Reproductive strategy: an essential component in the success of incipient colonies of the invasive Argentine ant (original) (raw)
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Understanding the invasion process of an exotic species could be useful to manage its dispersion in natural habitats. To that effect, we provide new data on the queens' biological and physiological characteristics in Linepithema humile (MAYR, 1868) colonies from both the invasion front (contact area) and the totally invaded area (invaded area) in order to examine the differences between them. We analyze: 1) queen densities per liter of nest soil, 2) fat content (%), 3) oviposition rates, and 4) the queen / worker thorax volume ratios of individuals from nests situated in the contact and invaded zones. All these parameters are good estimators of the invasive capabilities of colonies, as they are related to dispersion speed and successful colony foundation. Although we did not detect physiological differences in the fat content and oviposition rates of queens from the two zones, we found evidence of differences in the social structure of nests (queen densities) and in the morphology of queens (queen / worker thorax volume ratios) between nests from the invasion's contact and invaded zones. In the former there were bigger queens and higher queen densities than in the latter. Those differences are probably a response to the different ecological contexts of the two zones and would provide the colonies in the contact zone of the invasion with a higher invasiveness potential for competing with the native ant community for empty niches and resources.
Researches on Population Ecology, 1995
In contrast to what is generally believed, the reproductive strategies of ants are remarkably diverse and include such different phenomena, as wingless female and male sexuals, reproduction by mated workers, thelytokous parthenogenesis, and complete workerlessness. We review the various reproductive life histories and investigate them in the light of recent models on the evolution of dispersal strategies and multiple-queening. It appears that most deviations from "normal" colony propagation can be explained by a decreased success of dispersal and solitary founding by solitary queens in certain types of habitats. Consequently, alternative reproductive strategies are found especially in those species, in which environmental conditions or a highly specialized way of life are thought to make solitary founding costly. Among the key factors, which determine the success of reproductive strategies, appear to be spatial and temporal distribution of habitats and the availability of nest sites.
Annals of the Entomological Society of America, 2012
The ecological success of invasive ants has been linked to their ability to form expansive supercolonies. In the Argentine ant, Linepithema humile (Mayr), increased productivity and competitive ability of introduced supercolonies in several places, e.g., California and southern Europe, has been linked to high population densities that could have been attained via fusion of nonaggressive and genetically similar nests. Recently, we have found that introduced L. humile colonies in the southeastern United States, which have higher levels of intraspecific aggression and genetic diversity than those in California and southern Europe, sometimes also fuse; yet it is unclear what the longer term consequences of such colony fusion might be. In this study, we examined whether fusion of these southeastern United States L. humile colonies results in larger colonies by recording colony size and productivity in pairs that fused and in pairs that did not fuse. After 6 mo, colonies that fused produced 47% more workers and had twice as many queens as colony pairs that did not fuse. Also, fused colonies had an overall per capita colony productivity (number of brood and workers produced per queen and per worker) comparable to that of nonfused pairs and unpaired controls. Furthermore, all queens contributed to worker pupae production in fused colonies. Thus, fusion of initially aggressive southeastern United States L. humile colonies results in colonies with higher worker number without decreasing per capita productivity. Moreover, offspring contribution by all queens in fused colonies may alter colony genotypic composition resulting in reduced intraspecific aggression that in turn promotes further fusion. This process may be relevant to the establishment of incipient colonies in areas where multiple introductions have occurred.
Partitioning of reproduction among queens in the Argentine ant, Linepithema humile
Animal Behaviour, 2001
We investigated how queens share parentage (skew) in the Argentine ant, Linepithema humile, a social insect with multiple queens (polygyny). Overall, maternity of 546 male and female sexuals that mated successfully was determined with microsatellites in 26 colonies consisting of two queens and workers. The first main finding was that queens all contributed to sexual production. However, there was a significant departure from equal contribution to male and female sexual production in a notable proportion of colonies. Overall, reproductive skew for sexual (male and female) production was relatively low but higher than reproductive skew for egg production. The second interesting result was that there was a trade-off in the relative contribution of queens to male and female production. The queens contributing more to male production contributed significantly less to female sexual production. Finally, there was no significant association between colony productivity and the degree of reproductive skew. The relatively low reproductive skew is in line with predictions of the so-called concession models of reproductive skew because, in the Argentine ant, relatedness between queens is low and ecological constraints on dispersal nonexistent or weak.
The polygynous invasive ant Lasius neglectus was described from Budapest, Hungary, as an unicolonial species, with no apparent colony barriers, and inferred intranidal mating without a nuptial flight. Here we analyze additional morphological characteristics of gynes, their physiological condition at emergence and at the time of mating and we describe the productivity of different types of colony founding in the laboratory. A low increase in dry weight and in fat content from emergence to mating indicates that gynes can only succeed in dependent colony founding. However, the queen-worker thorax volume ratio is typical of a species with independent colony founding and we were able to demonstrate independent colony founding in the laboratory (both haplo-and pleometrotic). Brood development in independent founding is rapid and the number of nanitics higher than in other Lasius species. Both colony budding and dependent colony founding could also be demonstrated in the laboratory. Worker oviposition was absent. The carbohydrate content of newly mated queens is consistent with the observed loss of mating flight of this species. However the relative wing area clearly indicates that L. neglectus queens should be able to fly. Therefore, both queen morphology and physiological state at maturity show that L. neglectus is intermediate between a monogynous, free-living, non pest ant and a multiqueened (polygynic) invasive tramp ant. This neglected ant thus offers interesting opportunities to study the origin of unicoloniality and the spread of this species in northeast Spain.
