Variability selection in hominid evolution

Variability selection (abbreviated as VS) is a process considered to link adaptive change to large degrees of environment variability. Its application to hominid evolution is based, in part, on the pronounced rise in environmental remodeling that took place over the past several million years. The VS hypothesis differs from prior views of hominid evolution, which stress the consistent selective effects associated with specific habitats or directional trends (e.g., woodland, savanna expansion, cooling). According to the VS hypothesis, wide fluctuations over time created a growing disparity in adaptive conditions. Inconsistency in selection eventually caused habitat-specific adaptations to be replaced by structures and behaviors responsive to complex environmental change. Key hominid adaptations, in fact, emerged during times of heightened variability. Early bipedality, encephalized brains, and complex human sociality appear to signify a sequence of VS adaptations—i.e., a ratcheting up of versatility and responsiveness to novel environments experienced over the past 6 million years. The adaptive results of VS cannot be extrapolated from selection within a single environmental shift or relatively stable habitat. If some complex traits indeed require disparities in adaptive setting (and relative fitness) in order to evolve, the VS idea counters the prevailing view that adaptive change necessitates long-term, directional consistency in selection. © 1998 Wiley-Liss, Inc.     

Effect of flower identity and diversity on reducing aphid populations via natural enemy communities

Floral plantings are often used in agriculture to attract pollinator communities, but they also play an important role in recruiting and establishing natural communities for natural pest control. Inconsistent effects of floral plantings for pest control may be a result of an absence of mechanistic insights and a reliance on the idea that simply increasing flower diversity will benefit these services. A more tailored set of flower species may be needed to benefit the natural enemies through provision of nectar and alternative prey. We used an outside pot experiment to investigate the effect of three flower plants (Fagopyrum esculentum, Vicia faba, and Trifolium pratense) on reducing aphid pests on four different plant cultivars of barley (Hordeum vulgare), over two years. We grew the four cultivars of barley alone, next to a single flower or next to a mixture of flowers, and observed aphid and natural enemy colonization across the growing season. Aphid population sizes were reduced on all barley cultivars grown next to a flower with stronger pest suppression when all flowers were present. Each flower species recruited a different community of non‐barley aphids that, in turn, varied in their ability to establish the natural enemy populations and subsequently the ability to reduce barley aphid populations. Overall, increased pest suppression in the mixed treatments was a result of numerous weaker interactions between different flower, aphid, and natural enemy species, rather than a few dominant interactions. Natural enemy communities could be enhanced by incorporating flower species that vary in their ability to attract and host alternative prey (i.e., non‐pest aphids) as well as suitable nectar provisioning. We can use our knowledge of ecological interactions to tailor floral plantings to increase the effectiveness of pest control services.     

Highly Replicated Evolution of Parapatric Ecotypes

Parallel evolution of ecotypes occurs when selection independently drives the evolution of similar traits across similar environments. The multiple origins of ecotypes are often inferred based on a phylogeny that clusters populations according to geographic location and not by the environment they occupy. However, the use of phylogenies to infer parallel evolution in closely related populations is problematic because gene flow and incomplete lineage sorting can uncouple the genetic structure at neutral markers from the colonization history of populations. Here, we demonstrate multiple origins within ecotypes of an Australian wildflower, Senecio lautus. We observed strong genetic structure as well as phylogenetic clustering by geography and show that this is unlikely due to gene flow between parapatric ecotypes, which was surprisingly low. We further confirm this analytically by demonstrating that phylogenetic distortion due to gene flow often requires higher levels of migration than those observed in S. lautus. Our results imply that selection can repeatedly create similar phenotypes despite the perceived homogenizing effects of gene flow.     

Effector and target cells in the assessment of natural cytotoxic activity of rhesus monkeys

In humans, decreased natural killer cell (NK) activity has been associated with stressful life events, whereas acute arousal and disturbance frequently has been reported to result in increased NK activity. This bidirectional immune modulation prompted us to investigate the effects of a social stressor on the lymphocyte cytolytic activity of 31 infant rhesus monkeys. The first of three studies evaluated the effects of an 8 hr maternal separation on the infants' cytolytic response against the K562 target-cell line. A finding of increased lytic activity indicated a need for a longer evaluation—after a 24 hr separation—and an additional assessment of two other target-cell lines, Raji and Daudi. The observation of decreased lytic responses to Raji and Daudi, in association with increased lysis of K562, warranted a third study to delineate which rhesus effector cells were responsible for lysis of the K562 and Raji target cells. By isolating cell subsets, it was possible to observe that the majority of unprimed cytotoxic activity resided in the CD3- population of cells, but that the CD3 + CD8 + population also mediated a significant amount of cytotoxicity against both targets. In conclusion, these findings support earlier studies indicating that maternal separation results in significant immune alterations in infant monkeys. However, the complex nature of changes in cytotoxic responses during prolonged stress revealed that different lymphocyte populations engage in parallel and compensatory alterations. © 1996 Wiley-Liss, Inc.     

