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

巴哈马陆螺地理多样性的起源：现代模式的化石历史Glenn A.GoodFriend，Stephen J.Gould和M.G.HarasewychEAR-0106936陆地蜗牛Cerion以其贝壳形态的极端地理多样性而闻名：非常不同的形式彼此相邻出现，它们之间具有陡峭的特征梯度。这项研究旨在揭示巴哈马长岛东海岸长约12公里的一段约12公里长的地理多样性的历史和可能的原因，在那里出现了5种不同的形态。从现代(活的)形式的地理模式开始，我们将通过对沿海风沙沉积中存在的钉螺的全新世化石记录的挖掘和分析，来追溯这些模式。加州来自大约25-30个地点的每个地点的20-35个贝壳将通过氨基酸外消旋(对照一系列放射性碳年龄进行校准)并进行形态分析来获得时间和地理序列。PIS将评估关于这些钉螺地理多样性起源的几种替代方案：1.这些模式相对稳定和古老，是地理上连续的钉螺种群在原位分化的结果。选择将是地理多样性的主要原因。地理格局是相对动态的，是种群动态过程的结果，如扩散和灭绝。这些模式可能有不同的起源：a.通过飓风等方式破坏广泛区域的Cerion种群，为源自近来源或远距离分散的蜗牛重新定居开辟了广阔的区域；种群扩大和相遇。大范围的环境事件将是地理多样性的主要控制因素。Cerion种群通常处于流动状态，局部灭绝和重新建立种群，有时是从远距离扩散。随机的人口过程和较小规模的环境事件(例如，风暴带来的洗地扇)将是主要的控制因素。根据初步结果，我们可以预期有大约5000-6000年前的CEION的详细记录。一项平行的研究将利用mDNA序列来研究生物形式之间的关系。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.