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Profile of wild Neotropical spiny rats (Trinomys, Echimyidae) in two behavioral tests
Physiology & Behavior 79 (2003) 129 – 133
Brief communication
Profile of wild Neotropical spiny rats (Trinomys, Echimyidae) in two behavioral tests P. Manaf a, S. Moratob,1, E. Spinelli Oliveiraa,* a
b
Departamento de Biologia, FFCLRP, Universidade de Sa˜o Paulo, Av. Bandeirantes, 3900, Ribeira˜o Preto, SP, CEP 14040-901, Brazil Departamento de Psicologia e Educac¸a˜o, FFCLRP, Universidade de Sa˜o Paulo, Av. Bandeirantes, 3900, Ribeira˜o Preto, SP, CEP 14040-901, Brazil Received 24 October 2002; received in revised form 17 March 2003; accepted 7 April 2003
Abstract The performance of three closely related species of spiny rats was compared in the elevated plus-maze and in the open-field tests. Laboratory rats were also evaluated. It was hypothesized that such tests should reveal differences in anxiety and exploratory profile among the wild species, which differ with respect to habitat, type of social organization and locomotion pattern. No consistent differences were found among the spiny rats, as assessed by conventional parameters, while such differences were detected between the domesticated lines. The social spiny rats (Trinomys yonenagae), which live in dunes, differed from the solitary sylvan species (T. iheringi and T. albispinus) in only one index of anxiety (open arms end-exploring). Nevertheless, thigmotaxis in novel environments exists in these spiny rats just as it does in the laboratory rats. During the tests, the sylvan species relied on erratic movements and T. iheringi was the most active species, whereas T. yonenagae employed vigilance and direct escape locomotion. This latter feature may be due to challenges imposed by open environments. Defecation score was reduced for all wild rats: it may represent a predation avoidance response. Concerning ethological measures, T. iheringi presented the highest scores of grooming, in both test situations, and T. albispinus the highest scores of rearing in the open-field. The great within-species variability found in the spiny rats may have concealed anxiety differences among them, despite the ability of both tests to reveal plesiomorphic behavioral characteristics, such as thigmotaxis. Our results also support the use of ethological approach in these tests. D 2003 Elsevier Inc. All rights reserved. Keywords: Neotropical spiny rats; Trinomys; Echimyidae; Caviomorph; Elevated plus-maze; Open-field; Anxiety; Exploration of open spaces; Grooming; Defecation; Plesiomorphy
1. Introduction Numerous studies have previously addressed the responses of laboratory rodents in the elevated plus-maze (EPM) and in the open-field (OF) [1– 10], assessing the level of anxiety associated to the exploration of open spaces and the spontaneous activity in novel situations. Ultimately, it is hoped that the results of such studies can be related to the behavioral patterns of species in their natural habitats. Comparative studies revealed that domestication might attenuate defensiveness in rodents [11]. Therefore, it is important to determine the responses of wild animals in behavioral tests before such results are interpreted as an * Corresponding author. Tel.: +55-16-602-3633; fax: +55-16-6023666. E-mail addresses: [email protected] (P. Manaf), [email protected] (S. Morato), [email protected] (E. Spinelli Oliveira). 1 Tel.: + 55-16-602-3662; fax: + 55-16-633-5668. 0031-9384/03/$ – see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0031-9384(03)00121-5
expression of antipredatory defense. Wild voles, small rodents that are heavily predated upon, showed preference for protected areas in the EPM, a response that was modified by anxiolytic drugs [8]. This study also emphasizes the need for concordance between species-specific repertoire and the models of anxiety employed: anomalous behavioral patterns may be elicited when the test situation is not adequate [8]. In the case of a wild-derived population of house mice, elevated scores in the open arms associated with display of unusual behavioral categories in the plus-maze, were considered indicative of a state of great, instead of small reactivity [9]. The authors emphasize the importance of an ethological approach in interpreting exceptional behaviors in the EPM [9]. In the present work, the behavior of Neotropical caviomorph rodents, Trinomys iheringi Thomas (1911), Trinomys yonenagae Rocha (1995) and Trinomys albispinus minor Reis and Pessoa (1995), was compared in two tests (EPM and OF). These rats represent an interesting
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P. Manaf et al. / Physiology & Behavior 79 (2003) 129–133
Table 1 Origin localities of the spiny rat specimens Morro do Chape´u, BA
Iguape, SP 0
Coordinates Morphoclimatic domain
0
8°59 S, 39°54 W Subtropical Atlantic Rainforest 3000 – 4000 22a High density of trees (20 – 30 m), rich flora of epiphytes
Annual precipitation (mm) Air temperature (°C) Plant covering
0
Ibiraba, BA
0
11°33 S, 41°09 W Semiarid Caatinga (1000 m above sea level) 900 – 1200 24.5a Flora highly heterogeneous and relatively more open than a typical humid forest
10°480S, 42°500W Semiarid Caatinga (422 m above sea level) 692a,b 26.2a,b Sparse plant covering of low profile and low heterogeneity
Sources: INMET, BR, 2003 [12,16,19]. a Expressed as annual mean. b Dr. P. L. B. Rocha, personal communication.
