The morphology of organismsis generally well matched totheir environment, presum-ably because expression of theirgenes is tailored either at the popu-lation or the individual level to suit local conditions: for example,snake populations that persistentlyencounter large prey may accumu-late gene mutations that specify alarge head size, or head growthmay be increased in individualsnakes to meet local demands(adaptive developmental plasticity)1.Here we test the relative contribu-tions of genetics and environmentto the jaw sizes of two tiger snakepopulations: one that consumessmall prey on the mainland, and an islandpopulation that relies on larger prey andhas a larger jaw size. Although the idea ofadaptive plasticity in response to environ-mental pressures is controversial2,we findthat both factors influence the difference injaw size between the two populations, andthe influence of developmental plasticity isgreater in the island population.Snakes are ideally suited to our investiga-tion because their jaw length constrains theirmaximal ingestible prey size and so reflectsadaptation to local prey resources3.Tigersnakes (Notechis scutatus, Elapidae; Fig. 1)are viviparous Australian snakes4.We stud-ied one mainland population (at Herds-man’s Lake: 31° 55 S, 115° 48 E) and oneisland population 25 km away (CarnacIsland:32° 07 S,115° 39 E).Adult mainlandsnakes feed on frogs and mice, whereas adultisland snakes mostly take silver-gull chicks(mean prey masses, 12 g compared with 30 g; circumference, 33 mm compared with78 mm)6.In keeping with this dietary diver-gence,the island snakes grow larger and havelarger heads relative to their body length5,6.To investigate whether this geographicdivergence in relative head size is driven bygenes that encode for head size or by theexposure of growing snakes to larger prey, wecaptured pregnant females in early summerand maintained them under laboratory con-ditions until they gave birth in the autumn.They were housed individually with access towater and a heat source, and given laboratorymice as food. Nine island females and thir-teen mainland females gave birth to 123 and129 neonates, respectively. We randomlyselected one or two neonates from each litterand raised them under the same conditionsas their mothers.Half the neonates received large mice asprey, whereas the others were given the sametotal mass of smaller mice as prey: that is,mice fed to the two treatment groups differed in average prey mass (F3,81101.8,P<0.001) and circumference (F3,81101.7,P 0.001). The amount of food providedmonthly was similar among the four groupsof young snakes (island and mainlandsnakes, each fed either small or large prey;F3,750.29, P0.84), and led to similargrowth trajectories in body mass(F4,1041.36, P0.25) and snout–ventlength (F3,780.09,P0.96).All snakes weremeasured for jaw and skull length on fouroccasions over 8 months using digital callipers (0.1 mm). The standardized husbandry conditions and split-clutchdesign should have minimized any maternaleffects on offspring traits.Head sizes were significantly plastic inCarnac Island juveniles with respect to skullbrief communicationsNATURE|VOL 431|16 SEPTEMBER 2004|www.nature.com/nature 261length (results not shown; repeatedmeasures MANOVA; Wilks’0.41, P0.03; interaction oftime and prey size, F3,453.10,P 0.036) and jaw length (Wilks’0.25, P 0.0015; interactionF3,4519.15, P 0.0001); theseeffects were not evident in main-land juveniles (all P0.24) (Fig.2).Exposure to larger prey thereforeseems to increase the head size ofthe island snakes more than that of the mainland snakes (two-wayANOVA,with origin and treatmentas factors and the successive mea-surements of jaw length as therepeated measure: interactionF3,785.66,P 0.0015) (Fig.2).These results indicate that adaptationcould be influenced both by genes encodingfor head size and by developmental plast-icity. First, neonates of island snakes hadlarger heads than mainland snakes, despitesimilar body sizes (ANCOVA with locationas the factor, log body-length as the covari-ate,log jaw-length as the dependent variable:F1,24425.65, P 0.001). This geographicdivergence is apparent at birth, so presum-ably reflects hard-wired genetic differences.Second, the relative jaw sizes of islandsnakes fed on large prey rapidly increased rel-ative to the jaws of their siblings fed on smallprey,whereas the mainland snakes showed nosuch effect (Fig. 2). We conclude that islandtiger snakes can consume larger prey thanmainland conspecifics for two reasons: first,they may carry genes that determine a largerrelative head size;and second, their head sizesenlarge facultatively if they eat large prey.Our study demonstrates an importantecological role for adaptive plasticity, andhighlights the impossibility of dividing phe-notypic variation into simplistic categoriesof ‘nature’ and ‘nurture’7.Tiger snakes arehighly flexible predators that track preyresources by means of a complex adaptiveresponse. This response involves not onlyhard-wired traits that match phenotype todifferences in long-term average conditions,but also a developmentally plastic compo-nent that matches individuals within eachgeneration to fluctuations in prey size.Fabien Aubret*†‡, Richard Shine§,Xavier Bonnet*§*CEBC–CNRS, 79360 Villiers en Bois, France†Université de Poitiers, Conseil Général des Deux-Sèvres, 79360 Villiers en Bois, France‡School of Animal Biology, University of WesternAustralia, Crawley, Perth, Western Australia 6009,Australia§Biological Sciences A08, University of Sydney,Adaptive developmental plasticity in snakesGenes and environment stretch snake jaws to meet the demands of prey size.13141516171819Jaw length (mm)123456789Time after birth (months)Figure 2 Relative jaw length of growing tiger snakes as a functionof prey size. Neonatal snakes from the mainland (Herdsman'sLake; n20; squares) and from Carnac Island (n19; circles)were born and kept in captivity. The young snakes were fed weekly on mice. Within each group, half of the snakes were givenlarge prey (mice, 1.8–5.0 g; 2.5–4.7 mm in circumference; filled symbols) and the other half received small prey (mice, 1.7–1.8 g;2.3–2.5 mm; open symbols). Jaw size of island snakes exposedto large prey increases significantly more than for mainlandsnakes (mean valuess. d.).Figure 1 On an island in southwestern Australia, tiger snakes feed mostly