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

该奖项由极地项目办公室的南极地质和地球物理项目提供，支持对西摩岛进行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。这是南极洲从冷温带气候向今天的极地气候转变的开始。变冷趋势强烈影响了南极浅水海洋群落的结构，这些影响在现代南极群落中物种之间的特殊生态关系中仍然很明显。始新世晚期的降温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碎骨捕食。始新世末期，捕食减少使得大量的蛇蛉类（脆星）和海百合类（海百合）出现在浅水环境中。这些低捕食群落出现在南极半岛西摩岛晚始新世La Meseta组上部密集的棘皮动物化石组合中。今天，密集的蛇和海百合在南极洲的浅水栖息地很常见，但通常已经被来自温带和热带纬度类似栖息地的捕食者所消灭；它们在南极洲持续到今天是始新世气候变冷的重要生态遗产。尽管捕食减少对南极蛇科动物和海百合动物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。本研究将研究始新世晚期腹足类动物（蜗牛）和双壳类动物（蛤）的进化生态学。根据软体动物对温度下降和捕食水平变化的预测反应，一系列假设将在拉梅塞塔地层进行测试。在始新世晚期，腹足类动物外壳的形状、捕食其他软体动物的活动（通过在它们的外壳上钻孔）以及捕食对软体动物外壳厚度的影响应该发生了显著变化。首先，腹足类动物外壳的防御特征，如脊椎和肋骨，应该随着温度的升高而下降，因此，粉碎骨骼的捕食者的活动减少了。其次，掠食性腹足类动物对双壳类猎物的钻探应该随着时间的推移而增加，因为随着温度的下降，钻探者自己应该受到更低的捕食压力。因此，随着时间的推移，钻壳应该会变得越来越普遍。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）与温度对进化的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。西摩岛蕴藏着地球历史上这一关键时期在南极洲唯一容易接近的化石露头。因此，西摩岛上的拉梅塞塔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，在未来的几十年到几个世纪里，全球气候变化可能会增加一些温带沿海地区的上升流。最近的生态学证据表明，由此导致的海水温度降低可能会减少这些地区的捕食行为。了解La Meseta动物群对始新世晚期全球变冷的反应，将为了解现代底栖生物群落快速变化的结构提供直接的见解。

9908856 BlakeThis 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.