Is personality dependent of growth rate in red junglefowl (Gallus gallus)?

Institutionen för fysik, kemi och biologi Examensarbete 16 hp

Is personality dependent of growth rate in red

junglefowl (Gallus gallus)?

Andreas Calais

LiTH-IFM- Ex--13/2794—SE

Handledare: Hanne Løvlie, Linköpings universitet

Assisterande handledare: Josefina Zidar, Linköpings universitet Examinator: Anders Hargeby, Linköpings universitet

Institutionen för fysik, kemi och biologi Linköpings universitet

This report is a degree thesis at the Bachelors level (16 ECTS credits) performed by the author in collaboration with two study colleagues, Johan Almberg and Josefin Kvarnström. This cooperation included some parts of the planning of the study, and the collection of data. Each student has written and structured the report in all its parts individually. How the collected data were divided is described in the section ‘Materials and methods’ of the report.

Rapporttyp Report category Examensarbete C-uppsats Språk/Language Engelska/English Titel/Title:

Is personality dependent of growth rate in red junglefowl (Gallus gallus)?

Författare/Author:

Andreas Calais

Sammanfattning/Abstract:

Personality has been reported in a large variety of animal species, but it is not obvious why animals have personality. Variation in physiological traits, such as growth rate, should theoretically affect variation in behaviours and thus can explain why we observe variation in personalities. Growth rate is, theoretically, positively correlated with active personality types. Empirical studies have reported this pattern in different fish species, but there are not yet many studies on endothermic animals. I have therefore scored behaviours of 100 red junglefowl (Gallus gallus) chicks in four personality assays; novel arena, novel object, tonic immobility, and a proactive-reactive test, together with recording variation in growth rate of these individuals. The chicks individual growth rate (% day-1) were calculated and the relationship between personality and growth rate investigated. There was significant difference in growth rate between the sexes, where males grew faster than females, detected already at one week of age. However, no

significant correlations between behavioural traits and growth rate were observed, indicating that personality seem to be independent of growth rate. Further studies should therefore investigate the generality of this finding, and alternative underlying mechanisms for variation in personality should be explored.

ISBN

LITH-IFM-G-EX—13/2794—SE

__________________________________________________ ISRN

__________________________________________________

Serietitel och serienummer ISSN

Title of series, numbering

Handledare/Supervisor Hanne Løvlie Biträdande handledare/Assistant supervisor

Josefina Zidar

Ort/Location: Linköping

Nyckelord/Keyword:

Behaviour, Chicken, Growth rate, Life-history traits, Personality, Red junglefowl Datum/Date

2013-06-04

URL för elektronisk version

Institutionen för fysik, kemi och biologi

Department of Physics, Chemistry and Biology

Avdelningen för biologi

Contents

1 Abstract ... 2

2 Introduction ... 2

3 Material & methods ... 4

3.1 Animals and management ... 4

3.2 Experimental set-up ... 5 3.2.1 Growth rate ... 5 3.2.2 Novel arena ... 5 3.2.3 Novel object ... 5 3.2.4 Tonic immobility ... 6 3.2.5 Proactive-reactive ... 6 3.3 Statistical analysis ... 8 4 Results ... 9 5 Discussion ... 13 5.1 Conclusion... 16 6 Acknowledgements ... 16 7 References ... 16

1 Abstract

Personality has been reported in a large variety of animal species, but it is not obvious why animals have personality. Variation in physiological traits, such as growth rate, should theoretically affect variation in behaviours and thus can explain why we observe variation in

personalities. Growth rate is, theoretically, positively correlated with active personality types. Empirical studies have reported this pattern in different fish species, but there are not yet many studies on endothermic animals. I have therefore scored behaviours of 100 red junglefowl (Gallus gallus) chicks in four personality assays; novel arena, novel object, tonic immobility, and a proactive-reactive test, together with recording

variation in growth rate of these individuals. The chicks individual growth rate (% day-1) were calculated and the relationship between

personality and growth rate investigated. There was significant difference in growth rate between the sexes, where males grew faster than females, detected already at one week of age. However, no significant correlations between behavioural traits and growth rate were observed, indicating that personality seem to be independent of growth rate. Further studies should therefore investigate the generality of this finding, and alternative

underlying mechanisms for variation in personality should be explored.

