Does Host Plant Drive Variation in Microbial Gut Communities in a Recently Shifted Pest?

Biotic interactions can modulate the responses of organisms to environmental stresses, including diet changes. Gut microbes have substantial effects on diverse ecological and evolutionary traits of their hosts, and microbial communities can be highly dynamic within and between individuals in space and time. Modulations of the gut microbiome composition and their potential role in the success of a species to maintain itself in a new environment have been poorly studied to date. Here we examine this question in a large wood-boring beetle Cacosceles newmannii (Cerambycidae), that was recently found thriving on a newly colonized host plant. Using 16S metabarcoding, we assessed the gut bacterial community composition of larvae collected in an infested field and in "common garden" conditions, fed under laboratory-controlled conditions on four either suspected or known hosts (sugarcane, tea tree, wattle, and eucalyptus). We analysed microbiome variation (i.e. diversity and differentiation), measured fitness-related larval growth, and studied host plant lignin and cellulose contents, since their degradation is especially challenging for wood-boring insects. We show that sugarcane seems to be a much more favourable host for larval growth. Bacterial diversity level was the highest in field-collected larvae, whereas lab-reared larvae fed on sugarcane showed a relatively low level of diversity but very specific bacterial variants. Bacterial communities were mainly dominated by Proteobacteria, but were significantly different between sugarcane-fed lab-reared larvae and any other hosts or field-collected larvae. We identified changes in the gut microbiome associated with different hosts over a short time frame, which support the hypothesis of a role of the microbiome in host switches.

A meta-analysis for assessing the contributions of trypsin and chymotrypsin as the two major endoproteases in protein hydrolysis in fish intestine.

For the majority of fish species, regardless of being gastric or agastric, trypsin and chymotrypsin are known as the two main alkaline proteases responsible for the initial stage of protein hydrolysis in the fish intestine. Although the critical role of these proteases for protein hydrolysis in fish intestine is without doubt, the relative input of each enzyme in protein hydrolysis is still unclear. Data used in the present study has been retrieved from a bibliographic search using the Dimensions application (https://app.dimensions.ai/discover/publication tool). Retrieved articles were carefully inspected to identify whether they contained the description of the development of ontogenetic activities for trypsin, chymotrypsin, and total alkaline proteases in fish intestine. From the list of consulted articles, 21 studies were chosen based on correlation coefficients (Pearson correlation test), and four groups of fish were identified with high significant correlation between 1) the activity of chymotrypsin and total alkaline proteases; 2) the activity of trypsin, chymotrypsin, and total alkaline proteases; 3) the activity of trypsin and total alkaline proteases, and 4) mainly negative correlation between trypsin, chymotrypsin, and total alkaline proteases. These results indicated that the relative inputs of trypsin and chymotrypsin in protein hydrolysis may vary significantly among different fish species, which is a crucial point for proper understanding of species-specific digestive traits in both natural and aquaculture scenarios.

Decreased nutrient digestibility due to viscosity is independent of the amount of dietary fibre fed to growing pigs.

Fibre content and its effect on chyme viscosity are associated with changes in the digestive system of humans and pigs. It is unclear if fibre content and viscosity affect digestive function independently or interactively. We evaluated apparent ileal digestibility (AID) of nutrients and intestinal function in thirty-six ileal-cannulated barrows fed for 29 d either maize-soyabean meal (MSBM) or high-fibre MSBM + 30 % distillers dried grains with solubles (MSBM + DDGS) modified to three levels of viscosity by adding 5 % non-viscous cellulose (CEL), 6·5 % medium-viscous carboxymethylcellulose (MCMC) or 6·5 % high-viscous CMC (HCMC). Digesta were collected on days 27 and 28 and intestinal samples on day 29. Feeding CMC, regardless of fibre content, increased viscosity of whole digesta (P = 0·003) and digesta supernatant (P < 0·0001) compared with CEL. Feeding MSBM + DDGS or CMC decreased AID of DM (P = 0·003; P < 0·0001) and crude protein (P = 0·02; P < 0·0001) compared with MSBM or CEL. Feeding CMC regardless of fibre content increased jejunal crypt depth (P = 0·02) and ileal goblet cell area (P = 0·004) compared with CEL. Adding DDGS or CMC did not affect villus height and gene expression of jejunal monosaccharide and amino acid transporters. Feeding HCMC, regardless of fibre content, elevated amylase activity by 46 and 50 % in jejunal (P = 0·03) and ileal digesta (P = 0·01) compared with CEL. In summary, diets with increased viscosity decreased nutrient digestibility and induced intestinal changes that were independent of the amount of fibre fed.

