Aim: Both theory and empirical data suggest that life histories of insular species slow down (the “island syndrome”). Insular individuals are hypothesized to lay smaller clutches of larger eggs compared with individuals belonging to closely related mainland species. Most lizards have variable clutch sizes and can lay any number between one egg and a species-specific maximum which can be well over 50 eggs. Many lizards, such as geckos and anoles, however, lay invariant small clutches of one or two eggs, and may thus be unable to manifest some aspects of the island syndrome. We tested whether insular species with either variable or invariant clutch sizes respond to insularity differently. Location: Worldwide. Methods: We assembled data on egg, clutch, hatchling and female sizes and brood frequencies of 2,511 lizard species. We tested whether the predictions of the island syndrome were met for lizards laying invariant versus variable clutches, controlling for female size and phylogenetic non-independence. We further examined whether geckos and anoles, the major clades with invariant clutches, differ from other lizards in the way they respond to insularity. Results: On islands, species with variable clutch sizes lay smaller clutches of larger eggs, from which larger hatchlings emerge, compared with mainland species. Lizards with invariant clutch sizes, however, decrease clutch size and increase clutch frequency but not hatchling or egg size, compared with mainland species. Main conclusions: Lizards with invariant clutch sizes may be unable to increase egg and hatchling sizes because of limitations set by the female body cavity and pelvic opening, or by arboreality. They nonetheless lay smaller clutches on islands and increase clutch frequency. We suggest that this may result from lower seasonality of tropical islands, leading to a greater spread of reproductive effort. Alternatively, the higher clutch frequency on tropical islands could result from fluctuations in population densities caused by tropical storms.
- egg volume
- invariant clutch size
- island biogeography
- island syndrome
- reversed island syndrome
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics