Larval and post-larval development of the branchiopod clam shrimp Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Conchostraca, Spinicaudata)

The larval and post-larval development of Cyclestheria hislopi is examined by SEM. There are at least nine stages (excluding the adult) – six larval and three post-larval stages. The first four stages are passed within the egg-membrane. The larval and the post-larval phase are separated by a profound change in morphology that takes place between stages VI and VII. The larva shifts from a dorso-ventrally flattened 'larval' appearance up to stage VI to a laterally flattened, more 'adult' appearance from stage VII. New morphological data have been revealed by this study, including (1) a large and globular larval dorsal organ; (2) the carapace starts its development from the segments of the first and second maxillae; (3) the anterior ramus of the second antenna in adult Cyclestheria hislopi is the endopod, and the posterior ramus the exopod. Direct development of the brood in Cyclestheria hislopi – unique among conchostracans – is compared with that of the Cladocera. If Cyclestheria is the sister group to the Cladocera, as favoured in this work, the classical neoteny theory of the Cladocera must be reconsidered, as there is no particular similarity between any adults of the Cladocera and any of the larval stages of Cyclestheria . It is suggested that Cyclestheria displays the type of development present in a cladoceran ancestor. A comparison between Cyclestheria and the Upper Cambrian 'Orsten' fossil Rehbachiella kinnekullensis reveals a remarkable similarity in the endite morphology of the trunk limbs.     

Demography of a population of Moina micrura kurz (Crustacea: Cladocera) in a temporary pond,peninsula of paraguaná, Venezuela

A population of M. micrura Kurz from a shallow, muddy and temporary pond, located in Peninsula of Paraguaná, western Venezuela, was studied from filling to drying phase. Population density, age structure, fecundity, and length of females, were determined. This population showed a low population density (< 50 ind/1), a low and density-dependent fecundity (mean eggs/adults = 1.3; mean clutch size = 2.1 eggs + embryos), and low juveniles to adults ratio (0.71). No significant correlation was detected between mean clutch size and mean body length of ovigerous females. Our results suggest effects of food limitations, and fish predation on demographic parameters of this population. Still, in unfavourable conditions, some demographics features associated to opportunistic species were evident.     

External morphology of the male of Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Spinicaudata), with a comparison of male claspers among the Conchostraca and Cladocera and its bearing on phylogeny of the 'bivalved' Branchiopoda

The adult male of Cyclestheria hislopi, sole member of the spinicaudate conchostracan clam shrimp family Cyclestheriidae and a species of potential phylogenetic importance, is described for the first time. Several previously unknown features are revealed. Among these are (1) the morphology of the dorsal organ, which is roughly similar in shape to the supposedly homologous structure in other clam shrimps but bears a relatively large, centrally located pore unique to the species; (2) an anterior cuticular pore presumably leading to the ‘internal’ space surrounding the compound eyes, and thereby homologous to the same pore in other clam shrimps and in the Notostraca; (3) the spination and setation of the antennae and thoracopods, and (4) the mature male first thoracopods (claspers). The male claspers are paired and essentially equal in size and shape on right and left sides of the body. The second pair of thoracopods are not modified as claspers, a situation different from all other spinicaudate families but shared (plesiomorphic we propose) with the laevicaudatans and most cladocerans. The claspers bear a field of special spine-like setae on the extremity of the ‘palm’; this setal type, previously unrecognized, is unique to Cyclestheria. The palm of the clasper also bears two palps (one very small), as in other conchostracan species (both laevicaudatans and spinicaudatans). The movable finger of the clasper, modified from the thoracopod endopod, bears a row of long setae along its outer extremity, also unique. Cyclestheria exhibits a mixture of characters, some unique and others typical of the Spinicaudata (Conchostraca). Cladoceran clasper types are briefly reviewed. as are the claspers in the Spinicaudata and Laevicaudata (Conchostraca). Morphology of the clasper of Cyclestheria shows typical spinicaudate characters. It is suggested that claspers on the first thoracopods may be a synapomorphy for the Conchostraca and the Cladocera. The possible role of Cyclestheria or a Cyclestheria-like ancestor in cladoceran phylogeny is briefly discussed in light of recent suggestions (Martin and Cash-Clark, 1995) of cladoceran monophyly and possible ancestral relationships with this genus. Some possibilities concerning the phylogenetic position of Cyclestheria–either as a sister group to the rest of the Spinicaudata or as a sister group to the Cladocera—are discussed.     