2 Introduction

It is becoming more and more clear that personality (defined as individual differences in behavioural responses consistent over time and/or contexts, Sih et al. 2003, 2004; Stamps 2007) is not restricted to only humans. Personality has been reported in a great variety of animals, such as primates (Gosling 2001), birds (Groothuis & Carere 2005), reptiles (Stapley 2006), amphibians (Sih et al. 2003), spiders (Johnson & Sih 2005) and insects (Sih & Watters 2005). Individuals are observed to differ in for example aggressiveness (Riechert & Hedrick 1993), exploration (Dingemanse et al. 2002) and fearfulness (Boissy 1995). Even though personality is widespread in the animal kingdom, it is not obvious why this type of variation exists. Intuitively, a fully plastic individual would benefit from being able to change tactics for different situations. However, being flexible may come with some costs; if the environment is changing continuously, trying to change tactics might lead to inappropriate responses or taking too long time to respond (Dall et al. 2004). Instead it can be beneficial to apply less plastic behavioural responses that will perform well for most different situations which the animal expects to come across (Dall et al. 2004; Stamps 2007).

An explanation to why individuals of the same species have different personalities in the same habitat and at the same time could be that individuals vary in underlying traits, such as physiology or morphology (Dall et al. 2004; Stamps 2007). When there is variation in these

underlying traits, there should also be variation in the expression of particular behaviours, and as a result having a personality would be an adaptation (Dall et al. 2004; McElreath & Strimling 2006). One

physiological trait that typically varies between individuals within the same species is growth rate (Stamps 2007). An individual benefits from a consistent growth rate and there is typically a trade-off between growth and mortality (Stamps 2007). This means that individuals with different growth rates might end up with a similar overall fitness and a relationship between growth rate, mortality and behavioural traits emerges (Stamps 2007). Even if animals are housed individually with the same conditions, with the possibility of maximal growth rate, consistent individual

differences in growth rate are still observed (Ragland & Carter 2004; Martins et al. 2005). This eliminates the suggestion that different growth rates are only caused by environmental and social factors. Another support for the hypothesis that every individual of a particular species benefits from a consistent growth rate, is the concept of compensatory growth (Stamps 2007). If the growth rate of an individual is slowed down for some time due to for example low food levels, low temperatures or man-made experiments, this individual will, when the conditions are back to normal, have a higher growth rate to compensate or ‘catch up’ for what it has lost (Stamps 2007). This compensatory growth can result in costs as increased risk of disease, higher mortality rates, and even reduced adult cognitive abilities (Fisher et al. 2006; Stoks et al. 2006). These statements together indicate that it is beneficial to maintain an individual consistent growth rate (Stamps 2007).

More active personalities, with behavioural pattern including high risk-taking, aggressiveness and boldness, are, at least theoretically, predicted to be positively correlated with high growth rate (Stamps 2007; Biro & Stamps 2008).There are some empirical studies that have reported correlations between growth rate and personality. Hoogenboom and colleagues (2013) reported a positive correlation between foraging, territoriality, shelter-association and growth rate in juvenile brown trout (Salmo trutta). Ward and colleagues (2004) reported a positive

correlation between boldness and growth rate in three-spined sticklebacks (Gasterosteus aculeatus). One of the few studies that have looked at a potential relationship between growth rate and behavioural variation in a non-fish vertebrate, found a tendency for a positive relationship between growth rate and activity across domestic dog breeds (Canis lupus

familiaris, Careau et al. 2010). Other reports have failed to find

correlations between personality and growth rate (arctic char, Salvelinus alpinus, Laakkonen & Hirvonen 2007; rainbow trout, Oncorhynchus mykiss, Conrad & Sih 2009; pike, Esox lucius, Nyqvist et al. 2012). Further studies are therefore needed to determine the theoretically

predicted relationship between growth rate and personality, particularly in other species but fish. I have in this study therefore focused on links between variation in growth rate and personality in an avian species. In this study the relationship between personality and growth rate during the juvenile stage was investigated in red junglefowl (Gallus gallus), the ancestor to the domesticated chickens (Gallus gallus domesticus,

Fumihito et al. 1994). Red junglefowl are easily kept and bred in captivity and as an endothermic animals, they should provide a better comparison to other common model organisms than studies on fish species.

