黑斑侧褶蛙蝌蚪断尾后的补偿生长和发育研究

动物在经历不利的生长条件或环境后往往出现补偿生长。研究了黑斑侧褶蛙(Pelophylax nigromaculatus)蝌蚪经历来自食蚊鱼(Gambusia affinis)捕食造成断尾损伤后的补偿生长模式、断尾损失对蝌蚪游泳能力以及变态时间与大小的影响。结果表明,经历捕食压力后,全尾组和1/3断尾组蝌蚪的体长显著大于1/2断尾组蝌蚪的体长,全尾组和1/3断尾组之间的蝌蚪体长差异不显著;第19天时,1/2断尾组蝌蚪经过补偿生长后体长显著大于全尾组蝌蚪,1/3断尾组与全尾组和1/2断尾组之间的蝌蚪体长差异均不显著;三个实验组之间蝌蚪尾长差异不显著;全尾组蝌蚪的疾游速显著大于1/2断尾组蝌蚪的疾游速,1/3断尾组蝌蚪的疾游速与全尾组和1/2断尾组之间差异不显著,表明严重断尾对蝌蚪疾游速产生了消极影响。三个实验组蝌蚪的变态时间和变态前后形态差异均不显著。黑斑侧褶蛙蝌蚪能够在变态前调整生长轨迹补偿早期捕食风险造成的生长损失,断尾损失并不影响变态时间与大小,断尾超过一半的蝌蚪经过补偿生长后仍要付出一定的运动代价。     

小麦吸浆虫保幼激素酯酶和保幼激素环氧水解酶基因的克隆及在滞育和变态发育过程中的表达动态

【目的】保幼激素(juvenile hormone, JH)在小麦吸浆虫Sitodiplosis mosellana滞育诱导及滞育后静息状态的维持中发挥着重要作用。保幼激素酯酶(hormone esterase, JHE)和保幼激素环氧水解酶(juvenile hormone epoxide hydrolase, JHEH)是调控JH滴度的重要降解酶。本研究旨在探讨JHE和JHEH在小麦吸浆虫滞育和变态发育中潜在功能。【方法】通过RT-PCR和RACE技术从小麦吸浆虫滞育前幼虫克隆JHE和JHEH全长cDNA序列;利用生物信息学软件分析其核苷酸及编码蛋白特性;采用qPCR技术分析其在小麦吸浆虫滞育不同时期(滞育前、滞育期、滞育后静息期和滞育后发育)3龄幼虫及1龄幼虫到成虫不同发育阶段(1-2龄幼虫、预蛹、初蛹、中蛹、后蛹、雌成虫和雄成虫)中的表达水平。【结果】克隆获得了cDNA全长分别为3 102和1 980 bp的小麦吸浆虫SmJHE和SmJHEH基因(GenBank登录号分别为MG876768和MG876769),其开放阅读框分别长1 740和1 371 bp,分别编码579和456个氨基酸,预测蛋白分子量分别为65.67和51.65 kD。SmJHE蛋白含有5个JHE家族特有的保守模块,SmJHEH含有催化三联体Asp228, Asp404和His431及组成阴氧离子洞的两个Tyr(Tyr299和Tyr374)和HGWP花样结构。序列比对和进化分析表明,SmJHE和SmJHEH均与双翅目(Diptera)长角亚目(Nematocera)昆虫同源蛋白氨基酸序列一致性较高,亲缘关系最近。不同滞育时期的表达模式表明,SmJHE和SmJHEH在滞育前期(1龄到滞育前的3龄幼虫早期)表达量变化不明显,进入滞育后表达量基本维持恒定,但均在滞育后静息阶段的当年12月至翌年1月最低。发育表达模式表明,幼虫恢复发育后SmJHE表达量逐渐升高,预蛹期达到最高,在雌成虫中的表达量显著低于雄成虫中的;SmJHEH表达量则在预蛹期最低,在雌成虫中最高。【结论】SmJHE和SmJHEH参与小麦吸浆虫滞育调控,其表达量的降低与滞育后静息阶段JH的累积有关;SmJHE在发育过程中表达量的升高可能参与幼虫到蛹的变态,表达量的降低可能与生殖发育有关。     

