Predator-induced allometric changes in the tail spine length of Daphnia: A distinct resource allocation strategy

Abstract

Understanding resource allocation strategies underlying inducible defense is a challenging scientific issue, because of the difficulty in measuring resource allocations of defensive traits. We examined allometric changes to evaluate resource allocation strategies on the tail spine of Daphnia within and between species and further explore the allometric changes at different developmental stages and their relationship with growth and reproduction. We found that four Daphnia species (Daphnia magna, Daphnia sinensis, Daphnia galeata and Daphnia mitsukuri) can perform significant inducible defensive responses when exposed to fish kairomone. Different from the other Daphnia species, D. mitsukuri significantly enhanced the allometric slope of its tail spine when exposed to fish kairomone. We also found that allometric changes among different D. mitsukuri clones are significant in adult individuals. Furthermore, the allometric changes show a significant negative interaction with individual growth, indicating that a trade-off may exist between the resource allocations of tail spine elongation and growth. This study highlights the species-specific allometric changes in tail spine elongation and provides an explanation for this from resource allocations.