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Surf and Turf: Predation by Egg-Eating Snakes Has Led to the Evolution of Parental Care in a Terrestrial Lizard

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Surf and Turf: Predation by Egg-Eating Snakes Has Led to the Evolution of Parental Care in a Terrestrial Lizard

David A Pike et al. Sci Rep.

Abstract

Animals display a great diversity of parental care tactics that ultimately enhance offspring survival, but how such behaviors evolve remains unknown for most systems. Here, we studied the evolution of maternal care, in the form of nest guarding, in a single population of long-tailed sun skink (Eutropis longicaudata) living on Orchid Island (Taiwan). This species typically does not provide protection to its offspring. Using a common garden experiment, we show that maternal care is genetically determined in this population. Through field manipulations, we demonstrate that care provides a significant increase in egg survival on Orchid Island by reducing predation from egg-eating snakes (Oligodon formosanus); this predator is not abundant in other populations of the lizard, which do not display parental care. Finally, using extensive field surveys, we show that the seasonal availability of green sea turtle (Chelonia mydas) nests is the cause for the high abundance of snake predators on Orchid Island, with the snakes consuming lizard eggs when green turtle eggs are not available. Together, these lines of evidence provide the first full demonstration of how predation can trigger the evolution of parental care in a species derived from a non-caring ancestor.

Figures

Figure 1
Figure 1. Predation rates of lizard nests and associated predators.
Proportion of long-tailed sun skink eggs hatching from three populations without any form of nest protection ((a) for the mainland, Green Island, and Orchid Island, n = 108, 60, and 450 eggs) and when nests were protected by predator-excluding mesh (n = 1000, 70, and 156 eggs). Known causes of egg mortality, expressed as the numbers of eggs preyed on by snakes or ants and fungi (b).
Figure 2
Figure 2. Snakes observed on concrete walls on Green island and Orchid Island when turtle eggs on Orchid Island are available (May–October) and not available (November–April) from 1997–2008.
Figure 3
Figure 3. Relationships between sea turtle nesting and egg-eating snake abundance on Orchid Island, Taiwan.
Egg-eating snake abundance depends upon sea turtle nest availability (a). When more egg-eating snakes are at the sea turtle nesting beach, fewer are found inland (b). Ultimately, there is a negative relationship between sea turtle nest availability and the proportion of snakes inland (c). Circles show annual values (n = 11) and squares show monthly values (n = 5).
Figure 4
Figure 4. Seasonal patterns of nesting activity and nest predation on Orchid Island, Taiwan.
Sea turtle nesting is highly seasonal and coincides with egg-eating snake abundances at the beach, whereas lizard nesting occurred in each month ((a) n = 5). Proportions represent the number of monthly observations as a function of the total number. In May and September, >99% of snakes are inland, at the lizard nesting site. Predation rates of lizard nests are highest when proportionately more snakes are inland (b).

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