The Philosophy of Gutloading
AcknowledgementsI would like to thank Anthony Herrel and Walter Tapondjou for their helpful advice on where to look for relevant papers.
1. Introduction
Recently, it was suggested to me that our current gutloading practices might be wrong-headed. In particular, I was told that because chameleons cannot digest much of the plant material we are feeding our bugs, that they derive no benefit from our sometimes-monumental gutloading efforts. This struck me as odd, since I thought the point of gutloading was to have the bugs do the digesting—thus turning what would be indigestible plant matter into nutrients that our chameleons can access. Maybe, however, my interlocutor was right in calling this a fairy tale. Maybe, it isn’t healthy to have such a multitude of ingredients in our gutloading regimes—ingredients that are not only foreign to chameleons, but which might not even contribute to chameleon nutrition because they cannot be digested.
In all fairness, I think the point s/he was trying to make was that wild chameleons rarely eat large nutrient-dense food items, consuming instead many small nutrient-poor insects such as flies, bees and beetles. There is certainly evidence to support this. Several researchers have noted a high percentage of dipterans (flies) in the diet of multiple species (Tapondjou, 2019), (Karen-Rotem, Bouskila, & Geffen, 2006). Tapondjou’s study focuses on the montane species of Cameroon (e.g. T. montium, T. quadricornis, etc.), while Karen-Rotem et al. observe fruit fly predation on the Seychelles. Likewise Pleguezuelos et al. report that during the spring, the diet of Chamaeleo chamaeleon is comprised heavily of hymenopterans—i.e. bees and wasps (Pleguezuelos, Poveda, Monterrubio, & Ontiveros, 1999). Finally, Burrage notes a significant level of coleopterans—ground beetles, in particular—in the diet of some chameleons (Burrage, 1973).[1]
This blog is intended to explore the philosophy of gutloading. In particular, I want to investigate whether the view suggested to me in my conversation (see paragraph 1), presents good reasons for changing our gutloading regimes. While I will certainly be relying on as much empirical research as possible, I also want to add some conceptual analysis to the debate, so please forgive my penchant for the armchair. Finally, I want to make clear that my attempting to address the content of certain online information is precisely that—an attempt to address the content. If information is proffered as empirically based, it is subject to scrutiny on that very same empirical basis. If arguments are martialed on a conceptual basis, they too are candidates for conceptual evaluation. Nowhere in what follows will I be engaging in ad hominem attacks, and I sincerely hope that my work here will not be perceived as such.[2]To work, then…
2. Categorizing the views
Some organizational housekeeping is in order at the outset. I want to define two broad camps with respect to gutloading:
- Theory 1: We gutload to increase the nutrient content of our feeder insects. Our access to feeder variety comes nowhere near the wild diet, which we assume is replete with a variety of nutrients derived not only from the diversity of the wild insects consumed, but the variety in their respective diets. We infer from the fact that chameleons appear to have demanding nutritional requirements, and from the fact that our feeder insects fall far short of said requirements, that the wild insects on which our chameleons prey must be chalk-full of essential nutrients. If not, how are wild chameleons having their nutritional needs met? Our intuitive response is to feed our feeder insects a variety of nutrient rich foods in the hopes of compensating. Such items include common plant-based fare such as 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: Some of the most common insect prey of many wild chameleons are small items such as flies, bees, wasps and beetles. Among other things, these insects are often involved in pollination, and will certainly be carrying pollen and nectar both on them, and in their gut contents. Chameleons must therefore consume large amounts of pollen and nectar. The consumption of these small insects, coupled with their pollen/nectar content, satisfies the majority of the nutritional requirements of our chameleons. Obviously, there will be other less commonly consumed insects (and even vertebrates), but bees, wasps, flies, beetles and their pollen/nectar content account for a majority of chameleon nutrition.
a. In fact, the most common food items consumed by wild chameleons are actually nutritionally poor. Chameleons are perfectly adapted to live on such a diet.
