Study of the in vitro development of the parthenogenetic egg of daphnia carinata king (Cladocera: Daphnidae)

The embryonic development of Daphnia carinata King was studied under laboratory conditions. Detailed observations were made at frequent intervals and conspicuous morphological changes were recorded. The results were compared with those of other allied tropical and temperate forms. While the basic pattern of development is similar to that of other daphnids, the duration of the total period of development as well as of the individual stages in this species differed from those of other tropical and temperate forms.     

Divergent life history traits in two closely related species of Simocephalus (Cladocera: Daphnidae) inhabiting lentic environments in Venezuela

We describe life history tactics under laboratory conditions of two species of cladocerans of the genus Simocephalus. The populations live in two habitats with different characteristics. S. acutirostratus was isolated from a small temporary pool without fish. S. latirostris was found in the marginal vegetation of a reservoir with fish. Their life history was monitored for differences in traits such as clutch size, neonate size, age distribution, reproductive effort and adult survival. Our results show that S. acutirostratus (the larger-sized species) grows until it reaches the optimal foraging size and then begins to reproduce, while S. latirostris (the smaller-sized species) starts breeding before reaching the optimal foraging size, allocating energy mainly to reproduction. We explore the possibility that divergences in life history may arise as a response to environmental stress such as that produced by fishes.     

Naturally occurring interspecific hybridization inSimocephalus (Cladocera,Daphniidae): its potential significance

Among the Cladocera, the occurrence of interspecific hybrids in nature has been reported frequently but rarely adequately documented. During the course of a survey of the genetic variation and population structure of several species ofSimocephalus in ponds in southern Ontario, Canada, readily distinguishable congeners often co-occurred in a pond. Occasionally, clones were recovered that were intermediate in phenotype (as determined from both morphological and electrophoretic analyses) between two species. Two different hybrid clones have been examined in detail to determine the parentals involved in the crosses. Evidence from field and laboratory studies is presented to document the hybrid nature of these clones. Factors favouring formation and long-term survival of hybrids in littoral zone and pelagic species are discussed.     

The biology of Simocephalus acutirostratus King (Cladocera: Daphnidae)-laboratory studies of life span, instar duration, egg production, growth and stages in embryonic development

The life cycle of the cladoceran Simocephalus acutirostratus has been studied in the laboratory with reference to its total life span, duration of instars, egg production and growth. It has four pre-adult and eighteen adult instars and produces about 248 eggs during a mean life span of 44 days within a temperature range of 28°C-30°C. Egg production was found to be bimodal, with a sharp decline towards the end of the life cycle. The present results are compared and discussed with those of other tropical and temperate daphnids. It has been shown that while this species resembles most other daphnids (D. middendorffiana, D. pulex, D. carinata) in the growth pattern of pre-adult instars, it resembles the temperate D. pulex in having a relatively long life span, relatively high egg production and slow rate of growth. While studies on embryonic development of S. acutirostratus resemble the growth stages of the temperate Daphnia magna, there are differences in the total period of development between the two species. In the latter aspect, however, the present species closely resembles other tropical daphnids.     

A comparison of populations from the Daphnia similis group (Cladocera: Daphniidae)

European populations of Daphnia similis Claus have been compared with populations from tropical Asia. Daphnia similoides n. sp. from tropical Asia was described as the sibling species of D. similis. The female has characteristic neonate, postabdomen, head, and ephippium. The male has characteristic rostrum, antennules, and the distalmost part of the postabdomen. The D. similis group was compared with D. carinata s. str. Australian populations.     

Genetic variation in Simocephalus (Anomopoda: Daphniidae) in North America: patterns and consequences

The presumption of intercontinental distributions of many species of Anomopoda has been reinforced by their considerable morphological uniformity and ease of passive dispersal via ephippial eggs. To test the validity of this dogma, genetic variation among taxa in the cladoceran genus Simocephalus was examined on a continental scale. Genetic variability (percentage polymorphic loci = 8.8%, individual heterozygosity = 3.4%) was comparable to that determined on a local scale in Simocephalus and somewhat less than for other zooplankton groups. Four species complexes were distinguished allozymically with unique allelic substitutions found for at least two loci between these taxa. Eight species in North America were differentiated within these complexes (Nei s genetic distance, D>0.30), all of which were clearly separated from two European species. Both S. cf. vetulus and S. cf. serrulatus are broadly distributed in North America, and intraspecific divergence is relatively low. In contrast, S. cf. congener and S. cf. exspinosus represent species complexes, both consisting of several species, differentiated allozymically and morphologically. The concept of generalist species with moderate genetic variation throughout a broad range and specialist species, genetically depauperate, with restricted distributions, is explored.     

