amino acid sequences. They also predicted that the cytosolic PGI's in higher plants would be considerably different than the plastid PGI's, given the hypothesized prokaryotic origin of plastid DNA, though would be more similar to eucaryotes. In 1996 Gottlieb and Ford reported that the cytosolic duplicated genes PGI1 and PGI2 were ancestral to all ''Clarkia'', but that some species had a silenced PGI2, and that the PGI2 had been silenced at least four times independently. Gottlieb's second to last paper studied PGI duplications in other genera of the Onagraceae

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