Sceloporus melanorhinus Bocourt (Pastel Tree Lizard)

Castiglia, Riccardo, Annesi, Flavia, Bezerra, Alexandra M. R., García, Andrés & Flores-Villela, Oscar, 2010, Cytotaxonomy and DNA taxonomy of lizards (Squamata, Sauria) from a tropical dry forest in the Chamela-Cuixmala Biosphere Reserve on the coast of Jalisco, Mexico, Zootaxa 2508, pp. 1-29 : 13-14

Sceloporus melanorhinus Bocourt (Pastel Tree Lizard)

Specimens analysed: two females (CEAC18, CEAC17), one male (CEAC15).

Distribution: Pacific coast of Mexico, from Jalisco to central depression of Chiapas, and adjacent Guatemala.

Subspecies: S. m. melanorhinus , Pacific coast of Oaxaca; S. m. calligaster, from Nayarit, to Guerrero; S. m. stuarti, central depression of Chiapas, and adjacent Guatemala.

Karyotype and DNA taxonomy: intraspecific variation in karyotype has been reported in this species (Cole 1970; Hall 1973; 2009). Males have 2n = 39 (20 macrochromosomes, 19 microcromosomes) while females 2n = 40 (20 macrochromosomes, 20 microchromosomes). The odd chromosomal number in males is due to presence of a medium sized metacentric Y chromosomes probably generated by the centric fusion of one autosomal acrocentric and a true Y microchromosome. In fact, males show the presence of a trivalent formation in males diakinesis corresponding to an X1X2 Y ( Hall 1973; 2009).

Moreover, another chromosomal polymorphism was noted since the species is polymorphic for an enlarged microchromosome (Em). Of seven S. melanorhinus karyotyped by Cole (1970), two of three individuals from one locality near Acapulco (Guerrero) were heterozygous for the Em, while the third individual from that locality and the remaining four from Tuxtla Gutierrez (Chiapas) and in a female near Colima lacked it. Of the six S. melanorhinus karyotyped by Hall (1973), only one from Rio Maria Basio, western Manzanillo (Colima), was heterozygous Em; while all of the remaining specimens, representing a second locality near Manzanillo and two localities near San Bias (Nayarit), lacked the Em chromosome.

This chromosomal variation due to Em chromosome does not match with subspecies designation, because different karyotypes have been found even in the same population.

The three specimens studied here shown two different karyotypes. The two females shows a karyotype with 20 macro- and 20 microchromosomes (not shown). In the male (CEAC15 - Fig. 6 ), the karyotype shows the additional medium-sized unpaired and biarmed chromosome identified by Hall (2009) as the Y chromosome. The enlarged microchromosome (Em) is lacking in the specimens here analyzed. The rDNA 16S has been studied for a single specimens from Guerrero, S of Chilpancingo ( Wiens & Reeder 1997). The divergence between the specimen from Chamela and that from Guerrero is 3%, a value found commonly among populations of the same species in reptiles.

Figures

FIGURE 6. Karyotypes of Sceloporus melanorhinus; specimen CEAC 15 male (2 n = 39). Sex chromosomes are tentatively identified following Hall (1973, 2009).