Harmful alga trades off growth and toxicity in response to cues from dead phytoplankton

Abstract

Organisms are under selection pressure to recognize predators and assess predation risk to avoid becoming prey. In some cases, the presence of injured competitors alerts individuals to the likelihood that predators are nearby. Previous studies have shown that the marine dinoflagellate Alexandrium minutum responds to chemical cues from copepods by dramatically upregulating sodium channel-blocking toxins that appear to function as defenses against copepod grazing. However, it is unknown whether A. minutum uses other cues, such as damaged phytoplankton, some of which are its competitors, to assess predation risk and subsequently increase its resistance to predators. To investigate the role of dead phytoplankton cues in chemical defense plasticity, A. minutum was exposed for 3 days to chemical cues from six different phytoplankton. Chemical cues from dead, unrelated, historically co-occurring phytoplankton species induced toxin production in A. minutum coincident with a decrease in growth. In contrast, exposure to chemical cues from more closely related dead phytoplankton, either conspecific or congeneric, suppressed toxin production in A. minutum relative to their absence. This was coupled with a modest, yet significant, increase in growth. The consistent inverse relationship between toxin production and growth suggests that A. minutum experiences a trade-off. Together, these results reveal that relatedness of dead phytoplankton is important in how A. minutum utilizes resources for growth and defense.

Predator-induced defence in a dinoflagellate generates benefits without direct costs

“…and did not find any correlation between growth rate and toxin production under light-replete conditions, and even a positive correlation under limiting light. Brown & Kubanek [11] recently demonstrated a negative relation between toxin content and growth rate in Alexandrium minutum exposed to lysed cells of various other species of dinoflagellates, thus suggesting a trade-off. However, the correlation may also result from allelochemical substances in the lysed cells reducing growth [12].…”

Dinophyceae use exudates as weapons against the parasiteAmoebophryasp. (Syndiniales)

“…However, it is also known that Alexandrium spp. can modulate its allelochemical potency against microalgae in response to changing physicochemical conditions (Martens et al ., 2016; Long et al ., 2019) but also its toxicity in response to cues from dead microalgal cells (Brown & Kubanek, 2020). It was also observed that genes associated with defensive responses such as the production of reactive oxygen species were overexpressed in a non-allelopathic strain of A. fundyense exposed to Amoebophrya sp.…”

Predator cues target signaling pathways in toxic algal metabolome

“…After about 40 h, all cultures were harvested with processing of treatments and controls intermixed over about 2.5 h within 4 h of the start of the light cycle. An aliquot of each culture was harvested by centrifugation for targeted toxin analysis of GTXs 1–4, using methods similar to those described in Brown and Kubanek (2020), and an unpaired Welch's t ‐test was performed in GraphPad Prism 9.0 to compare toxin concentrations between treatments and controls. The remaining portion of each culture was harvested by vacuum filtration and extracted in a manner similar to Poulson‐Ellestad et al (2014).…”