by: Lucas Thow, Gabrielle di Gironimo, Annie Quadros and Lily Ragsdale
The forests of Costa Rica are home to a wide range of amazing creatures. Large or small, cleverly camouflaged or vividly coloured, their presence is what makes Costa Rica one of the most biodiverse regions in the world. Despite their beauty, many of the species can be lethal if not properly handled, or in some cases, completely avoided. A common defense many species have developed throughout their evolution is the use of toxins, dangerous to both predators and humans alike. Toxins are found in species of all types, however they may vary in chemical composition, potency and method of transfer from species to species. Below are four species common to the Costa Rican forests, each with it’s own form of toxic defense.
Strawberry poison dart frog
The Strawberry poison dart frog (Oophaga pumilio) is a common species of poisonous frog found throughout Central America. It’s habitat ranges from eastern Nicaragua, through Costa Rica, and into north-eastern Panama. This species is often found dwelling on rainforest floors, under low growing vegetation (Penner 2011). The species is considered to be of Least Concern status on the IUCN Red List, meaning the threat of it’s extinction is extremely low (IUCN 2015).
Figure 1: strawberry poison dart frog habitat region.
Strawberry poison dart frogs can easily be identified by their bright and vivid coloration. The entire body of the frog is a bright red-orange colour, save for it’s feet, and often times entire hind legs, which are a metallic gray-blue speckled with black. The frog is often referred to as the “blue-jeans” poison dart frog due to the colour of it’s hind legs. Relatively small in size, the Strawberry poison dart frog ranges from 17-24mm in length (Sandmeier 2001). The aposematic coloration of the frog is used as a warning mechanism to alert predators of it’s poisonous nature (Summer et. al. 2001). The coloration within the species is incredibly diverse, which is said to be due to sexual selection over time, however other research suggests their vivid coloration could have developed in correlation with their toxicity (Summer et. al. 2001). Despite their small size, their presence rarely goes unnoticed due to the characteristic “chirp” noise they often emit (Penner 2011).
Figure 2: strawberry poison dart frog common morph.
The term “poison dart frog” is derived from the frog’s toxin being used for coating the tips of indigenous tribes’ blow-darts. The toxins were generally extracted via one of two methods: the first was to simply rub the tip of the dart on the frog’s moist back, and the second is to heat the frog up to a temperature at which it would sweat and secrete the toxins, which would then be collected.
Figure 3: poison retrieval from poison dart frog.
The Strawberry poison dart frog is considered to be the most toxic in the Oophaga genus, but not the most poisonous among frog species. When agitated, the poison dart frog secretes a liquid containing alkaloids, a nitrogen based organic compound that causes blocking of the Na+ channels of the affected species’ nervous system, resulting in paralysis (Elder 2006). Certain similar dart frog species, such as the Golden dart frog (Phyllobates terribilis) are toxic enough to kill a 150lb. human with only 136 micrograms of it’s secretion (Elder 2006). Interestingly, the frogs themselves do not produce the toxins which they carry; these toxins are acquired through the small insects which they prey on, who have built up small toxin levels through the plants that they consume (Penner 2011).
Golden Orb weaver spider
The golden orb weaver spider is a unique, highly fascinating, venomous species of spider that can be found in many of the warmer regions of the world, from Southeast Asia to Australia, to the Americas all the way up to the United States (Weems 2004). Its name arises from the golden coloration of its silk, while it body colour ranges from silver to dark plum to orange, with brown, yellow-stripped legs (Australian Museum 2015).
The golden orb weaver spins one of the strongest and toughest webs in the world, and unlike most other spider species, their intricate webs are much like permanent homes, often lasting for multiple years (Ria Tan 2001). They use their webs, which are strung between trees in forests, to catch a variety of medium to large flying insects, such as wasps, moths, flies and butterflies (Weems 2004). Though they do not feed on them, their webs have even been known to entangle small birds! Birds also happen to be the main predator of this spider species. The male golden orb weaver, whose size is approximately 5mm, is significantly smaller than his female counterpart, who is usually 2-4 cm in length. Males have been known to take advantage of this difference in size by living on the female’s web, feeding off her catches without her even noticing. The male is even able to inseminate the female without her realizing, often while she is distracted by eating (Ria Tan 2001). Once fertilized, the female will dig a hole and bury her egg pouch underground. The golden orb weaver has a potent venom, which it injects into its prey through its chelicerae, or jaws, in order to paralyze it (Australian Museum 2015). Though the venom is a neurotoxin, it is not considered lethal to humans, and results only in redness, mild pain around the area of the bite, and a blister, which usually subsides after one full day.
