Keynotes 2024

One of the fundamental challenges of studying animal behaviour in the open ocean is the sheer scale of the environment and the ephemeral nature of observable behaviour. Particularly when applied to predator-prey aggregations, being in the right place at the right time to not only observe, but to quantify interactions between and within species has proven a logistical problem for decades. Now, with rapidly advancing technology we are able to obtain high resolution data of grouping marine predators and their schooling prey for the first time. This information, in combination with attack and capture rates of individual prey fish, has provided unprecedented insights into the functions and mechanisms of group-hunting behaviour in the open ocean. In this talk I will outline some of the ways that both predators and prey try to outdo each other in this ongoing arms race.

Behavior plays a pivotal role in survival and reproduction of animals and has long been assumed to be a driver of diversification processes such as evolutionary radiations. The lack of technologies and frameworks to accurately quantify and compare animal behavioral traits across species, and to study the genetic underpinnings of these complex traits, has long hindered the integration of animal behavior in evolutionary studies and adaptive radiation research. Recently, we showcased that a behavioral trait is part of the niche-adaptation syndrome in one of the largest adaptive radiations worldwide: the cichlid fishes of Lake Tanganyika. In particular, we examined a fundamental and widespread behavioral trait, exploratory behavior, by integrating quantitative behavioral data from 57 cichlid species (702 wild-caught individuals) with high-resolution ecomorphological and genomic information. We demonstrated that cichlid species differ consistently in their tendency to explore and that this variation is linked to macrohabitat niche adaptations. Furthermore, we uncovered a correlation between the genotypes at a single-nucleus polymorphism upstream of the AMPA glutamate-receptor regulatory gene cacng5b and variation in exploratory tendency within and across species. A major effect of this locus on the behavioral phenotype could be validated through two synergistic functional approaches. These novel findings set the stage for future research addressing the mechanisms through which behavior drives diversification.

Movement is a key process through which animals can influence their immediate and lifetime fitness. Challenging ecological conditions can generate trade-offs fostering the emergence of consistently different movement strategies at the individual and at the group level within populations. Partial migration, for instance, is a widespread phenomenon across taxa in which different movement strategies between groups may be linked to life-history trade-offs. In cases where different movement strategies can be used to increase fitness, navigation capabilities might be under selection. Consequently, migrating animals may have evolved mechanisms allowing them to process external cues in cue-based navigation, or to navigate using memory-based mechanisms in the absence of any obvious environmental gradients. In the first part, I will discuss differences in navigation capabilities in partially migrating populations (i.e., migrant vs. non-migrant) using a reciprocal translocation experiment on a freshwater predator that recently adapted for life in a challenging environment (brackish water). With animals being forced to either complete their entire life cycle in brackish water at the cost of offspring survival, or to travel to freshwater bodies yearly to reproduce (i.e., trade-off movement costs for offspring survival), adaptations in physiology or in movement behaviour can be expected between groups. At the individual level, the evolution of animal personality (i.e., consistent individual differences in behaviour) has also been hypothesized to be mediated by life-history trade-offs. But so far, support for this hypothesis has been mixed which may in part be due to important environmental effects being obscured by the dominant use of captive systems (as opposed to wild systems) in personality research. In the second part, I will use a combination of captive tests, molecular methods and wild tracking in a juvenile marine predator known to be subjected to a trade-off between growth and mortality to demonstrate under which ecological conditions personality is linked to wild behaviour and to life-history trade-offs. When foraging in a complex and dynamic environment, success can be highly driven by the decisions to move from a resource patch to the next or not (explore-exploit trade-off). In a third part I will present a unique study system where foragers and their mobile aquatic prey are simultaneously monitored to understand how individuals can track resource gradients in their environment to maximise their foraging success in the field.

Evidence is accumulating that substantial among-individual phenotypic variation can emerge even under highly standardized (i.e. near-identical) genetic and environmental conditions. Up to know, it remains an open question whether these apparently stochastic among-individual differences really matter. One of the most direct ways to answer this question is to investigate whether phenotypic differences that emerge under genetic and environmental standardization extend to those aspects of the phenotype that directly affect fitness. To address this question, we performed a long-term life-history experiment with naturally clonal Amazon mollies (Poecilia formosa), separated on day 1 of their life into identical environments. Maintaining highly standardized conditions for over 800 days, we closely monitored 38 individuals from birth until death. We assessed early-life behavioral profiles by recording individuals for 10 hours per day over the first 28 days of their lives and characterized reproductive profiles over 4 broods per individual, quantifying in total 2522 offspring and 152 broods. We find (i) early-life behavioral individuality in activity and feeding patterns as well as (ii) substantial variation in fitness measures: consistent among-individual differences in the size of offspring and broods produced and differences in lifespan. (iii) Early-life activity profiles are predictive of lifespan: fish that are more active die sooner. These findings provide experimental evidence that apparently stochastic variation emerging under highly standardized conditions can have major fitness consequences, thereby demonstrating that our understanding of how genetic and environmental variation generate phenotypic variation is incomplete, and that even minute genetic and environmental differences can have profound consequences.