Ages, biostratigraphic datums, and coiling ratios of Pulleniatina in sediments from DSDP Holes 15-154A and 16-157

Pliocene and Pleistocene planktonic foraminiferal biogeography and paleoceanography have been examined in Deep Sea Drilling Project (DSDP) sites of the Panama Basin (Pacific Ocean) and Colombian and Venezuelan Basins (Atlantic Ocean) to determine the timing of the isolation of Atlantic and Pacific tropical planktonic faunas resulting from the development of the Central American isthmus. Previous studies have suggested a late Miocene to middle Pliocene occurrence of this event. The Panama Basin (DSDP site 157) and the Colombian Basin (DSDP site 154A) share two early Pliocene biogeographic events: (1) great abundance of sinistral coiling Neogloboquadrina pachyderma at 4.3 m.y. ago at site 157 and 0.7 m.y. later at site 154A, and (2) a sinistral-to-dextral change in the coiling-direction preference in Pulleniatina 3.5 m.y. ago at both locations. Identification of these events farther to the east in the Venezuelan Basin (DSDP site 148) is complicated by insufficient lower Pliocene core recovery, but abundant sinistral N. pachydcrma appear to have extended far to the east in the Caribbean 3.6 m.y. ago; perhaps the early Pliocene abundance of this form is not indicative of cool water. The coiling-direction history and stratigraphic ranges of Pulleniatina became different in the Atlantic and Pacific Oceans during the early Pliocene; this is inferred to result from geographic isolation of the assemblages. Saito (1976) used the temporary disappearance of this genus from Atlantic waters at 3.5 m.y. ago to mark the closure of the Isthmus of Panama, but I show that in the Colombian Basin (site 154A) its disappearance was closer to 3.1 m.y. ago. This suggests the possibility of surface-water communication between the Atlantic and Pacific until that time.

Oxygen, hydrogen, and carbon isotopic compositions in deep sea cherts, porcellanites, and coexisting carbonates from DSDP Legs 2, 3, 6, 7, 11, 14, 16, 17, and 20

Seventy four samples of DSDP recovered cherts of Jurassic to Miocene age from varying locations, and 27 samples of on-land exposed cherts were analyzed for the isotopic composition of their oxygen and hydrogen. These studies were accompanied by mineralogical analyses and some isotopic analyses of the coexisting carbonates. d18O of chert ranges between 27 and 39%. relative to SMOW, d18O of porcellanite - between 30 and 42%. The consistent enrichment of opal-CT in porcellanites in 18O with respect to coexisting microcrystalline quartz in chert is probably a reflection of a different temperature (depth) of diagenesis of the two phases. d18O of deep sea cherts generally decrease with increasing age, indicating an overall cpoling of the ocean bottom during the last 150 m.y. A comparison of this trend with that recorded by benthonic foraminifera (Douglas and Savin, 1975; http://www.deepseadrilling.org/32/volume/dsdp32_15.pdf) indicates the possibility of d18O in deep sea cherts not being frozen in until several tens of millions of years after deposition. Cherts of any Age show a spread of d18O values, increasing diagenesis being reflected in a lowering of d18O. Drusy quartz has the lowest d18O values. On-land exposed cherts are consistently depleted in 18O in comparison to their deep sea time equivalent cherts. Water extracted from deep sea cherts ranges between 0.5 and 1.4 wt %. dD of this water ranges between -78 and -95%. and is not a function of d18O of the cherts (or the temperature of their formation).

云南省纳帕海自然保护区越冬黑颈鹤的集群特征

下载PDF阅读器2004年10月-2005年5月,在云南纳帕海自然保护区采用定点扫描法对越冬黑颈鹤(Grus nigricollis)的集群类犁和集群大小进行了观察.结果表明黑颈鹤夜间集群夜栖,形成较大的夜栖群,平均群体大小为67.9只(16-157,n=17):按照有无灰鹤加入,又将其分为同种集群和混种集群两种类型,其中同种集群的黑颈鹤数量占整个越冬种群的65.3%.在白昼,黑颈鹤以家庭鹤、集群鹤及特殊群体3种类型活动,家庭鹤和集群鹤的平均大小分别为2.7只(2-4,n=145)和16.1只(3-65,n=1017).黑颈鹤的集群大小并不稳定,在日内和月份间均有明显变化(P=0.000＜0.05).存越冬期,最大集群形成于12月,其次为11月和1月;在日内,早上8时集群最大,随后减小并保持相对稳定,18时黑颈鹤开始向夜栖地靠拢,使得集群再次开始增大.随后观察中还发现,黑颈鹤的家庭解体过程开始于3月底,当幼鹤被成鹤驱逐离群后,逐渐加入集群鹤活动,从而使得家庭鹤和集群鹤的大小和组成发生改变.黑颈鹤的集群大小和组成受自身状况、种内关系、天气、食物等多种因素的共同影响,随时间和季节变动而发生变化,是对自身、种群和环境条件变化的综合反映.

