Aspects of eating behaviors "disinhibition" and "restraint" are related to weight gain and BMI in women

Objective: The causes of adult weight gain leading to obesity are uncertain. We examined the association of adult weight gain and obesity with subscales of eating behavior characteristics in older women. Methods and Procedures: Current height and weight, eating behavior subscales (disinhibition subscales—habitual, situational, and emotional; restraint subscales—flexible and rigid; hunger subscales—internal and external) as assessed using the Eating Inventory (EI), and self‐reported body weight at six prior age intervals were reported by 535 women aged 55–65 years. Multiple regression analysis was used to examine the relationships between EI subscale scores and weight change from the age interval of 30–39 to 55–60 years and current BMI. Results: The strongest correlate of weight gain over 20 years was susceptibility to overeating in response to everyday cues within the environment (habitual disinhibition; partial correlation coefficient (r) = 0.25, P < 0.001); susceptibility to overeating in response to emotional states such as depression (emotional disinhibition) was a quantitatively weaker but significant correlate (partial r = 0.17, P < 0.001), and susceptibility to overeating in response to specific situations such as social occasions (situational disinhibition) was not associated with weight gain. Flexible control of dietary restraint attenuated the influence of habitual disinhibition in particular on weight gain and BMI, and was less effective in attenuating associations of emotional or situational disinhibition. Discussion: Lifestyle modification programs for prevention and treatment of adult‐onset obesity currently focus on reducing situational and emotional overeating; the results of this study suggest that a stronger emphasis on strategies that target habitual overeating may be warranted.     

Multidimensional Measures of Impulsivity in Obsessive-Compulsive Disorder: Cannot Wait and Stop

Objective

Although the relationship between obsessive compulsive disorder (OCD) and impulsivity has long been debated, impulsivity has not been systematically examined in clinical samples of OCD. Meanwhile, recent findings suggest that impulsivity is multi-dimensional construct that can be examined through several constructs. Therefore, this study is aimed to evaluate multiple facets of impulsivity in OCD.

Method

The recruitment includes 80 OCD and 76 healthy control participants. Participants completed a test battery comprising three behavioral tasks of stop signal task (SST), delay discounting task (DDT) and balloon analog risk test (BART), and one self-report measure of the Barratt Impulsiveness scale (BIS-11).

Results

OCD subjects showed significantly lower stop signal reaction time of SST reflecting higher action impulsivity and higher delay discounting parameter of DDT suggesting increased choice impulsivity but significantly lower adjusted mean pump of BART implying lower risk taking propensity of BART than healthy control.

Conclusion

Increased Action and choice impulsivity, and decreased risk taking propensities were found in OCD. These findings seem to be consistent with clinical characteristics of OCD such as greater preference for or avoid risky situations (avoidance), inability to wait tension relief may provoke safety behaviors (compulsion) and inability to stop already started behaviors (repetition).     

Food and emotion

The relationship between eating and emotion has always interested researchers of human behavior. This relationship varies according to the particular characteristics of the individual and according to the specific emotional state. We consider findings on the reciprocal interactions between, on the one hand, emotions and food intake, and, on the other, the psychological and emotional consequences of losing weight and dieting. Theories on the relationship between emotions and eating behaviors have their origin in the literature on obesity. The psychosomatic theory of obesity proposes that eating may reduce anxiety, and that the obese overeat in order to reduce discomfort. The internal/external theory of obesity hypothesizes that overweight people do not recognize physiological cues of hunger or satiety because of faulty learning. It thus predicts that normal weight people will alter (either increase or decrease) their eating when stressed, while obese people will eat regardless of their physiological state. The restraint hypothesis postulates that people who chronically restrict their food intake overeat in the presence of disinhibitors such as the perception of having overeaten, alcohol or stress. These theories are examined in the light of present research and their implications on eating disorders are presented.     