model, which allows a phylogenetic approach: they belong to the same genus but have different life-styles [12,13]. T. iheringi inhabits dense climax rainforests and shelters under logs [14]. T. yonenagae, on the other hand, inhabits dunes where it builds complex galleries and leaves the burrows only at night [12]. Differently from the two other species, it displays saltatorial rather than quadrupetal locomotion, and it is colonial [12,15]. The third species, T. albispinus minor, was collected in isolated forested habitats, which are more open than typical rainforests [16]. Comparisons between two lines of laboratory rats will be used as control and to allow discussion within a phylogenetic framework. Since the three species of spiny rats differ in their degree of sociability, locomotion, and are subjected to different predation forces while foraging in areas that are either open or closed, two a priori hypotheses were examined. First, T. yonenagae, from dunes, will rely less in thigmotaxis than the other sylvan species. Second, the former species will
express less exploratory activities than the latter species, since it is routinely exposed to open areas where predation is the greatest upon individuals that are highly mobile.
2. Material and methods 2.1. Subjects and habitats All individuals were treated ethically according to Brazilian laws (IBAMA 097/97-129/98). Wild adult animals were caught in Iguape (T. iheringi, 4 females: 174 ± 11 g, 3 males: 203 ± 19 g), in Ibiraba (T. yonenagae, 9 females: 138 ± 5 g, 7 males: 131 ± 11 g) and in Morro do Chape´u (T. albispinus, 2 females: 187 ± 29 g, 6 males: 181 ± 9 g); all localities are situated in Brazil (Table 1). Rattus norvegicus (Wistar, 6 females: 180 ± 3 g, 12 males: 224 ± 5 g and McCollum hooded 12 females: 192 ± 2 g, 18 males: 210 ± 4 g) were from local suppliers.
Table 2 Plus maze and open field profiles of spiny rats (Trinomys) and domesticated rats (R. norvegicus) during a test period of 5 min (mean ± S.E.M.) T. iheringi (n = 7)
T. yonenagae (n = 16)
Plus maze Time end-exploring (s) No. rearing No. grooming Time grooming (s) Fecal boluses
29 ± 8.5 6.4 ± 1.7 2 ± 0.3 * 15.3 ± 2.9 * 0
7.1 ± 3.4 * 7.4 ± 2 0.3 ± 0.2 2.6 ± 1.3 0.6 ± 0.5
Open field Crossings centre Crossings periphery Crossings total Time centre (s) No. rearing No. grooming Time grooming (s) Fecal boluses
38.7 ± 11.9 143.9 ± 25.2 182.6 ± 23 36.3 ± 15.7 7 ± 1.9 1.4 ± 0.2 * 9.4 ± 1.9 * 4.4 ± 2.2
46.6 ± 7.7 112.6 ± 22.2 159.3 ± 28.5 80.1 ± 17 16.3 ± 4.7 0.3 ± 0.2 1.1 ± 0.6 0.9 ± 0.6
T. albispinus (n = 8)
Albino rats (n = 18)
Hooded rats (n = 30)
25.3 ± 6.2 13.5 ± 2.5 0.6 ± 0.3 2.4 ± 1.6 1.3 ± 0.8
8.9 ± 2.5 19.9 ± 1.7y 3.2 ± 0.5y 26.2 ± 7.9y 3 ± 0.7
13.8 ± 2.1 15.8 ± 1 5.7 ± 0.4 67.6 ± 6.3 2.2 ± 0.5
77 ± 20.1 133.6 ± 22 210.6 ± 28.6 77.6 ± 15.2 33.1 ± 2.5 * 0.3 ± 0.2 2.5 ± 1.6 1.3 ± 0.8
14.4 ± 1.6 99.9 ± 6.5 114.4 ± 7 13.3 ± 2.3 23.6 ± 2.7 3 ± 0.5y 31 ± 6y 3.6 ± 0.6
13.7 ± 1.7 94.5 ± 5 108.2 ± 5.4 11.5 ± 1.7 25.2 ± 1.5 5.4 ± 0.4 45.7 ± 4.3 4 ± 0.5
The Kruskal – Wallis and the post hoc Dunn tests were used to compare the three groups of Trinomys, and the Mann – Whitney U test (two tailed) to compare Wistar vs. McCollum (hooded) rat groups, for each measure. * Significantly different, P < .05, from the other two groups of spiny rats. y P < .05.
