Mussel and dogwhelk distribution along the north‐west Atlantic coast: testing predictions derived from the abundant‐centre model

Aim We performed the first test of predictions from the abundant‐centre model using north‐west Atlantic coastal organisms. We tested the hypotheses that the density of intertidal mussels (Mytilus edulis and M. trossulus) and dogwhelks (Nucella lapillus) and mussel age and size would peak at an intermediate location along their distribution range. We also assessed the latitudinal variation in critical aerial exposure time. Location North‐west Atlantic coast between Newfoundland (Canada) and New York (USA), covering 1800 km of shoreline. Methods Using a nested design, we measured mussel density, age and size and dogwhelk density in 60 wave‐exposed rocky intertidal sites spread evenly in six regions. Critical aerial exposure times were determined using online data. Results Mytilus edulis peaked in abundance in Maine and was much less abundant in the other regions. Mytilus trossulus peaked in abundance in southern Nova Scotia and Maine, was less abundant in the other regions to the north, and was absent in the southernmost region (New York). Both mussel species were least abundant in a northern region (Cape Breton), although not in the northernmost region (Newfoundland). Critical aerial exposure times were negatively correlated with overall mussel density. Mussel age and size were similar among regions. Dogwhelks peaked in abundance in Maine and were much less abundant in the other regions, being positively correlated with overall mussel density across regions. Main conclusions Density data for M. edulis and N. lapillus provide limited support for an abundant‐centre pattern, while M. trossulus shows a clear ramped‐south distribution. Critical aerial exposure times suggest that physiological stress during summer and winter low tides may be lowest in Maine and southern Nova Scotia, which might partially explain mussel predominance in those regions. Winter ice scour in Cape Breton may explain the abundance trough observed there. Mussel size and age may be more limited by wave exposure at our sites (as they all face open waters) than by regional differences in environmental stress. Dogwhelks, which prey on mussels, seem to respond positively to prey density at the regional scale. Our study supports the notion that, while the abundant‐centre model is a useful starting point for research, it often represents an oversimplification of reality.     

华北蜜粉源植物的研究*

在调查、收集、整理的基础上,初步筛选出蜜粉源植物 1 176 种及变种,隶属于 106 科 426 属,以刺槐、枣树、荆条、油菜等植物组成主要蜜源。华北是我国重要商品蜜生产基地。最后对华北地区蜜粉源植物的开发利用与保护提出了建议。     

Summer diapause and nymphal growth in a subtropical cockroach: response to changing photoperiod

Abstract.  The effects of photoperiod on nymphal growth and adult reproduction were investigated in a small cockroach, Margattea satsumana, living on the subtropical, Hachijo island (33°N), Japan. Nymphal development is slow under constant photoperiods at 25 °C. The shortest mean duration of nymphal development (176 days) is observed at LD 14 : 10 h, followed by LD 12 : 12 h (221 days) and LD 16 : 8 h (309 days). Nymphal development is further prolonged when the nymphs are transferred from LD 12 : 12 to LD 16 : 8 h at 90 days after hatching. However, rapid and synchronized development is observed when nymphs were transferred in the opposite direction. A decreased change in photoperiod from LD 14 : 10 to LD 12 : 12 h also reduces the duration of nymphal development, and this cannot be explained by the results obtained at constant photoperiods. Similarly, nymphs reared at LD 16 : 8 h during the first 60 days mature more rapidly when transferred to LD 12 : 12 h than when transferred to LD 14 : 10 h. The developmental suppression induced by long days may represent a form of summer diapause that is terminated rapidly by short days. Based on these observations and field-census data, it is suggested that this cockroach has a univoltine life cycle overwintering as nondiapause adults, and that this life cycle is stabilized by the response to changing photoperiod.     

Temporal, spatial, and ecological modes of evolution of Eurasian Mus based on mitochondrial and nuclear gene sequences

We sequenced mitochondrial (cytochrome b, 12S rRNA) and nuclear (IRBP, RAG1) genes for 17 species of the Old World murine genus Mus, drawn primarily from the Eurasian subgenus Mus. Phylogenetic analysis of the newly and previously available sequences support recognition of four subgenera within Mus (Mus, Coelomys, Nannomys, and Pyromys), with an unresolved basal polytomy. Our data further indicate that the subgenus Mus contains three distinct 'species groups': (1) a Mus booduga Species Group, also including Mus terricolor and Mus fragilicauda (probably also Mus famulus); (2) a Mus cervicolor Species Group, also including Mus caroli and Mus cookii; and (3) a Mus musculus Species Group, also including Mus macedonicus, Mus spicilegus, and Mus spretus. Species diversity in Eurasian Mus is probably explicable in terms of several phases of range expansion and vicariance, and by a propensity within the group to undergo biotope transitions. IRBP and RAG1 molecular clocks for Mus date the origin of subgenera to around 5-6 mya and the origin of Species Groups within subgenus Mus to around 2-3 mya. The temporal pattern of evolution among Eurasian Mus is more complex than that within the Eurasian temperate genus Apodemus.     