Reticular contraction frequency and ruminal gas dome development in goats do not differ between grass and browse diets.

In investigations of differences between ruminant species feeding on browse or grass, it is often unclear whether observed differences are animal- or forage-specific. Ruminant species have been classified as 'moose-type', with little rumen content stratification, or 'cattle-type' with a distinct rumen contents stratification, including a gas layer. To which extent putative differences in forestomach motility are involved in these patterns is unknown. Using sonography, we investigated the frequency of reticular contractions and the stratification of rumen contents in goats fed exclusively on grass hay (n = 6) or dried browse (n = 5) directly after feeding, and after another 6 and 12 h with no access to feed. The frequency of reticular contractions decreased from immediately after feeding (1.8 ± 0.3 min-1 ) to 6 h afterwards (1.2 ± 0.2 min-1 ) and then remained constant, with no difference between diets. A gas dome became more visible over time, but neither its incidence nor its extent differed between diets. The results are in accord with classifying goats as 'cattle-type' in terms of their digestive physiology, and they add to a growing body of evidence that differences in digestive physiology between ruminant species are more due to species characteristics than different kinds of ingested forages.

No size-dependent net particle retention in the hindgut of horses.

Sieve analyses of hindgut contents of horses as well as observations in horses where plastic markers had been applied to a caecal cannula suggested that there may be a discrimination by particle size in the passage or retention of digesta. Here, we performed a similar experiment with five caecum-cannulated horses (562 ± 31 kg) fed a constant amount (6.81 kg dry matter/day) of grass hay. Passage markers representing the liquid (Co-EDTA) as well as the particulate digesta phase (Yb-undefined; Cr mordanted fibre 1-2 mm; Ce-mordanted fibre 8 mm) were given as a pulse-dose into the cannula to measure their mean retention times (MRT). The MRTs were compared by repeated-measurements analysis of variance. The MRT in the hindgut was 22.2 ± 2.4 h for Co, 25.0 ± 3.4 h for Yb, 26.2 ± 1.6 h for Cr and 26.3 ± 1.5 h for Ce. Whereas differences between the particle marker MRTs were not significant (padj. > 0.05), significant differences were observed between the solute marker Co and each of the particle markers Cr and Ce (padj. < 0.009). The results confirm the well-known significant, albeit small, difference in MRT in horses between the fluid and the particle digesta phase, and corroborate another recent study that used a combination of whole, marked hay and individual marker analysis in different particle size fractions of the faeces, which also did not detect a selective retention of any particle size class.

Effect of oral administration of a single bolus of six different protein sources on digestive physiology of red seabream Pagrus major juveniles.

To reveal direct effects of various protein sources on digestive physiology of red seabream, Pagrus major (38.5 ± 0.4 g), six different protein sources of fishmeal (FM), soybean meal (SBM), corn gluten meal (CGM), soy protein concentrate (SPC), poultry by-product meal (PBM), and poultry-feather meal (PFM) were orally administered to fish (2 mg protein/g body weight) and sampled at 1.5 h and 3 h after administration. Gallbladder weight of fish administered FM, PBM, and PFM decreased after administration (p < 0.0001), while no difference was observed in the other ingredients compared to a non-protein sham control group, indicating that animal protein sources could more strongly stimulate bile secretion than plant protein sources in red seabream. Trypsin and chymotrypsin activity in the intestinal content markedly increased by the FM, SBM, and PFM administration (p < 0.0001). Lipase and amylase activity was also increased by FM and SBM but also by CGM for lipase and by PBM and PFM for amylase (p < 0.0001). These indicate that stimulation effect of the secretion of digestive enzymes is largely different among the protein sources. This might be due to the absorptive capacity of the protein source since intestinal absorption parameter genes (anpep, cpa, ggt1, and atp1a2) also increased by the FM, SBM, PBM or PFM (p < 0.05). In addition to the secretion levels of bile and digestive enzymes, gene expression levels of bile related genes (cyp7a1, cyp8b1, and shp) and digestion-regulating genes (casr and cck) were increased by the FM, SBM, PFM, and/or PBM administration, suggesting that animal proteins and SBM could be potent digestive stimulants compared to CGM and SPC. This study first revealed that single protein sources directly influence digestive enzyme secretion and bile secretion in fish. Information about the direct effect of each single source on digestive physiology could help to design feed formulation with less fishmeal.