b. This obsession with packing so many foreign nutrients into our feeders might actually be causing shortened life expectancy due to toxic effects, or obesity.
c. Relatedly, no one has ever studied the nutritional make-up of the wild chameleon diet, so there just isn’t any evidence to support the fact that the gut contents of an insect that has eaten e.g. butternut squash are at all helpful.
d. What we ought to be aiming for is to replicate those aspects of the chameleon diet that chameleons have evolved (over thousands of years) to experience.
e. Chameleons cannot digest most of the items theory 1) would have us feed to our insects, such as blueberries, kale or spirulina. So, as it turns out, our efforts here are futile.
There are doubtless more implicit premises here, and theory 2) is not restricted to only one. What is important is that some combination of additional corollaries must to be at work, if the disagreement is substantive.
I propose to deal with the conceptual points first, so that the proceeding parts of the blog can deal with the empirical evidence. The conceptual points, so far as I can see, are c and d. Premise c. makes the claim that no one has ever studied the nutritional make-up of the wild chameleon diet. While that is an empirical claim, the inference that there is thus no evidence to support the use of ingredients such as butternut squash in our gutloads has a conceptual implication. Namely, if it is true that that no one has ever studied the nutritional make-up of the wild chameleon diet, then there is also no evidence to tell against the use of butternut squash in our gutloads. A lack of any empirical data cannot be used to tell against one option while simultaneously supporting the other. The absence of data seems like a pretty poor evidentiary candidate for either side. Moreover, if it is true that no one has every studied the nutritional make-up of the wild chameleon diet, then the first claim in a. seems puzzling. How do we know the gut contents of dipterans and hymenopterans are nutritionally poor, given that no one has studied this (as per c.)? To be fair, it doesn’t make a lot of sense for flying insects to be bursting with gut contents—they have to fly after all.
Premise d. makes a normative claim about how we ought to approach chameleon husbandry. While I have no problem with some normative claims in this context, this particular one is tenuous. Humans have evolved teeth to last them throughout their natural lives (when our average lifespan was 25-30). Unfortunately, we now live far longer than our teeth can last without assistance. Sometime in last few hundred years we noticed that regular brushing of our teeth contributed to their longevity. Indeed, a more recent development showed that the use of fluoride in toothpaste helped even more. Both of these tooth husbandry practices can be thought of as unnatural. However, since living to 85 is unnatural, and we want to live to 85, we have to employ unnatural husbandry techniques to see that we are able to eat chicken wings well into our 60’s. More to the point, it seems like chameleons are living longer in captivity than they ever do in the wild. So, while the nutritional requirements they have evolved to live with in the wild might be sufficient for a 2 year lifespan, what about a 10 year lifespan? In short, it is not entirely obvious that we ought to tailor our nutrition regimes to match nature, since captives are already living unnaturally long lives.
3. The wild chameleon diet.
I cited some data in the second introductory paragraph that suggests that dipterans, hymenopterans and coleopterans constitute a large part of the diet some wild chameleons (Burrage, 1973) (Karen-Rotem, Bouskila, & Geffen, 2006) (Necas, 2019) (Pleguezuelos, Poveda, Monterrubio, & Ontiveros, 1999) (Tapondjou, 2019). This was partly in the service of making theory 2) appear less incredible to those who have never encountered it. What I did not mention was that wild chameleons also consume a large number of other insects. Moreover, the percentage any one order of insects in the diet of wild chameleons varies strongly with the time of year. Insect populations wax and wane with the season, as do the feeding grounds of many chameleon species[3]. Caterpillars, abundant in the spring, disappear in the summer to be replaced by their adult form. Carrion flies abound during periods of drought and famine when large numbers of animals fall victim to starvation/dehydration. Even the abundance of bees has a natural ebb and flow. This is merely to point out that chameleons are indiscriminate feeders, consuming prey items according to their abundance (Necas, 1999/2004, p. 34). It is therefore unsurprising to find that although dipterans and hymenopterans figure heavily in the spring diet of C. chamaeleon—29% and 32%, respectively—orthopterans (which include crickets and locusts) comprise 40%-50% of the diet in summer and fall (Pleguezuelos, Poveda, Monterrubio, & Ontiveros, 1999).
