Patterns of genome size in the copepoda

Adult somatic nuclear DNA contents are reported for eleven cyclopoid species (Megacyclops latipes, Mesocyclops edax, M. longisetus, M. ruttneri, M. leuckarti, M. woutersi, Macrocyclops albidus, Cyclops strenuus, Acanthocyclops robustus, Diothona oculata, Thermocyclops crassus) and for the harpacticoid Tigriopus californicus and range from 0.50 to 4.1 pg DNA per nucleus. These diploid genome sizes are consistent with previously published values for four Cyclops species (0.28–1.8 pg DNA per nucleus), but are strikingly smaller than those reported for marine calanoids (4.32–24.92 pg DNA per nucleus). We discuss three explanations, none of them exclusive of another, to account for the smaller size and range of cyclopoid genome sizes relative to calanoid genome sizes: (1) higher prevalence of chromatin diminution in the Cyclopoida, (2) phylogenetic structure or older age of the Calanoida relative to Cyclopoida and (3) nucleotypic selection that may influence life history variation and fitness. Measurements of genome size were made on Feulgen stained, somatic cell nuclei, using scanning microdensitometry which is well suited to the sparse and heterogeneous populations of copepod nuclei. The importance of measuring large numbers of nuclei per specimen, possible sources of variation associated with cytophotometric measurements, and appropriate use of internal reference standards and stoichiometry of the Feulgen stained nuclei are discussed.     

Description of a new Nipergasilus species (Family: Ergasilidae) from the gills of grey mullet

A new Nipergasilus species is described from the gills of the grey mullet Valamugil cunnesius from several localities in India and Pakistan. The new species is closely related to Nipergasilus bora (Yamaguti, 1939) which is also recorded here on three species of grey mullet. The genus Nipergasilus is redefined in order to accommodate the second species.     

Components of morphological variation in Baikalian endemial cyclopid Acanthocyclops signifer complex from different localities

Use of traditional methods for morphological studies only permits the analysis of a small part of the information embodied in morphological structures. Besides comparing populations using the mean values of characters which allows one to estimate their morphological similarity, analysis of variation among individuals within a population can be informative. Variation among individuals consists of factorial and stochastic components. The factorial component is an upper estimate of genetic heterogeneity and thus permits one to evaluate the population's adaptability. The stochastic component (estimated by fluctuating asymmetry, i.e. random deviations from perfect bilateral symmetry), being a measure of developmental stability, is an indicator of a population's fitness. Assessment of measurement error is necessary for assessment of the true value of the stochastic component and for selection of the most informative characters. Such analysis allows one to extract additional information from morphological data in comparison with methods traditionally used on copepods. This approach was applied to an analysis of morphological variation in the study of the Baikalian endemic cyclopoid Acanthocyclops signifer (Mazepova) from three different isolated localities. Characters typically used in studies of taxonomy of this group are considered here. Measurement error was rather high (more than 50% of the stochastic component), which can be explained by technical difficulties of measuring the characters. All populations differ in the mean values of the characters. This shows the taxonomic heterogeneity of this group and reveals the necessity of its taxonomic revision. Populations also differ in the level of stochastic and factorial components of the total variance. The data are interpreted from the point of view of taxonomy and the possible evolution of the group.     

Arenopontia (Neoleptastacus) huysi, sp. nov. (Crustacea, Copepoda, Harpacticoida) from marine interstitial of Montenegro (S.E. Europe)

A new species of Arenopontia (Neoleptastacus) is described on the basis of a single female collected from one sandy beach in Montenegro, Adriatic Sea. With the addition of the new species, the subgenus Neoleptastacus now includes 18 species throughout the world. At the end of this paper there is a key for their determination. Received: 20 March 1999 / Received in revised form: 15 September 1999 / Accepted: 21 September 1999     

The distribution of microcrustacea in the littoral zone of a freshwater lake

The distribution of microcrustacea in the water column, sediments and on different macrophyte species was examined in the littoral zone of Jack Lake, Nova Scotia, Canada. Large numbers of microcrustacea occurred in association with macrophytes, suggesting that this habitat should receive greater attention in future studies of microcrustacean numbers, biomass, and production. The relative abundance of different microcrustacea varied considerably among sediments, macrophytes and water column samples. Although microcrustacean species composition differed among macrophyte groups, consistent differences in absolute numbers per gram could not be demonstrated. Epiphytic microcrustacean community structure also varied among depth strata in Jack Lake. Few epiphytic and benthic microcrustacea migrated into the water column on a diurnal basis.     

