Asexual diapause in the rotifer Synchaeta pectinata: Fitness costs and trade-offs associated with phenotypic variation in a natural population.

摘要

Ecological and evolutionary implications of polymorphism and polyphenism in the asexual diapause of the rotifer Synchaeta pectinata from Star Lake, VT, were explored via field, laboratory, and theoretical investigations. S. pectinata is a monogonont rotifer that inhabits temporally variable lakes. Under low food conditions it switches to production of asexual diapausing eggs.; A field investigation in Star Lake, VT, examined the occurrence of S. pectinata, its preferred food Cryptomonas spp., and the incidence of diapausing egg production. Substantial diapausing egg production was observed, with considerable clonal variation in both diapause propensity (strong and weak) and duration (short-term 2 week and long-term 3 month). Long-term eggs were the dominant type produced, and occurred in two pulses concurrent with low food. Data suggest that diapausing eggs produced early in the season hatched contributing to a population increase, and that low oxygen concentrations do not induce diapause.; Life-table experiments were conducted on 4 strong and 4 weak diapause propensity clones to determine the effect of diapause propensity on reproductive parameters. Strong propensity clones produced fewer offspring over their lifetime, leading to lower r{dollar}rmsb{lcub}max{rcub}{dollar} values relative to weak propensity clones. These data suggest a high direct cost associated with increased diapause propensity. Fitness trade-offs associated with opportunity costs of inappropriate allocation to diapause by clonal strategies in variable environments were examined via 2 experiments using a weak/strong diapause propensity clonal pair cultured together under 3 different food regime treatments. Control treatments tested for the direct cost of propensity. Experimental treatments tested for the costs of inappropriate reproductive allocation, and differed in the severity of food limitation. Results show that different strategies are favored by different environmental regimes and that substantial opportunity costs exist.; Analytic and numerical simulation models were developed to examine the evolution of polyphenism (bet-hedging and phenotypic plasticity) in temporally variable environments. Model results show that bet-hedging is favored in unpredictable environments while phenotypic plasticity is favored in predictable environments. A mixed strategy is favored in environments of intermediate predictability suggesting that some degree of error in phenotypic determination is adaptive.; Addition experimental work examined Daphnia's failure to vertically orient itself away from discrete layers of the toxic cyanobacterium, Anabaena.