3 Material & methods

3.1 Animals and management

In this study, I used 100 (46 males and 54 females) red junglefowl chicks from the day they hatched and until they were about 6 weeks old. The parents of these birds are part of a population kept and bred at Wood-Gush animal facility of Linköping University, Sweden, since 1998. This population originates from animals obtained from a red junglefowl

population at a zoological park in the north of Sweden (Frösö zoo), which were originally brought from Thailand (Schütz et al. 2001). The chicks in this study came from two batches of eggs, hatching 3 weeks apart in the Kruijt animal facility of Linköping University. The chicks were kept in cages with a floor area of 0.5-3 m2, increasing with the chicks’ age. The floors of the cages were covered with wood shavings and heat lamps were placed on a height of approximately 60 cm. Food (‘Pullfor’) and water were always available. The light was set on a 12-12 hour cycle and the temperature was kept around 27 ºC. During scoring of the personality of chicks, chicks were transferred to another lab at Linköping University where they were placed in smaller cages when not used in the study. These cages had otherwise the same conditions as in the Kruijt animal facility and birds were allowed acclimatisation before observations took place. All observations took place between 19/3-16/5 2013. The

experiment and all its procedures were approved by a Swedish regional ethical committee.

3.2 Experimental set-up 3.2.1 Growth rate

All chicks were weighed once a week to follow their weight gain over time. Weights were obtained with the accuracy of 0.1 grams by the use of a digital scale.

3.2.2 Novel arena

When the chicks were 4 weeks old they were tested in a novel arena for investigating individual variation in exploration, activity and fearfulness (Réale et al. 2007). Two identical arenas were used for the possibility to test two chicks at the same time. The arenas were measuring 76x114 cm and were made of 7 mm thick plywood with a wire net as a roof. The floor consisted of a rubber mat, partially covered with wood shavings. Familiar food and water containers were presented in the arenas to

obscure the view and encourage exploration. The lighting was turned off when two chicks were carried from their cages to the two arenas. The chicks were placed in one of the corners of the arenas and to prevent the chicks from being disturbed by movements, two video cameras were used and the observers viewed the film directly on two monitors about 5 m away from the test arenas. As soon as possible after placing the chicks in the arenas, the lighting was turned on and the recordings started.

Instantaneous recording for 10 minutes with 10 seconds intervals were used to record behaviours such as: stand, walk, run, alert stand, alert walk, head down, peck, groom, escape and lie down (Table 1). Latencies to the chick started moving and vocalising, as well as total number of escape attempts, were recorded. The arenas were divided in six imaginary squares (38x38 cm) and the number of square changes an individual conducted was noted to measure movement. The data from this test was recorded together with Johan Almberg and Josefin Kvarnström, and is also used in their theses.

3.2.3 Novel object

Immediately following the novel arena test, a novel object test was carried out to investigate individual variation in neophobia (Réale et al. 2007). The lighting was turned off and a brown and yellow plush animal (spherical, about 15 cm in diameter, with yellow eyes and an about 15 cm long tail) was placed in the opposing corner from the chick. After this, the same procedure as in the novel arena test followed and the same

behaviours were recorded for 10 minutes (Table 1). The data from this test was recorded together with Johan Almberg and Josefin Kvarnström, and is also used in their theses.

