Inter- and intraspecific differences in the life history and growth of Caridina spp. (Decapoda: Atyidae) in Hong Kong streams

1. The life‐history pattern of three populations of Caridina cantonensis (Atyidae) and one population of Caridina serrata were studied in four Hong Kong streams: Pak Ngau Shek (PNS), Kap Man Hang (KMH), Pak Tam Chung (PTC), and Lung Fu Shan (LFS). Caridina cantonensis occurred at PNS, KMH and PTC while C. serrata was present at LFS only. Monthly quantitative sampling was carried out at each study site over 2 years to investigate life‐history patterns and cohort‐specific growth rates. 2. Breeding by both species was mainly restricted to the wet season, and there was an increase in the incidence of ovigerous females as water temperatures rose at the start of the summer monsoon. The number of cohorts and the frequency of recruitment of C. cantonensis (one to three times each year) were highly site‐specific, but consistent between years. 3. Shrimp growth was size‐dependent, and decreased with increasing body size. Caridina cantonensis at PTC had the highest cohort‐specific growth rates (0.05–0.14 mg ash‐free dry weight (AFDW) mg^?1 day^?1), followed by C. serrata at LFS (6% lower), and C. cantonensis at KMH and PNS (16–39% lower). Shrimp life spans exceeded 1 year (17–22 months), depending on site and species. 4. Sexual maturity occurred at an earlier age and at a smaller size in populations with higher growth rates. Shrimps at PTC and LFS matured at approximately 4 months old; this was 3 months earlier than at KMH and 5 months earlier than at PNS. Females of C. cantonensis at PTC and C. serrata at LFS may have bred twice during each breeding season, while females in the other two populations bred once only. The number of cohorts produced by each population in each year did not vary between the years of the study. Most sexually mature individuals only survived long enough (for 10–12 months after maturation) to breed during one season. 5. The mean brood size of C. cantonensis varied among streams and was 25–28% larger at PNS and KMH than at PTC. Egg size did not differ among populations. Larger brood sizes at PNS and KMH may have been a consequence of increased availability of algal food in these unshaded stream sites. Caridina serrata had similar egg and brood sizes to C. cantonensis, but females were smaller and reproductive investment was higher. Thus, the degree of intraspecific variation in atyid breeding in Hong Kong was at least equal to, if not greater than, the extent of interspecific variation. Interspecific differences in life history may reflect the frequency of droughts and spate intensity experienced by C. serrata at LFS.     

用改进的差别显示法克隆R6大鼠细胞的癌相关基因

为了识别参与细胞癌变的基因,本文选择p53135-val-过表达正常细胞系R6#13-8及其自发转化癌变细胞系T2作为研究材料,在克隆差异表达基因的同时,建立了一种简单、快速的差异表达基因分离的方法,并已克隆到2个与细胞癌变相关的候选新基因。本文所得的实验结果表明这种方法实验步骤简单,避免使用同位素,RT-PCR扩增带的重复性好,能克隆到大于500bp的差异表达cDNA片段,差异表达的PCRcDNA片段假阳性率低,并可广泛适用于在两个或两个以上相对应真核细胞RNA群体中分离和克隆特异表达基因。研究结果还提示在R6#13-8自发转化为T2的过程中涉及多个基因的激活与失活,这两个细胞系之间存在明显的基因表达差异。     

Callus Growth and Plantlet Regeneration in Taro, Colocasia esculenta var. esculenta (L) Schott (Araceae)

Explants of taro cultivars belonging to Colocasia esculentavar. esculenta have been nearly impossible to culture untilrecently. Here, we describe a method which induces callus formationfrom bud explants of Colocasia esculenta var. esculenta cv.Akalomamale, brings about shoot and root production, and leadsto plantlet regeneration. The medium used is half-strength Murashige-Skoog(HMS) solution containing 25 ml taro tuber extract (TE), 2 mg2, 4, 5-trichlorophenoxyacetic acid and 200 mg glutamine 1^–1.TE is an important requirement for bud explants and callus tissues.Root induction on callus-derived shoots (i.e. plantlet formation)occurs on HMS containing only 25 ml TE and 100 ml coconut water1^–1. Taro, Colocasia esculenta var. esculenta (L) Schott (Araceae), coconut water, micropropagation, plantlet regeneration, root formation, taro extract, tissue culture