NORTH-WESTERN JOURNAL OF ZOOLOGY 10 (2): 245-250 ©NwjZ, Oradea, , 2014 Article No.: 141101 http://biozoojournals.ro/nwjz/index.html

‘Nasty neighbour’ effect in pratensis Retz. (: Formicidae)

Klára BENEDEK1 and Ottília Tímea KÓBORI2

1. Sapientia Hungarian University of Transylvania, Department of Horticulture, Op. 9, P.O. Box 4, 540485 Tîrgu Mureş / Corunca, Romania. 2. Hungarian Academy of Sciences, Biological Research Centre, Institute of Plant Biology, Budapest, . *Corresponding author, K. Benedek, E-mail: [email protected]

Received: 4. October 2013 / Accepted: 18. November 2014 / Available online: 31. January 2014 / Printed: December 2014

Abstract. Aggressive behaviour in towards non-nestmates is profoundly studied. In many species there is connection between spatial distance and level of aggression. Some species follow the ‘dear enemy phenomenon’ avoiding aggression with neighbours and hostility being enhanced between non-nestmates from higher distances. By contrast, the ‘nasty neighbour’ effect is known in the case where workers are more aggressive with adjacent colonies. The aim of our study was to detect the effect of distance on the aggression level of Formica pratensis colonies, at Fânaţele Clujului Nature Reserve (Romania). Aggressiveness tests between colonies through workers from different distances were carried out. The nests were categorized into three groups: first neighbours, second neighbours and non-neighbours. Our results showed that the Formica pratensis population from Fânaţele Clujului is monodomous. Workers from first neighbours’ nests were more aggressive than those from second neighbours and non-neighbours colonies.

Key words: Formica pratensis, monodomous, intraspecific aggression, ‘nasty neighbour’ effect.

Introduction phenomenon' (reviewed in Temeles 1994) suggests the avoidance of conflicts with neighbouring colo- Workers of an colony can compete with con- nies to reduce the costs of territory defence specifics and certainly with individuals of other (Heinze et al. 1996, Beye et al. 1998, Pirk et al. ant species. To eliminate intruders it is essential to 2001, Dimarco et al. 2010). It is also possible that distinguish colonymates from non-colonymates neighbouring nests are closer relatives and the (Vander Meer & Morel 1998, Sturgis & Gordon similarity in nestmate recognition cues could lead 2012). In many ant species the clue to nestmate to lower levels of aggression between such nests recognition is the cuticular hydrocarbon profile of (Pirk et al. 2001). individuals (Lahav et al. 1999, Howard & Blom- By contrast, the level of aggression is posi- quist 2005, Brandstaetter et al. 2008, Martin & tively correlated with the increase of spatial dis- Drijfhout 2009, Bos & d’Ettorre 2012, Sturgis & tance between colonies (Sanada-Morimura et al. Gordon 2012, Krasnec & Breed 2013). Cuticular 2003, Wilgenburg 2007, Gordon 2010). The in- hydrocarbon profile has genetically- (Vander Meer creased aggressiveness towards conspecifics from & Morel 1998, Gamboa 2004, Dani et al. 2005, Sor- nearby is known as ‘nasty neighbour’ effect (Te- vari et al. 2008, Martin & Drijfhout 2009) and envi- meles 1994). Several authors demonstrated this ef- ronmentally- (Heinze et al. 1996, Liang & fect in Pristomyrmex pungens (Sanada-Morimura et Silverman 2000, Dani et al. 2005, Gordon 2010) de- al. 2003), Iridomirmex purpureus (van Wilgenburg et termined components. Aggressive interactions oc- al. 2007), Linepithema humile (Thomas et al. 2007), cur when workers detect chemical recognition Oecophylla smaragdina (Newey et al. 2009) or in the cues that differ from a familiar template (Vander termite Nasutitermes corniger (Dunn and Messier Meer & Morel 1998, Ozaki et al. 2005, Martin et al. 1999). Sanada-Morimura et al. (2003) and van 2012). Genetic relatedness (Beye et al. 1997, Holzer Wilgenburg et al. (2007) explained the phenome- et al., 2006, Pirk et al., 2001, Thurin & Aron, 2008) non by the encounter-induced hostility. According and chemical distance (Foitzik et al. 2007, Martin to this theory, individuals with territorial behav- et al. 2009, 2012) affect the level of aggression in iour from stable habitats like workers of some so- ants. Aggression fluctuations with spatial distance cial colonies can learn recognition cues of are also described. Some ant species avoid being neighbouring conspecifics when they meet at food aggressive with close neighbours (Heinze et al. sources. Over time, workers from different colo- 1996, Thomas et al. 1999, Katzerke et al. 2006, Di- nies within a common vicinity use the cues to rec- marco et al. 2010, Tanner & Adler 2009, Tanner & ognize, or ‘know,' each other. They behave more Keller 2012, Roux et al. 2013). The 'dear enemy aggressively with these close neighbours com- 246 K. Benedek & O.T. Kóbori

Figure 1. The four study sites at Fânaţele Clujului Nature Reserve (source: Google Earth).

