Jeong Mi Hwang

Exposure of mayfly Ephemera orientalis (Ephemeroptera) eggs to heavy metals and discovery of biomarkers

The objective of this study was to assess acute toxicity of heavy metals in eggs of mayfly Ephemera orientalis McLachlan, and to elucidate relationships between heavy metal toxicity and protein expression patterns determined using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Acute toxicity analysis was conducted using five heavy metals (cadmium, chromium, copper, lead, and mercury), and the toxicity endpoint was established from the egg hatching rate during a 14-day exposure period. Median hatching toxicity (HC₅₀) values were determined for each heavy metal, and the most toxic heavy metal was found to be mercury (0.11 mg/L), followed by copper (0.32 mg/L) and lead (4.39 mg/L). E. orientalis eggs were highly tolerant to cadmium and chromium (>120 mg/L). Proteinchip array analysis using a strong anion exchange proteinchip (Q10) in conjunction with SELDI-TOF-MS was used to assess the protein expression patterns after exposure to heavy metals at the EHC10 (prohibiting hatching concentration to 10% eggs), except for cadmium and chromium, which were used at concentrations of 1, 10, and 100mg/L. Three novel biomarker candidate proteins, i.e., 4269, 4283, and 4623 m/z, were identified for the detection of heavy metal toxicity in aquatic ecosystems at the level of HC₁₀ in E. orientalis eggs. SELDI-TOF MS analysis for detecting differential expression of proteins was found to be more effective than Q10 proteinchip separation in the mayfly eggs.

Life history and secondary production of Ephemera orientalis (Ephemeroptera: Ephemeridae) from the Han River in Seoul, Korea

In this study, we investigated the life history of Ephemera orientalis, a common lowland burrowing mayfly which resides in temperate East Asia and often causes a serious nuisance to people due to mass emergence from the Han River in Seoul, Korea. Larvae were sampled monthly (every two weeks during the emergence period) from April 2006 to June 2007 using a Surber sampler (50 × 50 cm, mesh 0.25 mm, two replicates). The mean density of E. orientalis was found to be 105.88±42.14 indiv/m2 during the study period. On the basis of the larval body size distribution and emergence time, we concluded that E. orientalis has a univoltine life cycle with two distinct cohort groups, S1-group emerging in May–June and S2-group in August–September. The estimated annual production of the larvae was 1350.84 mg DW/m2; the mean biomass was 325.17 mg DW/m2; the annual production to mean biomass ratio (P/B) was 4.15. Mean water temperature during the study period was 15.02±6.84°C. The accumulated degree days for the S1- and S2-groups were 2565.07 and 2,621.69 degree days, respectively. This study shows that the Han River population of E. orientalis lacks the fast growing cohort (F-group) in May–August, and demonstrates a relatively higher secondary production than that of other stream mayflies (e.g. Gapyeong stream population of E. orientalis).

Molecular phylogeny evidence of altitudinal distribution and habitat adaptation in Korean Ephemera species (Ephemeroptera: Ephemeridae)

Molecular phylogeny of the four Korean Ephemera species, Ephemera orientalis, E. sachalinensis, E. strigata, and E. separigata, was inferred from 630 bp sequences of the partial mitochondrial cytochrome c oxidase I (COI) gene. Results indicated that mean intraspecific sequence divergences were 0.70%, whereas mean interspecific divergences were 15.75%, and 17 samples were distinguished to four species correctly by COI sequences. The results also demonstrated that four species of Korean Ephemera assembled a monophyletic group with high support in maximum parsimony and maximum likelihood analyses. This Ephemera group was divided into two major clades of E. orientalis–E. sachalinensis and E. strigata–E. separigata. Furthermore, we demonstrated that this phylogeny explained altitudinal and habitat adaptations of Korean Ephemera species. The E. orientalis–E. sachalinensis clade, a widespread and lowland‐adapted mayfly group, retained plesiomorphic traits such as paired stripes on abdominal segments and was regarded as plesiotypic in terms of habitat adaptation, compared to the geographically more limited and upland‐adapted E. strigata–E. separigata clade.

Four-year successive rearing of Glyptotendipes tokunagai Sasa (Diptera: Chironomidae) under laboratory condition

The dipteran Chironomidae have been commonly used as water quality indicators and toxicity test organisms. Two chironomids, Chironomus riparius Meigan and C. tentans Fabricius, are standard test organisms for toxicity (OECD), but their distribution is limited in Korea. The purpose of this study was to establish a Korean native chironomid species as a toxicity test organism. Glyptotendipes tokunagai Sasa, distributed widely in Korean streams, was selected and reared successively under laboratory conditions for over 30 generations over 4 years.

Long‐term monitoring of the life history of a riverine mayfly Ephemera orientalis (Ephemeroptera: Ephemeridae) in the Han River in Seoul, Korea

Climatic change often affects life history aspects of aquatic insects. Long‐term monitoring was conducted to understand the life history variability of the riverine mayfly Ephemera orientalis in the Han river, where habitat is largely disturbed by summer floods. Water level of the study site, Godeok‐dong area in Seoul, is regulated by the Paldang Dam located approximately 14 km above the study site. E. orientalis often emerged in large numbers around the study area. Larvae were sampled monthly from April 2006 to July 2010 using a Surber sampler (50 × 50 cm, mesh 0.25 mm, two replicates). Additional qualitative sampling was conducted using a hand net. As a result, based on the larval body size distribution, E. orientalis had a univoltine life cycle with two distinct slow growing cohort groups: the S1group emerged during May–June and the S2 group emerged during August–September. Our previous study conducted in Gapyeong stream in Gyeonggi‐do showed that E. orientalis normally had three cohort groups, S‐1 and S‐2 groups and the F‐group (a fast growing cohort developed during May–August). However, the Han River population of E. orientalis lacked such a fast growing cohort. It is most probable that habitat disturbances caused by high water level during the rainy season negatively affected the development of the fast growing cohort (F‐group) in the Han River area. The relationships between monthly E. orientalis population data and water level in the Han River are presented.