P. Manaf et al. / Physiology & Behavior 79 (2003) 129–133
2.2. Housing and maintenance Animals were housed individually (spiny rats) or in groups of six (domesticated rats) in standard laboratory cages (40 34 16 cm). Spiny rats were kept singly because the sylvan species are able to engage in ferocious fights when confronted with cospecifics. All wild rodents were housed for 2 months prior to experimental use to acclimate to the conditions in the laboratory (23 ± 1 °C; 12:12-h light– dark cycles, lights on at 7 a.m.). Their diet was supplemented with fresh edible items. Water and food pellets were available ad libitum. 2.3. Apparatus and procedures For OF: a wooden arena (60 60 30 cm) with the floor marked off in 10 cm2 comprised a peripheral and a central area (20 and 16 squares, respectively). For EPM: a wooden cross-shaped maze, 50 cm high, with two opposing open arms (50 10 cm), and two opposing closed arms (50 10 40 cm). To minimize handling on the day of testing, a procedure previously described was used [9]. The OP test was carried out 48 h after the EPM test and both procedures were conducted between 8 and 10 a.m. (room luminosity: 10 lx). Each session lasted 5 min and the apparatus was cleaned between sessions. A camera (Sony CCD-10 ) positioned 1.90 m above the apparatus video recorded all sessions.
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T. iheringi had a greater frequency of entries in the open arm and in the closed arms than T. yonenagae; both species did not differ from T. albispinus (Fig. 1). No differences were found regarding the other parameters studied (Fig. 1). T. yonenagae did not differ significantly from T. albispinus in the frequency or in the time spent in grooming, however, for each groups these values were significantly less than the ones found for T. iheringi; no differences were observed in the frequency of rearing events or the number of fecal pellets among the three species (Table 2). Wistar rats had a greater score of entries in the enclosed arms than hooded rats (Fig. 1). On the other hand, the latter presented a greater frequency of entries in the open arms than did the former (Fig. 1). Furthermore, the hooded group spent more time on the open arms than did the Wistar rats (Fig. 1), and it showed greater ratio of entries on the open arms than the albino ones. No statistical differences were observed in time spent exploring the extremities of the open arms (Table 2). Wistars reared more than hooded rats did, while the frequency and time spent by the former in grooming was smaller than
2.4. Behavioral measures Four ethological measures were evaluated in both tests: the frequency and time spent in grooming, the frequency of rearing, and defecation. Conventional measures were (a) in EPM, the frequencies of open and closed entries, the ratio of entries, time spent exploring the open arms and its extremities; (b) in OF, the time spent in the central area, the number of crossings in the central (C) and in the peripheral areas, the total (T), and the ratio of crossings (C:T). 2.5. Statistical analysis Data for Trinomys were subjected to Kruskal – Wallis test, followed by Dunn multiple comparison post hoc test. Data for laboratory rats were subjected to Mann –Whitney twotailed U test.
3. Results 3.1. The elevated plus-maze test The inhabitant of dunes (T. yonenagae) spent less time exploring the extremities of the open arms than did the sylvan species (T. iheringi and T. albispinus), but no significant differences were seen in the latter groups (Table 2).
Fig. 1. Frequency of entries in the closed arms, time spent and frequency of entries into open arms during a test period of 5 min with spiny rats (Trinomys) and domesticated Wistar and McCollum (hooded) rats (R. norvegicus). The midline of a box gives the median, the bottom and the top give the 25% and 75% quartiles, the deviation indicators give the 10% and 90% percentiles, and values beyond this range are plotted individually. T. iheringi (ihe, n = 7), T. yonenagae (yon, n = 16), T. albispinus (alb, n = 8), Wistar rats (n = 18), and hooded rats (n = 30). Comparisons were made among the three groups of Trinomys (Kruskal – Wallis and post hoc Dunn tests), and between the two strains of rats (Mann – Whitney U test, two tailed). * P < .05, * * P < .02.
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that of the latter, and no differences were seen in the number of fecal pellets between the domesticated rats (Table 2). 3.2. The open-field test No differences were observed among spiny rats for conventional measures but they differed in relation to the ethological variables: T. iheringi showed more grooming than the other species did, whereas T. albispinus reared more often than T. iheringi and T. yonenagae did (Table 2). Although no significant differences were found in the number of fecal pellets, T. yonenagae did not defecated a single time (Table 2). Hooded rats showed more grooming than the white ones; no differences were found in any of the other parameters studied in the OF (Table 2).
