Oviposition strategies of conifer seed chalcids in relation to host phenology

Insects are considered the most important predators of seed cones, the female reproductive structures of conifers, prior to seed dispersal. Slightly more than 100 genera of insects are known to parasitize conifer seed cones. The most diverse (i.e., number of species) of these genera is Megastigmus (Hymenoptera: Torymidae), which comprises many important seed pests of native and exotic conifers. Seed chalcids, Megastigmus spp., lay eggs inside the developing ovules of host conifers and, until recently, oviposition was believed to occur only in fertilized ovules. Ovule development begins just after pollination, but stops if cells are not fertilized. The morphological stage of cone development at the time of oviposition by seed chalcids has been established for many species; however, knowledge of ovule development at that time has been documented for only one species, M. spermotrophus. Megastigmus spermotrophus oviposits in Douglas-fir ovules after pollination but before fertilization. Unlike the unfertilized ovules, those containing a M. spermotrophus larva continue to develop, whether fertilized or not, stressing the need to broaden our understanding of the insect–plant interactions for this entire genus. To achieve this task, we reviewed the scientific literature and assembled information pertaining to the timing of oviposition and to the pollination and fertilization periods of their respective host(s). More specifically, we were searching for circumstantial evidence that other species of Megastigmus associated with conifers could behave (i.e., oviposit before ovule fertilization) and impact on female gametophyte (i.e., prevent abortion) like M. spermotrophus. The evidence from our compilation suggests that seed chalcids infesting Pinaceae may also oviposit before ovule fertilization, just like M. spermotrophus, whereas those infesting Cupressaceae seemingly oviposit after ovule fertilization. Based on this evidence, we hypothesize that all species of Megastigmus associated with Pinaceae can oviposit in unfertilized ovules, whereas those exploiting Cupressaceae cannot, and thus oviposit only in already fully developed fertilized seeds. Furthermore, we predict that the presence of a larva in unfertilized ovules of all Pinaceae will influence the development of the female gametophyte by preventing its abortion. This influence on the Pinaceae can be interpreted as an ability to parasitize any of the potential seeds present in a seed cone, and as such represents a much more efficient oviposition strategy than searching and locating only fertilized seeds. Concomitantly, this ability has likely led to an overestimation of the impact of the species of seed chalcid infesting Pinaceae on seed production.     

Learned arbitrary responses to light in mice without rods or cones

The aim of this investigation was to discover whether mice lacking classical photoreceptors (rods and cones) can nevertheless be trained to respond to light. Mice with the coneless ( cl) transgene have an attenuated diphtheria toxin fused to a cone opsin promotor. Mutant mice homozygous for the retinal degeneration ( rd) gene undergo loss of their rods. By mating these two strains, mice lacking both cones and rods can be generated (Lucas et al. 1999). Such coneless-rodless mice were able to use light as a signal to make a behavioural response to avoid impending shock. Nevertheless, especially initially, they used the light as a cue less often than wildtype controls, indicating that normally the rods and cones are used for such responses. However, other photoreceptors are able to take over this role to some extent. When the lights were covered with opaque material, the performance of rodless-coneless mice dropped to chance level, indicating that they had been using the light as a cue for avoidance.     

Germination of Deyeuxia angustifolia as affected by soil type, burial depth, water depth and oxygen level

Deyeuxia angustifolia is a dominant species in the Sanjiang Plain, the largest freshwater marsh wetland in China. However, this species has declined because of great environment changes. In the effects of sea-level rise and greenhouse gas, magnitude and frequency of flood and rate of deposit in wetland increased greatly. Thus, in this paper, effects of soil environment (soil type, burial depth, water depth and oxygen concentration) on seed germination of D. angustifolia were investigated. Both soil type and burial depth affected seedling emergence. Seedlings emerged through 1-, 2-, 4-mm sand, and at 1-and 2-mm mud. Regardless of soil, seedling emergence time increased and emergence percentage decreased with increasing burial depth. For example, seedlings started to emerge on the 4th day and the final emergence percentage was 30% when covered with1-mm mud, whereas the initial emergence time was on the 6th day and the final emergence percentage was only 8% when covered with 2-mm mud. At the same burial depth, emergence percentage was higher in sand than in mud. Increasing water depth inhibited seed germination. Germination percentage in 2-cm water level (20%) was 1.2 times higher than that in 12-cm water level (9%). Oxygen concentration also affected germination. In the 21% oxygen concentration, germination was started on the 2nd day and the germination percentage was 36%, while seed started to germinate on the 4th day and the germination percentage was only 3% at the 7% oxygen concentration. These data indicate that seed germination of D. angustifolia was highly sensitive to soil type, burial depth, water depth, oxygen concentration, and these responses may be an explicit indication of maladjustment to environment changes, and an important reason accounting for the decline of this species in the Sanjiang Plain.     

