Phrynosoma systematics, comparative reproductive ecology, and conservation of a Texas native

Ecologists use phylogenies as tools for understanding underlying evolutionary patterns and historical influence on species’ biology, physiology, and behavior. Phylogenetic relationships of Phrynosoma, horned lizards, were analyzed using sequences that encode the genes cytochrome b, ND4, 12S rRNA and 16S rRNA, as well as morphological characters. Field work was conducted on Mexican Phrynosoma to collect basic ecological information such as locality where each species was found, seasonal and daily activity periods, and reproductive cycles. Evolution of viviparity in Phrynosoma was studied in the context of the cold-climate hypothesis using generated phylogenies and data collected from field and museum specimens and data in the literature. Viviparous species showed two distinct reproductive patterns that were more divergent between closely related taxa. Reproductive cycles of viviparous species suggested this mode of reproduction is more labile and cycles may shift to enable sympatric and syntopic species to coexist. Viviparous species were found at significantly higher minimal and median (but not maximum) altitudes compared to oviparous species, suggesting viviparous species are restricted to higher elevations. No difference in latitude was found between oviparous and viviparous species. A strong phylogenetic component overshadowed differences in geographic range and altitude. Oviparous and viviparous clades separated early in the evolution of the genus and reproductive mode was maintained in each lineage. Reconstruction of a hypothetical ancestor suggested the ancestor of Phrynosoma inhabited altitudes 1654 - 1747 m in north-central Mexico. Oviparous species invaded lower altitudes while viviparous species remained at higher altitudes. Conservation of Texas horned lizards (Phrynosoma cornutum) was studied at 100 localities in Texas. Records from over 3,000 museum specimens and a large survey of Texans were used to study range and abundance patterns. Lizard censuses at 100 localities confirmed anecdotal reports the species had declined significantly in eastern and central portions of Texas, while more stable populations still existed in south and west Texas. Land-use patterns reflected loss of P. cornutum populations that occurred in the 1960s and 1970s. However, invasion of Solenopsis invicta and rise in pesticides used to kill all ants, including the lizards’ preferred diet, Pogonomyrmex, has led to an overall decline in food resources where habitat may still be viable.