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Preference for meat is not innate in dogs
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           1 3  Journal of Ethology  ISSN 0289-0771Volume 32Number 1 J Ethol (2014) 32:15-22DOI 10.1007/s10164-013-0388-7 Preference for meat is not innate in dogs Anandarup Bhadra & Anindita Bhadra           1 3 Your article is protected by copyright andall rights are held exclusively by JapanEthological Society and Springer Japan. Thise-offprint is for personal use only and shall notbe self-archived in electronic repositories. Ifyou wish to self-archive your article, pleaseuse the accepted manuscript version forposting on your own website. You mayfurther deposit the accepted manuscriptversion in any repository, provided it is onlymade publicly available 12 months afterofficial publication or later and providedacknowledgement is given to the srcinalsource of publication and a link is insertedto the published article on Springer'swebsite. The link must be accompanied bythe following text: "The final publication isavailable at link.springer.com”.  ARTICLE Preference for meat is not innate in dogs Anandarup Bhadra  • Anindita Bhadra Received: 25 June 2013/Accepted: 1 October 2013/Published online: 19 October 2013   Japan Ethological Society and Springer Japan 2013 Abstract  Indian free-ranging dogs live in a carbohydrate-rich environment as scavengers in and around human set-tlements. They rarely hunt and consequently do notencounter rich sources of protein. Instead, they haveadapted to a diet of primarily carbohydrates. As descen-dents of the exclusively carnivorous wolves, they aresubjected to the evolutionary load of a physiologicaldemand for proteins. To meet their protein needs, theyresort to a Rule of Thumb—if it smells like meat, eat it.Pups face high competition from group and non-groupmembers and are in a phase of rapid growth with highprotein demands. Following the Rule of Thumb, they canacquire more protein at the cost of increased competitionand reduced supplementary non-protein nutrition. How-ever, if the mother supplements their diet with protein-richregurgitates and/or milk, then the pups can benefit by beinggeneralists. Using a choice test in the field, we show that,while adults have a clear preference for meat, pups have nosuch preference, and they even eagerly eat degraded pro-tein. Thus, the Rule of Thumb used by adult dogs forefficient scavenging is not innate and needs to be learned.The Rule of Thumb might be acquired by cultural trans-mission, through exposure to meat in the mother’s regur-gitate, or while accompanying her on foraging trips. Keywords  Scavengers    Dogs    Rule of Thumb   Innate    Pups    Cultural transmission Introduction Adult food preferences in mammals are shaped by geneticpredispositions (Scott 1946; Nachman 1959) and by sub- sequent learning experiences (LeMagnen 1967; Rozin1967). For example, the flavor of mother’s milk providescues such that the pups preferentially eat what the motherdid, in rats (Galef and Henderson 1972) and also in pigs(Campbell 1976). The swallowing of amniotic fluid beforebirth seems to affect food preference in the adult stage inhumans (Mennella and Beauchamp 1994) and in sheep(Mistretta and Bradley 1983), suggesting that learning canbegin even before birth. The peripheral gustatory system of puppies is already developed at birth but does not reach theadult form until later in life (Ferrell 1984a), such thatgenetic predispositions can constrain taste perception.Early experiences of food also seem to have an impact ondog food preference (Kuo 1967; Mugford 1977; Ferrell 1984b) which is strongly influenced by the mother, throughoffering regurgitated partly digested food before weaning(Thorne 1995) and also through foraging in the presence of the pup.Besides the possibility of the strong influence of mother’s diet on pups, the pup’s own experience alsoshapes its diet. Evidence of learning has been seen in dogswhere flavor experience and physiological effect are wellseparated in time, such that classical conditioning is inad-equate for an explanation (McFarland 1978). Neophobia orfear of something new is uncommon in dogs, but it hasbeen reported in the case of food (Thorne 1995). Neophiliaor preference for something new is common when it comes Electronic supplementary material  The online version of thisarticle (doi:10.1007/s10164-013-0388-7) contains supplementarymaterial, which is available to authorized users.A. Bhadra    A. Bhadra ( & )Behaviour and Ecology Lab, Department of Biological Sciences,Indian Institute of Science Education and Research, P.O. BCKVMain Campus, Mohanpur, Nadia, Calcutta 741252,West Bengal, Indiae-mail: abhadra@iiserkol.ac.in  1 3 J Ethol (2014) 32:15–22DOI 10.1007/s10164-013-0388-7  to food (Mugford 1977; Griffin et al. 1984). Aversion develops rapidly for food which have a negative physio-logical response, as has been demonstrated in coyotes(Ellins et al. 1977) and to a lesser degree in dogs (Rathore1984). So a pup’s food preferences may be innate, condi-tioned by experience or learned either through culturaltransmission from the mother or through active teaching byher.Wolves hunt for meat and occasionally scavenge (Mechand Boitani 2003; Forbes and Theberge 1992), while their modern-day descendents—pet dogs—are fed by theirowners in controlled amounts, often leading to