Wednesday, March 15, 2017

Cobras - Cytotoxicity as a Defensive Innovation and Its Co-Evolution with Hooding, Aposematic Marking, and Spitting

Bryan Frye and a cobra.
A University of Queensland-led international study has revealed how one of the world's most feared types of snakes -- cobras -- developed their potent venom.

Associate Professor Bryan Fry of UQ's School of Biological Sciences said cobras were killers in Africa and Asia, and caused crippling social and economic burdens through the number of survivors who needed amputations due to the snake's flesh-eating venom.

"While we knew the results of their venom, how the cobra's unique defensive venom evolved remained a mystery until now," he said.

"Our study discovered the evolutionary factors shaping not only cobra venom, but also the ornate markings on their hoods, and the extremely bright warning colourings present in some species."

The research team studied 29 cobra species and related snakes, finding that the flesh-destroying venom first evolved alongside the broad hoods that make cobras so distinctive.

Dr Fry said further increases in the potency of the toxins subsequently occurred parallel to their warning strategies such as hood markings, body banding, red colouring and spitting.

"Their spectacular hoods and eye-catching patterns evolved to warn off potential predators because unlike other snakes, which use their venom purely for predation, cobras also use it in defence," he said.

"For the longest time it was thought that only spitting cobras had these defensive toxins in high amounts in their venoms, however we've shown that they are widespread in cobras.

"These results show the fundamental importance of studying basic evolution and how it relates to human health."

Dr Fry said the next step in the team's research was to conduct broad antivenom testing.

"Globally, snakebite is the most neglected of all tropical diseases and antivenom manufacturers are leaving the market in favour of products that are cheaper to produce and have a bigger market," he said.

"Antivenom is expensive to make, has a short shelf life and a small market located in developing countries.

"Therefore, we need to do further research to see how well those remaining antivenoms neutralise not only the toxins that kill a person, but also those that would cause a severe injury."

He said there may also be a benefit to this research in cancer treatment.

"Any kind of compound that selectively kills cells could be a good thing," Dr Fry said.

"These chemicals may lead to new cancer treatments if we can find ones that are more potent to cancer cells than normal healthy cells.

"Cobras are a rich resource of novel compounds in this way so there may ultimately be a silver lining to this very dark cloud."


Citation

Panagides N, Jackson TN, Ikonomopoulo MP. Arbuckle K, Pretzler R, Yang DC, Ali SA, Koludarov I, Dobson J, Sanker B, Asselin A, Santana RC, Hendrikx I, van der Ploeg H. Tai-A-Pin J, van den Bergh R. Kerkkamp HM, Vonk FJ, Naude A, Strydom MA, Jacobsz L, Dunstan N. Jaeger M, Hodgson WC, Miles J, Fry BG. 2017 How the Cobra Got Its Flesh-Eating Venom: Cytotoxicity as a Defensive Innovation and Its Co-Evolution with Hooding, Aposematic Marking, and Spitting. Toxins  9, 103.

Monday, March 13, 2017

Hypsiboas punctatus, the first fluorescent frog

Before and after. The polka-dot tree frog in natural light
 (top) and under UV (bottom.)Photo credit: Julian Faivovich
 & Carlos Taboada 
The first fluorescent frogs have been discovered in South America. The green fluorescence is due to a compound found in the lymph and skin glands of the polka-dot treefrog (Hypsiboas punctatus). At twilight, the phenomenon enhances the frogs’ brightness and may help them communicate with each other.

Fluorescence has previously been reported in fish, scorpions and birds, but never amongst the 7000 plus species of amphibians. The blue–green glow of the polka-dot tree frog was observed when they were under UV light and is linked to a new fluorescent compound, not previously known in nature. The compound absorbs light in the violet–ultraviolet region and emits blue–green light. Time-of-flight mass spectrometry showed that the main fluorescent compound was the molecule Hyloin-L1. NMR revealed an N-methyl-dihydroisoquinolinone core.