阴山山脉天然侧柏林的基本特征

阴山山脉是中国天然侧柏(Platycladus orientalis)林分布的西北界, 侧柏林也是阴山山脉最主要的森林群落之一。它具有较好的固坡、保土、涵养水源及改善生境的作用。为了解阴山山脉天然侧柏林种群、群落特征和空间分布规律以更好地为侧柏林的经营提供理论依据, 我们以阴山山脉大青山及乌拉山段天然侧柏林为研究对象, 通过样方调查, 分析了侧柏林的植物区系特征, 并根据群落各层片物种优势度将该区侧柏林划分为6个群丛类型, 分析了各群丛特征及其空间分布的生态序列。结果表明: (1)阴山山脉天然侧柏林群落共出现维管植物96种, 隶属于30科70属, 种的地理成分包括8个类型18个亚型, 其中东古北极分布最多, 其次为东亚分布; (2)从群落结构分析, 发育良好的侧柏群落表现为完整的乔木层和草本层, 灌木盖度普遍偏低, 基本不能成层, 在干扰较为严重的地段甚至消失; (3)各群丛侧柏的径级结构基本呈正态分布, 属于稳定的群落类型, 侧柏的平均株高随胸径的增大整体呈增长型; (4)该区侧柏林受干扰较严重, 加之严酷的生境条件, 建群种侧柏的平均胸径较小且植株分叉较多, 不适合作为用材林, 建议将其作为生态公益林及种源林加以保护利用。     

新疆北部草地典型灌木的碳氮特征

灌木在维持干旱半干旱区生态系统稳定性方面发挥着重要的作用。该研究调查了新疆北部草地典型灌木物种, 并分析了这些灌木叶、枝、茎的碳(C)、氮(N)含量特征, 可为新疆草地植被碳氮储量的准确估算以及碳氮循环过程提供基础数据。结果表明: 北疆地区草地的典型灌木有白刺(Nitraria spp.)、刺旋花(Convolvulus tragacanthoides)、红砂(Reaumuria soongarica)、假木贼(Anabasis spp.)、 锦鸡儿(Caragana spp.)、麻黄(Ephedra spp.)、沙拐枣(Calligonum mongolicum)、梭梭(Haloxylon spp.)、金丝桃叶绣线菊(Spiraea hypericifolia)、驼绒藜(Krascheninnikovia spp.)、小蓬(Nanophyton erinaceum)、盐爪爪(Kalidium spp.)、猪毛菜(Salsola spp.)等, 归属于蔷薇科、豆科、麻黄科、柽柳科、蒺藜科、蓼科、旋花科、藜科。北疆草地典型灌木各器官C含量为茎(45.76 ± 3.43)% >枝(44.27 ± 4.51)% >叶(39.15 ± 5.91)%, N含量为叶(2.21 ± 0.59)% >枝(1.55 ± 0.44)% >茎(1.34 ± 0.35)%, C:N为茎(36.74 ± 10.80) >枝(31.07 ± 10.43) >叶(18.94 ± 5.82)。灌木地上部分C含量为(43.77 ± 4.43)%, N含量为(1.56 ± 0.45)%, C:N为(31.78 ± 10.12); C含量变异程度较小, 变异系数为10%, N含量的变异系数为27%, C:N的变异系数为32%。灌木同一器官的C、N含量及C:N在不同科间有显著差异, 蔷薇科各器官的C含量显著大于其他科(p < 0.05); 豆科叶和茎的N含量显著大于其他科(p < 0.05), 麻黄科枝的N含量显著大于其他科(p < 0.05); 旋花科叶和枝的C:N显著大于其他科(p < 0.05), 蔷薇科茎的C:N显著大于其他科(p < 0.05)。     

