The feeding behaviour of caterpillars (Manduca sexta) on tobacco and on artificial diet

ABSTRACT. Feeding behaviour of fifth instar tobacco hornworm caterpillars, Manduca sexta (Johansen) (Lepidoptera; Sphingidae), eating tobacco or artificial diet, is quantitatively described. The insects grow at the same rate on both foods. There is no daily rhythm of feeding behaviour. For most insects, feeding on either food occurs in bouts with the lengths of interfeed gaps and of feeding bouts appearing to be distributed randomly. However, in many insects there is a strong correlation between the length of a feeding period and that of the preceding non-feeding period.
The proportion of time spent feeding on tobacco is much greater than on artificial diet. On tobacco, feeding periods are separated by shorter interfeed gaps than on the artificial diet, while the rate of bout initiation is similar on either food.
On both tobacco and artificial diet, the proportion of time spent feeding increases as the fifth stadium proceeds. This is due to both longer feeding bouts and shorter gaps. The rate of food acquisition within bouts does not change during the stadium.     

The temporal structure of feeding behavior

Meals have long been considered relevant units of feeding behavior. Large data sets of feeding behavior of cattle, pigs, chickens, ducks, turkeys, dolphins, and rats were analyzed with the aims of 1) describing the temporal structure of feeding behavior and 2) developing appropriate methods for estimating meal criteria. Longer (between-meal) intervals were never distributed as the negative exponential assumed by traditional methods, such as log-survivorship analysis, but as a skewed Gaussian, which can be (almost) normalized by log-transformation of interval lengths. Log-transformation can also normalize frequency distributions of within-meal intervals. Meal criteria, i.e., the longest interval considered to occur within meals, can be estimated after fitting models consisting of Gaussian functions alone or of one Weibull and one or more Gaussian functions to the distribution of log-transformed interval lengths. Nonuniform data sets may require disaggregation before this can be achieved. Observations from all species were in conflict with assumptions of random behavior that underlie traditional methods for criteria estimation. Instead, the observed structure of feeding behavior is consistent with 1) a decrease in satiety associated with an increase in the probability of animals starting a meal with time since the last meal and 2) an increase in satiation associated with an increase in the probability of animals ending a meal with the amount of food already consumed. The novel methodology proposed here will avoid biased conclusions from analyses of feeding behavior associated with previous methods and, as demonstrated, can be applied across a range of species to address questions relevant to the control of food intake.     

Short-term regulation of food intake by the brown honeyeater,Lichmera indistincta

• 1.1. Regardless of nectar concentration, there are strong positive correlations between the durations of feeding bouts by Lichmera indistincta and subsequent inter-bout intervals, and energy intake during feeding bouts and energy expenditure during subsequent inter-bout intervals.
• 2.2. Energy utilization by L. indistincta conforms to an accumulation-depletion model, with a portion of the energy acquired during each feeding bout contributing to the gradual diurnal storage of energy that is subsequently used for maintenance during non-foraging periods.
• 3.3. L. indistincta compensates for a decrease in nectar concentration by increasing the frequency of feeding bouts and decreasing the duration of inter-bout intervals.
• 4.4. Changes in the duration of inter-bout intervals caused by alterations to the calorific value of nectar drunk can be explained in terms of the rate at which the stomach empties.

     

A positive feedback model for switching between two activities

We describe a model for the alternation between two activities. Each activity has an associated tendency, and the model performs the activity with the higher tendency. The tendencies depend on both negative and positive feedback from the performance of the activities. In general the behaviour of the model is periodic, with bout, durations that depend on the ratio of the maximum response rates. Increasing the maximum rate of a behaviour increases the magnitude of its bouts. The behaviour of the model is similar in several respects to the model developed by Ludlow (1980), which suggests that it may not be easy to distinguish between various models of feeding and drinking behaviour.     