After flushing the stomach contents of several species, Tapondjou (2019) reports four orders of arthropods as comprising the lion’s share of the trioceros species of Cameroon. In order from highest frequency to lowest these are as follows: dipterans (flies) and coleopterans (beetles), with hemipterans (plant sucking true bugs, e.g. cicadas, aphids, etc.) and orthopterans (crickets and locusts) tied for the number three spot. Surprisingly, a 2003 study of Trioceros montium, T. pfefferi and T. quadricornis reveals some additional high percentage food items including arachnids (spiders), lepidopterons (moths/butterflies), and blattodeans (cockroaches, termites, mantids) (Hofer, Baur, & Bersier, 2003). The findings below have been reproduced from (Hofer, Baur, & Bersier, 2003):
There is no doubt that dipterans and hymenopterans play a significant role in the wild diet. However, these numbers also suggest that spiders (arachnids), crickets/locusts (orthopterans), true bugs (hemipterans/heteropterans), butterflies/moths/caterpillars (lepidopterons), beetles (coleopterans), and cockroaches/termites (blattodeans) play a significant role. Indeed, arachnids and heteropterans appear to rank ahead of both dipterans and hymenopterans in the diet of T. montium, and continue to rank among the top food items for all three species. Again, this does not tell against the importance of flies and bees in the wild diet, but it certainly suggests a variety in the wild diet of these three species.
In a similar study of Rhampholeon spectrum, Trioceros owenii, T. cristatus and Chamaeleo gracilis, Akani et al. reveal that orthopterans rank among the top food items consumed. The findings of Akani et al. are reproduced below (Akani, Ogbalu, & Luiselli, 2001)[4]:
Surprisingly, dipterans are poorly represented in this data. And, with the exception of the abundance of ants and termites found in the ground dwelling species (R. spectrum and T. cristatus), the next runners up after orthopterans are arachnids, lepidopterons, and hemipterans. Note that vespoidea, apoideae (both in hymenoptera) and coleopterans figure minimally in the diet of all four species. While this might be surprising, there is still plenty of evidence for the relative frequency of dipterans and hymenopterans in the diet of wild chameleons. In a study about the relationship between bite force and prey hardness, Measey et al. provide the following data (Measy, Rebelo, Herrel, Vanhooydonck, & Tolley, 2011):
This study shows the high percentage of hymenopterans, dipterans and coleopterans in the wild diet of Bradypodion pumilum. But once again, hemipterans, lepidopterons, arachnids, and (to a lesser extent) orthopterans, figure importantly in the results. Now, it should be noted that B. pumilum is a diminutive species, so the abundance of collembolans and absence of larger prey items is not surprising.
