Adelphobates castaneoticus

Adelphobates castaneoticus
Caldwell & Myers, 1990

 
Adelphobates Castaneoticus and Adelphobates quinquevittatus:  A Delicate Web

Both A. quinquevittatus (quinqs) and A. castaneoticus (castis) are closely associated with Brazil nut trees.  Although quinqs and the Brazil nut trees range fairly widely throughout the Amazon Rainforest, it is the casti, known only from Brazilian rainforests, that is actually commonly known as the “The Brazil Nut poison dart frog.” The name castaneoticus comes from Castanah, which is the Portuguese name for the nut.

The preferred tadpole deposition sites for both quinqs and castis are the rain-filled seed pods from the Brazil nut tree that fall to the forest floor. The pods, which can weigh more than five lbs (over 2.27 kilograms), drop from heights as great as 200ft and hit the ground with tremendous force remaining completely intact. Smashing into tree trunks and boulders will not crack them. These seed pods are so dense that it can take 20 minutes or longer to cut one open with a hack saw.

There is, however, one animal with an appetite for Brazil nuts that also has the jaws and chisel-like teeth powerful enough to chew through the giant seed pods. It’s the agouti.

Agoutis (Dasyprocta sp.) are New World cousins of the guinea pig, native to Central and South America. They are solitary, burrowing animals that scour the forest floor for the giant seed pods, gnaw large holes in them, and remove the crescent-shaped hard-shelled seeds. Seeds that are not eaten immediately are buried throughout the rainforest with the expectation that they will be retrieved and consumed at some point in the future. Inevitably, stashes are lost or forgotten, and these will germinate and become seedlings. If conditions are favorable, they will become sturdy saplings with the fortitude to exist until sunlight penetrates the forest canopy and reaches the forest floor.  A tremendously advantageous adaptation of the Brazil nut tree is that it can remain somewhat in “stasis” as a sapling for years in the shadiest reaches of the rainforest. When light finally reaches the sapling, typically due to the felling of an aged or diseased tree (if not by man), a growth spurt is triggered, thus, engaging the young Brazil nut tree in a race with surrounding germination and saplings, all vying for the life-saving chance to fill in the new light gap in the canopy. Losers wither in the darkness. Winners may mature to become centuries-old sentinels of the rainforests.

Before castis or quinqs can deposit their tadpoles in Brazil nut pods; before the agoutis can chew them open and dine on their contents; and before the giant pods can drop with the force of cannon balls onto the forest floor, another precise series of events must continually occur.

Endemic to lowland, non-flooding areas of the Amazon Rainforest from 5°N to 14°S in Venezuela, Colombia, Peru, Bolivia, Suriname, Guyana, and Brazil [1], Brazil nut trees (Bertholletia excels) push far beyond the other vegetation which form the rainforest canopy. If not felled by disease, parasites or man, these giants can reach heights of over 200 feet (over 60 meters) and can live for centuries.  They bloom during the dry season between the months of September and December with peak blooming occurring in October and November. The individual blooms only last a day, providing a fairly brief opportunity for pollination.

Brazil nut trees are essentially allogamous, requiring the services of cross-pollinating agents, such as birds, bats and insects. Fruiting does not occur via self-pollination (same flower); although fruit can occasionally result via geitonogamous pollination (same tree, different flower); however, the rate of germination for the resulting seeds has not been determined.

There are a number of birds, bats and smaller bees that are known to feed on the nectar of Brazil nut flowers; however, for one reason or another they are not effective pollinators. Birds and bats have tongues that can access the nectar, but pollen capture and transfer is apparently negligible. Smaller bees and other insects can slip in to feed without having to pry open the flower, thus not having sufficient contact with the flower’s anthers or stigma, or without collecting pollen in amounts sufficient for effective pollinating.

Enter the brilliantly jewel-toned euglossine bees. These are a tribe of large-bodied bees also known as orchid bees, and several species within this tribe are known to be the primary pollinators of Brazil nut tree flowers. These are the bees large enough to pry open the lids of the Brazil nut tree’s flowers and have tongues long enough to access their nectar while coating themselves in pollen, which is then transferred from flower to flower and tree to tree.

In addition to Brazil nut tree flowers, male euglossine bees also collect the nectar and fragrances from certain orchids. The scents from these orchids and from other sources are stored in special compartments in the bees’ hind legs and released in order to attract mates. Orchids in general are notorious for having evolved as “specialists” that attract very specific pollinators, insuring the perpetuation of the species and avoiding or at least minimizing hybridization. Males of the orchid bee species known to pollinate Brazil nut tree flowers collect the fragrances from orchids of the genera Casteum and Stanahopea, which are the primary ingredients in the scent combinations concocted to attract female orchid bees. Some studies have suggested that the fragrance-producing chemicals may also enhance the male bee’s wing color, further aiding in the attraction of mates.

These orchids do not grow in disturbed habitats. They are endemic to particular, pristine regions of the rainforest where the environmental parameters are narrow. Therefore, the orchid bees which are specifically attracted to them also require these conditions in order to reproduce. Without pristine rainforests, these orchids cannot exist in the wild. Without these orchids, the male orchid bees could not attract mates, and therefore, could not reproduce. Without the orchid bees, the Brazil nut trees could not be pollinated effectively enough to produce fruit enough to perpetuate their existence. Euglossine bees are solitary in habit. They do not build hives and cannot be contained, raised, carted around, released and recaptured by bee keepers in the manner to which humans have become accustomed in other parts of the world. Furthermore, hand pollination of these massive trees that bear short-lived flowers is labor-intensive and impractical. This is precisely why commercial attempts at farming Brazil nut trees have essentially been abysmal. According to the IUCN Red List of Threatened Species, “The sustainable harvesting of nuts by indigenous people in extractive forest reserves offers the most promising protection for the remaining natural stands.” [2]

The bottom line is that the forests need to be preserved intact.

Conservation status for Adelphobates castaneoticus: Under threat from the usual suspects (deforestation, illegal collecting, etc.), it is abundant within its range.

[1] Psyche: Journal of Etymology 2012 (2012), Article ID 978019

[2] IUCNRedlist.org