A novel flexible method to split feeding behaviour into bouts

Before meal patterns can be analysed properly, a biologically relevant meal criterion must be determined in order to group short-term feeding behaviour into meals. Existing methodologies are based on modelling of the frequency distributions of intervals between feeding events but these methods cannot be used if the proper distributions cannot be clearly identified. For such cases we developed two new methods – (1) based on the analysis of the distribution of between-meal interval lengths only and (2) based on the analysis of changes in the probability of animals starting to feed with time since the last feeding event. Both methods were developed using a data set of over 700,000 records of visits to feeders obtained with broilers (Gallus gallus) aged between 2 and 5 weeks. The two methods resulted in meal criteria estimates of 20.1 and 17.5 min, respectively, which, when applied to the data set, gave statistically significant but very small differences in meal characteristics. The new methods were tested against an independent cow (Bos taurus) data set and the resultant meal criteria compared with those predicted by an existing method. The two novel methods estimated meal criteria for cows at 27.9 and 35.5 min, compared with 28.9 min for the existing method. Again, these differences in meal criteria resulted in only very small differences in meal characteristics. Even though meal criteria were relatively similar for birds and cows, characteristics such as average daily number of meals (10.9 and 5.9), meal size (12.5 g and 7.4 kg) and meal duration (7.7 and 31.4 min) were very different. The analyses show that, if the appropriate distributions of intervals cannot be identified, meal criteria can still be estimated for species as diverse as mature cows and young birds by the novel methodologies developed here.     

Organization rules and timing in kestrel grooming

Grooming bouts were observed for 200 h in two captive American kestrels (Falco sparverius sparverius). Two types of bouts were found, long and short; the bout length distribution for long bouts approximated a geometric distribution, which can be interpreted as a discrete variant of the survival function. Transition rules in long bouts were based on anatomical proximity. Grooming movements clustered together on the basis of anatomical regions and function. Timing processes could either be accounted for by a three-level hierarchy involving two different types of distributions, or a four-level hierarchy of identical distributions. In the former model, grooming acts per cluster, clusters per preening session and preening sessions per bout all yielded frequency distributions of the geometric type, suggesting that grooming could be controlled by a hierarchy of random processes.     

Mechanisms of Change in the Ontogeny of Black-tailed Prairie Dog Time Budgets

This study examines the behavioral mechanisms underlying changes in the time allocation patterns of black-tailed prairie dog (Sciuridae: Cynomys ludovicianus) pups. Previous analyses of time budgets had revealed substantial differences between pups (young of the year) and adults, and that pup time budgets changed significantly over time. This paper shows that these differences were due to two mechanisms: pups generally differed from adults in the frequency of performance of different behaviors; however, changes in pup behavior over time were due to changes in both bout frequencies and durations. Other influences on bout durations were also examined. Time of day dramatically affected the duration of most behaviors, with vigilance bouts longest in the morning and feeding bouts longest in the evening. The presence of a pup's mother above ground and the height of the vegetation a pup was in had much less influence on bout durations. Multiple regression analyses were used to identify other potential influences (e.g., weather and social conditions) on bout lengths. Of these, the distance of a pup from the nearest burrow produced the strongest relationships.     

Feeding patterns of a specialist and a generalist grasshopper: electronic monitoring on their host plants

Abstract Hypochlora alba (Dodge) is a specialist grasshopper that lives and feeds almost exclusively on Artemisia ludoviciana Nutt., a sage plant mostly avoided as food by generalist or polyphagous grasshoppers, such as Melanoplus sanguinipes (Fabr.). Adaptations to feeding on the pubescent sage foliage containing high levels of allelochemics may involve behavioural as well as physiological specialization. Using an electronic device to monitor feeding activity, we compared feeding periodicity, bout length, bout frequency, and overall time spent feeding by H.alba on sage foliage and by M.sanguinipes on seedling ryegrass ( Lolium perenne L.), the plants on which they had been reared. Although both species fed for about the same amount of time per day (c. 4–5%), they achieved this by two different feeding patterns. H. alba had feeding bouts averaging c. 10 min each, compared to c. 4–5 min for M.sanguinipes. Bout frequency was reversed, with M.sanguinipes feeding about once every hour and H.alba about half as often. Bout length for both species was unaffected by phase of the photoperiod while bout frequency, and consequently the rate of feeding in min/h, was typically reduced by two-thirds or more during the dark phase. The relationship of grasshopper feeding behaviour to host plant specialization is discussed.     

