Metamorphosis reverses the behavioural phenotype in Rana arvalis along a latitudinal gradient

1. Understanding how demographic processes and environmental conditions shape behavioural variation across populations is pivotal in evolutionary ecology. However, the role that such processes play in the link between behaviour and life-history traits across populations remains largely unclear. 2. The moor frog (Rana arvalis) has colonized Sweden via two distinct routes from south via Denmark and from north via Finland. We collected R. arvalis eggs from multiple populations along a 1700 km latitudinal gradient across Northern Europe and raised tadpoles in a common garden experiment. We assessed developmental growth and proactivity levels in ca. 300 individuals at two key stages of anuran larval development: tadpoles (Gosner stage 32) and froglets (Gosner stage 46). 3. We found strong behavioural differences along the latitudinal gradient and between developmental stages. Tadpoles from northernmost populations were bolder (shorter times to leave a shelter) and showed higher activity levels in an open field test compared to those from southern populations. 4. However, these behavioural patterns reversed at the froglet stage, with individuals from northern populations showing reduced proactivity that those from southern populations. Further analyses indicated significant associations between developmental growth and boldness, with contrasting patterns across developmental stages and colonization routes. 5. In line with recent revisitations of the pace-of-life syndrome theory (POLS) for animal personality, our findings suggest a decoupling of correlations between behaviour and life history traits across ontogeny, likely reflecting adaptive responses to divergent ecological and demographic constraints along the latitudinal gradient.