Condition-dependence,genotype-by-environment interactions and the lek paradox

The lek paradox states that maintaining genetic variation necessary for 'indirect benefit' models of female choice is difficult, and two interrelated solutions have been proposed. 'Genic capture' assumes condition-dependence of sexual traits, while genotype-by-environment interactions (GEIs) offer an additional way to maintain diversity. However, condition-dependence, particularly with GEIs, implies that environmental variation can blur the relationship between male displays and offspring fitness. These issues have been treated separately in the past. Here we combine them in a population genetic model, and show that predictions change not only in magnitude but also in direction when the timing of dispersal between environments relative to the life cycle is changed. GEIs can dramatically improve the evolution of costly female preferences, but also hamper it if much dispersal occurs between the life history stage where condition is determined and mating. This situation also arises if selection or mutation rates are too high. In general, our results highlight that when evaluating any mechanism promoted as a potential resolution of the lek paradox, it is not sufficient to focus on its effects on genetic variation. It also has to be assessed to what extent the proposed mechanism blurs the association between male attractiveness and offspring fitness; the net balance of these two effects can be positive or negative, and often strongly context-dependent.     

Condition-dependence, genotype-by-environment interactions and the lek paradox

The lek paradox states that maintaining genetic variation necessary for ‘indirect benefit’ models of female choice is difficult, and two interrelated solutions have been proposed. ‘Genic capture’ assumes condition-dependence of sexual traits, while genotype-by-environment interactions (GEIs) offer an additional way to maintain diversity. However, condition-dependence, particularly with GEIs, implies that environmental variation can blur the relationship between male displays and offspring fitness. These issues have been treated separately in the past. Here we combine them in a population genetic model, and show that predictions change not only in magnitude but also in direction when the timing of dispersal between environments relative to the life cycle is changed. GEIs can dramatically improve the evolution of costly female preferences, but also hamper it if much dispersal occurs between the life history stage where condition is determined and mating. This situation also arises if selection or mutation rates are too high. In general, our results highlight that when evaluating any mechanism promoted as a potential resolution of the lek paradox, it is not sufficient to focus on its effects on genetic variation. It also has to be assessed to what extent the proposed mechanism blurs the association between male attractiveness and offspring fitness; the net balance of these two effects can be positive or negative, and often strongly context-dependent.     

油松雌性不育系球果蛋白质双向电泳技术的建立

本文建立了油松雌性不育系雌球果蛋白质组研究中的双向电泳技术.第一向采用固定pH值梯度(IPG)胶条在IPGphorTM等电聚焦仪上进行等电聚焦,第二向在恒功率且恒温条件下于Ettan-DALTTMⅡ高通量电泳仪上进行SDS-PAGE电泳,以银染和考马斯亮蓝两种方法染色.通过对全蛋白的提取、胶条pH值和胶条肿胀等技术环节的优化和比较,得到了重复性很高,分离效果良好的蛋白质双向图谱.     

根田鼠母体捕食应激对其雌性子代雄性化效应的研究

本研究了根田鼠母体捕食应激对其雌性子代雄性化的效应。母体捕食应激使雌性子代在鼻端探究、生殖区探究、试图探究和爬跨及尾随等性行为中花费的时间最多,阴道开口时间显延迟,生殖器与肛门间距离显增大,而母体食物限制和断乳应激子代则未明显呈现上述特征。母体捕食应激使其雌性子代显地降低对雄性个体的性吸引力。因此,母体捕食应激使雌性子代在性行为、形态特征及性吸引力方面呈现雄性化效应,主要归结于捕食应激引起母体内分泌的改变所致;此效应仅产生于胚胎性分化的特定关键时期。全结果检验了田鼠类母体捕食应激对其雌性子代性分化有显影响的假设。     

蓝尾石龙子的生长、两性异形及雌性繁殖

报道蓝尾石龙子（Eumeces elegans)的生长、两性异形和雌性繁殖,性成熟个体体色的两性差异显著,成年雄性体长、头长和头宽显著大于成年雌性,幼体体长生长率无显著的两性差异。成年雄体体长生长率显著大于成年雌体,因此,个体大小的两性异形是性成熟后发生的,体长小于50mm的幼体,头长和头宽无性差异;当体长大于50mm。雄性头长和头宽随体长的生长率显著大于雌性。并导致头部大小的两性异形,并随个体发育变得越来越显著,蓝尾石龙子产卵雌体的最小体长为69.3mm,大于此体长的雌体均年产单窝卵。窝卵数、窝卵重和平均卵重均与雌体体长呈正相关,平均值分别为6.4、2.783和0.554g。窝卵数与雌体产后状态无关,蓝尾石龙子雌体主要通过增加窝卵数和卵大小来增加繁殖输出。     

东北虎雌性生殖系统的组织学

对10月份意外死亡的2例东北虎（Panthera tigris altaica)雌性生殖系统进行了组织学研究。卵巢基质中分布着一定数量的有腔卵泡及闭锁卵泡。间质腺不发达,在闭锁卵泡上皮样细胞增殖,形成一定量的间质腺细胞。输卵管漏半斗部至峡部黏膜上皮由柱状逐渐转化炎立方,黏膜形成许多皱褶,皱褶以漏斗部和壶腹部最多,子宫内膜上皮为单层立方上皮。6岁个体子宫腺上皮为单层柱状上皮;2岁个体在子宫角处的子宫腺上皮为单层柱状上皮,在子宫体外多为单层立方上皮,子宫腺密度从卵巢端到子宫体端呈阶梯下降,阴道黏膜上皮大多为2－3层的复层扁平上皮。     

