Vol.:(0123456789) 1 3 Journal of Chemical Ecology https://doi.org/10.1007/s10886-021-01315-5 Grazer‑Induced Chemical Defense in a Microcystin‑Producing Microcystis aeruginosa (Cyanobacteria) Exposed to Daphnia gessneri Infochemicals Mauro Cesar Palmeira Vilar 1  · Thiago Ferreira da Costa Pena Rodrigues 1  · Aloysio da Silva Ferrão‑Filho 2  · Sandra Maria Feliciano de Oliveira e Azevedo 1 Received: 28 July 2021 / Revised: 9 September 2021 / Accepted: 14 September 2021 © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021 Abstract Cyanobacteria are photosynthetic microorganisms that compose phytoplankton and therefore have a trophic relationship with zooplankton, which represent an important link for energy fux in aquatic food webs. Several species can form blooms and produce bioactive metabolites known as cyanotoxins. However, the ecological and adaptative role of these toxins are still under debate. Many studies have addressed the cyanotoxins’ function in defense against herbivory when grazing pres- sure by zooplankton plays a role in phytoplankton top-down control. Thus, the present study evaluated the ecophysiological responses of the cyanobacterial strain Microcystis aeruginosa NPLJ-4 underlying the chemical induced defense against the cladoceran Daphnia gessneri. Exposure to predator infochemicals consisted of cultures established in ASM-1 medium prepared in a fltrate from a culture of adults of D. gessneri at an environmentally relevant density. Daphnia infochemicals promoted a signifcant increase in toxin production by M. aeruginosa. However, no diferences in growth were observed, despite a signifcant increase in both maximum photosynthetic efciency and electron transport rate in response to zooplank- ton. Additionally, there was no signifcant variation in the production of exopolysaccharides. Overall, although a grazer- induced defense response was demonstrated, there were no efects on M. aeruginosa ftness, which maintained its growth in the presence of Daphnia alarm cues. Keywords Zooplankton · Kairomone · Microcystins · Cyanobacteria · Predator–prey Introduction Cyanobacteria naturally occur in the phytoplankton community, contributing to primary production and comprising part of the zooplankton diet in aquatic food webs (Moustaka-Gouni and Sommer 2020). However, several cyanobacterial genera produce a range of bioactive secondary metabolites, which can impact zooplankton survivorship and reproduction (Esterhuizen-Londt et al. 2016; Ferrão-Filho and Kozlowsky-Suzuki 2011; Ferrão- Filho et al. 2019; Nandini et al. 2017) and even swimming and feeding behavior (Bownik 2016, 2017; Ferrão-Filho et al. 2020; Ferrão-Filho et al. 2014,), thereby limiting its role in phytoplankton top-down control. Among toxic cyanobacteria, Microcystis is a worldwide distributed genus that has been reported to form dense blooms and produce toxic peptides, such as microcyst- ins (MCs) and other cyanopeptides (Harke et al. 2016; Huang and Zimba 2019). MCs are chemically charac- terized as cyclic heptapeptides and classifed according to their action mechanism as potent inhibitors of phos- phatases protein 1 and 2A (Carmichael et al. 2001). Up to date more than 270 MC variants are reported according to structural variations resulted from frequent substitutions and demethylations in amino acids at positions 2 and 4, Thiago Ferreira da Costa Pena Rodrigues have contributed equally to this study. * Mauro Cesar Palmeira Vilar maurovilar@gmail.com 1 Laboratory of Ecophysiology and Toxicology of Cyanobacteria, Carlos Chagas Filho Institute of Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro 21949-902, Brazil 2 Laboratory of Evaluation and Promotion of Environmental Health, Instituto Oswaldo Cruz, FIOCRUZ, Rio de Janeiro, RJ 21040-360, Brazil