MadSci Network: Zoology |
The group of lizards you refer to, the whiptails of the south-western US, have fascinated zoologists and geneticists for years. Of the 11 or so whiptail species, about one-third are unisexual, reproducing by parthenogenesis, or development of an unfertilized egg. While I have not studied these lizards myself in the field, I would not identify the unisexual forms as subspecies, since they cannot interbreed with sexually reproducing closely related groups. I would tend to call each a separate species. There are probably herpetologists that would disagree with that classification, however. The mechanism of reproduction among the unisexual species seems to involve production of haploid eggs by females (which is quite normal). The eggs develop, however, without fertilization by sperm, and chromosomes double at some point to create diploid adults. This doubling of chromosomes does not allow any new rearrangements of genetic information, so all offspring are genetically identical ("a clone") of the previous generation. At least a couple of these unisexual species have been identified as hybrid offspring resulting from the mating of two other species of normal whiptails. For example, the unisexual New Mexico whiptail (Cnemidophorus neomexicanus) appears to be the result of a crossbreeding of the western whiptail (C. tigris) and the little striped whiptail (C. inornatus). Sexual reproduction seems to work normally in the latter two species. Check in a good field guide to see pictures of these and related whiptails. A good scientific reference to this field of study is: "Unisexual Lizards," by C.J. Cole, in _Scientific American_, Jan. 1984, pp. 94-100. See also "Parthenogenesis in Lizards" in Nov/Dec. '89 issue of _Reptiles & Amphibians Magazine_