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Aspidoscelis is a taxonomic genus of whiptail lizards in Teiidae. It contains both sexually reproducing species and all-female lineages that reproduce by parthenogenesis. This variation makes a closely related set of animals useful for studying how reproduction and chromosome organization interact.^[ref]

In a 2011 experiment, researchers crossed a triploid parthenogenetic female lineage with males of a sexually reproducing lineage. The resulting four-copy hybrid offspring were checked with molecular and chromosome measurements. Some female offspring themselves reproduced by parthenogenesis, establishing laboratory lineages able to reproduce without repeating the original cross.^[ref]

A chromosome-set calculation clarifies the change: an unreduced egg carrying three sets can combine with a sperm carrying one set to make a four-set offspring, $3n+n=4n$. This is tetraploidy, rather than merely four copies of one selected gene. Producing one viable hybrid is also different from demonstrating that its descendants can reproduce. The experiment tested both steps, linking the immediate effects of a cross to the persistence of a new reproductive lineage.

Gymnophthalmidae is a family of lizards within Lacertoidea, often called microteiids. It is distinct from Teiidae, despite that historical common name. Its members include forms with fairly conventional limbs and forms with strongly reduced limbs and elongated bodies, making the family useful for studying how a body plan changes during evolution.^[ref]

A morphological study distinguished modest reductions, such as losing one or two finger or toe bones, from much more extensive reductions that can leave no externally distinct adult limb. The investigators compared digit arrangements and also examined gene expression in developing reduced limbs. Adult anatomy and embryonic development consequently provide complementary observations of the same evolutionary problem.^[ref]

For an anatomical example, two feet can each have four visible digits while differing in which digit is absent or in the number of bones within each remaining digit. Merely counting visible toes collapses those possibilities into one score. Recording the detailed bone pattern and placing it on a phylogenetic tree gives a more informative test of whether superficially similar reductions share an evolutionary origin.

Lacertidae is a family of lizards within Lacertoidea, distinct from Teiidae, Gymnophthalmidae and amphisbaenians. It provides an important comparison for the latter group: common ancestry can connect normally limbed lizards with highly modified burrowing forms, so a wormlike body is not by itself a reliable map of evolutionary relationships.^[ref]

Lacertidae is also a useful system for investigating thermoregulation. A 2019 comparative study related environmental temperatures to thermal physiology and to the evolutionary histories inferred from genomic data. Behavioral choices, such as basking or using shaded shelter, are relevant because the air temperature at a site is not automatically an animal's body temperature.^[ref]

For an illustrative measurement design, offer a lizard a range of warm and cool positions and record both its chosen position and body temperature. Repeating the assay at different background temperatures distinguishes an available environment from the temperature the animal actively selects. Comparisons between species then require the same measurement protocol and an account of their relatedness; otherwise a difference caused by the assay or shared ancestry can be mistaken for an independent adaptation.

Lacertoidea is a branch of Squamata containing Lacertidae, Teiidae, Gymnophthalmidae and amphisbaenians. It groups lineages by common ancestry, despite striking differences in their visible bodies. In particular, a burrowing, nearly limbless amphisbaenian can be more closely related to a normally limbed member of Lacertidae than superficial resemblance to a snake suggests.^[ref]

This grouping is a useful test of convergent evolution. Imagine recording only whether an animal has external legs: many otherwise unrelated burrowing forms would receive the same score. Recording hundreds of anatomical characters and comparing many genes supplies additional, partly independent evidence. The 2015 integrated analysis used 691 morphological characters and 46 genes, and included fossils as well as living species. Its combined analyses recovered Lacertoidea, while some deeper relationships depended on uncertain placements of fossil taxa.^[ref]

Teiidae is a family of lizards within Lacertoidea, including the whiptails of Aspidoscelis. It is a separate lineage from Gymnophthalmidae. Beyond their place in reptile classification, some whiptails offer a striking example of parthenogenesis: females produce offspring without fertilization.^[ref]

In a 2010 study of parthenogenetic Aspidoscelis, investigators asked how eggs could retain the parental complement of chromosomes and preserve heterozygosity. Chromosome imaging and fluorescent probes showed an extra premeiotic doubling, followed by pairing of genetically identical chromosome copies. The cells still underwent meiosis and chromosomal crossover; reproduction did not simply bypass the entire meiotic program.^[ref]

A simplified genetic example explains the significance. Begin with distinguishable chromosome versions $A$ and $B$. After copying, matching $A$ with another $A$ and $B$ with another $B$ permits exchange between equivalent copies while retaining both parental versions in the unreduced egg. This differs from mechanisms that discard one version and thereby lose heterozygosity. The finding concerns particular parthenogenetic species; it does not make every member of Teiidae an asexual animal.