High genetic differentiation among wild populations of alien Medicago sativa in Lithuania

Alfalfa (Medicago sativa; =M. sativa ssp. sativa) in Lithuania is sown as albuminous forage for cattle due to favourable climatic condition. Over many generations, alfalfa plants have escaped from cultivation fields into natural ecosystems and established wild populations. We collected and analyzed individuals from seventeen wild populations of M. sativa. Using random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) analyses, 117 RAPD and 64 ISSR reproducible and highly polymorphic (90.8% for RAPD and 86.3% for ISSR) loci were established. AMOVA showed a high genetic differentiation of M. sativa populations for both types of DNA markers utilized. According to RAPD markers, the genetic variability among populations was 63.1% and 57.0% when ISSR markers were used. Taken together, these results demonstrate that wild populations of M. sativa possess a high potential of genetic variability, that could potentially result in colonization of natural ecosystems. The UPGMA cluster analysis also showed that the DNA markers discovered in this study can distinguish between M. sativa and M. falcata (=M. sativa ssp. falcata) populations and therefore may be used to study the genetic impact of M. sativa on the native populations of M. falcata.     

Role of small rodents in the seed dispersal process: Microcavia australis consuming Prosopis flexuosa fruits

Understanding the functional role of animal species in seed dispersal is central to determining how biotic interactions could be affected by anthropogenic drivers. In the Monte Desert, mammals play different functional roles in Prosopis flexuosa seed dispersal, acting as opportunistic frugivores (endozoochorous medium‐sized and large mammals) or seed hoarders (some small sigmodontine rodents). Our objective was assessing the functional role of Microcavia australis, a small hystricognathi rodent, in the fruit removal and seed deposition stages of P. flexuosa seed dispersal, compared to sympatric sigmodontine rodents. In situ, we quantified fruit removal by small rodents during non‐fruiting and fruiting periods, and determined the distance seeds were transported, particularly by M. australis. In laboratory experiments, we analysed how M. australis stores seeds (through scatter‐ or larder‐hoarding) and how many seeds are left in caches as living seeds, relative to previous data on sigmodontine rodents. To conduct field studies, we established sampling stations under randomly chosen P. flexuosa trees at the Ñacuñán Man and Biosphere Reserve. We analysed fruit removal by small rodents and seed dispersal distance by M. australis using camera traps focused on P. flexuosa fruits covered with wire screen, which only allowed entry of small animals. In laboratory trials, we provided animals with a known number of fruits and assessed seed conditions after removal. Small rodents removed 75.7% of fruit supplied during the non‐fruiting period and 53.2% during the fruiting period. Microcavia australis and Graomys griseoflavus were the main fruit removers. Microcavia australis transported seeds to a mean distance of 462 cm and cached seeds mainly in scatter‐hoards, similarly as Eligmodontia typus. All transported seeds were left in fruit segments or covered only by the endocarp, never as predated seeds. Microcavia australis disperses P. flexuosa seeds by carrying fruits away from a source to consume them and then by scatter‐hoarding fruits and seeds.     

Comparing composition of social groups,mating system and social behaviour in two populations of Microcavia australis

Microcavia australis is a semifossorial, diurnal and social rodent, native to South America. The objective was to determine and compare the composition of social groups, mating system and social behaviours of cavies in two populations of the Monte (El Leoncito and Ñacuñán). The two sites differ in climate conditions and plant resource availability. Trapping was carried out on 7–11 consecutive days at three times of the year (food abundance, food shortage, reproduction), from 2003 to 2005. Individuals were identified with metal ear tags. Continuous focal samplings were performed during 4 days. The female/male proportion per group was 1/1 at both sites which, together with the absence of sexual dimorphism in body size (0.94), the accomplishment of oestrus synchronization, the large size of scrotal testes during the reproductive season and sexual patterns, suggests a promiscuous mating system. Social groups were larger and with more adults at the site with more severe climate conditions (El Leoncito). The index of association among individuals was higher at El Leoncito. Cavies could use seismic communication to avoid encounters ending in fights at El Leoncito, and the agonistic behaviour was significantly lower in this population.     

