Diversity of Reproductive Systems in Plants:

Ecology, Evolution and Conservation, Abstructs

Relationship between flowering duration andfloral sex allocation within inflorescences in Aquilegiabuergeriana

Tomoyuki Itagaki and Satoki Sakai (Graduate School of LifeSciences, Tohoku University)

Flowering duration of a flower may affect male and female reproductive success of the flower. Hence, if flowering duration differs among flowers within inflorescences, the reproductive success of each flower may also differ among these flowers. We compared flowering duration (=male and female duration), floral sex allocation (=the number of pollen grains and ovules), and reproductive success (=pollen removal and seed production) between early- and late-opened flowers within inflorescences in Aquilegia buergeriana. The purpose of this study was to examine whether the difference in male and female duration leads to the differentiation in floral sex allocation among flowers within inflorescences.

(1) Male function. The number of pollen grains removed was greater in flowers with long male duration in both early- and late-opened flowers, indicating that male duration may positively affect male reproductive success. Furthermore, male duration was longer and the number of pollen grains per flower was greater in early-opened flowers than in late-opened ones. Therefore, male reproductive success was greater in early-opened flowers than in late-opened flowers because of the long male duration in the former flowers.

(2) Female function. There was no significant relationship between seed production per flower and female duration. This suggests that female duration has no effect on female reproductive success. In our study, however, female duration was slightly longer and the numbers of ovules and seeds per flower were greater in early-opened flowers than in late-opened ones. Other factors such as resource availability of individual flowers may affect resource allocation to female function.

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Does interaction between bees reduce theirforaging area?

: bee-removal experiments in a net cage

Takashi T. Makino and Satoki Sakai (Graduate School of LifeScience, Tohoku University)

Makino and Sakai (unpublished) showed that the main foraging plants of bumblebees seemed to differ among bees though their foraging areas overlapped. If interaction between bees determines their foraging areas, the foraging area of a bee become small when many bees are foraging simultaneously, and vice versa. To examine this, we carried out bee-removal experiments in a 20.0 x 20.0 m net cage with a height of 2.0 m.

In the cage, we set 37 potted plants (Salvia farinacea) in a hexagonal array, and allowed bumblebees (Bombus ignitus) to forage freely on those plants. To find a bee with relatively small foraging area, we followed some bees that were randomly selected out of about 20 bees foraging simultaneously. Then we removed all the other foraging bees except for the bee with a small foraging area, and observed the change of the foraging area of the focal bee under no interaction with other bees. We conducted this for five different bees.

After the removal of bees, the focal bees began to visit plants they had seldom used under interaction with other bees. Namely, we found that bees with small foraging areas extended their foraging areas when they were released from the interaction between bees. This result suggests that the interaction between bees is an important determinative of their foraging area. The result also means that bumblebees could adjust their foraging area in response to other foragers. Further studies are necessary to clarify what keys bees used to interact with other bees.

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