Pollinaria Reconfiguration Mechanism of Widespread Euro-Mediterranean Orchids: The Effects of Increasing Air Temperature

Abstract

Orchids are fascinating for many reasons: their reproductive strategies, their pollination systems and the various morphological adaptations they have evolved, including the presence of pollen grains agglomerated into two masses, called pollinia, which form a structure known as a pollinarium. After withdrawal from a flower, the pollinarium undergoes a bending movement such that the pollen masses become correctly orientated to strike the stigma. We evaluated the duration of pollinator visits to inflorescences and the effects of temperature on pollinaria reconfiguration in eight orchid species in order to analyze the effects of increasing air temperature on the changes in bending time, and thus on geitonogamy levels. The impact of temperature on insect behavior was not assessed because our priority was to understand the effects of temperature on the process of pollinaria reconfiguration. All the examined species showed natural reconfiguration times that were 1.7-3.0 times longer than the pollinator residency times. A higher temperature showed a reduction in bending time regardless of the species tested. However, the bending time was never shorter than the residence time of the insects on the flower. Our data showed that high temperatures had a limited effect on the pollinarium reconfiguration time, thus indicating that high temperatures had a limited effect on folding compared to the effect that it had on the viability of the pollen.

Keywords: orchids; pollinaria bending; pollinaria reconfiguration; pollinarium; pollinators.

Figure 1

Flower (A), column (B) and pollinarium (C) of an orchid. P = petal, s = sepal, l = labellum, c = column, st = stigma, pl = pollinarium, po = pollinium, ca = caudicle, v = viscidium. Scale bar: 1 cm.

Figure 2

Photos (5×) of the bending movement of pollinaria. Ophrys sphegodes (A) just removed with toothpicks, (B) after 30 s, (C) after 90 s and (D) after 160 s; Dactylorhiza sambucina (E) just removed with toothpicks, (F) after 10 sec, (G) after 15 s, (H) after 25 s, and (I) after 35 s. After photo (D,I) no further bending movements were observed. Scale bar: 1 cm.

Figure 3

Pollinator residency time (black bars) and pollinaria reconfiguration time (white bars) of examined orchids in the field. AMO = Anacamptis morio, APY = A. pyramidalis, DSA = Dactylorhiza sambucina, NUS = Neotinea ustulata, OMA = Orchis mascula, OMI = Orchis militaris, OIN = Ophrys insectifera, OSP = O. sphegodes.

Figure 4

Reconfiguration time of pollinaria stored at high temperatures (35–50 °C) of food-deceptive orchids (A) and sexually deceptive orchids (B).

Figure 5

Pollinator residency time (black line) and reconfiguration time of pollinaria stored at 50 °C (white bars) of examined orchids. AMO = Anacamptis morio, APY = A. pyramidalis, DSA = Dactylorhiza sambucina, NUS = Neotinea ustulata, OMA = Orchis mascula, OMI = Orchis militaris, OIN = Ophrys insectifera, OSP = O. sphegodes.