Typically pollination is an exchange of services. A pollinator arrives, collects pollen and a reward. Then it flies to another flower, leaves some pollen and gets another reward. But this isn’t always the case. Orchids, in particular, can be sneaky.
Insects aren’t just after food. Many orchids take advantage of the urge to mate. It’s not uncommon for part of an orchid to resemble a female insect and hit a male with pollen when it arrives. Disappointed, the insect leaves for another female, or possibly another orchid, delivering the pollen without reward.
It is known that Telipogon peruvianus uses sexual deception for pollination, but it’s not been clear how. Does it look like a female? Does it smell like a female? A new study by Carlos Martel and colleagues suggests it’s doing something more interesting. The orchid is mimicking two things at once.
Carlos Martel has been busy with Telipogon, discovering a few species himself. I asked him what drew him to T. peruvianus. “It was in part a matter of luck. As part of my doctoral project, I was interested in understanding the pollination ecology in the genus Telipogon, which is highly diverse (more than 200 species in the genus and many more waiting description!) and their flowers are big and showy. I asked William Nauray, who was working on Telipogon from Southern Peru, for a suitable place to find many Telipogon individuals, as most Telipogon species have scattered distributions and only a few individuals per population, and he recommended me to work in Marcapata with T. peruvianus, an endemic and highly restricted species, but with many individuals occurring in the same place.”
With so many species of Telipogon it’s not surprising that a lot of them look similar. Martel explained there are clues if you have the eye for it. “There are two kinds of Telipogon species. Most species have conspicuous flowers (yellow petals and lip and a dark red central part) and a small group of species with minute flowers which are not colourful. In general, flowers of different Telipogon species can be very similar, but the key factors for species differentiation are those associated with the central part of the flower (callus and column), as those interact directly with the pollinators.”
In the case of the team found that the scents matched a female Eudejeania fly, the tiny fly that pollinates T. peruvianus. The difference in size between the fly and flower and some reading were the clues to what was going on. “There were already some mentions that flowers of some Telipogon species resemble a female fly seated on a flower. This was not the case of T. peruvianus, as it does not the characteristic setae on their flowers. I started believing that T. peruvianus mimics two organisms after identifying the pollinator (less than 2 cm long) and relating it to the Telipogon flower size (ca. 6 cm diameter!), and seeing that pollinators usually feed on nectar on daisies with yellow ray florets. If Telipogon mimics the female only, the species would not need to invest in producing such big flowers.”
The reason a male Eudejeania fly would be interested in a female on a flower isn’t just about sex. The flower the orchid mimics is the daisy that Eudejeania flies feed on. The combination of sex and food makes an even stronger lure for male flies.
It might also seem that the colour of the orchid would mimic the colour of the daisy, but Martel found the reality is a little more complicated. “Initially I thought color mimicry was involved as Telipogon and the daisy have yellow flowers to the human eye. But I was surprised that the reflectances were highly different. However, everything made sense after seeing that the white part of T. peruvianus flowers reflects UV light, which the daisy also does. More reading led to the research of Anne Gaskett and colleagues. They found convergent evolution via chromatic and achromatic contrast in two sexually deceptive orchid genera pollinated by the same wasp species.”
Finding T. peruvianus uses contrast as a signal is a mix of both familiar and strange, Martel said. “There are already some studies showing that contrast is an important cue for flower detectability by pollinators. However, as far as I know, there are no examples showing that contrast is involved in any deceptive pollination system. It was suggested that contrast would also be an important cue in pollination systems involving sexual deception as species of two Australian orchid genera produce flowers, which are highly contrasting with their environment, but no colour mimicry was apparent.”
While the flower is easy enough to find if you are a fly, Martel found it’s more difficult for humans. “It was very challenging. In general, Andean topography makes everything more complicated, especially when you consider the high altitudes at which Telipogon species can be found. Most Telipogon species occurs in the cloud forest between 2000 and 3500 m above sea level, characterized by contrasting weather (i.e., temperature below zero at night, with often cloudy and rainy days). For my study on T. peruvianus, I was based in a very small town called Marcapata (3000 m), which was on the hill in front of where T. peruvianus is found (2850 m). To reach T. peruvianus populations, I went down a hill every day, cross the Araza river by foot and then walk to the boundaries of the forest (around one hour by walk in total). This was my routine for around nine months for three years.
Working in these conditions doesn’t just make getting to the flowers difficult. You also have to get samples back. Fortunately, Martel was not short of help. “In Marcapata, I was hosted by a kind couple Jose and Juana Gutierrez. They allowed me to use their home freezer to store my samples and even went to my sampling sites with me on several occasions. T. peruvianus can be found in only two localities, one in front of Marcapata town and the other, on the other side of the mountain. In Marcapata, dozens of plants blooming can be found in a small area between August and September.”
Martel has research plans for the future, but they will involve leaving Telipogon behind. “There are a few more papers coming out about Telipogon pollination (records reporting self-pollination and pollination involving pseudocopulation) and taxonomy. It is an exciting genus to work with, but to be honest, it was very challenging, and I will not start any other project on Telipogon until I have better conditions to make the field work less complicated. There are other nice pollination systems that are not so complicated.”
Gaskett, A. C., Endler, J. A., & Phillips, R. D. (2016). Convergent evolution of sexual deception via chromatic and achromatic contrast rather than colour mimicry. Evolutionary Ecology, 31(2), 205–227. https://doi.org/10.1007/s10682-016-9863-2
Martel, C., Cairampoma, L., Stauffer, F. W., & Ayasse, M. (2016). Telipogon peruvianus (Orchidaceae) Flowers Elicit Pre-Mating Behaviour in Eudejeania (Tachinidae) Males for Pollination. PLOS ONE, 11(11), e0165896. https://doi.org/10.1371/journal.pone.0165896
Martel, C., Francke, W., & Ayasse, M. (2019). The chemical and visual basis in the pollination of the neotropical sexually deceptive orchid Telipogon peruvianus (Orchidaceae). New Phytologist. https://doi.org/10.1111/nph.15902