3.2.4 Tonic immobility

The day after the novel arena and novel object tests each chick were tested for tonic immobility, used as a measure of variation in fearfulness (Forkman et al. 2007). The chicks were one by one placed on their backs in a V-shaped wooden stand in a dimmed room and a slight pressure was applied on the chicks’ breasts for 15 seconds by the observer’s hand to induce tonic immobility. Another hand was placed over the chick’s head to calm it down. The latency for the chicks to start moving their heads and the latency to jump back up on its feet were noted. The chicks were given three attempts to enter tonic immobility and if they did not succeed, the time 0 seconds was noted. If a chick jumped back up on its feet in less than 3 seconds it was tested again. If a chick stayed in tonic immobility for 10 minutes, the test was interrupted and the maximum time was noted (600 seconds). The data from this test was collected by Josefin

Kvarnström, and was also used in her thesis.

3.2.5 Proactive-reactive

When the chicks were 5 weeks old, 56 (29 males and 27 females) of them were trained and tested in a U-shaped arena for routine building and

response to broken routines. This was done to capture individual variation along the proactive-reactive gradient, where more reactive individuals form a routine slower compared to more proactive individuals, but show more flexible responses if the routine is broken (Koolhaas et al. 1999). The arena was measuring 76x114 cm and were made of 7 mm thick plywood with a wire net as a roof (Figure 1). A wall (wire net the first 18 cm and plywood the last 72 cm) divided the arena in two corridors (38 cm wide), which created the shape of a U. In one of the ends of the U, an extra box of 38x38 cm was placed as a start position for the chicks. The floor consisted of a rubber mat partially covered with wood shavings. Meal worms were offered in a plastic dish behind the plywood wall, out of sight from the chicks start position (Figure 1). During the tests, two video cameras were used to be able to observe the chick without

disturbing it and the observers viewed the film directly on two monitors behind a screen about 5 m away from the test arena. The arena was

divided in seven imaginary squares (38x38 cm) and the number of square changes was noted to measure movement. The chicks were trained to run around the U-shaped arena to get the meal worms by showing them the right route with the use of the observers’ hands and meal worms. When a chick successfully ran from the start position directly to the meal worms without turning around, five times in a row, it was considered to have

individuals. When the routine was formed, a shortcut through the arena was opened by removing the wire net between the corridors and a wall of wire net was inserted right around the corner of the U to block the

original route (Figure 1b). The chick was once again placed at the starting position and the time it took for the chick to find the shortcut was

recorded, together with the response individuals had on the routine being broken. Instantaneous recording with 10 seconds intervals were used, until the chick had found the meal worms, to capture the same behaviours as in the novel arena and novel object tests (Table 1). Also the latency for the chicks to start stress vocalising (for more details and sonogram see Collias 1987) was noted. The data from this test was recorded together with Johan Almberg, and is also used in his thesis.

Figure 1. Sketch of the arena for a) the proactive-reactive training, and b) the proactive-reactive test of red junglefowl chicks. Thick black lines represents plywood walls, thick grey double lines represents wire net walls, thin grey dotted lines represents the imaginary division of the arena. The grey circle shows the placement of the meal worm dish.

Table 1. Recorded behaviours of red junglefowl chicks in the novel arena, novel object and proactive-reactive tests.

Behaviour Description

Stand Standing still in upright position, stomach not touching ground, neck contracted

Walk In the process of putting one foot in front of the other, head bobbing forward and backward in time with the steps

Run Fast locomotion, often accompanied by flapping wings

Alert stand Standing still in upright position, stomach not touching ground, stretched neck

Alert walk In the process of putting one foot in front of the other, posture more erect than in ‘walk’, stretched neck, head not bobbing

Head down Standing still, not pecking, but beak pointing towards ground, looking at ground

Peck At the moment of a quick knock with the beak at the ground, wall or object; or between several subsequent pecks

Groom Pulls beak through plumage, or pecks at feet or plumage

Escape Jumps vertically towards the net roof

Lie down Lying down, stomach touching ground

3.3 Statistical analysis

The chicks’ individual growth rate (GR), expressed as relative body mass increase per day (% day-1), was calculated using the formula:

GR = 100 (ln W2 – ln W1) t -1

(1) where W1 is the initial weight (g), W2 is the final weight (g) and t is the

time elapsed in days (Cutts et al. 1998).

