±120 species in 9 sceloporine iguanid lizard genera are surveyed for modes of correlation between speciation and distribution, ecology, phylogeny, and chromosomal variability. The most common mode correlates speciation with allopatric isolation, no chromosomal, and little ecological change. 8 genera with less than 15 species each, show only this mode. Some Sceloporus show another mode: speciation not clearly involving allopatry correlates with ecological shifts and the fixation of negatively heterotic chromosomal mutations. 5 chromosomally derived lines include rapidly formed chains or cascades of chromosomal speciation. Species ending 3 chains are either ecologically superspecialist or superdominant and have used up substrates for particular types of chromosomal changes. Ancestral and derived species in the most recent chain contact geographically in hybrid zones less than 1000 meters wide, where they hybridize and backcross freely, but paradoxically, they exchange no chromosomes or genes. Even in Sceloporus, less than 25% of the speciation events involve chromosomal-change, yet nearly 60 of its ±75 species have such changes in their phylogenies. Allopatric speciation models explain all features of the first mode, but not the second. A sequence of 3 models accounts for the conditions associated with chromosomal speciation. Each is falsifiable, at least statistically, and tests are suggested.
Historical note, 2003: This manuscript was first submitted in 1977 to Evolutionary Biology and circulated widely in photocopy form. I withdrew it when I received a well meant review by a colleague who had clearly failed to understand the research paradigm I was working in, and said the writing was "unscientific". The reasons for this withdrawal are described in the draft paper, Hall, W.P. 1979a. An Evolutionist in an Epistemological Wonderland: Preface (1979) to Cascades and Sinks. Epistemological Wonderland and the present draft were submitted together to Evolutionary Theory in 1979, and accepted for publication, but with some suggestions for change (see attached editorial correspondence, van Valen 1979a, 1979b). I again withdrew the papers for further work.
The issues dealt with in Epistemological Wonderland were expanded and published as: Hall, W.P. 1983. Modes of speciation and evolution in the sceloporine iguanid lizards. I. Epistemology of the comparative approach and introduction to the problem. (in) A.G.J. Rhodin and K. Miyata, eds. Advances in Herpetology and Evolutionary Biology - Essays in Honor of Ernest E Williams. Museum of Comparative Zoology, Cambridge Mass. pp.643-679. Part II, never properly begun, was intended to resolve taxonomic issues underlying the comparative approach. The present paper, with substantial revisions, probably would have formed Part III.
To independently test the hybrid sink hypothesis presented in my thesis and this paper, I organized a project with Jacek Szymura at Jagellonian University in Krakow, and Jeffrey Mitton at the University of Colorado, Boulder, to expand on Szymura's explorations of the hybridization between Bombina bombina and B. variegata in central Europe. The nearly complete MS of this study, J.M. Szymura, J.B. Mitton and W.P. Hall. Population Genetic Analysis of a Narrow Hybrid Zone Between Bombina bombina L. AND B. variegata L. (Anura; Discoglossidae) In Poland), is presented on this Web site.
Work on all of these projects had to be suspended in August 1979 when I packed for a move back to the US to take up a one-year half time visiting asst. professorship at the University of Maryland, College Park. On arrival in College Park, I discovered that my workspace consisted of a converted janitor's closet, with room for a desk, a single file cabinet and a few shelves over the desk, and no support for access to cytology or darkroom facilities for the preparation of graphics. The income from the temporary position was also insufficient to rent enough space to unpack my research library at home. My employment circumstances in 1980 were such that it was also abundantly clear that I had no possibility of a continuing future in evolutionary biology. As a consequence it was physically and psychologically impossible for me to continue work on any of these projects or even to engage in further correspondence relating to them. However, the World Wide Web now provides me with the ability to present the work as a nearly completed web of knowledge about possible roles of chromosomal variation and hybridization in speciation.
