Induction of sexual reproduction in Brachionus plicatilis (Monogononta, Rotifera) by a density‐dependent chemical cue

Crowding induced the production of mictic (male-producing) females in Brachionus calyciflorus from two North American strains and an Australian strain. The specificity of this response to crowding was tested by culturing single individuals of a North American clone in three treatment conditions: a small volume (high density), a large volume (low density), and a large volume with a high density of an Australian clone. The results were consistent and clear in six experiments using different combinations of clones. Crowding low-density individuals of the North American strains with the Australian strain failed to induce them to produce mictic females. The mictic-female response in this treatment was similar to that in the low-density treatment, and both of these responses were significantly lower than that in the high-density treatment. Since the mictic-female response to crowding in Brachionus is mediated by a chemical produced by the rotifers themselves, the chemical inducers produced by the Australian and North American strains must be different. Taxonomically specific responses to crowding should increase fitness by assuring that sexual reproduction in the heterogonic life cycle coincides with a high population density of individuals able to mate with one another and, thus, when the production of fertilized resting eggs can be maximized. This would be especially important in plankton communities with diverse rotifer assemblages and multiple congeneric species. Otherwise, a low-density population of a species could be induced to initiate bisexual reproduction by populations of other species, curtailing its potential for population growth via female parthenogenesis and limiting its production of resting eggs in the future.Changes in zooplankton demographics and reproductive mode may occur at high population densities, and they can be induced by chemicals produced by the population itself. Crowding in laboratory populations of cladocerans and rotifers can affect feeding, growth, age at first reproduction, and fecundity. In many of these cases, the positive or negative effects of crowding are attributable to unidentified chemicals produced by the population

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Specificity of crowding response that induces sexuality in the rotifer Brachionus

Gilbert

2003

“…First, the type of signal that induces the production of mictic females can differ across genera. It can be high population density in Brachionus (Gilbert 2002(Gilbert , 2003aStelzer and Snell 2003), Epiphanes (Pourriot and Rougier 1999;Schröder and Gilbert unpubl. data), and Rhinoglena frontalis (Schröder and Gilbert unpubl.…”

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confidence: 99%

“…data). The density cue is known to be a chemical in Brachionus plicatilis Stelzer and Snell 2003) and taxonomically specific in Brachionus calyciflorus (Gilbert 2003b). Other primary stimuli are long photoperiods in Notommata and Trichocerca (Pourriot 1963;Pourriot and Clément 1975) and dietary tocopherol (vitamin E) in Asplanchna (Gilbert and Thompson 1968;Gilbert 1980a,b;Gilbert and Confer 1986).…”

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confidence: 99%

Rotifers from diapausing, fertilized eggs: Unique features and emergence

Gilbert

Schröder

2004

Sexual reproduction in cyclically parthenogenetic rotifers results in the production of diapausing, fertilized (resting) eggs, which can survive for decades in sediment egg banks. Stem females hatching from these eggs can differ from genetically identical ones produced in subsequent parthenogenetic generations. Differences involve the inhibition of sexual reproduction, which may persist for many parthenogenetic generations; reduced morphology (apterous Polyarthra, shorter-spined Brachionus); and larger stores of lipid. These features of stem females may facilitate colonization by favoring population growth via female parthenogenesis and by decreasing food requirements for survival and reproduction. Fertilized eggs in dried sediments probably hatch soon after being flooded by rising water levels. Eggs in permanently submerged sediments may be in environments that inhibit hatching (e.g., darkness, low water temperature, low dissolved oxygen) and hatch only when brought to the sediment surface or resuspended into the water column by currents or bioturbation. Laboratory experiments show that the hatching of diapausing, fertilized eggs can require light and temperatures suitable for population development or specific changes in temperature consistent with a new growing season. The limited data that exist on their emergence from fertilized eggs in natural systems come from sediment traps, from the occurrence in the water column of apterous Polyarthra or empty egg shells, and from calculations of negative mortality rates of planktonic populations. Fertilized eggs often hatch at the beginning of the growth season but may continue to hatch intermittently thereafter. The extremely high genotypic diversity of some natural rotifer populations indicates extensive hatching of stem females from the sediment egg bank.

“…Medium from crowded cultures induces mixis in Brachionus species (Gilbert 2003;Stelzer and Snell 2003), and negatively affects several demographic parameters in various rotifer species (Kirk 1998;Yoshinaga et al 1999). To understand the variety of crowding responses described in zooplankton literature, at least two types of crowding-related chemicals need to be distinguished.…”

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confidence: 99%

Infochemical‐mediated trophic interactions between the rotifer Brachionus calyciflorus and its food algae

Verschoor

Zadereev

Mooij

2007

We studied how chemicals obtained as filtrates from algal monocultures (algal chemicals) and from rotifer cultures with or without algae (rotifer chemicals) affected feeding rates of the rotifer Brachionus calyciflorus on its food algae, both directly and indirectly (through chemical-induced changes in algal morphology). Algal chemicals had a strong stimulating effect on the feeding rate of B. calyciflorus, but these effects were counteracted by rotifer chemicals. In functional response experiments, rotifer chemicals lowered maximum ingestion rates and had strong effects on assimilation rates and assimilation efficiencies of B. calyciflorus, probably due to the release of unspecific (auto)toxic metabolites. Furthermore, rotifer chemicals induced colony formation in the food alga Scenedesmus obliquus. Above the optimum particle size for ingestion by B. calyciflorus, larger algal colony sizes increased the food-handling time, thus lowering ingestion and assimilation rates. Through their effects on trophic interactions, infochemicals may play a role in structuring and the functioning of aquatic food webs.