Allelopathic interactions between the macrophyte Egeria densa and plankton (alga, Scenedesmus acutus and cladocerans, Simocephalus spp.): a laboratory study

Allelopathic interactions between macrophytes and zooplankton are important to understand the plankton dynamics in shallow waterbodies. Egeria densa is a native, perennial, submerged macrophyte in the tropical and subtropical zones of South America. It has been introduced to Central and North America and is now common in many Mexican lakes. This macrophyte produces chemical substances that negatively affect some phytoplankton species. However, it is not clear how zooplankton species adapt different life history strategies in the chemical presence of this macrophyte. Here, we tested the direct and indirect effects of allelochemicals released by E. densa on the population growth of Scenedesmus acutus and on the demographic variables of three species of Simocephalus, S. exspinosus, S. serrulatus and S. mixtus (via alga exposed to the macrophyte allelochemicals). To quantify the effect of E. densa on S. acutus we set up four treatments: control, artificial Egeria, natural Egeria and allelochemicals from Egeria. To test the allelochemical effects on Simocephalus species, we compared four treatments: Control, indirect effect (using S. acutus grown on Egeria-allelochemicals), direct effect (using Egeria-conditioned medium) and together with both these kinds of direct and indirect effects. Scenedesmus had the highest cell density in the presence of allelochemicals from Egeria, followed by controls. The specific algal growth rate (µ) between control and allelochemicals treatment was not significant (P<0.05). However, the µ of alga in the presence of artificial or natural Egeria was significantly lower than controls or in treatment involving allelochemicals. The age-specific survivorship of the three cladoceran species was longer in treatments containing Egeria-conditioned medium. Cladocerans receiving Egeria conditioned-medium and algae cultured on macrophyte-allelochemicals also had a longer survivorship. Daily fecundity of S. serrulatus increased after reaching mid-age while S. expinosus and S. mixtus showed continuous reproduction starting from the first week. In general, Egeria-allelochemicals enhanced the age-specific reproductive output for all the three cladoceran species. The average lifespan of the three Simocephalus varied from 17 to 46 days, depending on the cladoceran species and treatment. S. serrulatus had lower lifespan compared to other two cladoceran species. For the three species, lifespan significantly increased in treatments containing macrophyte-conditioned medium + algae grown on the plant-allelochemicals; also under these conditions, both gross and net reproductive rates were significantly enhanced. This stimulatory effect was also evident in generation time (about 50% higher). The rate of population increase ranged from 0.23 to 0.38 per day for the three tested Simocephalus species but there were no significant differences (P˃0.05) among treatments. Our results suggest that the biological activity as well as physical structure of E. densa had negative effects on S. acutus population growth but had stimulatory effects on the demography of Simocephalus.

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Demographic responses of selected rotifers (Rotifera) and cladocerans (Cladocera) fed toxic Microcystis aeruginosa (Cyanobacteria)

Fundamental and Applied Limnology / Archiv für Hydrobiologie ◽

10.1127/fal/2020/1285 ◽

2020 ◽

Vol 193 (3) ◽

pp. 261-274

Author(s):

Alfredo Pérez-Morales ◽

S.S.S. Sarma ◽

S. Nandini ◽

Cristian Alberto Espinosa-Rodríguez ◽

Ligia Rivera-De la Parra

Keyword(s):

Population Growth ◽

Life Table ◽

Microcystis Aeruginosa ◽

Green Algae ◽

Somatic Growth ◽

Phytoplankton Species ◽

Scenedesmus Acutus ◽

Cladoceran Species ◽

Toxic Cyanobacteria ◽

Demographic Responses

Tropical waterbodies contain several species of toxic cyanobacteria including Microcystis, which adversely affect the somatic growth, survival and fecundity of zooplankton. Scenedesmus, one of the most common green algae, is even found in Microcystis -dominated waterbodies. It is, therefore possible that in natural ponds, rotifers and cladocerans feed on mixed phytoplankton species containing algae and cyanobacteria. In this work, we quantified demographic responses of three rotifer species (Brachionus calyciflorus, B. rubens, and Plationus patulus), and three cladoceran species (Simocephalus mixtus, Daphnia cf. mendotae and Moina macrocopa) fed toxic Microcystis aeruginosa only or mixed with Scenedesmus acutus. The highest population growth for both rotifer and cladoceran species was observed when Scenedesmus was offered alone or at 75 % of the diet. Daphnia cf. mendotae and B. rubens were less affected by Microcystis while M. macrocopa and B. calyciflorus were more adversely influenced, which was also corroborated by life table demography. In competition bioassays, D. cf. mendotae was more efficient, alone or in competition, when fed with 50 or 25 % of Microcystis. This work explains the dynamics of the zooplanktonic community against gradual changes in phytoplankton due to the presence of cyanobacteria.

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The relative importance of direct and indirect effects of hunting mortality on the population dynamics of brown bears

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.1840 ◽

2015 ◽

Vol 282 (1798) ◽

pp. 20141840 ◽

Cited By ~ 31

Author(s):

Jacinthe Gosselin ◽

Andreas Zedrosser ◽

Jon E. Swenson ◽

Fanie Pelletier

Keyword(s):

Population Dynamics ◽

Population Growth ◽

Indirect Effects ◽

Ursus Arctos ◽

Brown Bear ◽

Relative Importance ◽

Direct And Indirect Effects ◽

Negative Effects ◽

Hunting Pressure ◽

Demographic Rates

There is increasing evidence of indirect effects of hunting on populations. In species with sexually selected infanticide (SSI), hunting may decrease juvenile survival by increasing male turnover. We aimed to evaluate the relative importance of direct and indirect effects of hunting via SSI on the population dynamics of the Scandinavian brown bear ( Ursus arctos ). We performed prospective and retrospective demographic perturbation analyses for periods with low and high hunting pressures. All demographic rates, except yearling survival, were lower under high hunting pressure, which led to a decline in population growth under high hunting pressure ( λ = 0.975; 95% CI = 0.914–1.011). Hunting had negative indirect effects on the population through an increase in SSI, which lowered cub survival and possibly also fecundity rates. Our study suggests that SSI could explain 13.6% of the variation in population growth. Hunting also affected the relative importance of survival and fecundity of adult females for population growth, with fecundity being more important under low hunting pressure and survival more important under high hunting pressure. Our study sheds light on the importance of direct and indirect effects of hunting on population dynamics, and supports the contention that hunting can have indirect negative effects on populations through SSI.

