Ecology of Diaptomus leptopus s. a. Forbes 1882 (Copepoda: Calanoida) under temporary pond conditions

An ecological study of the calanoid copepod Diaptomus leptopus under temporary pond conditions was undertaken from March 4 to July 24, 1970, in Windsor, Ontario, Canada. Twice weekly samples were taken from a single station in the pond and among the more important physical-chemical parameters measured were: temperature, precipitation, depth, dissolved oxygen, total alkalinity, total hardness and pH. Initially the desmid Closterium sp. was the dominant phytoplankter but subsequent to May 26, the diatoms, mainly Navicula sp. were most abundant. The dominant zooplankters were the copepods Diaptomus leptopus, Cylcops bicuspidatus thomasi and the cladocerans Daphnia schødleri, Daphnia pulex and Moina recticostris. A positive linear correlation, which was barely significant at the 5% level (r = 0.539) was found between total calanoida and total cladocera. Clutch size in Diaptomus leptopus appeared to decrease with increasing water temperature. A tendency in this species towards suppression of the reproductive activity was associated with increases in the total cladoceran population. Overall metasomal lengths of adult males were less than those reported in the literature. Possible mechanisms of overwintering of this species in the absence of winter eggs is discussed briefly.     

Distribution quantified by microtopography in an assemblage of saxicolous mosses

Microtopography was quantified and related to plant microdistribution in an assemblage of bryophytes on granitic rocks in the inland chaparral of San Diego County, California, U.S.A. The dominant species, Grimmia laevigata, grew mostly on north-, east-, and west-facing surfaces with slope less than 60°. Other bryophytes tended to grow on steep, concave, north- and west-facing surfaces. Occurrence of these latter species was strongly associated with shade, as estimated from microtopography. The relationship of microdistribution to microclimate and ultimately to plant physiology can probably be successfully defined in systems such as this.Nomenclature follows Crum et al. (1973) for bryophytes and Munz (1974) for vascular plants.I thank W. C. Oechel for arranging access to the San Diego State University research area at Echo Valley and to facilities maintained there by the Systems Ecology Research Group; D. Alpert, C. Harkins, C. M. M. Hermida, J. Jacobson, and C. Scheidlinger for assistance with portions of the field work; M. P. Harthill and B. D. Mishler for help with identification of mosses; H. A. Mooney for comments on an earlier draft; and R. E. Cook and N. G. Miller for advice and support in many forms. This work was supported by National Science Foundation Grant DEB-7906428 and by a grant from the William and Alice Hinckley Scholarship Fund.     

Avian peptidase isozymes: Tissue distributions,substrate affinities,and assignment of homology

Peptidase (EC 3.4.13.9 and EC 3.4.13.11) isozymes were examined from 14 tissues of 19 species of birds, representing 8 families and 6 orders, via horizontal starch gel electrophoresis. Peptidases were detected by employing histochemical staining techniques utilizing 13 di-, tri-, and tetrapeptides as substrates. It was determined that there is a minimum of six presumptive structural gene loci encoding peptidases in birds (excluding those encoding cytosol aminopeptidase; EC 3.4.11.1). The products of the peptidase loci were widely expressed in most tissues with the exception of Pep-F, which was restricted to pancreas. Products of most loci have multiple, overlapping substrate affinities (except for the products of Pep-D, which react only with a peptide containing a carboxyterminal proline). By using a combination of differential electrophoretic mobility and substrate preferences, the products of the various peptidase loci can be distinguished from one another. The homologies of the avian peptidases with those in other vertebrates were tentatively established and it is suggested that the nomenclature proposed by Rapleyet al. (Ann. Hum. Genet. 34:307, 1971) be applied to avian peptidases. Financial support for this research was provided by several Organismal Biology Grants provided through the Department of Biology, UCLA; UCLA Travel and Research Grants; and a NSF Doctoral Dissertation Improvement Grant (BSR 85-01245) to RHM; and the UCLA Biomedical Support Grant and UCLA Committee on Research Grant (U.R. 3674) to D. G. Buth.     

Prey selection by Chaoborus punctipennis under laboratory conditions

Equal numbers of Diaphanosoma leuchtenbergianum, Daphnia parvula, and Diaptomus pallidus were offered to individual, fourth-instar larvae of Chaoborus punctipennis. When the prey species were presented separately to the larvae, 100% of the Diaphanosoma, 67% of the Daphnia, and 57% of the Diaptomus were consumed. However, when the three species were offered to the predator concurrently, 90% of the Diaphanosoma, 10% of the Daphnia and < 1% of the Diaptomus were eaten. This strong selection for Diaphanosoma was consistent at three prey densities.     

