Geographic differentiation and speciation in Cerion–a preliminary discussion of patterns and processes

Cerion's exuberant morphological diversity (600 described 'species') combined with the extreme rarity of reproductive isolation among morphotypes (only one unambiguous case of sympatry in the Bahamas) has long made this genus an object of fascination for evolutionists and of frustration for taxonomists. We have pursued an integrated approach of genetic and morphometric study based on field investigations of ecology and biogeography in the Bahamas. Cerion's morphotypes are not distributed haphazardly, but show definite patterns of correlation with habitat and geography. Although all morphotypes interbreed, hybrid zones tend to be narrow and characterized by highly local genetic anomalies–unique alleles present in neither parental population. Different patterns of covariance in ontogeny, and habitat preferences, also indicate mat the morphotypes are distinctive, non-amalgamating entities (despite little difference in the frequencies of structural genes among them) that may be called species once a definition based on strict reproductive isolation is abandoned. Variation in structural genes, anatomy and morphology is non-concordant, but orderly for each criterion. Similar morphologies are often polyphyletic and evolved repeatedly as one possible ontogenetic route within a developmental program common to all Cerion. Although we cannot always distinguish among competing causes for observed patterns, we can establish genetic, morphological, anatomical, and biogeographic criteria for decisions when adequate evidence is available. The species of Cerion will be reduced by more than an order of magnitude from a list currently described.     

THE DYNAMICS OF TWO HYBRID ZONES IN APPALACHIAN SALAMANDERS OF THE GENUS PLETHODON

Two zones of intergradation between populations of Plethodon have been studied for 18 and 20 years, respectively. The data consist of systematic scores of colors, made at least twice annually. Near Heintooga Overlook in the Balsam Mountains (Great Smoky Mountains National Park), the salamanders' cheeks are gray. Proceeding north toward the Smokies, there is increasing frequency and intensity of red color at two, four, and six miles. There has been no change in the scores at any location. The width of the zone and our failure to detect any change can be explained by assuming neutrality of the character and random diffusion during the probable time since contact between the two intergrading forms, which most likely took place after the Hypsithermal Interval, 8,000–5,000 BP. At Coweeta Hydrologic Laboratory in the Nantahala Mountains, Plethodon jordani and P. glutinosus hybridize at intermediate elevations. The lateral white spots of glutinosus decrease and the red on the legs of jordani increases with elevation from 685 m to 1,052 m. At the higher elevation, the proportion of animals scored as “pure” jordani declined significantly from 1974 to 1990, an indication that the hybrid zone is spreading upward. The rate of spread is too great to be explained by random diffusion, so selection for glutinosus characters is the best explanation. The rate of spread of the hybrid zone indicates that hybridization began 60–65 years ago, at the end of the time of intense timbering. Such human disturbances have caused hybridization in other organisms.     

Temporal deposition of incremental and discontinuous zones in the otoliths of Oreochromis niloticus (L.)

Ultrathin sections of otoliths were prepared and studied with the transmission electron microscope. The discontinuous zone starts to grow at night, 3 h before light-on, and is completed a few hours after light-on. The growth of the incremental zone follows immediately afterwards and continues approximately until light-off. There is little material deposited onto the otolith at night before the start of discontinuous zone deposition.     

青藏高原生态屏障区环境基本公共服务的非均衡性及其成因——基于青海村镇居民点的实证分析

环境基本公共服务是青藏高原生态屏障区生态环境治理及农牧民人居环境品质提升的关键环节,揭示其配置均衡状态及失效原因,对提升青藏高原环境基本公共服务均等化水平、降低生态屏障区内人类活动的生态环境胁迫风险具有重要意义。以青海省4315个村镇居民点为对象,选取生活垃圾处理、生活污水处理、卫生户厕改造3项特征指标,定量测度村镇环境基本公共服务配置非均衡性,运用有序多分类及二元逻辑斯蒂回归模型解析非均衡性的生成原因。结果显示：青海环境基本公共服务水平总体偏低,处于低和极低等级的村镇居民点占37.13%和37.84%;环境基本公共服务非均衡性受配置成本、人口社会、经济收入和基层管理因素的多重影响,自然地理的高寒性和交通区位的偏远性是生成非均衡性的重要因素;人口社会因素的规模报酬递增效应使非均衡性加剧,大分散、小聚居的农牧民定居点通常是服务配置的弱势区域,经济收入和基层管理因素分别是非均衡性加剧的内因和外因。建议在青藏高原生态屏障区实施递进式均衡配置模式及适应性管理,建立就地消纳与跨区处理结合的弹性生活垃圾处置体系,推广耐低温分散化污水处置模式和生态化处置技术体系,适应高寒环境的户厕改造技术研发和农牧...     

