Flower Mimics The Smell of Dying Bees to Attract Pollinators

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Pollinator deception is rampant in the plant world. There are serious advantages in tricking your pollinators into thinking they are getting a reward without actually providing one. We have discussed sexual deception in the past ([1] [2]), as well as a case of food deception but a recent discovery has shed light on a new form of food deception in the flowering plant world. It is a strategy that has evolved in a distant relative of the milkweeds and it involves smelling like a dying bee. 

The plant in question is known scientifically as Ceropegia sandersonii. It is a vining species native to South Africa. Like the rest of the members of this genus, C. sandersonii produces bizarrely beautiful flowers that function as pitfall traps. Insects attracted to these blossoms fall down inside and remain trapped for a period of time. As they scramble around inside they inevitably pick up packets of pollen called pollinia. After about a day of imprisonment, the flowers begin to wilt, releasing the insects inside. With any luck these insects will be duped by yet another flower of the same species, and thus pollination is achieved.

How this group of vines goes about attracting potential pollinators varies but, in the case of C. sandersonii, it means smelling like prey. This intriguing plant requires a unique group of kleptoparasitic flies for pollination. Kleptoparasites are any species that make their living by stealing food from other organisms. The flies in question specialize on sucking the juices out of bees that have been attacked by spiders. As the spider liquefies the hapless bee, these flies sneak in and get their fill.

Researchers noticed these flies were frequent visitors of C. sandersonii flowers so they decided to take a closer look at the chemicals responsible for floral scent. Their analyses revealed that the compounds released by the flowers were surprisingly similar to those released by dying bees. In fact, roughly 60% of these compounds were an exact match. Thanks to this discovery, the team hopes that closer inspection of similar flowers will reveal even more unique forms of food mimicry within this genus.

Photo Credits: [1] [2]

Further Reading: [1]

Color Changing Asters

Fall is here and the asters are out in force. Their floral displays are some of the last we will see before the first fall frost takes its toll. Their beauty is something of legend and I could sit in a field and stare at them for hours. In doing so, an interesting pattern becomes apparent. Have you ever noticed that the disc flowers of the many aster species gradually turn from yellow to red? Whereas this certainly correlates with age, there must be some sort of evolutionary reason for this.

Indeed, there is. If you sat and watched as bees hurriedly dashed from plant to plant, you may notice that they seem to prefer flowers with yellow discs over those with red. The plot thickens. What about these different colored discs makes them more or less appealing to bees desperately in need of fuel? The answer is pollen.

A closer observation would reveal that yellow disks contain more pollen than those with red discs. Of course, this does relate to age. Flowers with red discs are older and have already had most of their pollen removed. In this way, the color change seems to be signaling that the older flowers are not worth visiting. Certainly the bees notice this. But why go through the trouble of keeping spent flowers? Why not speed up senescence and pour that extra energy into seed production?

Well, its all about cues. Bees being the epitome of search image foragers are more likely to visit plants with larger floral displays. By retaining these old, spent flowers, the asters are maintaining a larger sign post that ensures continued pollinator visitation and thus increases their chances of cross pollination. The bees simply learn over time to ignore the red disc flowers once they have landed. In this way, they maximize their benefit as well.

Further Reading: [1]