Regulation of rotifer densities by crustacean zooplankton in an oligotrophic montane lake in British Columbia

Summary To examine the relative demographic effects of predation and competition for food in rotifers during spring and summer in an oligotrophic lake, predator and competitor densities and food supplies were experimentally altered inside large enclosures. Abundances of rotifer species were positively correlated with experimental densities of fourth instar Chaoborus trivittatus larvae, a major crustacean predator in 1976. Experimental alteration of the densities of Daphnia rosea and Diaptomus leptopus and D. kenai in 1978 produced highly significant increases in rotifer biomass only under Daphnia removal, but not under copepod removal. Inorganic fertilizer additions to enclosures in 1978 and 1979 revealed minimal rotifer increases unless pulsed additions were large or Daphnia were also excluded. Large demographic reponses of rotifers to low fertilizer loadings in the absence of Daphnia confirmed the pre-eminence of competitive food limitation in producing rotifer scarcity in summer.     

Prey preference and utilization by Mesostoma lingua (Turbellaria,Rhabdocoela) at a low arctic site

The rhabdocoel Mesostoma lingua is a common inhabitant of rock bluff ponds in the area of Churchill, Manitoba. Unlike most flatworms it has the ability to prey actively on zooplankton. Among the zooplankton, Mesostoma prefers Daphnia pulex, Simocephalus vetulus, and Diaptomus tyrrelli. Larger calanoid copepods are difficult to capture and take much longer to consume. Growth in Mesostoma is maintained when individuals consume 0.5 Daphnia day^–1 and is maximal at 4 Daphnia day^–1. In comparison, Mesostoma maintained growth only when offered the copepod Diaptomus victoriaensis at the rate of 8–10 individuals-day^–1. Mesostoma may be an important agent in structuring pond zooplankton communities in the arctic, producing a shift in dominance away from cladocerans such as Daphnia toward larger calanoid copepods.     

Short term experiments on calanoid-cyclopoid-phytoplankton interactions

To investigate their potential effects on each other in nature, calanoid (Diaptomus clavipes and D. siciloides) and cyclopoid (Acanthocyclops vernalis and Mesocyclops edax) copepod populations were manipulated in 5 liter aquaria in laboratory experiments of 20–60 days duration. Diaptomus generally had a strongly negative effect on both cyclopoid species. The cyclopoids established populations more successfully when introduced to aquaria before calanoids than they did when calanoids were already present. On the other hand, whether introduced earlier or later than the cyclopoids, Diaptomus populations were unaffected by Acanthocyclops and were strongly depressed by Mesocyclops. Diaptomus effects on the phytoplankton were often strong but varied markedly among experiments. They included reduction of populations of edible algae, such as Chlamydomonas, which are essential for both calanoid and cyclopoid nauplii, and large increases in inedible algae, such as Kirchneriella. Feeding experiments revealed that under conditions of food scarcity Acanthocyclops nauplii survived less well than did Diaptomus nauplii. Competition for edible phytoplankton seemed to be a key factor in the calanoid-cyclopoid interactions, since the survival of herbivorous cyclopoid larvae determined the abundance of the predaceous adults. This indicates that the competitive effects of calanoids on cyclopoids often may exceed the predative effects of cyclopoids on calanoids.     

Field evidence for stoichiometric relationships between zooplankton and N and P availability in a shallow calcareous lake

1. According to stoichiometric theory, zooplankters have a species‐specific elemental composition. Daphniids have a relatively high phosphorus concentration in their tissues and copepods high nitrogen. Daphniids should, therefore, be more sensitive to phosphorus limitation and copepods more sensitive to nitrogen. A 2‐year study of a shallow marl lake in the west of Ireland investigated whether population fluctuations of the two dominant taxa, Daphnia spp. and the calanoid Eudiaptomus gracilis, were associated with the availability of phosphorus and nitrogen. 2. In accordance with stoichiometric predictions, Daphnia and Eudiaptomus reproduction had contrasting relationships with dietary phosphorus and nitrogen availability. Egg production by Daphnia was negatively associated with the ratio of dissolved inorganic nitrogen (DIN) : total phosphorus (TP) and the ratio of light to TP which was used as an indirect index for seston carbon (C) : phosphorus (P). Conversely calanoid egg production had a positive relationship with the DIN : TP ratio and was unrelated to the estimated C : P (light : TP) ratio. 3. Daphnia biomass was not, however, correlated with phosphorus availability, and neither was calanoid biomass correlated with nitrogen. The high ratio of DIN : TP when Daphnia dominated the zooplankton biomass and the low ratio when calanoids dominated, is consistent with Daphnia acting as a sink for phosphorus and calanoids as a sink for nitrogen and suggests consumer‐driven nutrient recycling.     