Frugivory Specialization in Birds and Fruit Chemistry Structure Mutualistic Networks across the Neotropics.

AbstractThe interaction between fruit chemistry and the physiological traits of frugivores is expected to shape the structure of mutualistic seed dispersal networks, but it has been understudied compared with the role of morphological trait matching in structuring interaction patterns. For instance, highly frugivorous birds (i.e., birds that have fruits as the main component of their diets), which characteristically have fast gut passage times, are expected to avoid feeding on lipid-rich fruits because of the long gut retention times associated with lipid digestion. Here, we compiled data from 84 studies conducted in the Neotropics that used focal plant methods to record 35,815 feeding visits made by 317 bird species (155 genera in 28 families) to 165 plant species (82 genera in 48 families). We investigated the relationship between the degree of frugivory of birds (i.e., how much of their diet is composed of fruit) at the genus level and their visits to plant genera that vary in fruit lipid content. We used a hierarchical modeling of species communities approach that accounted for the effects of differences in body size, bird and plant phylogeny, and spatial location of study sites. We found that birds with a low degree of frugivory (e.g., predominantly insectivores) tend to have the highest increase in visitation rates as fruits become more lipid rich, while birds that are more frugivorous tend to increase visits at a lower rate or even decrease visitation rates as lipids increase in fruits. This balance between degree of frugivory and visitation rates to lipid-poor and lipid-rich fruits provides a mechanism to explain specialized dispersal systems and the occurrence of certain physiological nutritional filters, ultimately helping us to understand community-wide interaction patterns between birds and plants.

Identification and characterization of the Atlantic salmon peptide transporter 1a.

Peptide transporter 1 (PepT1) mediates the uptake of dietary di-/tripeptides in vertebrates. However, in teleost fish gut, more than one PepT1-type transporter might operate, because of teleost-specific whole gen(om)e duplication event(s) that occurred during evolution. Here, we describe a novel teleost di-/tripeptide transporter, i.e., the Atlantic salmon (Salmo salar) peptide transporter 1a [PepT1a; or solute carrier family 15 member 1a (Slc15a1a)], which is a paralog (77% similarity and 64% identity at the amino acid level) of the well-described Atlantic salmon peptide transporter 1b [PepT1b, alias PepT1; or solute carrier family 15 member 1b (Slc15a1b)]. Comparative analysis and evolutionary relationships of gene/protein sequences were conducted after ad hoc database mining. Tissue mRNA expression analysis was performed by quantitative real-time PCR, whereas transport function analysis was accomplished by heterologous expression in Xenopus laevis oocytes and two-electrode voltage-clamp measurements. Atlantic salmon pept1a is highly expressed in the proximal intestine (pyloric ceca ≈ anterior midgut > midgut >> posterior midgut), in the same gut regions as pept1b but notably ~5-fold less abundant. Like PepT1b, Atlantic salmon PepT1a is a low-affinity/high-capacity system. Functional analysis showed electrogenic, Na+-independent/pH-dependent transport and apparent substrate affinity (K0.5) values for Gly-Gln of 1.593 mmol/L at pH 7.6 and 0.076 mmol/L at pH 6.5. In summary, we show that a piscine PepT1a-type transporter is functional. Defining the role of Atlantic salmon PepT1a in the gut will help to understand the evolutionary and functional relationships among peptide transporters. Its functional characterization will contribute to elucidate the relevance of peptide transporters in Atlantic salmon nutritional physiology.