4. Discussion To our knowledge, this is the first comparison of the behavior of three closely related species of Neotropical caviomorph rodents in a well-validated experimental paradigm of anxiety (EPM), or locomotion with or without a high emotional component (OF). Our results do not support the hypothesis that rats from dunes would rely less in thigmotaxis than the sylvan species, as could be expected from animals that routinely explore open spaces. All spiny species showed a clear preference for protected areas in both tests, just like other small rodents [4]. The domesticated rats also showed such preference, in agreement with data from the literature [3 –5,17,18]. The analysis of our data under the perspective of the accepted phylogeny of Trinomys [13] suggests that, as thigmotaxis for Rattus (out-group) and Trinomys is similar, it may represent the plesiomorphic state for the entire clade. Differences in the level of anxiety and activity between R. norvegicus were detected: hooded ones were less anxious and less active than were albino rats, as has been previously described [10]. Nonetheless, the results from the spiny rats are difficult to interpret. There was a clear consistency of the responses of domesticated rats, but this was not the case for the spiny rats: only one index of anxiety was statistically different among the wild species, whereas all three measured conventional anxiety indices were significantly different in the domesticated rats. This consistency and the small variability of responses could be a consequence of domestication and reduced genetic diversity among individuals of the same line. The great within-species variability found in spiny rats may have concealed anxiety differences among them. This high variability in behavioral responses corresponds to the high genetic diversity already described for Trinomys [13]. Differential adaptation to a laboratory environment, the effect of individual housing and the effects of the enorm-
ous change in habitat could at least partially account for the results of the present work. The differences that were found indicate smaller levels of anxiety for T. iheringi, the rainforest-dweller, than for T. yonenagae, the dunes-dweller, with T. albispinus occupying an indefinable position. Alternatively, since T. iheringi showed greater number of enclosed and closed arm entries than T. yonenagae the former species can be considered simply more active than the latter. This is in agreement with ecological data, which show that T. iheringi presents home range larger than the ones presented by other rodents of comparable body size inhabiting rainforests [19]. Spiny rats differ according to their locomotion [12]. In the present study, T. yonenagae employed stop-and-go search in both experimental situations. This pattern of locomotion is characterized by a high component of vigilance and may account for the small scores of T. yonenagae exploring the open arms, since it did not dart to the end, as T. iheringi did. Thus, the apparent fearfulness of T. yonenagae can be related of its locomotor pattern and to a probable antipredator strategy. A benefit of pausing is reduced attack rate by predator, which is more likely to prey moving animals [20]. Our interpretation is supported by observations made in the field (P. L. B. Rocha, personal communication) [12] and in our own laboratory [15]: T. yonenagae, the species from the sand dunes, displays more organized antipredatory strategies, based on vigilance, than the sylvan species. Further studies recording risk assessment behaviors, such as scanning, stretched attend postures and flatback approach, as recommended in the literature [9] are needed to be done to confirm our interpretation of the qualitative observations on the patterns of locomotion. Concerning ethological measures, T. iheringi presented the highest scores of grooming, in both test situations, and T. albispinus the highest scores of rearing in the open-field. The defecation response of the spiny rats was small in all groups in both tests. According to the literature, the number of fecal pellets is related to the level of emotionality in laboratory rodents: great scores indicate high emotionality [2,5]. Studies with guinea pigs (Cavia porcellus) in the open-field also revealed small defecation scores [6]. Since spiny rats and guinea pigs are both caviomorph rodents, we speculate that a small defecation score in novel situations may be a characteristic shared by members of the group, and a predation avoidance response. These results support the use of ethological approach in behavioral tests using wild rats [21].
Acknowledgements We acknowledge the support of CNPq (10.0847/96.0 and 52.3094/95.7) and FAPESP (96/6205-6). We thank Dr. S. F. Perry, Dr. A. S. Abe, Dr. P. L. B. Rocha and the reviewers for critical comments. We are also indebted to Dr. P. L. B. Rocha for his support and participation in the field trips.
P. Manaf et al. / Physiology & Behavior 79 (2003) 129–133
