The role of ancestral phenotypic plasticity in evolutionary diversification: population density effects in horned beetles

Adaptive maternal behavioral plasticity and developmental programming mitigate the transgenerational effects of temperature in dung beetles

“…Plasticity therefore has great potential to facilitate both short-term ecological adjustments and long-term evolutionary adaptation to novel environments. Yet few study systems exist that allow simultaneous assessment of the role of phenotypic plasticity in short-term adaptive responses, its potential effects on phenotypes and fitness in subsequent generations, and its contribution to population divergences (Pfennig et al 2010, Donelson et al 2017, Casasa and Moczek 2018. In this study, we investigated the adaptive significance of both maternal behavioral plasticity and larval developmental plasticity in mitigating the fitness-reducing effects of temperature stress among rapidly diverging populations of dung beetles.…”

Plastic responses to novel environments are biased towards phenotype dimensions with high additive genetic variation

“…The "plasticity-first" hypothesis proposes that environmentally induced phenotypic variation initiates and directs adaptive genetic divergence along particular trajectories (1,2). This has been demonstrated experimentally (3,4), and the observation that plastic responses sometimes are aligned with population divergence in morphology, physiology, and behavior makes it a plausible explanation for adaptive divergence in the wild (5)(6)(7)(8)(9)(10). However, whether or not evolutionary divergence generally is disposed to follow the direction of environmentally induced phenotypes is contested and poorly understood (reviewed in refs.…”

Developmental bias in horned dung beetles and its contributions to innovation, adaptation, and resilience

“…In controlled lab conditions, native beetles were subject to either very high (Western Australia-like) or very low (Eastern US-like) adult densities, and just 3 weeks of this treatment were sufficient to induce measurable plasticity in four of the six traits studied. However, by itself this observation does not reject the possibility of a "plasticity first" scenario: while plasticity in response to a novel environment is assumed to not be able to anticipate adaptive variation (Moczek, 2007), to facilitate adaptive evolution, it is only necessary that variation among ancestral reaction norms encompasses at least some novel variants that selection can promote (Casasa & Moczek, 2018b; Figure 2c). For these two traits, results are consistent with a "plasticity first" scenario, whereby plastic responses to environmental conditions unveil phenotypic variation that is later canalized by selection (Levis & Pfennig, 2016).…”

“…Since introduction, both Eastern US and Western Australian populations have diverged rapidly in diverse traits, both from each other and relative to their Mediterranean source population. Trait differences between populations are maintained in common garden conditions, and include morphology (e.g., adult body size, allometric threshold for horn induction, male genitalia shape, female fore tibia shape), development and physiology (e.g., degree and timing of sensitivity to juvenile hormone, sensitivity to serotonin upregulation, duration of larval development, developmental responses to temperature stress), and behavioral and life-history traits ( Considering six of these traits (body size and horn allometry threshold for morphology; brood ball mass and nesting depth for behavior; and brood ball number and eclosion success for life history), a recent study by Casasa and Moczek (2018b) examined the presence and direction of plasticity in response to variation in adult density in the Mediterranean source population. Trait differences between populations are maintained in common garden conditions, and include morphology (e.g., adult body size, allometric threshold for horn induction, male genitalia shape, female fore tibia shape), development and physiology (e.g., degree and timing of sensitivity to juvenile hormone, sensitivity to serotonin upregulation, duration of larval development, developmental responses to temperature stress), and behavioral and life-history traits ( Considering six of these traits (body size and horn allometry threshold for morphology; brood ball mass and nesting depth for behavior; and brood ball number and eclosion success for life history), a recent study by Casasa and Moczek (2018b) examined the presence and direction of plasticity in response to variation in adult density in the Mediterranean source population.…”

“…In the preceding sections, we focused on these same levels of biological organization, and explored how evolutionary processes may be biased towards deploying the same pre-existing and preassembled genes and gene networks in the advent of novel structures (Linz et al, 2019;Shubin et al, 2009), and discussed how environment-responsive development may be primed to generate well-integrated, functional, and sometimes adaptive variants in the face of ecological stressors (Casasa & Moczek, 2018b). Plastic responses in beetles derived from an ancestral Mediterranean population to experimentally controlled high (red) or low (blue) densities yield significant phenotypic differences that parallel both direction and magnitude of evolved, canalized differences between high density Western Australian (WA, red) and low density Eastern US (US, blue) populations (data are from Beckers et al, 2015 andMoczek, 2018b). Here, we suggest that these F I G U R E 2 Developmental bias through developmental plasticity.…”