The Philosophy of Gutloading
5. Insects and the work they do
As I said previously, I was under the impression that though chameleons can’t digest many of the gutload ingredients we use, they can certainly access the nutrients of these ingredients via the gut contents of our feeder insects. In other words, chameleons do not have to digest the gutload ingredients because the insects have already done the heavy lifting—reducing relatively indigestible (for chameleons) ingredients to bio-available nutrients. It was thus surprising to learn that, whether overtly, or by implication, some researchers found this view dubious. While I do not have the skills required to do justice to the biochemistry of insect digestion, I can perhaps say a few intelligent things. For a sad gloss of insect digestion, see the endnotes [7].
A recent study suggests that—in addition to the help from the symbiotic microorganisms found in the digestive tracts of many insects—insects themselves are capable of breaking down a notoriously difficult to digest substance—namely, cellulose (Calderon-Cortes, Quesada, Wantanabe, Cano-Camacho, & Oyama, 2012). That insects have developed means of doing this is evidence of a robust digestive system. More to the point, several studies show that insects have the ability to reduce many otherwise indigestible food items to bio-available nutrients for the animals that consume them. Evidence from Feltwell (1974)and Carroll et al. (1997)supports that plant-eating insects—lepidopteron larva, in this instance—sequester a variety of carotenoids from their herbivorous fare; and one study traces the flow of these nutrients to the plumage of the insectivorous birds that eat them (Partali, Liaaen-Jensen, Slagsvold, & Lifjeld, 1987). This last study is significant because the intermediate lepidopterons not only broke down the relatively difficult to digest leaves containing the carotenoids, but the study also found that the carotenoids were passed on to the birds unchanged; i.e. the caterpillars broke down the plant matter into nutrients that they themselves did not assimilate, but passed straight on to the birds in a usable form—presumably via their gut contents.
I belabour this point not because I find it particularly ground breaking (it’s basically just an example showing that food chains exist), but because this appears to be in doubt by advocates of theory 2). When a chameleon’s inability to digest certain gutload ingredients is used as an argument against theory 1) this is precisely what is being argued. More clearly, to argue that we should not use e.g. squash in our gutloads because chameleons can’t digest it, just is to deny/ignore the digestive work of the intermediate insects. As a side point, I have heard arguments to the effect that e.g. blueberries should not be used in our gutloads because blueberries are very unnatural to chameleons. If our gutload ingredients are broken down to their constituent nutrients by our insects, then it does not seem to matter whether these nutrients are derived from blueberries, or the native flora of Madagascar. Perhaps, however, I misunderstand. Perhaps the point is that it is doubtful that the insects can digest many of our gutload ingredients. While I don’t think this is the case, there is evidence that even synthetic material is not immune to the digestive efficiency of some insects. In a recent study, mealworms were able to survive on, and digest, Styrofoam (Nukmal, Umar, Amanda, & Kanedi, 2018). While I would advise against gutloading with this particular ingredient, this suggests that insects really are prodigious digesters.[8]
6. Flamingoes and Fish and Flies, oh my!
Between 10 and 25 million years ago, the surface of the earth expanded with the divergence of two plates in what is today east Africa. Spanning from the southern part of Sudan, and stretching south as far as Mozambique [9], this great rift valley, as it has become known, is a hot spot for chameleon diversity—second only to Madagascar in both diversity and endemism (Tolley & Herrel, 2014).
A multitude of other species also calls this oasis home. Among them is the lesser Flamingo Phoeniconaias minor Geoffroy—a species that seasonally inhabits both the three giant rift lakes—known for their endemic populations of the cichlids so beloved in the tropical fish hobby—and the high altitude lakes on either side of the eastern rift. Recently both the flamingo and some cichlids species have come under the threat of pollution. In particular, heavy metals have begun poisoning the main food source they share (Ballot, et al., 2004), (Vareschi & Jacobs, 1985). Not confined to the larger, low altitude rift lakes of Malawi (500m a.s.l.) and Tanganyika (773m a.s.l), the contamination has lead to several mass die-offs in the high-altitude lakes of Bogoria (990m a.s.l.), Victoria (1135m a.s.l.), Elementeita (1670m a.s.l.) and Nakuru (1760m a.s.l.) (Ballot, et al., 2004). The cichlid and flamingo populations are not the only victim of the environmental pollution: chironomid larva are also significant consumers of the contaminated resource (Vareschi & Jacobs, 1985).