Effect of collection and acclimation period on grazing rates of limnetic zooplankton

Grazing rates of Daphnia sp. and Diaptomus oregonensis measured using an in situ method (Haney 1971) were compared with rates measured by collecting animals in vertical townets and placing them in experimental chambers either immediately or after a 24-h acclimation period. Experiments with acclimation yielded grazing rates of Daphnia that were statistically higher than in situ rates, whereas experiments conducted without acclimation yielded significantly lower rates. In situ grazing rates of Diaptomus were statistically higher than those for both townet techniques; experiments without an acclimation yielded higher rates than those for experiments with a 24-h acclimation period.     

The effects of spatial habitat structure on population variability of freshwater snails

Experiments were conducted to examine the effects of a habitat's spatial structure on population variability in two species of freshwater snails (Physa acuta and Austropeplea ollula). To alter the spatial structure of the habitat, vinyl chloride plates were hung in experimental tanks, providing three types of spatial structure: Complex structure, Simple structure and Control (no structure). In Experiment 1, the average number of individuals in a tank did not differ among the three types of structure 2 months after the introduction of the snails, but the variability of the number of individuals in the Complex structure tanks was lowest, whereas the variability in the Control tanks was highest. In Experiment 2, in addition to the spatial structure of the habitat, three types of species interaction were designed as experimental treatments: only P. acuta was introduced into the tanks (P. acuta tanks), only A. ollula was introduced into the tanks (A. ollulatanks) and both P. acuta and A. ollula were introduced into the tanks (two-species tanks). For the P. acuta tanks, the variability of the number of P. acuta individuals in the Complex structure tanks was lowest, and the variability in the Control tanks was highest when the effect of the number of individuals in a tank was subtracted. For the A. ollula tanks and the two-species tanks, there were no significant differences in the variability of the population size among the different treatments of spatial structure. The spatial distribution of P. acuta was more uniform than the distribution of A. ollula on the plates of complex structure. Our results indicate that the spatial structure of the habitat influences the variability of population size (the variance of the number of individuals in different populations during the earlier period after the introduction of the snails), but the effects depend on the spatial behavior of individuals and the interaction with other species.     

A New Acanthocyclops Kiefer, 1927 (Copepoda: Cyclopoida) from Central Mexico with Comments on the Distributionof the Genus in Middle America

A new species of Acanthocyclops Kiefer is described from central Mexico. It differs from its congeners by a combination of characters including mainly: 11–13 antennular segments, a spine formula of 3444 and modified setae on legs 2–4. The presence of a compound distal antennular segment is aberrant within the Cyclopoida. The new species seems to be related to Nearctic forms of the vernalis –robustus clade. Ancestors of this lineage probably reached central Mexico as a result of glaciation events and the new species is a remain of stranded postglacial populations; some of these forms were succesful in colonizing tropical lands. A key for the identification of the species of Acanthocyclops recorded in Mexico is included. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Freshwater Zooplankton of Sri Lanka,with a Discussion of Tropical Freshwater Zooplankton Composition

Based on the study of over 500 zooplankton samples collected in Sri Lanka (Ceylon) during 1965–1974, the species composition from different habitats is analysed. The zooplankton assemblage is typically tropical with relatively few species of Cladocera and Copepoda. The Rotifera include a large number of species of the genus Brachionus. The limnetic zooplankton resembles the pond zooplankton closely in that all the eurytopic species found in the different types of habitats, including ponds, also occur in the limnetic zooplankton. The large Cladocera belonging to the genus Daphnia are very rare. In general, large zooplankters are absent. The size composition of the zooplankton has a smaller range than in temperate regions. This is due to the absence of large-sized zooplankton species. The reasons for the differences in species variety and size composition between zooplankton of temperate and tropical regions is perhaps due to a number of factors. These include the effects of high and uniform temperatures, food availability and predation by fish and invertebrates.     

