The Origin of Geographic Diversity in the Bahamian Land Snail Cerion: The Fossil History of Modern Patterns

巴哈马陆生蜗牛Cerion地理多样性的起源：现代模式的化石史。G.陆地蜗牛Cerion因其壳形态的极端地理多样性而引人注目：非常不同的形式彼此相邻，它们之间有陡峭的特征梯度。 本研究旨在揭示沿着一段长约100公里的山地植物地理多样性的历史和可能的原因。巴哈马长岛东海岸12公里处，有5种独特的形式。 从现代（活的）形式的地理模式开始，我们将通过挖掘和分析沿着海岸的风成沙沉积物中存在的蜗牛的全新世化石记录来追踪这些模式。 约20-35个贝壳，每个大约。25-30个地点将通过氨基酸外消旋（根据一系列放射性碳年龄校准）进行测年，并进行形态分析，以获得时间和地理序列。 PI将评估几个替代方案的起源，这些蜗牛的地理多样性：1。格局是相对稳定和古老的，在地理上连续的蜗牛种群的原位分化。 选择将是地理多样性的主要原因。地理格局是相对动态的，是扩散和灭绝等人口动态过程的结果。 这些模式可能有各种各样的起源：a。通过以下方式在广大区域内消灭铈离子种群，一场飓风，打开了一个广阔的区域，让来自近源或远距离扩散的蜗牛繁殖;种群扩大并相遇。 大规模的环境事件将是地理多样性的主要控制因素。铈离子种群通常处于流动状态，局部灭绝和重新建立种群，有时来自长距离扩散。 随机人口过程和较小规模的环境事件（例如，根据初步的结果，我们可以期望有一个详细的记录Cerion回到CA。距今5000-6000年。 一项平行的研究将使用mDNA序列来研究生命形式的关系。 这些研究将有助于理解生物地理多样性的起源和维持。

ABSTRACTThe origin of geographic diversity in the Bahamian land snail Cerion: the fossil history of modern patternsGlenn A.Goodfriend, Stephen J. Gould, and M. G. HarasewychEAR-0106936 The land snail Cerion is noteable for its extreme geographic diversity in shell morphology: very different forms occur adjacent to each other, with steep character gradients between them. This study is aimed at revealing the history and possible causes of the geographic diversity along a stretch of ca. 12 km of the east coast of Long Island, Bahamas, where 5 distinctive forms occur. Starting with the geographic patterns of the modern (living) forms, we will follow these patterns back in time through excavation and analysis of the Holocene fossil record of the snails present in the eolian sand deposits along the coast. Ca. 20-35 shells from each of ca. 25-30 sites will be dated by amino acid racemization (calibrated against a series of radiocarbon ages) and analyzed morphmetrically to obtain temporal and geographic series. PIs will evaluate several alternative scenarios concerning the origin of geographic diversity in these snails:1. The patterns are relatively stable and old, resulting from in situ differentiation of geographically continuous populations of snails. Selection would be the primary cause of geographic diversity.2. Geographic patterns are relatively dynamic and result from population dynamic processes such as dispersal and extirpation. These patterns could have various origins:a. Destriuction of Cerion populations across a broad region by, e.g., a hurricane, opens up a broad region for recolonization by snails originating from nearly sources or long-distance dispersal; the populations expand and meet. Broad scale environmental events would be the primary control of geographic diversity.b. Cerion populations are typically in a state of flux, with local extirpations and re-establishment of populations, sometimes from long-distance dispersal. Stochastic population processes and smaller scale environmental events (e.g., washover fans from storms) would be the primary control.Based on preliminary results, we can expect to have a detailed record of Cerion back to ca. 5000-6000 yr BP. A parallel study will look at the relationships of living forms using mDNA sequences. These studies will contribute to understanding the origin and maintenance of geographic diversity of organisms.