The ontogenetic shift in thermoregulatory behaviour of newt larvae: testing the 'enemy-free temperatures' hypothesis

Growth and development affect life-history traits, and consequently organismal fitness. The inevitable increase in body size during ontogeny is associated with changes in both resource use and predation risk, which results in the ontogenetic shift in habitat preferences. In this study, we examined whether the shift in preferred body temperatures ( T _ps) of newt larvae Triturus alpestris increases the T _ps deviation of the most vulnerable stages (after hatching and during metamorphosis) from the T _ps range of their main predator, dragonfly larvae Aeshna cyanea – the 'predator-free temperatures' hypothesis. Analyses of thermoregulatory behaviour in the laboratory thermal gradient showed that freshly hatched newt larvae maintained lower water temperatures than larvae in later stages, whose T _ps largely fell into the T _ps range of dragonfly larvae. With respect to the thermal quality of natural habitat, the anti-predator effectiveness of the T _ps shift decreased during development. Water temperatures in natural habitats were located largely below the preferred body temperature range of both newt and dragonfly larvae, which limits their potential thermal niche partitioning. We conclude that factors other than predator avoidance drive the ontogenetic T _ps shift in our model system.     

果蝇变态过程中的细胞凋亡和细胞自噬

程序化细胞死亡(programmed cell death,PCD)分为I型PCD细胞凋亡(apoptosis)和II型PCD细胞自噬(autophagy)。果蝇等完全变态昆虫有2种类型的器官:即细胞内分裂器官(如脂肪体、表皮、唾液腺、中肠、马氏管等)和有丝分裂器官(复眼、翅膀、足、神经系统等)。在昆虫变态过程中,细胞内分裂器官进行器官重建,幼虫器官大量发生细胞凋亡和细胞自噬到最后完全消亡,同时成虫器官由干细胞从新生成;而有丝分裂器官则由幼虫器官直接发育为成虫器官。在果蝇等昆虫的变态过程中,细胞凋亡和细胞自噬在幼虫器官的死亡和成虫器官的生成中发挥了非常重要的作用。文章简要介绍细胞凋亡和细胞自噬在果蝇变态过程中的生理功能和分子调控机制。     

Stage dependent influences of polydnaviruses and the parasitoid larva on host ecdysteroids

In the solitary egg-larval parasitoid Chelonus inanitus (Braconidae) both polydnavirus and the parasitoid larva manipulate host development. Parasitization leads to a premature drop in juvenile hormone titre and a precocious onset of metamorphosis in the 5th larval instar. The C. inanitus bracovirus (CiBV) alone causes a reduction in host ecdysteroid titres at the pupal cell formation stage and prevents pupation. Here we report three new findings. (1) We show that parasitization causes a reduction in haemolymph ecdysteroid titre immediately after the moult to the 5th instar; similarly low values were seen in nonparasitized larvae after the moult to the 6th instar. These data along with parasitoid removal experiments indicate that the low ecdysteroid titre after the moult is a very early sign of the upcoming metamorphosis. (2) In vitro experiments with prothoracic glands and brain extracts showed that CiBV affects both prothoracic glands and prothoracicotropic hormone after the stage of pupal cell formation. (3) In the haemolymph of parasitized larvae the ecdysteroid titre increased in the late cell formation stage, i.e. immediately before egression of the parasitoid. In vitro experiments showed that late 2nd instar parasitoids release ecdysteroids and are thus very likely responsible for the rise in host ecdysteroids.     

