LDLo does not differentiate from LD50 across studies.
64 out of 167 ophidian species had at least one LDLo value. These 64 ophidian species had 243 LDLo values, and 532 LD50 values. In the meta-dataset, 26 of these 64 ophidian species (~ 40%) had an LDmin that was, indeed, an LDLo. However, 24 of the 64 ophidian species (~ 37.5%) had LDLo values that were the meta-study LDmax, which was against expectations.
For Figs. 2 and 3, the range fraction is determined by Eq. 1. This way, relative toxicity between ophidian species is normalized, and comparison of variation can be done between ophidian species. In Fig. 2, the mean of the LDLo fractions is 28.3%, and the mean of the LD50 fractions is 27.2%. The standard deviation of the LDLo fractions mean is 29.4%, and standard error is 3.7%. The standard deviation of the LD50 fractions mean is 22.4%, and standard error is 2.8%. Even by the less stringent method of standard error, this is insignificant. Thus, the mean of the LDLo and LD50 range fractions for the 64 out of 167 are not meaningfully differentiated.
However, one might argue that significant difference might be seen in LDLo values for single test-animal-species, as shown in Fig. 3. Here, as above, the data does not show this. Instead it shows that for 4 out of 11 test-animal-species, mean LDLo is higher than LD50, and exceeds standard error. (Mouse, guinea pig, dog, frog. Monkey was excluded due to low N for LD50.) Note that this also occurs for the highest N dataset (mouse). There is only 1 test-animal-species (rabbit) where mean LD50 is higher than LDLo and exceeds standard error as expected. However, rabbit has a low N and this disappears when median is used. (Standard error not shown for median.) Only the mouse test-animal-species exceeds standard error if median is used, and it still shows LDLo higher than LD50.
Strengthening this point, for 10 ophidian species, both LDmin and LDmax were LDLo’s. The median number of DB entries for an ophidian species with one or more LDLo values was 4.
Consequently, because LDLo did not differentiate significantly from LD50 when examined across studies, LDLo designations were categorized together with LD50 for the rest of this meta-analysis.
Route of inoculation minimum and maximum lethal dose
In Fig. 4, there is good support for the concept that IC (intra-cerebral) < IV (intra-venous) < IP (intra-peritoneal) < IM (intra-muscular) < SC (subcutaneous). This is the only hypothesis not falsified in this analysis. However there are contradictory instances.
Out of 29 intracerebral injections (IC), 16 were LDmin values, which is as expected. So, approximately half the time, an IC injection was the minimum, and the N should be meaningful at 29. Using a synthetic x-axis the 0.9062 R2 coefficient of determination suggests that approximately 91% of the distribution fits the assumption that route of inoculation varies as IC < IV < IP < IM < SC. The curve fit for LDmax shows the opposite trend, with a good R2 suggesting 75% of results can be attributed to route of inoculation distributed in this manner. This latter R2 being lower agrees with LDmax having higher variance (not shown).
However, 13 out of 249 of the subcutaneous injections were LDmin values, which makes this, unexpectedly the route of highest toxicity for 7.8% of the 167 ophidian species. Out of these 13, there were 4 venoms with strong hemotoxic or nephrotoxic effects, the other 9 were neurotoxic.
Of the intracerebral inoculations, 2 were LDmax, the opposite of expectations, (Notechis scutatus and Naja atra), which is 1.2% of the 167 ophidian species. Notechis scutatus and Naja atra contain both pre and post synaptic neurotoxins. Notechis scutatus had 26 DB entries and Naja atra had 17, so this should probably not be an artifact of a low number of studies performed for each. The percentages of these paradoxical SC and IC inverted cases are about the same, at 7% and 5% of their respective route of inoculation.
Venom toxicity range fold change
The range of venom toxicity per ophidian species within the mouse test species has a mean average of 2.22 logs (168 fold change) within a single test-animal-species, as shown in Fig. 5. This is 4.2 times the 1.6 logs (40 fold change) documented in literature for toxicity difference between test-animal-species, as discussed above. For all test-animal-species together, the mean range is 3.2 logs (1597 fold change), which is 40 times what current literature indicates.