Maintenance of genetic variation and moderate differentiation among populations under sex-biased dispersal in the common voleMicrotus arvalis in patchy habitats

We present a microgeographic analysis of 34 allozyme loci and the control region of mitochondrial DNA (mtDNA) in the common voleMicrotus arvalis (Pallas, 1779), performed to assess the effects of environmental heterogeneity on the distribution of genetic variation among populations in the Biebrza river valley, NE Poland. The common vole occurs there in two types of habitat: open grassland and pastures around the valley (GP populations); and abandoned fields on small hills isolated by wetlands (SH populations). No significant genetic differences were found between SH and GP populations with respect to allelic richness, nor average observed and expected heterozygosities. The average genetic differentiation at allozyme loci among the SH populations was significantly lower (F _ST =0.066) than among the GP populations located around the Biebrza valley (F _ST =0.112), and an isolation by distance pattern was detected (r=0.26,pr<0.05). Mitochondrial DNA differentiation among the GP populations was great (F _ST =0.357,p<0.01), indicating that female dispersal was 4.4–6.5 times lower than for males. Our results and reviewed published data onM. arvalis dispersal suggest that common vole dispersal in patchy natural and semi-natural habitats is male-biased and could generate moderate population divergence, with relatively high levels of genetic variation retained within populations.     

Effect of mutation on genetic differentiation among nonequilibrium populations

The usefulness of GST and similar measures of genetic differentiation has been questioned repeatedly because of their dependence on the amount of heterozygosity within populations, creating problems when comparing degrees of divergence at loci with different mutation rates. Although the effect of mutation on GST is expected to be small in the early phases of divergence, it is unclear for how long after separation from a common ancestral population that GST is largely unaffected by mutation and by the resulting effect on heterozygosity. We address this question through analysis of the recursion equations for gene identity under the infinite allele model of mutation, and derive conditions describing when the effect of mutation on GST can be ignored under mutation-migration-drift equilibrium conditions and during the preceding transition phase. An important result is that during the transition phase GST is not only affected by mutation, but also by the heterozygosity in the base population from which the subpopulations diverged. The effect of mutation on GST is significant from the very start of the divergence process when initial heterozygosity is low, whereas GST is only weakly affected by mutation in the early phases of differentiation when initial heterozygosity is high. Thus, differentiation following a severe bottleneck is strongly dependent on mutation. The standardized measure of differentiation, G'ST, suggested by Hedrick (2005), may be helpful when comparing amounts of divergence at loci with different mutation rates under steady-state conditions, provided that migration is very low. In many other situations the use of G'ST might be misleading, however, and its application should be exercised with caution.     

High genetic differentiation and cross-shelf patterns of genetic diversity among Great Barrier Reef populations of Symbiodinium

The resilience of Symbiodinium harboured by corals is dependent on the genetic diversity and extent of connectivity among reef populations. This study presents genetic analyses of Great Barrier Reef (GBR) populations of clade C Symbiodinium hosted by the alcyonacean coral, Sinularia flexibilis. Allelic variation at four newly developed microsatellite loci demonstrated that Symbiodinium populations are genetically differentiated at all spatial scales from 16 to 1,360 km (pairwise Φ_ST = 0.01–0.47, mean = 0.22); the only exception being two neighbouring populations in the Cairns region separated by 17 km. This indicates that gene flow is restricted for Symbiodinium C hosted by S. flexibilis on the GBR. Patterns of population structure reflect longshore circulation patterns and limited cross-shelf mixing, suggesting that passive transport by currents is the primary mechanism of dispersal in Symbiodinium types that are acquired horizontally. There was no correlation between the genetic structure of Symbiodinium populations and their host S. flexibilis, most likely because different factors affect the dispersal and recruitment of each partner in the symbiosis. The genetic diversity of these Symbiodinium reef populations is on average 1.5 times lower on inshore reefs than on offshore reefs. Lower inshore diversity may reflect the impact of recent bleaching events on Sinularia assemblages, which have been more widespread and severe on inshore reefs, but may also have been shaped by historical sea level fluctuations or recent migration patterns. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Communicated by Biology Editor Dr. Ruth Gates.     

