Precocious maturation and semi-multivoltine lifecycle in a subtropical grass lizard, Takydromus toyamai

There are many short-lived animals, but those displaying a lifecycle with more than one generation per year (multivoltine lifecycle) are rare among terrestrial vertebrates. The multivoltine lifecycle requires rapid growth and maturation and a long active season. Thus, small lizards in humid tropical or subtropical areas are candidates for multivoltine lifecycles. To test this prediction, we conducted a capture-mark-recapture study of a subtropical grass lizard, Takydromus toyamai, endemic to Miyako Islands, Japan. Juveniles grew very quickly, averaging 0.3 mm/day in the warm season, and attained sexual maturity at 2.5 months post-hatching. The breeding season was very long, and hatchlings emerged from May to November. The prolonged breeding season and rapid growth to maturity allowed some individuals to produce a second generation in their first year. Estimates of hatching date from growth rates indicated that many females that hatched in May-June became gravid 76-120 days after hatching and 122-165 days after oviposition of the eggs from which they hatched. Analyses of juvenile survivorship and month of hatching suggest that nearly half of breeding adults were members of multivoltine generations, although the 2 generations were not discrete. The species is short-lived, with only 16% of individuals surviving beyond 12 months, and few individuals reproduced in a second year. We refer to this condition as a "semi-multivoltine lifecycle." Individuals that hatch late in the season defer reproduction until the following year and become founders of the next season's cohort. This putative advantage of late-hatching individuals may have driven the evolution of this lifecycle.