Genomic and biochemical evidence of dietary adaptation in a marine herbivorous fish.

Adopting a new diet is a significant evolutionary change, and can profoundly affect an animal's physiology, biochemistry, ecology and genome. To study this evolutionary transition, we investigated the physiology and genomics of digestion of a derived herbivorous fish, Cebidichthys violaceus. We sequenced and assembled its genome (N50 = 6.7 Mb) and digestive transcriptome, and revealed the molecular changes related to digestive enzymes (carbohydrases, proteases and lipases), finding abundant evidence of molecular adaptation. Specifically, two gene families experienced expansion in copy number and adaptive amino acid substitutions: amylase and carboxyl ester lipase (cel), which are involved in the digestion of carbohydrates and lipids, respectively. Both show elevated levels of gene expression and increased enzyme activity. Because carbohydrates are abundant in the prickleback's diet and lipids are rare, these findings suggest that such dietary specialization involves both exploiting abundant resources and scavenging rare ones, especially essential nutrients, like essential fatty acids.

Genetic evidence of widespread variation in ethanol metabolism among mammals: revisiting the 'myth' of natural intoxication.

Humans have a long evolutionary relationship with ethanol, pre-dating anthropogenic sources, and possess unusually efficient ethanol metabolism, through a mutation that evolved in our last common ancestor with African great apes. Increased exposure to dietary ethanol through fermenting fruits and nectars is hypothesized to have selected for this in our lineage. Yet, other mammals have frugivorous and nectarivorous diets, raising the possibility of natural ethanol exposure and adaptation in other taxa. We conduct a comparative genetic analysis of alcohol dehydrogenase class IV (ADH IV) across mammals to provide insight into their evolutionary history with ethanol. We find genetic variation and multiple pseudogenization events in ADH IV, indicating the ability to metabolize ethanol is variable. We suggest that ADH enzymes are evolutionarily plastic and show promise for revealing dietary adaptation. We further highlight the derived condition of humans and draw attention to problems with modelling the physiological responses of other mammals on them, a practice that has led to potentially erroneous conclusions about the likelihood of natural intoxication in wild animals. It is a fallacy to assume that other animals share our metabolic adaptations, rather than taking into consideration each species' unique physiology.

Anatomy, immunology, digestive physiology and microbiota of the salmonid intestine: Knowns and unknowns under the impact of an expanding industrialized production.

Increased industrialized production of salmonids challenges aspects concerning available feed resources and animal welfare. The immune system plays a key component in this respect. Novel feed ingredients may trigger unwarranted immune responses again affecting the well-being of the fish. Here we review our current knowledge concerning salmon intestinal anatomy, immunity, digestive physiology and microbiota in the context of industrialized feeding regimes. We point out knowledge gaps and indicate promising novel technologies to improve salmonid intestinal health.

Estimation of minimum tolerated milk temperature for feeding dairy calves with small- and large-aperture teat bottles: A complementary dose-response study.

At birth, calves are functionally monogastric and remain so for the first weeks of life. Milk in the rumen may cause indigestion, diarrhea, and reduced growth. Calves are often fed cold milk from a large-aperture teat, but warm milk and sucking behavior are believed to trigger the esophageal reflex. The aim of this study was to use radiography to estimate the lowest milk temperature that can be given to dairy calves at high and low intake rates without causing milk in the rumen. Our hypothesis was that cold milk drunk at high speed would cause insufficient closure of the esophageal groove and hence milk in the rumen. Fifteen Norwegian Red calves, 9 to 27 d of age, weighing between 45.5 and 71.0 kg, were tested according to the response surface pathway design. Each calf was offered 4 L of milk from both a small- (2 mm) and a large-aperture (19 mm) teat. The milk contained barium sulfate, and radiography was applied before, during, and after the milk meal. Following radiography, the calves were returned to a group pen and observed for 2 h using continuous live behavioral observation to detect signs of abdominal pain or discomfort. Starting with a low number of subjects and increasing this number with increasing design levels reduces the sample size without reducing the statistical power. The minimum milk temperature was estimated to be 8°C. No behavioral signs of pain or discomfort were observed, but shivering was noted in several calves drinking 8°C milk. These results strengthen the argument that calves can be fed large milk meals without risk of causing milk in the rumen, even cold milk drunk at high speed.