References [1] Denenberg VH. Open-field behavior in the rat: what does it mean? Ann N Y Acad Sci 1969;159:852 – 9. [2] Archer J. Tests for emotionality in rats and mice: a review. Anim Behav 1973;21:205 – 35. [3] Treit D, Menard J, Royan C. Anxiogenic stimuli in the elevated plusmaze. Pharmacol Biochem Behav 1993;44:463 – 9. [4] Rodgers RJ, Cole JC. The elevated plus-maze: pharmacology, methodology and ethology. In: Cooper SJ, Hendrie CA, editors. Ethology and psychopharmacology. Chichester: Wiley; 1994. p. 9 – 44. [5] Ramos A, Morme`de P. Stress and emotionality: a multidimensional and genetic approach. Neurosci Biobehav Rev 1998;22:1 – 20. [6] Suarez SD, Gallup GG. Open-field behavior in guinea pigs: developmental and adaptive considerations. Behav Processes 1982;7: 267 – 74. [7] Hendrie CA, Weiss SM, Eilam D. Exploration and predation models of anxiety: evidence from laboratory and wild species. Pharmacol Biochem Behav 1996;54:13 – 20. [8] Hendrie CA, Eilam D, Weiss SM. Effects of diazepam and buspirone on the behaviour of wild voles (Microtus socialis) in two models of anxiety. Pharmacol Biochem Behav 1997;58:573 – 6. [9] Holmes A, Parmigiani S, Ferrari PF, Palanza P, Rodgers RJ. Behavioral profile of wild mice in the elevated plus-maze test for anxiety. Physiol Behav 2000;71:509 – 16. [10] Handley SL, McBlane JW. An assessment of the elevated x-maze for studying anxiety and anxiety-modulating drugs. J Pharmacol Toxicol Methods 1993;29:129 – 38. [11] Blanchard RJ, Flannely KJ, Blanchard DC. Defensive behavior of
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laboratory and wild Rattus norvegicus. J Comp Psychol 1986;100: 101 – 7. Rocha PBL. Proechimys yonenagae, a new species of spiny rat (Rodentia: Echimyidae) from fossil sand dunes in the Brazilian Caatinga. Mammalia 1995;59:537 – 49. Lara MC, Patton J. Evolutionary diversification of spiny rats (genus Trinomys, Rodentia: Echimyidae) in the Atlantic Forest of Brazil. Zool J Linn Soc 2000;130:661 – 86. Pessoa LM, Reis SF. Proechimys iheringi. Mamm Species 1996; 536:1 – 4. Manaf P, Spinelli Oliveira E. Behavioral repertoire of the spiny rat Proechimys (Trinomys) yonenagae (Rodentia: Echimyidae) in captivity. Revista de Etologia 2000;2:3 – 15. Reis SF, Pessoa LM. Proechimys albispinus minor, a new subspecies from the state of Bahia, northeastern Brazil (Rodentia: Echimyidae). Z Sa¨ugetierkunde 1995;60:237 – 42. Hogg S. A review of the validity and variability of the elevated plusmaze as an animal model of anxiety. Pharmacol Biochem Behav 1996; 54:21 – 30. Morato S, Branda˜o ML. Paradoxical increase of exploratory behavior in the elevated plus-maze by rats exposed to two kinds of aversive stimuli. Braz J Med Biol Res 1997;30:1113 – 20. Bergallo HG. Ecology of a small mammal community in an Atlantic Forest area in Southeastern Brazil. Stud Neotrop Fauna Environ 1994; 29:197 – 217. McAdam AG, Kramer DL. Vigilance as a benefit of intermittent locomotion in small mammals. Anim Behav 1998;55:109 – 17. Rodgers RJ, Cao BJ, Dalvi A, Holmes A. Animal models of anxiety: an ethological perspective. Braz J Med Biol Res 1997;30:289 – 304.
Brief communication
Profile of wild Neotropical spiny rats (Trinomys, Echimyidae) in two behavioral tests P. Manaf a, S. Moratob,1, E. Spinelli Oliveiraa,* a
b
Departamento de Biologia, FFCLRP, Universidade de Sa˜o Paulo, Av. Bandeirantes, 3900, Ribeira˜o Preto, SP, CEP 14040-901, Brazil Departamento de Psicologia e Educac¸a˜o, FFCLRP, Universidade de Sa˜o Paulo, Av. Bandeirantes, 3900, Ribeira˜o Preto, SP, CEP 14040-901, Brazil Received 24 October 2002; received in revised form 17 March 2003; accepted 7 April 2003
Abstract The performance of three closely related species of spiny rats was compared in the elevated plus-maze and in the open-field tests. Laboratory rats were also evaluated. It was hypothesized that such tests should reveal differences in anxiety and exploratory profile among the wild species, which differ with respect to habitat, type of social organization and locomotion pattern. No consistent differences were found among the spiny rats, as assessed by conventional parameters, while such differences were detected between the domesticated lines. The social spiny rats (Trinomys yonenagae), which live in dunes, differed from the solitary sylvan species (T. iheringi and T. albispinus) in only one index of anxiety (open arms end-exploring). Nevertheless, thigmotaxis in novel environments exists in these spiny rats just as it does in the laboratory rats. During the tests, the sylvan species relied on erratic movements and T. iheringi was the most active species, whereas T. yonenagae employed vigilance and direct escape locomotion. This latter feature may be due to challenges imposed by open environments. Defecation score was reduced for all wild rats: it may represent a predation avoidance response. Concerning ethological measures, T. iheringi presented the highest scores of grooming, in both test situations, and T. albispinus the highest scores of rearing in the open-field. The great within-species variability found in the spiny rats may have concealed anxiety differences among them, despite the ability of both tests to reveal plesiomorphic behavioral characteristics, such as thigmotaxis. Our results also support the use of ethological approach in these tests. D 2003 Elsevier Inc. All rights reserved. Keywords: Neotropical spiny rats; Trinomys; Echimyidae; Caviomorph; Elevated plus-maze; Open-field; Anxiety; Exploration of open spaces; Grooming; Defecation; Plesiomorphy