Soil seed bank and seedling populations of Hordeum murinum and Cardaria draba in saffron fields

Geostatistical techniques were used to characterize the spatial relationship between Hordeum murinum and Cardaria draba seedling and soil seed bank over the entire growing season of 2004–2005 in three saffron (Crocus sativus) fields, located in Southern Khorasan (33°N latitude, 57°E longitude), Iran. The maps of H. murinum seed bank density corresponded moderately to those seedling density in a and strongly to those in b and c fields. The emergence percentage of C. draba was higher than for H. murinum in all fields. Semivariograms showed spatial autocorrelation in seed bank and seedling populations of H. murinum and C. draba in all fields. Grey-scale field maps of C. draba seed banks corresponded visually to maps of seedling populations and could have been used to target control efforts, but visual correspondence between H. murinum seed bank and seedling maps was poor.     

Seed drops and caches by the harvester ant Messor barbarus: do they contribute to seed dispersal in Mediterranean grasslands?

 To determine whether the harvester ant Messor barbarus acts as a seed disperser in Mediterranean grasslands, the accuracy level of seed processing was assessed in the field by quantifying seed drops by loaded foragers. In the vicinity of exploited seed patches 3 times as many diaspores were found as in controls due to seed losses by foragers. Over trails, up to 30% of harvested seeds were dropped, singly, by workers but all were recovered by nestmates within 24 h. Seeds were also dropped within temporary caches with very few viable diaspores being left per cache when ants no longer used the trail. Globally, ant-dispersed diaspores accounted for only 0.1% of seeds harvested by M. barbarus. We discuss the possible significance for grassland vegetation of harvester-ant-mediated seed dispersal. Received: 26 January 2000 / Accepted in revised form: 20 June 2000     

Role of post-dispersal seed and seedling predation in establishment of dandelion (Taraxacum agg.) plants

Dandelion Taraxacum agg. (formerly Taraxacum officinale G.H. Weber ex Wiggers) is a common weed species associated with pastures, grasslands and no-tillage cropping systems throughout its native range in Europe, and more recently introduced into North America, Australasia and elsewhere. Following wind-dispersal from the parent plant, its seeds are subject to predation from a host of invertebrate predators. Similarly, seedling predation may also significantly limit dandelion recruitment. Although such post-dispersal mortality is central to our understanding of dandelion population dynamics and therefore weed control, the precise spatio-temporal role played by different putative seed and seedling predators is poorly understood. Here we studied how seed viability, and seed and seedling predation influenced dandelion recruitment at two contrasting sites in central Europe. The abundance in the field and seed and seedling consumption in the laboratory were determined for the main groups of predators—ground beetles (Coleoptera: Carabiade), terrestrial isopods (Isopoda: Oniscidea) and molluscs (Gastopoda: Pulmonata). At particular sites, seed viability and seedling predation were negatively correlated while the percentage of seeds that succumbed to seed predation was similar. Combined factors accounted for the death of 98% and 87% of exposed seeds. Ground beetles (particularly Amara spp.) and terrestrial isopods (Armadillidium vulgare) were efficient and dominant seed predators, while slugs (Arion lusitanicus) and isopods were important predators of seedlings. While there was no seasonal trend in the intensity of seed predation it decreased towards autumn in parallel with the feeding activity of the declining population of A. lusitanicus. The mortality factors thus varied in their importance, largely between sites and less with the course of the season. Although seed inviability, seed and seedling predation did not stop the recruitment of dandelion seedlings they are crucial factors limiting dandelion populations. Methods of increasing the efficiency of predation of seed as a means of managing weeds are worthy of further study, particularly in areas where dandelion is an invasive species.     