Since chironomids are dipterans, and since we know dipterans figure centrally the diet of many wild chameleons (see above), it seems like any chameleons in the affected areas might be at risk. Since this area is home to many species of Trioceros, Kinyongia and Rieppellion—especially those that prefer higher elevations—it appears even the wild brethren of our beloved pets are not immune. Though concerning, this is not news. That pollution affects wild animals the world over is hardly an earth-shattering revelation. Indeed, some of the referenced studies are decades old, and wild chameleons are far more threatened by habitat loss than they are this particular problem.
So what exactly is the point here? This blog is about gutloading, right? Fair enough…If you think that the pollutants in the food source could be passed on to chameleons because they eat the flies whose larva eat the food source, then you should also believe that the nutrients in the food source could also be passed on to the chameleons. Interestingly, one of the gutload ingredients that has figured prominently in recent gutloading debates is this very food source that holds such a place of importance in some of the food chains in the rift valley: Arthrospira platensis, i.e. one of the main sources of the dietary supplement we know as spirulina. In a rare moment of literary coincidence, one of the gutload supplements that has caused such a rift in the philosophy of gutloading occurs centrally in the Great Rift Valley, whence comes many of our favourite species.
The arguments proffered against the use of spirulina generally come in one of two forms. The first is to question whether chameleons can even digest spirulina. We looked at this in the section on insects. There was evidence to show that insects are excellent at breaking down hard to digest elements into nutrients that are bio-available to the animals that consume them. And while we didn’t look at spirulina directly, we know that the larva of some dipterans feed on in. So, all in all, there appears to be good reasons to think that it doesn’t matter whether chameleons can digest it, since the insects that we feed them can.
The second kind of argument against spirulina contends that spirulina is pretty foreign to the wild chameleon diet, and wild chameleons would almost never encounter it within their food chains. We have just seen evidence that not only does spirulina occur in the wild ranges of many species (even at high elevations), but it figures importantly in several food chains. Yes, it is an aquatic algae (actually it’s a cyanobacteria, but no matter), but we know food chains can cross the aquatic/terrestrial threshold. Dragonflies are one example (remember T. cristatus appears to love them); but more importantly, there are other species of dipteran whose larva actually live off the relevant algae (see Vareschi & Jacobs, 1985). We know from the wild diet studies we examined, dipterans are some of the most common prey items of many species. And while this is far from definitive proof, I find it perfectly plausible to think that spirulina is not all that foreign to wild chameleons. Indeed, I would be surprised if there weren’t more than just one or two species of larval dipterans that consumed spirulina (Arthrospira platensis), and that the nutrients therefrom reach the wild chameleon species of the area with sufficient frequency to make a nutritional difference/contribution. One final relevant fact about spirulina is that it’s not confined to mainland Africa. The freshwater and brackish lakes of Madagascar are also home to abundant populations of the relevant species (Scheldeman, et al., 1999). Below, I have reproduced a distribution map that focuses on just one species of chameleon whose natural range coincides with some of the lakes mentioned above. The map is courtesy of Bill Strand and Petr Necas (Strand & Necas, 2018).
7. Tallying up the data…and maybe some more conceptual analysis
So where exactly are we with respect to the gutloading debate? This has been a long and arduous trek through conceptual analysis, the wild diet of ten species of chameleons, insects and their amazing digestive power, food chains, the nutritional value of bee pollen, and the distribution of the cyanobacterial sources of spirulina. But what have we actually accomplished?
We began with two approaches to gutloading. I’ll reproduce both theories below.
Theory 1:
1. Chameleons have demanding nutritional requirements, which we assume are met by the variety of insects they eat, and the variety of nutrients those insects contain.
2. We can’t replicate this variety in captivity so...
3. We gutload to increase the nutritional contents of our feeder insects in the hopes of making up for this deficiency.
4. Ingredients include apples, oranges, bananas, blueberries, carrots, squash and various high calcium greens. Other additives include bee pollen, spirulina powder, hibiscus flowers, prickly pears, nuts, kelp, and powdered plant products such as mulberry, hibiscus and alfalfa powders.
Theory 2:
a. Flies, bees and wasps are the main food items in the wild chameleon diet.
b. These food items are not stuffed full of plant material, they generally contain pollen.
c. Pollen is one of the few good gutloading ingredients, and when combined with the nutritional value of the insects bearing the pollen (bees, wasps, etc…) the combination ought to satisfy the bulk of a chameleon’s nutritional requirements.
d. Since chameleons can’t digest plant material, stuffing our insects full of plant material is pointless (and may even be harmful?).