Postembryonal morphological variation of <Emphasis Type="Italic">Daphnia galeata</Emphasis> in water bodies of different types

Despite many ecological studies the population morphological variability within the freshwater crustacean genus Daphnia is poorly investigated, especially during postembryonic development. Unusual phenotypic plasticity of some Daphnia species results in tremendous difficulties in morphological species delineation. The ontogenetic morphological variation of this species was studied, revealing the general trends in body shape variation in different populations. The morphotypes of size and age groups of D. galeata turned out to be more variable at the mouth of the Kargat River (Lake Chany basin) than in Lake Todzha (Bol’ shoi Yenisei River basin); however, the growth of characters such as the helmet and tail spine was described by an allometric function and their absolute sizes decreased with age in Daphnia from both water basins. It is shown that the first mature size-and-age group of D. galeata is most suitable for investigating population morphological variation.     

Food quality triggers the reproductive mode in the cyclical parthenogen <Emphasis Type="Italic">Daphnia</Emphasis> (Cladocera)

Cyclic parthenogenesis (heterogony) is a widespread reproductive mode found in diverse taxa such as digenean trematodes, gall wasps, gall midges, aphids, cladocerans and rotifers. It is of particular interest as it combines the advantages of asexual reproduction (rapid population growth) and sexual reproduction (recombination). Usually sexual reproduction is initiated when, or slightly before, environmental conditions deteriorate, and often results in the production of resting stages. The optimal timing of diapause induction must thus be under strong natural selection. Using the cladoceran Daphnia as a model system, we show here for the first time that the switch from parthenogenetic to sexual reproduction in a cyclical parthenogenetic organism can be influenced by the chemical composition of food. Under crowding conditions Daphnia reproduced parthenogenetically with subitaneous eggs when fed the algal species Cryptomonas sp., but started the production of resting eggs when fed with the green algal species Scenedesmus obliquus. Supplementation experiments with lipids and especially proteins showed that the induction of resting egg production in two clones of different Daphnia species was due to a dietary deficiency in the green alga. Hence, the low food quality induced a switch in the reproductive mode that may contribute to optimal timing of the sexual reproduction of Daphnia in nature. Furthermore, our results have two other major implications: first, they suggest that protein compounds should be added to the list of diet constituents potentially limiting or influencing Daphnia reproduction. Second, we show that the role of food quality goes far beyond the up to now documented effects of food quality on somatic growth and trophic transfer efficiency of herbivores: due to its effects on sexual reproduction and the production of resting eggs, food quality might influence genetic diversity and long-term persistence of Daphnia in lakes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Discrimination by freshwater zooplankton between single algal cells differing in nutritional status

Summary Grazing rates of a freshwater copepod (Diaptomus kenai) and a freshwater cladoceran (Daphnia rosea) on the green alga Selenastrum minutum were determined to be dependent on the nutritional status of individual cells. Cells that were less nitrogen limited were ingested at a greater rate than cells reared under more nitrogen limited conditions. Diaptomus displayed active discrimination, possibly via chemodetection, while Daphnia expressed passive selection, probably via differential retention on filters. These results suggest that the impact of grazing zooplankton varies with the physiological state of components of the phytoplankton community.     

Crustacean zooplankton assemblages in freshwaters of tropical Australia

Throughout tropical Australia eulimnetic zooplankton is composed of 7 calanoid copepods, 5 cyclopoid copepods and 12 cladocerans. A further 10 cyclopoids and 9 cladocerans occur as littoral strays, making 43 species in all. Dominants include Diaptomus lumholtzi, Mesocyclops notius, Thermocyclops decipiens, Diaphanosoma excisum, Ceriodaphnia cornuta, and Moina micrura. Momentary species composition averages 1.0 calanoids, 1.3 cyclopoids and 2.0 cladocerans. These assemblages are not only less complex than in temperate Australia, but also are not as rich as in most other tropical regions. The main contributors to these differences are calanoids and cladocerans respectively. Nevertheless, as elsewhere, most zooplankters in tropical Australia are eurytropic, widely distributed and small.     