Field and laboratory studies on Daphnia carinata King (Cladocera: Daphnidae) from a seasonal tropical pond

The life history and seasonal variation in egg production of Daphnia carinata King, with reference to the seasonal variation in physico-chemical as well as biological factors of a tropical temporary pond, were studied. Laboratory observations on the life history of D. carinata were also made. The seasonal events of D. carinata are discussed in relation to recent studies on Cladocerans.     

Life history and population dynamics of the western mosquitofish: a comparison of natural and introduced populations

Life history and population dynamic patterns of Gambusia affinis in southeastern Louisiana varied spatially and temporally in 1990 and 1991, but were consistent with previous reports of this species in the southern regions of its natural range. Several differences exist among populations in different geographic regions within the United States, as reported in the literature, which do not follow a' native v . introduced' dichotomy: (1) brood size decreases and offspring size increases from north to south; (2) large overwintered females in northern areas produce more broods within a season than those in southern populations, while the reverse is true for young-of–year females; (3) minimum size at first reproduction follows a seasonal pattern within populations, but tends to be smaller in southern and larger in northern and Hawaiian populations; (4) synchronous reproduction early in the season is characteristic of northern populations, but does not occur in southern areas; and (5) mosquitofish reproduce year–round in Hawaii, while 'southern' populations within the continental U.S. cease reproduction during winter.     

Cyclestheria hislopi (Crustacea: Branchiopoda): A group of morphologically cryptic species with origins in the Cretaceous

Cyclestheria hislopi is thought to be the only extant species of Cyclestherida. It is the sister taxon of all Cladocera and displays morphological characteristics intermediate of Spinicaudata and Cladocera. Using one mitochondrial (COI) and two nuclear (EF1α and 28S rRNA) markers, we tested the hypothesis that C. hislopi represents a single circumtropic species. South American (French Guiana), Asian (India, Indonesia, Singapore) and several Australian populations were included in our investigation. Phylogenetic and genetic distance analyses revealed remarkable intercontinental genetic differentiation (uncorrected p-distances COI > 13%, EF1α > 3% and 28S > 4%). Each continent was found to have at least one distinct Cyclestheria species, with Australia boasting four distinct main lineages which may be attributed to two to three species. The divergence of these species (constituting crown group Cyclestherida) was, on the basis of phylogenetic analyses of COI and EF1α combined with molecular clock estimates using several fossil branchiopod calibration points or a COI substitution rate of 1.4% per million years, dated to the Cretaceous. This was when the South American lineage split from the Asian–Australian lineage, with the latter diverging further in the Paleogene. Today’s circumtropic distribution of Cyclestheria may be best explained by a combination of Gondwana vicariance and later dispersal across Asia and Australia when the tectonic plates of the two continents drew closer in the early Miocene. The lack of morphological differentiation that has taken place in this taxon over such a long evolutionary period contrasts with the high level of differentiation and diversification observed in its sister taxon the Cladocera. Further insights into the evolution of Cyclestheria may help us to understand the evolutionary success of the Cladocera.     

