One or two eggs: what underlies clutch size variation within a gecko species?

Although the majority of reptiles show variable clutch sizes, geckos have a fixed clutch size (one or two eggs) and modify reproductive output by changing the offspring size or clutch frequency. However, the clutch size of several geckos is not strictly fixed at the species level; they actually lay both single- and double-egg clutches. We still do not fully understand if clutch size variation within a gecko species is due to adaptive control or reproductive failure like accidental absorption of one of two eggs. This study investigated differences between single- and double-egg clutches of a gecko species in terms of reproductive frequency, egg size, and offspring trait. I housed mourning geckos Lepidodactylus lugubris in a controlled environment and observed their reproduction for seven years. No large differences between single- and double-egg clutches were detected in reproductive frequency and egg size, indicating that life-history trade-offs do not explain much about clutch size variation. Single-egg was comparable in egg size to double-egg, but hatchlings from single-egg showed significantly lower body condition than did those from double-egg. These results suggest that the single-egg is not only a reduction of reproductive output per clutch, but it may provide negative effect on ontogeny.