北美香柏雌球果的发育

用扫描电镜(SEM)观察了北美香柏 Thuja occidentalis 雌球果的发育过程。在北京,北美香柏的雌球果是在八月初由营养芽转变而来,雌球果一般有4~6对苞片,中间2~3对可育,每一苞片腋部着生两枚胚珠,在可育苞片腋部最先观察到一扁平的隆起,并在其上分化出两个胚珠原基,接着分化出珠被和珠心,最后形成扁平而两侧对称的胚珠。在北美香柏雌球果发育过程中,约一半的雌球果在2~3对可育苞片中位于下面的1~2对的腋部产生3个胚珠原基,中间一个较小,并在以后的发育中逐渐退化。由此推测北美香柏的雌球果可能是由祖先类群中每一苞片具多于2个胚珠的雌球果演化而来。在光镜下对雌球果维管系统的观察发现,传粉前幼小雌球果的苞片内仅有一束维管束,传粉后随着苞片基部的居间生长,有4—8束维管束在苞片内形成,但是新发育的维管束木质部和韧皮部相对位置与正常叶性器官一致,这与在以往报道的柏科植物成熟雌球果的苞片中均有反向维管束的发育不同。北美香柏雌球果早期发育和维管束分析结果支持傅德志和杨亲二提出的解释裸子植物生殖器官形态演化的“苞鳞-种鳞复合体”理论。关键词北美香柏;雌球果的发育;胚珠分化;SEM     

A positive association between oviposition and fruit set: female choice or manipulation?

The relationship between where a female chooses to oviposit and her larvae’s performance at those sites is critical to both the ecology and evolution of plant-insect interactions. For predispersal seed predators that do not themselves pollinate their host and whose larvae are sessile, females must be able to predict which flowers will ultimately be pollinated and set fruit, or be able to manipulate flowers in some way to ensure they set fruit. Otherwise, their offspring will perish. Here we describe the results of an experiment in which we tested if female Hylemya (Diptera: Anthomyiidae) are choosing oviposition sites wisely, or if they are manipulating flowers of their host, Ipomopsis aggregata (Polemoniaceae), in some way to ensure fruit set. Previous work in this system established a positive correlation between oviposition and fruit set. By bagging females on flowers, we removed their ability to choose flowers on which to oviposit. We found that flowers females oviposited on, whether bagged (”no choice”) or unbagged (”female choice”), had a significantly higher probability of setting fruit than ”control” flowers that we bagged but did not cage females on. In addition, we tested if Hylemya prefer particular architectural locations of flowers and if those locations correspond with higher than average fruit set. Although flowers at the distal end of the plant, and those most proximal to the main stem, were more likely to set fruit overall, Hylemya was no more likely to oviposit on those flowers than others on the plant. Taken together, our results suggest that Hylemya is somehow able to manipulate its host to ensure fruit set and thus the provisioning of their larvae. Received: 3 December 1999 / Accepted: 23 March 2000     

Behavior of adult and young grassland songbirds at fledging

The behavior of adults and young at the time of fledging is one of the least understood aspects of the breeding ecology of birds. Current hypotheses propose that fledging occurs either as a result of parent‐offspring conflict or nestling choice. We used video recordings to monitor the behavior of nestling and adult grassland songbirds at the time of fledging. We observed 525 nestlings from 166 nests of 15 bird species nesting in grasslands of Alberta, Canada, and Wisconsin, USA. Overall, 78% of nestlings used terrestrial locomotion for fledging and 22% used wing‐assisted locomotion. Species varied in propensity for using wing‐assisted locomotion when fledging, with nestling Grasshopper Sparrows (Ammodramus savannarum) and Henslow's Sparrows (Centronyx henslowii) often doing so (47% of fledgings) and nestling Song Sparrows (Melospiza melodia), Common Yellowthroats (Geothlypis trichas), and Chestnut‐collared Longspurs (Calcarius ornatus) rarely doing so (3.5% of fledgings). For 390 fledging events at 127 nests, camera placement allowed adults near nests to be observed. Of these, most young fledged (81.5%) when no adult was present at nests. Of 72 fledging events that occurred when an adult was either at or approaching a nest, 49 (68.1%) involved feeding. Of those 49 fledgings, 30 (62.1%) occurred when one or more nestlings jumped or ran from nests to be fed as an adult approached nests. The low probability of nestlings fledging while an adult was at nests, and the tendency of young to jump or run from nests when adults did approach nests with food minimize opportunities for parents to withhold food to motivate nestlings to fledge. These results suggest that the nestling choice hypothesis best explains fledging by nestlings of ground‐nesting grassland songbirds, and fledging results in families shifting from being place‐based to being mobile and spatially dispersed.     

Simple mathematical models to describe the rate of mating in insect populations

Simple models are constructed to describe the rate of mating in insect populations. The models are based on the assumption of random mate-searching in a closed habitat, including four parameters, i.e., population size, sex ratio, searching efficiency and male's capacity on mating frequency. The modes of effects of these parameters on the rate of mating are analyzed and some principles deduced are discussed in relation to the mating process in natural populations.