Interspecific differences in cuticular hydrocarbon profiles of Myrmica ants are sufficiently consistent to explain host specificity by Maculinea (large blue) butterflies

Abstract

The chemical signatures on the cuticles of five common Myrmica ant species were analysed (49 colonies of M. rubra, M. ruginodis, M. sabuleti, M. scabrinodis and M. schencki), each ant being the specific host of one of the five threatened European species of Maculinea butterfly. The cuticular hydrocarbon profile (based on the relative abundance of each chemical) of each ant species was highly distinctive, even between the morphologically similar species M. sabuleti and M. scabrinodis. There was no significant difference in the chemical profiles of workers and larvae from any colony. Nor was there much pattern in the intraspecific variation: colonies from the same populations were significantly, but only slightly, more similar to each other than to colonies from distant populations. M. rubra showed remarkably little variation between populations sampled widely from northern Russia, Ukraine, Scotland and southern England. The data were compared with published profiles of M. rubra and two North American Myrmica species, and with a quantitative reanalysis of data for Maculinea rebeli caterpillars. We conclude that the hydrocarbon profiles of Myrmica species are sufficiently and consistently different for chemical mimicry to explain the pattern of host specificity recorded for the European Maculinea butterflies. The optimum strategy for chemical mimicry in each of the two life-styles of Maculinea larvae is discussed: we suggest that predatory species might benefit from mimicking the median profile of their model whereas the "cuckoo" species would benefit when variation between siblings encompasses a large range of the variation recorded within a local population of the model species.

The “Evolutionarily Significant Unit” concept and its applicability in biological conservation

“…After spending 10-15 days feeding on a species-specific food plant, Maculinea larvae drop to the ground and wait until they are found and carried into an ant nest by a Myrmica worker (Elmes et al 1991a;Akino et al 1999;Elmes et al 2002;Thomas 2002). Adoption of the parasite caterpillars by the host ants is mediated by chemical deception (Akino et al 1999;Schönrogge et al 2004;Nash et al 2008;Fürst et al 2011).…”

“…By contrast, caterpillars adopted within nests of other Myrmica species suppress their secretions and rely on the passive acquisition of their current host colony odour ). Acquired camouflage alone, however, is an insufficient mechanism to survive periods of stress or deprivation inside the colony, when worker ants become more discriminating (Elmes et al 2002).…”

Development of parasitic Maculinea teleius (Lepidoptera, Lycaenidae) larvae in laboratory nests of four Myrmica ant host species

“…It is known that cuticular hydrocarbons play an important role, both during the initial as well as the full integration phase of cuckoo Maculinea larvae with their host ant species (Akino et al, 1999;Elmes et al, 2002;Schönrogge et al, 2004;. Schönrogge et al (2004) showed that M. 'rebeli' larvae reared by colonies of its primary host species use chemical mimicry by an active production of hydrocarbons in addition to those found on pre-adoption larvae (and not necessarily shared with the host), whereas larvae kept in nests of non-host species seem to acquire chemical compounds from ants.…”

“…Maculinea larvae first feed on specific food plants and in their final instar they are adopted by Myrmica workers and taken into ant colonies where they spend 11-23 months Schönrogge et al, 2000;Witek et al, 2006). It is known that Maculinea larvae are picked up and carried to nests by workers of any Myrmica species that encounter them (Elmes et al, 1991a(Elmes et al, , 2002Akino et al, 1999;Thomas, 2002). The next and more important step is 'initial integration' into the ant society which takes place within the first 24-48 h inside the colony.…”

Myrmica ants host highly diverse parasitic communities: from social parasites to microbes

“…The adoption of the caterpillars by ants is mediated by chemical deception (Akino et al, 1999;Schönrogge et al, 2004;Fürst et al, 2012). As it has been demonstrated in the case of the cuckoo butterflies, Maculinea alcon (cruciata ecotype) preadoption caterpillars synthesize a simple mixture of cuticular hydrocarbons (CHC) that weakly mimic those of Myrmica species in general, but that have the closest match to the hydrocarbon signature of their local host ant M. schencki (Akino et al, 1999;Elmes et al, 2002). Yet the low level of chemical similarity means that preadoption butterfly caterpillars could be retrieved by any foraging Myrmica species that happen to encounter it, and not just by M. schencki (Akino et al, 1999;Elmes et al, 2002;Schönrogge et al, 2004;Thomas et al, 2013) although in the laboratory adoption appears to be the most rapid with this local, main host ant species.…”