The effects of food level on the life history variables of the two closely related rotifer species Keratella tropica and Keratella valga

Abstract

Keratella tropica and Keratella valga are very similar in external morphology. K. tropica is a warm water species, and occurs in tropical and subtropical regions. K. valga is a eurythermal and widespread species. In subtropical shallow lakes, K. tropica has a higher density than K. valga. In the present study, K. tropica and K. valga were collected, respectively, from Lake Tingtang and Lake Jinghu in Wuhu city, Anhui, China, and their life history variables were compared at four levels (0.5×106, 1.0×106, 2.0×106 and 4.0×106 cells.mL-1) of Scenedesmus obliquus at 20°C. The results showed that both rotifer species had the same response to increasing food levels as regards duration of reproductive and post-reproductive periods, average lifespan, life expectancy at hatching, generation time, net reproductive rate and intrinsic rate of population increase, but differed in their duration of pre-reproductive period. The duration of pre-reproductive period of the rotifers was significantly affected by food level, species and their interaction (P<0.01), the duration of reproductive period was affected by species and the interaction between food level and species (P<0.05), and the average lifespan, the life expectancy at hatching, the generation time and the net reproductive rate were all significantly affected by species (P<0.01). Regardless of the effect of food level, the duration of pre-reproductive and reproductive periods, the average lifespan, the life expectancy at hatching, the generation time and the net reproductive rate of K. tropica were longer or higher than those of K. valga. The higher density of K. tropica in subtropical lakes might be attributed to its longer lifespan and higher reproductive rate.