What I wanted to know was whether theory 2) offered good reasons to rethink the gutloading practices in theory 1). I began to investigate the empirical strength of each point. In section 3, we looked at the admittedly scant data available on the wild chameleon diet. The studies suggest that while dipterans, hymenopterans and coleopterans do play an important part in the wild diet, hemipterans, orthopterans, and arachnids and often lepidopterons, play an equal role. Indeed, in several of the studies, orthopterans and hemipterans and even arachnids were just as common as dipterans in the wild diet, and much more so than hymenopterans. This suggests that whatever nutritional elements these other insects bring to the table might be important to take into account when deciding on our gutloading regimes. So, in contrast to the first point of theory 2), there is evidence that suggests that flies, bees and beetles do not occupy the overwhelming majority of the wild chameleon diet. However, because we didn’t yet know whether pollen could account for the majority of the nutrients found in the other commonly consumed insects, we looked briefly at the nutritional value of pollen (section 4).
We found that pollen is indeed something of a chameleon superfood, but that it isn’t perfect. For one thing, the exactly nutrient profile of pollen varies drastically according geographic region and the plants involved. Although I didn’t previously mention this, I doubt whether many of us are getting African pollen. So the pollen we are using may differ significantly from the natural pollen that our chameleons ingest, which I suppose makes anything but African pollen somewhat unnatural. More importantly, the evidence suggests that pollen might be lacking in the carotenoid department. If carotenoids are important, then this might count as a shortcoming. We also found that pollen had a poor calcium to phosphorus ratio. Last, we noted that there has been some question about pollen’s digestibility. This, we concluded might be a problem but the data is not especially strong...In any case, if the insects that bear the pollen do some of the digestive work, then even chameleons—with their short digestive systems—might derive real benefits.
This last point led us to section 5., where we learned that many insects are excellent digesters, capable of breaking down anything from cellulose to Styrofoam. We saw evidence that insect digestion was able to break down green leaves, extract a variety of carotenoids from them, and make those carotenoids available to the animals that eventually consumed them—animals that did not have the digestive capacity to extract these nutrients themselves. So, while insects can almost certainly digest pollen, they are equally capable of digesting a variety of plant material, and, in so doing, turn the components contained therein into nutrients that can be passed up the food chain to the animals that prey on them. (This was part of the reason why Finke’s article (2003)was so fascinating: he provides a gutload recipe to amend the ca : p ratio of our feeders without dusting…see footnote 8). In short, the premise that we shouldn’t feed e.g. squash to our bugs since chameleons can’t digest plant matter appears to miss something important about the purpose and mechanics of gutloading.
Finally, in section 6, we looked at one gutload ingredient that appears to be a sticking point between the two sides: spirulina. We found not only that spirulina occurs naturally in abundance in the home ranges of many chameleons, but evidence that it plays an important part in several wild food chains. In particular, the evidence suggests that spirulina is a primary food source for the larva of at least one dipteran. While not conclusive, this certainly adds to the plausibility that spirulina is not all that foreign to chameleons. Indeed, coupled with the facts about insect digestion, spirulina might turn out to be a lot more natural to chameleons than was previously thought. To be fair, I did not go into all the nutritional components of spirulina; and to be honest, I think it too will fall short of being a perfect gutload ingredient. Like pollen, spirulina will have limitations and shortcomings—one of which is that its calcium to phosphorus ratio is hardly better at 1:1.
8. Conclusion
This blog sits on the periphery of a much deeper debate about what has become know as naturalistic husbandry. I find something very appealing about the current trend towards replicating nature; however, I think the far reaching implications of the theory are poorly understood, and there are some significant conceptual, as well as empirical, challenges to be addressed in this arena. I attempted to steer clear of this particular issue as much as possible in this blog. This was partly because I think naturalistic husbandry deserves a blog entry of its own, partly because I think there are a number of confusions with the idea, and mostly because I wanted to address the philosophy of gutloading on its own terms—be they conceptual or empirical—rather than through the lens of naturalistic husbandry. Unfortunately, I was not entirely successful, and for that, I beg your forgiveness.
My goal here was to evaluate a challenge to our current gutloading philosophy. I tried to represent the challenging position as accurately as possible, and to evaluate its central tenets on the same grounds on which they are put forth. I certainly do not think I have proven anything here. However, I think I have found some empirical evidence that runs counter to of some of the doctrines involved in theory 2). At the very least, I have provided reasons for questioning the certainty with which theory 2) has been proffered....regardless of who is doing the proffering. The reason I chose to address this particular topic is that several eminent and well-respected members of our community have offered advice on this subject, and newcomers are easily swayed by big names, and illustrious monikers. To their credit, these big names frequently repeat the sage advice that individuals should do their own research, and think critically. I sincerely hope that this advice is sincere, and that it isn’t given with the tacit implication that the research should be focused on one website, and that the critical thinking should be directed towards any view that disagrees with the information therein. I hope that this blog represents precisely the kind of research and critical thinking to which the advice refers, but time and reactions will be the judge.