In a similar study, the diets of Bradypodion melanocephalum and B. thamnobates are assessed (Da Silva, Carne, Measey, Herrel, & Tolley, 2016). Here too, dipterans are well represent—as are coleopterans, arachnids, and orthopterans. Hemipterans constitute a huge portion of the diet of B. melanocephalum, and isopods appear to be the prey of choice for females of the species[5]. Curiously, hymenopterans rate low relative to the dipterans. It is important to note that in this and the previous study, wild diets vary with the biotopes of the relevant species: the grassland populations consume different proportions of various prey items than those from the forest. While not surprising, this last fact supports the opportunistic aspect of the wild diet: chameleons eat what they can get. Trivial though such a fact seems, it might have more explanatory force than it appears to. I’ll come back to this in the foot notes, but just consider which insects are likely to occupy the most geographical range when mobility is concerned[6]…Anyways, back to the last chart; reproduced here are the findings of Da Silva et al. (Da Silva, Carne, Measey, Herrel, & Tolley, 2016):
So what does all this have to do with gutloading…remember gutloading? This blog is about it. Well, recall that the view levied against our common gut-loading practices insists that the wild diet of chameleons consists mainly of dipterans, hymenopterans and coleopterans; i.e. flies, bees and beetles. And an accompanying thesis was that the only nutrients we know for sure that these insects contain are those contained in the pollen with which they are in frequent contact. That is, our focus with respect to gutloading should be on pollen and its ilk. While it certainly appears that chameleons ingest a lot of pollen given their proclivity for dipterans, what about the other prey items that are often consumed in relatively high numbers? What of the orthopterans, hemipterans, isopods, arachnids, lepidopterons and blattodeans? Indeed, even the beetles—touted as important in virtue of their pollen content—are a diverse group, many of which are detrivorous and folivorous. A good percentage of so-called “true-bugs”, i.e. hemipterans, are sap-sucking folivores—extracting nutrients from the sap of a wide variety of plants. And I imagine that the gut contents of spiders would count as bioavailable par excellence, since their venom liquefies the nutrients of their prey. It seems like these other arthropods might contribute to the overall nutrition of wild chameleons, since they in fact appear to represent a significant portion of the wild diet.
To summarize, chameleons do in fact consume many dipterans, coleopterans and some hymenopterans. However a study shows that T. montium, T. pfefferi and T. quadricornis consume more hemipterans than hymenopterans, and more arachnids than both. Orthopterans, Lepidopterons, coleopterans and blattodeans also occupy significant portions of one or more of their respective diets (Hofer, Baur, & Bersier, 2003). Surprisingly, another study reveals that dipterans figure low in the diet of R. spectrum, T. owenii, T. cristatus and C. gracilis—all of which appear to rely heavily on orthopterans, arachnids and, to a lesser extent, lepidopterons (Akani, Ogbalu, & Luiselli, 2001). Interestingly, T. cristatus appears to have a penchant for dragon/damselflies. This last point is interesting since, so far as I know, the order Odonata is composed exclusively of carnivores, so there isn’t a lot of pollen gathering there. Just as interesting, the larval phase of many dragon/damsel flies is aquatic, which means some chameleon food chains have aquatic origins. Our Bradypodion species certainly consume many dipterans, but hemipterans figure just as importantly in the data. Dipterans take the number one spot in the wild diet of B. pumilum, but hemipteran and coleopteran numbers are double those of hymenopterans (Measy, Rebelo, Herrel, Vanhooydonck, & Tolley, 2011). Hymenopterans figure equally poorly in the diet of B. melanocephalum and B. thamnobates, which prefers dipterans, hemipterans, arachnids, coleopterans and orthopterans (Da Silva, Carne, Measey, Herrel, & Tolley, 2016).
While all this data is interesting, it is far from conclusive. Dietary data from 5 studies covering only 10 species is far from the whole picture. Worse still, the studies focus on less commonly kept species, instead of veileds, panthers and Jackson’s, so it is not clear how relevant the data is for us. However, information is scarce here, and we can only do what we can with what we have. What we can glean is this: some chameleon species consume large amounts of non-pollinating insects as well as pollinators. And while chameleons have been observed positioning themselves on bushes frequented by bees and other pollinators, the above data seems equally important. That being said, we have not yet investigated the nutrient contents of pollen; so it could turn out that, regardless of what the abovementioned insects bring to the nutrient table, so to speak, pollen will already have it.
4. Pollen
Bee pollen is used the world over for its many reported health benefits; and just as it is used all over the world, so too is it farmed. There appears to be scarcely a continent on which bee pollen isn’t harvested for commercial use. Unsurprisingly, the nutrient content of pollen collected from various locations differs. (Gardana, Del Bo, Quicazan, Correa, & Simonetti, 2018). However, a general picture seems possible. Reproduced below are three charts—1. (Denisow & Denisow-Pietrzyk, 2016), 2. and 3. (Human & Nicolson, 2006)—representing some of the main nutrients in pollen. Again, nutritional data varies from region to region, but charts 2. and 3. are from the pollen of a plant native to southern Africa:
1. 2. 3.