pared to workers being from greater distances. with cows and sheep was high. According to Temeles (1994), the occurrence of More than 100 Formica pratensis nests were detected nasty neighbour or dear enemy effect depends on here in spring 2004 in a limited area. The nest number was decreasing dramatically from autumn 2004 to spring the risk represented by neighbours. 2005. From 2005 to 2007 the nest number was constant. The aim of our study was to find differences in The study was carried out in four different sites, signed the level of aggression of Formica pratensis workers from I. to IV. (Fig. 1). The nest number was 18 on the I. coming from colonies situated at different spatial site (Fig. 2.), and 5 on the IV. site (Fig. 3.).Two nests were distances. Similar studies were carried out in present at the II. (11 m apart) and III. sites (60 apart). on Formica pratensis (Beye et al. 1998, Pirk et al. 2001) and demonstrated a positive correla- Applied methods Aggressiveness tests were used in order to determine tion between aggression level and spatial distance level of aggression between individuals from different between nests. Because differences in aggressive nests. This method is frequently used to analyse nestmate behaviour of other ant species from different recognition and behaviour of ants and other social populations are known (Thomas et al. 1999, towards conspecifics and allospecifics (Beye et al. 1997, Wilgenburg 2007), we specifically ask if these re- 1998, Langen et al 2000, Pirk et al. 2001, Chapuisat et al. sults could be generalized or there is plasticity in 2004, Katzerke et al. 2006, Thomas et al. 2007, Wilgenburg the behaviour of this species. 2007, Martin et al. 2009, Newey et al. 2009, Dimarco et al. 2010, Krasnec & Breed 2013, Roux et al. 2013). The tests The following hypotheses were taken into ac- were carried out with one worker marked with nail pol- count: ants from neighbouring colonies are more ish on the back of the pronotum from one nest and three tolerant with each other than those from greater unmarked workers from the other nest. The ants were distances, or ants from neighbouring colonies are placed in a plastic glass covered by net which allowed air more aggressive to each other than those from exchange. Aggressiveness tests with ants from nests situ- greater distances. ated in various distances were applied to detect the effect of spatial distance on the level of aggression. In addition, tests with workers from the same nest were carried out to Material and methods identify differences between the intranest and close neighbour’s aggressiveness. In all cases interactions of in- Study site dividuals with the marked, focal specimen were re- The fieldwork was carried out from 2004 August to 2006 corded. Aggressiveness tests with unmarked workers April at Fânaţele Clujului Nature Reserve (46°50’N, from the same nest were also carried out to control for the 23°37’E, Fig. 1). The area is situated in the north part of effect of marking, but in this case only two workers were Cluj-Napoca (Romania), 5 km away from the city. The av- used. Thus the interactions in this case could also be ana- erage annual temperature is 14.5°C, and average annual lysed as behavioural acts towards one focal individual. rainfall is less than 500 millimetres (Ghişa 1944 in Vicol Each test was performed for five minutes. 1989). Due to the special local climate, the vegetation is The following behavioural categories were distin- thermophilic (Vicol 1989). Many rare, therefore valuable, guished: plant species are present in the reservation (Vicol 1989). 1. non-aggressive interactions: ignoring and mutual The researched area was a grassland overgrown with feeding; wild rose (Rosa canina) and hawthorn (Crataegus 2. aggressive interactions: mandible gaping, charg- monogyna). In spite of protected status of the area, anthro- ing, fighting and avoiding. The tested nests were categorized into three groups pogenic perturbation represented by hikers and grazing

‘Nasty neighbour’ effect in Formica pratensis 247

Figure 2. The map of nests on the I. site in spring 2007. Figure 3. The map of nests on the IV. site in spring 2007.

in terms of distance: first neighbours (less than 20 m and Table 1. The number of different aggressiveness tests. no other nests were present between the tested nests), Spring (2006) Summer (2005) second neighbours (more than 30 m and there was one or First neighbour 28 30 more nests between the tested nests), and non-neighbours Second neighbour 27 20 (more than 300 m). A total of 198 tests were performed Non-neighbour 23 29 (Table 1.). Unmarked 17 -

