View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002oversimplifies the process of phenotypic evolution,which is a combination of selection and inheritance.Evolutionary change in a trait is equal to theproduct of the strength of selection on the trait andits heritability (the percentage of variation in a traitthat is controlled by additive effects of genes; seeFutuyma, 1986). Thus if shell thickness of the preyand claw strength of the predator were toexperience exactly the same strength of selection,the species with the greater heritability for thetrait in question would evolve faster. If selectionis unequal, as the life-dinner principle predicts,the rate of evolutionary change may still be equalif heritabilities differ. If selection is stronger onprey than on predators, prey should have lessgenetic variation in their defenses, based onFisher’s fundamental theorem of natural selection,which states that the rate of increase in fitness islimited by the amount of additive genetic variation(Brodie and Brodie, 1999). If this is the case,heritability differences might balance theasymmetry in strength of selection predicted bythe life-dinner principle, resulting in comparablerates of evolution.Brodie and Brodie (1999) noted that a majordifference between predator-prey interactions andother victim-exploiter systems is the intimacy ofthe interaction (i.e., the extent to which each speciesexperiences the consequences of the interaction).In predator-prey interactions, prey that do notsuccessfully escape face the direct consequence ofinteraction with the predator; that is, death (or zerofitness). By contrast, predators, in their interactionwith prey, are able to avoid many of the selectiveconsequences that would occur in a more intimateinteraction; this inequality in interaction may helpexplain why selection on prey is thought to bestronger than on predators (Brodie and Brodie,1999). The consequences for the individualpredator of losing a prey may be strong enough tostart an arms race. But the predictability of thisconsequence for any individual predator is low(Fig. 2B); a predator might capture the very nextprey it interacts with, negating the consequencesof the prior interaction, or may switch to analternative prey (Brodie and Brodie, 1999).Brodie and Brodie (1999) argued that the onlypredator-prey systems likely to result in acoevolutionary arms race (in which selectionpressures between predator and prey aresymmetrical) are systems in which predators interactwith dangerous prey, a conclusion Vermeij (1982b)also advocated. If a prey is dangerous to a predator,the predictability of consequences for the predatoris expected to be high (small residuals) (Fig. 2A)and therefore selection is strong. Coevolution islikely to occur in this system of interacting predatorsand dangerous prey. In this sense predators are“forced” into experiencing selection from dangerousprey (Brodie and Brodie, 1999). This situation leadsinevitably to an evolutionary response in the predatoras long as variation in the predator’s offensive trait(either morphological or behavioral) is present.The dangerous prey concept was used toexplain evolutionary shifts in stereotypic placementof holes drilled by naticids on confamilial prey(Dietl and Alexander, 2000). Because an escapedaggressive prey may become the predator and drillits former attacker (a case of the hunter becomingthe hunted), naticid prey may be considereddangerous to their confamilial predators. Naticidsmay have shifted the position of drill holes onconfamilial prey in order to neutralize thepotentially larger prey foot or more aggressiveretaliatory behaviors of such dangerous prey (Dietland Alexander, 2000). This concept remainsrelatively unexplored in the fossil record ofpredator-prey interactions.The interaction between predatory crabs andtheir hard-shelled prey also may have acoevolutionary component. If we were to playDevil’s advocate, West et al.’s (1991) example ofthe interaction between Tanganyikan gastropodsand crabs discussed earlier could involvecoevolution between predator and prey if theevolution of more powerful claws of the predatorwere a counter-adaptation to increased defensivestrength of the prey’s shell. This could result fromthe increased likelihood of breakage or damage totheir claws (as a consequence of fatigue failure),which occurs commonly in living crab species(Juanes and Hartwick, 1990); in this case, the362