Testing the Role of Predation in Morphological Evolution of Marine Prey

捕食，一种有机体为了食物而杀死另一种生物的行为，被认为对物种的进化和多样性(数量)有很大影响。我们目前正在经历生物多样性危机(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说提供了一个长期的自然实验室。然而，捕食是很难估计的，因为直接观察过去是不可能的。因此，我们需要一种在没有直接观察的情况下估计捕食行为的方法。一种解决方案是利用捕食的痕迹，如海洋无脊椎动物猎物贝壳上的疤痕，来估计捕食的频率。例如，螃蟹经常用它们强大的爪子来撕裂贝壳，从而定期以蛤壳为食。如果攻击失败，文蛤的壳就会再生，现在壳上有修复的伤疤；我们可以在化石上看到这样的伤疤。*这项研究的目标是测试捕食是否一直是海洋生物随时间进化的重要因素，更具体地说，是测试升级假说。海洋捕食者和猎物的主要辐射(多种物种的快速进化)发生在两个时间间隔：中古生代(4.15亿-3亿年前)和白垩纪-早新生代(1.5亿-3500万年前)。在这两种情况下，捕食者都变得更大、更强壮，猎物发展出更好的防御能力，比如脊椎或更厚的贝壳。这表明捕食对猎物的进化很重要，但我们想要进行更严格的测试-我们将比较捕食痕迹(指示攻击)的频率与猎物外壳形状(如获得脊椎)随时间的变化以及猎物祖先-后代血统中可能的反捕食性变化。如果猎物的防御能力随着攻击的增加而从祖先传给后代，那么猎物很可能是在进化以应对捕食。如果升级是正确的，那么我们应该观察到这种增加外壳防御的相同模式，以应对不同生物群、不同地点和不同时间的攻击增加。因此，我们将研究来自切萨皮克湾地区的早新生代双壳类(文蛤、贝类)，以及来自加拿大艾伯塔省(曾经是浅海)的中古生代腕足类(一种外表与双壳类相似的贝类，曾是非常常见的贝类)。如果我们能够在如此不同的环境中确认物种升级，我们不仅将证明一条适用于整个生命历史的自然规律，而且我们还将极大地提高我们对捕食如何影响进化和现代生物多样性的理解，而这些知识可能被证明对长期的保护工作至关重要。

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.