Exploratory decisions of Trinidadian guppies when uncertain about predation risk

Rapid Neural DNA Methylation Responses to Predation Stress in Trinidadian Guppies

DNA methylation (DNAm) is a well-studied epigenetic mechanism implicated in environmentally induced phenotypes and phenotypic plasticity. However, few studies investigate the timescale of DNAm shifts. Thus, it is uncertain whether DNAm can change on timescales relevant for rapid phenotypic shifts, such as during the expression of short-term behavioural plasticity. DNAm could be especially reactive in the brain, potentially increasing its relevance for behavioural plasticity. Most research investigating neural changes in methylation has been conducted in mammalian systems, on isolated individuals, and using stressors that are less ecologically relevant, reducing their generalisability to other natural systems. We exposed pairs of male and female Trinidadian guppies (Poecilia reticulata) to alarm cue, conspecific skin extract that reliably induces anti-predator behaviour, or a control cue. Whole-genome bisulphite sequencing on whole brains at various time points following cue exposure (0.5, 1, 4, 24, and 72 h) allowed us to uncover the timescale of neural DNAm responses. Males and females both showed rapid shifts in DNAm in as little as 0.5 h. However, males and females differed in the time course of their responses: both sexes showed a peak in the number of loci showing significant responses at 4 h, but males showed an additional peak at 72 h. We suggest that this finding could be due to the differing longer-term plastic responses between the sexes. This study shows that DNAm can be rapidly induced by an ecologically relevant stressor in fish and suggests that DNAm could be involved in short-term behavioural plasticity.

Uncertainty about predation risk: a conceptual review

Uncertainty has long been of interest to economists and psychologists and has more recently gained attention among ecologists. In the ecological world, animals must regularly make decisions related to finding resources and avoiding threats. Here, we describe uncertainty as a perceptual phenomenon of decision-makers, and we focus specifically on the functional ecology of such uncertainty regarding predation risk. Like all uncertainty, uncertainty about predation risk reflects informational limitations. When cues are available, they may be novel (i.e. unknown information), incomplete, unreliable, overly abundant and complex, or conflicting. We review recent studies that have used these informational limitations to induce uncertainty of predation risk. These studies have typically used either over-responses to novelty (i.e. neophobia) or memory attenuation as proxies for measuring uncertainty. Because changes in the environment, particularly unpredictable changes, drive informational limitations, we describe studies assessing unpredictable variance in spatio-temporal predation risk, intensity of predation risk, predator encounter rate, and predator diversity. We also highlight anthropogenic changes within habitats that are likely to have dramatic impacts on information availability and thus uncertainty in antipredator decisions in the modern world.

Social information-mediated population dynamics in non-grouping prey

Abstract

Inadvertent social information (ISI) use, i.e., the exploitation of social cues including the presence and behaviour of others, has been predicted to mediate population-level processes even in the absence of cohesive grouping. However, we know little about how such effects may arise when the prey population lacks social structure beyond the spatiotemporal autocorrelation originating from the random movement of individuals. In this study, we built an individual-based model where predator avoidance behaviour could spread among randomly moving prey through the network of nearby observers. We qualitatively assessed how ISI use may affect prey population size when cue detection was associated with different probabilities and fitness costs, and characterised the structural properties of the emerging detection networks that would provide pathways for information spread in prey. We found that ISI use was among the most influential model parameters affecting prey abundance and increased equilibrium population sizes in most examined scenarios. Moreover, it could substantially contribute to population survival under high predation pressure, but this effect strongly depended on the level of predator detection ability. When prey exploited social cues in the presence of high predation risk, the observed detection networks consisted of a large number of connected components with small sizes and small ego networks; this resulted in efficient information spread among connected individuals in the detection networks. Our study provides hypothetical mechanisms about how temporary local densities may allow information diffusion about predation threats among conspecifics and facilitate population stability and persistence in non-grouping animals.

Significance statement

The exploitation of inadvertently produced social cues may not only modify individual behaviour but also fundamentally influence population dynamics and species interactions. Using an individual-based model, we investigated how the detection and spread of adaptive antipredator behaviour may cascade to changes in the demographic performance of randomly moving (i.e., non-grouping) prey. We found that social information use contributed to population stability and persistence by reducing predation-related per capita mortality and raising equilibrium population sizes when predator detection ability reached a sufficient level. We also showed that temporary detection networks had structural properties that allowed efficient information spread among prey under high predation pressure. Our work represents a general modelling approach that could be adapted to specific predator-prey systems and scrutinise how temporary local densities allow dynamic information diffusion about predation threats and facilitate population stability in non-grouping animals.