Reading, writing, slogging along
Jun. 5th, 2014 10:40 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
rebeccmeisterThere are certain stages of the writing process that get to be a real slog. Mostly, the "refinement" stages. I spent a ridiculous portion of the day yesterday trying to make sure I had a solid understanding of everything that's known about connections between diet and resting metabolism (short answer: not much, actually). Part of the problem is that most efforts to classify and measure what different animals are eating have been inadequate. In a lot of cases, it's possible to generate a list of the different things an animal is eating (as in this article on sparkly bat poop), but that doesn't say much about what a specific animal has eaten, in specific amounts, or what nutrients the animal has gotten from the things it has eaten. And the things eaten by a specific animal can vary tremendously. The closest I got was a review that talked about feeding sea lions either squid (low-quality diet) or herring (high-quality diet), and feeding vampire bats either regular blood or diluted blood (Cruz-Neto and Bozinovic 2004 - full references at the end).
One of the insights from that review was that neither the sea lions nor the bats responded to the low-quality foods by upping their intake. This contrasts greatly with what happens in grasshoppers (and crickets, to some extent), who will start to pig out if you give them dilute foods. Grasshoppers are such good eaters that in a lot of cases they can almost completely compensate for differences in nutrient dilution. So, that in and of itself, is interesting, but means that comparisons with the sea lions and vampire bats won't be very helpful except on a very crude level.
...but these insights are not going into the current manuscript, because they're too much of a tangent. Which meant I had to self-redirect and think about the problem from other angles.
The good news is that the people interested in digestive physiology have done much more comparative work that involves detailed examinations of diets than the people interested in metabolism (so far!). So I could find cases where people have found amazingly good and strong associations between the things animals eat and the digestive enzymes they produce.
Anyway, we'll see whether my arguments on that whole front wind up holding water, or whether they wind up getting cut from the paper.
And that was work for one sentence in one paragraph in the Discussion.
Today, I need to spend more time thinking about comparisons between ectotherms versus endotherms. Ectotherms are animals whose body temperature is passively regulated by the environment - things like reptiles, crickets, and grasshoppers, who still behaviorally thermoregulate by basking in the sun. Endotherms are able to generate heat to maintain a core body temperature. One of the coolest endotherms I learned about in Comparative Physiology is tuna fish. Knowing that tuna are endotherms makes it harder for me to ever eat them (on top of knowing that they're long-lived predators and that we're overfishing the oceans like crazy).
Anyway - for my purposes, I think one of the big distinctions I need to highlight between endotherms and ectotherms is that endotherms are able to use "diet-induced thermogenesis" as a regulatory mechanism when feeding on diets with a protein-carbohydrate ratio that is mismatched when compared to their preferred/optimal ratio. A paper (Huang et al) got published in 2013 where researchers fed a group of 279 mice one of 25 diets with different ratios and total amounts of protein, carbohydrate and fat, and then measured their body surface temperature at 25 weeks of age. They found that body surface temperature increased with the total amount of energy consumed, and specifically with amounts of protein, carbohydrate, and fat making similar contributions to temperature based on the kJ eaten.
Previous work has suggested that the mechanisms for diet-induced thermogenesis are best developed in animals adapted to habitually low-protein diets - things like nectar- and fruit-eating bats and marmosets (Stock 1999). But what about ectotherms, like my crickets? Does this all mean that the work in ectotherms can't be meaningfully compared to the work in endotherms?
...and those are the questions to address for today.
References
Cruz-Neto AF, Bozinovic F (2004) The relationship between diet quality and basal metabolic rate in endotherms: Insights from intraspecific analysis. Physiological and Biochemical Zoology 77:877-889.
Huang X, Hancock DP, Gosby AK, McMahon AC, Solon SMC, Le Couteur DG, Conigrave AD, Raubenheimer D, Simpson SJ (2013) Effects of dietary protein to carbohydrate balance on energy intake, fat storage, and heat production in mice. Obesity 21:85-92. doi:10.1002/oby.20007
Stock MJ (1999) Gluttony and thermogenesis revisited. International Journal of Obesity 23:1105-1117.
One of the insights from that review was that neither the sea lions nor the bats responded to the low-quality foods by upping their intake. This contrasts greatly with what happens in grasshoppers (and crickets, to some extent), who will start to pig out if you give them dilute foods. Grasshoppers are such good eaters that in a lot of cases they can almost completely compensate for differences in nutrient dilution. So, that in and of itself, is interesting, but means that comparisons with the sea lions and vampire bats won't be very helpful except on a very crude level.
...but these insights are not going into the current manuscript, because they're too much of a tangent. Which meant I had to self-redirect and think about the problem from other angles.
The good news is that the people interested in digestive physiology have done much more comparative work that involves detailed examinations of diets than the people interested in metabolism (so far!). So I could find cases where people have found amazingly good and strong associations between the things animals eat and the digestive enzymes they produce.
Anyway, we'll see whether my arguments on that whole front wind up holding water, or whether they wind up getting cut from the paper.
And that was work for one sentence in one paragraph in the Discussion.
Today, I need to spend more time thinking about comparisons between ectotherms versus endotherms. Ectotherms are animals whose body temperature is passively regulated by the environment - things like reptiles, crickets, and grasshoppers, who still behaviorally thermoregulate by basking in the sun. Endotherms are able to generate heat to maintain a core body temperature. One of the coolest endotherms I learned about in Comparative Physiology is tuna fish. Knowing that tuna are endotherms makes it harder for me to ever eat them (on top of knowing that they're long-lived predators and that we're overfishing the oceans like crazy).
Anyway - for my purposes, I think one of the big distinctions I need to highlight between endotherms and ectotherms is that endotherms are able to use "diet-induced thermogenesis" as a regulatory mechanism when feeding on diets with a protein-carbohydrate ratio that is mismatched when compared to their preferred/optimal ratio. A paper (Huang et al) got published in 2013 where researchers fed a group of 279 mice one of 25 diets with different ratios and total amounts of protein, carbohydrate and fat, and then measured their body surface temperature at 25 weeks of age. They found that body surface temperature increased with the total amount of energy consumed, and specifically with amounts of protein, carbohydrate, and fat making similar contributions to temperature based on the kJ eaten.
Previous work has suggested that the mechanisms for diet-induced thermogenesis are best developed in animals adapted to habitually low-protein diets - things like nectar- and fruit-eating bats and marmosets (Stock 1999). But what about ectotherms, like my crickets? Does this all mean that the work in ectotherms can't be meaningfully compared to the work in endotherms?
...and those are the questions to address for today.
References
Cruz-Neto AF, Bozinovic F (2004) The relationship between diet quality and basal metabolic rate in endotherms: Insights from intraspecific analysis. Physiological and Biochemical Zoology 77:877-889.
Huang X, Hancock DP, Gosby AK, McMahon AC, Solon SMC, Le Couteur DG, Conigrave AD, Raubenheimer D, Simpson SJ (2013) Effects of dietary protein to carbohydrate balance on energy intake, fat storage, and heat production in mice. Obesity 21:85-92. doi:10.1002/oby.20007
Stock MJ (1999) Gluttony and thermogenesis revisited. International Journal of Obesity 23:1105-1117.