Using radius frequency distribution functions as a metric for quantifying root systems

Root radius frequency distributions have been measured to quantify the effect of plant type, environment and methodology on root systems, however, to date the results of such studies have not been synthesised. We propose that cumulative frequency distribution functions can be used as a metric to describe root systems because (1) statistical properties of the frequency distribution can be determined, (2) the parameters for these can be used as a means of comparison, and (3) the analytical expressions can be easily incorporated into models that are dependent upon root geometry. We collated a database of 96 root radii frequency distributions and botanical and methodology traits for each distribution. To determine if there was a frequency distribution function that was best suited to root radii measurements we fitted the exponential, Rayleigh, normal, log-normal, logistic and Weibull cumulative distribution functions to each distribution in our database. We found that the log-normal function provided the best fit to these distributions and that none of the distribution functions was better or worse suited to particular shapes. We derived analytical expressions for root surface and volume and found that they are a valid, and simpler method for incorporating root architectural traits into analytical models. We also found that growth habit and growth media had a significant effect on mean root radius.     

The platinum-carbon replication of a homogenous population of gold particles makes log-normal distributions of shadow widths and lengths

Gold particles were prepared, dried on grids and shadowed at 45° with a 1.2 nm platinum-carbon (Pt-C) film using the shadowing conditions previously described for the freeze-fracture of gastric parietal cell membranes. The particle diameters and the particle shadow widths and lengths were measured using an image analysis system. Statistical analysis of 2000 diameters, shadow widths and shadow lengths indicated that a homogenous population of particles had a normal frequency distribution of diameters (mean diameter 14.5 ± 1.5 nm) and that the Pt-C shadowing transformed that normal curve into a log-normal frequency distribution of shadow widths. The frequency distribution of shadow lengths was log-normal too. We conclude that a statistical partition of experimental frequency distributions of particle shadow widths and lengths of natural membranes to determine the number and parameters of individual components should involve log-normal subdistributions rather than normal ones.     

The Sexual Behaviour of the Great Crested Newt,Triturus cristatus (Amphibia: Salamandridae)

The sexual behaviour of Triturus cristatus is described. The first stage of sexual behaviour consists of an orientation phase in which the male approaches the female, sniffs her and moves in front of and perpendicular to her. The second stage is a prolonged period of static display with two different tail movements, called Fan and Lash, in 13.8 ± 1.3 bouts (x? ± SE) with intervals of 10.5 ± 0.3 s between bouts. Each bout contains 6.7 ± 0.3 regular Fan beats at a frequency of 0.5–0.8 Hz. This Fanning provides olfactory and mechanical stimulation to the female. 15% of bouts also contain a violent Lash, in which the male rapidly slaps the female's flank. Some Lashes are used to stop the female when she tries to move away. In the third stage of the sexual sequence, the male turns away, Creeps for 6.7 ± 0.3 s (x? ± SE) and then Quivers his tail. A receptive female follows and touches his tail, and the male deposits a spermatophore and then turns to one side with his tail folded along his flank in a position called Brake. The female now approaches again and the male steps away sideways in a movement called Rebrake. After several Rebrakes the male stops, the female touches his tail and the spermatophore may now be picked up in her cloaca. This sequence can be repeated several times during one encounter. This behaviour is discussed in relation to previous studies of courtship in this genus.     