End notes
[1]I should note here that these references do not speak to the nutrients of these insects’ respective gut contents, but merely the fact that these insects are frequently eaten. So while they support the view that these insects figure importantly in the diet of wild chameleons, they are silent on the specific nutrients that might or might not be found in their respective intestinal tracts.
[2]Alas, I fear disappointment with every word…sad face.
[3]During breeding season, a number of species leave the trees in search of mates. This puts them in contact with a different insect species than they would encounter in the canopy.
[4]It should be noted here that R. spectrum and T. cristatus are species found close to the ground, so their penchant for ants and termites is less than relevant in discussions of arboreal species.
[5]Might this indicate a form of calcium self-regulation?
[6] Chameleons are opportunistic feeders: They eat what they can. While no one has overtly suggested that chameleons are specialized for flying prey such as flies and bees, etc., the frequency that such items occur in the natural diet seemed to be tacitly taken as evidence for something like a proclivity, or general liking. Chameleons eat lots of flies, so they must like flies! I don’t disagree that this explanation is intuitive; however, I think it admits of more than one plausible explanation. It is not hard to think that the complicated visual apparatus of the chameleon evolved, at least in part, because of their penchant for fast moving insects like e.g. wasps. I, myself, have thought this on occasion. However, it seems equally plausible that the forces of evolution that selected for chameleon eyes did so, not for moving insects, but for movement in general. After all, their eyes are paramount in the detection of predators as well. Natural sprinters, they are not; so they better be able to spot predators before predators spot them (would a wild one-eyed chameleon be more likely to starve to death or be eaten?). If we assume that evolution may have selected for those individuals whose eyes best detected movement, then there is less force to the causal explanation between a chameleon’s visual apparatus and flying insects. If nature simply selected for movement detection, then the chameleon’s seeming penchant for flying insects—given that they are among the most active—might be an accidental effect. That is, it might not be the case that chameleons have evolved to eat mostly flying, fast-moving insects, but that how they evolved made their frequent feeding on such insects more probable. Also, note that chameleons are “cruise foragers” (Measey, Raselimanana, & Herrel, 2014). They don’t exactly sit-and-wait for prey, but nor do they hunt in the way as, say, lions do. Rather, they move from one area to another, then stop and visually scan. If something catches their eye, they track it, and will move into position if that insect comes within range. Again, this is pure speculation, but if I think about it, what kind of insect is liable to attract the attention of a chameleon from a distance then move into striking range from perhaps several yards away and a meter or two in height? Certainly it is not going to be a cockroach, nor an ant. Likely, it will be some flying insect. But this doesn’t mean that chameleons evolved to eat flying insects. The explanation could just as easily go the other way around: Chameleons eat flying insects because of how they evolved, and how they evolved may have not had that much to do with their prey selection. Again, this is just speculation.
[7]Insect digestion begins with maceration (chewing), where food matter is mechanically broken down and mixed with digestive enzymes (in arachnids, these digestive enzymes are injected into the prey, turning its insides into a liquid mass that can then be ingested). Having been sufficiently reduced, the food then passes on through the esophagus into the crop—an organ for storing food. Food undergoes some further digestion in the crop due to the digestive enzymes in the saliva, and those regurgitated from the mid-gut. Interestingly digestive enzymes can move both forward and backward in the digestive tract (Woodring, Hoffman, & Lorenz, 2007)—something that would probably be less than comfortable for us humans (acid reflux much?). In between the crop and the mid-gut, some insects have a structure of jagged, knife-like protrusions that add further mechanical breakdown of food. Food then passes on to the midgut, where the main enzymatic breakdown of food occurs. Fun fact: orthopterans (crickets and grasshoppers) don’t appear to employ peristalsis in their mid-gut (Woodring, Hoffman, & Lorenz, 2007); one wonders whether this delays the advancement of food through the digestive tract, and enables more thorough digestion. After breaking down and absorbing the majority of nutrients from the food, the leftover passes on to the hindgut where water re-absorption (just like in chameleons) and final…um…poop-making takes place.
[8)Admittedly, gutloading is certainly an inaccurate art. Very few of us are lab testing the nutrient constituents of our gutloads. However, studies have shown that a mathematical approach to gutloading common feeder insects can significantly increase their nutritional value (Finke, 2003). For those fastidious gutloaders, I highly recommend this paper!
[9]In fact, the rift actually forks in southern Tanzania, with one branch continuing south, and the other looping back around north along the borders of Zambia, Burundi, Rwanda the DRC and Uganda, terminating at the South Sudan border.
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