Production Of Chemical Cues Research Articles

Toxic Microcystis (cyanobacteria) inhibit recruitment of the bloom‐enhancing invasive bivalve Limnoperna fortunei

Summary Toxic cyanobacterial blooms and biological invasions are major threats to freshwater systems worldwide. While usually dealt with independently, the two threats can interact to produce synergistic or antagonistic outcomes. The aim of this survey is to analyse interactions between the cyanobacterium Microcystis spp. and the Asian invasive mussel Limnoperna fortunei. On the basis of 9 years of observational data in a large subtropical reservoir (Salto Grande, Argentina–Uruguay), we analyse causal relationships between recurring summer–early autumn blooms of Microcystis spp. and recruitment by L. fortunei. Reproduction of the mussel was interrupted during dry summers (January–April), coinciding with periods of peak Microcystis spp. growth and low water discharge (which favours build‐up of algal biomass). On the other hand, wet summers with high discharge rates were characterised by low Microcystis spp. densities and high numbers of L. fortunei larvae in the water column. Of the seven South American waterbodies investigated, Salto Grande was the only one with very marked cyanobacterial blooms and where larval numbers decrease to near zero during January–April; in all others, reproduction peaks in January–April. The assumption that microcystin‐producing algae are responsible for these troughs during periods when elsewhere larvae are very abundant was reinforced by experimental results indicating that microcystin‐LR is highly toxic to the mussel's larvae, eliminating 58–100% of animals in 48 h at 10–20 μg L−1. Paradoxically, high concentrations of microcystin in water are probably partly due to L. fortunei's own activity, which enhances growth of Microcystis spp. through modification of nutrient concentrations, selective grazing of solitary Microcystis spp. cells over colonial ones and production of chemical cues that trigger the formation of colonies. These interactions have important implications for the management of biofouling of industrial raw cooling water facilities by the byssate mussels, as well as policies oriented at curtailing the spread of the invasive bivalve.

Interpreting the smells of predation: how alarm cues and kairomones induce different prey defences

Summary 1. For phenotypically plastic organisms to produce phenotypes that are well matched to their environment, they must acquire information about their environment. For inducible defences, cues from damaged prey and cues from predators both have the potential to provide important information, yet we know little about the relative importance of these separate sources of information for behavioural and morphological defences. We also do not know the point during a predation event at which kairomones are produced, i.e. whether they are produced constitutively, during prey attack or during prey digestion. 2. We exposed leopard frog tadpoles (Rana pipiens) to nine predator cue treatments involving several combinations of cues from damaged conspecifics or heterospecifics, starved predators, predators only chewing prey, predators only digesting prey or predators chewing and digesting prey. 3. We quantified two behavioural defences. Tadpole hiding behaviour was induced only by cues from crushed tadpoles. Reduced tadpole activity was induced only by cues from predators digesting tadpoles or predators chewing + digesting tadpoles. 4. We also quantified tadpole mass and two size‐adjusted morphological traits that are known to be phenotypically plastic. Mass was unaffected by the cue treatments. Relative body length was affected (i.e. there were differences among some treatments), but none of the treatments significantly differed from the no‐predator control. Relative tail depth was affected by the treatments and deeper tails were induced only when tadpoles were exposed to cues from predators digesting tadpoles or cues from predators chewing + digesting tadpoles. 5. These results demonstrate that some prey species can discriminate among a diverse set of potential cues from heterospecific prey, conspecific prey and predators. Moreover, the results illustrate that the cues responsible for the full suite of behavioural and morphological defences are not induced by tadpole crushing nor can they be induced by generalized digestive chemicals produced when predators digest their prey. Instead, both prey damage and predator digestion of conspecific tissues appear to be important for communicating predatory risk to phenotypically plastic anuran prey. Importantly, the production of chemical cues by predators may be unavoidable and prey have evolved the ability to eavesdrop on these signals.