Early larval ontogeny of the Permo-Carboniferous temnospondyl Sclerocephalus

The early larval development of the temnospondyl Sclerocephalus sp. is analyzed, based on 38 specimens from the Lower Rotliegend (Permo-Carboniferous boundary) of the Saar-Nahe Basin (south-west Germany). The study focuses on the smallest larval specimens, which exemplify changes in both proportions and ossification patterns. In comparison with dissorophoid larvae, the skull ossifies more fully and at a much faster rate; the smallest specimens already have completely formed circumorbital bones that are sutured throughout. Sculpturing undergoes two marked changes, first from uniformly pitted to pits of variable size and regional differentiation, and finally to the origin of ridges. The palate of small larvae differs from that of larger specimens in patterns of dentition, having more teeth including a denticle field on the cultriform process. The mandible of small larvae is described for the first time, being narrower than in adults and having three dentigerous coronoid elements. The smallest specimens have poorly ossified neural arches, lack vertebral centra, and have faintly ossified humeri, femora, and very poorly developed distal elements. The posterior ribs, metapodia, and phalanges appeared after the dermal elements of the pectoral girdle, whereas the scapulocoracoid and ischium are absent throughout the larval period. Early growth and differentiation of the limbs and the ilium illustrates the developmental patterning of the appendages, which proceeded from proximal to distal. Dermal squamation is uniform in small stages, consisting of round or oval osteoderms with pronounced growth rings; in large larvae, they start to differentiate in certain body regions.     

The ontogeny of Pseudis platensis (Anura,Hylidae): Heterochrony and the effects of larval development on postmetamorphic life

Recent studies have described the giant tadpole, delayed metamorphic transformations, and absence of postmetamorphic growth of the skeleton of Pseudis Platensis. These features address questions about derived patterns of life cycles and the role of the heterochrony during the metamorphosis in anurans. Using anatomical methods, we provide new data on the development of reproductive, digestive and integument systems, and age inference obtained from ontogenetic series of Pseudis platensis. Our results indicate that at the end of metamorphosis, the adult skin is completely differentiated, including the calcified dermal layer; the testis has seminiferous tubules with spermatogonia, spermatocytes, and spermatids; ovarian sacs present previtellogenic ova; and the adult digestive tract is fully formed. The froglets differ from adults only in being unable to reproduce. The entire life cycle of P. platensis can occur in 4 years. In the first year, larval development, growth to adult size, and gonad differentiation are completed. Long larval development rather than size of the tadpoles seems to be involved in the absence of juvenile stages. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Comparison of fatty acid contents and composition in major lipid classes of larvae and adults of mosquitoes (Diptera: Culicidae) from a steppe region

Emerging aquatic insects, including mosquitoes, are known to transfer to terrestrial ecosystems specific essential biochemicals, such as polyunsaturated fatty acids (PUFA). We studied fatty acid (FA) composition and contents of dominant mosquito populations (Diptera: Culicidae), that is, Anopheles messeae, Ochlerotatus caspius, Oc. flavescens, Oc. euedes, Oc. subdiversus, Oc. cataphylla, and Aedes cinereus, inhabited a steppe wetland of a temperate climate zone to fill up the gap in their lipid knowledge. The polar lipid and triacylglycerol fractions of larvae and adults were compared. In most studied mosquito species, we first found and identified a number of short‐chain PUFA, for example, prominent 14:2n‐6 and 14:3n‐3, which were not earlier documented in living organisms. These PUFA, although occurred in low levels in adult mosquitoes, can be potentially used as markers of mosquito biomass in terrestrial food webs. We hypothesize that these acids might be synthesized (or retroconverted) by the mosquitoes. Using FA trophic markers accumulated in triacylglycerols, trophic relations of the mosquitoes were accessed. The larval diet comprised green algae, cryptophytes, and dinoflagellates and provided the mosquitoes with essential n‐3 PUFA, linolenic, and eicosapentaenoic acids. As a result, both larvae and adults of the studied mosquitoes had comparatively high content of the essential PUFA. Comparison of FA proportions in polar lipids versus storage lipids shown that during mosquito metamorphosis transfer of essential eicosapentaenoic and arachidonic acids from the reserve in storage lipids of larvae to functional polar lipids in adults occurred.