Rapid adaptation of Brachionus angularis (Rotifera) to invasion by Brachionus calyciflorus

Abstract

To test the hypothesis that Brachionus angularis can rapidly develop local adaptation to invasion by other monogonont rotifers, replicate populations of B. angularis were exposed to two environments invaded by B. calyciflorus at different inoculation densities and an environment free from invaders. During the selection experiment, the density of each population was reduced to starting conditions every 3 days, and the changes in population growth rate and mictic ratio of B. angularis were continuously tracked. During the 81-day (69 asexual generations) period of selection, the B. angularis populations in the environments with invaders showed a significant increase in growth rate but a non-significant change in mictic ratio over time when compared with those in the environment without invaders. A common garden experiment revealed that when exposed to the environments with invaders, the B. angularis populations evolved in the environments with invaders had higher growth rates than those evolved in the environment without invaders, and the opposite was also true, indicating that local adaptation was rapidly formed. Info-chemicals released by invaders to the environment might increase the heritability of higher growth rates, and thus facilitate the local adaptation of B. angularis populations to invasion by B. calyciflorus.