Copepod post-embryonic durations: pattern,conformity, and predictability. The realities of isochronal and equiproportional development,and trends in the opepodid-naupliar duration ratio

A collation of post-embryonic durations for freshwater and marine calanoid, cyclopoid and harpacticoid copepods is provided, and examined for patterns and conformities which may be of predictive value. Most of the analysis concerns calanoids. Only the genus Acartia exhibits evidence of equal stage duration (isochronality). Accordingly, isochronal development must be rejected as a general pattern in copepods — with various implications to the study of their production. Conversely, relative stage durations are surprisingly comparable in a wide range of copepods across a broad range of temperatures and food levels. A loose consistency is evident among copepod species generally, (interspecific equiproportionality), but within given genera, a striking regularity, here termed intergeneric equiproportionality (IGE) is evident. Patterns of IGE are consistent with selectively adaptive life-history traits, and IGE thus offers predictive prospects which are of both quantitative and qualitative (heuristic) value. Empirical support which exists for IGE among marine calanoids suggests that in contrast to isochronality and interspecific equiproportionality, IGE is indeed a real, and ultimately quantifiable feature of copepod development. Within calanoids, the ratio of total copepodid to total naupliar duration (Dc/Dn) appears independent of temperature, shows little relationship to adult body mass, but is inversely related to food supply, markedly so in freshwater forms. In this context, changes in the ratio are attributable largely to influences of food supply upon copepodid development times: naupliar durations appear relatively independent of food concentrations during development. Considerably higher Dc/Dn ratios in freshwater than in marine calanoids conceivably arise from selective influences of different nutritional conditions and size-selective predation pressures in freshwater and marine environments. In the generally high predation environment of freshwaters, acceleration of naupliar development potentially reduces the vulnerability of these smaller stages to size-selective tactile predation, while larger copepodid instars are able to reduce the opposing size-selective influences of visual planktivores by virtue of their escape responses to suction attack. Within the spectrum of copepod life histories and development schedules, ecologically consistent trends of this nature await formal recognition. The present recognition of IGE is a modest initiative in this quest. Both naupliar and copepodid durations are inverse monotonic functions of temperature. Several mathematical expressions which account for this temperature-duration response are provided. The response envelope is much tighter for naupliar than copepodid durations. Predictability of temperature-duration responses accordingly declines ontogenetically from egg to naupliar to copepodid stages.     

A new species of Ochridacyclops (Kiefer, 1937) (Copepoda, Cyclopoida) from Japan

A new species of cyclopoid copepod, Ochridacyclops nipponensis is described from Japan. This is the third species of the genus. The type material was collected from small streams in the mountainous regions in Shikoku. The new species can easily be distinguished from other members of genus by its 12-segmented antennule, by the proportional length of genital double-somite relative to the length of 3 free abdominal somites, and by the shape of caudal rami. The male is unknown.     

The distribution and abundance of Lernaeocera lusci (Copepoda) on hake (Merluccius merluccius) and bid (Trisopterus luscus) (Teleostei)

Distribution patterns, mean intensity and prevalence of Lernaeocera lusci (Copepoda, Pennellidae) in its 2 hosts Trisopterus luscus (Teleostei, Gadidae) and Merluccius merluccius (Teleostei, Merlucciidae) were examined, together with parasitic abundance and aggregation in relation to the size of the host. The mean parasite abundance and the variance to mean abundance ratio increased with host size, suggesting that the accumulation of this parasite had no noticeable impact on the structure of either host population. Merluccius merluccius being a newly colonized host in the Mediterranean, these results are discussed in relation to current ideas on the evolution of pathogenicity in heterospecific associations.     

Copepods of the genus Halicyclops (Cyclopidae) from Belize

Halicyclops tetracanthus sp.n. and H. venezuelaensis Lindberg were found in the Sittee River Estuary, Belize. The new species is distinguished from all its congeners by having a distal spine and two spiniform heterogeneously ornamented setae on the inner margin of the terminal endopodal segment of legs 2 and 3. Halicyclops venezuelaensis, previously known only from Venezuela is redescribed based on specimens of both sexes. Differences in the ornamentation as well as in the relative length of some setae of the maxilla and maxilliped are pointed out as additional useful characters in the taxonomy of Halicyclops. This is the first record of Halicyclops in Belize.     

Halicyclops korodiensis Onabamiro (Crustacea,Copepoda) in the estuary of the Warri River,Nigeria, West Africa

Halicyclops korodiensis Onabamiro was recorded in plankton samples of the brackish waters of the Warri River, Nigeria, West Africa. It is redescribed and figured.