Electrophoretic profiles and biological activities: intraspecific variation in the venom of the Malayan pit viper (Calloselasma rhodostoma) – Daltry et al. 1996
- Abstract: This snake’s venom has been thoroughly studied but the degree to which the venom actually varies from individual to individual is less clear. Using banding profiles they found that there is a strong geographic variation which was congruent with variations in biological activities in the venom.
- Introduction: Most studies that observed this species had pooled the venom from a number of individuals which means that individual variation could not be seen. This is a problem when it comes to snake bites because the inconsistencies in venom composition between individuals can cause for bites from the same species to manifest a variety of symptoms, we have seen this before where this also leads to ineffective anti-venom. The aim of this study was to investigate the patterns of geographic variation as well as whether body size and gender impacted composition. They tested this by figuring out the venoms effects as well as ran electrophoresis to see if the profiles corresponded with differences seen.
- Methods: n= 96 wild caught snakes from multiple areas were used, their venom was collected within 12hrs of capture and immediately desiccated (we now know that this may have caused them to lose potency over time as well). Further 10 were collected from captive from a zoo. n=106 total
Isoelectric focusing: reverse osmosis was conducted to rehydrate the venom and then electrophoresis was done.
Determination of biological activities: 17 wild caught representing a wide range of localities were subjected to 7 assays of biological activity: Phosphodiesterase assay, alkaline phosphomonoesterase assay, L-amino acid oxidase assay, Arginine ester hydrolase assay, 5′- nucleotidase assay, thrombin-like activity and hemorrhagic activity. - Results:
Sexual Variation in isoelectric banding profiles: Females from Java, Malayasia and Thailand (n=33) have an intense band of pI 6.90 which was absent from the males of this area (n=48). In Vietnam, all the snakes lacked this band but every female (n=9) produced a pI 5.90 band in this while the males (n=6) did not.
Ontogenic variation in…: Different life stages and sizes had distinct band profiles, for example hatchlings produced band pI 7.00 while band pI 8.25 was only produced by specimens that were older than a year.
Geographic variation in…: Because of ontogenic effects they only compared adults of the area for geographic variation to keep it consistent. -> smart move. They found geographical distinct profiles using PC scores, check for specifics.
Variation in venom biological activities: electrophoretic profiles were compared to the 7 enzymatic activities of each venom sample using a Mantel test, and found it to be extremely significant, and this basically means that the more dissimilar the venom electrophoretic profile, the more dissimilar the effects of the venom. -> basically lifted this verbatim, and pretty obvious conclusion but its a good fact to cement. - Discussion:
Found that there are significant differences in snakes of the same species.
Geographic variation: Found that snakes of the same locality were prone to having more similar venom, but this was not the case for the spatial distribution of the snakes throughout the locality. For example snakes were more similar in venom to another group in the locality versus the closest proximity. Also found that adult malayan pit vipers of wild snakes and captive snakes proved to be almost identical in electrophoretic profiles, indicating that the geographical changes seen are genetically inherited rather than environmentally induced. However this does not mean that the venoms are identical, you can have venom proteins that are structurally and functionally different but still share the same net charge thus producing identical profiles, therefore it cannot be said that they would produce identical effects. Remember this! This is a key argument against all the flak we’ll get about cognitive welfare not being enough of a force to alter venom composition. Most studies have only looked at profiles which is not conclusive enough to say the venom is the same.
Sexual Variation: Females did have an extra band that was absent in their male counterparts but the study was unable to pinpoint a biological difference that consistently could explain the missing band. Other studies have noted sexual differences between venoms as well but have usually used a small n so pretty much the same, unable to pinpoint a reason.
Ontogenic: There are distinct band profiles attributed to life stage, even with juveniles and adults of the same locality. The general rule is that juvenile vipers have a higher toxicity, higher coagulant activity and lower proteolytic activity compared to adults, with mounting evidence that these differences are a result of ontogenic changes to the snake’s diet.
Individual Variation: They found that even snakes of similar body size, gender, locality and sampling time still produced venoms with notable differences, this is expected given then genetic variation in a gene pool. Basically that when you have a large number of individuals in an area the variation in the venom components would be great especially if you have individuals intermingling with other areas. On the contrary if you have a small number of individuals isolated to a small area say through allopatric speciation (geographical barrier?) then the venom components become a lot more homogenous. They pitch a theory that these individual variations we see are b/c of the difference in time between their last venom expulsion, but another study showed that this only changes things quantitatively and not qualitatively however just from previous readings I could have sworn that when certain proteins are expressed at a lower quantity compared to others in the solution, then their bands may become absent or reduced in the electrophoresis profile, so maybe it doesn’t change qualitatively but it does get observed differently by the instrument?
Implications of intraspecific variation in venom composition: The key to the snake bite care is identifying the type of snake that caused it (even better if you can somehow make an insta-antivenom from the individual by drawing out some of the venom from blood? -> just spitballing impossible hypotheticals). But most people can’t identify and snakes of the same species produce a variety of different bite symptoms especially if they are widespread. Also the problem with antivenom working only on the venoms that were initially introduced are a big problem, antivenom from specific adult rattlesnakes don’t work on bites from juveniles. Their answer is maybe to pool venoms from different age groups and hit every difference possible and create antivenom based on geographic region rather than just purely single snakes or age groups. Also different localities and genders have different thrombin activities which are key for antivenom, for exmaple Krabi province female had more than double the potency than the Chumphon male, so maybe choosing specific localities with benchmark higher protein activities is a way of covering all your bases? - Conclusion: Make sure to record -> capture locality, size, gender, date of venom extraction, nutritional health, age, reproductive condition of the snakes when comparing venom samples.
Al3xandria 