Molecular and morphological patterns across Acanthocyclops vernalis‐robustus species complex (Copepoda,Cyclopoida)

Bláha, M., Hulák, M., Slouková, J. & Tě?itel, J. (2010). Molecular and morphological patterns across Acanthocyclops vernalis‐robustus species complex (Copepoda, Cyclopoida).—Zoologica Scripta, 39, 259–268. Morphological traits within Acanthocyclops (Kiefer, 1927) are highly variable, and morphology is too constrained to give complete information of phylogenetic relationships. This study combined morphological and molecular techniques to investigate the taxonomic and phylogenetic relationships of three species of Acanthocyclops (Acanthocyclops trajani, Acanthocyclops einslei and Acanthocyclops vernalis) inhabiting continental Europe. Morphological indices subjected to principal component analysis (PCA) separated sample populations into three distinct clusters corresponding with the taxonomic status of the species analysed. In addition, the taxonomy status of A. trajani and A. einslei was in agreement with molecular data; however, the intraspecific variation in sequences of 12S rRNA was lower in contrast to specimens morphologically determined as A. vernalis, which were divided into two deeply divergent clades, based on mtDNA sequence divergences. Moreover, high sequence divergence (26%) between these clades indicated the existence of another species that may not be a sister taxon of A. vernalis s.s. Results point to the need for further taxonomic work on Acanthocyclops.     

Size-dependent habitat choice in Daphnia galeata Sars and size-structured interactions among zooplankton in a subarctic lake (lake Lombola, Norway)

Seasonal changes in vertical distribution of Daphnia galeata and other zooplankters were monitored in lake Lombola (69° 07&prime; N). Depth-habitat use, availability of edible algae and zooplankton densities were recorded to examine seasonal changes in intensity of competition between Daphnia and the other herbivores in the lake. Early in July, the exephippial generation of Daphnia aggregated near the surface, independently of body-size. In late July, when fish planktivory was expected to increase, the daphnids moved down during the day. In August, as intraspecific competition for food intensified, small and large Daphnia partitioned the water column, with larger individuals staying deeper. In September, Daphnia became dominated by large individuals, edible phytoplankton reached the seasonal minimum, and the vertical distribution of Daphnia gradually stretched out towards the surface. The observations on food availability and zooplankton densities suggest that interspecific competition intensified by the end of July. Species and stages that were most exposed to exploitative and interference competition by Daphnia were those staying deeper, because their vertical distribution overlapped more with the larger, competitively superior daphnids. These susceptible competitors included Keratella cochlearis and Synchaeta, among the rotifers, and nauplii and early copepodite stages of Cyclops scutifer. Depth-habitat use is discussed in relation to copepod development, zooplankton dynamics and predator-mediated coexistence.     

Horizontal distribution of pelagic zooplankton in relation to predation gradients

An investigation was conducted examining the horizontal and vertical distribution of zooplankton in Lake Miramar, a southern California reservoir. Daphnia and Mesocyclops populations were most abundant offshore and in deeper water during the day but appeared to move toward shore and upward at night. The results of inshore zooplankton sampling provided no evidence chat the diel horizontal migration pattern was a result of sampler avoidance by zooplankton. Inshore-offshore differences in Daphnia and Mesocyclops abundance and diel migrations were reduced during winter and early spring. Rotifer zooplankters exhibited less seasonal variation in their horizontal distributions than did the large crustacean zooplankters at all times of the year. It is hypothesized that the spatial distribution of zooplankton is related to predation gradients in Lake Miramar. The dominant planktivore in the reservoir, young-of-the-year Micropterus salmoides. was abundant from late May through December and much less so from January to early May. They were largely restricted to the littoral zone and this produced horizontal gradients of planktivory which varied in strength seasonally and from day lo night. It appears that crustacean zooplankton in Lake Miramar avoid areas with abundant planktivores during the day but migrate into these areas at night when the intensity of planktivory is reduced. Rotifers exhibit less horizontal heterogeneity and no significant diel migrations, which is attributed to the reduced risk of predation that rotifers experience relative to crustacean zooplankters. A graphical model is proposed to integrate our understanding of diel vertical and horizontal migrations of zooplankton. In this model, gradients of predation are completely vertical in offshore areas and strongly horizontal in near shore areas. Gradients of food availability are roughly similar to those of predation intensity. Plankiers respond to these gradients by migrating in a path parallel to gradients of predation at dawn and parallel to gradients of food availability after dark.