1. Introduction Numerous studies have previously addressed the responses of laboratory rodents in the elevated plus-maze (EPM) and in the open-field (OF) [1– 10], assessing the level of anxiety associated to the exploration of open spaces and the spontaneous activity in novel situations. Ultimately, it is hoped that the results of such studies can be related to the behavioral patterns of species in their natural habitats. Comparative studies revealed that domestication might attenuate defensiveness in rodents [11]. Therefore, it is important to determine the responses of wild animals in behavioral tests before such results are interpreted as an * Corresponding author. Tel.: +55-16-602-3633; fax: +55-16-6023666. E-mail addresses: [email protected] (P. Manaf), [email protected] (S. Morato), [email protected] (E. Spinelli Oliveira). 1 Tel.: + 55-16-602-3662; fax: + 55-16-633-5668. 0031-9384/03/$ – see front matter D 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0031-9384(03)00121-5
expression of antipredatory defense. Wild voles, small rodents that are heavily predated upon, showed preference for protected areas in the EPM, a response that was modified by anxiolytic drugs [8]. This study also emphasizes the need for concordance between species-specific repertoire and the models of anxiety employed: anomalous behavioral patterns may be elicited when the test situation is not adequate [8]. In the case of a wild-derived population of house mice, elevated scores in the open arms associated with display of unusual behavioral categories in the plus-maze, were considered indicative of a state of great, instead of small reactivity [9]. The authors emphasize the importance of an ethological approach in interpreting exceptional behaviors in the EPM [9]. In the present work, the behavior of Neotropical caviomorph rodents, Trinomys iheringi Thomas (1911), Trinomys yonenagae Rocha (1995) and Trinomys albispinus minor Reis and Pessoa (1995), was compared in two tests (EPM and OF). These rats represent an interesting
130
P. Manaf et al. / Physiology & Behavior 79 (2003) 129–133
Table 1 Origin localities of the spiny rat specimens Morro do Chape´u, BA
Iguape, SP 0
Coordinates Morphoclimatic domain
0
8°59 S, 39°54 W Subtropical Atlantic Rainforest 3000 – 4000 22a High density of trees (20 – 30 m), rich flora of epiphytes
Annual precipitation (mm) Air temperature (°C) Plant covering
0
Ibiraba, BA
0
11°33 S, 41°09 W Semiarid Caatinga (1000 m above sea level) 900 – 1200 24.5a Flora highly heterogeneous and relatively more open than a typical humid forest
10°480S, 42°500W Semiarid Caatinga (422 m above sea level) 692a,b 26.2a,b Sparse plant covering of low profile and low heterogeneity
Sources: INMET, BR, 2003 [12,16,19]. a Expressed as annual mean. b Dr. P. L. B. Rocha, personal communication.
model, which allows a phylogenetic approach: they belong to the same genus but have different life-styles [12,13]. T. iheringi inhabits dense climax rainforests and shelters under logs [14]. T. yonenagae, on the other hand, inhabits dunes where it builds complex galleries and leaves the burrows only at night [12]. Differently from the two other species, it displays saltatorial rather than quadrupetal locomotion, and it is colonial [12,15]. The third species, T. albispinus minor, was collected in isolated forested habitats, which are more open than typical rainforests [16]. Comparisons between two lines of laboratory rats will be used as control and to allow discussion within a phylogenetic framework. Since the three species of spiny rats differ in their degree of sociability, locomotion, and are subjected to different predation forces while foraging in areas that are either open or closed, two a priori hypotheses were examined. First, T. yonenagae, from dunes, will rely less in thigmotaxis than the other sylvan species. Second, the former species will
express less exploratory activities than the latter species, since it is routinely exposed to open areas where predation is the greatest upon individuals that are highly mobile.
2. Material and methods 2.1. Subjects and habitats All individuals were treated ethically according to Brazilian laws (IBAMA 097/97-129/98). Wild adult animals were caught in Iguape (T. iheringi, 4 females: 174 ± 11 g, 3 males: 203 ± 19 g), in Ibiraba (T. yonenagae, 9 females: 138 ± 5 g, 7 males: 131 ± 11 g) and in Morro do Chape´u (T. albispinus, 2 females: 187 ± 29 g, 6 males: 181 ± 9 g); all localities are situated in Brazil (Table 1). Rattus norvegicus (Wistar, 6 females: 180 ± 3 g, 12 males: 224 ± 5 g and McCollum hooded 12 females: 192 ± 2 g, 18 males: 210 ± 4 g) were from local suppliers.