‘It is basically a benzamide with a methoxy group added on, which makes the absorption band fall on the edge of the visible spectrum,’ notes Andrew Beeby at Durham University, UK, who was not involved in the study. He adds that this ‘DayGlow frog’ adds to our growing awareness of bioluminescence. The isoquinolinone structure has never before been described in any animals, only in plants. The chromophore seems to be the cyclic benzamide.

‘This is very different from fluorophores found in other vertebrates, which are usually proteins or polyenic chains,’ says author Maria Gabriela Lagorio, a photochemist at the University of Buenos Aires, Argentina. ‘The chromophore itself is well known, but the class of the secondary compound is completely new,’ adds co-author Norberto Peporine Lopes, a natural product chemist at the University of São Paulo in Brazil.

Hyloin L-1 (H-L1) is the molecule that is principally responsible for the polka-dot tree frogs’ fluorescence, although the other molecules pictured also contribute Biologist Karen Carleton at the University of Maryland notes that like many colourful compounds, ‘it contains lots of carbon–carbon double bonds with lots of π electronics that can easily be excited at visible wavelengths. It is also similar to a compound like 11-cis retinal, which is the chromophore that our eye uses to absorb light.’

The discovery is a bolt out of the blue for most in the field. ‘We were not expecting this bio-fluorescence. It was an incredible surprise,’ says Lopes. He suspects the frog, which has translucent skin, uses the phenomenon to communicate. Lagorio agrees: ‘Amphibian species have photoreceptors in their eyes maximally attuned to blue and green vision, so we expect that these compounds enhance the brightness of these frogs under conditions of twilight.’ The team has now begun examining the polka-dot’s relatives. ‘We expect that this will be a more universal phenomenon with perhaps 100 or 200 species showing this property,’ says Lopes.

‘It would be interesting to investigate if [fluorescence] has a role in species recognition, or whether it facilitates the formation of couples,’ notes Bibiana Rojas, ecologist at the University of Jyväskylä, Finland. ‘Fluorescence would be potentially very useful in a noisy environment and in a habitat with dense foliage, as it would make individuals brighter.’

Citation

Taboada C, Brunetti AE, Pedron FN, Neto FC,  Estrin DA, Bari SE, Chemes LB,  Lopes NP, Lagorio MG, Faivovich J. 2017. Naturally occurring fluorescence in frogs. PNAS 2017 doi:10.1073/pnas.1701053114

Saturday, March 11, 2017

A new homalopsid snake from Myanmar

Gyiophis salweenensis Photo credit. Evan Quah
The 54th species of homalopid snake has been described by Quah et al. (2017). The new species, Gyiophis salweenensis was described from the lowlands of Mawlamyine District in Mon state, southeastern Myanmar. The authors suggest that Gyiophis salweenensis  is presumed to be closely related to G. maculosa Blanford and G. vorisi Murphy based on the similarities in scales and coloration but can be separated from G. maculosa by the shape of its first three dorsal scale rows that are square, ventral scale pattern that lacks a central spot, and a faint stripe on dorsal scale rows 1–4. It can be further distinguished from G. vorisi by its lower number of ventral scales (129 vs. 142–152), lower number of subcaudals (30/29 vs. 41–58), narrow rostral scale, and having more rows of spots on the dorsum (four vs. three). A preliminary molecular analysis using 1050 base pairs of cytochrome b (cytb) recovered G. salweenensis  as the sister species to the Chinese Mud Snake (Myrrophis chinensis). G. maculosa and G. vorisi were unavailable for the analysis. The discovery of G. salweenensis sp. nov. highlights the need for more surveys into the herpetological diversity of eastern Myanmar which remains very much underestimated.

Citation
Quah ES, Grismer LL, L Jr PE, Thura MK, Zin T, Kyaw H, Lwin N, Grismer MS, Murdoch Ml. 2017. A new species of Mud Snake (Serpentes, Homalopsidae, Gyiophis Murphy & Voris, 2014) from Myanmar with a first molecular phylogenetic assessment of the genus. Zootaxa. 4238(4):571-82.