Influence of niche similarity on hybridization between Myriophyllum sibiricum and M. spicatum

The impact of ecological factors on natural hybridization is of widespread interest. Here, we asked whether climate niche influences hybridization between the two closely related plant species Myriophyllum sibiricum and M. spicatum. Eight microsatellite loci and two chloroplast fragments were used to investigate the occurrence of hybridization between these two species in two co‐occurring regions: north‐east China (NEC) and the Qinghai‐Tibetan Plateau (QTP). The climate niches of the species were quantified by principal component analysis with bioclimatic data, and niche comparisons were performed between the two species in each region. Reciprocal hybridization was observed, and M. sibiricum was favoured as the maternal species. Furthermore, hybrids were rare in NEC but common in the QTP. Accordingly, in NEC, the two species were climatically distinct, and hybrids only occurred in the narrow geographical or ecological transition zone, whereas in the QTP, obvious niche overlaps were found for the two species, and hybrids occurred in multiple contact zones. This association between hybridization pattern and climate niche similarity suggests that the level of hybridization was promoted by niche overlap. Compared with the parental species, similar climate niches were found for the hybrid populations in the QTP, indicating that other environmental factors rather than climate were important for hybrid persistence. Our findings highlight the significance of climate niche with respect to hybridization patterns in plants.     

华北地区中华蒙潮虫(甲壳动物亚门:等足目)种群遗传多样性研究

中华蒙潮虫Mongoloniscus sinensis(Dollfus,1901)隶属于甲壳动物亚门Crustacea等足目Isopoda潮虫亚目Oniscidea,中国特有种。为了探究中华蒙潮虫的种群遗传分化和系统进化关系,采用PCR对采自华北地区10个地理种群89只个体线粒体2个基因COⅠ和ND5进行联合分析。结果表明:1)中华蒙潮虫COⅠ部分基因长604 bp,ND5部分基因长615 bp,拼接序列长1 219 bp,T、C、A和G含量分别为41.0%、11.2%、30.8%和17.0%,具有显著的A+T偏倚;变异位点503个(占总核苷酸序列的41.3%),序列间的转换/颠换比值为2.8。2)89只个体共45种单倍型,单倍型多样性0.964,核苷酸多样性0.005 6,整体遗传多样性水平中等;单倍型H1、H15、H16、H21、H41为2～3个种群共享单倍型。3)联合基因(COⅠ+ND5)系统发育树表明,最早出现的是华北以北地区(山西大同、河北石家庄),最晚分化出的是华北以南地区(山西临汾、陕西西安未央区、河南新乡),演化路线为从北向南,个别种群单倍型未按地理来源形成明显的簇群。4)平均遗传分化指数为0.513,基因流为0.24;分子变异分析结果表明,种群的变异与分化主要来自种群内部,错配分布呈多峰,结合中性检验(Tajima's D=-1.429;Fu's F_s=6.499),发现中华蒙潮虫近期未经历扩张,但种群内部分化显著,增长平稳。本研究首次基于线粒体多基因联合分析了中华蒙潮虫种群遗传多样性。     

热带亚热带退化生态系统的恢复与复合农林业

我国热带亚热带是人口和环境压力最大的区域之一。原有自然生态系统遭到很大的破坏,退化生态系统大面积增加,这是严重制约农业生产发展的重要因素。长期的恢复生态学定点研究表明,通过综合整治,使退化生态系统得以恢复与重建,具有重大的生态效益、经济效益和社会效益。在丘陵山区进行退化生态系统的恢复与重建实践中所构建的“林果草(牧)鱼”复合生态系统,是高产、高质、高效的复合农林业模式,是促进地方农业经济发展的有效途径。     

