Global Climate Change and the Evolutionary Ecology of Antarctic Mollusks in the Late Eocene

9908828阿伦森该奖项由极地项目办公室南极地质和地球物理项目提供，支持西摩岛的古生态和古环境研究。始新世晚期的全球气候变化对南极洲产生了重要影响。这是从南极洲的冷温带气候过渡到今天存在的极地气候的开始。冷却的趋势强烈影响了浅水区的结构，南极海洋群落，这些影响仍然是明显的物种生活在现代南极社区之间的特殊生态关系。始新世晚期的冷却减少了鱼类和螃蟹的数量，这反过来又减少了对无脊椎动物的捕食。在始新世末期，减少的捕食使得密集的蛇尾类（brittlestar）和海百合类（海百合）出现在浅水环境中。这些低捕食社区出现在晚始新世La Meseta组的上部，在南极半岛西摩岛，密集的化石棘皮动物组合。今天，密集的蛇类和海百合种群在南极洲的浅水栖息地很常见，但通常已经被温带和热带纬度类似栖息地的捕食者消灭了;它们在南极洲的持续存在是始新世气候变冷的重要生态遗产。尽管捕食减少对南极海百合和海百合的影响现在已经有了很好的记录，但冷却对更丰富的软体动物的影响还没有被调查过。本研究将探讨始新世晚期腹足类（蜗牛）和双壳类（蛤）的演化生态学，并根据预测的软体动物对温度下降和捕食水平变化的反应，在La Meseta组中检验一系列假设。腹足类贝壳的形状，腹足类通过在贝壳上钻孔捕食其他软体动物的活动，以及捕食对软体动物贝壳厚度的影响，应该在始新世晚期发生了显着变化。首先，防御功能的腹足类贝壳，如刺和肋骨，应下降的温度，因此，活动的捕食者的粉碎。第二，钻双壳类猎物的捕食腹足类动物应增加随着时间的推移，因为钻孔机本身应该受到较低的捕食压力，随着温度的下降。因此，随着时间的推移，钻孔炮弹应该会越来越常见。第三，随着时间的推移，贝壳厚度的模式将有可能将温度下降的直接生理影响（在较低的温度下更难产生贝壳，因此应该更薄）与温度对进化生物相互作用的间接影响（增加钻探捕食应该导致更厚的贝壳）分开。西摩岛包含了地球历史上这一关键时期在南极洲唯一容易获得的化石露头。因此，西摩岛上的La Meseta地层为了解气候变化如何影响南极海洋群落提供了一个独特的机会。实际上，全球气候变化可能会在未来几十年至几个世纪内增加一些温带沿海地区的上升流。最近的生态证据表明，由此造成的海水温度下降可能会减少这些地区的捕食活动。了解La Meseta动物群对始新世晚期全球变冷的反应，将直接洞察现代底栖生物群落结构的快速变化。

9908828AronsonThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports a paleoecological and paleoenvironmental study of Seymour Island. Global climate change late in the Eocene epoch had an important influence in Antarctica. This was the beginning of the transition from a cool-temperate climate in Antarctica to the polar climate that exists there today. The cooling trend strongly influenced the structure of shallow-water, Antarctic marine communities, and these effects are still evident in the peculiar ecological relationships among species living in modern Antarctic communities. Cooling late in the Eocene reduced the abundance of fish and crabs, which in turn reduced skeleton-crushing predation on invertebrates. Reduced predation allowed dense populations of ophiuroids (brittlestars) and crinoids (sea lilies) to appear in shallow-water settings at the end of the Eocene. These low-predation communities appear as dense fossil echinoderm assemblages in the upper portion of the late Eocene La Meseta Formation on Seymour Island, off the Antarctic Peninsula. Today, dense ophiuroid and crinoid populations are common in shallow-water habitats in Antarctica but generally have been eliminated by predators from similar habitats at temperate and tropical latitudes; their persistence in Antarctica to this day is an important ecological legacy of climatic cooling in the Eocene. Although the influence of declining predation on Antarctic ophiuroids and crinoids is now well documented, the effects of cooling on the more abundant mollusks have not been investigated. This study will examine the evolutionary ecology of gastropods (snails) and bivalves (clams) in the late Eocene.A series of hypotheses will be tested in the La Meseta Formation, based on the predicted responses of mollusks to declining temperature and changing levels of predation. The shapes of gastropod shells, the activities of gastropods that prey on other mollusks by drilling holes in their shells, and the effects of predation on the thickness of mollusk shells should have changed significantly through late Eocene time. First, defensive features of gastropod shells, such as spines and ribbing, should decline as temperature and, therefore, the activity of skeleton-crushing predators declined. Second, drilling of bivalve prey by predatory gastropods should increase with time since the drillers should themselves have been subject to lower predation pressure as temperature declined. Drilled shells, therefore, should become more common through time. Third, patterns in the thickness of shells through time will make it possible to separate the direct, physiological effects of declining temperature (shells are more difficult to produce at cooler temperatures, and so should be thinner) from the indirect effects of temperature on evolving biological interactions (increased drilling predation should result in thicker shells). Seymour Island contains the only fossil outcrops readily accessible in Antarctica from this crucial period in Earth history. The La Meseta Formation on Seymour Island thus provides a unique opportunity to learn how climate change affected Antarctic marine communities. In practical terms, global climate change will probably increase upwelling over the next few decades to centuries in some temperate coastal regions. Recent ecological evidence suggests that the resultant lowering of sea temperatures could lower predation in those areas. Understanding the response of the La Meseta faunas to global cooling in the late Eocene will provide direct insight into the rapidly changing structure of modern benthic communities.