Table 2 Plus maze and open field profiles of spiny rats (Trinomys) and domesticated rats (R. norvegicus) during a test period of 5 min (mean ± S.E.M.) T. iheringi (n = 7)
T. yonenagae (n = 16)
Plus maze Time end-exploring (s) No. rearing No. grooming Time grooming (s) Fecal boluses
29 ± 8.5 6.4 ± 1.7 2 ± 0.3 * 15.3 ± 2.9 * 0
7.1 ± 3.4 * 7.4 ± 2 0.3 ± 0.2 2.6 ± 1.3 0.6 ± 0.5
Open field Crossings centre Crossings periphery Crossings total Time centre (s) No. rearing No. grooming Time grooming (s) Fecal boluses
38.7 ± 11.9 143.9 ± 25.2 182.6 ± 23 36.3 ± 15.7 7 ± 1.9 1.4 ± 0.2 * 9.4 ± 1.9 * 4.4 ± 2.2
46.6 ± 7.7 112.6 ± 22.2 159.3 ± 28.5 80.1 ± 17 16.3 ± 4.7 0.3 ± 0.2 1.1 ± 0.6 0.9 ± 0.6
T. albispinus (n = 8)
Albino rats (n = 18)
Hooded rats (n = 30)
25.3 ± 6.2 13.5 ± 2.5 0.6 ± 0.3 2.4 ± 1.6 1.3 ± 0.8
8.9 ± 2.5 19.9 ± 1.7y 3.2 ± 0.5y 26.2 ± 7.9y 3 ± 0.7
13.8 ± 2.1 15.8 ± 1 5.7 ± 0.4 67.6 ± 6.3 2.2 ± 0.5
77 ± 20.1 133.6 ± 22 210.6 ± 28.6 77.6 ± 15.2 33.1 ± 2.5 * 0.3 ± 0.2 2.5 ± 1.6 1.3 ± 0.8
14.4 ± 1.6 99.9 ± 6.5 114.4 ± 7 13.3 ± 2.3 23.6 ± 2.7 3 ± 0.5y 31 ± 6y 3.6 ± 0.6
13.7 ± 1.7 94.5 ± 5 108.2 ± 5.4 11.5 ± 1.7 25.2 ± 1.5 5.4 ± 0.4 45.7 ± 4.3 4 ± 0.5
The Kruskal – Wallis and the post hoc Dunn tests were used to compare the three groups of Trinomys, and the Mann – Whitney U test (two tailed) to compare Wistar vs. McCollum (hooded) rat groups, for each measure. * Significantly different, P < .05, from the other two groups of spiny rats. y P < .05.
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2.2. Housing and maintenance Animals were housed individually (spiny rats) or in groups of six (domesticated rats) in standard laboratory cages (40 34 16 cm). Spiny rats were kept singly because the sylvan species are able to engage in ferocious fights when confronted with cospecifics. All wild rodents were housed for 2 months prior to experimental use to acclimate to the conditions in the laboratory (23 ± 1 °C; 12:12-h light– dark cycles, lights on at 7 a.m.). Their diet was supplemented with fresh edible items. Water and food pellets were available ad libitum. 2.3. Apparatus and procedures For OF: a wooden arena (60 60 30 cm) with the floor marked off in 10 cm2 comprised a peripheral and a central area (20 and 16 squares, respectively). For EPM: a wooden cross-shaped maze, 50 cm high, with two opposing open arms (50 10 cm), and two opposing closed arms (50 10 40 cm). To minimize handling on the day of testing, a procedure previously described was used [9]. The OP test was carried out 48 h after the EPM test and both procedures were conducted between 8 and 10 a.m. (room luminosity: 10 lx). Each session lasted 5 min and the apparatus was cleaned between sessions. A camera (Sony CCD-10 ) positioned 1.90 m above the apparatus video recorded all sessions.
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T. iheringi had a greater frequency of entries in the open arm and in the closed arms than T. yonenagae; both species did not differ from T. albispinus (Fig. 1). No differences were found regarding the other parameters studied (Fig. 1). T. yonenagae did not differ significantly from T. albispinus in the frequency or in the time spent in grooming, however, for each groups these values were significantly less than the ones found for T. iheringi; no differences were observed in the frequency of rearing events or the number of fecal pellets among the three species (Table 2). Wistar rats had a greater score of entries in the enclosed arms than hooded rats (Fig. 1). On the other hand, the latter presented a greater frequency of entries in the open arms than did the former (Fig. 1). Furthermore, the hooded group spent more time on the open arms than did the Wistar rats (Fig. 1), and it showed greater ratio of entries on the open arms than the albino ones. No statistical differences were observed in time spent exploring the extremities of the open arms (Table 2). Wistars reared more than hooded rats did, while the frequency and time spent by the former in grooming was smaller than
2.4. Behavioral measures Four ethological measures were evaluated in both tests: the frequency and time spent in grooming, the frequency of rearing, and defecation. Conventional measures were (a) in EPM, the frequencies of open and closed entries, the ratio of entries, time spent exploring the open arms and its extremities; (b) in OF, the time spent in the central area, the number of crossings in the central (C) and in the peripheral areas, the total (T), and the ratio of crossings (C:T). 2.5. Statistical analysis Data for Trinomys were subjected to Kruskal – Wallis test, followed by Dunn multiple comparison post hoc test. Data for laboratory rats were subjected to Mann –Whitney twotailed U test.
3. Results 3.1. The elevated plus-maze test The inhabitant of dunes (T. yonenagae) spent less time exploring the extremities of the open arms than did the sylvan species (T. iheringi and T. albispinus), but no significant differences were seen in the latter groups (Table 2).
