Effects of products released by Aphanizomenon flos‐aquae and purified saxitoxin on the movements of Daphnia carinata feeding appendages

The freshwater cyanobacterium Lyngbya wollei forms dense mats in lentic systems throughout the southeastern United States and produces paralytic shellfish poisons (PSPs), such as saxitoxins, that could provide a chemical defense against herbivory. In addition, Lyngbya filaments are surrounded by a prominent extracellular polysaccharide sheath that might function as a structural defense against herbivory. We investigated the roles of PSPs and sheath structure in deterring consumption of Lyngbya by an omnivorous amphipod, Hyalella azteca. A series of two-choice feeding assays paired Lyngbya with a highly palatable green alga, Rhizoclonium hieroglyphicum. These assays included comparisons of whole Lyngbya and Rhizoclonium, freeze-dried and ground Lyngbya and Rhizoclonium, artificial food treated with Lyngbya crude extract, artificial food treated with pure saxitoxin, and artificial food containing Lyngbya sheath material, with and without Lyngbya crude extract. Hyalella preferred whole, live Rhizoclonium over fresh Lyngbya. Similarly, Hyalella preferred freeze-dried and ground Rhizoclonium over Lyngbya. However, Hyalella preferred treated foods containing Lyngbya crude extract or pure saxitoxin over control foods. The sheath constituted over 55% of the total dry mass of Lyngbya. In assays combining sheath material and crude extract in artificial foods, Hyalella avoided foods containing sheath material. Therefore, morphological defenses play an important role in deterring consumption of Lyngbya by Hyalella, whereas PSPs stimulate feeding. Our study indicates that structural defenses can partially explain the high abundance of filamentous cyanobacteria observed in aquatic communities under grazing pressure.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Amphipod herbivory on the freshwater cyanobacterium Lyngbya wollei: Chemical stimulants and morphological defenses

Camacho

Thacker

2006

“…Chemical cues seem more promising as daphnids have often been shown to respond to a variety of such cues. For example, Haney et al (1995) showed that exudates of toxic cyanobacteria lead to an immediate reduction of feeding behavior in D. carinata, and that after the exudates were removed, feeding returned to normal. This and other behaviors, such as predator-induced vertical migration in daphnids, clearly demonstrate chemically mediated behavioral responses (see review by Larsson and Dodson 1993).…”

Section: Discussionmentioning

confidence: 99%

Adaptive feeding behavior of Duphnia magna in response to short‐term starvation

Plath¹

1998

Feeding behavior of Daphnia has been intensely studied, yet the generally observed behavior of maximal feeding at low food concentrations contradicts the predictions of optimal foraging theory. To explore this inconsistency, 1 investigated the behavioral feeding response of Daphnia magna through direct observation of thoracic filtering appendage beat rates at low food concentrations. I observed animals that were subjected to either varying starvation periods or to different food concentrations prior to the experiments. Starvation led to a behaviorally mediated decrease in appendage beat rate, which depended on the food concentration at which the daphnids were cultured. Starved daphnids consistently showed an almost immediate increase in their appendage beat rate once food was added, irrespective of the length of the starvation period (from 1 to 3 d). Therefore, the initial decrease in appendage beat rate displayed by animals during starvation could not have been caused by the deprivation of energy (exhaustion) alone. Furthermore, the food conditions under which the animals were cultured influenced the behavioral response. After 1 h of starvation, animals cultured at high food level showed no behavioral response to the addition of food, while animals cultured at low food level increased their appendage beat rate significantly. The results of this study contradict the maximal feeding strategy and highlight problems of the optimal foraging strategy.

“…HAB toxins easily fit these criteria and each may have evolved to play an active role in one or more intrinsic and (or) extrinsic functions. For instance, saxitoxins, the etiological agent of PSP may play an intrinsic role in DNA metabolism (Mickelson and Yentsch 1979;Anderson and Cheng 1988), or N storage (Anderson et al 1990b), and (or) an extrinsic role as an antipredation compound (White and Maranda 1978;Haney et al 1995). The precise evolutionary pressure(s) driving the synlhesis of each HAB toxin remains enigmatic, in large part because the toxins are chemically distinct ( Fig.…”

Section: Hab Toxins As Secondary Metabolitesmentioning

confidence: 99%

Marine algal toxins: Biochemistry, genetics, and molecular biology

Plumley

1997

Toxic compounds are frequently, but not universally, associated with alg,al blooms. Several dinoflagellate and diatom species are capable of toxin synthesis. Some bacteria are also capable of synthesizing at least one family of "algal" toxins. Previous work on algal toxins can be broadly grouped in four categories: observations on the variability in toxin production by single species or among strains of a species, frequently as a function of environmental growth conditions; isotope feeding studies to reveal the identity of the substrates that are precursors to the toxin compounds; the genetics of toxin production; and the pharmacological aspects of toxins. Information gleaned from these studies provides a firm foundation for launching more contemporaneous research efforts to understand the biochemistry and molecular biology of toxins. The goals are to develop an understanding of the machinery (i.e. the enzymes and the genes that encode them) required to synthesize toxins, to understand how this machinery is regulated by environmental conditions, and gain insights as to how the tox n biosynthetic genes evolved and(or) have been spread through the marine community.The production of toxic compounds is a common, but not universal, characteristic of harmful algal blooms (HABs). Surprisingly, only a few HAB toxins have been characterized and these are synthesized by only a limited number of algal species (Steidinger 1993). Toxigenic algae may, however, exert an inordinately large adverse impact on other members of the community because toxins can flow through aquatic food chains in a manner analogous to the movement of carbon or energy (Smayda 1992). Toxigenic algae thus may have significant impacts on ecosystem processes as toxins affect viability, growth, fecundity, and recruitment of a wide range of organisms.This manuscript is concerned with the biochemistry and genetics of toxin production by HAB species. Most information is for marine toxins as these have been better documented than the freshwater toxins. Saxitoxins, the causative agent of paralytic shellfish poisoning, are used as a model throughout this review as they are the best characterized marine toxin in terms of biochemistry and genetics. The physiology and ecology of the organisms that synthesize saxitoxins are also better documented than for other HAB species; this information permits a more robust interpretation of biochemical and genetic data for the saxitoxins than for other HAB toxins. Inauspiciously, very little is known about the molecular biology of HAB toxins, making this topic difficult to review. The goal in writing the molecular section was to interpret the biochemical, genetic, and physiological data in a context that would encourage and arouse others to Acknowledgments