Maculinea nausithous Exploits Myrmica scabrinodis in Transylvania: Unusual Host Ant Species of a Myrmecophilous Butterfly in an Isolated Region (Lepidoptera: Lycaenidae; Hymenoptera: Formicidae)

Maculinea nausithous Exploits Myrmica scabrinodis in Transylvania: Unusual Host Ant Species of a Myrmecophilous Butterfly in an Isolated Region (Lepidoptera: Lycaenidae; Hymenoptera: Formicidae) by András Tartally1, László Rákosy2, Tibor-Csaba Vizauer3, Marin Goia4, & Zoltán Varga1 ABSTRACT Isolated populations of the myrmecophilous Dusky Large Blue butterfly (Maculinea nausithous) occur in Transylvania (Romania). The hitherto unknown host ant specificity of these populations was investigated at two sites, where Myrmica scabrinodis was the only potential host ant found. A total of 107 M. scabrinodis nests were opened in early summer to check for the presence of M. nausithous larvae, and two of them contained overwintered larvae. Our observations suggest that, like the habitat, the host ant of these isolated populations essentially differs from other central European M. nausithous populations studied, which use exclusively Myrmica rubra. Keywords: host specificity, local host, Maculinea nausithous, myrmecophily, Myrmica scabrinodis, Transylvania INTRODUCTION Larvae of Maculinea5 nausithous (Bergsträsser) are obligate social parasites of Myrmica Latreille ant nests, after developing on Sanguisorba officinalis L. host plant (e.g. Thomas et al. 1989). The identification of the local host ant species is not only crucial for the conservation of this vulnerable butterfly (Munguira & Martín 1999, Settele et al. 2005, IUCN 2006), but also because 1Department of Evolutionary Zoology and Human Biology, University of Debrecen, H-4032, Egyetem tér 1, Debrecen, Hungary (tartal[email protected]) 2Department of Taxonomy and Ecology, Babes-Bolyai University, RO-3400, Clinicilor Street 5-7, Cluj, Romania 3Council of Cluj County, RO400124, B-dul 21 Decembrie 1989, Nr. 58, Cluj, Romania 4RO-400451, Aleea Azuga, Nr. 9/32, Cluj, Romania 5Editor's note: There appears to be a difference in the usage of this name. See Pech et al. 2008 in which the generic name Phenagris is used. 373 374 Sociobiology Vol. 51, No. 2, 2008 it can help shed light on the evolution of this type of parasitic interaction (Elmes et al. 1998, Als et al. 2004). M. nausithous almost exclusively exploits Myrmica rubra (Linnaeus) nests in Europe (Thomas et al. 1989, Elmes et al. 1998, Korb 1998, Stankiewicz & Sielezniew 2002, Als et al. 2004, Tartally & Varga 2005; Fig. 1). However, Maculinea host ant specificity may vary between regions (e.g. Elmes et al. 1998), and M. nausithous has some rather isolated populations in Transylvania (Romania) (Rákosy & Lászlóffy 1997; Fig. 1) that differ somewhat in habitat from other M. nausithous sites. The aim of this study was therefore to investigate host ant use in these isolated populations. MATERIALS AND METHODS Only two M. nausithous sites are known from Transylvania (Fig. 1). Both of them are in the Câmpia Transilvaniei region, near Cluj-Napoca: one at Răscruci (N46°54', E 23°47' 485 m a.s.l.; exact localities are not given to avoid exploitation), another at Fânaţele Clujului (N46°51', E23°37'; 540 m; more details of this site are given by Rákosy & Lászlóffy 1997). Both sites are Fig. 1. The distribution and host ant use of Maculinea nausithous in and around the Carpathian-Basin. F: Fânaţele Clujului, R: Răscruci (the sites investigated in this study), +: myrmecologically investigated (by A.T.) Sanguisorba officinalis–Maculinea teleius sites where M. scabrinodis was recorded, o: such sites where M. scabrinodis was not recorded (data from Bálint 1996, Wynhoff 1998, recent and unpublished data; see also Tartally & Varga 2005: Fig. 3). 375 Tartally, A. et al. — Myrmica scabrinodis: Host of Maculinea nausithous semi-dry meadows with steppe character, with sporadic small boggy depressions (Fig. 2). S. officinalis, the host plant, occurs in a mosaic in these small depressions, creating potential metapopulation networks of M. nausithous subpopulations (e.g. Hanski 1999). Both known sites were investigated in this study, but it should be noted that the Câmpia Transilvaniei region is rather poorly studied, so that occurrence of other, as yet undiscovered, M. nausithous sites in the area is likely. To obtain data on host specificity, Myrmica nests within 2 m of S. officinalis host plants were carefully opened (usually without full excavation, to minimize disturbance) on both sites, and the presence or absence of M. nausithous larvae was recorded. Nests within 2m of host plants were chosen as this is the approximate foraging zone of Myrmica workers, and nests further from the host plants are unlikely to adopt Maculinea larvae (Elmes et al. 1998). The investigations were from late May to early July 2002 and 2007, so that all the recorded larvae had spent the winter in their host nests, surviving one of the most critical periods for the butterfly (Elmes et al. 2004). Investigations were Fig. 2: The site at Răscruci where Maculinea nausithous larvae were found in Myrmica scabrinodis nests (photo by L. Rákosy; compare with Tartally & Varga 2005: Fig. 2, where M. nausithous was found with Myrmica rubra). 