腾格里沙漠东南缘荒漠草地不同群落类型土壤有机碳分布及储量特征

荒漠生态系统环境的复杂性及其高度的空间异质性是土壤碳储量估算结果不确定性的重要因素。通过调查取样和室内分析, 研究了腾格里沙漠东南缘10种主要荒漠草地群落各土壤层(0-5、5-10、10-20、20-30、30-50、50-70和70-100 cm土层)的土壤有机碳(SOC)含量、垂直分布特征和影响因素, 以及0-5、0-20、0-50和0-100 cm土层剖面的土壤有机碳密度(SOCD)。结果显示, 灌木群落是SOC含量的重要影响因素, 各土层SOC含量在10种群落间均存在显著差异。从土壤表层到深层, SOC含量主要表现为由高至低和先升高后降低两种特征。SOC含量与黏粉粒含量、全氮(N)、全磷(P)和电导率呈显著的正相关关系, 与砂粒含量呈显著的负相关关系。各群落之间, 0-5、0-20、0-50和0-100 cm土层剖面的SOCD均存在显著差异, 其平均值分别为0.118、0.478、1.159和1.936 kg·m ^-2。这一结果低于全球和全国草地SOCD的平均值, 利用全国数据或该研究的平均值可能会高估或低估区域土壤有机碳储量, 因此利用不同群落的SOCD能增加荒漠地区土壤有机碳储量估算的确定性。     

松嫩退化草地芦苇不同叶位叶片营养元素代谢特征

对松嫩草地不同退化程度样地的芦苇(Phragmites australis)各叶位叶片的生长及营养元素代谢特征进行分析, 以探讨土壤盐碱化对芦苇叶片营养元素代谢的影响及其适应机制。结果表明: 松嫩草地土壤中Na ⁺含量、全盐含量、pH值是衡量土壤盐碱化程度的主要决定因子, 从典型草地到重度退化草地, 土壤盐碱化程度逐级加剧。芦苇具有一定程度的耐盐碱性, 植株高度和地上部分生物量随土壤盐分增加而降低。检测出10种营养元素: K、Na、Ca、Mg、Fe、Cu、Zn、Mn、P、B, 主成分分析结果显示全部样本均处于95%的置信区间内。方差分析结果表明, 芦苇不同叶位叶片对营养元素的富集能力有所差异。K、P含量随叶位降低而减少; 而Na、Ca、Mg呈现相反分布规律。Fe、Cu集中分布在功能叶和老叶中; Mn只大量聚集在老叶中; 而Zn集中分布在幼叶中。表明土壤盐碱化对老叶营养元素的影响大于幼叶, Na在老叶中的大量积累保护了幼叶免于或者减轻离子的毒害。功能叶和老叶中Ca、Mg、Fe、Cu的积累有利于保障芦苇正常的光合作用。盐碱胁迫下幼叶仍维持较高K、P含量, 这不仅为幼叶的生长提供所需营养, 同时提高了其抗逆性, 这可能是芦苇的生理响应策略。     

Potential predation of the exotic Amblyseius swirskii on Euseius concordis (Acari: Phytoseiidae), a predatory mite commonly found in Brazil

Intra/interspecific predation by A. swirskii.

Both Benin and Netherlands populations of Amblyseius swirskii engaged in cannibalism, and in predation on Euseius concordis larvae. Provision of pollen decreased cannibalism considerably, but had a smaller effect on predation on E. concordis. Potential effect of the eventual introduction of A. swirskii for control of Bemisia tabaci in Brazil is discussed.     

Biological control of the exotic invasive snail Pomacea canaliculata with the indigenous medicinal leech Whitmania pigra

The apple snail Pomacea canaliculata has been an invasive species in China for decades and causes enormous losses to agriculture. The predation capability of the leech Whitmania pigra on P. canaliculata was studied for its economic benefit and potential application. In the present study, the leech W. pigra exhibited a strong predatory capacity in controlling P. canaliculata under both laboratory and field conditions, and it showed no bias towards consuming smaller snails during the experiments. More than 80% of the 80 snails (of which half had reached maturity) were preyed upon by 20 developing leeches (2–7?g) in miniature rice fields over a 15-day period, and the number of rice seedlings damaged by P. canaliculata was decreased in the presence of W. pigra. In a separate experiment, 15 developing snails were exposed to caged leeches and conspecific snails for four weeks. The food intake and growth of P. canaliculata were inhibited under the predation risk imposed by W. pigra, but the feeding rate, food conversion efficiency and survival of P. canaliculata were not conspicuously influenced.