To test for differences in growth rates and hatching weights between the sexes, Mann-Whitney U tests were performed.

The behaviours ‘alert stand’ and ‘alert walk’ were combined and converted to a ‘vigilance’ score in the novel arena, novel object and proactive-reactive tests. In the novel arena test, behaviours ‘head down’, ‘peck’, ‘lie down’ and ‘groom’ were combined and considered describing

behaviour ‘freeze’. These behaviours were therefore not analysed further. The behaviours in this study were chosen because they have been showed to be consist over time and/or context, which means they indicate

personality types (R = 0.27 - 0.51, data presented by Johan Almberg, LiTH-IFM- 13/2787—SE, and Josefin Kvarnström, LiTH-IFM- Ex--13/2795—SE). The different behaviours from the tests were all tested against growth rate by the use of Spearman rank correlations. All analyses were conducted in Statistica©. Values are showed as mean ± SE.

4 Results

Hatching weights did not differ between the sexes (males: 29.4 ± 0.35 g, females: 29.0 ± 0.30 g, Z = 0.67, P = 0.500, n = 100). However, growth rate differed significantly between the sexes, with males growing faster than females already at 1 week of age (Figure 2). Therefore, further analyses were performed for males and females separately.

Figure 2. Comparison of growth rate (mean ± SE) between male and female red junglefowl chicks at different ages (7-34 days of age; 7 days: Z = 3.67, 14 days: Z = 5.22, 20 days: Z = 6.71, 27 days: Z = 6.75, 34 days: Z = 7.22. All P < 0.001 and n = 100).

The number of training sessions required for an individual to form a routine in the proactive-reactive test showed a significant positive correlation with growth rate in females (Figure 3a). However, this correlation was no longer significant when two extremely low values were removed (Figure 3b). None of the other behaviours showed significant correlations with growth rate (Table 2).

*** *** *** *** *** 2.0 4.0 6.0 8.0 7 14 20 27 34 G row th rate ( % day -1) Age (days) Males Females

Figure 3. The relationship between growth rate and the number of training sessions required for female red junglefowl chicks to form a routine in the proactive-reactive test. a) R = 0.44, P = 0.021, n = 27, b) two outliers removed, R = 0.32, P = 0.119, n = 25.

Some behaviours tended to show non-significant directions in there correlations with growth rate, with different patterns observed for males and females. In the novel arena test, growth rate tended to be negatively correlated to the behaviour ‘walk’ in females, while there was no

correlation at all observed for this behaviour in males (Table 2). In the novel object test, there tended to be a positive correlation between growth rate and the latency to interact with the novel object in females, but males did not show any correlation (Table 2). In the proactive-reactive test, the behaviour ‘walk’ tended to be negatively correlated to growth rate in females (Table 2) and the number of training sessions required for an individual to form a routine was positively correlated with growth rate in females (Figure 3). Males did not show any correlations for these traits (Table 2). The number of square changes per second in the proactive-reactive test tended to show a negative correlation in females and no correlation in males (Table 2).

0 25 50 75 3.9 4.9 5.9 Num be r of trai ni ng s 0 25 50 75 3.9 4.9 5.9

Growth rate (% day -1₎

Table 2. The relationship between growth rate and behaviours from the four

testsred junglefowl chicks were exposed to. n, R and P values are obtained

from the Spearman rank correlations. Significant correlations are symbolised with an asterisk *.

Test Sex Behaviour n R P

Novel arena Male Stand 46 0.19 0.218

Walk 46 0.01 0.951 Run 46 -0.16 0.282 Vigilance 46 -0.19 0.206 Calm 46 0.11 0.471 Freeze 46 -0.02 0.875 Latency to move 46 0.21 0.162 Latency to vocalise 46 0.03 0.818

Latency to explore all areas 46 -0.02 0.873

Number of escape attempts 46 0.11 0.473

Number of square changes 46 -0.05 0.751

Female Stand 54 -0.10 0.494 Walk 54 -0.23 0.093 Run 54 -0.05 0.720 Vigilance 54 0.08 0.578 Calm 54 0.01 0.952 Freeze 54 -0.01 0.939 Latency to move 54 0.21 0.128 Latency to vocalise 54 -0.02 0.897

