One Kairomone and Multiple Effects in Daphnia Species—5α-Cyprinol Sulfate Induces Morphological Defenses in the Invasive Species Daphnia lumholtzi

Meike Hahn,Eric Von Elert

doi:10.3389/fevo.2022.804521

Abstract

Recently, the first chemical cues, which induce defenses in freshwater zooplankton of the genus Daphnia have been identified. Still it is unknown how general these so-called kairomones are and if they are perceived by and thereby benefitting invasive species. We here report the chemical identity of the fish-derived chemical signal that induces morphological defensive structures in the invasive species Daphnia lumholtzi. We used bioassay-guided isolation (LC-MS) of incubation water of fish and identified the bile salt 5α-cyprinol sulfate (5α-CPS) as the kairomone. We confirmed this finding by bioassays, in which D. lumholtzi was exposed to purified 5α-CPS sulfate from fish bile and showed that 10 pM 5α-CPS induces significantly elongated helmets and spines in relation to body length. These results identify on one hand another Daphnia species besides Daphnia magna, which is responding to this particular fish-borne kairomone, and on the other hand they reveal another defense that the kairomone induces besides diel vertical migration (DVM). Taken together a high evolutionary conservancy of the molecular mechanism behind inducible defenses in Daphnia spp. against fish can be deduced. It is reasonable to expect that 5α-CPS is involved in further predator—prey communication between Daphnia and fish, which may be of special ecological relevance with regard to invasive species as D. lumholtzi.

Highlights

Freshwater crustaceans of the keystone genus Daphnia are known for a variety of inducible defenses which protect them from predation and which are induced by predator derived infochemicals (Tollrian, 1994; Von Elert and Loose, 1996; Effertz and Von Elert, 2014)
We showed that fish-derived kairomone(s) that induce morphological defenses in Daphnia lumholtzi can be extracted by C18 solid-phase from incubation water of roach (Rutilus rutilus, Cyprinidae): The exposure of D. lumholtzi to an extract of fish incubation water (EFI) resulted in relative elongation of helmet and tail spine compared to those of animals exposed to methanolic extract of tap water (ETW) (Figure 1)
The relative helmet length of D. lumholtzi exposed to fraction 3 (∼48%) was comparable to that of animals exposed to crude EFI (52%) and 12% longer than that of animals exposed to the negative control (∼36%)

Summary

Introduction

Freshwater crustaceans of the keystone genus Daphnia are known for a variety of inducible defenses which protect them from predation and which are induced by predator derived infochemicals (Tollrian, 1994; Von Elert and Loose, 1996; Effertz and Von Elert, 2014). Though the first of chemical cues, which induce particular defenses in Daphnia, have recently been identified (Weiss et al, 2018; Hahn et al, 2019), it is still uncertain how universal these so-called kairomones are and if they are perceived by and thereby benefitting invasive species like Daphnia lumholtzi as well. Fish Kairomone Inducing Morphological Defenses to chemically perceive the presence of an invertebrate or a vertebrate predator is not surprising considering that Daphnia sp. It has already been shown that independent internal signaling pathways are involved in the response to chemical cues from Chaoborus and fish in Daphnia (Weiss et al, 2012)

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Results

Discussion

Conclusion