The Association of Body Weight,Dietary Intake,and Energy Expenditure with Dietary Restraint and Disinhibition

LAWSON, OLGA J, DONALD A WILLIAMSON, CATHERINE M CHAMPAGNE, JAMES P DELANY, ELLEN R BROOKS, PAULA M HOWAT, PATRICIA J WOZNIAK, GEORGE A BRAY AND DONNA H RYAN. The association of body weight, dietary intake, and energy expenditure with dietary restraint and disinhibition. Obes Res. 1995;3:153–161. The hypotheses that dieting and/or overeating are associated with adiposity, eating disturbances, and lowered energy expenditure were tested in this study. A sample of 44 premenopausal women scoring high and low on measures of dietary restraint and disinhibition of dietary control, as measured by the Three Factor Eating Questionnaire, was studied. A 2 × 2 factorial design was employed (High/Low Restraint x High/Low Disinhibition). Dependent variables were: body composition, dietary intake, activity, resting metabolic rate, and thermic effect of food. Unrestrained overeaters (Low Restraint/High Disinhibition group) were very obese. High Dietary Restraint was associated with intent to diet and controlled eating. High scores on the Disinhibition Scale were associated with episodic overeating. Groups did not differ in resting metabolic rate (controlled for fat-free mass). Lower thermic effect of food was found to be associated with the obesity found in High Disinhibition subjects. Thus, Dietary Restraint was not associated with significant adverse effects upon physical or psychological health. High Disinhibition, however, was associated with adiposity and significant disturbances of eating.     

Prenatal and Postnatal Exposure to DDT by Breast Milk Analysis in Canary Islands

Introduction

The use of p,p′-dichlorodiphenyltrichloroethane (DDT) has been banned since the late 1970s due to its toxicity. However, its long half-life makes it persistent in the environment and, consequently, almost everyone has DDT residues in the body. Human milk constitutes an ideal non-conventional matrix to investigate environmental chronic exposure to organochlorine compounds (OCs) residues. The study aimed to identify potential population risk factors of exposure to DDT due to the proximity to countries where it is still used.

Methods

Seventy-two consecutive lactating women were prospectively included in Tenerife, Canary Islands (Spain). A validated questionnaire was used to obtain socioeconomic, demographics data, and daily habits during pregnancy. DDT levels in breast milk were measured by gas chromatography with-electron capture detector (GC-ECD). Anthropometrics measurements in newborns were obtained.

Results

Thirty-four out of 72 (47.2%) of the analysed milk samples presented detectable levels of DDT (mean: 0.92 ng/g), ranging between 0.08 to 16.96 ng/g. The socio-demographic variables did not significantly differ between detectable DDT and non-detectable DDT groups. We found positive association between DDT levels and vegetables (OR (95%CI): 1.23 (1.01–1.50)) and poultry meat (OR (95%CI): 2.05 (1.16–3.60)) consumption, and also between the presence of DDT in breast milk and gestational age (OR (95%CI): 0.59 (0.40–0.90)).

Conclusions

DDT is present in breast milk of women at the time of delivery. Residual levels and the spread from countries still using DDT explain DDT detection from vegetables and from animal origin food. The presence of this compound in breast milk represents a pre- and postnatal exposure hazard for foetuses and infants due to chronic bioaccumulation and poor elimination, with possible deleterious effects on health. This data should be used to raise awareness of the risks of OCs exposure and to help establish health policies in order to avoid its use worldwide and thus, to prevent its propagation.     

