Rapid gain and loss of evolutionary resistance to the harmful dinoflagellate Cochlodinium polykrikoides in the copepod Acartia tonsa

Abstract

Evolutionary resistance of the copepod Acartia tonsa to the dinoflagellate Cochlodinium polykrikoides was investigated to establish whether zooplankton can rapidly adapt to harmful algal blooms (HABs). Copepod resistance was evaluated by egg production rates when feeding on C. polykrikoides relative to the nontoxic flagellate Rhodomonas lens. An experiment with six geographically separate A. tonsa populations demonstrated that the copepods collected during C. polykrikoides blooms within eastern Long Island bays were significantly more resistant to C. polykrikoides than their conspecifics in nearby nonbloom regions. An artificial selection experiment with a naïve A. tonsa population demonstrated that copepod resistance significantly increased when individuals were chronically exposed to C. polykrikoides (three times greater than the control after four generations). Following a two-generation relaxation of selection, however, the elevated resistance in A. tonsa was completely lost. Such rapid gain and loss of resistance suggests that copepod adaptation to C. polykrikoides in the bays of eastern Long Island may mainly result from the selection of resistant genotypes by an ongoing bloom event rather than prior HABs, which could shape trophic interactions between zooplankton and harmful algae.

Copepod avoidance of thin chemical layers of harmful algal compounds

“…While A. tonsa is broadly sympatric with the harmful dinoflagellate K. brevis , the population from which our copepods were drawn likely has little, although some, historic exposure to K. brevis (Tester et al ). When considering the lability of adaptive resistance for A. tonsa in response to other toxic species (Jiang et al ), it likely our copepods are behaving as naïve grazers with respect to K. brevis . We discuss the importance of interpreting our findings in the context naïve vs. sympatric grazers below.…”

“…A critical component in understanding HAB dynamics and associated multi‐scale ecological impacts is quantifying the behavioral and physiological interactions of harmful alga (HA) with copepod grazers, the predominant primary consumers of HA (e.g., Turner ). Interactions of HA and copepods are species‐specific and documented effects include physiological (fecundity, overall fitness: Prince et al ; Waggett et al ), behavioral (swimming speeds, trajectory shapes, sampling, feeding, mating: Breier and Buskey ; Cohen et al ; Schultz and Kiørboe ; Hong et al ), and evolutionary (toxin resistance, biogeographic: Dam and Haley ; Jiang et al ) phenomena. These studies collectively show HA‐induced modification of copepod physiology and feeding and swimming behaviors with significant ecological implications.…”

Clonal Variation in Growth Plasticity within a Bosmina longirostris Population: The Potential for Resistance to Toxic Cyanobacteria

“…The resistance ( R ) of each clone to dietary cyanobacteria was measured as the relative change in growth rates on the “poor” diet ( g poor ) compared with the “good” diet ( g good ): R = g poor / g good . This index was slightly modified from that used by Hairston et al [20], but provides a more explicit indication of resistance [32]. The higher the index value is, the stronger the resistance of bosminids to toxic cyanobacteria.…”

Evolutionary Adaptation of Marine Zooplankton to Global Change

“…The evolution of grazer adaptation to phytoplankton toxins is now well established in both the ocean (Colin & Dam 2002Jiang et al 2011;Zheng et al 2011) and freshwater (Hairston et al 1999(Hairston et al , 2001Sarnelle & Wilson 2005). The pattern is similar in all cases: Populations with a longer history of exposure to toxic algae have enhanced performance when challenged with toxic algae relative to those populations that have little or no exposure historythat is, naïve populations (Figure 2).…”

“…A logical consequence of this process is that the evolutionary clock for toxin-tolerant phenotypes is partly reset after blooms wane. Additional indirect evidence for this notion is the observation of the rapid loss of toxin-tolerant phenotypes in copepod populations when selection is relaxed in the laboratory ( Jiang et al 2011). The extent to which polymorphisms are prevalent in grazer populations is unknown, but a simple prediction can be made that the degree of polymorphism is inversely proportional to the temporal and spatial scale of toxic algal blooms.…”