In two experiments, the social influence on choosing between two novel diets was analyzed. In Experiment 1, a group of rats (demonstrators) ingested a novel flavor cue presented in powdered food or in a 4% sucrose solution. Afterwards, demonstrators interacted with a group of observer rats for 30 minutes. Preferences for the cue flavor and another flavor were tested in observers using a two-choice test in the same or in the opposite substrate (solid/liquid) as their demonstrators. When tested with solid foods, observers displayed higher intake of the flavor consumed by the demonstrators, regardless of whether the demonstrators had consumed it as a solid or liquid. However, when observers were tested with solutions, there was no demonstration of the same preference. Experiment 2 focused on solutions, presenting them at test either with the flavor as a water solution alone, or as a solution plus an aerosol presentation. In addition, a single-cue testing procedure was used to allow examination of the palatability (assessed through the analysis of licking behavior) of the test solutions. Under single-cue testing procedures with solutions, observer rats did consume more of the flavors previously consumed by the demonstrator animals, but there was no effect of social learning on the palatability of the test flavors. These results suggest that socially conditioned flavor preferences can be reliably observed with fluid solutions, will transfer between different substrates, and affect consumption to a greater degree than palatability. However, future experiments need to be performed to confirm some of these suggestions. | Chilean Government 11140576 Leverhulme Trust RPG-2014-342

In two experiments, the social influence on choosing between two novel diets was analyzed. In Experiment 1, a group of rats (demonstrators) ingested a novel flavor cue presented in powdered food or in a 4% sucrose solution. Afterwards, demonstrators interacted with a group of observer rats for 30 minutes. Preferences for the cue flavor and another flavor were tested in observers using a two-choice test in the same or in the opposite substrate (solid/liquid) as their demonstrators. When tested with solid foods, observers displayed higher intake of the flavor consumed by the demonstrators, regardless of whether the demonstrators had consumed it as a solid or liquid. However, when observers were tested with solutions, there was no demonstration of the same preference. Experiment 2 focused on solutions, presenting them at test either with the flavor as a water solution alone, or as a solution plus an aerosol presentation. In addition, a single-cue testing procedure was used to allow examination of the palatability (assessed through the analysis of licking behavior) of the test solutions. Under single-cue testing procedures with solutions, observer rats did consume more of the flavors previously consumed by the demonstrator animals, but there was no effect of social learning on the palatability of the test flavors. These results suggest that socially conditioned flavor preferences can be reliably observed with fluid solutions, will transfer between different substrates, and affect consumption to a greater degree than palatability. However, future experiments need to be performed to confirm some of these suggestions.

Animals do not eat whatever food item they encounter, but choose different foods that best match their requirements. Fish exhibit such “nutritional wisdom” and adapt their feeding behaviour and food intake according to their needs and the nutritional properties of diets. In this paper, we tested the ability of Nile tilapia to select between diets with a balanced or unbalanced composition of essential amino acids. To this end, three different diets were prepared: a gelatine based diet (D1), a gelatine diet supplemented with three essential amino acids (EAA, l-tryptophane, l-methionine, l-threonine) (D2), and a diet containing only cellulose and the three crystalline EAA (D3). In addition, the putative role of both orosensorial factors (using pellets vs capsules) and social interactions (single vs groups of ten fish) was investigated. To this end, a total of 68 male tilapia of about 141 ± 48 g (mean ± S.D.) were challenged, individually or in groups, to select between D1 vs D2 using pellets dispensed by self-feeders (exp. 1). In another experiment (exp. 2), 11 individual fish were challenged to select encapsulated diets with non flavour or smell proprieties (D1 vs D2), and in exp. 3 fish were challenged to self-supplementation in EAA (D1 vs D3). The results showed the ability of tilapia to avoid the EAA-deficient diet, choosing 82.2% D2 in the case of individual fish, and 80.8% D2 in the case of fish groups. Dietary selection was not directly driven by the orosensorial characteristics of food, since tilapia sustained a higher preference for D2 when fed with encapsulated diets. Finally, in exp. 3 tilapia self-supplemented the EAA deficiency by selecting a synchronised combination of D1 and D3 that matched their nutritional requirements. These findings highlighted the capacity of fish to make dietary selection based on the EAA content, which should be considered when discussing food intake regulation mechanisms, and diet formulation and supplementation with EAA.