Genetic differentiation among populations of the shortfinned eel Anguilla australis from East Australia and New Zealand

Variability at seven microsatellite loci was used to survey the genetic population structure of the shortfinned eel Anguilla australis . Samples were collected from six estuaries along the east coast of Australia and from three estuaries around New Zealand. Hierarchical analysis of molecular variance of the five loci with good fit to Hardy–Weinberg genotypic proportions detected highly significant differences among samples ( F _ST= 0·016, P < 0·001). The fixation index between countries ( F _CT= 0·012, P < 0·001) was more than double the index among samples within countries ( F _SC= 0·005, P < 0·05). An unweighted pair-group method with arithmetic mean (UPGMA) tree also supported the separation of Australian and New Zealand populations, as did assignment tests, which correctly assigned 80 and 84% of the individuals to Australia and New Zealand, respectively. Isolation-by-distance appeared among samples overall ( r = 0·807, P < 0·001), but not among samples within countries ( r = 0·027, P > 0·05 in Australia; r = 0·762, P > 0·05 in New Zealand). These findings indicate that populations of A. australis in East Australia and in New Zealand may be reproductively isolated from one another. Genetic differentiation among populations of A. australis was two- to 10-fold higher than that among populations of other temperate eels in the North Atlantic Ocean, suggesting that two group of A. australis may reflect sub-species. Anguilla australis in the two countries have different genetic structures and thus require separate management. Genetic isolation between Australian and New Zealand populations indicates that juveniles recruit independently into these two regions from geographically or temporally isolated spawning areas.     

暗褐蝈螽不同地理种群间的遗传分化

利用线粒体COI基因片段研究了我国吉林、辽宁、内蒙古、河北和四川的暗褐蝈螽(Gampsocleis sedakovii)12个地理种群间的遗传分化。结果表明: 36条626 bp的mtDNA-COI基因片段中共检测到单倍型29种, 多态位点71个, 其中简约信号位点37个, 单一多态位点34个。分子变异等级分析(AMOVA)的计算结果显示, 群体内变异仅占总变异的37.23%, 明显小于群体间变异, Fst值为0.62770, 各群体间呈现明显的遗传分化。最大简约法(MP)系统发育分析结果显示, 暗褐蝈螽的12个地理种群以极高的自举支持度(100%)聚类, 形成两个独立的分枝。由于两个分枝的聚类结果与基于形态学特征划分的两个亚种(Gampsocleis sedakovii sedakovii和Gampsocleis sedakovii obscura)并不对应。综合采集地的生境, 初步推测暗褐蝈螽两个亚种间的形态学差异可能是由于它们所处生境不同所引起。在12个地理种群中, 只有内蒙古通辽(NTL)的个体在两个分枝中均有出现。单倍型分布格局研究发现, 单倍型H10是内蒙古通辽(NTL)、鄂温克(NEWK)和吉林吉林(JJL)3个地理种群的共享单倍型, 说明它们来自于共同的祖先。研究结果支持我国的东北地区是暗褐蝈螽遗传分化中心的观点, 但不支持基于形态学特征划分的两个亚种。     

Regional genetic differentiation among populations of Cladocora caespitosa in the Western Mediterranean

Cladocora caespitosa is the only reef-forming zooxanthellate scleractinian in the Mediterranean Sea. This endemic coral has suffered severe mortality events at different Mediterranean sites owing to anomalous summer heat waves related to global climate change. In this study, we assessed genetic structure and gene flow among four populations of this species in the Western Mediterranean Sea: Cape Palos (SE Spain), Cala Galdana (Balearic Islands), Columbretes Islands, and L’Ametlla (NE Spain). The results obtained from Bayesian approaches, F _ST statistics, and Bayesian analysis of migration rates suggest certain levels of genetic differentiation driven by high levels of self-recruitment, a fact that is supported by egg-retention mechanisms. Conversely, genetic connectivity among distant populations, even if generally low, seems to be related to sporadic dispersal events through regional surface currents linked to the spawning period that occurs at the end of summer-beginning of autumn. These features, together with a certain isolation of the Columbretes Islands, could explain the regional genetic differentiation found among populations. These results help to better understand population structure and connectivity of the species and will serve as an approach for further studies on different aspects of the biology and ecology of C. caespitosa.     