松果采摘对小兴安岭主要林型红松土壤种子库和幼苗库的影响

为了探讨人为采摘松果对小兴安岭主要林型红松(Pinus koraiensis)土壤种子库和幼苗库的影响,选择阔叶红松林以及与阔叶红松林相邻的红松人工林、落叶松(Larix gmelini)人工林、白桦(Betula platyphylla)林和云冷杉林,各设置10 m×240 m的样带,调查了红松土壤种子库和幼苗库。主要结果如下:①主要林型间红松土壤种子库数量具有明显的差异,阔叶红松林最多,落叶松人工林次之,白桦林最少;②鼠类取食过或被破坏等动物侵害的种子占81.9%～90.4%,完好种子只有在阔叶红松林和落叶松人工林中发现,分别为4.3%和4.9%;③红松种子主要分布在0～10 cm层中(71.4%～91.3%);④红松幼苗库的密度云冷杉林最高(1 613株.hm-2),红松人工林最低(167株.hm-2),其中阔叶红松林(296株.hm-2)和白桦林(854株.hm-2)的幼苗密度分别为采摘前的1/68～1/9和1/9～1/4.5;⑤从龄级分布上看,松果采摘前阔叶红松林低龄级幼苗的数量较多,随着龄级的增大明显减少,呈倒J型分布;白桦林各龄级幼苗密度相差不大。人为采摘松果后,阔叶红松林各龄级间密度相差不大;白桦林呈倒J型分布。     

Oviposition markers in Callosobruchus maculatus F. and Callosobruchus rhodesianus pic. (coleoptera,bruchidae): Assymmetry of interspecific responses

The bean weevils Callosobruchus maculatus (F.) and C. rhodesianus (Pic.) both laid fewer eggs on previously infested adzuki beans than on fresh beans, even after eggs were removed. A variety of experimental treatments demonstrated the existence of an oviposition marker with ether soluble components. Callosobruchus rhodesianus was inhibited from ovipositing by the C. maculatus marker, but not vice versa.     

Internal dispersal of seeds by waterfowl: effect of seed size on gut passage time and germination patterns

Long distance dispersal may have important consequences for gene flow and community structure. The dispersal of many plants depends on transport by vertebrate seed dispersers. The shapes of seed shadows produced by vertebrates depend both on movement patterns of the dispersers and on the dynamics and effects of passage through the disperser’s gut (i.e. the retention time, survival and germination of ingested seeds). A combination of experiments with captive waterbirds and aquatic plant seeds was used to analyse the following: (a) the effects of inter- and intra-specific variation in seed size and duck species on seed retention time in the gut and (b) the relationship between retention time and the percent germination and germination rates of seeds. Among the three Scirpus species used, those with smaller seeds showed higher survival after ingestion by birds and longer retention times inside their guts than those with larger seeds. For Potamogeton pectinatus, only seeds from the smaller size class (<8 mg) survived ingestion. Retention time affected the percent germination and germination rate of Scirpus seeds but in a manner that varied for the different plant and bird species studied. We recorded both linear and non-linear effects of retention time on percent germination. In addition, germination rate was positively correlated with retention time in Scirpus litoralis but negatively correlated in Scirpus lacustris. Small seed size can favour dispersal over larger distances. However, the effects of retention time on percent germination can modify the seed shadows produced by birds due to higher percent germination of seeds retained for short or intermediate periods. The changes in dispersal quality associated with dispersal distance (which is expected to be positively related to retention time) will affect the probability of seedling establishment over longer distances and, thus, the spatial characteristics of the effective seed shadow.     

Geographic variations in seed dispersal by ants: are plant and seed traits decisive?

The effect of local ant species on the dispersal success of a myrmecochorous plant, Helleborus foetidus, was analyzed in two populations of the Iberian Peninsula (Caurel and Cazorla, respectively). The contribution of the various local ant species to dispersal was very unequal. While 5 and 19 ant taxa visited the plants of Caurel and Cazorla, respectively, most removal activity (67 and 80%) was performed by two species only (Formica lugubris and Camponotus cruentatus, respectively). Visits by dispersers were also unequally distributed between neighboring plants. While some plants were always visited during the period of seed release, others were never visited. A regression model indicated that this pattern might be explained by two plant traits: ants preferred to visit plants that released more seeds and whose elaiosomes were richer in oleic acid. Although it has long been known that this compound triggers removal by ants, it is the first demonstration that quantitative variations in elaiosome traits contribute to variation in dispersal success. Finally, other variables being equal, morphological traits (seed size, elaiosome size, and elaiosome/seed size ratio) did not affect ant behavior. Although myrmecochory has long been considered a diffuse interaction, our results support the idea that, at local scale, a limited number of ant species may be decisive to its evolution.     

A unique strategy of host colony exploitation in a parasitic ant: workers of<Emphasis Type="Italic"> Polyrhachis lama</Emphasis> rear their brood in neighbouring host nests

The formicine ant Polyrhachis lama is a social parasite, exploiting its ponerine host ant species Diacamma sp. In most social parasitic associations, the parasitic species are closely related to their host species group, evolving directly from independent ancestors of the host species. However, in the Polyrhachis lama–Diacamma sp. association, the associated species belong to different ant subfamilies. Based on preliminary field surveys, we had presumed that P. lama might have given up its reproductive division of labour, i.e. workers would be able to produce males as well as workers and females parthenogenetically. In this study, this hypothesis was disproved: Polyrhachis lama workers cannot be fertilized and are only able to produce males. In the host–parasite association originating from nests possessing a P. lama queen, workers penetrate surrounding Diacamma sp. nests, carrying brood for rearing within these satellite nests. In this peculiar way, a single P. lama colony is able to exploit several Diacamma sp. colonies simultaneously.     