Animals do not eat whatever food item they encounter, but choose different foods that best match their requirements. Fish exhibit such “nutritional wisdom” and adapt their feeding behaviour and food intake according to their needs and the nutritional properties of diets. In this paper, we tested the ability of Nile tilapia to select between diets with a balanced or unbalanced composition of essential amino acids. To this end, three different diets were prepared: a gelatine based diet (D₁), a gelatine diet supplemented with three essential amino acids (EAA, l-tryptophane, l-methionine, l-threonine) (D₂), and a diet containing only cellulose and the three crystalline EAA (D₃). In addition, the putative role of both orosensorial factors (using pellets vs capsules) and social interactions (single vs groups of ten fish) was investigated. To this end, a total of 68 male tilapia of about 141±48g (mean±S.D.) were challenged, individually or in groups, to select between D₁vs D₂ using pellets dispensed by self-feeders (exp. 1). In another experiment (exp. 2), 11 individual fish were challenged to select encapsulated diets with non flavour or smell proprieties (D₁vs D₂₎, and in exp. 3 fish were challenged to self-supplementation in EAA (D₁vs D₃). The results showed the ability of tilapia to avoid the EAA-deficient diet, choosing 82.2% D₂ in the case of individual fish, and 80.8% D₂ in the case of fish groups. Dietary selection was not directly driven by the orosensorial characteristics of food, since tilapia sustained a higher preference for D₂ when fed with encapsulated diets. Finally, in exp. 3 tilapia self-supplemented the EAA deficiency by selecting a synchronised combination of D₁ and D₃ that matched their nutritional requirements. These findings highlighted the capacity of fish to make dietary selection based on the EAA content, which should be considered when discussing food intake regulation mechanisms, and diet formulation and supplementation with EAA.

Pigs may have retained the capacity to choose feeds based on their nutritional requirements, even after decades in which they are not allowed to select their diet composition due to the common feeding systems of the intensive pig industry. We used 480 early-weaned piglets in two experiments to assess their ability to select and prefer protein-related sources, depending on their protein status. Piglets were fed after weaning with two isoenergetic diets formulated to contain an optimal or sub-optimal crude-protein (CP) content, a high-protein (HP, 204 g CP/kg as-fed) or a low-protein diet (LP, 142 g CP/kg), respectively. In Experiment 1, the preference of piglets was assessed by using a choice test between protein (porcine digestible peptides [PDP] 40 g/L) and carbohydrate (sucrose 40 g/L) water-based solutions for a period of 3 min. Piglets showed higher intake and preference for the sucrose 40 g/L than for the PDP 40 g/L solution, independently of the dietary CP content (9.8 mL/kg body weight [BW] vs. 3.7 mL/kg BW and 10.4 mL/kg BW vs. 43 mL/kg BW in HP and LP pigs, respectively). In Experiment 2, piglets were given eight training sessions in which two equally preferred flavors were mixed with protein (porcine animal plasma 60 g/L, CSp) or carbohydrate (maltodextrin 60 g/L, CSc) solutions. In the subsequent choice test, piglets fed the HP diet showed a tendency to a higher intake of CSc than of CSp (6.5 mL/kg BW vs. 5.4 mL/kg BW). On the other hand, piglets fed the LP diet showed a higher intake and preference for CSp than for CSc (15.5 ml/kg BW vs. 102 mL/kg BW), differences being higher for medium and low BW piglets than for heavy ones. The results show that piglets are unable to express a specific appetite for protein to correct previous underfeeding with it; however, they may show an appropriate dietary selection pattern in order to overcome protein deficiency through associative learning. | Spanish Government (Ministerio de Ciencia e Innovacion) PET2008_0002 Chilean Government