Decision‐Making Deficits and Overeating: A Risk Model for Obesity

Objective: To demonstrate that human overeating is not just a passive response to salient environmental triggers and powerful physiological drives; it is also about making choices. The ventromedial prefrontal cortex has been strongly implicated in the neural circuitry necessary for making advantageous decisions when various options for action are available. Decision‐making deficits have been found in patients with ventromedial prefrontal cortex lesions and in those with substance dependence—impairments that reflect an inability to advantageously assess future consequences. That is, they choose immediate rewards in the face of future long‐term negative consequences. Research Methods and Procedures: We extended this research to the study of overeating and overweight, testing a regression model that predicted that poor decision making (as assessed by a validated computerized gambling task) and a tendency to overeat under stress would correlate with higher BMI in a group of healthy adult women (N = 41) representing a broad range of body weights. Results: We found statistically significant main effects for both independent variables in the predicted direction (p < 0.05; R² = 0.35). Indeed, the decision‐making impairments across the 100 trials of the computer task were greater in those with high BMI than in previous studies with drug addicts. Discussion: Findings suggested that cortical and subcortical processes, which regulate one's ability to inhibit short‐term rewards when the long‐term consequences are deleterious, may also influence eating behaviors in a culture dominated by so many, and such varied, sources of palatable and calorically dense sources of energy.     

Ecological momentary assessment of obesogenic eating behavior: combining person-specific and environmental predictors

Obesity has been promoted by a food environment that encourages excessive caloric intake. An understanding of how the food environment contributes to obesogenic eating behavior in different types of individuals may facilitate healthy weight control efforts. In this study, Ecological Momentary Assessment (EMA) via palmtop computers was used to collect real-time information about participants' environment and eating patterns to predict overeating (i.e., greater than usual intake during routine meals/snacks, and eating outside of a participant's normal routine) that could lead to weight gain. Thirty-nine women (BMI = 21.6 ± 1.8; age = 20.1 ± 2.0 years; 61% white) of normal weight (BMI 18.5-25) completed the Three Factor Eating Questionnaire and the Power of Food Scale (PFS), and carried a palmtop computer for 7-10 days, which prompted them to answer questions about eating events, including a count of the types of good tasting high-calorie foods that were available. None of the self-report measures predicted overeating, but BMI interacted with the number of palatable foods available to predict overeating (P = 0.035). Compared to leaner individuals who reported a relatively low frequency of overeating regardless of the availability of palatable food, the probability of overeating among heavier individuals was very low in the absence of palatable food, but quickly increased in proportion to the number of palatable foods available. Our findings suggest that the eating behavior of those with higher relative weights is susceptible to the presence of palatable foods in the environment. Individuals practicing weight control may benefit from limiting their exposure to good tasting high-calorie food in their immediate environment.     

Hyperactive hypothalamus,motivated and non‐distractible chronic overeating in ADAR2 transgenic mice

ADAR2 transgenic mice misexpressing the RNA editing enzyme ADAR2 (Adenosine Deaminase that act on RNA) show characteristics of overeating and experience adult onset obesity. Behavioral patterns and brain changes related to a possible addictive overeating in these transgenic mice were explored as transgenic mice display chronic hyperphagia. ADAR2 transgenic mice were assessed in their food preference and motivation to overeat in a competing reward environment with ad lib access to a running wheel and food. Metabolic activity of brain and peripheral tissue were assessed with [¹⁸F] fluorodeoxyglucose positron emission tomography (FDG‐PET) and RNA expression of feeding related genes, ADAR2, dopamine and opiate receptors from the hypothalamus and striatum were examined. The results indicate that ADAR2 transgenic mice exhibit, (1) a food preference for diets with higher fat content, (2) significantly increased food intake that is non‐distractible in a competing reward environment, (3) significantly increased messenger RNA (mRNA) expressions of ADAR2, serotonin 2C receptor (5HT_2CR), D1, D2 and mu opioid receptors and no change in corticotropin‐releasing hormone mRNAs and significantly reduced ADAR2 protein expression in the hypothalamus, (4) significantly increased D1 receptor and altered bioamines with no change in ADAR2, mu opioid and D2 receptor mRNA expression in the striatum and (5) significantly greater glucose metabolism in the hypothalamus, brain stem, right hippocampus, left and right mid brain regions and suprascapular peripheral tissue than controls. These results suggest that highly motivated and goal‐oriented overeating behaviors of ADAR2 transgenic mice are associated with altered feeding, reward‐related mRNAs and hyperactive brain mesolimbic region .     