The sentineling—Foraging trade‐off in dominant and subordinate Arabian babblers

Many cooperative breeders forage under predation risks, sentineling is a central activity, and groupmates have to balance between sentineling and foraging. The optimal balance between sentinel activity and foraging may differ among dominant and subordinate individuals, as dominants are more efficient foragers. Two theoretical models pertain to this balance and predict when individuals with different foraging abilities should switch between the two activities on the basis of their energetic state. In one of these models, individuals must attain a critical energetic level by dusk to pass the night, and in the second model fitness is monotonically increasing with the energetic state. We tested these models in the cooperatively breeding Arabian babbler, Turdoides squamiceps. We measured the length of sentinel bouts and the gaps between them both in natural conditions and following experimental feeding. Following feeding ad libitum, subordinates expanded their sentinel bouts significantly more than dominants in comparison with natural conditions. These findings are consistent with the first model, but not with the second. In the experiment, we measured the mass of mealworms consumed by each individual following a sentinel bout relative to its body mass. This ratio was larger for subordinates, indicating that they ended their sentinel bouts at a lower energetic state than dominants. This finding is consistent with the second model, but not with the first. Immediately after eating ad libitum, in 62% of the cases the first behavior performed by the babblers was a new sentinel bout, but in 17% it was a mutual interaction with a groupmate, indicating that social interactions also play a role in the trade‐off vis‐à‐vis sentinel activity.     

An Investigation of Assessment Games During Fallow Deer Fights

An improved understanding of the decision rules used by competing animals can be achieved by examining both the temporal structure and display rate of competitors during a contest. Current models of animal competition make different predictions regarding the behaviour of competing animals and the present study evaluates the predictions of three such models, the energetic war of attrition (eWOA), the sequential assessment game (SAG) and the cumulative assessment model (CAM) by applying them to the fighting behaviour of male fallow deer (Dama dama L.). There was no difference in rate at which the jump clash and backward push were recorded over fight duration; therefore, in terms of the temporal distribution of behavioural acts within fights, the jump clash and backward push conformed to the predictions of the SAG. There was a difference between winners and losers of fights for the frequency that the jump clash and backward push were recorded consistent with both the SAG and CAM. Analysis of bout duration showed that there was a decrease in the duration of subsequent bouts of fighting; this is only permitted under eWOA. In so far as current assessment models permit interpretation of the data, our results meet only a limited number of predictions of any one model. Given the difficulty in interpreting our data within the context of current assessment models, recommendations for the development of more complex models are presented.     

Rats Eat a Cafeteria-Style Diet to Excess but Eat Smaller Amounts and Less Frequently when Tested with Chow

Background

Obesity is associated with excessive consumption of palatable, energy dense foods. The present study used an animal model to examine feeding patterns during exposure to and withdrawal from these foods.

Methods

Male Sprague Dawley rats were exposed to standard lab chow only (Chow rats) or a range of cafeteria-style foods eaten by people (Caf rats). After 1, 4, 7 and 10 weeks of diet in their home cage, rats were subjected to 24-hour test sessions in a Comprehensive Lab Animal Monitoring System (CLAMS). In the first two test sessions, Chow rats were exposed to standard lab chow only while Caf rats were exposed to a biscuit and high-fat chow diet. In the final two test sessions, half the rats in each group were switched to the opposing diet. In each session we recorded numbers of bouts, energy consumed per bout, and intervals between bouts across the entire 24 hours.

Results

Relative to Chow rats, Caf rats initiated fewer bouts but consumed more energy per bout; however, their motivation to feed in the CLAMS declined over time, which was attributed to reduced variety of foods relative to their home cage diet. This decline in motivation was especially pronounced among Caf rats switched from the palatable CLAMS diet to standard lab chow only: the reduced energy intake in this group was due to a modest decline in bout frequency and a dramatic decline in bout size.

Conclusions

Exposure to a cafeteria-diet, rich in variety, altered feeding patterns, reduced rats'' motivation to consume palatable foods in the absence of variety, and further diminished motivation to feed when palatable foods were withdrawn and replaced with chow. Hence, variety is a key factor in driving excessive consumption of energy dense foods, and therefore, excessive weight gain.     