Intranest - 24 Statistical analysis Percentages of interaction types were considered for sta- tistical analyses. Aggressive interactions were detected during To analyze the social structure of the nest complexes, all tests between nests from different distances. we compared the intranest aggression level and that The majority of the aggressive interactions were among ants from close neighbour nests. mandible gaping, but charging, fighting and To analyse the connection between spatial distance avoiding interactions also occurred (Figs 4, 5 and and aggressiveness, results from tests among from first, second, and non-neighbour colonies were compared with 6). Kruskal–Wallis test. Pairwise Mann-Whitney U test com- Only ignoring interactions were found at in- parisons were applied in those cases where significant tranest tests and the proportion of this type of in- differences were detected on the basis of Kruskal–Wallis teraction was significantly higher than at those at tests. Bonferroni-correction was applied for statistical er- close neighbours tests (Mann Whitney U-test, rors occurring from post hoc cross-comparisons. Because Nclose neighbours=30, Nintranest=24, Medianclose neighbours= of the well known seasonal differences of aggressive be- 40, Medianintranest=100, zignoring=-4.631, pignoring< haviour at Formica pratensis (Beye et al. 1998, Pirk et al. 2001), data from the two studied seasons were analyzed 0.001). separately. The statistical analysis was carried out using Our results from spring showed significant SPSS for Windows, version 12.0 (SPSS Inc., Chicago, IL, differences in the percentages of ignoring interac- USA) statistical software. tions and cumulated percentages of aggressive in- teractions (mandible gapping, charging and fight- ing) among the three test combinations (Fig. 7). Results The cumulative percentage of aggressive interac- tions was higher between first neighbours and Marking had no significant effect on the behaviour lower between non-neighbours from the same nest of ants. Our results show no significant differences complex and non-neighbours from different terri- in the proportion of different behavioural catego- tories. Percentage of ignoring interactions was ries between marked and unmarked workers significantly lower between first neighbours (Fig. (Mann Whitney U-test, Nmarked=17, Nunmarked=17, 7, Table 2). We detected no significant difference zignoring=-0.293, pignoring=0.785, zmandible gapping=-0.189, in the level of aggression between second pmandible gapping=0.865, zcharging=-1.632, pcharging=0.289, neighbours and non-neighbours (Fig. 7, Table 2.). zavoiding=-0.207, pavoiding=0.891). Percentage of avoiding interactions was similar 248 K. Benedek & O.T. Kóbori

Figure 4. Percentages of interaction types between workers from close neighbouring nests (N= 58).

Figure 5. Percentages of interaction types between workers from second neighbouring nests (N= 47).

between the three test types (Fig. 7). Pirk et al. 2001). In spite of these results ‘nasty No significant differences of aggression level neighbour effect was proved’ at Formica pratensis were detected in summer (Kruskal – Wallis test, population from Fânaţele Clujului: the behavior of

Nfirst neighbour=30, Nfirst neighbour=20, Nnon-neighbour=29, workers from adjacent nests was more aggressive

χ2ignoring=3.005, pignoring=0.223, χ2all aggressive=2.605, pall than those from non-adjacent colonies. Despite of aggressive=0.272, χ2avoiding=0.294, p avoiding=0.863). the relatively large number of neighbouring nests, the population was probably formed by monodo- mous nests at the time of the study. The popula- Discussion tion structure formed only by monodomous colo- nies could contribute to the higher aggression Beye et al. (1998) and Pirk et al. (2001) reported level between first neighbours. Monodomous Formica pratensis: populations formed by poly- and colonies of territorial ant species are often more monodomous colonies from Sweden, demonstrat- aggressive than polydomous ones (Pisarski 1982, ing the ‘dear enemy’ phenomenon: the aggression Pirk et al. 2001, Martin et al. 2009, Sorvari et al. level increased by the distance (Beye et al. 1998, 2008), and in this way the conflict between

‘Nasty neighbour’ effect in Formica pratensis 249

Figure 6. Percentages of interaction types between workers from non- neighbouring nests (N= 52).

Table 2. Comparison of the percentages of different interaction types between workers from different distances in spring. The tested ants are 1 – first neighbours, 2 – second neighbours, 3 – non-neighbours (Mann-Whitney U

test, N1= 28, N2= 27, N3= 23).

1 vs 2 z1_2 1 vs 3 z1_3 2 vs 3 z2_3 ignore < -2.641* < -2-535* = -0.332 mandible gapping+ charge+ fight > 2.132* > -3.155** = -0.974

pBonferroni correction *< 0.05, **< 0.005

neighbouring monodomous nests could be stronger, as in mixed populations. A possible reason for the nasty neighbour ef- fect detected at the Formica pratensis population from Fânaţele Clujului could be the increased competition: the factors that lead to the nest ex- tinctions could enhance the level of competition between the neighbouring colonies. The exact rea- sons of the nest extinction are still unknown but probably the high anthropogenic perturbation promoted the process. In this situation the colony members that have to defend the resources, might feel a stronger risk neighbours than strangers, so the hostility against the adjacent nest increase. Plasticity in aggressive behavior is known in other ant species too. Tanner & Adler (2009) demon- strated that the aggressive behavior of Formica xe- rophila depends on the habitat type and the nu- merical superiority against the enemy. Aggressive behaviour of Iridomyrmex purpureus workers from Figure 7. Percentages of interaction types between work- ers from different distances in spring. The tested ants two different areas was different: Thomas et al. are 1 – first neighbours, 2 –second neighbours, 3 – non- (1999) established increasing aggressiveness as

neighbours (Kruskal–Wallis test, N1=28, N2=27, N3=23, spatial distance grows, and Wilgenburg (2007) χ2ignoring=9.210, pignoring =0.01; χ2all negative=10.380, p all negative demonstrated the contrary of this in one popula- =0.006; χ2avoidance=3.481, p avoidance=0.175). tion where the pressure of competition was high.

250 K. Benedek & O.T. Kóbori

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