Influence of altered light conditions and grazers on Scrippsiella trochoidea (Dinophyceae) cyst ­formation

Abstract

We investigated whether or not the presence of copepods and different light conditions induced cyst formation in dinoflagellates. Scrippsiella trochoidea was exposed to Acartia tonsa directly and indirectly (grazer filtrate), in high light and low light conditions. The ingestion, faecal production and egg production of A. tonsa were compared between diets of S. trochoidea vegetative cells and temporary cysts. We found no effect of direct or indirect exposure to A. tonsa on S. trochoidea cyst formation in either high light or low light conditions. Controls and A. tonsa treatments kept in light displayed around 20% temporary cysts, whereas controls and A. tonsa treatments in low light were shown to have 50 to 80% temporary cysts. Thus, low light conditions had a strong effect on temporary cyst formation. No hypnocysts were observed in any experiment, which is probably related to the longer incubation times needed for their observation. Feeding on diets dominated by temporary cysts compared to vegetative cells decreased ingestion by a factor of 2.7, while faecal and egg production decreased by a factor of 2.2 and 2.9, respectively, suggesting that induction of temporary cysts in response to A. tonsa could be a survival strategy. However, S. trochoidea does not possess any grazer-induced defence in terms of temporary cyst formation, as it did not produce temporary cysts when exposed to A. tonsa. Rather, induction of temporary cysts seems to be controlled by decreased light intensity, which is a favorable trait for this species when driven to water depths where light is scarce.

Effects of light and prey availability on Arctic freshwater protist communities examined by high-throughput DNA and RNA sequencing

“…The mixotrophic capacity of species of Scrippsiella and Woloszynskia to feed on small eukaryote cells (Jeong et al ., ; Kang et al ., ) may explain the strong persistence of these pigmented dinoflagellates at low light. The relatively lower proportion of Scrippsiella reads detected by cDNA in the low light, compared with high light, was consistent with reports of encystment at low irradiances (Rintala et al ., ; Lundgren & Granéli, ). In contrast, Woloszynskia reads were significantly (Metastats P ‐value < 0.05) more represented in the low light bottles.…”

Towards an Ecological Understanding of Dinoflagellate Cyst Functions

“…For pellicle cysts, similar investigations into the effect of anoxia are for the most part lacking. The formation of pellicle cysts as a strategy to cope with darkness has been reported for species of the genus Scrippsiella [ 86 ], in which respiratory rates in the dark were reduced to very low levels [ 86 , 87 ].…”

“…The same study also suggested that dinoflagellate cysts are able to detect chemical signals emitted by predators. However, in another report, there was no apparent influence of the copepod Acartia tonsa on the formation of pellicle cysts by Scrippsiella trochoidea [ 86 ]. In this dinoflagellate species, allelopathic effects on pellicle cyst formation may provide a defensive response to deleterious chemical cues [ 88 ].…”

Transcriptomic Analyses of Scrippsiella trochoidea Reveals Processes Regulating Encystment and Dormancy in the Life Cycle of a Dinoflagellate, with a Particular Attention to the Role of Abscisic Acid

“…Resting cysts in sediments can resist harsh environmental conditions and are protected from viruses, grazers and parasite attacks (Ribeiro et al, 2011 ; Bravo and Figueroa, 2014 ). Encystment is usually considered to be an adaptive response to environmental stresses, such as nutrient depletion (Anderson et al, 1984 ; Grigorszky et al, 2006 ), changes in temperature (Sgrosso et al, 2001 ; Grigorszky et al, 2006 ), salinity (Zonneveld and Susek, 2007 ), day length (Sgrosso et al, 2001 ), high cell densities (Garcés et al, 2004 ) and bacterial attack (Lundgren and Granéli, 2011 ). However, little has been understood about the endogenous regulatory factors and physiological mechanisms for resting cyst fosrmation and germination (i.e., encystment and excystment) (Tang et al, 2016 ).…”