哺乳动物适应性进化的分子机制探讨——若味受体基因和犁鼻器受体1基因的研究

动物的适应进化是生物学研究的最基本的问题之一。虽然，人们早从形态学上研究了动物的适应现象，但是对适应的遗传学机制知之甚少。动物感觉系统对周围环境的适应是动物适应进化中的一个关键问题。因此，我们选取了动物感觉系统中苦味受体基因家族（T2R）和犁鼻器受体1基因家族（VIR）为研究对象，对哺乳动物适应性进化的分子机制进行探讨。通过生物信息学和分子生物学手段相结合，我们在哺乳动物6个目共16个物种中获得了157个的苦味味觉受体基因，并对这些TZR基因的系统发育关系进行分析，结果显示哺乳动物的TZR基因家族经历了"生一和一灭"的进化模式，即频繁的基因重复和假基因化。另外，结果还显示这些基因可以被分为3个主要类群，分别命名为A，B和C。有趣的是，B和C类群的基因在所研究的物种间普遍是一对一的直系同源的，而A类群基因则显示了种属或世系特异性。有可能B和C类群的基因是识别哺乳动物共同的苦味物质所必需的，而A类群基因则是用于识别具有种属特异性的苦味物质。这个分析还揭示了在系统发育关系上近相关的基因在它们的染色体位置上也是靠近的，这证明了串联重复是新的TZR基因产生的主要方式。此外，通过核昔酸的异义替换数和同义替换数的比较显示不同物种新近产生的基因所编码的受体蛋白在膜外区的异义替换数显著地大于同义替换数，提示着这些通过基因重复产生的新基因受到了正选择的作用。在自然界中，许多的天然有毒物质一般都是苦的，因此，我们推测哺乳动物TZR基因的分"化选择是为了使其在探索新的生活环境和寻找新食物时能够辨别出更多不同的有毒物质，更好地适应新环境。此外，我们还研究了苦味受体基因和甜味／鲜味受体基因的进化途径。结果显示苦味受体基因和甜味／鲜味受体基因在进化上具有远相关，并具有不同的进化途径，提示着这可能是导致了这些受体基因具有不同功能，传导不同味觉的原因。犁鼻受体噬因家族（VIR）是哺乳动物的信息素受体。应用生物信息学手，我们从大鼠和小鼠的基因组中分别得到了152和115个VIR基因。大鼠VIR基因家族包含11个亚家族，其中10个是与小鼠共享的，而M家族是大鼠特有的；另夕卜大鼠缺少了H和I亚家族，而这两个亚家族存在于小鼠的基因组中。系统发育关系分析发现，"生一和一灭"进化模式也在V1R基因的进化过程中占了主导地位。所有检测到的亚家族都出现于啮齿目和灵长目分歧之后，这说明V1R基因的多样性反映了这一基因家族在啮齿目内基因重复、丢失，基因漂变及自然选择等作用的动态过程。我们的分析还表明大部分不同亚家族下的基因簇爆发的时间接近于大、小鼠分歧的时间。此外，用最大似然法分析的结果表明在这些基因簇中异义替换和同义替换的比值远大于1，揭示了正选择在这些基因的分化过程的作用。一般认为V1R在动物识别信息素过程中起重要的作用，因此我们推测V1R基因的适应性进化是为了使不同的哺乳动物能够识别不同的、复杂的信息素。

(Table DR1) Biogenic silica and chert in the Pacific Ocean, DSDP and ODP data

Evidence for the dissolution of biogenic silica at the base of pelagic sections supports the hypothesis that much of the chert formed in the Pacific derives from the dissolution and reprecipitation of this silica by hydrothermal waters. As ocean bottom waters flow into and through the crust, they become warmer. Initially they remain less saturated with respect to dissolved silica than pore water in the overlying sediments. With the diffusion of heat, dissolved ions, and to some extent the advection of water itself, biogenic silica in the basal part of the sedimentary section is dissolved. Upon conductively cooling, these pore waters precipitate chert layers. The most common thickness for the basal silica-free zone (20 m) lies below the most common height of the top of the chert interval above basement (50 m). This mode of chert formation explains the frequent occurrence of chert layers at very shallow subbottom depths in pelagic sections of the Pacific. It is also consistent with the common occurrence of cherts