Genetic diversity within a declining natural population of Ferocactus histrix (DC) Lindsay

Ferocactus histrix is a barrel cactus that is widespread in Mexico. A population located in Llanos de Ojuelos, a semiarid zone representative of many disturbed regions in north‐central Mexico, was studied. Over a period of 10 years (1997 to 2007), the average number of individuals decreased from 21.95 to 3.53 plants per 300 m². A change in population size structure was also registered over this period of time. In 2008, a plot selected on the basis of plant abundance was established within the population and a genetic analysis was conducted with ISTR and ISSR markers. This analysis revealed low levels of genetic diversity (expected heterozygosity (H_E) = 0.073, Shannon index (I) = 0.113 and H_E = 0.178, I = 0.271, respectively) compared with those of most studied cacti species. The genetic diversity between the different life stages was also evaluated, and a gradual decrease in levels of genetic variation was observed from adults to juveniles and seedlings (H_E = 0.130, I = 0.192 to H_E = 0.103, I = 0.157). These differences, however, were not significant. Loci fixation and a decrease in the frequency of rare alleles were observed in seedling and juvenile classes. The decline in genetic variation may be associated with recent bottlenecks experienced by the population of F. histrix. If the sizes of local populations of F. histrix continue to decrease, genetic variation will be gradually lost, and the risk of extinction will increase.     

Daphnia (Ctenodaphnia) brooksi (Crustacea: Cladocera), a new species from eastern Utah

A single population of an unusual ctenodaphnid was sampled in a shallow, turbid, temporary pond in eastern Utah in 1965. The animals resemble the African Daphnia (Ctenodaphnia) barbata, but show several morphological differences, and are therefore given the new name Daphnia (Ctenodaphnia) brooksi. Repeated efforts to collect this species since 1965 have failed, suggesting either the species is very rare, or the type population represented an instance of long-distance migration.     

Observations on the population dynamics of Potamothrix hammoniensis (Michaelsen, 1901) (Tubificidae,Oligochaeta) in Lake Isacova in the Danube Delta

The Danube Delta is one of the widest wetland systems in Europe and Lake Isacova is one of the biggest lakes in the Delta. The oligochaete community in the Lake comprised 52% of the total benthic fauna and Potamothrix hammoniensis (Michaelsen, 1901) (Tubificidae, Oligochaeta) represented more than 90% of the oligochaetes sampled. During September 1991 – August 1994, the proportion of ovigerous individuals of P. hammoniensis represented less than 20% of the total population, with localised differences in the Lake occurring over time. Breeding and cocoon production in the study period started in March of the year, when the water temperature was about 7 °C, and lasted until May 1992 and June 1993, respectively. The newly hatched individuals reached the highest proportion in May. Although large individuals were found again by the end of September (1991) and the beginning of October (1993), no spermatozeugmata in their spermathecae or cocoons were observed during November and October, respectively. Member of this cohort bred and started cocoon deposition during the following spring, after about 11 months of maturation (from April to March). A second, less intensive period of breeding was recorded during August 1992 and this lasted until the beginning of September 1993. However, cocoons from this latter period did not show embryonic growth and hatching until the autumn floods bring oxygenated water to the bottom level. This resulted in a period of rapid development followed by the mass hatching of cocoons. These specimens needed a maximum of 9 month (from October to July) to reach sexual maturity.     

Experimental studies on the development of Lernaeocera branchialis (Copepoda: Pennellidae): population processes from egg production to maturation on the flatfish host

Quantitative population dynamical information derived from laboratory- and field-based experiments is provided for the fish-parasitic copepod, Lernaeocera branchialis, infecting flounder (Platichthys flesus) and whiting (Merlangius merlangus). Adult, post-metamorphosis females from whiting can produce more than one set of egg-strings. The mean number of eggs in each egg-string pair was 1445. At 10 °C these eggs took about 12.7 d after extrusion before hatching of NI nauplii began. Hatching took up to 12 days to be completed with an exponentially declining pattern of output over this period. In the laboratory about 44% of the egg-string egg population successfully passed through the NI to NII nauplius moult and the NII to copepodid moult to produce infective copepodids, a process lasting about 2 d. The non-feeding copepodids had a maximum survival time at 10 °C of 18 d, with a time to 50% survival of 7.5 d. In laboratory infection experiments at 10 °C, copepodids infected flounder and passed through all their developmental stages to adulthood and copulation in a minimum of 25 d. Field experiments on the seabed off Lowestoft in June 1987 with a sea temperature of about 16 °C suggested that the developmental period in those conditions could be as short as 11 d. Previously uninfected flounder in the field experiments became naturally infected with copepodids at a mean rate of not less than 30 parasites per fish d^–1.     

