Diurnal and annual rhythms in trees

Trees, perennial phanerophytes, display a rich variety of rhythmic phenomena. These are either due to exclusive environmental entrainment or due to the functioning of endogenous oscillators independent of the environment. Both types of rhythms are covered in this review. Purely environment controlled rhythms may be considered as a prelude to endogenous rhythms. Environment controlled rhythms discussed are (i) the diurnal rhythms of nyctinastic and heliotropic leaf movements and oscillatory phenomena of photosynthesis, such as the midday depression and Crassulacean acid metabolism (CAM), and (ii) the annual rhythms of annual growth ring formation, autumnal leaf senescence, over wintering mechanisms and flowering. Among the diurnal rhythms, nyctinastic movements and CAM are also free-running endogenous rhythms showing the operation of circadian clocks in trees. In leaf senescence, over wintering, and flowering control, photoperiod sensing is involved which suggests the participation of endogenous clocks. A question asked is if diurnal and annual rhythms are mechanistically correlated. Evidently, phenological phenomena based on photoperiodism (as dependent on measurement of night length) are co-ordinately regulated by the phytochrome system and the circadian clocks and many aspects of annual developments and over wintering are linked to photoperiodism. The existence in trees of circadian clock genes as known to be anchored in the genome of A. thaliana can be assessed by attempts of alignment with the sequenced genome of Populus or by isolating cDNA clones from trees to check them against the genome of A. thaliana. At extreme latitudes near the equator and north of the polar circle trees also display photoperiod-independent phenological phenomena. In the polar region, total irradiance of red and far red light could possibly be involved and the signalling pathway then involves phytochrome, and thus, may still be similar to that of photoperiodism. At the equator, total daily light irradiance received or sensing the dynamics of daily changes in solar irradiance are essential and it remains enigmatic whether signalling cascades are either attached to the circadian clocks in a still unknown way or totally independent of circadian clocks.     

“Balancing” balancing selection? Assortative mating at the major histocompatibility complex despite molecular signatures of balancing selection

In vertebrate animals, genes of the major histocompatibility complex (MHC) determine the set of pathogens to which an individual's adaptive immune system can respond. MHC genes are extraordinarily polymorphic, often showing elevated nonsynonymous relative to synonymous sequence variation and sharing presumably ancient polymorphisms between lineages. These patterns likely reflect pathogen‐mediated balancing selection, for example, rare‐allele or heterozygote advantage. Such selection is often reinforced by disassortative mating at MHC. We characterized exon 2 of MHC class II, corresponding to the hypervariable peptide‐binding region, in song sparrows (Melospiza melodia). We compared nonsynonymous to synonymous sequence variation in order to identify positively selected sites; assessed evidence for trans‐species polymorphisms indicating ancient balancing selection; and compared MHC similarity of socially mated pairs to expectations under random mating. Six codons showed elevated ratios of nonsynonymous to synonymous variation, consistent with balancing selection, and we characterized several alleles similar to those occurring in at least four other avian families. Despite this evidence for historical balancing selection, mated pairs were significantly more similar at MHC than were randomly generated pairings. Nonrandom mating at MHC thus appears to partially counteract, not reinforce, pathogen‐mediated balancing selection in this system. We suggest that in systems where individual fitness does not increase monotonically with MHC diversity, assortative mating may help to avoid excessive offspring heterozygosity that could otherwise arise from long‐standing balancing selection.     

Population Structure of Tundra Swans Wintering in Eastern North America

ABSTRACT Our objective was to determine whether there were subpopulations within the eastern population of tundra swans (Cygnus columbianus columbianus) wintering along the mid-Atlantic coast. Movement rates between regions were substantial enough to result in continual mixing of wintering birds. Thus, we were unable to identify distinct subpopulations based on exclusive use of specific wintering areas. These birds should therefore be monitored, and their harvest managed, as if they were one population.     

杨小舟蛾越冬蛹的空间分布格局

通过对杨小舟Micromelalophatroglodyta(Graeser)越冬蛹在土壤中水平方向和垂直深度分布格局的调查、分析 ,认为杨小舟蛾越冬蛹在土壤中呈聚集型分布 ,分布的基本单位是个体群 ;该虫大部分集中在树冠投影下 ,距寄主主干半径 1 2 0～ 1 60cm地表的枯枝落叶和杂草层中。     

越冬期间库尔勒香梨不同器官抗寒指标随气温的变化

以越冬期间库尔勒香梨花芽、树干、枝条等器官为材料,测定了不同器官形成层组织抗氧化酶(SOD、CAT、POD)活性、可溶性蛋白含量、相对电导率等抗寒指标,同时监测了果园气温和树干阳阴面形成层温度,并采用隶属函数评价不同器官抗寒性,分析越冬期气温对新疆库尔勒香梨不同器官抗寒指标和抗寒性的影响。结果表明:(1)在库尔勒香梨越冬期间,不同器官同一抗寒指标和同一器官不同抗寒指标随气温、树干阳阴面形成层温度差的变化趋势有所不同,但总体上抗寒指标均与气温呈负相关关系,而与树干阳阴面形成层温度差均呈正相关关系。(2)各器官形成层可溶性蛋白含量与其抗氧化酶活性呈正相关关系,SOD、CAT活性与POD活性呈正相关关系,并以CAT与POD活性相关性最强。(3)利用隶属函数法综合分析结果显示,贡献率最大的是CAT活性和可溶性蛋白含量,不同器官抗寒性强弱顺序为花芽组织树干阴面形成层枝条形成层树干阳面形成层。研究发现,库尔勒香梨各器官形成层POD和CAT活性在越冬期间较低气温和较强烈形成层温度变化时较高,并以SOD对低温伤害和形成层温度变化最敏感;整个越冬期抗寒性强的器官表现出较高的可溶性蛋白含量和较低的相对电导率;形成层温度变化与抗寒生理指标变化之间具有较好的相关性,在一定范围内能够反映机体受到的低温冻害程度。     

