Factors Affecting Egg-ratio in Planktonic Rotifers

Abstract

EdmondsonÕs egg ratio (number of amictic eggs per female) is an important life history variable, which has been in wide use to understand and predict patterns of population growth in planktonic rotifers under field conditions. It is also useful as an indicator of the health of rotifers under culture conditions. Generally, an inverse relationship exists between the egg ratio and the density of females in a population. A number of abiotic and biotic factors influence the egg ratio. For example, temperature can cause marked changes in the egg ratio by influencing the frequency of egg production and the hatching times of parthenogenetic eggs. Also, preferential feeding on ovigerous females of rotifers by invertebrate predators such as Asplanchna will lower the egg ratios of the population. The easy detachment of eggs, as may be the case in some members of the Brachionidae especially during enhanced reproduction when food levels are high, may also cause an underestimation of the egg ratio. In this review, we discuss the egg ratio of selected rotifer species in relation to the role of diel changes in egg production, the frequency or the intensity of feeding, the problems of distinguishing between different egg types and the negative effect of stressors such as toxicants and diet quality.

The effect of medium on selected life-history traits in three clones of Lecane inermis (Rotifera) from activated sludge

“…When resources are not limited and population densities are low, planktonic rotifers produce 3 to 5 eggs per female per day. When food becomes limited, population growth reaches a stationary phase, and amictic egg production declines (Sarma et al 2005). Our research showed that the addition of molasses caused a significant increase in the number of live rotifers and the ER in both mineral water and filtrate, and it also resulted in a lower mortality rate.…”

“…In particular, recognising the factors affecting the growth rate of L. inermis is crucial before using the rotifers on an industrial scale. It has been shown that environmental conditions greatly influence rotifer growth both in nature and laboratory (Lubzens et al 2001;Sarma et al 2005). The rotifers that inhabit activated sludge are subject to extreme conditions, which exert strong selection pressure.…”

“…The ER measure (Edmondson 1960) can be used as an indicator for predicting changes in natural zooplankton populations. Despite some limitations reviewed by Sarma et al (2005), this measure is very useful in predicting natural population growth. It can also be used as a prediction criterion for production and culture quality in mass cultures of rotifers.…”

“…It can also be used as a prediction criterion for production and culture quality in mass cultures of rotifers. If food concentration, temperature and population density conditions are good, the ER can reach the value of 3.0 (Sarma et al 2005). When resources are not limited and population densities are low, planktonic rotifers produce 3 to 5 eggs per female per day.…”

“…According to Edmondson (1946), this is one of the most fecund rotifers, as its populations are usually dominated by amictic females (Miller 1931) that lay 13 to 24 eggs during their lifetime of approximately 9 days (Edmondson 1946). It has been shown that temperature and food availability are among the most important factors affecting rotifer reproduction (Edmondson 1946;Lubzens et al 2001;Sarma et al 2005). Lecane inermis inhabits different environments, feeding on various strains of unicellular bacteria and green algae as well as filamentous bacteria (Miller 1931;Fia"kowska & Pajdak-Stó s 2008).…”