LAMPROPELTINI, Dowling, 1975

Cole, Charles J. & Hardy, Laurence M., 2019, Karyotypes of Six Species of Colubrid Snakes from the Western Hemisphere, and the 140 - Million-Year-Old Ancestral Karyotype of Serpentes, American Museum Novitates 2019 (3926), pp. 1-16 : 6

COMPARISONS WITHIN LAMPROPELTINI AND OTHER COLUBRIDS

Representatives of nearly all genera of the Lampropeltini have been karyotyped, including Arizona , Bogertophis , Cemophora , Lampropeltis , Pantherophis , and Pituophis . This clade diverged from other Colubrids about 24.5 mybp (million years before the present; Pyron and Burbrink, 2009; note that dates for nodes within phylogenies are estimates). Nearly all these snakes share a basic karyotype extremely similar to that of Lampropeltis triangulum ( fig. 1C ), but with variation in centromere position on one or a few of the smaller macrochromosomes. The similarities include the following details: diploid chromosome number; number of macro-and microchromosomes; and relative sizes and centromere positions on nearly all the macro-chromosomes, including chromosome 6 being telocentric. This condition is shared by a great number of species of colubroids from around the world that have been karyotyped, with minor variation (e.g., see karyotypes in Kobel, 1967; Becak and Becak, 1969; Bianchi et al., 1969; Bury et al., 1970; Dutt, 1970; Itoh et al., 1970; Baker et al., 1972; Singh, 1972, 1974; Ivanov, 1975; Hardy, 1976; Van Devender and Cole, 1977; De Smet, 1978; Mengden and Stock, 1980; Cole and Hardy, 1981; Gutiérrez et al., 1984; Yang et al., 1986; Moreno et al., 1987; Tan et al., 1987; Wei et al., 1992; Aprea et al., 2003; Matsubara et al., 2006; Mezzasalma et al., 2014). Neverthe-less, some species have strikingly different karyotypes (e.g., Bogertophis subocularis ; see Baker et al., 1971). Even so, the basic shared karyotype occurs in the species representing the ancestral form (see below), most of the recently derived forms, and the vast majority of the species. In the phylogeny of the Lampropeltini ( Pyron and Burbrink, 2009; Pyron et al., 2013), the ancestor of Arizona and Rhinocheilus apparently split off prior to the common ancestor of Cemophora and Lampropeltis , so it appears as if the shift in centromere position on chromosome 6 and apparent loss of a pair of chromosomes in Cemophora occurred after the clade to Cemophora diverged. In fact, Kobel (1967) and Aprea et al. (2003) reported that the basic karyotype of the Lampropeltini occurs in the European Coronella austriaca , including the detail of chromosome 6 being telocentric. This species was used as the outgroup by Pyron and Burbrink (2009), which, if correct, extends existence of the same ancestral karyotype back to approximately 24 mybp or more.

Looking further back throughout the phylogeny of Colubroidea to the common ancestor with the Viperidae and Pareatidae , to more than approximately 75 mybp ( Pyron and Burbrink, 2012), the majority of the known karyotypes remain similar again, although with some differences in centromere positions on chromosomes 5–8 and more frequent divergence from having 20 microchromosomes (e.g., Yang et al., 1989 and other references above). Nevertheless, Ota (1999) found in Pareas iwasakii (representing the related family Pareatidae ) the same basic karyotype as occurs in Lampropeltis triangulum , and it was also found in 41 out of 43 species of the Viperidae , representing diverse genera from several continents (see literature review by Cole, 1990). The same basic karyotype was also found in Homalopsis buccata by Pinthong et al. (2013). Deviations from this ancestral karyotype, as in Oxybelis aeneus reported here and in North American natricines ( Baker et al., 1972; Eberle, 1972) appear to be recent modifications on a few specific clades.

Figures

FIGURE 1. Snake chromosomes. A. Karyotype of Cemophora coccinea (2n = 34, with 16 macrochromosomes and 18 microchromosomes), AMNH R-107321, male, with homomorphic sex chromosomes, ZZ. B. Heteromorphic pair of sex chromosomes (ZW) from a female Cemophora coccinea, AMNH R-110750. Scale bar = 10 µm. C. Karyotype of Lampropeltis triangulum (2n = 36, with 16 macrochromosomes and 20 microchromosomes), AMNH R-109512, male, with one more pair of microchromosomes (arrow) than in A, with C representing the ancestral karyotype of colubroids.