Abstract Detail

Reproductive Processes

Ohashi, Kazuharu [1], Jürgens, Andreas [2].

Three options are better than two: complementary nature of different pollination modes in Salix caprea.

Mixed pollination systems have been reported for many angiosperm species. Some species are pollinated by both diurnal and nocturnal animals. Others utilize animal pollinators in combination with wind pollination. Here, we report on a dioecious willow, Salix caprea L., which employs all three pollination modes by producing small pollen grains and nectar, as well as by switching different floral scent compounds between day and night to specifically attract diurnal bees and nocturnal moths. We tested whether and how the combination of three pollination modes in S. caprea serves as an insurance mechanism against reproductive failure. In four field populations of S. caprea in Germany, we addressed the following questions: (a) How is each pollination mode limited by mate availability? (b) Does the use of three pollination modes increase the total seed set? (c) How do plants reduce negative interactions between diurnal and nocturnal pollinators? For each female tree, 7-28 inflorescences were selected and assigned to six treatments, among which we compared seed set: (i) open pollination, (ii) diurnal pollination, (iii) nocturnal pollination, (iv) wind pollination, (v) artificial pollination, (vi) no pollination. We also recorded the onset of anthesis with time-lapse photography. Finally, we examined pollen longevity in 24˚C and -20˚C. Pollen limitation was observed in all populations. The three modes were complementary with regard to mate availability. Wind pollination was most strongly limited by the distance to the nearest male, and also limited by the directional diversity of nearby males. Besides, nocturnal pollination was much less effective than diurnal pollination but significantly increased the total seed set. This was most evident in a population where male availability was extremely low: nocturnal pollination resulted in a slight but significant increase in seed set compared to wind pollination. The onset of flower anthesis peaked at sunset, which would prioritize the visits by nocturnal moths. Nocturnal opening of flowers might be a way to avoid the potential tradeoff between pollen wastage by diurnal bees and pollination by infrequent but more efficient nocturnal moths. Cold night temperatures had no negative effect either on seed set or pollen viability. Overall, the three pollination modes in S. caprea maximize total seed set by complementing each other with regard to mate availability, while reducing potential conflicts over the opportunity of pollination contribution between diurnal and nocturnal pollinators.

1 - University of Tsukuba, School of Life and Environmental Science, Tennodai 1-1-1, Tsukuba, Ibaraki, 305-8572, JAPAN
2 - Technische Universität Darmstadt, Biology, Schnittspahnstrasse 4, Darmstadt, Hessen, 64287, GERMANY

Keywords:
anemophily
Dioecy
diurnal pollinators
entomophily
generalized pollination systems
nocturnal pollinators
reproductive assurance
tradeoff
local mating environment.

Presentation Type: Oral Paper
Session: REP2, Reproductive Processes 2
Location: Virtual/Virtual
Date: Wednesday, July 29th, 2020
Time: 1:45 PM
Number: REP2006
Abstract ID:507
Candidate for Awards:None