Field evidence for non-host predator avoidance in a manipulated amphipod

Manipulative parasites are known to alter the spatial distribution of their intermediate hosts in a way that enables trophic transmission to definitive hosts. However, field data on the ecological implications of such changes are lacking. In particular, little is known about the spatial coexistence between infected prey and dead-end predators after a parasite-induced habitat shift. Here, we used an Amphipoda (Gammarus roeseli)–Acanthocephala (Polymorphus minutus) association to investigate how infection with a manipulative parasite affects the predation risk by non-hosts within the invertebrate community. First, we collected invertebrates by sampling various natural habitats and calculated the distribution amplitude of amphipods according to their infection status. Infection with P. minutus significantly reduced the habitat breadth in G. roeseli, parasitised individuals being mainly found in floating materials whereas uninfected ones were widespread throughout the sampled habitats. Second, to test if these changes also affect the risk for P. minutus to be ingested by non-hosts, we estimated the predation risk experienced by G. roeseli within the macro-invertebrate community. The habitat overlap between potential invertebrate predators and G. roeseli showed that the spatial probability of encounter was lower for P. minutus-infected amphipods than for uninfected conspecifics. For the first time, to our knowledge, a study used ecological tools to bring field evidence for the spatial avoidance of dead-end predators in a manipulated amphipod.     

Mutualistic Benefits Generate an Unequal Distribution of Risky Activities Among Unrelated Group Members

Recent studies provide a new challenge to the adequacy of theories concerning the evolution of cooperation among nonrelatives: some individuals perform high-risk activities while others do not. We examined a communal hymenopteran species, Lasioglossum (Chilalictus) hemichalceum, to determine why group members engaged in demonstrably risky activities (foraging) tolerate the selfish behavior (remaining in the nest) of unrelated nestmates. Experimental removal of adult females indicated that their presence is required for the protection of brood from ant predators. Nonforagers ensure the continued presence of adults in the nest if the risk-taking foragers die, thereby safeguarding the survival of forager offspring. This results in an unequal distribution of risky activities within social groups in which avoidance of risky activities by some group members is ultimately beneficial to risk takers. Received: 10 June 1997 / Accepted in revised form: 25 May 1998     

Sand-swimming behaviour reduces ectoparasitism in an iguanian lizard

Social interactions may shape brain development. In primitively eusocial insects, the mushroom body (MB), an area of the brain associated with sensory integration and learning, is larger in queens than in workers. This may reflect a strategy of neural investment in queens or it may be a plastic response to social interactions in the nest. Here, we show that nest foundresses—the reproductive females who will become queens but are solitary until their first workers are born—have larger MBs than workers in the primitively eusocial sweat bee Augochlorella aurata. Whole brain size and optic lobe size do not differ between the two groups, but foundresses also have larger antennal lobes than workers. This shows that increased neural investment in MBs precedes social group formation. Larger MBs among foundresses may reflect the increased larval nutrition provisioned to future queens and the lack of social aggression from a dominant queen upon adult emergence.

     

Prenatal ultrasonographic diagnosis of radial-ray reduction malformations

Radial-ray reduction malformations (RRRMs) may occur isolated or in association with other anomalies. The data of seven fetuses born with RRRMs were collected. Six fetuses had associated lethal abnormalities of the central nervous system, urogenital system, and/or heart, detected by ultrasound. In five cases, it was possible to establish the precise diagnosis, enabling an informed prognosis and subsequent genetic counselling. The diagnoses were: Edwards syndrome (n=3), VACTERL association (n=1), and Poland-Moebius-like complex (n= 1). In two cases, a complete diagnosis was not possible because of inadequate evaluation of these fetuses before and/or after birth. A proposal is given for the diagnostic approach for infants with RRRMs detected in the antenatal period by means of ultrasonography.     

