Army imposters: diversification of army ant-mimicking beetles with their Eciton hosts

Abstract

Colonies of neotropical army ants of the genus Eciton Latreille offer some of the most captivating examples of intricate interactions between species, with hundreds of associated species already described in colonies of Eciton burchellii Westwood. Among this plethora of species found with Eciton colonies, two genera of staphylinid beetles, Ecitomorpha Wasmann, and Ecitophya Wasmann, have evolved to mimic the appearance and parallel the colouration of the most abundant ant worker cast. Here, we study for the first time the association of these antmimicking beetles with their ant host in an evolutionary and population genetics framework. The central emphasis is on colonies of E. burchellii, the only Eciton species that harbours both genera of ant-mimicking beetles. Phylogenetic and population structure analyses using the same mtDNA COI region (802bp) for ants and beetles indicated that speciation patterns of the myrmecophiles were congruent with specialization to a particular Eciton (sub)species. Therefore, current taxonomic treatments of Eciton and its Ecitomorpha and Ecitophya associates need revision. Molecular clock analyses suggested that diversification of the Eciton hosts pre-date that of their guests, with a possible earlier association of Ecitophya (found with a large number of Eciton species) than with Ecitomorpha (found only with E. burchellii colonies). Population-level analyses revealed that patterns of diversification for the myrmecophiles are also consistent with specialisation to a particular host across broad geographical areas but not at small geographical scales, with gene flow within each species found between host colonies even across landscape features that are strong barriers for Eciton female-mediated gene flow.

Eciton Army Ants—Umbrella Species for Conservation in Neotropical Forests

“…However, further taxonomic revisions are required to delimit species and subspecies boundaries. For example, a phylogeographic study based on mitochondrial DNA sequences indicated that genetic divergence of E. burchellii foreli and E. b. parvispinum colonies was higher than between other morphologically described species [51].…”

“…species within the genus Alloiodites [37], to host-specific and only found with colonies of a single Eciton species, e.g. Ecitophya, Ecitomorpha [51]. Some beetles are found in refuse deposits feeding either on dead workers or booty refuse, with reports of flying between bivouacs (e.g.…”

“…However, later taxonomic treatments lumped several species into a single one, due to the difficulties in finding consistent morphological characters, including colouration, to separate species [104,106]. Using an evolutionary and population genetics framework, analyses of mitochondrial DNA sequences of Eciton hosts and their associated Ecitomorpha and Ecitophya, collected in different areas in east and west Panama, revealed that the speciation pattern of these two myrmecophiles was congruent with specialization to a single species (or subspecies) of Eciton host [51]. Molecular clock analyses conducted in this study suggested that Eciton host diversification pre-dated that of their hunting guests, and that Ecitophya have been associated with Eciton for a longer period of evolutionary time than Ecitomorpha [51].…”

“…Using an evolutionary and population genetics framework, analyses of mitochondrial DNA sequences of Eciton hosts and their associated Ecitomorpha and Ecitophya, collected in different areas in east and west Panama, revealed that the speciation pattern of these two myrmecophiles was congruent with specialization to a single species (or subspecies) of Eciton host [51]. Molecular clock analyses conducted in this study suggested that Eciton host diversification pre-dated that of their hunting guests, and that Ecitophya have been associated with Eciton for a longer period of evolutionary time than Ecitomorpha [51]. Furthermore, patterns of diversification of the two hunting guests were also consistent across broad geographical areas but not at small geographical scales, with evidence of gene flow between colonies even across large water features [51].…”

Benefits of insect colours: a review from social insect studies

“…This type of mimicry is named Batesian; and mimetic species are highly variable in the degree of their similarity to models (Edmunds 2000 ). Pérez-Espona et al ( 2018 ) studied Ecitomorpha and Ecitophya beetle species which were protected from predation through mimicry (body shape and colour) to the army ant Eciton burchellii . On the other hand, there are some examples when less chemically defended social insects mimic those which are stronger protected.…”