Resource partitioning in two coexisting cladocerans,Daphnia magna and Scapheloberis kingi (Anomopoda: Daphniidae), in north-eastern Algeria

Life-history traits of two coexisting cladocerans, Daphnia magna Straus and Scapheloberis kingi Sars, inhabiting a temporary pond in north-eastern Algeria were monitored in 2013 under laboratory conditions. Their life histories were compared for differences in traits such as age and size at first reproduction, size of neonates, brood size, number of broods per female, total life span and intrinsic rate of increase (r_m). Data were recorded during their entire life cycle. Daphnia magna, the larger species, could possibly be more successful in colonising temporary habitats than S. kingi because it allocates more energy to reproduction. Scapheloberis kingi, the smaller species, starts reproduction early, resulting in a smaller brood size and a shorter life span with fewer broods. Consequently, S. kingi produces a smaller number of neonates during its lifetime and has a lower r_m. In contrast, D. magna delays reproduction but produces a larger brood size and, because it is longer-lived, produces more broods and so produces a greater number of neonates and has a higher r_m over its lifetime.     

Seasonal Dynamics of a Chironomus plumosus (L.) (Diptera,Chironomidae) Population from a Fish Pond in Southern Bohemia

A population of Chironomus plumosus (L.) from a fish pond has been investigated for two years. Quantitative benthic samples and emergence traps were used to study the seasonal dynamics. Effect of some factors on the duration of development was studied in laboratory experiments. Data on larval abundance, length frequency analysis and emergence of adults suggest a bivoltine life cycle. The population of C. plumosus investigated showed a pronounced tendency to dormancy, even under long-day conditions. Factors regulating the bivoltine life cycle are discussed.     

Studies on population dynamics and spatial distribution of leafhoppers in vineyards (Homoptera: Cicadellidae)

Thirty-two species of Cicadellidae, including the Macropsinae, Agalliinae, Penthimiinae, Aphrodinae, Cicadellinae, Typhlocybinae and Deltocephalinae, 10 of which were already known as phytoplasma vectors, were captured in vineyards using yellow sticky traps. Adult population dynamics of the most abundant species of Penthimiinae and Deltocephalinae were studied over the whole growing season. Penthimia nigra was captured in May and June, Anoplotettix fuscovenosus in June-August, Fieberiella florii in August-October, Macrosteles sexnotatus in May and October, Scaphoideus titanus in July-September, Thamnotettix spp. (Th. confinis, Th. dilutior, Th. exemtus, Th. zelleri) in April-June, while Euscelidius variegatus, Neoaliturus fenestratus, Platymetopius major and Psammotettix spp. (P. alienus, P. confinis) were trapped throughout the growing season. The aggregation level of the above species was investigated by means of Taylor's power law. A. fuscovenosus showed a nearly random distribution in vineyards (0.95 < b < 1.11), while N. fenestratus, P. major and S. titanus were strongly aggregated (1.32 < b < 1.81). The other species showed intermediate levels of aggregation (1.12 > b < 1.32). The results indicate that at least six Deltocephalinae species, A. fuscovenosus, E. variegatus, F. florii, M. sexnotatus, N. fenestratus and S. titanus, known as phytoplasma vectors and commonly found in vineyards, could play a role in Grapevine Yellows (GY) epidemiology. GY transmission trials with these species are needed.     

The population ecology of Amorbus Dallas (Hemiptera: Coreidae) species in Australia

Species of Amorbus Dallas (Hemiptera: Coreidae) appear to exhibit a tight link between oviposition preference and nymphal performance: females apparently select vigorous plant modules to facilitate the development of their offspring. Such behaviour suggests that these insects should exhibit population dynamics consistent with the latent classification proposed by Price et al. (1990). While this empirical hypothesis is intuitively appealing it does not appear to incorporate current population dynamics theory. Berryman's ecodynamics (1992) offers the potential to describe a species' population dynamics which is grounded in a quantitative theoretical framework. The population ecology of Amorbus species from Australia is considered in relation to these hypotheses.     

