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STUDENT SATELLITE SYMPOSIUM 2010

Phenotypic Plasticity and its Role in Evolution

 

ABSTRACTS

The evolution of plastic traits by genetic accommodation

FRED NIJHOUT
Department of Biology, Duke University, Durham, North Carolina, USA

Understanding the mechanism behind the origin of complex novel traits is one of the great challenges of evolutionary developmental biology. It has been hypothesized that phenotypic plasticity can facilitate the evolution of novel traits, but the mechanisms by which environmentally induced novel phenotypes can become genetically fixed remain largely unexplored. The origin of novelty via phenotypic plasticity can be understood in the light of the interactions between developmental mechanisms that produce plastic phenotypes and developmental mechanisms that stabilize phenotypes. These mechanisms can greatly enhance standing genetic variation which allows rapid adaptive evolution. Of particular interest in the evolution of novelty are cases in which the ancestral and novel phenotypes are maintained as adaptive plastic alternatives. The genetic fine tuning of such alternative phenotypes to their respective environments is called genetic accommodation. In this talk I will review recent insights into the developmental mechanisms that underlie adaptive phenotypic plasticity and that mediate genetic accommodation.

 

Learning, inducible defenses, and adaptation to novel predators

CHRIS NEUFELD*, TIM EDGELL
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, CANADA

In the northeast Pacific, the recent arrival of the European green crab, Carcinus maenas, offers an attractive opportunity to study the mechanisms used by prey to recognize and respond to novel predators. In the first of two laboratory experiments, we exposed na•ve whelks to effluent from two species of predatory crab, the native red rock crab Cancer productus and the invasive European green crab Carcinus maenas. Whelks responded adaptively to Cancer by increasing shell thickness but showed no such response to Carcinus. In a second laboratory experiment, we investigated whether native whelks could detect and respond to Carcunis after preconditioning with crab cues (Cancer or Carcinus) paired with the scent of damaged conspecific whelks. Preconditioned whelks grew thicker, more-predator-resistant shells when later exposed to effluent from introduced crabs (Carcinus) alone. However, whelks responded to Carcinus regardless of whether whelks were preconditioned with introduced (Carcinus)- or native (Cancer) crab cues paired with the scent of damaged conspecific whelks. Therefore, our results are not consistent with associative learning but instead suggest another mechanism (such as heightened cue sensitivity) may have facilitated the induced response to Carcinus. These results provide some of the first evidence that past experience can alter the expression of a latent inducible morphological defense in response to cues from a novel predator. Similar work in other systems will determine the importance of behavioural plasticity in ensuring prey population persistence following the arrival of other novel predators.

 

Interplay among phenotypic plasticity, local adaptation, and gene flow

ERIKA CRISPO
Department of Biology, McGill University, Montreal, Quebec, CANADA

Genetic adaptation and phenotypic plasticity are two ways in which organisms can adapt to local environmental conditions. The relative contribution of each is predicted to be influenced by variation in selection. Plasticity's ability to enhance adaptation might allow for increased gene flow among selective environments, and/or high levels of gene flow might result in the evolution of increased plasticity. I examine these possibilities in the cichlid fish, Pseudocrenilabrus multicolor, from high-oxygen rivers and low-oxygen swamps in Uganda. Using microsatellite markers, I found that gene flow is not reduced between divergent oxygen environments relative to within them. Using a reciprocal split-brood rearing experiment, with offspring raised under high- and low-oxygen conditions, I estimated plasticity and phenotypic divergence among six populations. Plasticity of ecologically-relevant morphological traits is high overall and variable among populations. In the most geographically discrete populations, the relative contribution of local adaptation is stronger and plasticity weaker than in populations with increased potential for gene flow between environments. Plasticity might thus have evolved in response to gene flow between river and swamp environments. Future work is needed to strengthen causality inferences for interactions among local adaptation, plasticity, and gene flow in natural systems.

 

Inducible defenses in an invaded marine food chain: Why cue specificity matters

EMILY GRASON*, BEN MINER
Biology Department, Western Washington University, Bellingham, Washington USA

Inducible defenses are important in structuring native communities, but it is often assumed that they do not play a significant role in novel predator-prey interactions because prey cannot recognize a novel predator. However, recent research has demonstrated that novel predators can induce defenses in prey. We investigated whether predation cues from the native rock crab, Cancer productus, induce behavioral defenses in two invasive species of whelk, the Atlantic (Urosalpinx cinerea), and Japanese (Ocinebrina inornata) oyster drills. Both drill species increased avoidance behavior and decreased feeding rates by 48% - 67% in response to effluent from native crabs consuming conspecific drills. To determine which components of the predation cues drills respond to, we conducted an additional experiment with Atlantic drills, parsing the predation effluent into major constituents. Cues from injured conspecifics elicited the largest responses, and were similar in effect to cues from predators consuming conspecifics. Additionally, cues from crabs also induced defenses, though more weakly than cues from injured conspecifics. The response to crabs indicates drills can recognize a relatively novel predator. Further, the generalized risk assessment strategy of Atlantic drills could have adaptive value in new habitats where drills are exposed to unfamiliar predators.

 

Variation in tenacity and tube foot morphology among sea stars from different wave exposure regimes

KURTIS HAYNE
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, CANADA

Echinoderms, particularly sea stars, have specialized attachment mechanisms allowing them to temporarily adhere to a substrate and then release; these attachment and release cycles are responsible for locomotion while maintaining attachment to the substratum. Many marine organisms exhibit plastic responses to different wave exposure regimes that reduce probability of dislodgement in exposed areas. Pisaster ochraceus a cosmopolitan pacific sea star can be found in almost all gradients of wave exposure and has been shown to display adaptive features to these various flow conditions, showing differential attachment tenacities based on differential ambient flow.

 

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