重庆主城河岸带植物群落功能性状与土壤理化性质的关系

基于功能性状视角开展植物群落与环境关系的研究有助于揭示植物的适应策略。然而,目前关于城市河岸带植物群落功能性状的研究较少。为此选取10项植物功能性状指标和14项土壤理化性质指标,探究重庆主城3种生境类型河岸带(自然型河岸带(NRZ)、农耕主导型河岸带(FRZ)和开发建设主导型河岸带(BRZ))植物群落功能性状与土壤因子特征及互作机制。结果表明：(1)与NRZ生境相比,FRZ生境中的土壤速效磷、速效钾和氧化还原电位和BRZ生境中的土壤含水量显著偏高(P<0.05);FRZ和BRZ生境中的土壤pH值和全磷含量显著偏高,而土壤有机质、全钾和全氮含量显著偏低(P<0.05)。(2)与NRZ生境相比,FRZ生境中的比根长和比根表面积显著较高,茎干物质含量和叶干物质含量显著较低;BRZ生境中仅茎干物质含量显著较低(P<0.05)。(3)冗余分析结果表明,影响各生境类型河岸带植物群落功能性状的土壤因子不同,NRZ生境为土壤容重、含水量和硝态氮,FRZ生境为土壤铵态氮、全磷和有机质,BRZ生境则是土壤含水量、温度和速效磷。研究发现与自然状态相比,农业和建筑类型的人为干扰导致重庆主城河...     

植被的PE(可能蒸散)指标与植被-气候分类(三)几种主要方法与PEP程序介绍

Holdridge的生命地带分类系统由于其指标的计算十分简便与对植被的对应性强而受到国际植被生态学界与环境科学研究者的重视。特别是近年来在环境的评价、生态区划与预测全球变化对生态系统的影响等方面得到较多采用。该系统对中国各植被地带的气候台站资料进行计算分析的结果表明有较好的适应性。但由于该系统发展于中美洲的热带地区,因而在中国的亚热带地区须进行局部的调整。但采用该系统将有利于与世界各地的气候一植被分类系统的统一与对比研究。通过回归计算表明,该系统的可能蒸散率(PER)指标与CHIKUGO模型的辐射干燥度(RDI)显著相关。因而可以采用便于取得资料与易于计算的PER来进行潜在第一性生产力(NPP)的估算。对中国各植被地带的计算结果令人满意,可进一步用于在全球变化条件下,中国各植被地带或生态系统主要类型及其NPP变化的预测。     

Diverging growth and resilience of Pinus tabulaeformis and Pinus massoniana to droughts in north-south transition zone,central China

Climate transition zone is a sensitive area of climate change and ecological transition where forests are vulnerable to climate extremes. Extreme droughts are increasing in frequency and magnitude under climate change, resulting in structure and function changes of forest ecosystems. Here, to analyze climate-growth relationships and quantify tree resilience to extreme droughts, we developed six tree-ring-width chronologies from P. tabulaeformis and P. massoniana sampling sites in Mt. Jigong region, Central China. The results indicated that all chronologies from the two species had good consistency, precipitation in current April and mean temperature in current August or mean minimum temperature from current August to October were the main limiting factors of the two tree species growth, but the responses of P. massoniana ring-width to climatic factors was more complex than that of P. tabulaeformis. The results also showed that tree growth of 1999–2005 was the lowest growing period during 1979–2018, and P. massoniana grew better than P. tabulaeformis before 2005 and vice versa after 2005. Comparing low growth years of trees, we identified to study tree growth resilience. The calculations from 1988, 1999–2005 and 2011 drought years indicated that P. tabulaeformis had more increased resilience to extreme droughts than that of P. massoniana, and the two species had stronger ecological recovery and resilience under global warming and non-extreme drought conditions in the recent 40 years. These results have implications for predicting tree resilience and identifying tree species in heterogeneous forest landscapes vulnerable to future climate change in climatic transition zone.     