越冬期黑颈鹤个体行为生态的研究

越冬期黑颈鹤的个体行为可分为：取食、保养、争斗、警戒、运动行为、种间关系及领域性。随着冬季食物资源的逐渐减少,在取食行为中幼鹤由乞食、被成鹤供食转为向成鹤抢食。有些家族鹤为保证食物资源而建立领域,领域大小与家族内成员数无关,且在冬季（甚至１天内）是变化的。为获得食物和保卫领域,黑颈鹤之间（或与灰鹤之间）常发生争斗,争斗的主要形式是仪式化威胁。     

无人机调查白鹤种群数量和越冬分布

白鹤(Leucogeranus Leucogeranus)是国家Ⅰ级重点保护野生动物,唯一一种极度濒危(CR)鹤类,分布和种群数量是评估其濒危程度的重要参数。无人机调查作为目前生态学研究的一个重要调查方法,为查明白鹤的越冬分布、种群数量及幼鸟比例,于2022年1月使用地面监测结合无人机调查的方法在江西、山东、安徽、湖南、湖北等地的湖泊和农田中开展越冬白鹤调查。野外调查共记录白鹤5607只,网络信息检索在调查区域外的8个地点记录白鹤9只,合计记录越冬白鹤5616只。其中江西鄱阳湖记录到越冬白鹤4813只,占总数的85.7%,主要分布在康山垦殖场、五星垦殖场和成新垦殖场;山东黄河三角洲记录到越冬白鹤625只,占总数的11.1%。安徽、湖南、湖北分别记录到越冬白鹤34,63和72只。对部分群体的白鹤幼鸟数量进行统计,4680只白鹤中,记录到幼鸟674只,幼鸟比例为14.4%,其中湖南越冬白鹤幼鸟比例最高,达28.6%,山东越冬白鹤幼鸟比例最低,为11.5%。调查刷新了白鹤种群数量,证实了山东黄河三角洲是目前除江西鄱阳湖外最重要的白鹤越冬地,缓解了白鹤越冬期过度集中的压力。基于本研究结果,我们...     

Differential selection according to the degree of cheating in a status signal

The maintenance of honesty in a badge-of-status system is not fully understood, despite numerous empirical and theoretical studies. Our experiment examined the relationship between a status signal and winter survival, and the long-term costs of cheating, by manipulating badge size in male house sparrows, Passer domesticus. The effect of badge-size manipulation on survival was complex owing to the significant interactions between the treatments and original (natural) badge size, and between the treatments and age classes (yearlings and older birds). Nevertheless, in the experimental (badge-enlargement) group, males with originally large badges had increased winter survival, while males with originally small badges had decreased survival. This indicates that differential selection can act on a trait according to the degree of cheating.     

Strategy of auditory discrimination of scale in Java sparrows: they use both "imagery" and specific cues

We examined whether Java sparrows use imagery of auditory stimuli (imagery is a subject's mental representation of a stimulus by which the subject's behaviour may be governed under stimulus control even in the absence of the physical stimulus). Three types of ascending tone sequences were used. In the intact scale, sequence tones were played in ascending order. In the intact-masked scale, part of the sequence was masked by noise but the remaining scale was identical with the intact scale, whereas in the violated scale, the sequence could be heard as if tones were played slowly (Experiment 1) or quickly (Experiment 2). Subjects were divided into two groups: one group was trained to respond to the intact and intact-masked scales and to suppress response to the violation scale (imagery-positive group). The contingency was reversed for the other (violation-positive) group. In Experiment 1, all the birds acquired discrimination, but successful transfer to novel stimuli was observed only in the imagery-positive group, suggesting that the imagery of the tone sequence was used as a discriminative cue. Experiment 2 confirmed that the stimulus duration was a discriminative cue for both groups, suggesting that the birds also acquired discrimination using only specific cues.     

Territory establishment,song learning strategies and survival in song sparrows

In most songbirds, the processes of song learning and territory establishment overlap in the early life and a young bird usually winds up with songs matching those of his territorial neighbors in his first breeding season. In the present study, we examined the relationships among the timing of territory establishment, the pattern of song learning and territorial success in a sedentary population of song sparrows (Melospiza melodia). Males in this population tend to learn their songs from their neighbors and consequently they show high song sharing with neighbors and use these shared songs preferentially in interactions with them. Males also show significant variation in the timing of territory establishment, ranging from their natal summer to the next spring. Using a three-year dataset, we found that the timing of territory establishment did not systematically affect the composition of the song repertoire of the tutee: early establishers and late establishers learned equally as much from their primary tutors and had a similar number of tutors and similar repertoire sizes, nor did timing of territory establishment affect subsequent survival on territory. Therefore, the song-learning program of song sparrows seems versatile enough to lead to high song sharing even for birds that establish territories relatively late.