Lynda Beladjal

Diaspore Dispersal of Anostraca by Flying Insects

Abstract Fairy shrimps (Anostraca) live in temporary waters. Dominant among their predators are aquatic insects, especially diving beetles (Dytiscidae). Mastication of the eggs of the fairy shrimp Branchipus schaefferi and their passage through the digestive tract of smaller beetles, like Ilybius fenestratus, has a positive effect on hatching afterwards. Dytiscidae could be important vectors for aerial dispersal of diaspores among ponds which are not directly connected to a stream channel. Such long-distance dispersal can be of critical importance for population survival and gene flow among communities living in temporary habitats.

EGG SAC STRUCTURE OF ZYGIELLA X-NOTATA (ARACHNIDA, ARANEIDAE)

Abstract A detailed examination of the egg sac of Zygiella x-notata (Clerck 1757) revealed its structure, composition and different fibers. All egg sacs were composed of a basic layer, an insulation layer and an outer layer. The insulation layer consisted of two layers of cylindrical (or tubuliform) fibers with different diameters and probably with different mechanical properties. Knowing the complete structure of the egg sac allows us to locate and extract the needed fibers for further research and to observe how the egg sac composition alters in relation to the habitat.

AN ANALYSIS OF THE SETATION PATTERN OF THE LIMBS IN ANOSTRACA (CRUSTACEA) - USING THE ALGERIAN SPECIES AS AN EXAMPLE

The implantation, number, and structure of the setae on the endopodites and exopodites of the limbs, and the setulation of the setae of endite I of all Anostracan species found in Algeria are analysed by light and scanning electron microscopy and graphically represented. The data disclose significant variation among the genera Artemia, Branchinella, Branchipus, Chirocephalus, Streptocephalus and Tanymastigites, and between the related congeners Streptocephalus torvicornis and S. rubricaudatus.

B-chromosomes and male-biased sex ratio with paternal inheritance in the fairy shrimp Branchipus schaefferi (Crustacea, Anostraca)

This study reports on male-biased sex ratios in west Mediterranean populations of the freshwater anostracan Branchipus schaefferi (Crustacea, Anostraca, Branchipodidae), in contrast to populations elsewhere. Crossing experiments over several generations indicate a clear paternal inheritance of the trait, possibly with a dosage effect. Various mechanisms which may underlie this phenomenon are discussed, the most plausible being the presence of one or more supernumerary (‘B’) chromosomes – as evidenced by karyological observations – interfering with sex determination and probably having an accumulation mechanism in male individuals.

Pheromones inhibit the hatching of diapausing Anostraca (Crustacea: Branchiopoda)

Hatching of resting eggs of Streptocephalus torvicornis (Waga, 1942) and Branchipus schaefferi Fischer, 1834, two sympatric fairy shrimps, was tested using medium in which these two species and Chirocephalus diaphanus (Prevost, 1803) had been raised. The medium of adults inhibited the hatching of conspecific nauplii, even when diluted by 50% using distilled water. Streptocephalus torvicornis resting eggs hatch in the medium of C. diaphanus but not in the medium of B. schaefferi. Resting eggs of B. schaefferi hatched in low numbers in S. torvicornis medium, and in high numbers in that of C. diaphanus.There appears to be one or more substances associated with the presence of adults of conspecifics and sympatrics which exceed the influences of abiotic factors, such as light, pH, conductivity and osmotic pressure in fresh media. We propose that this substance(s) functions as a pheromone to inhibit further hatching once a population of adults is present.

Feeding strategy of two sympatric anostracan species (Crustacea)

The transport rate of chalk, clay particles and algal cells (Scenedesmus sp.) through the digestive tract of Streptocephalus torvicornis and Branchipus schaefferi is described under experimental conditions. Differences in transport rate as well as in the degree of digestion at a fixed particle density of algae were found. In S. torvicornis, the transport rate is higher and the digestion of algae lower than in B. schaefferi. These differences might reflect trophic differences related to niche partitioning in these sympatric species.

DISPERSAL OF FAIRY SHRIMP CHIROCEPHALUS DIAPHANUS (BRANCHIOPODA: ANOSTRACA) BY THE TROUT (SALMO TRUTTA)

Abstract The presence of small trout together with fairy shrimp (Chirocephalus diaphanus) in isolated corrie lakelets in the French Pyrenees suggests that the fish might be agents of dispersal of the shrimp, if resting eggs could survive ingestion and freezing. Resting eggs in ovigerous females of Chirocephalus diaphanus can pass through the digestive tract of a trout and be subsequently frozen without losing their viability. Subsequently fecal pellets were collected from each fish. The gut passage time of C. diaphanus eggs were up to 4 days. Resting eggs recovered from fecal pellets were counted, frozen and then incubated. Hatching of nauplii began after 32 days, and 50.9% (sd. 29.4) hatched over the following 7 days. Ovigerous females of lab cultured C. diaphanus were administered to four trout Salmon trutta kept in separate tanks. Therefore, fish can aid upstream dispersion of these fairy shrimp.

Chirocephalus ponticus n.sp. (Crustacea: Anostraca) and its affinities to the other Turkish species of the genus

Chirocephalus ponticus n.sp. (Crustacea: Anostraca) from Turkey is described. The new species is characterized by the form of the second antenna and the frontal appendages of the male. This species seems to be related to C. turkestanicus Daday. Furthermore, analysis of limb structure reveals differences between the three Chirocephalus species previously known from Turkey: C. paphlagonicus, C. vornatscheriand C. diaphanus. New localities for these species are reported.

Life cycle and genetic differences of two Branchipus schaefferi populations from Morocco (Anostraca: Crustacea)

The somatic growth, longevity, and reproduction of two Moroccan anostracan populations from different climatic areas were studied under standardized laboratory conditions. Both populations were subjected to allozyme analyses covering four loci, and molecular analyses of the variable regions, the Internal Transcribed Spacers (ITS1 & ITS2) intervening the nuclear ribosomal genes (18S, 5.8S, 28S rDNA). The ecological characteristics of the life cycle of each population are presented, together with their genetic differences and phylogenetic relationships.

Effect of salinity stress on the life history variables of Branchipus schaefferi Fisher, 1834 (Crustacea: Anostraca)

BackgroundFreshwater anostracans inhabit ephemeral water bodies in which as the water level decreases due to evaporation the salt concentration increases. Thus, for most anostracans salinity becomes the major stress factor.ResultsWe tested five concentrations of NaCl (0 to 8 g/l) on the life table demography of Branchipus schaefferi fed Chlorella (alga). Age-specific survivorship curves of male and female B. schaefferi showed nearly a similar pattern in that increased salt concentration resulted in decreased survivorship. The age-specific reproduction (mx) of females showed several peaks of cyst production at 0 and 1 g/l salinity while in treatments containing salt at 4 or 8 g/l, there were fewer peaks. Average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase were all significantly influenced by the salt concentration in the medium. The highest value of net reproductive rate (970 cysts/female) was in treatments containing 0 g/l of salt, while the lowest was 13 cysts/female at 8 g/l. The rate of population increase (r) varied from 0.52 to 0.32 per day depending on the salt concentration in the medium.ConclusionThe low survival and offspring production of B. schaefferi at higher salinity levels suggests that this species is unlikely to colonize inland saline water bodies. Therefore, the temporary ponds in which it is found, proper conservative measures must be taken to protect this species.