The reproductive biology of the genusBaldellia (Alismataceae)

The reproductive biology of the genusBaldellia was studied under cultivation and in nature.B. ranunculoides subsp.repens is self-incompatible whereasB. ranunculoides subsp.ranunculoides andB. alpestris are self-compatible. Bud-pollination occurs in theB. alpestris. Self-incompatibility correlates with the production of fewer, larger, more showy flowers, higher pollen production (but reduced pollen grain size), fewer carpels and smaller seeds. Resource allocation to sexual reproduction is inversely correlated with the degree of vegetative growth.B. ranunculoides subsp.repens produces more ramets than subsp.ranunculoides, which reproduces mainly by seeds.B. alpestris is intermediate between the two since it is self-compatible, produces fewer, larger seed than subsp.ranunculoides and is also able to propagate by vegetative means.     

The life history parameters of Diaphanosoma excisum (Cladocera), grown in different culturing media

Life history parameters of Diaphanosoma excisum (SARS) were derived from culture tube experiments with media comprising mohua oil cake, mustard oil cake, cow dung and rice bran. Body length, longevity, fecundity and progeny production were highest in rice bran medium. First reproduction time (A) in different media ranged from 2 to 6 days, while the reproduction peak (T) varied from 4 to 13 days. The total offspring per female (S) was directly dependent upon the mean number of eggs per female per life span. The intrinsic (r) and finite rate (e^r) of natural increase were larger for rice bran than for other media.     

The pollination biology ofHibbertia stricta (Dilleniaceae)

The exines of pollen grains ofHibbertia stricta (DC.)R. Br. exF. Muell. (Sect.Pleurandra) wear an oily, yellow pollen coat that stains positively for lipids. The pollen is collected by asocial bees, exclusively. The most common floral foragers are members of the genusLasioglossum (subgenusChilalictus;Halictidae) and they harvest pollen via thoracic vibration. As these bees cling to the inflated anthers their pollen smeared bodies come in contact with either of the two wet, nonpapillate stigmas. The stigmas respond positively to cytochemical tests for the presence of esterase immediately following expansion of the corolla, indicating the effective pollination period. The foraging patterns of the bees are narrowly to broadly polylectic. AsH. stricta flowers are nectarless, it is not surprising that bees bearing mixed pollen loads always carry the pollen of at least one nectariferous, coblooming plant. The pollination biology ofH. stricta is compared with otherHibbertia spp. and with pollen flowers in general.     

On the taxonomy and geographical distribution of the superfamily Sidoidea Baird, 1850 (Crustacea: Cladocera)

A systematic revision of the superfamily Sidoidea Baird, 1850 is carried out based on a considerable amount of material, including types. Unification of the families Sididae and Holopedidae in one group is found to be justified. Two new tribes of the recently isolated subfamily Sidinae Baird, 1850 are described. In considering the systematics of taxa at a species level, special attention is given to the genus Diaphanosoma. Its taxonomy is far from satisfactory but most species may be included in two morphoecological groups. The distribution of some genera and species is analyzed and their regions of origin and ranges are discussed.     

Centrosome inheritance in the parthenogenetic egg of the collembolan Folsomia candida

Unfertilized eggs commonly lack centrioles, which are usually provided by the male gamete at fertilization, and are unable to assemble functional reproducing centrosomes. However, some insect species lay eggs that develop to adulthood without a contribution from sperm. We report that the oocyte of the parthenogenetic collembolan Folsomia candida is able to self-assemble microtubule-based asters in the absence of pre-existing maternal centrosomes. The asters, which develop near the innermost pole of the meiotic apparatus, interact with the female chromatin to form the first mitotic spindle. The appearance of microtubule-based asters in the cytoplasm of the activated Folsomia oocyte might represent a conserved mechanism for centrosome formation during insect parthenogenesis. We also report that the architecture of the female meiotic apparatus and the structure of the mitotic spindles during the early embryonic divisions are unusual in comparison with that of insects.This work was made possible by grants from PAR (University of Siena) and PRIN to G.C.     

Cladocera (Crustacea) from Nicaragua

Thirty-one Cladocera taxa are recorded from lakes, rivers and ponds of Western Nicaragua. They include Alona bromelicola sp. nov. found in water accumulations in epiphytic Bromeliads. The Cladocera recorded are neotropical and circumtropical. Other invertebrates found are also listed.     

Daphnia (Ctenodaphnia) hispanica sp. nov., a new daphnid (Cladocera) from Spain

Daphnia (C.) hispanica n. sp. has thoracic limbs of A D. (C.) atkinsoni type and is very similar toD. chevreuxi Richard, 1896. With this speciesD. (C.) hispanica shares the presence of a soft accessory seta on the outer side of the trunk of the first thoracic limb, apparently unique among the genusDaphnia. Although other morphological characteristics are very similar in this two species, a detailed comparison reveals that they can easily be separated as different species. The most useful features in differentiating both species are:D. (C.) hispanica has a dorsal crest in the head, its rostrum is longer, its accesory seta of the first thoracic limb is more developed, the juveniles are not helmeted and its male postabdomen lacks individual denticles on the anal and preanal margin.The new species is, up to now, restricted to Spain and inhabits the temporary and low mineralized waters of the steppe regions.     

