Proximate causes of a phylogenetic constraint on clutch size in parthenogenetic Aspidoscelis neotesselata (Squamata: Teiidae) and range expansion opportunities provided by hybridity

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Aspidoscelis neotesselata (Squamata: Teiidae), the triploid, parthenogenetic lizard endemic to southeastern Colorado, originated from a hybridization event involving normally parthenogenetic Aspidoscelis tesselata and bisexual Aspidoscelis sexlincata. A previous study of a sympatric assemblage of these taxa in the Higbee vicinity, Otero County, Colorado, found that A. neotesselata resembled A. tesselata in snout-vent length (SVL) and the much smaller A. sexlineata in clutch size, a pronounced departure from the clutch size predicted from the mean SVL of gravid females. The phylogenetic constraint hypothesis, that clutch size in A. neotesselata is influenced disproportionately by the genome acquired from A. sexlineata, was proposed to explain this enigma. Use of new characters in recently acquired samples of A. tesselata Pattern Class C (N = 44), A. neotesselata Pattern Classes A, B, and C (N = 132), and A. sexlineata (N = 31), revealed that clutch size in A. neotesselata is genetically constrained by both progenitors-a nonadditive component from A. tesselata (large egg volume) and an additive component from A. sexlineata (reduced body volume). Although mean oviductal egg volume, mean SVL for hatchlings of the year, and maximum observed body size were similar in A. neotesselata and A. tesselata, representatives of A. neotesselata attained reproductive maturity at smaller body sizes, and their oviductal eggs were proportionately longer and narrower than those of both progenitor species. Gravid individuals of A. neotesselata were intermediate to those of A. tesselata and A. sexlineata in body volume (BV) and SVL, but, as previously reported, the mean clutch sizes of A. neotesselata and A. sexlineata were similar and significantly smaller than that of A. tesselata. Statistically, egg volume was the least variable of the four primary reproductive attributes investigated. This would presumably ensure the production of hatchlings of adaptive size by each species, a factor that likely supersedes clutch size and body volume in maximizing individual fitness. Hybrid-derived polyploidy (i.e., the addition of an A. sexlineata genome to the diploid genome of A. tesselata) in A. neotesselata and the postformational origin of geographic Pattern Classes A, B, and C, have resulted in a constellation of adaptations that extend well beyond reproductive characteristics. These adaptations have permitted each of the three triploid pattern classes to exploit mutually exclusive habitats, some at a distance of 173 linear kilometers west-northwest of the northern range boundary of A. tesselata in southeastern Colorado. Copyright 2006 Society for the Study of Amphibians and Reptiles.

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