Pigs may have retained the capacity to choose feeds based on their nutritional requirements, even after decades in which they are not allowed to select their diet composition due to the common feeding systems of the intensive pig industry. We used 480 early-weaned piglets in two experiments to assess their ability to select and prefer protein-related sources, depending on their protein status. Piglets were fed after weaning with two isoenergetic diets formulated to contain an optimal or sub-optimal crude-protein (CP) content, a high-protein (HP, 204g CP/kg as-fed) or a low-protein diet (LP, 142g CP/kg), respectively. In Experiment 1, the preference of piglets was assessed by using a choice test between protein (porcine digestible peptides [PDP] 40g/L) and carbohydrate (sucrose 40g/L) water-based solutions for a period of 3min. Piglets showed higher intake and preference for the sucrose 40g/L than for the PDP 40g/L solution, independently of the dietary CP content (9.8mL/kg body weight [BW] vs. 3.7mL/kg BW and 10.4mL/kg BW vs. 4.3mL/kg BW in HP and LP pigs, respectively). In Experiment 2, piglets were given eight training sessions in which two equally preferred flavors were mixed with protein (porcine animal plasma 60g/L, CSp) or carbohydrate (maltodextrin 60g/L, CSc) solutions. In the subsequent choice test, piglets fed the HP diet showed a tendency to a higher intake of CSc than of CSp (6.5mL/kg BW vs. 5.4mL/kg BW). On the other hand, piglets fed the LP diet showed a higher intake and preference for CSp than for CSc (15.5mL/kg BW vs. 10.2mL/kg BW), differences being higher for medium and low BW piglets than for heavy ones. The results show that piglets are unable to express a specific appetite for protein to correct previous underfeeding with it; however, they may show an appropriate dietary selection pattern in order to overcome protein deficiency through associative learning.

Aggressive behaviors are widespread among animals and are critical in the competition for resources. The physiological mechanisms underlying aggression have mostly been examined in breeding males, in which gonadal androgens, acting in part through their aromatization to estrogens, have a key role. There are two alternative models that contribute to further understanding hormonal mechanisms underlying aggression: aggression displayed in the non-breeding season, when gonadal steroids are low, and female aggression. In this study we approach, for the first time, the modulatory role of estrogens and androgens upon non-breeding aggression in a wild female teleost fish. We characterized female aggression in the weakly electric fish Gymnotus omarorum and carried out acute treatments 1 h prior to agonistic encounters in dyads treated with either an aromatase inhibitor or an antagonist of androgen receptors. Anti-androgen treatment had no effect on behavior whereas acute aromatase inhibition caused a strong distortion of aggressive behavior. Territorial non-breeding aggression was robust and depended on rapid estrogen actions to maintain high levels of aggression, and ultimately reach conflict resolution from which dominant/subordinate status emerged. Our results, taken together with our own reports in males and the contributions from non-breeding aggression in bird and mammal models, suggest a common strategy involving fast-acting estrogens in the control of this behavior across species. In addition, further analysis of female non-breeding aggression may shed light on potential sexual differences in the fine tuning of social behaviors. | Agencia Nacional de Investigación e Innovación

Aggressive behaviors are widespread among animals and are critical in the competition for resources. The physiological mechanisms underlying aggression have mostly been examined in breeding males, in which gonadal androgens, acting in part through their aromatization to estrogens, have a key role. There are two alternative models that contribute to further understanding hormonal mechanisms underlying aggression: aggression displayed in the non-breeding season, when gonadal steroids are low, and female aggression. In this study we approach, for the first time, the modulatory role of estrogens and androgens upon non-breeding aggression in a wild female teleost fish. We characterized female aggression in the weakly electric fish Gymnotus omarorum and carried out acute treatments 1 h prior to agonistic encounters in dyads treated with either an aromatase inhibitor or an antagonist of androgen receptors. Anti-androgen treatment had no effect on behavior whereas acute aromatase inhibition caused a strong distortion of aggressive behavior. Territorial non-breeding aggression was robust and depended on rapid estrogen actions to maintain high levels of aggression, and ultimately reach conflict resolution from which dominant/subordinate status emerged. Our results, taken together with our own reports in males and the contributions from non-breeding aggression in bird and mammal models, suggest a common strategy involving fast-acting estrogens in the control of this behavior across species. In addition, further analysis of female non-breeding aggression may shed light on potential sexual differences in the fine tuning of social behaviors.