High genetic differentiation among remnant populations of the endangered Caesalpinia echinata Lam. (Leguminosae–Caesalpinioideae)

Forest fragments along the Atlantic coastland of Brazil have been highly impacted by extensive human activities for the last 400 years. Caesalpinia echinata (Leguminosae– Caesalpinioideae), brazilwood, was overexploited during this period due to its economical importance as a dye. As a result, the species has become endangered and today its total population size is very restricted. We have assessed the distribution of genetic variation between five natural populations of brazilwood by means of RAPD (random amplified polymorphic DNA) markers. Of the total genetic variability, 28.5% was attributable to differences between two geographical groups, 29.6% to population differences within groups and 42.0% to individual differences within populations. The high level of population differentiation observed is in contrast to that expected for a primarily outcrossed woody perennial plant, and suggests that there may be a degree of inbreeding. Our results are in agreement with previous studies which postulated that C. echinata has always occurred in clumps, being common in some places but rare in between. From a conservation point of view, different populations representing different regions should be protected and, yet, plants with different origins should not be synthesized into populations in a recovery process at the risk of loss and dilution of genetic information. This study demonstrates that RAPD markers were effective in establishing a clear correlation between genetic and geographical distance and in identifying areas of maximum diversity, and may be used as an initial approach to assess the partitioning of genetic variation in this endangered species.     

Genetic differentiation among local populations of the European hedgehog (Erinaceus europaeus) in mosaic habitats

Tissue samples from 160 European hedgehogs, Erinaceus europaeus , representing eight small populations from a highly fragmented landscape in Oxfordshire, UK, were screened for polymorphism at six microsatellite loci. Permutation analysis of allelic compositions revealed no evidence for linkage disequilibrium among loci. Genotype proportions within populations and at five loci did not differ from those expected at Hardy–Weinberg equilibrium. However, significant heterozygote deficit and amplification failure of several samples necessitated removal of one locus from the analysis. Mean observed heterozygosity was 0.70. Average Rho _ST was 0.079 and differed significantly from zero, suggesting restricted gene flow among local populations. Pairwise Nm values and geographical distance were not correlated, indicating that factors other than distance affected dispersal.     

泛希姬蝽不同地理种群的遗传多样性和遗传分化

泛希姬蝽Himacerus apterus(Fabricius)是半翅目姬蝽科中重要的天敌种类,本文旨在分析泛希姬蝽不同地理种群的遗传多样性和遗传分化情况。利用COI作为标记基因,使用DnaSP、Arlequin、MEGA等软件分析了中国4个省12个种群33个体的单倍型多样性、遗传结构分化、系统发育等。共发现19个单倍型,所有单倍型中仅H1为共享单倍型,为宁夏和陕西共有,且出现频率最高。总体单倍型多样性指数Hd=0.913,核苷酸多样性指数π=0.006,平均核苷酸差异数k=4.083。Tajima's D=-0.853,P>0.100,表明泛希姬蝽未经过种群扩张。AMOVA分析表明种群内的分子变异大于种群间分子变异,变异比例分别为45.393%和36.594%,遗传分化指数均大于0.250,差异水平极显著。泛希姬蝽不同地理种群遗传多样性较高,宁夏与内蒙古、山西、陕西省分组间存在极度的遗传分化。种群间遗传距离和地理距离无相关性,表明地理距离不是影响种群间遗传距离的重要因素。通过比较4个省采集点的环境特点,认为地区间基因流受限和气温、猎物的差异可能是影响遗传分化的重要因素。     

Identifying mechanisms of genetic differentiation among populations in vagile species: historical factors dominate genetic differentiation in seabirds

Elucidating the factors underlying the origin and maintenance of genetic variation among populations is crucial for our understanding of their ecology and evolution, and also to help identify conservation priorities. While intrinsic movement has been hypothesized as the major determinant of population genetic structuring in abundant vagile species, growing evidence indicates that vagility does not always predict genetic differentiation. However, identifying the determinants of genetic structuring can be challenging, and these are largely unknown for most vagile species. Although, in principle, levels of gene flow can be inferred from neutral allele frequency divergence among populations, underlying assumptions may be unrealistic. Moreover, molecular studies have suggested that contemporary gene flow has often not overridden historical influences on population genetic structure, which indicates potential inadequacies of any interpretations that fail to consider the influence of history in shaping that structure. This exhaustive review of the theoretical and empirical literature investigates the determinants of population genetic differentiation using seabirds as a model system for vagile taxa. Seabirds provide a tractable group within which to identify the determinants of genetic differentiation, given their widespread distribution in marine habitats and an abundance of ecological and genetic studies conducted on this group. Herein we evaluate mitochondrial DNA (mtDNA) variation in 73 seabird species. Lack of mutation–drift equilibrium observed in 19% of species coincided with lower estimates of genetic differentiation, suggesting that dynamic demographic histories can often lead to erroneous interpretations of contemporary gene flow, even in vagile species. Presence of land across the species sampling range, or sampling of breeding colonies representing ice‐free Pleistocene refuge zones, appear to be associated with genetic differentiation in Tropical and Southern Temperate species, respectively, indicating that long‐term barriers and persistence of populations are important for their genetic structuring. Conversely, biotic factors commonly considered to influence population genetic structure, such as spatial segregation during foraging, were inconsistently associated with population genetic differentiation. In light of these results, we recommend that genetic studies should consider potential historical events when identifying determinants of genetic differentiation among populations to avoid overestimating the role of contemporary factors, even for highly vagile taxa.     