A novel mutualism between an ant-plant and its resident pollinator

Pollination systems in which the host plant provides breeding sites for pollinators, invariably within flowers, are usually highly specialized mutualisms. We found that the pollinating bee Braunsapis puangensis breeds within the caulinary domatia of the semi-myrmecophyte Humboldtia brunonis (Fabaceae), an unusual ant-plant that is polymorphic for the presence of domatia and harbours a diverse invertebrate fauna including protective and non-protective ants in its domatia. B. puangensis is the most common flower visitor that carries the highest proportion of H. brunonis pollen. This myrmecophyte is pollen limited and cross-pollinated by bees in the daytime. Hence, the symbiotic pollinator could provide a benefit to trees bearing domatia by alleviating this limitation. We therefore report for the first time an unspecialised mutualism in which a pollinator is housed in a plant structure other than flowers. Here, the cost to the plant is lower than for conventional brood-site pollination mutualisms where the pollinator develops at the expense of plant reproductive structures. Myrmecophytes housing resident pollinators are unusual, as ants are known to be enemies of pollinators, and housing them together may decrease the benefits that these residents could individually provide to the host plant.     

Contrasting responses of seed yield to elevated carbon dioxide under field conditions within Phaseolus vulgaris

The rising concentration of carbon dioxide [CO₂] in the atmosphere represents an increase in a growth-limiting resource for C₃ crop species. Identification of lines or characteristics of lines which have superior yield at elevated [CO₂] could aid in adaptation to this global change. While intraspecific variation in responses to elevated [CO₂] has been found in several species, intraspecific differences in crop yield responses to elevated [CO₂] under field conditions have seldom been documented. In this 4-year study, the responses of photosynthesis, growth, pod number, seed number and size, and seed yield to the elevation of [CO₂] to 180 μmol mol⁻¹ above the current ambient concentration were examined in four varieties of Phaseolus vulgaris in the field, using open-top chambers. There was a significant variety by [CO₂] interaction for seed yield, with seed yield at elevated [CO₂] ranging from 0.89 to 1.39 times that at ambient [CO₂] (mean 1.17×) in the different varieties, when averaged over 4 years. The highest yielding variety at elevated [CO₂] was not the highest yielding variety at ambient [CO₂]. The varieties with the largest and smallest yield responses both had an indeterminate growth habit. Down-regulation of photosynthesis at elevated [CO₂] only occurred in the two indeterminate varieties, and there was no significant correlation between the response of single leaf photosynthetic rate and the response of seed yield to elevated [CO₂] among varieties, nor between the responses of stem mass and seed yield. The change in the number of pods at elevated [CO₂] was the primary determinant of the response of seed yield. These results indicate that significant variation in the response of seed yield to elevated [CO₂] under field conditions does exist among varieties of P. vulgaris, and that variation in the response of pod and seed number may be more important than variation in photosynthetic response.     

好氧颗粒污泥系统中溶解性微生物代谢产物的特征及主要组分

采用SBR反应器以絮状活性污泥为接种污泥培养好氧颗粒污泥,主要考察好氧颗粒污泥系统中溶解性微生物代谢产物(SMP)的产生、相对分子质量分布以及主要组成物质.结果表明SMP是出水COD的主要组分,浓度为71~85 mg·L-1,SMP的产生与微生物对基质的利用、微生物衰亡和胞外聚合物(EPS)的水解有关.相对分子质量分布表明大部分SMP相对分子质量小于3×103,所占比例为54.8%~71.7%,而相对分子质量大于100×103的组分只占总SMP的一小部分,所占比例为9.3%~14.5%.三维荧光光谱分析表明,出水SMP具有4个峰,分别属于类芳香蛋白质、类色氨酸蛋白质、类腐殖酸物质和类富里酸物质.气质联用(GC-MS)分析表明SMP主要成分为酯类、短链烷烃、烯烃和醇类,所占质量分数分别为39.0%、14.9%、11.7%和7.6%.其中邻苯二甲酸二酯是出水SMP中主要组成物质,所占质量分数为32.0%.     

Between pregnancy biological variability of first trimester markers of Down syndrome: implications for screening in subsequent pregnancies

In a group of 149 women who had undergone routine first trimester screening using fetal nuchal translucency thickness (NT) and maternal serum free β-hCG and pregnancy associated plasma protein-A (PAPP-A) in two consecutive pregnancies the within person between pregnancy biological variability of these markers has been assessed. For fetal NT there was no correlation between NT MoM in the first and second pregnancy (r=0.0800). For maternal serum free β-hCG MoM a significant correlation was observed (r=0.4174) as was also found for PAPP-A MoM (r=0.3270). The implications for such between pregnancy marker association is that women who have an increased risk of Down syndrome in their first pregnancy are 1.5–2 times more likely to repeat this event in their next pregnancy. This observation may be useful in counselling women in the first trimester screening of a subsequent pregnancy. Copyright © 2001 John Wiley & Sons, Ltd.