Reproductive roles predict sexual dimorphism in internal and external morphology of lake whitefish,Coregonus clupeaformis

Abstract – The different reproductive roles of the sexes can predict the direction and magnitude of sexual dimorphism of external and internal morphology. Males should have enlarged structures that enhance the acquisition of mating opportunities, whereas females are predicted to have enlarged organs that are associated with the production of eggs. We tested these predictions in male and female lake whitefish, a species in which both sexes have similar overall body size and shape. After controlling for body size, male lake whitefish had significantly longer jaws and pectoral and pelvic fins, larger hearts, and more muscle than females. Sexual dimorphism in relative muscle mass may be one of the most fundamental morphological differences between males and females. Females had relatively heavier livers than males. Because the liver is important for the breakdown of fats and vitellogenesis, selection should favour an enlarged liver in females for the processing of energy and the production of large numbers of eggs.     

The ecological fitness of ALS-resistant Amaranthus retroflexus and multiple-resistant Amaranthus blitoides

Summary Field studies were conducted to evaluate the ecological fitness of Amaranthus spp. biotypes that evolved resistance to either acetolactate synthase (ALS) inhibitors ( A. retroflexus , SuR), to triazine herbicides ( A. blitoides , SuS/TR), or to both ( A. blitoides , SuR/TR), and estimate their ecological fitness under competitive conditions. The plants were grown in monoculture and in replacement series experiments. The examined mixtures were 100%S, 75%S/25%R, 50%S/50%R, 25%S/75%R and 100%R, at a constant stand of 400 plants m⁻². The SuR and SuS A. retroflexus biotypes attained similar shoot dry biomass per plant, biomass per plot and relative yield total (RYT) = 1. In monoculture, the final shoot biomass of A. blitoides biotypes SuS/TS plants was higher than that of SuR/TR and SuS/TR. A negative effect of association was observed, amensalism, when SuS/TS was grown in mixture with SuR/TR, in favour of the wild type. However, SuR/TR and SuS/TR biomass was not influenced by the presence of the competitor. These data support the hypothesis that the ALS-resistance trait in A. retroflexus and A. blitoides is not associated with growth penalty and did not incur ecological cost in the field. We suggest that the cause of the observed reduction in growth rendering the SuS/TR and SuR/TR less fit than the wild type is due to the triazine resistance, and may facilitate their dissipation.     

The re-emergence of indigenous forest in an urban environment, Christchurch, New Zealand

Christchurch, the second largest city in New Zealand is a planned city on a coastal plain on the east coast of the South Island. The birth of the city and the subsequent century of development was characterised by colonial values and tree and garden planting with familiar European species along with those from Australia, North America, and eventually all other continents. The image of an “English garden city” with classical parks of oaks and willow-lined rivers became the accepted norm and the way in which the city has been promoted to potential tourists. Gardening is one of the top two recreational activities and exotic species greatly outnumber native species in the flora and in gardens. This has had serious consequences for the highly fragmented and degraded indigenous vegetation and its co-adapted wildlife. A few hardy indigenous species continued to regenerate through this period, but since the 1970s, there has been a progressive change of attitude and interest in reclaiming the natural heritage of the city, manifest in widespread private and public planting of indigenous species and active habitat restoration. In this article we examine the indigenous and exotic shrub and tree components of the Christchurch flora as planted street trees, in domestic gardens, and in parks. We also present data on shrub and tree regeneration in parks and domestic gardens in the city. Indications are that the more sensitive, less intrusive management of urban environments, combined with the greater density of indigenous seed sources, has allowed regeneration of a wide range of indigenous species across a broad spectrum of habitats – from neglected gardens to pavement cracks to exotic plantations. This is despite the competition from the prodigious seed banks and density of exotic trees, shrubs, and ground covers and albeit minimal impacts of introduced browsing and seed eating mammals. If the present trends continue through appropriate management and facilitation, these tentative signs of native forest regeneration should eventually proliferate into a sustainable mixed origin urban forest that resurrects and preserves the natural character of the region.     

Critical periods for weed control in cotton in Turkey

Field studies were conducted over 4 years in south‐eastern Turkey in 1999–2002 to establish the critical period for weed control (CPWC). This is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. A quantitative series of treatments of both increasing duration of weed interference and of the weed‐free period were applied. The beginning and end of CPWC were based on 5% acceptable yield loss levels which were determined by fitting logistic and Gompertz equations to relative yield data representing increasing duration of weed interference and weed‐free period, estimated as growing degree days (GDD). Total weed dry weight increased with increasing time prior to weed removal. Cotton heights were reduced by prolonged delays in weed removal in all treatments in all 4 years. The beginning of CPWC ranged from 100 to 159 GDD, and the end from 1006 to 1174 GDD, depending on the weed species present and their densities. Practical implications of this study are that herbicides (pre‐emergence residual or post‐emergence), or other weed control methods should be used in Turkey to eliminate weeds from 1–2 weeks post‐crop emergence up to 11–12 weeks. Such an approach would keep yield loss levels below 5%.     