天目山自然保护区银杏天然种群生命表

以种群生命表和生存分析理论为基础,采用空间代替时间法和分段匀滑技术,编制浙江天目山自然保护区银杏天然种群特定时间生命表,绘制其死亡率曲线、消失率曲线、存活曲线和生存函数曲线,分析种群数量动态变化.结果表明:银杏种群结构存在波动性,趋于Deevey Ⅱ型,其成年阶段的个体较丰富;银杏种群死亡率和消失率曲线变化趋势基本一致...     

种群生存力分析（PVA）的方法与应用

随着人们对资源的加速利用,生境丧失和破碎化导致物种濒危问题日益严重.以岛屿生物地理学为理论起源的种群生存力分析（PVA）,通过分析和模拟种群动态过程并建立灭绝概率与种群数量之间的关系,为濒危物种保护提供了重要的理论依据和研究途径.在过去的几十年中,种群生存力分析已成为保护生物学中一项重要的研究内容.目前种群生存力分析发展稳定,但对其实际预测能力和准确性尚存质疑,应用方面也有待进一步发展.种群生存力分析的进一步完善还需要在理论和方法上的创新,特别是籍于景观生态学和可持续性科学的理念,将空间分析手段、经济社会因素纳入到物种和种群的预测和管理上,从而使其具有更完整的理论基础和更高的实用价值.为此,本文对种群生存力分析的历史、基本概念、研究方法、模型应用和准确性进行了综述,并提出了有关的研究展望.     

自然种群中混沌的检测及其在种群动态研究中的意义

混沌现象广泛地存在于自然界,20世纪70年代以来,通过大量的生物模型模拟说明混沌也存在于生物系统中。几十年来生态学家一直在努力寻找混沌在自然生态系统存在的证据,但所获不多,这是源于自然的现实还是由于检测方法的不当和数据的局限?一直困扰着生态学家,自然界中对混沌的检测成为一个要点,也是一个难点。在概述混沌概念和性质的基础上,着重介绍目前在自然生态系统检测混沌的方法,对各种方法的应用条件和范围进行了概述。这些方法包括功率谱法、时间序列的自相关函数分析、模型参数估计、庞加莱截面法、全局和局域李雅普若夫特征指数的估计、吸引子关联维的确定、非线性预测。大量研究结果显示,虽然在自然界检测到的混沌的例子还不多,但其存在却是不容怀疑的。问题是什么样的系统在什么样的条件下会出现混沌?研究表明食物链的结构、种群的迁入和迁出、环境噪音都会对种群的复杂性动态特征产生影响。混沌动态可能对产生系统的多样性和适应性有利,它比随机系统对外界干扰的抵抗能力更强。自然界的变化和系统的维持是持续性和混沌相互矛盾统一的结果。害虫种群复杂性动态的研究为害虫的管理提供了更多的理论依据。混沌控制的理论和方法有可能为害虫管理提供新的思路和途径。在孤立的种群中,混沌会增加种群的灭绝概率,而在集合种群中,混沌动态降低了各局域种群的同步性和同时灭绝的倾向,所以混沌虽然能增加局域种群灭绝的概率,但却能减少整个集合种群灭绝的概率。系统结构及其时空动态与混沌及种群灭绝之间的关系,是保护生物学及生物多样性保护研究的一个重要方面。今后的研究应更多地从种群、群落、生态系统及景观不同层次上的时空动态入手,利用3S等信息技术和空间动态分析方法,研究复杂性动态产生的条件及其在系统调控中的作用机制。     