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Direct and indirect effects of leptin on preadipocyte proliferation and differentiation

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00860.2005 ◽

2006 ◽

Vol 290 (6) ◽

pp. R1557-R1564 ◽

Cited By ~ 42

Author(s):

Blair Wagoner ◽

Dorothy B. Hausman ◽

Ruth B. S. Harris

Keyword(s):

Adipose Tissue ◽

Conditioned Medium ◽

Indirect Effects ◽

Leptin Receptor ◽

Cell Number ◽

Direct And Indirect Effects ◽

Sprague Dawley ◽

Proliferation And Differentiation

Leptin has been shown to reduce body fat in vivo. Adipocytes express the leptin receptor; therefore, it is realistic to expect a direct effect of leptin on adipocyte growth and metabolism. In vitro studies examining the effect of leptin on adipocyte metabolism require supraphysiological doses of the protein to see a decrease in lipogenesis or stimulation of lipolysis, implying an indirect action of leptin. It also is possible that leptin reduces adipose mass by inhibiting preadipocyte proliferation (increase in cell number) and/or differentiation (lipid filling). Thus we determined direct and indirect effects of leptin on preadipocyte proliferation and differentiation in vitro. We tested the effect of leptin (0–500 ng/ml), serum from leptin-infused rats (0.25% by volume), and adipose tissue-conditioned medium from leptin-infused rats (0–30% by volume) on preadipocyte proliferation and differentiation in a primary culture of cells from male Sprague-Dawley rat adipose tissue. Leptin (50 ng/ml) stimulated proliferation of preadipocytes ( P < 0.05), but 250 and 500 ng leptin/ml inhibited proliferation of both preadipocyte and stromal vascular cell fractions ( P < 0.01), as measured by [3H]thymidine incorporation. Serum from leptin-infused rats inhibited proliferation of the adipose and stromal vascular fractions ( P = 0.01), but adipose tissue-conditioned medium had no effect on proliferation of either cell fraction. None of the treatments changed preadipocyte differentiation as measured by sn-glycerophosphate dehydrogenase activity. These results suggest that leptin could inhibit preadipocyte proliferation by modifying release of a factor from tissue other than adipose tissue.

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Direct and Indirect Effects of Resource P-Limitation Differentially Impact Population Growth, Life History and Body Elemental Composition of a Zooplankton Consumer

Frontiers in Microbiology ◽

10.3389/fmicb.2018.00172 ◽

2018 ◽

Vol 9 ◽

Cited By ~ 6

Author(s):

Libin Zhou ◽

Kimberley D. Lemmen ◽

Wei Zhang ◽

Steven A. J. Declerck

Keyword(s):

Life History ◽

Population Growth ◽

Elemental Composition ◽

Indirect Effects ◽

Direct And Indirect Effects ◽

P Limitation

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Review of the direct and indirect effects of warming and drought on scale insect pests of forest systems

Forestry An International Journal of Forest Research ◽

10.1093/forestry/cpaa033 ◽

2020 ◽

Cited By ~ 1

Author(s):

Steven D Frank

Keyword(s):

Population Growth ◽

Natural Enemies ◽

Indirect Effects ◽

Insect Pests ◽

Scale Insect ◽

Interactive Effects ◽

Scale Insects ◽

Insect Species ◽

Direct And Indirect Effects ◽

Tree Quality

Abstract Higher temperatures and drought are key aspects of global change with the potential to alter the distribution and severity of many arthropod pests in forest systems. Scale insects (Hemiptera: Coccoidea) infest many tree species and are among the most important pests of trees in urban and rural forests, plantations and other forest systems. Infestations of native or exotic scale insects can kill or sicken trees with economic and ecosystem-wide consequences. Warming can have direct effects on the life history, fitness and population dynamics of many scale insect species by increasing development rate, survival or fecundity. These direct benefits can increase the geographic distribution of scale insects and their consequences for tree health. Warming and drought can affect scale insects indirectly by altering the quality of their host trees. Additive or interactive effects of warming and drought can change tree quality in such a way that it increases scale insect fitness and population growth. However, the effects are species- and context-dependent with some scale insect species negatively affected by drought-induced changes in tree quality. Warming and drought are often coincident in urban forests and predicted to co-occur in many parts of the world under climate change scenarios. The individual and interactive effects of these factors require further research to inform predictions and management of scale insect pests. Warming also indirectly affects scale insects by altering interactions with natural enemies. This includes changes in natural enemy phenology, community composition and abundance. In addition, warming can alter scale insect phenology or voltinism causing asynchrony with natural enemies or population growth too rapid for natural enemies to suppress. Direct and indirect effects of warming and drought on scale insects can increase the potential for some exotic species to become established and for some native species to become invasive. Unfortunately, much research on scale insects is confined to a few particularly important native or exotic pests which limits our ability to predict the effects of warming on many current or potential pests. More research is required to understand how warming and drought affect scale insects, scale insect management and the forest systems they inhabit.

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