Testing the Role of Predation in Morphological Evolution of Marine Prey

捕食，一种生物杀死另一种生物以获取食物的行为，被认为会极大地影响物种的进化和多样性（数量）。我们目前正在经历一场生物多样性危机（每天有70个物种灭绝），因此了解影响多样性和进化的因素至关重要。有一种“升级”假说认为，大多数动物进化的主要原因是为了更好地保护自己免受捕食者的攻击。化石记录为检验这些假设提供了一个长期的自然实验室。然而，捕食很难估计，因为对过去的直接观察是不可能的。因此，我们需要一种不用直接观察就能估计捕食的方法。一种解决办法是利用捕食的痕迹，比如海洋无脊椎动物被捕食的贝壳上的伤疤，来估计捕食的频率。例如，螃蟹经常以蛤蜊为食，用它们有力的爪子折断蛤壳。如果攻击失败，蛤会重新长出外壳，外壳上现在有一个修复疤痕；我们可以在化石上看到这样的伤痕。

Predation, the act of an organism killing another for food, is believed to influence the evolution and diversity (the number) of species greatly. We currently are experiencing a biodiversity crisis (70 species go extinct per day) so understanding the factors that influence diversity and evolution is vital. There is a hypothesis of “escalation”, which suggests that the main reason why most animals evolve is to defend themselves better from their predators. The fossil record provides a long-term natural laboratory to examine such hypotheses. However, predation is hard to estimate because direct observations of the past are impossible. Thus, we need a means of estimating predation without direct observations. One solution is to use traces of predation, such as scars on the shells of marine invertebrate prey, to estimate the frequency of predation. For example, crabs regularly feed on clams by using their powerful claws to fracture the shell. If the attack fails, then the clam regrows its shell, which now has a repair scar; we can see such scars on fossils. The goal of this research is to test whether predation has been an important factor in the evolution of marine life through time, and more specifically, to test the hypothesis of escalation. There are two time intervals in which major radiations (rapid evolution of multiple species) of marine predators and prey occurred: the Mid-Paleozoic (415-300 million years ago), and the Cretaceous-Early Cenozoic (150-35 million years ago). In both cases, predators became larger and stronger, and the prey developed better defenses such as spines or thicker shells. This suggests that predation was important to prey evolution but we want to conduct a more rigorous test – we will compare the frequency of predation traces (indicating attacks) to possibly anti-predatory changes in the shape of the prey shell (such as acquisition of spines) over time, and within ancestor-descendant lineages of the prey. If prey defenses increased from ancestor to descendant at the same time as increases in attacks, then the prey were probably evolving in response to predation. If escalation is correct, then we should observe this same pattern of increased shell defenses in response to increased attacks in different groups of organisms, in different places, and at different times. We will therefore examine Early Cenozoic bivalves (clams, cockles) from the Chesapeake Bay region, and Mid-Paleozoic brachiopods (a type of shellfish that is similar in appearance to bivalves, and which once were very common) from Alberta, Canada (once a shallow sea). If we can confirm escalation in such widely different settings, we would not only demonstrate a natural law that is applicable through the history of life, but we also would greatly increase our understanding of how predation affects evolution and modern biodiversity at a time when such knowledge may prove crucial to long-term conservation efforts.