Effect of previous feeding conditions on survival in Daphnia pulicaria (Crustacea: Cladocera)

Survival of natural Daphnia populations without previous acclimatization in filtered water under laboratory conditions (starvation) was used as a parameter describing the actual competitive ability of populations in periods of food limitation. Two populations (1 and 2) of Daphnia pulicaria Forbes coming from two enclosures with a low (< 1 mgC l^–1) and a high (about 3 mgC l^–1) seston level were examined in their resistance to starvation. Juveniles of both populations survived better than adult females in the conditions without seston as well as in the control experiment, despite their much lower biomass. Animals from population 1 had lower mortality than those from population 2 in all variants of the experiment. The results confirm the hypothesis that the ability of daphnids to starve depends also on adaptation to previous feeding conditions.     

Lifetime egg production and egg mortality in the damselflyPyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae)

Artificial oviposition sites were used to estimate egg deposition rates in the field. Females laid an average of 10.76 eggs/minute with a mean duration of 22.81 minutes, giving an average clutch size of 245 eggs. Since one mating corresponded to one clutch of eggs, lifetime mating success was used as a measure of the number of clutches produced. Mean lifetime clutch production was 5.91 clutches per female, equating to 1447 eggs per female per lifetime. Eggs were hatched in the laboratory at temperatures comparable with those in the field. Hatching was highly synchronised and the overall hatching success was 75.1%. Causes of egg mortality in the laboratory were limited to infertility and unhatchability. Since no other sources of egg mortality could be found at the study site, this value was a good reflection of hatching success in the field. Lifetime egg production and hatching success were used to estimate the number of viable offspring produced per female, giving a higher order estimate of reproductive success than has previously been published for a zygopteran.     

Fecundity and egg fertility in the adult Colorado beetle (Leptinotarsa decemlineata) surviving larval infection by the fungus Beauveria bassiana

Secondary effects of the entomopathogenic hyphomycete Beauveria bassiana (Bals.) Vuill. were investigated on adults of Leptinotarsa decemlineata Say (Coleoptera:Chrysomelidae) treated as newly moulted 4th-instar larvae. Fecundity and egg hatching were monitored in surviving females mated with surviving males. When reared at 22°C, adult survivors showed a lessening of their reproductive potential during their whole life. According to the fungal inoculum dosage, the reductions of the total number of eggs laid per female and the mean number of eggs per egg mass ranged from 20% to 56% and from 18% to 46%, respectively. In contrast, at 25°C, the fecundity of survivors was not affected by the fungal infection. This variability of the secondary effects of B. bassiana according to temperature conditions might be related to the lower infection level of treated larvae at 25°C. Moreover, at both temperatures, eggs laid by females surviving fungal infection as larvae were as fertile as eggs laid by control insects. It is concluded that secondary effects of B. bassiana on the fecundity of the Colorado Potato Beetle are temperature-dependent and that they could become negligible at high temperatures under field conditions.

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Résumé Les effets secondaires de l'hyphomycète entomopathogène, Beauveria bassiana (Bals.) Vuill. sur la fécondité et la fertilité des insectes survivant à l'infection fongique ont été étudiés chez les adultes du doryphore Leptinotarsa decemlineata Say (Coleoptera:Chrysomelidae) issus de larves contaminées en début de 4ème stade. Les insectes maintenus à 22°C ont présenté une réduction de leur potentiel reproductif. Ainsi, suivant la dose d'inoculum fongique, le nombre total d'oeufs pondus par femelle et le nombre moyen d'oeufs par opplaque ont baissé de 20% à 56% et de 18% à 46%, respectivement. En revanche, à 25°C la fécondité des adultes survivants n'a pas été affectée par la maladie. Cette variabilité en fonction des conditions thermiques peut être liée à la diminution de l'effet-dose du champignon sur les larves à 25°C par rapport à 22°C. Par ailleurs, quelles que soient les conditions thermiques (22°C ou 25°C) on ne constate aucun changement significatif de la fertilité des oeufs pondus par les femelles survivantes. Les auteurs concluent que les effets secondaires de B. bassiana sur la fécondité du doryphore dépendent des conditions thermiques et qu'ils pourraient devenir négligeables à des températures élevées en plein champ.

     

The systematics of Australian Daphnia (Cladocera: Daphniidae). Multivariate morphometrics

Forty nine characters were measured in each of 76 male and 200 female Daphnia including specimens from all eleven taxa described from the genus in Australia, except D. jollyi. Separate multivariate analyses (cluster, principal components and discriminant) of males and females each revealed only five morphological groups in the genus corresponding to the species D. occidentalis, D. lumholtzi, D. cephalata, D. nivalis, and a conglomerate of all other taxa described from the D. carinata complex, D. carinata (sensu lato). Interpretation of the male results was straightforward, but that for females was not because of the occurrence of an environmentally induced seasonal change in morphology (cyclomorphosis) in females. Log transformations of the female data successfully isolated the effects of cyclomorphosis. The seasonal morphs formed two groups which were further differentiated into taxonomic groups.