The underdog invader: Breeding system and colony genetic structure of the dark rover ant (Brachymyrmex patagonicus Mayr)

Abstract

Ants are among the most successful species at invading new environments. Their success undeniably comes from their various modes of reproduction and colony breeding structures, which influence their dispersal ability, reproductive potential, and foraging strategies. Almost all invasive ant species studied so far form supercolonies, a dense network of interconnected nests comprising numerous queens, without aggression toward non-nestmates. This strategy results in invasive colonies that are able to grow extremely fast and large while avoiding intraspecific competition, allowing them to monopolize environmental resources and outcompete native species.Here, we developed and used 10 microsatellite markers to investigate the population structure and breeding system of the dark rover ant Brachymyrmex patagonicus Mayr in its introduced range. We determined whether this species exhibits a supercolonial structure by assessing whether different nests belonged to the same genetic colony. We inferred its dispersal ability by investigating isolation by distance and estimated the numbers of queens per colonies and mating per queen through parent-offspring inferences. We found that most of the colonies of B. patagonicus were comprised of a single nest, headed by a single queen. Each nest was distinct from one another, without isolation by distance, which suggests strong dispersal ability through nuptial flights. These features are commonly observed in noninvasive and native ant species, but they are surprising for a successful invasive ant, as they strongly differ from other invasive ants. Overall, we discuss how this seemingly unfavorable strategy for an invasive ant might favor the invasive success of the dark rover ant in the United States. K E Y W O R D Sants, colony breeding system, invasive species, monogyne, multicolonial structure

Divide and conquer: Multicolonial structure, nestmate recognition, and antagonistic behaviors in dense populations of the invasive ant Brachymyrmex patagonicus

“…Most trails analyzed in this study exhibited a relatively high level of relatedness, indicating the occurrence of a single reproductive queen in most colonies. These findings confirm previous results that a majority of invasive colonies of B. patagonicus are monogyne (Eyer et al, 2020). This study also highlights the need for multiple tools to efficiently infer the colony boundaries in socially complex species (Ellis et al, 2017;Eyer et al, 2017;Reiner Brodetzki & Hefetz, 2018).…”

“…High relatedness values between workers sampled on a given trail would suggest that they belong to a single colony. Moderate relatedness values may denote the foraging trail of a single, yet more diverse, colony (e.g., polygyne), as Eyer et al (2020) found the relatedness within polygyne colonies ranged from 0.16 to 0.64. In contrast, relatedness values close to zero would indicate that workers from different colonies forage on a common trail.…”

“…In 2007, this species has been reported in seven US states, but in less than a decade it has rapidly spread from coast to coast across 15 states and the Bahamas (Eyer et al, 2020;Guénard et al, 2012;Hill, 2017;MacGown et al, 2007;Martinez, 2010;Wheeler & Wheeler, 1978). More recently, this species has been reported in continental Asia (Guénard, 2018), Spain (Espadaler & Pradera, 2016), and Martinique (Carval et al, 2016).…”

“…Notably, in contrast with most invasive species, B. patagonicus does not form extensive supercolonies. Rather, each colony occupies a single nest, and the presence of a single or a few reproductive queens per colony enables significant relatedness among nestmates in many colonies (Eyer et al, 2020). A single queen, mated with up to four males, heads most of the colonies in four invasive populations in Texas, with only a fraction of the colonies (ca.…”

“…20%) being polygynous. This variation in the breeding system leads to a range of relatedness among nestmate workers between colonies, from genetically homogeneous colonies to more diverse ones (Eyer et al, 2020). Separate nests have been described in extremely close proximity (a few centimeters from each other), yet showed mutual tolerance, and populations were defined as extremely large, without an accurate estimation of colony density (MacGown et al, 2007).…”