采煤沉陷区苦草的生物学特性及其竞争机制

采煤活动所致的动态沉陷湿地具有动态性、高潜水位和生态脆弱性等特点,探明此类人工重构湿地的水生植物群落的生物学特性及其竞争机制,有助于为采煤沉陷区湿地水生植物群落修复提供科学依据。本研究以淮南潘集区人工构建的苦草群落(Ass. Vallisneria natans)为例,采用样方调查法,研究苦草的生物学特性及其与其他水生植物的竞争机制。结果表明,1)沉陷区苦草的生物学特性与浅水湖泊较一致。主要表现在苦草的繁殖方式、传粉方式、生活史方面,但研究区苦草以有性繁殖为主。2)沉陷区苦草能与以种子萌发形成的水烛群丛(Ass. Typha angustifolia)共生,但生物量低;在与形成两年以上的水烛群丛竞争中处于劣势,在水烛群丛盖度达到90%时苦草逐渐消失。3)沉陷区苦草在与浮叶植物莕菜群丛(Ass. Nymphoides peltatum)、苹群丛(Ass. Marsilea quadrifolia)竞争中处于弱势,其盖度、株高、生物量等指标都明显下降。4)沉陷区苦草在与沉水植物竹叶眼子菜群丛(Ass. Potamogeton malaianus)竞争中处于劣势,苦草与沉水植物黑藻群丛(Ass. Hydrilla verticillata)、狐尾藻群丛(Ass. Myriophyllum verticillatum)、大茨藻群丛(Ass. Najas marina)、金鱼藻群丛(Ass. Ceratophyllum demersum)占据不同水层空间,种间竞争不强烈,能较好地共存。总之,苦草较之于相似生长型的植物具有较明显的竞争优势,对于具有不同生活型,尤其是挺水植物和浮叶植物,处于竞争劣势。     

玉米螟卵龄对玉米螟赤眼蜂和松毛虫赤眼蜂种间竞争的影响

室内观察了松毛虫赤眼蜂和玉米螟赤眼蜂寄生亚洲玉米螟卵的寄生行为,以及两种赤眼蜂在单独和竞争情况下的寄生及其子代蜂受寄主卵龄的影响。结果发现:松毛虫赤眼蜂完成1次寄生所需时间显著短于玉米螟赤眼蜂,而产卵次数占总寄生次数的比例(40.16%)显著低于玉米螟赤眼蜂(66.26%)。单独寄生时,玉米螟卵龄对玉米螟赤眼蜂的子代雌蜂数和子代蜂存活无显著影响,但对松毛虫赤眼蜂具有显著影响,且死亡蜂数量随卵龄增大而增多。在竞争情况下,两种赤眼蜂子代总雌蜂数均增加;寄生6h和36h玉米螟卵产出的子代蜂显著小于单独寄生时的子代蜂;寄生12h卵的子代蜂死亡数(21头)显著高于寄生其他龄期的卵,但在其他卵龄间无显著差异。     

芦苇对空心莲子草从陆生环境向水生环境扩散的影响

[目的]探讨芦苇种植对空心莲子草从陆生境向水生境扩散的影响。[方法]模拟河岸带芦苇与空心莲子草生长状态,比较混种和控制条件下空心莲子草扩散及生物量变化。[结果]与控制条件下相比,芦苇种植使空心莲子草在陆生境纵向（沿陆地向水中的方向）与横向（与纵向垂直）扩散日变化率显著下降（P〈0．05）;水生境中均未出现显著差异;陆生境中横向和纵向扩散符合指数生长模型：Y=ae^bx＋y0;根生物量显著下降,达到50％;茎生物量下降16％,但其占比却上升62％。[结论]芦苇存在时,陆生境空心莲子草所受到的抑制要强于水生境;空心莲子草会通过提高其地上生物量占比,对芦苇抑制做出反应,以获取更多的光照。     

基于市场占有率分析的区域农业竞争力研究

根据统计资料运用模型对中国区域农业竞争力进行实证研究,对市场优势和竞争优势进行了排名。结果显示,各省市之间市场优势和竞争优势的排名不是完全一致的。     

Spatiotemporal density patterns of the pest predator Rhynchium haemorrhoidale (F.) along a land-use gradient in cacao agroforestry systems

Tropical insect species show year-round breeding activity due to favourable climatic conditions. However, most species also display seasonal reproductive peaks, but little is known about underlying causes of temporal density changes. We investigated population dynamics of the pest predator Rhynchium haemorrhoidale (F.) (Hymenoptera: Eumenidae) and its natural enemies in relation to season, climate and varying shade tree composition in cacao agroforestry systems in Central Sulawesi (Indonesia). Nesting of R. haemorrhoidale showed clear seasonality with highest densities in the wet season and lowest in the dry season, which was not related to changes in temperature. Wasp densities increased with land-use intensity, presumably because less-shaded areas offer more favourable climatic conditions and higher densities of the major prey, the cacao pest Agathodes caliginosalis (Lepidoptera: Pyralidae). Pupal body size was higher in June than in November indicating increasing intraspecific competition due to high wasp densities and food shortage at the beginning of the wet season. Body size between habitat types was similar, thus season appeared to be more important than habitat in terms of food supply. High wasp densities in the wet season were associated with high diversity of the altogether seven parasitoid species. In conclusion, we found a pronounced seasonality of the wasp R. haemorrhoidale and a preference for little shaded agroforestry, which may be due to enhanced temperature and density of its prey. Our data indicate a high potential for biological control of a major cacao pest by management of nesting sites of R. haemorrhoidale.