Immunological Detection of Convergent Evolution in the Frog Anotheca Spinosa (Hylidae)

Maxson, Linda R. (Department of Genetics and Development, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801) 1977. Immunological detection of convergent evolution in the frog Anotheca spinosa (Hylidae). Syst. Zool. 26:72-76.-Protein evolution is primarily a divergent process, proceeding independently of organismal or morphological evolution (Wilson et al., 1974). This makes proteins ideal tools for detecting cases of convergent anatomical evolution. A probable instance of convergent evolution, involving the monotypic genus Anotheca, was detected by comparative studies of serum albumin. On the one hand, Anotheca albumin is shown to be as similar to the albumins of several North American Hyla as the albumins of the North American Hyla are to one another. On the other hand, Anotheca albumin is very different from the albumins of the marsupial tree frogs, as different as are those of Hyla. Phylogenetic analysis of the albumin data indicates that Anotheca is phyletically a member of the subfamily Hylinae. Thus, its placement in the Amphignathodontinae was due to convergent morphological evolution in Anotheca to resemble the other genera of marsupial tree frogs. [Serum albumin; phylogenetic analysis; Hylidae.] The tree frog family Hylidae is composed of approximately 500 described species, with about 30 new species being described each year. The 32 currently recognized genera are collected into four subfamilies, based on morphological characters and life history (Duellman, 1970): Hylinae, Amphignathodontinae, Hemiphractinae, and Phyllomedusinae. Anotheca spinosa (a monotypic genus found only in Central America and Southern Mexico) is currently assigned to the Amphignathodontinae, along with the marsupial tree frogs, on the basis of cranial osteology and external morphology (Duellman, 1970). However, Anotheca differs from other amphignathodontine frogs in having less specialized breeding habits and in having a diploid chromosome number of 24, as do most Hylinae. In three of the remaining six amphignathodontine genera where karyotype analysis has been performed, Gastrotheca and Fritztana species have each shown diploid numbers of 26 and 28, and Flectonotus had a diploid number of 30 (Duellman, 1970; Bogart, 1973). These facts led Duellman and others to wonder whether Anotheca's anatomical similarity to the marsupial tree frogs might not have resulted from convergent evolution. An earlier study of hylid albumins (Maxson and Wilson, 1975) indicated the albumin of Anotheca to be more similar to that of Hyla regilla (a hyline tree frog) than it was to the albumins of the marsupial tree frogs (Tables 1 and 2). Indeed, Anotheca albumin was as close to Hyla regilla albumin as was the albumin of numerous other North American Hyla species (Maxon and Wilson, 1974). Since albumin evolves at a rather steady rate in frogs (Maxson et al., 1975), it appeared likely that upon phylogenetic analysis, Anotheca would prove to share a common ancestor with the Group 1 assemblage of' hyline lineages (Maxson and Wilson, 1975 and Fig. 1). MATERIALS AND METHODS Plasma and phenoxyethanol preserved muscle tissues from representatives of 60 species of hylid frogs were used as sources of albumin. Voucher specimens are deposited in the Museum of Vertebrate Zoology, University of California, Berkeley. Albumin was purified from plasma and