仓鼠属三个种的核型分析

本文分析了仓鼠属三个种的常规核型及G带核型,即大搬仓鼠(Cricetulus triton)2n=28,长尾仓鼠(C.longicaudatus)2n=24,花背仓鼠(C.barabensis)2n=22。讨论时结合文献报道的短尾仓鼠(C.eversmanni),无斑短尾仓鼠(C.curtatus),灰仓鼠(C.migratorius)的有关核型资料作了比较,结果证明:(1)染色体是鉴别这6个种类的有效方法之一。(2)大搬仓鼠具有较原始的核型,可能是祖先进化中的一个早期分枝。(3)这6个种类的染色体进化机制主要是罗伯逊融合,但也有染色体的断裂、易位和倒转。     

Experimental evolution of evolutionary potential in fluctuating environments

Variation is the raw material for evolution. Evolutionary potential is determined by the amount of genetic variation, but evolution can also alter the visibility of genetic variation to natural selection. Fluctuating environments are suggested to maintain genetic variation but they can also affect environmental variance, and thus, the visibility of genetic variation to natural selection. However, experimental studies testing these ideas are relatively scarce. In order to determine differences in evolutionary potential we quantified variance attributable to population, genotype and environment for populations of the bacterium Serratia marcescens. These populations had been experimentally evolved in constant and two fluctuating environments. We found that strains that evolved in fluctuating environments exhibited larger environmental variation suggesting that adaptation to fluctuations has decreased the visibility of genetic variation to selection.     

Somatic polyploidy examined by flow cytometry in Daphnia

Flow cytometry was used to examine the patterns of somatic polyploidyand to determine the haploid genome sizes in Daphnia. The averageproportions of polyploid nuclei among adult animals of D.pulex,D.longispina, D.pulex x D.longispina and D.magna equalled 27,24, 24 and 24%, respectively. Both interclonal and developmentallyregulated variation were observed in the level of somatic polyploidy.Adult animals expressed more extensive polyploidy than did juveniles.The estimates of the haploid genome sizes (C values) of D.pulex,D.longispina, D.pulex x D.longispina and D.magna equalled 0.32,0.27, 0.26 and 0.37 pg, respectively. These are the smallestgenomes reported in crustaceans. Apparently, somatic polyploidycompensates for the loss of genetic material and gives riseto genetic plasticity which may contribute to the considerablelevel of phenotypic plasticity observed in Daphina.     

Specificity of predator-induced neck spine and alteration in life history traits in Daphnia pulex

It has been proposed that the predator-induced defensive neck spine in Daphnia pulex has a demographic cost. Our results show that this cost is not merely an allocation cost related to the formation and maintenance of the neck spine. In a life table experiment, we tested whether spine induction and life history traits in D. pulex are affected by different invertebrate predators: first and third instar Chaoborus, fourth instar Mochlonyx and two size classes of Notonecta and Dytiscus larvae. D. pulex showed sensitivity to the different predators. Predator-exposure affected one or more of the following life history traits of D. pulex: the timing of first reproduction, clutch size, and growth. In some cases, exposure to predators altered life history traits when neck spine induction did not occur. These shifts in life history traits occurring in the absence of spine induction may be caused by behavioral or physiological changes triggered by the predators.     

Demographic costs of Chaoborus-induced defences in Daphnia pulex: a sensitivity analysis

Summary We examined the demographic costs of Chaoborus-induced defensive spine structures in Daphnia pulex. Our aim was to assess the role of resource limitation and the interaction effects of limiting food level and antipredator structures on fitness of D. pulex and to pinpoint those life stages that are most sensitive to changes in the defence regime. Chaoborus-induced and typical morphotypes of D. pulex were reared at high and low food concentrations. Instar-based matrix population models were used to quantify the effects of predator-induction, food and their interaction on fitness of D. pulex. Predator-induction caused a statistically significant reduction in fitness at low food levels, but not at high food levels. Sensitivity analyses revealed that the fitness effects were primarily due to changes in the growth rate in instars 1–5, and secondarily to small reductions in the fertility of instars 5–10. The interaction between Chaoborus exposure and low food concentration was negative, and mediated through growth and fertility components. Both these components were reduced more in the Chaoborus-exposed, low food treatment than would be expected in the absence of interaction.