Information theory and the neuropeptidergic regulation of seasonal reproduction in mammals and birds

Seasonal breeding in the temperate zone is a dramatic example of a naturally occurring change in physiology and behaviour. Cues that predict periods of environmental amelioration favourable for breeding must be processed by the brain so that the appropriate responses in reproductive physiology can be implemented. The neural integration of several environmental cues converges on discrete hypothalamic neurons in order to regulate reproductive physiology. Gonadotrophin-releasing hormone-1 (GnRH1) and Kisspeptin (Kiss1) neurons in avian and mammalian species, respectively, show marked variation in expression that is positively associated with breeding state. We applied the constancy/contingency model of predictability to investigate how GnRH1 and Kiss1 integrate different environmental cues to regulate reproduction. We show that variation in GnRH1 from a highly seasonal avian species exhibits a predictive change that is primarily based on contingency information. Opportunistic species have low measures of predictability and exhibit a greater contribution of constancy information that is sex-dependent. In hamsters, Kiss1 exhibited a predictive change in expression that was predominantly contingency information and is anatomically localized. The model applied here provides a framework for studies geared towards determining the impact of variation in climate patterns to reproductive success in vertebrate species.     

Maternal influence on diapause induction in Trichogramma (Hymenoptera: Trichogrammatidae): the dynamics of photosensitivity

It is known that the prepupal diapause in Trichogramma is dependent on temperature conditions of embryonic and larval development and on the photoperiodic conditions of preimaginal development of maternal females. However, the relative photosensitivity of different preimaginal stages has been never investigated. We studied the position of the photosensitive period over the preimaginal development of maternal females in T. embryophagum Htg. and T. principium Sug. et Sor. by transferring preimaginal stages between diapause‐averting ‘long’ day (L : D = 20 : 4) and diapause‐inducing ‘short’ day (L : D = 12 : 12). Results showed that the influence of maternal photoperiod on progeny diapause was determined during the late pupal stage (last days of preimaginal development at 20°C). During this time, the critical duration of the photoperiodic induction was extremely small: one short or long day caused almost the same effect as the permanent development under these conditions. As a whole, photoperiodic response in Trichogramma was found to be unusually rapid, labile and easily reversible which is probably explained by extremely small size and fast development of these egg parasitoids. The results of this study could be used for elaboration of optimal methods for Trichogramma mass rearing and storage and for prediction of its seasonal cycles under natural conditions.     

LED光质及光周期对香子含笑幼苗生长和光合特性的影响

香子含笑(Michelia gioii)为我国珍贵阔叶树种,在用材、香料、景观等方面具有重要价值。为了进一步培育优良苗木和开发利用其非木质资源,该研究将香子含笑幼苗放置在由2个光周期(12、16 h·d^-1)和4种光质(R:B=8:1、R:B=6:1、R:B:P:G =8:1:1:1、R:B:P:G=6:1:1:1,其中R、B、P、G分别代表红光、蓝光、紫光、绿光)两两组合成、光照强度一致的8个光照条件下生长。结果表明:(1)香子含笑幼苗的苗高和地径增长量、叶长宽比、最大净光合速率、暗呼吸速率及光补偿点在12 h·d^-1光周期R:B=6:1光质下最高,叶面积和叶绿素含量在16 h·d^-1光周期R:B:P:G=6:1:1:1光质下最高。(2)16 h·d^-1光周期处理下的苗高增长量、叶面积、质量指数、叶绿素a+b含量、叶绿素a/b比值、类胡萝卜素含量和光饱和点均高于12 h·d^-1光周期。(3)在红蓝组合光质基础上添加紫、绿光提高了幼苗的质量指数,并影响光合色素的合成和积累;(4)光质R:B=6:1与R:B=8:1相比,更具有促进香子含笑幼苗苗高、地径、叶片生长及提高光合作用的潜力。综上结果认为,对于促进香子含笑幼苗生长和进行光合作用,光周期为 16 h·d^-1光质为R:B:P:G=6:1:1:1光照条件的潜力较大,其次是光周期为12 h·d^-1光质为R:B=6:1的光照条件。     

A high-temperature water vapor equilibration method to determine non-exchangeable hydrogen isotope ratios of sugar,starch and cellulose

The analysis of the non-exchangeable hydrogen isotope ratio (δ²H_ne) in carbohydrates is mostly limited to the structural component cellulose, while simple high-throughput methods for δ²H_ne values of non-structural carbohydrates (NSC) such as sugar and starch do not yet exist. Here, we tested if the hot vapor equilibration method originally developed for cellulose is applicable for NSC, verified by comparison with the traditional nitration method. We set up a detailed analytical protocol and applied the method to plant extracts of leaves from species with different photosynthetic pathways (i.e., C₃, C₄ and CAM). δ²H_ne of commercial sugars and starch from different classes and sources, ranging from ?157.8 to +6.4‰, were reproducibly analysed with precision between 0.2‰ and 7.7‰. Mean δ²H_ne values of sugar are lowest in C₃ (?92.0‰), intermediate in C₄ (?32.5‰) and highest in CAM plants (6.0‰), with NSC being ²H-depleted compared to cellulose and sugar being generally more ²H-enriched than starch. Our results suggest that our method can be used in future studies to disentangle ²H-fractionation processes, for improving mechanistic δ²H_ne models for leaf and tree-ring cellulose and for further development of δ²H_ne in plant carbohydrates as a potential proxy for climate, hydrology, plant metabolism and physiology.     

Photoperiodic control of sugar release during the floral transition: What is the role of sugars in the florigenic signal?

Florigen is a mobile signal released by the leaves that reaching the shoot apical meristem (SAM), changes its developmental program from vegetative to reproductive. The protein FLOWERING LOCUS T (FT) constitutes an important element of the florigen, but other components such as sugars, have been also proposed to be part of this signal.^1-5 We have studied the accumulation and composition of starch during the floral transition in Arabidopsis thaliana in order to understand the role of carbon mobilization in this process. In A. thaliana and Antirrhinum majus the gene coding for the Granule-Bound Starch Synthase (GBSS) is regulated by the circadian clock^6,7 while in the green alga Chlamydomonas reinhardtii the homolog gene CrGBSS is controlled by photoperiod and circadian signals.^8,9 In a recent paper¹⁰ we described the role of the central photoperiodic factor CONSTANS (CO) in the regulation of GBSS expression in Arabidopsis. This regulation is in the basis of the change in the balance between starch and free sugars observed during the floral transition. We propose that this regulation may contribute to the florigenic signal and to the increase in sugar transport required during the flowering process.     

Patterns of diapause frequency and emergence in swede midges of southern Ontario

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