Patrick Walsh

Environmental conditions during early development can considerably shape individual behavior, and laboratory studies suggest that predator presence is an important factor influencing both within- and among-individual behavioral variation. To test this under natural conditions, we studied neotropical poison frog (Allobates femoralis) tadpoles from pools with and without dragonfly larvae (tadpole predators) under naturally varying environmental conditions. We measured 2 behavioral traits, distance moved in a novel environment and time to emerge from a shelter, across 4 repeated trials in predator-exposed (n = 48) and predator-naïve (n = 169) tadpoles. Predator-exposed tadpoles moved less, emerged later in their first trial and were more unpredictable in emergence time than predator-naïve individuals. Moreover, among-individual variation in both behaviors was higher in predator-exposed tadpoles, although behavioral repeatability did not differ significantly between predator-exposed and predator-naïve groups. Predator-naïve individuals exhibited behavioral and predictability syndromes, individuals that moved more also emerged sooner, and individuals more predictable in 1 behavior were more predictable in the other. Despite only being significant in predator-naïve individuals, these correlations did not differ between predator-exposed and predator-naïve groups. A personality–plasticity association occurred only in predator-exposed tadpoles: individuals that initially moved less showed less behavioral change across trials. These findings demonstrate that even in naturally variable environments, predation risk shapes behavioral variation at multiple levels, thereby contributing to the emergence and maintenance of “animal personality”.

Repeated social interactions with conspecifics and/or heterospecifics during early development may drive the differentiation of behaviour among individuals. This behavioural differentiation may occur through individuals behaving more different from each other on average and/or individuals behaving more consistently. Competition is a major form of social interaction and its impacts can depend on whether interactions occur between conspecifics or heterospecifics and the directionality of a response could be specific to different behavioural traits. To test this, we reared tungara frog tadpoles ( Engystomops pustulosus ) either in isolation, with a conspecific tadpole or with an aggressive heterospecific tadpole, the whistling frog tadpole, Leptodactylus fuscus . In each treatment, we measured the body size, activity, exploration and risk taking in the presence of a predator in focal E. pustulosus tadpoles six times during development. We used univariate and multivariate hierarchical mixed effect models to investigate the effect of treatment on mean behaviour and on among individual variance between and within individuals across behavioural traits. There was a strong effect of competition on behaviour, with different population and individual level responses across social treatments. Within their home tank, individuals were more consistent in their movements under conspecific competition but heterospecific competition caused more variance in the average movement among individuals. Behavioural responses were also trait specific as conspecific competition caused greater variability in movements among individuals in a novel environment. The results highlight that the impact of competition on inter-individual differences in behaviour is dependent on competitor species identity and is trait specific.

Plasticity in the timing of life history events and their impact on individual fitness, particularly the timing of and size at metamorphosis in animals with complex life cycles such as anuran amphibians, has long been of interest to ecologists. For different studies on life history plasticity to be comparable, there must be clearly defined and commonly agreed transition points, but it is unclear how consistently this is being performed in studies using anuran amphibians. In a review of 157 published studies, I found considerable variation in defining the end point of the larval phase. While a slight majority used the emergence of the forelimbs as the conclusion of the larval phase, some used a period within the developmental phase of metamorphic climax and others used the resorption of the tail. Studies included in this review, that assessed the same life history variable at two different developmental stages, reported some differences in results depending on which developmental stage was used. Recent evidence also shows that metamorphic climax is itself a period which can vary with environmental conditions, but, even in studies that included part or all of metamorphic climax in the larval phase, the treatment of individuals during metamorphic climax was not reported. Therefore, I argue that life history studies on anuran amphibians should distinguish the following phases: larval, metamorphic climax, juvenile, adult; that the end of the larval phase is best defined in ecological studies by forelimb emergence and that conditions under which individuals undergo metamorphic climax should be fully described.

Capsule Mean frequency of nocturnal egg-turning in Meadow Pipits is similar to that found in other passerines. Turning frequency changes during incubation, with time since the start of incubation exerting the strongest influence.