Sexual reproduction advances autumn leaf colours in mountain birch (Betula pubescens ssp. czerepanovii)

Autumnal change in leaf colour of deciduous trees is one of the most fascinating displays in nature. Current theories suggest that autumn leaf colours are adaptations to environmental stress. Here I report that the number of ripening female catkins altered timing of yellow autumn leaf colours in mountain birch. The tree's autumnal colour change was brought forward if the tree matured plenty of female catkins. Since yellow colour pigments in leaves are unmasked as leaf nitrogen is re-translocated, sexual reproduction may alter resource allocation at times of leaf senescence. Thus, our current view on the reasons for leaf senescence has to be re-examined, and a novel evolutionary explanation is needed for the appearance of yellow autumn leaf colours.     

关于一些植物学术语的中译等问题(三)

(1)确定rhizome的中文译名“根状茎”符合此术语的定义,同时认为另一中文译名“根茎”不符合有关定义,且易引起误解,应予废弃。(2)介绍了在中国植物学文献中稀见的2种属于有限花序类的花序类型,有限伞形花序和有限头状花序。根据有关欧美专家的花序研究,介绍了在中国植物学文献中放在无限花序类的隐头花序和柔荑花序系由聚伞花序演化而出,而应属于有限花序类的论断; 同时,作者提出楼梯草属梨序楼梯草组的雄隐头花序系由同属的骤尖楼梯草组的有限头状花序演化而出的论点。     

Folivorous larvae on flowers: do autumnal moths benefit from catkins of the mountain birch?

Immature leaves of birches and other deciduous trees and shrubs are the principal food resource for the larvae of the autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae). However, the larvae of this geometrid, which displays pronounced population cycles and causes massive forest defoliations in northernmost Europe, are also frequently found on the catkins of mountain birch, Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti (Betulaceae). To examine whether autumnal moth larvae visit birch catkins for their high nutritional value, we conducted two growth experiments in which the larval diet was supplemented with male catkins, and a single test where female catkins were used. We found that the presence of male catkins in the larval diet had a positive effect on the larvae, in relation to their pupal mass (reflecting life span fecundity), survival probability, as well as the duration of the larval period. The presence of female catkins in the diet did not affect larval performance. Our findings suggest that young autumnal moth larvae actively move to male catkins, which provide a nutritional benefit and thus lead to a better performance compared with those feeding elsewhere. Another possible benefit for young larvae choosing the catkins instead of leaves may involve predator or parasitoid avoidance.     

Androgyny of individuals and polygamy in populations of Salix myrsinifolia Salisb. in the south-western part of its geographical range (NE-Poland)

The aims of the study were to describe the phenomenon of androgyny (a change in the sexual behaviour of individuals) in Salix myrsinifolia, and to consider the implications of androgyny for the sex structure of local populations and for the sex structure of the species across a larger geographical range. Field surveys of the sexual behaviour of individuals and populations of Salix myrsinifolia were carried out over nine years (1989–1997) in an area of 40,000 km² of NE-Poland. More detailed studies were performed on populations in Polana Białowieska (the Białowieża Clearing) in the Białowieża Primeval Forest, in the Białystok area, in the Biebrza Valley and in the experimental garden and laboratory of the Białowieża Geobotanical Station.

The bisexuality of Salix myrsinifolia is basically expressed through the development of a number of different forms of catkin that are intermediate between those that are entirely male and those that are entirely female. Flowers on bisexual catkins are fully developed, as on monosexual ones, but the male segment usually develops prior to the female one. With the exception of one form, a clear partitioning between the male and female parts of the catkin remains. This partitioning of the genders mainly takes place transversely, but in one case longitudinally. It is thus usually possible to speak of the division of a bisexual catkin into male and female sectors.

In all three populations studied in detail, marked shrubs, on which bisexuality had been noted at the beginning, retained this trait throughout the 9-year observation period. However, there were changes in both the expression of bisexuality, i.e. the frequency of bisexual and monosexual catkins, and in the frequency of different patterns of bisexual catkin. Only bisexual individuals with a clear prevalence of female features retained their character. In the two larger populations studied, many originally monosexual individuals became bisexual during the study period.

In the south-western part of the range of S. myrsinifolia in NE-Poland all local populations were characterized by the presence of bisexual individuals and are thus polygamous. There was a close association between the presence of S. myrsinifolia and the degree of ruderalization of habitats. The degree of polygamy in a population was also significantly correlated with ruderalization. It is concluded that androgyny and polygamy may be favoured not only by changes in environmental conditions, but also by the particular pressures to which individuals and populations of a species may be subject at the edge of its geographical range.     

关于一些植物学术语的中译等问题(三)

(1)确定rhizome的中文译名"根状茎"符合此术语的定义,同时认为另一中文译名"根茎"不符合有关定义,且易引起误解,应予废弃。(2)介绍了在中国植物学文献中稀见的2种属于有限花序类的花序类型,有限伞形花序和有限头状花序。根据有关欧美专家的花序研究,介绍了在中国植物学文献中放在无限花序类的隐头花序和柔荑花序系由聚伞花序演化而出,而应属于有限花序类的论断;同时,作者提出楼梯草属梨序楼梯草组的雄隐头花序系由同属的骤尖楼梯草组的有限头状花序演化而出的论点。