小麦间作豌豆对麦长管蚜及其主要天敌种群动态的影响

为探索麦田物种多样性对麦长管蚜Sitobion avenae的生态调控效应,于2007年10月至2008年7月在河北省廊坊市进行田间小区试验,系统调查了豌豆与小麦分别以2∶2,2∶4,2∶6和2∶8比例行间作(分别记作2-2间作、2-4间作、2-6间作和2-8间作)种植模式下麦长管蚜种群数量的时序动态, 同时分析了麦田主要天敌种群数量的时序动态、丰富度、多样性指数及均匀度的变化。结果表明：在麦长管蚜发生高峰期,小麦与豌豆间作麦长管蚜无翅蚜的百株蚜量（平方根转换）极显著低于单作田(P<0.01),其中小麦单作（77.38）>2-2间作（68.62）>2-4间作（68.51）>2-8间作（65.19）>2-6间作（64.94）。尽管不同种植模式下,麦长管蚜主要天敌的动态变化趋势基本一致,但间作处理的优势天敌瓢虫类和蚜茧蜂类均有较高的种群密度,天敌群落的丰富度明显提高,Shannon-Wiener多样性指数增加,但均匀度下降。总之,小麦间作豌豆不仅有效降低了麦长管蚜的种群数量,同时也增加了天敌控制害虫的稳定性和可持续性。     

Sexually transmitted disease epidemics in a natural insect population

1. The epidemiology of sexually transmitted diseases (STDs) in human and domesticated populations is well documented. However, there has been less study of STDs in natural populations. 2. We investigated STD dynamics in the model system involving a host from the most speciose group of animals: the insects. We investigated temporal variation in the prevalence of the sexually transmitted mite Coccipolipus hippodamiae on its ladybird host, Adalia bipunctata. 3. Field surveys over two seasons showed a repeated pattern of a profound epidemic in the overwintered cohort and a later prevalence decline. 4. In order to understand the key factors in the dynamics of this system we studied the phenology of the host and simulated parasite dynamics in the overwintered cohort using a model with within-sex homogeneity in mating rate and field-measured parameter values. The similarity of natural and simulation prevalence levels allowed us to carry out sensitivity analysis and hence to identify the key determinants of the dynamics. 5. The observed pattern of periodic extreme prevalence combined with system persistence probably results from time lags in host recruitment and widespread promiscuity. 6. Our findings improve our understanding of STDs in natural populations and illustrate the importance of examining seasonality and time delays in population dynamics in order to fully understand the characteristics of natural populations and their parasites.     

鄂西北濒危植物红椿天然种群动态分析

采用相邻格子法对分布于鄂西北的3个红椿(Toona ciliata Roem.)天然种群(竹山、谷城T1和谷城T2)进行统计;采用立木径级结构代替种群年龄结构的方法,分析了各种群不同龄级的个体数量动态指数( Vn )、静态生命表及存活曲线,并对3个种群进行谱分析。结果表明：3个红椿种群均属于增长型种群,自然状态下竹山、谷城T1和谷城T2种群个体数量动态指数分别为46.27%、53.46%和37.71%,标准化存活曲线分别为Deevey Ⅲ型、DeeveyⅡ型和Deevey Ⅱ型。3个种群第2龄级﹝2.5 cm≤胸径(DBH)<7.5 cm〕幼树的死亡率均较高,竹山种群第3龄级(7.5 cm≤DBH<12.5 cm)幼树的死亡率最高,谷城T1种群第7龄级(27.5 cm≤DBH<32.5 cm)大树的死亡率最高,谷城T2种群第6龄级(22.5 cm≤DBH<27.5 cm)中树的死亡率最高;3个种群第1龄级( DBH<2.5 cm)和第2龄级个体的平均期望寿命均较高。竹山、谷城T1和谷城T2种群的基波振幅分别为1.0616、1.0971和0.7882,明显的小周期分别出现在第4、第2和第4波序,表明分布于鄂西北的红椿天然种群更新存在着周期性,且存在小周期的多谐波叠加,种群波动与龄级的Vn值相吻合。种群动态分析结果表明：由于红椿的强阳性生理特征,其天然种群受环境筛抑制和环境干扰,造成幼树个体损失和中龄级个体不足,这是造成红椿濒危的主要因素,因此,建议加强人为正向“干扰”以制造林窗、增强种群天然更新能力、引种造林,以保护和利用红椿这一濒危植物资源。