Genetic differentiation among populations of Sesleria albicans Kit. ex Schultes (Poaceae) from ecologically different habitats in central Europe

As observed for many other plant species, the populations of Sesleria albicans in Central Europe are located in habitats, which differ to a high degree from each other with regard to ecological factors such as nutrients, light and water as well as in type of land use. The species colonizes limestone cliffs, pavements, screes, grazed and mown grasslands, heaths, fens and open woodlands. In this study, we used random amplified polymorphic DNA (RAPD) analysis to investigate the genetic differentiation among 25 populations of S. albicans from six different types of habitat (beech forests, alpine and lowland rocky ridges, lowland screes, fens, calcareous grasslands). With RAPD analysis, 344 fragments could be amplified, of which 95.9% were polymorphic. The level of polymorphism ranged from 29.7 to 56.7% polymorphic bands per population and was correlated with population size. In an analysis of molecular variance (AMOVA), used to detect variation among individuals within populations, among populations from the same habitat and among different habitats, most of the genetic variation was found within populations (62.06%) and among populations from the same habitat (33.36%). In contrast, only a very low level of differentiation could be observed among different habitats (4.58%). The results of our study give only little evidence for an ecotypic differentiation of Sesleria albicans. This differentiation is principally conceivable, but obviously not related to the investigated RAPD loci.     

Low genetic differentiation among reed warbler Acrocephalus scirpaceus populations across Europe

Migratory birds generally have higher dispersal propensity than resident species and are thus expected to show less genetic differentiation. On the other hand, specific migration patterns may promote genetic structure, such as in situations where migratory divides impede random mixing of individuals. Here we investigated population genetic structure and gene flow patterns in a polytypic passerine, the reed warbler Acrocephalus scirpaceus which shows a migratory divide in central Europe. Using ten polymorphic microsatellite loci and extensive sampling we found low but significant overall genetic differentiation (F_ST=0.013, G’_ST=0.078, D=0.063). Hierarchical F‐statistics and barrier analyses showed low but significant genetic differentiation of Iberian populations, and also slight genetic differences across the migratory divide and between subspecies (A. s. scirpaceus and A. s. fuscus). Three individual‐based Bayesian methods, however, inferred a single genetic unit. Our study thus found low levels of genetic differentiation among reed warbler populations but this genetic differentiation was not pronounced enough to detect a clear population structure using the microsatellite data and no prior information on geographic location of the sampled individuals. This result indicates high levels of gene flow and suggests a possibly recent divergence of European populations after a rapid range expansion. Further studies are necessary to assess divergence times and to reveal the evolutionary history of the reed warbler populations.     

High levels of Y-chromosome differentiation among native Siberian populations and the genetic signature of a boreal hunter-gatherer way of life

We examined genetic variation on the nonrecombining portion of the Y chromosome (NRY) to investigate the paternal population structure of indigenous Siberian groups and to reconstruct the historical events leading to the peopling of Siberia. A set of 62 biallelic markers on the NRY were genotyped in 1432 males representing 18 Siberian populations, as well as nine populations from Central and East Asia and one from European Russia. A subset of these markers defines the 18 major NRY haplogroups (A-R) recently described by the Y Chromosome Consortium (YCC 2002). While only four of these 18 major NRY haplogroups accounted for -95% of Siberian Y-chromosome variation, native Siberian populations differed greatly in their haplogroup composition and exhibited the highest phiST value for any region of the world. When we divided our Siberian sample into four geographic regions versus five major linguistic groupings, analyses of molecular variance (AMOVA) indicated higher phiST and phiCT values for linguistic groups than for geographic groups. Mantel tests also supported the existence of NRY genetic patterns that were correlated with language, indicating that language affiliation might be a better predictor of the genetic affinity among Siberians than their present geographic position. The combined results, including those from a nested cladistic analysis, underscored the important role of directed dispersals, range expansions, and long-distance colonizations bound by common ethnic and linguistic affiliation in shaping the genetic landscape of Siberia. The Siberian pattern of reduced haplogroup diversity within populations combined with high levels of differentiation among populations may be a general feature characteristic of indigenous groups that have small effective population sizes and that have been isolated for long periods of time.     

