Dispersal polymorphisms in invasive fire ants

S1 Dataset. Fire ant queen flight morphology and flight durations. http://journals.plos.org/plosone/article/asset?unique&id=info:doi/10.1371/journal.pone.0153955.s001 doi:10.1371/journal.pone.0153955.s001 (XLSX)In the Found or Fly (FoF) hypothesis ant queens experience reproduction-dispersal tradeoffs such that queens with heavier abdomens are better at founding colonies but are worse flyers. We tested predictions of FoF in two globally invasive fire ants, Solenopsis geminata (Fabricius, 1804) and S. invicta (Buren, 1972). Colonies of these species may produce two different monogyne queen types—claustral queens with heavy abdomens that found colonies independently, and parasitic queens with small abdomens that enter conspecific nests. Claustral and parasitic queens were similarly sized, but the abdomens of claustral queens weighed twice as much as those of their parasitic counterparts. Their heavier abdomens adversely impacted morphological predictors of flight ability, resulting in 32–38% lower flight muscle ratios, 55–63% higher wing loading, and 32–33% higher abdomen drag. In lab experiments maximum flight durations in claustral S. invicta queens decreased by about 18 minutes for every milligram of abdomen mass. Combining our results into a simple fitness tradeoff model, we calculated that an average parasitic S. invicta queen could produce only 1/3 as many worker offspring as a claustral queen, but could fly 4 times as long and have a 17- to 36-fold larger potential colonization area. Investigations of dispersal polymorphisms and their associated tradeoffs promises to shed light on range expansions in invasive species, the evolution of alternative reproductive strategies, and the selective forces driving the recurrent evolution of parasitism in ants.This work was supported by the National Science Foundation Graduate Research Fellowship to JAH, and University of Oklahoma Alumni Fellowship to JAH.Ye

New record of the pavement ant, Tetramorium immigrans (Hymenoptera: Formicidae), in South Dakota with notes on its thermal tolerance and geographic distribution

The pavement ant, Tetramorium immigrans, is an abundant and widespread species across large portions of the United States. Yet despite its current distribution in Northeastern, Midwestern, Pacific, and Western states, there is a surprising lack of records from the Great Plains. Here we present an updated county list of T. immigrans from museum collections and research grade observations (459 counties; ~15% of US counties), highlighting the first records from one Great Plains state—South Dakota. Observations on community science platforms since 2006 have undoubtedly increased the awareness of T. immigrans (+329 counties; ~72% of all county records), however we posit that such platforms may also highlight the dispersal limitations of this species into the less urban, colder Northern Great Plains states of Montana, Nebraska, North Dakota, South Dakota, and Wyoming (~5% of 291 counties). As such, we offer novel information on T. immigrans’ thermal biology including measurements of critical thermal limits, knock-down resistance, and chill coma recovery. While T. immigrans can likely tolerate the warm summer temperatures found in South Dakota due to its heat tolerance hovering around 46°C, its lower ability to tolerate cold winter conditions may be a possible mechanism for its limited dispersal

Range expansion drives the evolution of alternate reproductive strategies in invasive fire ants

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

Range expansion drives the evolution of alternate reproductive strategies in invasive fire ants

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

Claustral versus parasitic morphology (colony averages).

<p>Similar results apply when comparing colony averages. Claustral queens have (A) lower flight muscle ratios, (B) higher wing loading, and (C) higher abdomen drag than parasitic queens of the same species. (D) Claustral founders in <i>S</i>. <i>geminata</i> have evolved larger wings than parasitic queens, but in <i>S</i>. <i>invicta</i> there is no difference in wing size among queen types.</p

Maximum flight duration versus queen morphology.

<p>Maximum flight duration versus queen morphology.</p

Fire ant queen flight morphology.

<p>Fire ant queen flight morphology.</p

Queen flight morphology and abdomen mass.

<p>For all queen morphs heavier abdomens impact flight morphology by (A) decreasing flight muscle ratio, (B) increasing wing loading, and (C) increasing abdomen drag. GC = <i>S</i>. <i>geminata</i> claustral, GP = <i>S</i>. <i>geminata</i> parasitic, IC = <i>S</i>. <i>invicta</i> claustral, IP = <i>S</i>. <i>invicta</i> parasitic.</p

Flight duration and morphology.

<p>In claustral <i>S</i>. <i>invicta</i> queens, (A) heavier abdomens decrease a queen’s flight endurance due to (B) lower flight muscle ratios and (C) higher wing loading. Quantile regressions are through the top quartile.</p

Claustral versus parasitic flight morphology (individual queens).

<p>Heavier abdomens mean claustral queens experience (A) lower flight muscle ratios, (B) higher wing loading, and (C) higher abdomen drag than parasitic queens of the same species. (D) Claustral founders in <i>S</i>. <i>geminata</i> have evolved larger wings than parasitic queens, compensating somewhat for the wing loading effects of heavier abdomens. In <i>S</i>. <i>invicta</i>, however, there is either no difference in wing size (see text) or claustral queens have slightly smaller wings.</p