Physical characteristics of gastrointestinal content of llama (Lama glama).

Changes in digesta dry matter (DM) and mean digesta particle size (MPS) along the gastrointestinal tract are well known in ruminants, but not in camelids. We collected digesta from the dorsal (d) and ventral (v) first forestomach compartment (C1), the second forestomach compartment (C2), three proximal segments and the subsequent glandular part of the third compartment (C3A-D), the caecum and the faeces twelve llamas (Lama glama). DM analysis indicates the presence of digesta stratification in the C1, the presence of fluid in the C2 to facilitate the sorting function of this compartment, the fluid-absorbing function of the proximal parts of the C3, the secretion of enzymes and digestive acids in the C3D, and the water-resorbing function of the lower intestinal tract. These findings illustrate the functional resemblance between the gastrointestinal tract of camelids and cattle-like ruminants (C1 equivalent to the rumen with stratified contents, C2 to the reticulum, C3A/B/C to the omasum and C3D to the abomasum). MPS analysis revealed a progressive reduction in MPS from the C1 to the distal C3. This gradual transition is different from the clear-cut threshold in ruminants between the reticulum and the omasum and had so far only been described in dromedaries (Camelus dromedarius). These findings indicate that regardless of the convergent property of rumination and resemblance of general mechanisms involved in contents stratification and particle sorting, differences between ruminants and camelids exist that could be interpreted as a more efficient functionality of the ruminant forestomach.

Body mass predicts isotope enrichment in herbivorous mammals.

Carbon isotopic signatures recorded in vertebrate tissues derive from ingested food and thus reflect ecologies and ecosystems. For almost two decades, most carbon isotope-based ecological interpretations of extant and extinct herbivorous mammals have used a single diet-bioapatite enrichment value (14‰). Assuming this single value applies to all herbivorous mammals, from tiny monkeys to giant elephants, it overlooks potential effects of distinct physiological and metabolic processes on carbon fractionation. By analysing a never before assessed herbivorous group spanning a broad range of body masses-sloths-we discovered considerable variation in diet-bioapatite δ13C enrichment among mammals. Statistical tests (ordinary least squares, quantile, robust regressions, Akaike information criterion model tests) document independence from phylogeny, and a previously unrecognized strong and significant correlation of δ13C enrichment with body mass for all mammalian herbivores. A single-factor body mass model outperforms all other single-factor or more complex combinatorial models evaluated, including for physiological variables (metabolic rate and body temperature proxies), and indicates that body mass alone predicts δ13C enrichment. These analyses, spanning more than 5 orders of magnitude of body sizes, yield a size-dependent prediction of isotopic enrichment across Mammalia and for distinct digestive physiologies, permitting reconstruction of foregut versus hindgut fermentation for fossils and refined mean annual palaeoprecipitation estimates based on δ13C of mammalian bioapatite.

Intestinal digestive enzyme modulation in house sparrow nestlings occurs within 24†h of a change in diet composition.

Nestling house sparrows near fledging age (12 days) were previously found to reversibly modulate the activity of their intestinal digestive enzymes in response to changes in diet composition. However, it is not known how quickly nestlings can adjust to new diets with different substrate compositions, nor is it known how early in life nestlings can modulate their enzyme activity in response to changes in diet. In the present study, 3-day-old nestlings were captured from the wild and fed and switched among contrasting diets - one high in protein and low in carbohydrate and another higher in carbohydrate and with lower, but adequate, protein - in order to determine (1) how quickly house sparrow nestlings could adjust to changes in diet composition, (2) how early in life nestlings could modulate their digestive enzyme activity in response to these changes and (3) which digestive enzymes could be modulated in house sparrow nestlings earlier in life. We found that house sparrow nestlings as young as 3 days post-hatch were capable of modulating their intestinal disaccharidase activity within 24 h of a change in diet composition, and nestlings gained the ability to modulate aminopeptidase-N by 6 or 7 days of age. To our knowledge, this is the first evidence of digestive enzyme modulation completed within 24 h of a change in diet in an avian species and the first study to show intestinal digestive enzyme modulation in response to changes in diet composition in any animal this early in development.