粉垄耕作对黄淮海北部土壤水分及其利用效率的影响

连年旋耕导致犁底层上移、耕层变浅、水分利用效率（Water Use Efficiency, WUE）降低,严重制约作物丰收增产,尤其进一步激化缺水地区的农业用水供需矛盾。合理的土壤耕作是有效的解决途径,为此在黄淮海北部引入了粉垄这种新型深土耕作措施。以旋耕和深松为对照,设置了粉垄30 cm、粉垄50 cm、粉垄30 cm 地膜、粉垄50 cm 地膜、粉垄30 cm裸地、粉垄50 cm裸地等共8个处理,探讨不同耕作措施对土壤水分变化过程及WUE的影响。基于土壤湿度等值线图、土壤贮水消耗和WUE的分析可知,（1）与旋耕和深松相比,粉垄耕作后的耕层疏松深厚、土壤调蓄水分能力增强、总耗水量降低、WUE提高,其中粉垄各处理的总耗水量比旋耕和深松分别减少了12.2%―16.4%、10.2%―14.5%,产量WUE则分别提高了28.3%―50.6%、19.1%―39.7%;（2）粉垄的作业深度越深越利于降雨入渗和土壤水分调蓄,但总耗水量有所增加,WUE略有下降,其中总耗水量增加了5.0%,小喇叭口期和灌浆中期的叶片WUE分别下降1.6%和1.0%,产量WUE降低2.1%;（3）粉垄后覆膜克服了表土跑墒的缺点,减少了耗水量,进一步提高了土壤调蓄水分的能力和WUE,且作业深度越深,WUE提升越多,其中粉垄30 cm 地膜、粉垄50 cm 地膜的产量WUE分别比粉垄30 cm、粉垄50 cm提高了8.5%和17.3%,粉垄50 cm 地膜的小喇叭口期和灌浆中期的叶片WUE以及产量WUE分别比粉垄30 cm 地膜提高了8.3%、7.4%和5.9%。研究结果表明,这种新型耕作措施为打破犁底层、解决耕层变浅、提高水分利用效率提供了一种新的可行方法。     

鼎湖山主要森林植物凋落物分解及其对N沉降的响应

研究了鼎湖山森林主要植物凋落物分解及其对模拟 N沉降的响应。凋落物分解速率随林分、树种和分解阶段不同而异。分解试验 3个月后 ,季风常绿阔叶林、混交林和马尾松林分解物残存量占起始量的比例平均分别为 0 .5 0 ,0 .80和 0 .87,且它们的差异均达显著水平 (p<0 .0 5 ) ;6个月后 ,这 3种林分的分解物残存量占起始量的比例平均分别为 0 .4 1、0 .73和 0 .70。试验 3个月后 ,所有试验树种中凋落物分解最快的树种是季风常绿阔叶林的锥栗 (Castanopsis chinensis,残存量占起始量的比例为0 .34)最慢为马尾松林中的马尾松 (Pinus massoniana,残存量占起始量的比例为 0 .87) ;经 6个月后 ,最快的树种是季风常绿阔叶林的华润楠 (Machilus chinensis,残存量占起始量的比例为 0 .2 5 ) ,最慢为混交林中的马尾松 (残存量占起始量的比例为0 .75 )。 N沉降对凋落物分解的影响也随林分、树种和分解阶段不同而异。在马尾松林中 ,N沉降仅在试验开始 3个月对马尾松针叶凋落物分解存在明显的促进作用 (p<0 .0 5 )。在混交林中 ,经 6个月试验后 ,低 N处理对马尾松针叶凋落物分解仍无明显作用 ,中 N处理则明显促进其分解 (p<0 .0 5 ) ,但在两次取样中 N沉降处理对荷木 (Schima superba)凋落物的分解均无显著影响。 N沉降增     

Bradyrhizobium elkanii, Bradyrhizobium yuanmingense and Bradyrhizobium japonicum are the main rhizobia associated with Vigna unguiculata and Vigna radiata in the subtropical region of China

Cowpea (Vigna unguiculata) and mung bean (Vigna radiata) are important legume crops yet their rhizobia have not been well characterized. In the present study, 62 rhizobial strains isolated from the root nodules of these plants grown in the subtropical region of China were analyzed via a polyphasic approach. The results showed that 90% of the analyzed strains belonged to or were related to Bradyrhizobium japonicum, Bradyrhizobium liaoningense, Bradyrhizobium yuanmingense and Bradyrhizobium elkanii, while the remaining represented Rhizobium leguminosarum, Rhizobium etli and Sinorhizobium fredii. Diverse nifH and nodC genes were found in these strains and their symbiotic genes were mainly coevolved with the housekeeping genes, indicating that the symbiotic genes were mainly maintained by vertical transfer in the studied rhizobial populations.