over-feed-ing (German 2006; Edney and Smith 1986; McGreevy and Thomson 2005). Free-ranging dogs exist in many coun-tries, like Mexico (Ortega-Pacheco et al. 2007; Daniels andBekoff  1989), Ecuador (Kruuk and Snell 1981), Zambia (Balogh 1993), Zimbabwe (Butler et al. 2004), Italy (Boitani 1983; Bonanni et al. 2010), India (Pal 2001; Vanak and Gompper 2009), Nepal and Japan (Kato andYamamoto 2003), etc. While they do occasionally hunt andbeg for food, they principally acquire food by scavenging(Vanak and Gompper 2009; Vanak et al. 2009; Spotte 2012), making them an ideal model system to study theeffects of the earliest form of domestication.Indian free-ranging dogs have appeared in many ancientIndian texts and folklore over the ages, sometimes as adomesticated animal and sometimes as a stray (Debroy2008). They have lived in their current state in India forgenerations and are well adapted to the scavenging lifestylesuch that, today, they are an integral part of the humanecology (Pal 2001). Indian free-ranging dogs do not oftenencounter meat during scavenging in waste dumps andwhile begging for food. Instead, they live on a carbohy-drate-rich omnivorous diet consisting of biscuits, breads,rice, lentil, fish bones, and occasional pieces of decom-posing meat from a carcass (and even mangoes, cow dung,and plastic; Bhadra et al., unpublished data). These dogshave adapted to their scavenging habit without actuallygiving up the preference for meat (Houpt et al. 1978;Bhadra et al., unpublished data). A possible mechanismmight have been the development of better digestion of carbohydrates. It is known that dogs are omnivorous ani-mals, adapted to a human-like diet, which might have beenthe result of their long history of domestication (NationalResearch Council 2006). This is substantiated by morerecent genetic analysis showing that the ability to digestcarbohydrates was one of the major genetic changes thatthe ancestors of dogs underwent during their transitionfrom wolves (Axelsson et al. 2013). Given the carbohy-drate-rich diet of these dogs, this would be an advantage interms of meeting their energy requirements, especially inareas like India where the human diet is chiefly comprisedof carbohydrates (Mohan et al. 2009). However, it seemsthat the dogs have behaviorally adapted to scavenging inand around human habitation by developing a Rule of Thumb for foraging—‘‘if it smells like meat, eat it’’. Thiswould enable them to always choose the food with a higherintensity of meat smell first, thus helping them sequesterhigher amounts of protein in their diet (Bhadra et al.,unpublished data). We wanted to test the hypothesis thatthis Rule of Thumb is an innate characteristic of the dogsand does not need to be learned. Materials and methods We used the one-time multi-option choice test (OTMCT)module for our experiment (Bhadra et al., unpublisheddata). The experimenter walked on the streets to locatedogs that were solitary, and used these for the trials. If other dogs were present in the vicinity, then the focal dogwas lured away to ensure that there would be no distur-bance during the trial. Thus, dogs were chosen at random,as and when they were encountered on the streets. The dogwas provided with three food options simultaneously suchthat all three were equally physically accessible. For this,the experimenter placed the three food items about 5 cm(2 in) from each other on a piece of cardboard and pre-sented this to the dog. The three food items were placed ina randomized fashion on the board across trials (see thevideo in ESM for details). All events including theinspection and eating of the food options were recorded inthe order of their occurrence. In the event of any other dogapproaching the food or interacting with the focal dog, thetrial was aborted. The data for only those cases where allthe options were at least inspected were used for analysis.Based on our qualitative observations, inspection wasdefined as ‘‘approaching within 2.5 cm (1 in) of the foodwith the snout extended and then sharp inhalation withflared nostrils’’. These dogs, living in a highly competitiveenvironment, could be expected to eat the preferred foodfirst, and so we recorded the order in which the food wasconsumed. The experiments were conducted in Kolkata(22  34 0 10.92 00 N, 88  22 0 10.92 00 E), West Bengal, India,between December 2011 and March 2012.In the OTMCT experiments, the quantity of food wastoo small ( \ 10 ml) to be a stimulus—we used small lumpsof food, approximately the size of an almond. The optionswere provided such that they were visually identical andthe only cue for the dogs to make the choice was the odorof each option. Each dog was given the choice test onlyonce to eliminate the effect of learning and to get a clearrepresentation of the preference already formed at thepopulation level. To ensure that we did not resampleindividuals, we carried out the trials at different localitieson different days, and, within a locality for consecutive 16 J Ethol (2014) 32:15–22  1 3  trials, we used visual identification of dogs and landmarksto eliminate such repeats. The experiment was conductedin two sets, one with adult dogs and the other with pupsaged 8–10 weeks. This age window was chosen becausethe pups learn to take solid food from external sources,begin exploring by themselves and wean at this age (Pal2008). In each set, our final sample