Growing attention in aquatic ecology is focusing on biogeographic patterns in microorganisms and whether these potential patterns can be explained within the framework of general ecology. The long-standing microbiologist’s credo ‘Everything is everywhere, but, the environment selects’ suggests that dispersal is not limiting for microbes, but that the environment is the primary determining factor in microbial community composition. Advances in molecular techniques have provided new evidence that biogeographic patterns exist in microbes and that dispersal limitation may actually have an important role, yet more recent study using extremely deep sequencing predicts that indeed everything is everywhere. Using a long-term field study of the ‘invasive’ marine haptophyte Prymnesium parvum, we characterize the environmental niche of P. parvum in a subtropical impoundment in the southern United States. Our analysis contributes to a growing body of evidence that indicates a primary role for environmental conditions, but not dispersal, in the lake-wide abundances and seasonal bloom patterns in this globally important microbe.
The rapid range expansion of the toxigenic marine haptophytic alga Prymnesium parvum in inland aquatic systems across the southern USA and beyond has prompted great interest in the ecology and evolutionary biology of this invasive bloom-forming species. Researchers have speculated that increased toxicity and heterotrophy in suboptimal environments allow blooms to develop in these new inland habitats that seem to represent extremes relative to P. parvum's perceived optimal niche. We used a laboratory-based study to elucidate the roles of salinity and nutrient availabilities in P. parvum growth and toxicity under environmental conditions representative of hypereutrophic reservoirs of the southwestern USA in which P. parvum blooms are now common. We found evidence that nutrient conditions favoring toxigenesis in P. parvum are suboptimal for growth and bloom formation, whereas conditions conducive to high growth rates are less favorable for toxigenesis. In contrast, both growth and toxicity scaled positively with salinity. Taken in the context of the documented biogeography of P. parvum and that toxigenesis in P. parvum probably evolved in support of heterotrophic nutrient acquisition, our results suggest that P. parvum's apparent range expansion into and across the USA is driven by increasing availabilities of salty and nutrient-rich systems, rather than by its toxigenic abilities.
Summary Anticipatory parental effects modulate population responses to environmental conditions and so are predicted to play a large role in the responses of organisms to global change. In response to one such aspect of global change, the eutrophication of freshwaters and associated blooms of the toxin‐producing cyanobacteria species Microcystis aeruginosa, the rotifer Brachionus calyciflorus produces larger offspring. We hypothesized that rotifers, with their short generational times, exposed to highly predictable cyanobacteria bloom conditions, may adaptively increase offspring investment and offspring fitness (i.e. the maternal match hypothesis). We explicitly tested the consequences of this differential investment by rearing offspring produced by rotifers reared under Microcystis and the nontoxigenic green alga Chlamydomonas, in a full factorial design, where offspring were raised under the maternal diet or the opposite food source. We measured age‐specific fecundity, survival and population growth rates under these conditions and found that maternal exposure to Microcystis decreased offspring survival and fecundity, regardless of offspring diet. Population growth rates, tested using aster models, differed significantly among maternal and neonate diets, but there was no significant interaction between the two factors. Our evidence thus leads us to reject the maternal match hypothesis in this case of rotifer–toxigenic algal bloom interactions and provides further support that toxigenic algal blooms may have extensive effects on grazer populations in ways that are not evaluated using traditional, single‐generation experimental methods. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12901/suppinfo is available for this article.
Transport of aquatic invasive species (AIS) by boats traveling up rivers and streams is an important mechanism of secondary spread of AIS into watersheds. Because physical barriers to AIS movement also prevent navigation, alternate methods for preventing spread are necessary while allowing upstream navigation. One promising approach is to lift boats over physical barriers and then use hot water immersion to kill AIS attached to the hull, motor, or fishing gear. However, few data have been published on the acute upper thermal tolerance limits of potential invaders treated in this manner. To test the potential effectiveness of this approach for a planned boat lift on the Fox River of northeastern WI, USA, acute upper thermal limits were determined for three AIS, adult zebra mussels (Dreissena polymorpha), quagga mussels (Dreissena rostriformis bugensis), and spiny water fleas (Bythotrephes longimanus) from the local area employing temperatures from 32 to 54°C and immersion times from 1 to 20 min. Mortality was determined after immersion followed by a 20-min recovery period. Immersion at 43°C for at least 5 min was required to ensure 100% mortality for all three species, but due to variability in the response by Bythotrephes a 10 min immersion would be more reliable. Overall there were no significant differences between the three species in acute upper thermal limits. Heated water can be an efficient, environmentally sound, and cost effective method of controlling AIS potentially transferred by boats, and our results should have both specific and wide-ranging applications in the prevention of the spread of aquatic invasive species.
Anthropogenic eutrophication has resulted in shifts in phytoplankton community composition worldwide which represent dramatic changes in resource quality and availability for grazers such as rotifers. For these grazers, harmful algal blooms may have consequences that persist across several generations. We hypothesized that rotifers exposed to a pulse of the toxigenic cyanobacterium Microcystis aeruginosa, would suffer demographic and physiological effects that decreased their ability to recover after cyanobacteria exposure. Additionally, we hypothesized that rotifer population recovery after harmful algal blooms is modulated by delayed effects of pre-bloom food availability. We used laboratory experiments to test the effects of switching from a high quality diet to toxigenic cyanobacteria on the physiological condition and associated life history changes of the common rotifer Brachionus calyciflorus. We found that M. aeruginosa exposure decreased fecundity of rotifers by 51.5%, and early exposure to high levels of the high-quality food Chlamydomonas sp. did not ameliorate this negative effect. Rotifers exposed to Microcystis produced lower quality offspring (by 16.6%). However, we found that the effect of Microcystis on offspring body size was dependent on the density of food available in early life. Exposure to high-density food for the first 3 d of life tempered the negative effects of Microcystis exposure, whereas initial exposure to low-density food resulted in a 9.0% decrease in offspring length. We found that the negative effects of exposure to toxigenic cyanobacteria may accumulate across generations and limit the ability of rotifer populations to withstand the predicted increasing frequency and duration of harmful algal blooms.
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