As I just spent several pages displaying a variety of charts, I will confine myself to a summary here. Bee pollen contains a multitude of nutritrients including proteins, carbohydrates, lipids, vitamins and minerals. The information on the chemical composition of bee pollen is widely available, and the reader can look at as many graphs and charts as s/he wishes. More importantly, the benefits of bee pollen in a gutload regime are not in question. What is in question is whether bee pollen would suffice as the primary gutload ingredient.
While interesting, data from several studies suggests that pollen might be lacking certain elements that we have come to believe are important for chameleons (though admittedly, this assumes we actually have a clue about chameleon nutrition). In a previous blog entry, the role of carotenoids as possible substitutes for preformed vitamin A was examined in detail. The stumbling block there was that, on one reasonable interpretation of the data found in Dierenfeld et al. (2002), chameleons appear not to be able to convert beta-carotene and beta-cryptoxanthin into preformed vitamin A. While the data is not conclusive, it has been suggested that perhaps some other carotenoid could fill this important role. The problem is that several studies show bee pollen to contain no more than five of the over one thousand known carotenoids (Margaoan, et al., 2014), (Gardana, Del Bo, Quicazan, Correa, & Simonetti, 2018), (Qiang-Qiang, Wang, Marcucci, Sawaya, Xue, & Wu, 2018), (Denisow & Denisow-Pietrzyk, 2016), (Margaoan, et al., 2014). Two of these, beta-carotene and beta-cryptoxanthin, are the carotenoids mentioned in the Dierenfeld study; another, lutein, is not a vitamin A precursor. For clarity’s sake, if a wide assortment of carotenoids is an important part of chameleon nutrition, then it seems like we’ll have to use some high carotenoid ingredient in our gutloads, in addition to bee pollen.
Another shortcoming of bee pollen is that it appears to have a poor calcium to phosphorus ratio. In Qiang-Qiang et al. (2018), pollen samples contained .2-5.8mg of calcium/100g of dry pollen, and .8-9.6mg of phosphorus/100g of dry pollen. Similar data appears on the above chart from Denisow et al. (2016). Again, this is not a strike against pollen per se, but merely data that suggests that wild chameleons must be getting enough calcium to not only offset the poor ca : p ratio of insects, but also of the large amount of pollen they are said to consume. Indeed, one might surmise that chameleons either have a steady environmental supply of calcium (dust on the leaves?), or else, that they’re finding prey that contains sufficient levels to buffer the poor ca : p ratio found in the high numbers of pollinators they are said to eat…or both.
To sum up, all sides agree that pollen is an excellent addition to any gutloading regime. However, it is entirely plausible that a vast assortment of carotenoids—carotenoids that pollen appears not to have—might be an important factor in chameleon nutrition (see my blog entitled The Current StAte, and Dierenfeld, Norkus, Carroll, & Ferguson, 2002).Pollen also appears to have a poor calcium to phosphorus ratio (Qiang-Qiang, Wang, Marcucci, Sawaya, Xue, & Wu, 2018), which means additional calcium is required. There is certainly more work to be done here. I want to mention one final slightly problematic attribute of pollen—namely, the fact that its digestibility has recently come into question (Franchi, Franchi, Corti, & Pompella, 1997). The aforementioned study focuses on human digestion, but one wonders whether chameleons would fare any better. Since chameleons have short digestive tracts incapable of processing hard to digest material such as plant matter (Necas, 2018a), one wonders whether pollen would present a challenge. On the other hand, this might be a moot point, if the pollen-bearing insects have already done some of the digestive labour for the would-be chameleon consumer…
see part 2