Latency to explore all areas 54 0.25 0.072

Number of escape attempts 54 -0.16 0.261

Test Sex Behaviour n R P

Novel object Male Stand 46 -0.05 0.764

Walk 46 -0.04 0.773

Run 46 -0.06 0.685

Vigilance 46 0.04 0.768

Latency to move 46 -0.02 0.884

Latency to vocalise 46 -0.20 0.198

Latency to explore all areas 46 0.01 0.961

Number of escape attempts 46 0.07 0.665

Number of square changes 46 -0.08 0.609

Female Stand 54 -0.06 0.684 Walk 54 -0.11 0.414 Run 54 -0.09 0.495 Vigilance 54 0.07 0.596 Latency to move 54 -0.20 0.150 Latency to vocalise 54 -0.01 0.967

Latency to explore all areas 54 0.09 0.513

Number of escape attempts 54 -0.06 0.661

Number of square changes 54 -0.10 0.455

Tonic immobility Male Latency to first head movement 46 0.12 0.441

Latency to stand 46 -0.07 0.668

Number of trials needed 46 -0.15 0.324

Female Latency to first head movement 54 0.18 0.192

Latency to stand 54 0.10 0.491

Test Sex Behaviour n R P

Proactive-reactive

Male Number of trainings 29 0.04 0.824

Walk 29 0.06 0.770

Vigilance 29 0.07 0.729

Time to find the meal worms 29 0.07 0.724

Square changes per second 29 0.18 0.346

Female Number of trainings 27 0.44 0.021*a

Walk 27 -0.33 0.093

Vigilance 27 0.30 0.130

Time to find the meal worms 27 0.23 0.251

Square changes per second 27 -0.28 0.163

a)

See Figure 3 for more details

5 Discussion

Contrary to what was theoretically predicted (Stamps 2007), the results of this study indicate that personality is not affected by variation in

individual growth rate, and it is one of few studies to show this, especially in endotherms.

There was a significant difference in growth rate between the sexes, with males growing faster than females. This could be seen as early in life as at the age of 1 week and up to the age of 5 weeks, which were the last time chicks were weight in this experiment (Figure 2). A difference in growth rate between the sexes is however not surprising. There is a sexual dimorphism in red junglefowl and males need to grow bigger in the same time as females (Parker & Garant 2005). The pattern revealed in this study, with no difference in hatching weights between the sexes but differences in juvenile growth rate have been reported for avian species before (Richter 1983; Mignon-Grasteau et al. 1999; Weimerskirch et al. 2000). Oddie and colleagues (2000) reported a significant body mass difference between the sexes in 9 days old great tits (Parus major), with males being heavier. At the age of 2 days, the sexes did not differ in body mass, which indicate a difference in growth rate almost as early in life as the one found in my study (Oddie et al. 2000).

The only behaviour that potentially showed a significant correlation with growth rate in this study was the number of training sessions required for an individual to form a routine in the proactive-reactive test, which

showed a positive correlation in females (Figure 3a). In theory, a proactive individual should form routines easily (Koolhaas et al. 1999) and, as it is an active individual, it should also have a high growth rate (Stamps 2007). This means that an individual with a high growth rate should, theoretically, form routines easily, opposite of what my results would suggest. Also, this correlation was only significant due to two outlying data points. There were two very small chicks that did not grow at a normal rate and if these were removed the correlation was no longer significant (Figure 3b). For males, the correlation between growth rate and the number of training sessions required to form a routine was absent (Table 2). This further suggests that the relationship between growth rate and behaviour may not be strong in the red junglefowl.

Despite the lack of strong relationships between behaviours and growth rate, some traits tended to show correlations, with opposing patterns in males and females. Activity in both the novel arena and the proactive-reactive test (‘walk’, and ‘number of square changes per second’) tended to be negatively correlated with growth rate in females, while there was no correlation or a tendency for a positive correlation observed in males (Table 2). These observations further confirm that the theoretically predicted relationship between growth rate and behaviour, at least in red junglefowl, is unclear.