The largest range fold change seen for an ophidian species tested in mouse for one route of inoculation is Boiga irregularis, 3 logs (1000 fold change), N(studies) = 14. The largest range fold change for an ophidian species tested only in mouse for all routes of inoculation is Crotalus horridus, 3.6 logs (4,150 fold change), N(studies) = 20, routes of inoculation: SC/IM. For one ophidian species data for all test-animal-species, including all routes of inoculation, the largest range fold change is Naja nivea, 4.46 logs (28,571 fold change), N (studies) = 22, N (test-animal-species) = 9, routes of inoculation: SC/IV between frog (LDmax) and rabbit (LDmin). These are among the highest N studies counts for ophidian species. Note that a specific ophidian species mentioned does not mean this species has been determined to be the most venomous, or the widest range of all.
One might ask whether the range fold change increasing holds up when a single species and single route of inoculation is examined. We see this in Fig. 6, where the range fold change is plotted against the number of studies. No curve fit is shown because there is insufficient data for determination. However, by inspection, one can see that the range fold change does appear to increase as the number of different studies rises.
Figure 7, which looks at single test species for multiple routes of inoculation, shows a linear regression trend that reaches significance for the range fold change increasing as the N for number of studies gets larger. This graph appears to signal the same thing that a set of ecological diversity transects continuing to increase would. It indicates that to fully characterize ophidian venom lethal doses, probably requires more than 50 different studies.
Regressions of LDmin
Null hypotheses for minimum lethal dose
A.) Minimum lethal dose within each ophidian species varies by less than a factor of 2. B.) The minimum lethal dose does not correlate with the number of times the lethal dose has been tested (e.g. the number of LD DB entries).
Minimum lethal dose varies by more than a factor of 2, and minimum lethal dose correlates with the number of times dose has been tested.
Regressions curve fit summary for LDmin, rounded.
Number of routes of inoculation
Number of test species tested
Number of LD DB entries (Number of studies)
Number of routes of inoculation correlation to LDmin
In Fig. 8, as the number of routes of inoculation increases, the likelihood of having more test-animal-species for the ophidian species also increases. The fitted curve is probably determined by the probability of inclusion of a lower lethal dose value rising as the number of inoculation routes goes to 5, because, as was seen above, IC < IV < IP < IM < SC does tend to hold true.
The N for the number of routes of inoculation 1 to 5 are, respectively: 30, 36, 61, 33, and 7.
Number of test-animal-species per ophidian species correlation to LDmin
Here in Fig. 9 the apparent drop visible in the fitted curve is 1.5 logs, a fold change of 32X. Similarly to the above, it should be expected that lethal dose would drop some with larger numbers of test-animal-species, because literature indicates that some animals are up to 1.6 logs (fold change of 40X) more susceptible to certain venoms than others, and there is some frog data in the dataset.
Additionally, the more test-animal-species there are for one ophidian species, the more likely it is that there will be more routes of inoculation. However, in the dataset, there are multiple instances of the same test-animal-species occupying LDmin and LDmax, and quite a few are very close to this state, which suggests that, indeed, the number of times an ophidian species is tested is a major factor.
Number of DB entries (studies reported) per ophidian species correlation to LDmin
In Fig. 10 the “All data LDmin” fitted curve does not control for different test species. To address this criticism, “Mouse LDmin” shows the same graph filtered for inoculation of mice only. The R2 value of 0.27 is not as good as the 0.36 R2 value is for all data, however, the N is lower, and by inspection, there is a nearly perfect match for the curves for the region where they both have data. If there were no correlate by number of studies per species, then the fitted curves should be flat, whereas, both fitted curves span over 2 logs, and have nearly identical exponents and quite close constants. Consequently, these data suggest that the primary correlate for lethality is the number of studies that have been performed.
Regressions on range fold change
The range fold change is Rmax ÷ Rmin. The R2 values for these regressions are larger than what we see above. These data indicate that there is a correlation for all measures with number of DB entries for lethal dose (number of studies reported). The number of routes of inoculation has a meaningful correlation for all data, and for single test species. I do not show these graphs, as they are redundant.
Table 2: Regressions on all data for range fold changes of highest over lowest dose. All data (LD-ADrf), single species (LD-SSrf), single species, single route (LD-SRrf).
R 2 below 0.20 not shown. N = 167 ophidian species.
Data, by species
Number of routes of inoculation
Number of species tested
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Number of LD DB entries