Raid process, activity pattern and influence of abiotic conditions in the slave-making ant Rossomyrmex minuchae (Hymenoptera, Formicidae)

Abstract

In the present work, we present the results of a study on the seasonal and daily activity, as well as on the raid process in Rossomyrmex minuchae. A comparative study of the annual and daily activity of the host species, Proformica longiseta, has also been made in parasitized and non-parasitized colonies. R. minuchae is an obligate slave-maker, in which the annual activity is strongly related to abiotic conditions, especially temperature and moisture of the soil. The raid process is comprised of three phases: scouting, assault of the host nest and robbing of the host brood. Recruitment of nestmates by mean of adult transport, concentration close to and invasion of the host nest, are the three tasks carried out by R. minuchae workers during the assault phase. Major differences between Rossomyrmex and Polyergus (the other obligate dulotic genus of the tribe Formicini) in terms of behaviour, both in nestmate recruitment and in the host-nest invasion, reflect different parasitic strategies in the two genera, supporting the assignment of these two genera to different phylogenetic groups.

Rossomyrmex, the Slave-Maker Ants from the Arid Steppe Environments

“…Despite this apparent difference in habitat (extended plains versus high mountains), the abiotic conditions are quite similar and are consistent with a typical arid steppe [7,18,19]. However, the main difference comes from the fact that the Spanish populations are small and are geographically isolated from each other [20].…”

“…Workers of the attacked nest can fight or flee although in Proformica the most common behaviour is flight probably because hosts always lose fights [24]. Interestingly, Rossomyrmex is the only reported slave-maker that exclusively uses adult transport and single recruitment chain instead of pheromones during raids [7,16,19], a behavior probably constrained by the arid habitat: raids take place in early summer when soil surface temperature can reach up to 30 ∘ C, a temperature for which pheromones would quickly evaporate [6,25]. This condition imposes that Rossomyrmex raids appears as less efficient than those carried out with pheromones; this together with the usually flee behavior of the Proformica hosts [19] permits the survival of several attacked nests [24].…”

“…This condition imposes that Rossomyrmex raids appears as less efficient than those carried out with pheromones; this together with the usually flee behavior of the Proformica hosts [19] permits the survival of several attacked nests [24]. Finally, another important difference in the raiding behavior of Rossomyrmex is that the return to the parasite nest with the robbed brood takes place at the following day of the assault instead of later in the same day [7].…”

“…Within the subfamily Formicinae only two genera fit the previous definition of slave-makers: Polyergus and Rossomyrmex [5][6][7]. The species of the Formica sanguinea group are facultative slave-makers [8,9].…”

“…Thus, in relation with the obligate slave-maker genera most of the published studies are focused on Polyergus biology (e.g., [10][11][12][13][14][15]) whereas the genus Rossomyrmex has received little attention, probably due to its geographic distribution and biology. However, this genus presents unique raiding [7,16] and mating [17] behaviors in ants (for a comparison with other Formicini genera see Table 1) that make its study very interesting from an evolutionary point of view.…”