| Aspidoscelis | |
|---|---|
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| California whiptail(Aspidoscelis tigris munda) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Family: | Teiidae |
| Genus: | Aspidoscelis Fitzinger, 1843 |
| Species | |
Over 40, see text.[1] | |
Aspidoscelis is agenus ofwhiptail lizards in thefamilyTeiidae.
Thenomenclature for the genusAspidoscelis was published byT.W. Reeder et al. in 2002. Manyspecies that were formerly included in the genusCnemidophorus are now consideredAspidoscelis based upon divergent characters between the two groups.
The nameAspidoscelis literally means "shield-leg", from the Ancient Greekaspido- ("shield") andskelos ("leg").[2]
The following species are recognized as being valid.[1][3]
Nota bene: Abinomial authority in parentheses indicates that the species was originally described in a genus other thanAspidoscelis.
In 2011, it was announced that aparthenogenetic hybridAspidocelis was bred in the laboratory.[4] This serves as a demonstration of how other hybrid parthenogens in this genus may have arisen.
Thirteen species withinAspidoscelis are unisexual, consisting entirely of females that reproduce through parthenogenesis—cloning unfertilized eggs to produce genetically identical offspring. These species originated through hybridization between divergent bisexual ancestral species, with the transition to asexual reproduction occurring in a single generation. This represents the largest group of unisexual vertebrate species known to science.[5]
The unisexual species exhibit varying chromosome numbers reflecting their hybrid origins. Diploid species formed through "primary hybrid speciation" when first-generation female hybrids of two distinct bisexual species began reproducing parthenogenetically. Triploid and tetraploid species arose through "genome addition," when cloned eggs of unisexual females were fertilized by males of bisexual species, resulting in offspring with additional chromosome sets.[5]
This hybridization seems separated by 15–25 million years of evolution. The parental species combinations have been determined through karyotypic, allozyme, and mitochondrial DNA studies. Early chromosome studies in the 1960s first revealed abnormal chromosome numbers in some unisexual species, indicating genome combinations from divergent species through hybridization.[5]
The unisexual species occur in two main geographic regions: the southwestern United States and northern Mexico, and southern Mexico with eastern Guatemala and Belize. Recent cellular research has revealed that chromosome number and genetic diversity are maintained across generations because identical, duplicated chromosomes pair during meiosis rather than homologous chromosomes.[5]
Examination of the evolutionary relationships ofAspidoscelis revealed that much hybridization and resultant introgression occurs between sexual species, but hybridization between two taxa with a patristic distance greater than 1% results in the creation of parthenogenetic offspring.[6] This finding supports the balance hypothesis (that a "sweet spot" of divergence is needed for two distinct species to create parthenogenetic lineages– to little divergence results in introgression, and too much results in offspring infertility or inviability).
Etymology:Aspidoscelis –aspido (Greek) shield; -skelos (Greek) meaning leg
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