376 Sociobiology Vol. 51, No. 2, 2008 completed before the pupation period in mid July, since M. teleius (Bergsträsser) and M. alcon (Denis & Schiffermüller) also develop in the boggy depressions (and M. arion (Linnaeus) in the adjacent drier patches at Fânaţele Clujului), and pupae of M. teleius and M. nausithous are rather similar (Śliwińska et al. 2006) which could result in the confusion of these two syntopic species. However, the identification of Maculinea larvae is straightforward (Śliwińska et al. 2006). The number and species of Maculinea larvae found was noted after determination using a 20x hand lens in the field. Five to ten workers were collected from each Myrmica nest opened, and were preserved in 67 % ethanol for identification in the laboratory (using keys in Seifert 1988). RESULTS A total of 107 Myrmica nests were found within 2 m from the S. officinalis host plants at the two sites (58 at Fânaţele Clujului and 49 at Răscruci), and checked for Maculinea larvae. All 107 nests proved to be M. scabrinodis Nylander. Two nests from Răscruci were infested by M. nausithous, both of them containing only a single M. nausithous larva. Larvae of M. alcon and M. teleius were also found in M. scabrinodis nests during our survey (A. Tartally, unpublished data), which is not surprising since M. scabrinodis is a common host ant of both butterflies (for a review: Elmes et al. 1998, Als et al. 2004). One of the two nests infested by M. nausithous also contained a M. teleius larva. DISCUSSION To our knowledge, this is the first study to provide data on the host ant use of M. nausithous in Transylvania. The use of M. scabrinodis as a host ant by M. nausithous is, on the one hand, not surprising, since this was the only Myrmica ant species found in the vicinity of the initial larval host plant, while on the other hand being highly unusual, as this butterfly is found almost exclusively in nests of Myrmica rubra in other parts of its range (Thomas et al. 1989, Elmes et al. 1998, Korb 1998, Stankiewicz & Sielezniew 2002, Tartally & Varga 2005 and M. Witek, pers. comm.). Although Myrmica rubra occurs in Transylvania, where it is connected with damp forested habitats in the eastern part of the Carpathian-Basin, this ant is not known from the sites investigated here, despite extensive surveys by local myrmecologists (B. 377 Tartally, A. et al. — Myrmica scabrinodis: Host of Maculinea nausithous Markó, pers. comm.). Other Myrmica species (M. hellenica Finzi, M. sabuleti Meinert, M. schencki Viereck, and M. specioides Bondroit) have been recorded from the drier patches (Markó 1998, Markó & Csősz 2001; B. Markó, pers. comm.; A. Tartally, pers. observ.), but only M. scabrinodis is known from the boggy depressions where M. nausithous can lay eggs on S. officinalis. Thomas et al. (2005) provide some warnings and guidelines about recording host ant use in Maculinea butterflies, and although the sample of infested nests that we found was small, we believe that the comprehensive survey that we made of the Myrmica fauna on the investigated sites means that these records represent genuine specialization. The rate of parasitism of M. scabrinodis nests that we found was low (1.9% of nests investigated overall, 4.1% of nests at Răscruci), which is an order of magnitude lower than parasitism rates previously recorded for M. nausithous (Stankiewicz & Sielezniew 2002, Tartally & Varga 2005, A. Tartally, unpublished data; Mean parasitism rate of other studies = 44.9%; GLM with Binomial Errors: c2 = 56.79, d.f. = 3, p <0.0001). If the M. nausithous populations one these sites persist as a local metapopulation, then high variance in parasitism rates between sub-populations might be expected, so the significance of the low parasitism rate awaits further investigation. Our records are not the first of M. nausithous exploiting M. scabrinodis, since Munguira & Martín (1999) report this ant as a M. nausithous host from Spain. However, apart from this one record, this widespread Myrmica species has not been recorded as a host of M. nausithous on the other European sites studied (although M. scabrinodis is often common on those sites), where M. rubra is used exclusively (Thomas et al. 1989, Elmes et al. 1998, Korb 1998, Stankiewicz & Sielezniew 2002, Tartally & Varga 2005; see Fig. 1). Interestingly M. nausithous occurs only in western parts of Hungary where M. rubra is common on S. officinalis sites, but this butterfly does not occur in central and eastern parts of Hungary where M. rubra is rare or missing from such sites. However, M. scabrinodis is common in most of the Hungarian S. officinalis sites investigated (Fig. 1). Hence, it is an open question as to why the eastern Hungarian S. officinalis sites are not colonised from Transylvania by M. scabrinodis using M. nausithous. One reason could be that the high mountains of Muntii Apuseni are barriers for the isolated Transylvanian M. nausithous populations that inhibit spread to eastern Hungary. Another possible explana- 378 Sociobiology Vol. 51, No. 2, 2008 tion is that M. teleius and M. alcon populations are in competition with M. nausithous in eastern Hungary through their common use of M. scabrinodis as their primary host ant (Tartally & Csősz 2004, Tartally & Varga 2005; A. Tartally, unpublished data). Interestingly M. nausithous does not occur at Şardu (in a hilly region at the western border of the Transylvanian-Basin; N46°52’, E23°24’; 480 m; the easternmost “+” on Fig. 1) where a potential M. nausithous site is known near to the Câmpia Transilvaniei region, with high densities of S. officinalis and M. scabrinodis (A. Tartally, unpublished data). This site is, however, used by M. teleius and M. alcon (both butterflies exploit M. scabrinodis and M. vandeli Bondroit for host ant; A. Tartally, unpublished data), and appears more similar to the central and western European M. nausithous sites (with bushy forest edges; see: Tartally & Varga 2005: Fig. 2) than the sites investigated in the Câmpia Transilvaniei region (which are meadows with some isolated bushes; Fig. 2). All these facts suggest that the Transylvanian M. nausithous populations represent a specific life form that needs further investigation and protection. 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