Female reproductive cycles in the northernmost populations of the two gekkonid lizards, Hemidactylus frenatus and Lepidodactylus lugubris

Lepidodactylus lugubris , a parthenogenetic gekkonid lizard of possible tropical origin, occurs on Kita‐Daitojima Island of the Ryukyu Archipelago and lays eggs almost throughout the year. The oviposition season of the sympatric population of another primary tropical, but bisexual gecko, Hemidactylus frenatus , is confined to between April and September. Laboratory experiments indicate that the hatching ratio of the egg reduces with the decrease of incubation temperature in both species. Some eggs of L. lugubris develop at 14°C of ambient temperature, wheras eggs of H. frenatus always die at temperatures of 18°C or lower. Examinations of stomach contents and fat body mass in the monthly samples suggest that food availability is not severely low for the geckos even during the winter, rejecting the previous assumption that food stress suppresses vitellogenesis in H. frenatus . No other environmental factors that may induce reproductive seasonality as phenotypic physiological responses were detected either. Tropical populations of H. frenatus and L. lugubris are known to lack distinct annual reproductive cyclicity. Thus, it is probable that the East Asian H. frenatus has evolved the winter quiescence of reproduction, presumably due to the poor embryonic tolerance of low temperatures. The absence of such seasonality in the sympatric L. lugubris seems to be attributable to its clonal nature which predicts the low genetic variability of the population from the colonization stage.