Several previous studies have found a positive correlation between growth rate and active behaviours such as boldness or aggressiveness in different fish species (e.g. Martin-Smith & Armstrong 2002; Ward et al. 2004; Hoogenboom et al. 2013), but very few studies on non-fish

vertebrates are available. One of the few reports of correlations between growth rate and personality in endotherms found a tendency for a positive correlation between growth rate and activity across different domestic dog breeds (Careau et al. 2010). In that study, authors were not able to correct for sex in the analyses, which could have had confounding effects on the results, and these results should be taken with some caution.

Domestic dog breeds are also highly subjected to artificial selection and are maybe not the best model organism to compare to other animals. Biro and Stamps (2008) presented a summarising table of all personality

growth rate correlations reported until that time. Most of the reports are, not surprisingly, from studies on fish species. But there are some results presented from studies on birds and mammals as well, however most of

rate and personality. The authors listed two studies on avian species; japanese quail (Coturnix coturnix japonica) and turkeys (Meleagris

gallopavo). However, Biro and Stamps (2008) used a correlation between body mass and growth rate in quail (Yang et al. 1998) as support for a relationship between personality and growth rate. Body mass may not be a good estimate of growth rate in birds, since birds only grow up until sexual maturation and is also a trait shown to have a relatively strong genetic component (van Noordwijk et al. 1988). The example presented on turkeys (Huff et al. 2007) showed a correlation between growth rate and activity across different breeds (selected for meat or egg production), thus the relationship was neither here based on actually measures of growth rates. The reports listed by Biro and Stamps (2008) of personality growth rate correlations in mammals mainly consist of studies on cattle. The only trait authors have used to estimate personality have been flight speed (away from humans, when humans are approaching), as a

measurement of temperament (another term typically used for personality). A low flight speed should be an indication of a calm temperament and are correlated with a higher average daily gain. Biro and Stamps (2008) also listed some studies on mice (selected for a high or low body mass over 90-108 generations) that showed correlations between exploratory behaviour/activity and growth rate (see references in Biro & Stamps 2008). When artificially selecting for only one trait, other correlated traits can unintendently change and the slow-growing mice showed a highly increased level of anxiety (Wirth-Dzięciolowska et al. 2005). The reports of personality growth rate correlations are mainly not from data on individuals, but from data comparing different breeds of a species. Taken together, the current reports of a relationship between variation in growth rate and personality of individuals are therefore scares.

My results suggest that growth rate is not a trait affecting personality strongly and further studies are needed to explore this predicted relationship further, together with studies aiming to determine which physiological traits that actually may have a relationship with personality, if growth rate show limited influences. A candidate trait for further

studies is for example variation in metabolic rate and personality. Biro and Stamps (2010) published a literature review which revealed a

positive correlation between basal metabolic rate, resting metabolic rate or standard metabolic rate and personality traits in fish, birds, mammals, crustaceans and insects. After that, several reports confirmed such a

positive relationship (Careau et al. 2011; Killen et al. 2011, 2012; Martins et al. 2011). But even these results are only weakly supported on an

found correlations between personality and metabolic rate (Kane et al. 2008; Lantová et al. 2011). If the relationships between personality and underlying physiological traits are as unclear as they seems to be, new ideas are encouraged to explain how personality can be considered an adaptation and maintained in populations, thus to overall improve our understanding of why animals have personality.

5.1 Conclusion

In conclusion, this report suggests that personality is not explained by variation in growth rate among individual red junglefowl chicks, and these results are of relevance for other vertebrate species complementing the previous reports of personality growth rate correlations in fish

species.

6 Acknowledgements

I would like to thank my supervisors Hanne Løvlie and Josefina Zidar for all their help and encouragement during the project. I would also like to thank Alexandra Balogh, Johan Almberg, Josefin Kvarnström and Elena Plana for a great teamwork with the behavioural assays.

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