Fluctuations in Density-Dependent Selection Drive the Evolution of a Pace-of-Life Syndrome Within and Between Populations

Abstract

The pace-of-life-syndrome (POLS) hypothesis posits that suites of traits are correlated along a slow-fast continuum due to life-history trade-offs. Despite widespread adoption, environmental conditions driving the emergence of POLS remain unclear. A recently proposed conceptual framework of POLS suggests that a slow-fast continuum should align to fluctuations in densitydependent selection. We tested three key predictions made by this framework with an ecoevolutionary agent-based population model. Selection acted on responsiveness (behavioral trait) to inter-patch resource differences and the reproductive investment threshold (life-history trait).Across environments with density fluctuations of different magnitudes, we observed the emergence of a common axis of trait covariation between and within populations, i.e. the evolution of a POLS. Slow-type (fast-type) populations with high (low) responsiveness and low (high) reproductive investment threshold were selected at high (low) population densities and less (more) intense and frequent density fluctuations. In support of the predictions, fast-type populations contained a higher degree of variation in traits and were associated with higher intrinsic reproductive rate (r0) and higher sensitivity to intraspecific competition (γ), pointing to a universal trade-off. While our findings support that POLS aligns with density-dependent selection, we discuss possible mechanisms which may lead to alternative evolutionary pathways.

Individual life histories: neither slow nor fast, just diverse

“…Whether the slow–fast continuum, defined by a series of trade-offs between life-history traits in time units [ 5 ], structures individual variation as it does across species is therefore even less clear. The existence of a slow–fast continuum of life histories among individuals has nevertheless been repeatedly assumed in behavioural ecology in regard to the concept of pace-of-life syndrome (POLS) [ 21 , 22 ]. Specifically, the POLS hypothesis posits that a series of behavioural and physiological axes of variation correlates with the individual slow–fast continuum [ 21 ].…”

Fitness, risk taking, and spatial behavior covary with boldness in experimental vole populations

“…(3) Reproductive success of males may be primarily determined by dominance rank (Dewsbury, 1982; Ellis, 1995) rather than personality per se , but both traits can be highly entangled so that boldness may predict dominance. (4) Among‐individual variation in behavior could be part of a larger pace‐of‐life syndrome (Dammhahn et al, 2018; Réale et al, 2010) and covariation between these traits might be maintained by density‐dependent selection (Milles et al, 2022; Wright et al, 2019). Microtine voles, in most places, frequently and predictably undergo massive fluctuations in population density, which are accompanied by population‐level differences in behavioral type (Eccard & Herde, 2013) and social environmental conditions.…”

“…( 3) Reproductive success of males may be primarily determined by dominance rank (Dewsbury, 1982;Ellis, 1995) rather than personality per se, but both traits can be highly entangled so that boldness may predict dominance. (4) Among-individual variation in behavior could be part of a larger pace-of-life syndrome (Dammhahn et al, 2018;Réale et al, 2010) and covariation between these traits might be maintained by density-dependent selection (Milles et al, 2022;Wright et al, 2019).…”

“…Life history trajectories may be related to favorable physiological and behavioral phenotypes, forming an extended pace‐of‐life syndrome (POLS, e.g., Careau et al, 2008; Dammhahn et al, 2018; Réale et al, 2010) with fast POL individuals increasing their fitness by higher risk taking, and slow POL individuals by avoiding risks (Wolf et al, 2007a; Wolf et al, 2007b; Wright et al, 2019). Thus, both variation in life histories and the associated among‐individual differences in behavior could potentially be explained through their eco‐evolutionary dynamics with fluctuations in population density (Milles et al, 2022; Wright et al, 2019), group size, or composition of personality in groups (Roth et al, 2019).…”

Fast adjustment of pace‐of‐life and risk‐taking to changes in food quality by altered gene expression in house mice

“…Correlational selection was originally thought to explain correlations between life history, behaviour and physiology. More recently, density-dependent selection via fluctuations in population densities over time has been suggested as a driving factor for POLS (Milles et al, 2022;Wright et al, 2019). Such processes require many generations.…”