Fig. 1. Frequency of entries in the closed arms, time spent and frequency of entries into open arms during a test period of 5 min with spiny rats (Trinomys) and domesticated Wistar and McCollum (hooded) rats (R. norvegicus). The midline of a box gives the median, the bottom and the top give the 25% and 75% quartiles, the deviation indicators give the 10% and 90% percentiles, and values beyond this range are plotted individually. T. iheringi (ihe, n = 7), T. yonenagae (yon, n = 16), T. albispinus (alb, n = 8), Wistar rats (n = 18), and hooded rats (n = 30). Comparisons were made among the three groups of Trinomys (Kruskal – Wallis and post hoc Dunn tests), and between the two strains of rats (Mann – Whitney U test, two tailed). * P < .05, * * P < .02.
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that of the latter, and no differences were seen in the number of fecal pellets between the domesticated rats (Table 2). 3.2. The open-field test No differences were observed among spiny rats for conventional measures but they differed in relation to the ethological variables: T. iheringi showed more grooming than the other species did, whereas T. albispinus reared more often than T. iheringi and T. yonenagae did (Table 2). Although no significant differences were found in the number of fecal pellets, T. yonenagae did not defecated a single time (Table 2). Hooded rats showed more grooming than the white ones; no differences were found in any of the other parameters studied in the OF (Table 2).
4. Discussion To our knowledge, this is the first comparison of the behavior of three closely related species of Neotropical caviomorph rodents in a well-validated experimental paradigm of anxiety (EPM), or locomotion with or without a high emotional component (OF). Our results do not support the hypothesis that rats from dunes would rely less in thigmotaxis than the sylvan species, as could be expected from animals that routinely explore open spaces. All spiny species showed a clear preference for protected areas in both tests, just like other small rodents [4]. The domesticated rats also showed such preference, in agreement with data from the literature [3 –5,17,18]. The analysis of our data under the perspective of the accepted phylogeny of Trinomys [13] suggests that, as thigmotaxis for Rattus (out-group) and Trinomys is similar, it may represent the plesiomorphic state for the entire clade. Differences in the level of anxiety and activity between R. norvegicus were detected: hooded ones were less anxious and less active than were albino rats, as has been previously described [10]. Nonetheless, the results from the spiny rats are difficult to interpret. There was a clear consistency of the responses of domesticated rats, but this was not the case for the spiny rats: only one index of anxiety was statistically different among the wild species, whereas all three measured conventional anxiety indices were significantly different in the domesticated rats. This consistency and the small variability of responses could be a consequence of domestication and reduced genetic diversity among individuals of the same line. The great within-species variability found in spiny rats may have concealed anxiety differences among them. This high variability in behavioral responses corresponds to the high genetic diversity already described for Trinomys [13]. Differential adaptation to a laboratory environment, the effect of individual housing and the effects of the enorm-
ous change in habitat could at least partially account for the results of the present work. The differences that were found indicate smaller levels of anxiety for T. iheringi, the rainforest-dweller, than for T. yonenagae, the dunes-dweller, with T. albispinus occupying an indefinable position. Alternatively, since T. iheringi showed greater number of enclosed and closed arm entries than T. yonenagae the former species can be considered simply more active than the latter. This is in agreement with ecological data, which show that T. iheringi presents home range larger than the ones presented by other rodents of comparable body size inhabiting rainforests [19]. Spiny rats differ according to their locomotion [12]. In the present study, T. yonenagae employed stop-and-go search in both experimental situations. This pattern of locomotion is characterized by a high component of vigilance and may account for the small scores of T. yonenagae exploring the open arms, since it did not dart to the end, as T. iheringi did. Thus, the apparent fearfulness of T. yonenagae can be related of its locomotor pattern and to a probable antipredator strategy. A benefit of pausing is reduced attack rate by predator, which is more likely to prey moving animals [20]. Our interpretation is supported by observations made in the field (P. L. B. Rocha, personal communication) [12] and in our own laboratory [15]: T. yonenagae, the species from the sand dunes, displays more organized antipredatory strategies, based on vigilance, than the sylvan species. Further studies recording risk assessment behaviors, such as scanning, stretched attend postures and flatback approach, as recommended in the literature [9] are needed to be done to confirm our interpretation of the qualitative observations on the patterns of locomotion. Concerning ethological measures, T. iheringi presented the highest scores of grooming, in both test situations, and T. albispinus the highest scores of rearing in the open-field. The defecation response of the spiny rats was small in all groups in both tests. According to the literature, the number of fecal pellets is related to the level of emotionality in laboratory rodents: great scores indicate high emotionality [2,5]. Studies with guinea pigs (Cavia porcellus) in the open-field also revealed small defecation scores [6]. Since spiny rats and guinea pigs are both caviomorph rodents, we speculate that a small defecation score in novel situations may be a characteristic shared by members of the group, and a predation avoidance response. These results support the use of ethological approach in behavioral tests using wild rats [21].
Acknowledgements We acknowledge the support of CNPq (10.0847/96.0 and 52.3094/95.7) and FAPESP (96/6205-6). We thank Dr. S. F. Perry, Dr. A. S. Abe, Dr. P. L. B. Rocha and the reviewers for critical comments. We are also indebted to Dr. P. L. B. Rocha for his support and participation in the field trips.
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