So Many Brands and Varieties to Choose from: Does This Compromise the Control of Food Intake in Humans?

The recent rise in obesity is widely attributed to changes in the dietary environment (e.g., increased availability of energy-dense foods and larger portion sizes). However, a critical feature of our “obesogenic environment” may have been overlooked - the dramatic increase in “dietary variability” (the tendency for specific mass-produced foods to be available in numerous varieties that differ in energy content). In this study we tested the hypothesis that dietary variability compromises the control of food intake in humans. Specifically, we examined the effects of dietary variability in pepperoni pizza on two key outcome variables; i) compensation for calories in pepperoni pizza and ii) expectations about the satiating properties of pepperoni pizza (expected satiation). We reasoned that dietary variability might generate uncertainty about the postingestive effects of a food. An internet-based questionnaire was completed by 199 adults. This revealed substantial variation in exposure to different varieties of pepperoni pizza. In a follow-up study (n= 66; 65% female), high pizza variability was associated with i) poorer compensation for calories in pepperoni pizza and ii) lower expected satiation for pepperoni pizza. Furthermore, the effect of uncertainty on caloric compensation was moderated by individual differences in decision making (loss aversion). For the first time, these findings highlight a process by which dietary variability may compromise food-intake control in humans. This is important because it exposes a new feature of Western diets (processed foods in particular) that might contribute to overeating and obesity.     

Neural signatures of economic preferences for risk and ambiguity

People often prefer the known over the unknown, sometimes sacrificing potential rewards for the sake of surety. Overcoming impulsive preferences for certainty in order to exploit uncertain but potentially lucrative options may require specialized neural mechanisms. Here, we demonstrate by functional magnetic resonance imaging (fMRI) that individuals' preferences for risk (uncertainty with known probabilities) and ambiguity (uncertainty with unknown probabilities) predict brain activation associated with decision making. Activation within the lateral prefrontal cortex was predicted by ambiguity preference and was also negatively correlated with an independent clinical measure of behavioral impulsiveness, suggesting that this region implements contextual analysis and inhibits impulsive responses. In contrast, activation of the posterior parietal cortex was predicted by risk preference. Together, this novel double dissociation indicates that decision making under ambiguity does not represent a special, more complex case of risky decision making; instead, these two forms of uncertainty are supported by distinct mechanisms.     

State-dependent decisions in nest site selection by a web-building spider

Foraging decisions may reflect a trade-off between food intake and safety and can also be influenced by the animal's internal state. Foraging in the web-building spider Stegodyphus lineatus depends on a capture web associated with a retreat (the nest). The relocation of nests, including the take-over of conspecific nests, may be viewed as a foraing decision, which depends on risk of exposure, cost of silk production and hunger state. We investigated a possible state-dependent trade-off in nest site choice of S. lineatus spiderlings. The philopatric nature ofS. lineatus implies a high risk of encounters with potentially cannibalistic conspecifics and a potential loss of inclusive fitness because encountered conspecifics are likely to be kin. To test for state dependence of foraging decisions, we compared preferences of well-fed and hungry spiders for their own nests and those of siblings and nonsiblings. We expected satiated spiders to prefer their own to conspecific nests and hungry spiders to choose the risky option of a conspecific nest. SinceS. lineatus is less aggressive towards kin, we tested the ability of spiders to discriminate kin by silk-bound cues. Because of this reduced aggression, preference for kin nests should be safer than preference for nonkin nests. A strong preference for self-nests demonstrated self-recognition in well-fed spiders. However, neither well-fed nor hungry spiders discriminated between nests of siblings and nonsiblings. Well-fed spiders preferred self-nests to empty chambers, but showed no discrimination between nonself-nests and empty chambers. Hungry spiders showed a reduced preference for self-nests, suggesting that hunger elicits a more risky foraging strategy. A tendency of hungry spiders to adopt the nests of conspecific spiders may reflect a silk-saving strategy. We conclude that S. lineatus spiders show state-dependent decision making in nest site selection. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Visual Cues Given by Humans Are Not Sufficient for Asian Elephants (Elephas maximus) to Find Hidden Food