Figure 4: golden orb weaver spider
The Bothrops asper, or Fer-de-Lance, is a venomous snake native to tropical Central America (Fer-de-lance), favouring moist and wet environments over drier climates (Streiter), however, that is not to say they are not present in dry tropical regions as well. In Costa Rica, this species is most common in lowlands of both the Pacific and Caribbean coasts up to an elevation of 1300-m (Streiter).
Species of the Bothrops genus are recognizable by their noticeably broad, flat heads; the Fer-de-Lance are actually named so for their lance heads (Encyclopedia Britannica). They are also pit vipers, so they have heat sensitive moveable fangs that are positioned between each large eye and nostril (Brown 2011); these are used to accurately attack and target their warm-blooded prey (Encyclopedia Britannica). Their eyes are also recognizable by their large, vertical pupils (Streiter). Bothrops aspers also exhibit dimorphism; the females are noticeably larger than the males from birth, as well as have more ventral and subcaudals scales (Brown 2011). Both males and females have distinct coloration patterns consisting of pale cream-coloured diamond shaped patterned bands on their back and sides that complement their dark brown/grey scales (Streiter). They are usually 4-7 feet long, with the females being noticeably larger than males, both as juveniles and as infants, and can reach up to ten times the size of a male Fer-de-Lance (Brown 2011). Juvenile females also have brown-tail tips while juvenile males have yellow ones, which they completely shed after maturation (Brown 2011).
Figure 5: pit-viper vs. nonvenomous snake
Figure 6: fer de lance snake
The Fer-de-Lance is considered the most dangerous snake in the Central America and is responsible for a majority of snake-induced deaths in humans (Strieter). Given their choice of diet, which ranges from small reptiles, invertebrates and arthropods as juveniles and slightly larger mammals as adults (Streiter), one could assume their natural defenses evolved to attack their prey more successfully, although this information has yet to be confirmed.
The Manchineel (Hippomane mancinella) is thought by many to be the worlds most dangerous tree. It is indigenous to Central America and the Caribbean (Sparman et. al. 2009). In central America the locals call it “Manzanita de la muerte” which means little apple of death (McLendon 2014). This name originates from the small apple shaped fruits produced by the tree. When ingested the fruits are reported to have a pleasantly sweet flavor. However, moments after ingestion tingling in the throat is felt, which quickly progresses into a burning sensation. Ingestion of the fruit ultimately leads to blistering of the mouth and throat and respiratory symptoms (Sparman et. al. 2009). The trees poison is not restricted to its fruit. Almost every part of the Manchineel including leaves, bark and sap are toxic. If skin comes in contact with Manchineel sap, bullous dermatitis and acute keratoconjunctivitis can occur (Sparman et. al. 2009). After brief exposure to the sap painful blisters can develop. The reason the Manchineel evolved such extreme toxic defenses is not yet confirmed. However, it is hypothesized that it may have something to do with how the tree reproduces. The Manchineel is located in costal areas and mangroves and uses the wind to disperse its seeds. Therefore, it is not necessary for animals to ingest the Manchineel fruits in order to spread seeds. Most animals are affected by the Manchineel’s potent toxins. However, certain species, like the iguana, are resistant.
Figure 7: Manchineel tree’s poisonous apple
Figure 8: Manchineel tree
Costa Rica’s great biodiversity and subsequent high levels of competition and predation have lead to incredible biological adaptations. Many organisms have evolved to use toxins. Some, like the Poison Dart Frog and Manchineel tree, secret poison as a defense mechanism. Others, such as the Golden Orb Weaver spider and Fer-de-Lance, use poison for predation. There is a huge diversity in the toxins found in organisms. Some poisons are lethal, with the intention to kill the predator or prey. Others result in unpleasant reactions like blisters, meant to deter predators. Just as some organisms have evolved to use toxins to their advantage, others have developed immunity to these toxins.
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Figure 3: https://dixonapbio-taxonomywiki 2015.wikispaces.com/Poison+dart+frog+(chordate-+amphibian)
Figure 4: Lily Ragsdale, 2016.