Genetic differentiation of Caridina cantonensis (Decapoda:Atyidae) in Hong Kong streams

Caridina cantonensis Yu 1938 is an atyid shrimp that is widespread in southern China, including Hong Kong. It is a fully freshwater species with an abbreviated larval development lacking planktonic stages. The population genetics of C. cantonensis in Hong Kong streams was studied at inter- and intradrainage scales using random amplified polymorphic DNA (RAPD) markers. Shrimps displayed low levels of within-population genetic variation (≤20% of total genotypic variance) but high levels of among-population variation (>50% of total genotypic variance) at both scales. High interdrainage genetic differentiation indicated that dispersal among catchments was limited, whereas high differentiation among populations at the intradrainage scale mainly resulted from natural barriers such as waterfalls. The effect of man-made barriers on population differentiation at the intradrainage scale was less marked than at the interdraineage scale. Levels of gene flow among populations within and among drainage systems were low, the estimated number of effective migrants/generation (Nem) was <0.1, and there was a trend toward relatively fewer alleles and lower heterozygosity in upstream populations than in downstream populations. Genetic differentiation between lowland populations from adjacent drainages was lower than for other pairwise combinations of populations, suggesting that interdrainage dispersal is likely during floods. The genetic structure of C. cantonensis populations in Hong Kong streams indicates that adaptation to local conditions in individual streams or sites within streams probably occurred. At a regional scale, this process might account for the large number of stenotopic species of Caridina in Asia. © 2005 by The North American Benthological Society.link_to_subscribed_fulltex

Stable isotope investigation of food use by Caridina spp. (Decapoda:Atyidae) in Hong Kong streams

Caridina spp. (Atyidae) are widespread and abundant omnivorous shrimps in tropical Asian streams. Spatial and seasonal variation in C and N stable isotope signatures of 2 species (Caridina cantonensis and C. serrata) and their potential food sources (leaf litter, fine particulate organic matter [FPOM], and periphyton) were investigated in 2 shaded and 2 unshaded Hong Kong streams. The objectives were to identify food sources used by shrimps and to determine whether food use changed according to riparian shading, season, developmental stage, and sex. Isotopic signatures of different species of leaf litter were similar to each other and distinct from FPOM signatures in all streams, whereas periphyton δ13C and δ15N signatures were similar to FPOM signatures. FPOM and periphyton showed seasonal variation in δ13C and δ15N signatures in all streams, but signatures of leaf litter showed relatively minor variation. δ13C signatures of FPOM were 7 to 12‰ (shaded streams) and 5 to 7‰ (unshaded streams) higher than those of leaf litter during the dry season, and 5 to 8‰ (shaded streams) and 4 to 7‰ (unshaded streams) higher during the wet than the dry season. δ15N signatures of FPOM were almost 2x those of leaf litter in all streams and seasons. Periphyton was generally ≤6‰ more 13C-enriched and ≤4‰ 15N-depleted than FPOM. Seasonal variation in δ13C signatures of shrimps and their food sources were consistent among streams, and were less 15N-depleted during the dry season. Dual-isotope multiple-source mixing models indicated that FPOM and periphyton were the main foods of adult (male and female) and juvenile C. cantonensis and C serrata. Leaf litter contributed 60% to the biomass of C. cantonensis in unshaded streams in the wet season, with the proportion slightly higher during the dry season. In shaded streams, periphyton contributed 35 to 60% to Caridina spp. biomass. Our results indicate that the Hong Kong atyids feed as omnivores, with herbivory as a primary feeding mode supplemented by collection of FPOM and limited direct consumption of allochthonous leaf litter. © 2005 by The North American Benthological Society.link_to_subscribed_fulltex