Regional genetic differentiation among northern high-latitude island populations of a broadcast-spawning coral

Knowledge of genetic connectivity is useful for understanding of the recovery potential of coral populations after various disturbances, such as coral mass bleaching. Population genetic studies in corals are mostly restricted to Australian and Caribbean species; studies in the northern Pacific are relatively limited. Using microsatellite markers, the population genetics of Acropora sp. 1 was examined between two regions in Japan, the Okinawa-Aka and Bonin Islands, which are separated by approximately 1,500 km of open water in a high-latitude area. Statistically significant but small genetic differentiation in Acropora sp. 1 was detected between and within these regions. Genetic diversity was not obviously reduced in populations of the Bonin Islands, which are relatively isolated. Thus, some level of connectivity appears to be maintained between the two regions, likely because of the high dispersal ability of this broadcast spawner.     

棉铃虫不同寄主种群遗传分化的RAPD分析

应用RAPD技术对生活于辣椒,烟草和番茄3种不同寄主上的棉铃虫（Helicover pa armigera)种群,并以烟草烟青虫（H.assulta)为外群进行了种群遗传分化的研究,研究结果表明：4个处理内个体间最大的遗传距离均小于处理间最小的遗传距离,烟青虫的遗传距离为0．177－0．346,棉铃虫的辣椒种群为0．289－0．404,烟草种群为0．396－0．505,番茄种群为0．329－0．382,采用UPDGA法进行聚类,并构建系统发育树。各处理成聚的遗传距离为：烟青虫是0．334,棉铃虫的辣椒种群是0．372,烟草种群是0．463,番茄种群是0．360。各处理均首先成聚,棉铃虫与烟青虫成聚的遗传距离（0．703）,稍大于棉铃虫各种群的成聚值（0．639）。上述结果表明,棉铃虫不同寄主种群已经存在明显的遗传分化。     

不同生境条件四合木(Tetraena mongolica)内源激素季节变化及种群差异

四合木(Tetraena mongolica Maxim)是西鄂尔多斯地区特有的单种属古地中海残遗植物.选择了分布区内有代表性的低山、台地、丘陵、高平原、倾斜平原5个典型生境的四合木种群为研究对象.对不同生境四合木种群密度、盖度、年龄结构和根际土壤理化性质进行研究,运用酶联免疫吸附法对四合木叶片内源激素(ABA、IAA、GA3、ZT)季节变化和生境间差异性进行探讨.结果表明:(1)不同生境四合木种群密度、盖度、年龄结构存在显著差异,且低山、台地、丘陵种群所处生境有利于幼苗更新,其密度和盖度均显著大于高平原和倾斜平原种群;(2)四合木根际土壤有机质含量、土壤含水量、营养元素(N、P、K)、微量元素(Fe、Mn、Cu、Zn、Mo、B)含量均较低,pH偏高,体现出贫瘠碱性化的荒漠土壤特点.运用数理统计将5个样地土壤理化性质进行聚类分析,分为两类:低山、台地、丘陵种群为一类(A类),高平原、倾斜平原为一类(B类).方差分析表明:A类样地土壤营养元素(N、P、K)和微量元素(全Fe、Mn、Zn、B、Mo与有效量)、土壤有机质含量及土壤含水量都显著高于B类,而pH值显著低于B类.(3)5个四合木种群ABA和GA3含量均表现为:8月份＞6月份＞5月份;IAA的含量和ZT的含量均表现为:6月份＞8月份＞5月份.方差分析表明:5月份IAA含量表现为在A类样地＞B类样地,8月份ABA含量和GA3含量表现为在A类样地＞B类样地.(4)四合木分布区存在较大的生境异质性,在其长期适应过程中,生境条件差异导致了种群在生理生态方面的分化.四合木种群密度、盖度、年龄结构以及土壤养分、水分和内源激素在生境间存在着差异.