From Herbivore to Pollinator Thanks to a Parasitoid

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In the Atlantic forests of Brazil resides a small orchid known scientifically as Dichaea cogniauxiana. Like most plant species, this orchid experiences plenty of pressure from herbivores. It faces rather intense pressures from two species of weevil in the genus Montella. These weevils are new to science and have yet been given full species status. What's more, they don't appear to eat the leaves of D. cogniauxiana. Instead, female weevils lay eggs in the developing fruits and the larvae hatch out and consume the seeds within. In other words, they treat the fruits like a nursery chamber.

This is where this relationship gets interesting. You see, the weevils themselves appear to take matters into their own hands. Instead of waiting to find already pollinated orchids, an event that can be exceedingly rare in these dense forests, these weevils go about pollinating the orchids themselves. Females have been observed picking up orchid pollinia and depositing the pollen onto the stigmas. In this way, they ensure that there will be developing fruits in which they can raise their young.

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Left unchecked, the weevil larvae readily consume all of the developing seeds within the pod, an unfortunate blow to the reproductive efforts of this tiny orchid. However, the situation changes when parasitoid wasps enter the mix. The wasps are also looking for a place to rear their young but the wasp larvae do not eat orchid seeds. Instead, the wasps must find juicy weevil larvae in which to lay their eggs. When the wasp larvae hatch out, they eat the weevil larvae from the inside out and this is where things get really interesting.

The wasp larvae develop at a much faster rate than do the weevil larvae. As such, they kill the weevil long before it has a chance to eat all of the orchid seeds. By doing so, the wasp has effectively rescued the orchids reproductive effort. Over a five year period, researchers based out of the University of Campinas found that orchid fruits in which wasp larvae have killed off the weevil larvae produced nearly as many seeds as uninfected fruits. As such, the parasitoid wasps have made effective pollinators out of otherwise destructive herbivorous weevils.

The fact that a third party (in this case a parasitic wasp) can change a herbivore into an effective pollinator is quite remarkable to say the least. It reminds us just how little we know about the intricate ways in which species interact and form communities. The authors note that even though pollination in this case represents selfing and thus reduced genetic diversity, it nonetheless increases the reproductive success of an orchid that naturally experiences low pollination rates to begin with. In the hyper diverse and competitive world of Brazilian rainforests, even self-pollination cab be a boost for this orchid.

Photo Credits: [1] [2]

Further Reading: [1]

Parasitic Protection

Strangler figs are remarkable organisms. Germinating in the canopy of another tree, their roots gradually wrap around the host, growing down towards to forest floor. Once in the soil, the interwoven structure of the fig begins to grow and swell. Over time, the strangler fig does what its name suggests, it strangles the host tree. Strangling is bad news for the host, however, new research suggests that strangler figs may actually provide some benefit to larger host trees, at least for part of its life. 

Cyclones are a force to be reckoned with. Their punishing winds can quickly topple even the sturdiest of trees. This is exactly what happened in 2013 when Cyclone Oswald struck Lamington National Park in Australia. Many trees fell victim to this storm but not all. Survival was not random and an interesting pattern started to emerge when researchers began surveying the damage. 

The hollow center of an ancient strangler fig where its host tree once grew and has long since rotted away.  

The hollow center of an ancient strangler fig where its host tree once grew and has long since rotted away.  

They found that large trees hosting strangler figs survived the storm whereas those without were more likely to be uprooted. It appears that hosting these parasitic figs just might have some benefits after all. There are a handful of mechanisms with which strangler figs could be helping their hosts. First is that figs spanning multiple trees may provide stability for the host and its neighbors. Another could come in the form of additional leaf area. The canopy of both the fig and its host tree may help reduce the impact of the cyclone winds. Additionally, once they make it to the soil, the roots of the strangler fig may act as guy-wires, keeping the host tree from uprooting. Finally, The interwoven roots of the strangler fig may act as scaffolding, providing additional structural integrity to the host tree. 

More work will be needed to see which of these are the most likely mechanisms. The mere fact that this parasitic relationship might not be so one-sided after all is quite interesting. What's more, by keeping large tree species alive through devastating cyclone events, the figs are essentially keeping legacy trees alive that can then reseed the surrounding forest. This could explain why host trees have not evolved any obvious mechanism to avoid strangler fig infestation. 

Further Reading: [1]

Broomrape: What's in a Name?

Dr. Reuven Jacobsohn, Agricultural Research Organization, Bugwood.org   licensed under a Creative Commons Attribution-Noncommercial 3.0 License.

Dr. Reuven Jacobsohn, Agricultural Research Organization, Bugwood.org
licensed under a Creative Commons Attribution-Noncommercial 3.0 License.

One can turn a lot of heads by speaking publicly of the plants in the family Orobanchaceae. This interesting and often beautiful parasitic plant family is collectively referred to as the broomrape family. Species with common names like “naked broomrape” and “spiked broomrape” can really make a casual plant conversation turn sour in no time.

Despite how heinous the name sounds, its origin is a bit more innocent. I have really grown to appreciate etymology. Learning the hidden meaning behind the words we utilize for taxonomy can be a lot of fun. It can also teach you a little bit more about the species itself. 

In this context, rape stems from the Latin word “rapum,” which roughly translates to “tuber” or “turnip.” Broom is an English word that, in this context, refers to a shrubby plant related to vetch, which is often parasitized by broomrapes. So, the literal meaning of broomrape is something akin to “broom tuber.” In other words, they are plants growing on the roots of vetch. So, yea, the more you know…

Further Reading: [1]

Photo by Ian Boyd licensed under CC BY-NC 2.0

Photo by Ian Boyd licensed under CC BY-NC 2.0

Photo by Martin Heigan licensed under CC BY-NC-ND 2.0

Photo by Martin Heigan licensed under CC BY-NC-ND 2.0

Photo by Park Ranger licensed under CC BY-NC-SA 2.0

Photo by Park Ranger licensed under CC BY-NC-SA 2.0

Photo by mpaola_andreoni licensed under CC BY-NC-ND 2.0

Photo by mpaola_andreoni licensed under CC BY-NC-ND 2.0