Applying wet sieving fecal particle size measurement to frugivores: A case study of the eastern chimpanzee (Pan troglodytes schweinfurthii).

OBJECTIVES: Fecal particle size (FPS) as quantified by wet sieving analysis is a measure of chewing efficiency relevant for the understanding of physiological adaptations and constraints in herbivores. FPS has not been investigated systematically in frugivores, and important methodological problems remain. In particular, food items that are not chewed may skew estimates of FPS. We address such methodological issues and also assess the influence of diet type and age on FPS in wild chimpanzees. MATERIALS AND METHODS: About 130 fecal samples of 38 individual chimpanzees (aged from 1.3 to ∼55 years) from the Kanyawara community of Kibale National Park (Uganda) were collected during three fruit seasons and analyzed using standardized wet sieves (pores from 16 to 0.025 mm). The effects of using different sieve series and excluding large seeds were investigated. We also assessed the relationship between FPS and sex, age, and fruit season. RESULTS: The treatment of seeds during the sieving process had a large influence on the results. FPS was not influenced by chimpanzee sex or age, but was smaller during a fig season (0.88 ± 0.31 mm) than during two drupe-fruit seasons (1.68 ± 0.37 mm) (0.025-4 mm sieves, excluding seeds). DISCUSSION: The absence of an age effect on FPS suggests that dental senescence might be less critical in chimpanzees, or in frugivores in general, than in folivorous herbivores. To increase the value of FPS studies for understanding frugivore and hominoid dietary evolution we propose modifications to prior herbivore protocols.

Effects of quebracho tannin extract and activated charcoal on nutrient digestibility, digesta passage and faeces composition in goats.

Irrigation agriculture of hot climates suffers from rapid soil organic carbon (C) turnover, high nitrogen (N) leaching and gaseous losses. In this context, we explored the possibility of supplementing ruminants with activated charcoal (AC) and condensed tannins (CT) to increase faecal concentration of long-lived C and slowly decomposable N. For this purpose, we fed AC and quebracho tannin extract (QTE, source of CT) to goats and determined nutrient digestibility, digesta passage and composition of faeces. The feeding trial comprised three periods, with 24 male goats assigned to five treatments and a control. On dry matter (DM) basis, the basal diet (control) consisted of 50% hay, 46.5% crushed maize and 3.5% soya bean meal. Treatment diets contained (on DM basis) 2% and 4% QTE (QTE2, QTE4), 1.5% and 3.0% AC (AC1.5, AC3.0) and a mixture of 2% QTE plus 1.5% AC (QTEAC). Samples of feed, refusals and faeces were analysed for chemical constituents; digesta passage was computed with a one-compartment Gamma-2 model from pulse-dose application of ytterbium-mordanted fibre and quantitative collection of faeces during 7 days. Compared to the control, organic matter and N digestibility were reduced with QTE2 and QTE4 (p ≤ 0.001), that of neutral and acid detergent fibre (NDFom, ADFom) decreased with QTE4, QTEAC and both AC treatments (p ≤ 0.001). Ruminal particle passage ranged from 0.051 h-1 (QTEAC) to 0.056 h-1 (control; p > 0.05). Apart from the correlation between total tract mean retention time and faecal C/N ratio (r = -0.35), passage parameters did not affect faeces quality. While faecal N concentration was not altered by both additives, AC enhanced faecal NDFom, ADFom and C concentrations (p ≤ 0.001). Whereas feeding up to 3% AC might slow down the decomposition of manure in the field without negatively affecting the digestive physiology of goats, including QTE seems not advantageous from a physiological and nutrient recycling perspective.

Dry matter and digesta particle size gradients along the goat digestive tract on grass and browse diets.

