Intraspecific phenotypic variation in life history traits of Daphnia galeata populations in response to fish kairomones

Abstract

Phenotypic plasticity is the ability of a genotype to produce different phenotypes depending on the environment. It has an influence on the adaptive potential to environmental change and the capability to adapt locally. Adaptation to environmental change happens at the population level, thereby contributing to genotypic and phenotypic variation within a species. Predation is an important ecological factor structuring communities and maintaining species diversity. Prey developed different strategies to reduce their vulnerability to predators by changing their behaviour, their morphology or their life history. Predator-induced life history responses in Daphnia have been investigated for decades, but intra-and inter-population variability was rarely addressed explicitly. We addressed this issue by conducting a common garden experiment with 24 clonal lines of European Daphnia galeata originating from four populations, each represented by six clonal lines. We recorded life history traits in the absence and presence of fish kairomones. Additionally, we looked at the shape of experimental individuals by conducting a geometric morphometric analysis, thus assessing predator-induced morphometric changes. Our data revealed high intraspecific phenotypic variation within and between four D. galeata populations, the potential to locally adapt to a vertebrate predator regime as well as an effect of the fish kairomones on morphology of D. galeata.

Keywords: Adaptive potential; Daphnia; Life history traits; Phenotypic plasticity; Population ecology; Predator-induced response.

Figure 1. Reaction norms for selected life history traits showing population differences (mean +/− SE).

Population Greifensee (popG, yellow), population Jordan Reservoir (popJ, black), population Lake Constance (popLC, magenta) and population Müggelsee (popM, green). (A) Age at first reproduction (‘AFR’). (B) Total number of offspring first brood (‘brood1’). (C) Total number of broods (‘broods’). (D) Total number of offspring (‘offspring’). (E) Somatic growth rate (‘SGR’). (F) Body length (‘size’).

Figure 2. Boxplots for selected life history traits showing population differences (median +/− SD).

(A) Age at first reproduction (‘AFR’). (B) Total number of offspring first brood (‘brood1’). (C) Total number of broods (‘broods’). (D) Total number of offspring (‘offspring’). (E) Somatic growth rate (‘SGR’). (F) Body length (‘size’).

Figure 3. Differences of somatic growth rate (dSGR).

Differences of somatic growth rate (dSGR) as μm per day (mean +/− SD); calculated as: mean of SGR (fish) minus mean SGR (control) equals dSGR per clonal line, sorted by populations. Each clonal line is displayed in its population specific colour. Population Greifensee (popG, yellow), population Jordan Reservoir (popJ, black), population Lake Constance (popLC, magenta) and population Müggelsee (popM, green).

Figure 4. Thin plate spline (TPS) grids of consensus shapes of superimposed Procrustes coordinates.

Control (red). Fish (green). (A) All specimens. (B) Population Greifensee (popG). (C) Population Jordan Reservoir (popJ). (D) Population Lake Constance (popLC). (E) Population Müggelsee (popM).