Antipredator responses of three Daphnia species within the D. longispina species complex to two invertebrate predators

Abstract

Prey communities in natural environments face a diverse array of predators with distinct hunting techniques. However, most studies have focused only on the interactions between a single prey species and one or more predators and typically only one of many induced defense traits, which limits our understanding of the broader effects of predators on prey communities. In this study, we conducted a common garden experiment using five clones each of three Daphnia species (D. cucullata, D. galeata, and D. longispina) from the D. longispina species complex to investigate the plasticity of predator-induced defenses in response to two predators in a community ecology setting. Five clones from each species were subjected to predator kairomones from two closely related invertebrate predators that are common in several European lakes, Bythotrephes longimanus or Leptodora kindtii for a duration of 10 days, and the morphological traits of body size, head size, spina size, and the presence of spinules on the ventral and dorsal carapace margins were measured. We show that among the species within this species complex there are different antipredator reactions to the invertebrate predators. The induced responses exhibited were species, trait, and predator-specific. Notably, D. galeata and D. cucullata developed distinctive helmets as defensive mechanisms, while microdefenses were induced in D. galeata and D. longispina, but not in D. cucullata. This demonstrates that the expression of micro- and macrodefenses across species was unrelated, highlighting the possible independent evolution of microstructures as defensive modules in Daphnia's antipredator strategies. This study is the first to document both micro- and macrodefensive phenotypic plasticity in three co-occurring Daphnia species within the D. longispina species complex. The differences in inducible defenses may have a substantial impact on how these three species cohabit with Bythotrephes and Leptodora.

Keywords: Bythotrephes; Daphnia; Daphnia longispina species complex; Leptodora; antipredator strategies; morphological defenses.

FIGURE 1

Measurements of various morphological traits of Daphnia species and the presence/absence of dorsal and ventral spinules.

FIGURE 2

Relationship between body size and spina size, head size, dorsal SBA, ventral SBA, and ventral spinule length for the three Daphnia species. Each treatment condition is shown with distinct letters (Bythotrephes (B), Control (C), and Leptodora (L)).

FIGURE 3

Responses (means ± 2 standard errors) of the three Daphnia species to three treatments (B: Bythotrephes, C: Control, L: Leptodora) for the traits body size, residual head size, residual spina size, residual dorsal SBA, ventral SBA, and residual ventral spinule length. Small dots represent the clonal means for the different treatment—species combinations.

FIGURE 4

Relationships among various residual mean traits. The colored letters in the figure correspond to three treatments, Bythotrephes (B), Control (C), and Leptodora (L) showing the mean of the clone among three Daphnia species. The r values in each box in the figure displays the Pearson correlation coefficient for the respective pair of residual traits, and asterisks indicate significant co‐variation between the respective traits (*p < .05, **p < .01, ***p < .001 (Ross, 2017)).

FIGURE 5

Relationship between residual head size and residual spina size among clonal means of each species in Lake Constance separately shown for the three predator treatments (Bythotrephes (B), Control (C), and Leptodora (L)). The lines represent the linear regressions of each species' residual head size as a function of its residual spina size.