Physical properties of the digesta vary along the ruminant digestive tract. They also vary within the forestomach, leading to varying degrees of rumen contents stratification in 'moose-type' (browsing) and 'cattle-type' (intermediate and grazing) ruminants. We investigated the dry matter concentration (DM) and the mean digesta particle size (MPS) within the forestomach and along the digestive tract in 10 goats fed grass hay or dried browse after a standardized 12-h fast, euthanasia and freezing in the natural position. In all animals, irrespective of diet, DM showed a peak in the omasum and an increase from caecum via colon towards the faeces and a decrease in MPS between the reticulum and the omasum. Both patterns are typical for ruminants in general. In the forestomach, there was little systematic difference between more cranial and more caudal locations ('horizontal stratification'), with the possible exception of large particle segregation in the dorsal rumen blindsac on the grass diet. In contrast, the typical (vertical) contents stratification was evident for DM (with drier contents dorsally) and, to a lower degree, for MPS (with larger particles dorsally). Although evident in both groups, this stratification was more pronounced on the grass diet. The results support the interpretation that differences in rumen contents stratification between ruminants are mainly an effect of species-specific physiology, but can be enhanced due to the diet consumed.

Daily rhythms of digestive enzyme activity and gene expression in gilthead seabream (Sparus aurata) during ontogeny.

In order to identify daily changes in digestive physiology in developing gilthead seabream larvae, the enzyme activity (trypsin, lipases and α-amylase) and gene expression (trypsinogen-try, chymotrypsinogen-ctrb, bile salt-activated lipase-cel1b, phospholipase A2-pla2 and α-amylase-amy2a) were measured during a 24h cycle in larvae reared under a 12h light/12h dark photoperiod. Larvae were sampled at 10, 18, 30 and 60days post-hatch. In each sampling day, larvae were sampled every 3h during a complete 24h cycle. The enzyme activity and gene expression exhibited a marked dependent behavior to the light/darkness cycle in all tested ages. The patterns of activity and expression of all tested enzymes were compared to the feeding pattern found in the same larvae, which showed a rhythmic feeding pattern with a strong light synchronization. In the four tested ages, the activities of trypsin, and to a lesser extent lipases and amylase, were related to feeding activity. Molecular expression of the pancreatic enzymes tended to increase during the night, probably as an anticipation of the forthcoming ingestion of food that will take place during the next light period. It follows that the enzymatic activities are being regulated at translational and/or post-translational level. The potential variability of enzyme secretion along the whole day is an important factor to take into account in future studies. A particularly striking consequence of the present results is the reliability of studies based in only one daily sample taken at the same hour of the day, as those focused to assess ontogeny of digestive enzymes.

Adaptation of Habrobracon hebetor (Hymenoptera: Braconidae) to Rearing on Ephestia kuehniella (Lepidoptera: Pyralidae) and Helicoverpa armigera (Lepidoptera: Noctuidae).

Food characteristics strongly regulate digestive enzymatic activity of insects through direct influences on their midgut mechanisms. Insect performance is better on diets that contain nutrients in proportions that fit its digestive enzymes. Little is known about the influences of rearing history on parasitism success of Habrobracon hebetor Say. This research focused on the effect of nutrient regulation on survival, development, and parasitism of H. hebetor. Life history and digestive enzyme activity of fourth-stage larvae of H. hebetor were studied when reared on Ephestia kuehniella Zeller. This parasitoid was then introduced to Helicoverpa armigera (Hübner), and above-mentioned parameters were also studied in the first and fourth generations after transfer. In term of parasitism success, H. hebetor preferred E. kuehniella over He. armigera. When the first and fourth generations of He. armigera-reared H. hebetor were compared, the rearing history affected the life history and enzymatic activity of the parasitoid. A better performance of H. hebetor was achieved after it was reared on He. armigera for the four generations. Because, digestive α-amylase and general protease of the parasitoid were matched with the new host, it used reserve energy for a better performance. Thus, a better performance of H. hebetor could be obtained when the parasitoid was reared on its original host for at least four generations.