Behavioral Ecology, 1998
Newly produced queens from monogyne (single-queen) colonies of the ant Solenopsis invicta usually initiate reproduction independently, that is, without worker assistance. However, some recently mated queens attempt to bypass this risky phase of new colony foundation by entering established nests to reproduce, although it is unclear how often these queens are successful in natural populations. We surveyed a mature monogyne population of 5. invicta in both 1995 and 1996 for colonies headed by queens incapable of independent colony founding (diploid-male-producing queens) in order to estimate the frequency of colonies that are headed by queens that initiated reproduction within established nests (adopted queens). Using the frequency of diploid-male-producing queens among the recently mated queens in this population, we estimated that the overall rate of queen replacement by adopted queens is about 0.7% per colony per year. Although theory suggests that a change to a novel queen reproductive tactic could be associated with a fundamental change in social organization (queen number), this does not appear to be the case in monogyne S. invicta. However, the evolution of nest-infiltrating reproductive tactics by queens in a monogyne population and the evolution of multiple-queen societies may result from similar ecological pressures facing newly mated queens. We therefore incorporate this strategy into an existing theoretical framework that was developed to explain the evolution of alternative social organizations in ants, providing testable predictions regarding the distribution and frequency of queen adoption in other single-queen ant societies. Key uxrrds: alternative reproductive tactics, fire ants, polygyny,
colonisation of the Argentine ant, Linepithema
2016
Background: The Argentine ant, Linepithema humile, is a widespread invasive ant species that has successfully established in nearly all continents across the globe. Argentine ants are characterised by a social structure known as unicoloniality, where territorial boundaries between nests are absent and intraspecific aggression is rare. This is particularly pronounced in introduced populations and results in the formation of large and spatially expansive supercolonies. Although it is amongst the most well studied of invasive ants, very little work has been done on this ant in South Africa. In this first study, we investigate the population structure of Argentine ants in South Africa. We use behavioural (aggression tests) and chemical (CHC) approaches to investigate the population structure of Argentine ants within the Western Cape, identify the number of supercolonies and infer number of introductions. Results: Both the aggression assays and chemical data revealed that the Western Cap...
A native ant armed to limit the spread of the Argentine ant
Biological Invasions, 2010
Argentine ants (Linepithema humile) usually actively displace native ants through a combination of rapid recruitment, high numerical dominance and intense aggressive fights. However, in some cases, native ants can offer a strong resistance. In Corsica, a French Mediterranean island, local resistance by the dominant Tapinoma nigerrimum has been proposed as a factor limiting Argentine ant invasion. With the aim of evaluating the abilities of T. nigerrimum in interference and exploitative competition, this study tested in the laboratory the aggressive interactions between this native dominant ant and the invasive Argentine ant. We used four different assays between L. humile and T. nigerrimum: (1) worker dyadic interactions, (2) symmetrical group interactions, (3) intruder introductions into an established resident colony, and (4) a competition for space and food. This study confirms the ability of Argentine ants to compete with native species, by initiating more fights, using cooperation and simultaneously deploying physical and chemical defenses. However, despite Argentine ant fighting capabilities, T. nigerrimum was more efficient in both interference and exploitative competition. Its superiority was obvious in the space and food competition assays, where T. nigerrimum dominated food in 100% of the replicates after 1 h and invaded Argentine ant nests while the reverse was never observed. The death feigning behavior exhibited by Argentine ant workers also suggests the native ant’s superiority. Our study thus demonstrates that T. nigerrimum can offer strong competition and so may be able to limit the spread of Argentine ants in Corsica. This confirms that interspecific competition from ecologically dominant native species can affect the invasion success of invaders, notably by decreasing the likelihood of incipient colony establishment and survival.
Range expansion drives the evolution of alternate reproductive strategies in invasive fire ants
NeoBiota, 2017
Many species are expanding their ranges in response to climate changes or species introductions. Expansion-related selection likely drives the evolution of dispersal and reproductive traits, especially in invasive species introduced into novel habitats. We used an agent-based model to investigate these relationships in the red imported fire ant, Solenopsis invicta, by tracking simulated populations over 25 years. Most colonies of this invasive species produce two types of queens practicing alternate reproductive strategies. Claustral queens found new colonies in vacant habitats, while parasitic queens take over existing colonies whose queens have died. We investigated how relative investment in the two queen types affects population demography, habitat occupancy, and range expansion. We found that parasitic queens extend the ecological lifespan of colonies, thereby increasing a population's overall habitat occupancy as well as average colony size (number of workers) and territory size. At the same time, investment in parasitic queens slowed the rate of range expansion by diverting investment from claustral queens. Divergent selection regimes caused edge and interior populations to evolve different levels of reproductive investment, such that interior populations invested heavily in parasitic queens whereas those at the edge invested almost entirely in claustral queens. Our results highlight factors shaping ant life histories, including the evolution of social parasitism, and have implications for the response of species to range shifts.