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Seasonal dormancy is a widespread mechanism for reducing energy expenditure during periods of low energy availability. Seasonal variation in activity and the cost of pumping water through the siphons were investigated to estimate the importance of activity regulation to the seasonal energy budget of the Antarctic clam, Laternula elliptica. In the laboratory, a metabolic rate of 26.35 μmol O2 h−1 was estimated for a 50-mm shell length L. elliptica pumping water at −0.4 °C. In the field, the proportion of time siphons were visible at the sediment surface varied seasonally (32% visible in June/July compared to 86% in December/January). L. elliptica were actively pumping for a minimum of 19% of each 24-h period during winter (August) compared to a summer maximum when animals were actively pumping for 73% of the time (February). This resulted in a 3.7-fold seasonal difference in the calculated energy consumption of a 50-mm L. elliptica (19.2 μmol O2 h−1 in February versus 5.0 μmol O2 h−1 in August), which closely matches the 3.0-fold seasonal variation in metabolic rate found previously. Seasonal variation in activity could therefore be responsible for much of the seasonal difference in energy consumption of L. elliptica. Inter-annual variation in timing of the seasonal activity maxima (January 2004 and March 1999) was correlated with variation in the timing of the summer plankton bloom in Ryder Bay. In the laboratory, periods of extended siphon closure (133 ± 114 min, mean ± SD) were accompanied by long periods of heart arrhythmia (167 ± 135 min), during which time blood oxygen levels dropped to values close to zero. Heart arrhythmia is most likely part of a hypo-metabolic adaptation to reduce energy costs during extended periods of siphon closure. Physiological and behavioural dormancy, with associated hypoxia tolerance, appear to be key mechanisms controlling the seasonal energy budget of L. elliptica.  相似文献
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赤霉素是一种高效能的广谱植物生长调节剂,能够促进植物的生长发育,具有重要的生物学功能。该文主要对国内外近年来有关赤霉素在木本植物季节性休眠解除中的应用、赤霉素解除木本植物季节性休眠的生理机制、赤霉素代谢相关基因在木本植物季节性休眠中的作用以及赤霉素解除木本植物季节性休眠的分子机制等方面的研究进展进行综述,同时对下一步的研究方向进行了展望,以期能够更好地阐述赤霉素解除木本植物季节性休眠的分子机制,为赤霉素在木本植物季节性休眠解除中的应用提供理论依据。  相似文献
3.
  • Dormancy cycles are an important mechanism for avoiding seed germination under unfavourable periods for seedling establishment. This mechanism has been scarcely studied in tropical species. Here, we studied three tropical and perennial species of Xyris, X. asperula, X. subsetigera and X. trachyphylla, to investigate in situ longevity and the existence of seasonal seed dormancy cycles.
  • Seeds of three species of Xyris were buried in their natural habitat, with samples exhumed bimonthly for 18 months. Germination of exhumed seeds was assessed under a 12‐h photoperiod over a broad range of temperatures. Seeds of X. trachyphylla were also subjected to treatments to overcome secondary dormancy.
  • Seeds of all species are able to form a persistent seed bank and exhibit seasonal changes in germinability. Secondary dormancy was acquired during the rainy summer and was overcome during the subsequent dry season (autumn/winter). Desiccation partially overcomes secondary dormancy in X. trachyphylla seeds.
  • Soil seed bank persistence and synchronisation of seed germination under favourable conditions for seedling establishment contribute to the persistence and regeneration of X. asperula, X. subsetigera and X. trachyphylla in their natural environment.
  相似文献
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Taxonomic investigations of the Delias mysis (Fabricius, 1775) complex from northern Australia indicate two additional species in the Australian fauna: Delias aestiva Butler, 1897 stat. rev. and Delias lara (Boisduval, 1836). The latter species, which is illustrated from Australia for the first time, was until recently known under the name Delias mysis onca Fruhstorfer, 1910. Evidence from adult morphology (male genitalia), colour pattern of the adult and immature stages, behaviour, and ecology indicates substantial phenotypic divergence between D. aestiva and D. mysis. Within Australian limits, all three taxa are allopatric: D aestiva is endemic to the Top End, Northen Territory, D. mysis mysis is restricted to northern and north‐eastern Queensland, whereas Delias lara lara is known only from three specimens from the Torres Strait islands, Queensland. Delias aestiva is perhaps the most remarkable member of the complex and indeed the genus, breeding in tropical mangrove habitats in coastal estuarine areas where the larvae specialize on mature foliage of the tree Excoecaria ovalis Endl. (Euphorbiaceae). This host preference is novel given the general tendency of Delias to feed on hemiparasitic plants in the order Santalales (Loranthaceae, Santalaceae and Viscaceae). Under laboratory conditions, however, larvae successfully completed development on the mistletoe genera Amyema, Dendrophthoe and Decaisnina (all Loranthaceae) with no significant reduction in larval survival. These findings, together with phylogenetic hypotheses of the Aporiina and Delias, indicate a recent evolutionary host shift from Loranthaceae to Euphorbiaceae. The foliage of Excoecaria produces toxic latex, which is composed of a variety of secondary plant compounds, including diterpenoids, triterpenoids, alkaloids and phorbol esters. The mechanism of detoxification has not been established, although the larvae of D. aestiva are gregarious, regurgitate fluid as part of their chemical defence, and the adults are highly aposematic. Adults are seasonal, being chiefly on the wing during the cooler dry season; during the wet season, the larval food plant is seasonally deciduous and it is suspected that the butterfly undergoes pupal diapause. The cryptically coloured green pupa and tendency to pupate singly in concealed situations of D. aestiva are highly unusual traits among Delias and are hypothesized to be adaptive responses associated with pupal diapause during the wet season. The unique habitat association, novel food plant specialization, and restricted distribution of D. aestiva emphasizess the biogeographical peculiarities of northern Australia, especially patterns of historical (vicariant) differentiation between the Top End and Cape York Peninsula within the Australian Monsoon Tropics. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 697–720.  相似文献
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