Recent research suggests that domesticated species – due to artificial selection by humans for specific, preferred behavioral traits – are better than wild animals at responding to visual cues given by humans about the location of hidden food. \Although this seems to be supported by studies on a range of domesticated (including dogs, goats and horses) and wild (including wolves and chimpanzees) animals, there is also evidence that exposure to humans positively influences the ability of both wild and domesticated animals to follow these same cues. Here, we test the performance of Asian elephants (Elephas maximus) on an object choice task that provides them with visual-only cues given by humans about the location of hidden food. Captive elephants are interesting candidates for investigating how both domestication and human exposure may impact cue-following as they represent a non-domesticated species with almost constant human interaction. As a group, the elephants (n = 7) in our study were unable to follow pointing, body orientation or a combination of both as honest signals of food location. They were, however, able to follow vocal commands with which they were already familiar in a novel context, suggesting the elephants are able to follow cues if they are sufficiently salient. Although the elephants’ inability to follow the visual cues provides partial support for the domestication hypothesis, an alternative explanation is that elephants may rely more heavily on other sensory modalities, specifically olfaction and audition. Further research will be needed to rule out this alternative explanation.     

The Balloon Analog Insurance Task (BAIT): a behavioral measure of protective risk management

Prior methods used to assess individual differences related to risk have not focused on an important component of risk management: how willing individuals are to pay for or take actions to insure what they already have. It is not clear whether this type of protective risk management taps into the same individual differences as does risk taking propensity measured by existing risk taking tasks. We developed a novel task to assess protective risk management, the Balloon Analog Insurance Task (BAIT), which is modeled after the Balloon Analog Risk Task (BART). In the BAIT, individuals are forced to decide how much money they are willing to pay in order to insure a specific fraction of their prior winnings given changing but imprecise levels of risk of monetary loss. Participants completed the BART and BAIT for real monetary rewards, and completed six self report questionnaires. The amount of insurance purchased on the BAIT was positively correlated with scores on the Intolerance of Uncertainty Scale and on the Checking scale of the revised Obsessive Compulsive Inventory. Conversely, the amount of insurance purchased was negatively correlated with scores on the Domain Specific Risk Taking Questionnaire, and on the Psychopathic Personality Inventory (PPI). Furthermore, relationships between insurance purchased and these scales remained significant after controlling for the BART in linear regression analyses, and the BART was only a significant predictor for measures on one scale--the PPI. Our results reveal that behavior on the BAIT taps into a number of individual differences that are not related to behavior on another measure of risk taking. We propose that the BAIT may provide a useful complement to the BART in the assessment of risk management style.     

Progesterone attenuates impulsive action in a Go/No-Go task for sucrose pellets in female and male rats

Impulsivity, or a tendency to act without anticipation of future consequences, is associated with drug abuse. Impulsivity is typically separated into two main measures, impulsive action and impulsive choice. Given the association of impulsivity and drug abuse, treatments that reduce impulsivity have been proposed as an effective method for countering drug addiction. Progesterone has emerged as a promising treatment, as it is associated with decreased addiction-related behaviors and impulsive action. The goal of the present study was to determine the effects of progesterone (PRO) on impulsive action for food: a Go/No-Go task. Female and male rats responded for sucrose pellets during a Go component when lever pressing was reinforced on a variable-interval 30-s schedule. During the alternate No-Go component, withholding a lever press was reinforced on a differential reinforcement of other (DRO) behavior 30-s schedule, where a lever press reset the DRO timer. Impulsive action was operationally defined as the inability to withhold a response during the No-Go component (i.e. the number of DRO resets). Once Go/No-Go behavior was stable, responding between rats treated with PRO (0.5 mg/kg) or vehicle was examined. Progesterone significantly decreased the total number of DRO resets in both males and females, but it did not affect VI responding for sucrose pellets. This suggests that PRO decreases motor impulsivity for sucrose pellets without affecting motivation for food. Thus, PRO may reduce motor impulsivity, a behavior underlying drug addiction.     