size was 60. Of theadults, 35 were female and 25 were male, while there were29 females, 23 males, and 8 individuals of unknown sexamong the pups sampled.In the experimental set (Experiment 1A), the pups weregiven a gradient of proteins in novel food. The optionsprovided in OTMCT were P1 (dog biscuit, 80 % protein);P2 (fresh Pedigree  , 24 % protein); P3 (1-day-old Pedi-gree  , protein degraded) (please see ESM for detailedcomposition). In the control set (Experiment 1B), adultswere given the same choice test. The dog biscuit actuallycontained some meat while Pedigree  did not containanimal tissue protein. The dogs often have to search forfood amidst rotting garbage, so it is important for them todistinguish between fresh and degraded protein. We usedthe stale Pedigree  as a source of degraded protein. Neitherthe pups nor the adults are likely to have been exposed toPedigree  or dog biscuit. The adults are known to discernbetween food options by smell (Houpt et al. 1978) andshould thus treat the options differently. Since adults fol-low the Rule of Thumb, they should prefer the dog biscuitwith the meat smell and avoid the stale protein. So, foradults, we expected the order of preference to beP1 [ P2 [ P3. We hypothesized that the juveniles shouldfollow the same order of preference as the adults if the Ruleof Thumb is innate.Absolute choice was defined as the total number of times each option was chosen in a particular experiment.Choice was taken as the complete consumption of a par-ticular option. Eating order was computed for eachexperiment. A 3  9  3 matrix was constructed with the threeoptions in the columns and the number of times each optionwas chosen first, second, and third, respectively, in therows. Now, a contingency Chi-squared test was carried outto determine whether the tables were random. If they weresignificantly different from random, then the option thatwas chosen first the highest number of times was taken tobe the first preference at the population level. Similarly, theoptions chosen second and third were also determined.We computed the average ranks for each event in anexperiment, thus getting an idea of the order of occurrenceof the inspection and eating of each type of food. Eachevent was assigned a rank based on the order of occurrence.Since there must be 3 inspections in each experiment and 3possible acts of consumption, each event could receive arank between 1 and 6. When an event did not occur (one of the options was not consumed), it was assigned the rank of 7, meaning it had a higher rank than if it had been eatenlast. The average of all the ranks for each event wascalculated. Results From absolute choice, the adults clearly prefer P1 over P2and P2 over P3 (two-tailed Fisher’s exact test; P1 - P2:  p \ 0.0001; P2 - P3:  p  =  0.048; and P1 - P3:  p \ 0.0001)(Fig. 1) whereas the pups prefer all three equally (two-tailed Fisher’s exact test; P1 - P2:  p  =  0.679; P2 - P3:  p  =  0.999; and P1 - P3:  p  =  0.999) (Fig. 1). In terms of eating order, adults eat P1 first, P2 second; and P3 third( v 2 =  74.233,  df   =  4,  p \ 0.0001) (Fig. 2; Table 1), while pups eat the food in random order ( v 2 =  3.797,  df   =  4,  p  =  0.434) (Fig. 2; Table 1). So pups do not discriminate between different foods (i.e., they show neither preferencenor aversion) while adults do prefer the meat smell andavoid the food containing degraded protein. The overallrejection rate in adults (96/180) is significantly higher thanthat in pups (7/180) (two-tailed Fisher’s exact test:  p \ 0.0001). Hence, we reject our null hypothesis, andconclude that the Rule of Thumb is not innate.This result was corroborated by the average ranks of theeating events, where adults clearly showed a hierarchicalorder of ranks (Rank  P1E =  4.20  ±  1.60, Rank  P2E =  5.85 ±  1.64, Rank  P3E =  6.73  ±  0.63) (Table 2) and pups didnot (Rank  P1E =  4.15  ±  1.53, Rank  P2E =  4.37  ±  1.78,Rank  P3E =  4.20  ±  1.75) (Table 2). All inspections occur-red in random order (Experiment 1A: Rank  P1I =  2.93 ±  1.49; Rank  P2I =  2.85  ±  1.69; Rank  P3I =  2.77  ±  1.58;Experiment 1B: Rank  P1I =  2.13  ±  0.98; Rank  P2I =  2.27 ±  1.01; Rank  P3I =  2.35  ±  1.36) (Table 2), but eating onlyoccurred after all the choices had been inspected by theadults (mean of ranks of all inspection for adults is2.25  ±  1.13 and mean of rank of all eatings for adultsis 5.59  ±  1.73; two-tailed Mann–Whitney test:  U   = 29968.000,  df1  =  180,  df2  =  180,  p \ 0.0001). Interest-ingly, in the case of the pups, eating did not begin after allthree options had been inspected. The pups seemed toinspect a food item and consume it immediately, beforeinspecting the next available option. The difference in theaverage ranks for each pair of inspection and eating wasnearly equal to 1 (P1 1.22  ±  0.74, P2 1.52  ±  1.33, P31.43  ±  1.05) in case of the pups, while it was more vari-able (P1 2.07  ±  1.47, P2 3.58  ±  1.79, P3 4.38  ±  1.58) inthe case of the adults. So, we checked how often inspectionof a particular food is followed immediately by its con-sumption, representing a situation when the pups would bedriven by their high hunger levels to eat what is edibleimmediately, without exploring all available options. Wecalled this possible strategy sniff and snatch (SNS)—this J Ethol (2014) 32:15–22 17  1 3
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