Respiratory pattern of captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis)

Cetacean respiration usually happen in bouts. The most widely applied quantitative method used to analyze the structure of these bouts is the log_e-survivorship analysis, based on the assumption that the respiratory intervals are distributed as negative exponentials. However, for the data collected from three captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis), we failed to obtain a convergent result with the application of log_e-survivorship analysis. However, the two-Gaussian model, which was recently proposed to analyze the feeding behavior of cows, was successfully fitted to the data. According to the fitting results, the overall respiratory pattern of the captive Yangtze finless porpoises can be described as a dive with a mean duration of around 30–40 s, followed by two or three ventilations with a mean interval of approximately 9 s. The average intra-bout intervals during both active and inactive periods are constant at 7.7–9.9 s for all individuals. However, when shifting from active to inactive states, the adult male and female decrease their mean numbers of respirations per bout and average length of inter-bout respiratory intervals, while the estimates of both parameters increase for the juvenile female. It was pointed out that the two-Gaussian model might be more adequate for cetacean respiratory-bout structure analyses than the log_e-survivorship technique.     

Suitability of feeding and chewing time for estimation of feed intake in dairy cows

Monitoring of feeding and rumination behaviour can provide useful information for dairy herd management. The feeding behaviour of dairy cows can be recorded by different techniques, such as video cameras, weighing troughs or chewing sensors. Among feeding characteristics, individual feed intake of cows is of utmost interest, but as weighing troughs have high space and cost requirements they are used primarily in research studies. The objective of the present study was to evaluate whether records on feeding time or chewing activity or a combination of both contain enough information to estimate feed intake with sufficient accuracy. Feed intake and feeding time per cow were recorded by means of weighing troughs. Concurrently, chewing activity of seven cows was recorded by MSR-ART pressure sensors during five to eight measuring days per cow. Feeding and chewing behaviour were evaluated in time slots (1 min) and additionally assigned to feeding bouts for further analysis. The 1 min time slots were classified into feeding/no feeding or chewing/no chewing by the two systems, and agreement was found in 92.2% of the records. On average, cows spent 270±39 min/day at the feeding troughs and chewed 262±48 min/day. The average fresh matter intake (FMI) was 49.6±5.1 kg/day. Feed intake was divided into 9.7 bouts/day during which cows fed in average 27.8±21.7 min/bout and chewed 27.0±23.1 min/bout. The correlation between FMI and feeding time was r=0.891 and between FMI and chewing time r=0.780 overall cows. Hence, both systems delivered suitable information for estimating feed intake.     

Food intake, conversion efficiency, and feeding behaviour of tobacco hornworm caterpillars given artificial diet of varying nutrient and water content

ABSTRACT Fifth stadium tobacco hornworm caterpillars, Manduca sexta (L.), given artificial diet diluted to varying extents with either cellulose or water compensated for the food's reduced nutrient content by eating more of it. This compensation was, however, in most cases not sufficient to maintain normal growth rates. When the water content of the diet was reduced, the insects ate less than the usual fresh weight of food but maintained their intake of nutrients. Nevertheless, growth rate was impaired. The insects were better able to compensate for dilution of their food with water than with cellulose. The efficiency of conversion of ingested food (ECI) was decreased when the diet was adulterated with cellulose. At moderate dilution (50% nutrient) this was due mostly to decreased approximate digestibility (AD), but at greater dilution (25% and 10% nutrient content) the efficiency of conversion of digested food (ECD) was decreased. ECI was maintained when the water content of the diet was increased to give 50% nutrient concentration, but was decreased when water content was changed more radically (200%, 25% and 10% nutrient diets). This was due mostly to increased metabolic costs (decreased ECD) in all cases. The retention time of food in the gut was progressively decreased (i.e. speed of passage was increased) as nutrients were replaced by cellulose. By contrast, dilution of the diet with water resulted in only slight changes in retention time, except at extreme dilution (10% nutrient content) when retention time was reduced. Compensation of food intake was achieved by spending more (or less) time eating. Video analysis of feeding behaviour showed that there were significant changes in the length of feeding bouts and of interfeed gaps when caterpillars fed on diets of altered composition. For diets diluted with cellulose, changes in bout length and bout frequency contributed substantially to the increased time spent feeding on the adulterated food. For diets diluted with water, however, almost all of the compensatory change in behaviour was due to increased bout length, with bout frequency affected only slightly. This suggests that volumetric feedback contributes principally to the termination of feeding bouts in caterpillars, while nutrient flow may affect both the initiation and termination of feeding.