Coding of reward risk by orbitofrontal neurons is mostly distinct from coding of reward value

Risky decision-making is altered in humans and animals with damage to the orbitofrontal cortex. However, the cellular function of the intact orbitofrontal cortex in processing information relevant for risky decisions is unknown. We recorded responses of single orbitofrontal neurons while monkeys viewed visual cues representing the key decision parameters, reward risk and value. Risk was defined as the mathematical variance of binary symmetric probability distributions of reward magnitudes; value was defined as non-risky reward magnitude. Monkeys displayed graded behavioral preferences for risky outcomes, as they did for value. A population of orbitofrontal neurons showed a distinctive risk signal: their cues and reward responses covaried monotonically with the variance of the different reward distributions without monotonically coding reward value. Furthermore, a small but statistically significant fraction of risk responses also coded reward value. These risk signals may provide physiological correlates for the role of the orbitofrontal cortex in risk processing.     

DAT1 polymorphism is associated with risk taking in the Balloon Analogue Risk Task (BART)

Twin-studies suggest that a significant portion of individual differences in the propensity to take risks resides in people's genetic make-up and there is evidence that variability in dopaminergic systems relates to individual differences in risky choice. We examined the link between risk taking in a risk taking task (the Balloon Analogue Risk Task, BART) and a variable number tandem repeat (VNTR) polymorphism in the 3'UTR of the dopamine transporter gene (SLC6A3/DAT1). Behavior in BART is known to be associated with activity in striatal reward-processing regions, and DAT1 is assumed to modulate striatal dopamine levels. We find that carriers of DAT1 alleles, which presumably result in lower striatal dopamine availability, showed more risk taking, relative to carriers of the alleles associated with higher striatal dopamine availability. Our analyses suggest that the mechanism underlying this association is diminished sensitivity to rewards among those who take more risks. Overall, our results support the notion that a behavioral genetic approach can be helpful in uncovering the basis of individual differences in risk taking.     

Roe deer at risk: teasing apart habitat selection and landscape constraints in risk exposure at multiple scales

Non‐consumptive effects of predators result from the cost of responses to perceived risk. Prey modulate risk exposure through flexible habitat selection at multiple scales which, in interaction with landscape constraints, determines their use of risky habitats. Identifying the relative contributions of landscape constraints and habitat selection to risk exposure is a critical first step towards a mechanistic understanding of non‐consumptive effects. Here, we provide an integrative multi‐scale study of roe deer spatial responses to variable hunting pressure along a landscape gradient of open habitats and dispersed refuges. Between low‐risk and high‐risk periods, we investigated shifts in 1) home‐range location, 2) probability of using risky habitats (between‐habitat scale) and 3) distance to the nearest refuge (within‐habitat scale). For 2) and 3), we disentangled the contributions of landscape constraints and habitat selection to risky habitat use. We found that when risk was high, roe deer did not shift their home‐range, but generally decreased their use of risky habitats, and sometimes reduced their distance to cover (particularly older animals). There was a functional response in between‐habitat selection, with animals living in more open landscapes responding more than those living in landscapes with more refuges. However, individuals living in more open landscapes avoided open risky habitat less. Finally, we found that among‐individual variation in risk exposure was generally, but not always, minimized by habitat selection across gradients of landscape constraints. To our knowledge, this is the first study simultaneously documenting prey responses to risk at the within‐habitat, between‐habitat and home‐range scales. Our results support the view that between‐habitat selection acts at a higher hierarchical level than within‐habitat selection, and provide a framework for disentangling the contributions of habitat selection and landscape constraints to risk exposure. Selection cannot always compensate for landscape constraints, indicating a need for further investigation of the processes underlying habitat selection.     

