Experimental investigation on weather cues for mast seeding of Fagus crenata

Although a recent study has suggested that the minimum temperature from late April to mid-May in the year preceding flowering causes mast seeding in Fagus crenata, no direct evidence is available to support this finding. The aim of the present investigation was, therefore, to test – in a field experiment – whether the minimum temperature determines mast seeding in F. crenata. We examined the effect of nighttime temperatures on flower-bud initiation in F. crenata by enclosing fruit-bearing branches in heated bags at night, thereby maintaining average nighttime temperatures of approximately 2°C above the ambient temperatures. Heating was applied at night from 21 April to 20 May, 21 May to 19 June, and 21 April to 19 June in 2001. Female inflorescence initiation was inhibited by the nocturnal heating in the period 21 April to 20 May and 21 May to 19 June. However, nocturnal heating from 21 April to 20 May was the more important based on the odds ratio of the former being much lower than that of the latter in a logistic regression model. Male inflorescence initiation was also inhibited by nocturnal heating from 21 April to 20 May. We therefore conclude that flower-bud initiation in F. crenata was controlled by nighttime temperatures between 21 April and 20 May.     

The phylogeny of the louse genus Brueelia does not reflect host phylogeny

The general flowering (GF) events of forests in south-east Asia are perhaps the most spectacular phenomena in tropical biology. GF events occur at multiyear intervals. In GF, most dipterocarp species and many plants of other families come into flower and set fruit massively; these species and plants rarely flower except during GF events. GF is unique, because it can occur over thousands of kilometers and involve hundreds of plant species representing diverse families and lifeforms. It also involves strict mast fruiting. Satiation of generalist seed predators has been considered a primary force for GF. However, recent observations indicate that several selective agents rather than a single major factor may shape GF. In addition to the satiation of generalist predators, promotion of pollination could be one of the selective factors for GF, since synchronized flowering of many species causes an increase in pollinator activity through immigration and population growth. Although environmental prediction for better establishment of seedlings may also be involved in GF, no field data have been reported to support this idea. Long-term monitoring and further understanding of GF are essential for the conservation of this unique and diverse tropical forest in south-east Asia, especially in a period of global climatic change. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 233–247.     

Prolonged diapause and seed predation by the acorn weevil,Curculio robustus,in relation to masting of the deciduous oak Quercus acutissima

Many researchers have studied the relationship between masting by trees and seed predation by insects. Most of these studies have been plant centered, with little focus on the insect perspective. To estimate the effect of mast seeding on insect seed predators, the life‐history traits of these insects must also be considered because some seed insects can survive lean years by prolonged diapause. In this study, I examined larval infestation of acorns and life‐history traits of the acorn weevil, Curculio robustus (Roelofs) (Coleoptera: Curculionidae), in relation to acorn production of the deciduous oak Quercus acutissima Carruthers (Fagaceae) in a coppice stand in central Japan in 2004–2009. Curculio robustus females oviposit into Q. acutissima acorns, inside which the larvae develop. Mature larvae leave acorns and burrow into the soil, where they overwinter. Although germination did occur in acorns infested by weevil larvae, the percentage of germination was lower in acorns damaged by many larvae. Acorn production in Q. acutissima varied considerably among years. Both the number of C. robustus larvae infesting acorns and the percentage of acorns infested were affected by the amount of acorns produced by Q. acutissima, and two successive lean years appeared to have a considerable impact on C. robustus population size. Consequently, only a small fraction of the acorns produced were lost to predation in a mast year after two successive lean years. However, C. robustus could survive the two successive lean years because of prolonged larval diapause, probably leading to a marked decrease in population size. These findings suggest that masting in Q. acutissima succeeds as a predator satiation strategy in response to acorn damage by C. robustus, and that C. robustus has developed prolonged diapause as a counter‐adaptation.     

Mast seeding in Abies balsamea, Acer saccharum and Betula alleghaniensis in an old growth, cold temperate forest of north-eastern North America

1 Several hypotheses have been put forward to explain the phenomenon of masting or mast seeding, i.e. the supra-annual, periodic production of a large number of seeds in long-lived plants. Some of these hypotheses deal with the proximate causes of masting (e.g. the climate hypothesis) but others are concerned mostly with ultimate, evolutionary explanations (e.g. the pollination efficiency hypothesis).
2 The seed production of three tree species, Abies balsamea , Acer saccharum and Betula alleghaniensis , was followed over a 7-year period in an old-growth, cold temperate forest of north-eastern North America. The main objectives were to determine the extent of interannual variations in seed production, to investigate the relationship between viable and potential seed crop and crop efficiency, and to explore the effects of climate on seed production.
3 Potential and viable seed production varied significantly among years for all three species. However, the timing of dispersal remained the same regardless of the level of seed production.
4 Seed rain was spatially less heterogeneous in years of high seed production, suggesting that most trees were reproducing in such years.
5 Over the 7-year period, there was a significant concordance among species in their viable seed crop and crop efficiency, but not in their potential seed crop. Crop efficiency was positively correlated to potential seed crop for Abies and Betula , but not for Acer .
6 High seed production was related to warm, dry conditions in the spring of the previous year (i.e. at reproductive bud initiation) but to a moist summer in the year of seed maturation.
7 Masting in these three species thus appears to be controlled by several factors, including climate and pollination efficiency.