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High fish predation pressure can trigger "induced defense" in Daphnia species, resulting in phenotypic plasticity in morphology, behavior, or life-history traits. The molecular mechanisms of defense morphogenesis (e.g. the tail spine and helmet) in Daphnia remain unclear. In the present study, the tail spine, helmet, and body of Daphnia galeata under fish and non-fish kairomones conditions were collected for transcriptome analysis. A total of 24 candidate genes related to the morphological defense of D. galeata were identified, including 2 trypsin, one cuticle protein, 1 C1qDC protein, and 2 ferritin genes. The function of the Dagcut gene (D. galeata cuticle protein gene) in relation to tail spine morphology was assessed using RNA interference (RNAi). Compared with the EGFP (Enhanced green fluorescent protein) treatment, after RNAi, the expression levels of the Dagcut gene (D. galeata cuticle protein gene) showed a significant decrease. Correspondingly, the tail spines of the offspring produced by D. galeata after RNAi of the Dagcut gene appeared curved during the experiment. In whole-mount in situ hybridization, a clear signal site was detected on the tail spine of D. galeata before RNAi which disappeared after RNAi. Our results suggest that the Dagcut gene may play an important role in tail spine formation of D. galeata , and will provide a theoretical basis for studying the molecular mechanisms of the morphological plasticity in cladocera in the future. [ABSTRACT FROM AUTHOR]

We investigated the effects of colonialMicrocystis aeruginosaand interspecific competition on the population dynamics and resting egg formation of two cladocerans. In the single-species culture experiments, highM. aeruginosaconcentrations favored the population growth ofMoina irrasabut strongly inhibited that ofDaphnia carinata. Small-bodiedM. irrasawas predominant over large-bodiedD. carinataregardless of the presence of the colonialM. aeruginosain the mixed cultures. The per capita cumulative number of ephippia and the percentage of ephippia containingD. carinataresting eggs both increased from under 0 to 10 mg/LM. aeruginosain the single-species culture but decreased in the mixed culture. However, the per capita cumulative ephippia number ofM. irrasain the mixed culture was higher than those in the single-species culture at the highM. aeruginosalevels. The effects ofM. aeruginosa, interspecific competition, and their combination on the per capita cumulative ephippia numbers of the two cladocerans were significant. The occurrence of ephippia was related to the higher population density of the two species. Our results suggest that interspecific competition inhibits the ephippium production and resting egg formation of the large-bodied cladocerans (D. carinata) in the presence of colonialM. aeruginosa. [ABSTRACT FROM AUTHOR]

A laboratory experiment was conducted to study the effects of different population density (D1: 100 ind·L-1, D2: 150 ind·L-1, D3: 300 ind·L-1) and culture volume (V1: 50 mL, V2: 100 mL, V3: 400 mL) on the growth and reproduction of Moina irrasa at 25 °C. At the same culture density, the body length of the M. irrasa females at their first pregnancy, the first brood, and the total offsprings per female decreased with the increase of culture volumes, while the sex ratio (male/female) of the offsprings was in adverse. At the same culture volumes, the total offsprings per female decreased with the increase of culture density. At D1V1, the body length of the females at their first pregnancy (0.95±0.10 mm) and the total offsprings (171.3±19.8 ind) per female were the maximum. At D3V2, the sex ratio was the maximum (0.54±0.05). Culture density, culture volume, and their interactions significantly affected the total offsprings per female and the sex ratio (P<0.001). [ABSTRACT FROM AUTHOR]

This paper studied the population dynamics and sexual reproduction of Moina irrasa at different water temperature and edible algal density. The population density of M. irrasa was obviously higher at high than at medium and low densities of edible algae, with the maximum at high edible algal density and 20 °C. At the same temperatures, the average number of the offsprings first produced by per female M. irrasa declined with decreasing edible algal density, and the maximum value appeared at 25 °C and at high edible algal density. The male offsprings produced were obviously higher at high than at medium and low edible algal densities. There was a significant correlation between the male density and the population density of M. irrasa. The number of ephippia produced by M. irrasa declined with decreasing edible algal density, and was higher at 25 °C than at other temperatures. Edible algal density had larger effects on the population dynamics and sexual reproduction of M. irrasa, as compared with temperature. [ABSTRACT FROM AUTHOR]

A laboratory experiment was conducted to study the effects of different population density (D1 : 100 ind x L(-1), D2 : 150 ind x L(-1), D3 : 300 ind x L(-1)) and culture volume (V1: 50 mL, V2 : 100 mL, V3 : 400 mL) on the growth and reproduction of Moina irrasa at 25 degrees C. At the same culture density, the body length of the M. irrasa females at their first pregnancy, the first brood, and the total offsprings per female decreased with the increase of culture volumes, while the sex ratio (male/female) of the offsprings was in adverse. At the same culture volumes, the total offsprings per female decreased with the increase of culture density. At D1 V1, the body length of the females at their first pregnancy (0.95 +/- 0.10 mm) and the total offsprings (171.3 +/- 19.8 ind) per female were the maximum. At D3V2, the sex ratio was the maximum (0.54 +/- 0.05). Culture density, culture volume, and their interactions significantly affected the total offsprings per female and the sex ratio (P < 0.001).

This paper studied the population dynamics and sexual reproduction of Moina irrasa at different water temperature and edible algal density. The population density of M. irrasa was obviously higher at high than at medium and low densities of edible algae, with the maximum at high edible algal density and 20 degrees C. At the same temperatures, the average number of the offsprings first produced by per female M. irrasa declined with decreasing edible algal density, and the maximum value appeared at 25 degrees C and at high edible algal density. The male offsprings produced were obviously higher at high than at medium and low edible algal densities. There was a significant correlation between the male density and the population density of M. irrasa. The number of ephippia produced by M. irrasa declined with decreasing edible algal density, and was higher at 25 degrees C than at other temperatures. Edible algal density had larger effects on the population dynamics and sexual reproduction of M. irrasa, as compared with temperature.