Allocation of Colony‐Level Foraging Effort in Vespula germanica in Response to Food Resource Quantity,Quality, and Associated Olfactory Cues

In social insects, selection takes place primarily at the level of the colony. Therefore, unlike solitary insects, social species are expected to forage at rates that maximize colony fitness rather than individual fitness. Workers can increase the net benefit of foraging by responding to increased resource availability, by responding more strongly to higher‐quality resources, and by decreasing the uncertainty with which nestmates find resources. Unlike many ants and social bees, no social wasp is known to utilize a nest‐based recruitment signal to inform nestmates of food location. On the other hand, wasps do learn the odor of food brought to the nest and use this cue to locate the food source outside the nest. Here, we quantify the effects of three food‐associated variables on the allocation of foraging effort in the yellowjacket Vespula germanica. We used an experimental approach to assess whether resource quantity, quality, or associated olfactory information affect the probability that a forager will leave the nest on a foraging trip. We addressed these questions by inserting a known amount of sucrose solution directly into nests and recording foraging effort (departure rate) over the subsequent hour‐long observation period. No differences were found in foraging effort because of the presence/absence of olfactory cues, but there was strong evidence that foraging effort increased in response to resource influx and resource quality. Thus, while olfactory cues are learned in the nest, only resource quality and the cue of increased amount of food in the nest factor into a forager's decision of whether or not to depart on a foraging trip. However, as prior work has shown, once a wasp forager leaves the nest, it uses the learned olfactory cues to aid in finding resources.     

G-protein gamma subunit GNG11 strongly regulates cellular senescence

GNG11 is a member of the gamma subunit family of heteromeric G-protein, but its function is entirely unknown. Here, we successfully characterized its specific role in cellular senescence. We have found that overexpression of GNG11 immediately induces cellular senescence in normal human fibroblasts, and its down-regulation by antisense cDNA extends their lifespan. Surprisingly, this gene is very rapidly induced by senescence-inducing agents such as H(2)O(2). Furthermore, overexpression of GNG11 activated ERK1/2 of the MAP kinase family, but did not Ras. Collectively, these results suggest a novel senescence pathway mediated by GNG11 in response to environmental cues.     

Coordinated Ontogeny of Food Preference and Responses to Chemical Food Stimuli by a Lizard Ctenosaura pectinata (Reptilia: Iguanidae)

When important ecological factors change predictably during the life of an organism, the ontogeny of related behaviors must be timed to maintain appropriate behavioral responsiveness to current ecological conditions. In the brown iguana, Ctenosaura pectinata , hatchlings in natural populations eat primarily insects, consuming little plant matter, whereas adults eat primarily plants, consuming some insects as well. We conducted laboratory experiments on diet preferences and responses to chemical cues that the lizards sampled by tongue-flicking and used to identify food. All hatchlings ate crickets, but only one of six ate romaine lettuce. They responded strongly to chemical cues from prey, as indicated by elevated tongue-flick rates, but not from romaine lettuce. All older individuals ate both crickets and romaine lettuce. They responded much more strongly to chemical cues from both crickets and romaine lettuce than to control chemicals, as indicated by higher proportions of individuals that bit and higher tongue-flick attack scores.
Thus, an ontogenetic change to increased responsiveness to plant chemical stimuli was coordinated with an ontogenetic change to an herbivorous diet. The mechanisms underlying these ontogenetic changes are unknown, but folivory may be unprofitable before juveniles acquire intestinal flora that degrade cellulose by ingestion of feces of adult conspecifics. Possible mechanisms are discussed, including the detection of chemical cues from appropriate food plants during consumption of feces from older individuals. Studies of other squamate reptiles suggest that exposure to these chemicals might affect both future responsiveness to the chemical cues and a tendency to eat the corresponding plants.