On the genetics of transplantation in the lizardCnemidophorus tigris

Evolution of parthenogenetic reproduction in Caucasian rock lizards: A review

Despite numerous works devoted to hybrid origin of parthenogenesis in reptiles, the causes of hybridization between different species, resulting in the origin of parthenogenetic forms, remain uncertain. Recent studies demonstrate that sexual species considered parental to parthenogenetic rock lizards (Darevskia spp) avoid interspecific mating in the secondary overlap areas. A specific combination of environmental factors during last glaciation period was critical for ectotherms, which led to a change in their distribution and sex ratio. Biased population structure (e.g., male bias) and limited available distributional range favoured the deviation of reproductive behaviour when species switched to interspecific mates. To date, at least seven diploid parthenogenetic species of rock lizards (Darevskia, Lacertidae) originated through interspecific hybridization in the past. The cytogenetic specifics of meiosis, in particular the weak checkpoints of prophase I, may have allowed the formation of hybrid karyotypes in rock lizards. Hybridization and polyploidization are two important evolutionary forces in the genus Darevskia. At present, throughout backcrossing between parthenogenetic and parental species, the triploid and tetraploid hybrid individuals appear annually, but no triploid species found among Darevskia spp on current stage of evolution. The speciation by hybridization with the long-term stage of diploid parthenogenetic species, non-distorted meiosis, together with the high ecological plasticity of Caucasian rock lizards provide us with a new model for considering the pathways and persistence of the evolution of parthenogenesis in vertebrates.

Genetic homogeneity based on skin histocompatibility and the evolution and systematics of parthenogenetic Cnemidophorus laredoensis (Sauria: Teiidae)

The parthenogenetic whiptail lizard Cnemidophorus laredoensis of Texas and México was derived from one or more hybrids between the gonochoristic species Cnemidophorus gularis and Cnemidophorus sexlineatus. We analyzed clonal structure in C. laredoensis on the basis of histocompatibility reactions to reciprocal skin grafting. Individuals of C. laredoensis rejected skin grafts from both parental species and from a hybrid between C. gularis and an undescribed parthenogenetic species. One lizard initially identified as C. laredoensis was found to be a triploid C. laredoensis × C. gularis hybrid, based on its histocompatibility reactions. The hybrid accepted grafts from individuals of C. laredoensis; however, C. laredoensis rejected grafts from this and a second hybrid. Seventeen individuals of C. laredoensis from six sites located throughout the range of the species in Texas were fully histocompatible, based on a large number of reciprocal skin grafts. Only three individuals of C. laredoensis from three sites donated grafts to other individuals of the species, but they were unable to host all or most of the reciprocal grafts. The skin histo compatibility among 17 individuals of C. laredoensis from six widely separated geographic sites points to a high level of genetic homogeneity in the species due to clonal descent from one parthenogenetic C. gularis × C. sexlineatus hybrid. Unidirectional rejection of skin grafts by three lizards could be a result of postformational mutations within this lineage, though this suggestion is open to question. The name C. laredoensis should be restricted to populations in Texas and México that are diagnostically identical with the parthenogenetic species described from two sites in Laredo, Webb County, Texas, in 1973.

Mixed leukocyte reaction, graft-versus-host reaction, and skin allograft rejection in the lizard, Chalcides ocellatus

In optimal seasonal conditions, splenocytes derived from adult lizards, Chalcides ocellatus, responded to vigorous proliferation in two- and one-way mixed leukocyte reaction cultures (MLRC). Data based on a large number of reciprocal MLRC provided evidence for the presence of strong and diverse lymphocyte activating determinants. These findings were fully confirmed in studies of systemic graft-versus-host reaction as intraperitoneal injection of splenocytes into newborn allogeneic recipients consistently induced splenomegaly, retarded growth and mortality. In favourable ambient conditions, adult lizards were also able to reject skin allografts in a subacute manner (mean survival time +/- S.E. = 28.8 +/- 0.88). The results clearly indicate that the lizard, Chalcides ocellatus, is endowed with an advanced type of cell-mediated immunity, and possesses strong and polymorphic histocompatibility antigens. Cellular alloreactivity in MLRC and towards skin grafts was, however, abrogated in winter and significantly diminished during spring through mid-summer as compared to mid-summer till autumn. The present study, thus, suggests that immunological defects attributed to reptiles might be more apparent than real, and essentially ascribable to the fact that the immune capacity of these ectothermic vertebrates is profoundly modulated by environmental conditions.