DOI: 10.5061/dryad.gc251
title: Data from: Does maternal care evolve through egg recognition or directed territoriality?

description: The mechanism which facilitates the evolution of maternal care is
 ambiguous in egg-laying terrestrial vertebrates: does the ability of
 mothers to recognize their own eggs lead them under some circumstances to
 begin providing care, or can maternal care evolve from simply being in
 close proximity to eggs (e.g., through territorial behavior)? This
 question is difficult to answer because in most species parental care is
 either absent altogether or present; in few species do we have the
 opportunity to observe intraspecific variation in the expression of
 parental care. We studied a population of long-tailed skinks (Eutropis
 longicaudata) in which females have recently evolved maternal care from a
 non-caring state. Females on Orchid Island, Taiwan remain with their eggs
 during incubation, and when doing so actively deter egg predation by
 egg-eating snakes (Oligodon formosanus); in all other populations females
 lack post-ovipositional maternal care. Nest-guarding females on Orchid
 Island: (1) showed antipredator behaviors only in the original nest-site
 in which they laid eggs, even after we removed all of the eggs or
 substituted them with those of a conspecific; (2) protect any eggs present
 inside the original nest-site (even when the eggs belong to a
 conspecific); and (3) develop this behavior while gravid (i.e., prior to
 laying eggs). This supports the hypothesis that long-tailed skinks are
 unable to recognize their own eggs, suggesting that maternal care is a
 directed form of territoriality only expressed towards egg-eating snakes,
 and only during reproduction. Nest guarding is among the most primitive
 forms of parental care, and the recent evolution of this behavior in a
 single population provides insight into one of the mechanisms by which
 parental care can originate in terrestrial vertebrates.
description: data for
 dryad_JEBDataset Key: 1. Is
 nest-guarding dependent upon nest location? This experiment tested whether
 the propensity of female lizards to attack egg-eating snakes varied
 depending upon whether the female was in the nest-site in which she
 originally laid eggs, or displaced to a novel site located nearby. We
 tested each female twice: once after displacing the female to a novel nest
 site located approximately 120 cm from the nest in which she originally
 laid eggs, and again after the female returned to the original nest. 2.
 Effects of recent disturbance. We tested for effects of recent disturbance
 (i.e., moving the female to a novel nest-site) by monitoring the
 anti-predator responses of an additional 40 egg-guarding females that were
 disturbed and then immediately tested against an intruding snake.
 Disturbance consisted of removing a female from her original nest hole,
 measuring and weighing it, and then returning it to the same hole.
 Immediately thereafter we encouraged a snake to enter the nest hole. 3.
 Will females guard conspecific eggs? This set of experiments tested the
 hypothesis that females can recognize their own eggs, which should result
 in females failing to defend the eggs of a conspecific. We removed the
 eggs from nest-guarding females (N = 28, clutch size ranging from 6-8) and
 immediately either returned the same eggs to the nest (N = 14 females) or
 replaced them with the same number of eggs from a different female (N = 14
 females). We then introduced a snake and recorded the response of each
 female. 4. Do females defend their shelter-site prior to laying eggs? We
 re-visited a different set of trials conducted by Huang (2006; Huang,
 W.-S. 2006. Parental care in the long-tailed skink, Mabuya longicaudata on
 a tropical Asian island. Animal Behaviour 72:791-795.) on female
 long-tailed skinks to determine whether reproductive status influences
 anti-predator behavior towards egg-eating snakes. We divided the 107
 females from Huang (2006) according to whether they were gravid (N = 12)
 or not gravid (N = 95). Female lizards were then tested against an
 intruding snake and the lizard’s response was recorded.