Highly divergent cuticular hydrocarbon profiles in the cleptobiotic ants of the Ectatomma ruidum species complex

Abstract

In social insects, chemical communication is the main communication mode among colony members, which use the blends of cuticular hydrocarbons as recognition cues to discriminate between nestmates and non-nestmates and to prevent the exploitation of their nest resources by aliens. The aim of this study was to assess the variation of nestmate recognition cues in the ant Ectatomma ruidum, a species complex with a considerably conserved morphology and one of the few ant species where intraspecific thievery, a form of cleptoparasitism, has been reported. We analyzed the cuticular hydrocarbon profiles of ants collected from a number of geographically separated populations, and examined DNA sequence data to assess their species identity. We focused on one species of the complex, E. ruidum sp. 3-4, whose species delineation remains controversial. We documented that several quantitative and qualitative traits of the cuticular hydrocarbon profiles varied significantly between populations, indicating that this species harbors more cuticular chemical phenotypic diversity than expected within a single species. In particular, there was a striking divergence among populations in the proportion of methylalkanes, alkenes, alkadienes and odd-chain components, which likely play a major role in nestmate/non-nestmate discrimination, a process which might have been crucial in these cleptobiotic ants. Further investigations are needed to test the hypothesis that biotic pressures, such as the need to discriminate conspecific intruders and limit thievery, could have played an important role in promoting the evolutionary divergence between populations in this ant species complex.

Genome-wide and cuticular hydrocarbon evidence shed light on potential drivers of speciation in a Neotropical ant species complex

“…New CHC extractions were performed following Peña-Carrillo et al (2021a). We used the Bray-Curtis distances as dissimilarity measures to calculate chemical distances between the 156 examined specimens based on the relative abundances of the simplified chemical profile.…”

“…We used the Bray-Curtis distances as dissimilarity measures to calculate chemical distances between the 156 examined specimens based on the relative abundances of the simplified chemical profile. This was obtained by summing the percentages of hydrocarbons with the same carbon-chain length by class (Peña-Carrillo et al 2021a). We then calculated the chemical distance between populations (centroids) and used them to obtain a hierarchical cluster dendrogram using the program Primer 6 & Permanova + (Anderson 2017).…”

“…3, 4 and 2x3) had a high number of polymorphic sites, and a detailed examination indicated the presence of two functional mt genomes within these specimens. Peña-Carrillo et al (2021a) analyzed the CHC profiles of specimens assigned to E. ruidum from populations across its known geographic distribution, focusing on the heteroplasmic populations from southeast Mexico. The CHC profiles varied considerably among populations, supporting the existence of various evolutionary lineages within the complex.…”

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“…As previously highlighted by Debout et al [80], such a predominance of queenless nests, combined with the fact that gynes were significantly more numerous in these queenless nests, could indicate that this species is polydomous. Based on the total number of complete nests collected (152) and the number of queenright nests among them (33), one could argue that an average polydomous colony has 4.6 nests. However, this figure should be taken with caution and probably overestimates the actual number of satellite nests in our study area since previous results [58,75] indicate that the absence of queens, at least in a fraction of the population, is a phenomenon that probably reflects the average natural mortality of colonies due to queen death or severe damage from heavy rains, as confirmed by the relatively high rate of abandoned nests (12.7%) reported in our study.…”

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“…These are Ectatomma ruidum sp. 1, 2, 3-4, 5 and a possible 2x3 hybrid [31][32][33][34]. In terms of habitat, this species complex is widely distributed, occupying agricultural systems, savannas, and forests from sea level to an altitude of 1500-1600 m [26] and up to 2200 m [35].…”