SURVIVAL OF HYBRIDS IN A MOSAIC HYBRID ZONE

The ground crickets Allonemobius fasciatus and A. socius meet in a mosaic hybrid zone that stretches from New Jersey at least as far west as Illinois. Within mixed populations from the contact zone, “pure” species individuals predominate. To determine whether hybrids are less viable than pure-species individuals, and to assess whether the high proportion of pure-species individuals in mixed populations results from hybrid inviability, we performed a cohort analysis. In this study, five mixed populations from the hybrid zone were each sampled three to five times from the fall of 1986 to the spring of 1988. Individuals were assigned to one of three categories based on their genotypes: A. socius (individuals harboring only alleles unique to A. socius), hybrid (individuals with alleles unique to both species), and A. fasciatus (individuals harboring only alleles unique to A. fasciatus). This sampling and measurement scheme permitted monitoring of the proportion of hybrid individuals in a population over time. The results were fairly consistent. The relative survival of A. socius was greater than the relative survival of members of the other two groups in four of the five populations. The relative viability of A. fasciatus was greater than that of hybrids in one population, approximately equal to that of hybrids in two populations, and less than that of hybrids in two populations. These results not only shed light on an important component of fitness, viability from hatching to adulthood, but they demonstrate that loss of hybrid individuals during the course of the field season will not explain deviations from random mating expectations present in mixed populations in late summer. The deviations must be due to assortative mating or to a reproductive barrier operating prior to egg hatch.     

EXTREME KARYOTYPIC VARIATION IN A MUS MUSCULUS DOMESTICUS HYBRID ZONE: THE TOBACCO MOUSE STORY REVISITED

The Robertsonian fusion is a common chromosomal mutation among mammal species and is especially prevalent in the West European house mouse, Mus musculus domesticus. More than 40 races of the house mouse exist in Europe, including the famous “tobacco mouse” (Poschiavo race) of Val Poschiavo, Switzerland. Documented here is the discovery of an extreme case of karyotypic variation in the neighboring Upper Valtellina, Italy. In a 20-km stretch of the valley, 32 karyotypes were observed, including five chromosomal races and 27 hybrid types. One previously unknown race is reported, the “Mid Valtellina” race, with a diploid number of 2n = 24 and the Robertsonian fusions Rb(1.3), Rb(4.6), Rb(5.15), Rb(7.18), Rb(8.12), Rb(9.14), Rb(11.13), and Rb(16.17). The Poschiavo race (2n = 26), Upper Valtellina race (2n = 24), Lower Valtellina race (2n = 22) and all-acrocentric race (2n = 40) were also present. The races form a patchy distribution, which we term a “mottled hybrid zone.” Geographical position, isolation, extinction, recolonization, and selection against hybrids are all believed to be instrumental in the origin and evolution of this complex system. Previous studies of house mice from Upper Valtellina indicated that two of the races in the valley (the Upper Valtellina and Poschiavo races) may have speciated in the village of Migiondo. We discuss the possibility that there may have been a reinforcement event in this village.     

Patterns of spatial distribution of phosphorus regeneration by zooplankton in a river-lake transitory zone

Studies on phosphorus regeneration by zooplankton occupying the Krutynia River - lake Kujno transitory zone showed the zone to consist of three parts. In the first one, under strong impact of river waters, P regeneration rate was low and dominated by small, pelagic rotifers. Species diversity index calculated for phosphorus regeneration was also low. In the second part, densely covered with macrophytes, the role of large-bodied littoral zooplankton in P regeneration became more important and the rate of the process and species diversity index markedly higher. The third part, a type of littoral-pelagic belt, was characterized by the highest P regeneration and species diversity index and a relatively higher contribution of pelagic forms of zooplankton to the process of phosphorus regeneration.