Phenotypic convergence along a gradient of predation risk

Abstract

A long-standing question in ecology is whether phenotypic plasticity, rather than selection per se, is responsible for phenotypic variation among populations. Plasticity can increase or decrease variation, but most previous studies have been limited to single populations, single traits and a small number of environments assessed using univariate reaction norms. Here, examining two genetically distinct populations of Daphnia pulex with different predation histories, we quantified predator-induced plasticity among 11 traits along a fine-scale gradient of predation risk by a predator (Chaoborus) common to both populations. We test the hypothesis that plasticity can be responsible for convergence in phenotypes among different populations by experimentally characterizing multivariate reaction norms with phenotypic trajectory analysis (PTA). Univariate analyses showed that all genotypes increased age and size at maturity, and invested in defensive spikes (neckteeth), but failed to quantitatively describe whole-organism response. In contrast, PTA quantified and qualified the phenotypic strategy the organism mobilized against the selection pressure. We demonstrate, at the whole-organism level, that the two populations occupy different areas of phenotypic space in the absence of predation but converge in phenotypic space as predation threat increases.

Energy storage and fecundity explain deviations from ecological stoichiometry predictions under global warming and size‐selective predation

“…This again suggests a trade‐off between development and growth (Dennis et al . ). Similarly, D. pulex accelerated development, yet reduced growth rate when exposed to fish kairomones (Beckerman, Wieski & Baird ; Beckerman, Rodgers & Dennis ).…”

City life on fast lanes: Urbanization induces an evolutionary shift towards a faster lifestyle in the water flea Daphnia

“…In short, this method first allows calculating the length (magnitude) and angle (or direction, θ) of multivariate vectors of trait change (here: between temperature treatments) and enables to compare these between groups (Figure a dashed lines). The method can further be extended to test for multivariate convergence or divergence of populations by comparing the orientation of the reaction norms (Dennis, Carter, Hentley, & Beckerman, ) and the Euclidean distances between centroids (Figure b full lines). This approach thus can also be used to assess whether groups are distinct in multivariate trait space, which in the current case tests whether the difference in the trajectory of the multivariate genotypic trait values between urban and rural populations in a certain temperature treatment is significantly different from 0 (see “evolutionary trajectories” Figure b).…”

Degree of high phenotypic plasticity in wild populations of Daphnia in early spring

“…2 and 4). Although the degree of inducible defense of Daphnia has been shown to be associated with predator density, i.e., high kairomone concentration, in several empirical studies (Tollrian, 1993;Dennis et al, 2010;Miyakawa et al, 2015), wild daphnia may not be as straightforward as implied by these empirical studies. In another field study, Luecke and Litt (1987) suggested that the rate of neck-teeth production of D. pulicaria did not correlate with the density of Chaoborus larvae.…”

“…Hammill et al (2008) scored two morphological traits of D. pulex and showed that the score increased as predator density increased. Dennis et al (2010) quantified the levels of inducible defense of D. pulex using 12 iso-female lineages with 11 traits, and reported the levels converged at higher levels of predation risk, even for different populations. Daphnia is known to exhibit clonal succession in the field (Weider, 1985;Stibor and Lampert, 2000), so it is necessary to clarify the relationship between the gene analysis of clones and their traits using multivariate analysis by long-term field study and laboratory experiment in the future.…”

“…Daphnia has been shown to exhibit inducible defenses in numerous experimental studies by making changes in several morphological features: total body size, head spine (i.e., helmet) size, and tail spine length can change, and neckteeth can be developed (Hebert and Grewe, 1985;Dodson, 1989;Laforsch and Tollrian, 2004). Several morphological defenses occur simultaneously (Boersma et al, 1998;Boeing et al, 2006), and have been revealed using multi variable analysis to vary within species (Dennis et al, 2010). Although multivariate analysis is useful tool for analysis of complex morphological defenses, few recent studies have assessed how morphological defenses vary with the seasons in wild Daphnia population (except of Pijanowska, 1990;Sell, 2000).…”