Prenolepis Imparis Research Articles

Critical thermal limits and temperature-dependent walking speed may mediate coexistence between the native winter ant (Prenolepis imparis) and the invasive Argentine ant (Linepithemahumile)

Comparing the thermal tolerance and performance of native and invasive species from varying climatic origins may explain why some native and invasive species can coexist. We compared the thermal niches of an invasive and native ant species. The Argentine ant (Linepithema humile) is an invasive species that has spread to Mediterranean climates worldwide, where it is associated with losses in native arthropod biodiversity. In northern California, long-term surveys of ant biodiversity have shown that the winter ant (Prenolepis imparis) is the native species best able to coexist with Argentine ants. Both species tend hemipteran scales for food, and previous research suggests that these species’ coexistence may depend on seasonal partitioning: winter ants are active primarily in the colder winter months, while Argentine ants are active primarily in the warmer months in northern California.We investigated the physiological basis of seasonal partitioning in Argentine and winter ants by a) measuring critical thermal limits, and b) comparing how ant walking speed varies with temperature. While both species had similar CTmax values, we found differences between the two species' critical thermal minima that may allow winter ants to remain functional at ecologically relevant temperatures between 0 and 2.5 °C. We also found that winter ants' walking speeds are significantly less temperature-dependent than those of Argentine ants. Winter ants walk faster than Argentine ants at low temperatures, which may allow the winter ants to remain active and forage at lower winter temperatures. These results suggest that partitioning based on differences in temperature tolerance promotes the winter ant's continued occupation of areas invaded by the Argentine ant.

Phylogeography and population genetics of a widespread cold-adapted ant, Prenolepis imparis.

As species arise, evolve and diverge, they are shaped by forces that unfold across short and long timescales and at both local and vast geographical scales. It is rare, however, to be able document this history across broad sweeps of time and space in a single species. Here, we report the results of a continental-scale phylogenomic analysis across the entire range of a widespread species. We analysed sequences of 1402 orthologous ultraconserved element (UCE) loci from 75 individuals to identify population genetic structure and historical demographic patterns across the continent-wide range of a cold-adapted ant, the winter ant, Prenolepis imparis. We recovered five well-supported, genetically isolated clades representing lineages that diverged from 8.2-2.2 million years ago. These include: (i) an early diverging lineage located in Florida, (ii) a lineage that spans the southern United States, (iii) populations that extend across the midwestern and northeastern United States, (iv) populations from the western United States and (v) populations in southwestern Arizona and Mexico. Population genetic analyses revealed little or no gene flow among these lineages, but patterns consistent with more recent gene flow among populations within lineages, and localized structure with migration in the western United States. High support for five major geographical lineages and lack of evidence of contemporary gene flow indicate in situ diversification across the species' range, producing relatively ancient lineages that persisted through subsequent climate change and glaciation during the Quaternary.

Changes in the core species of the ant-plant network of oak forest converted to grassland: replacement of its ant functional groups.

Land-use change in terrestrial environments is one of the main threats to biodiversity. The study of ant-plant networks has increased our knowledge of the diversity of interactions and structure of these communities; however, little is known about how land-use change affects ant-plant networks. Here we determine whether the change in land use, from native oak forest to induced grassland, affected the network properties of ant-plant networks in a temperate forest in Mexico. We hypothesize that the disturbed vegetation will be more nested and generalized due to the addition of generalist species to the network. The oak forest network comprises 47 plant species and 11 ant species, while the induced grassland network has 35 and 13, respectively. Floral nectar was the resource used most intensely by the ants in both vegetation types. The ant-plant network of the induced grassland was significantly more nested and generalist than that of the oak forest; however, none of the networks were nested when considering the frequency of interaction. In both vegetation types, the ants were more specialized than the plants, and niche overlap was low. This could be related to the dominant species present in each type of vegetation: Prenolepis imparis in the oak forest and Camponotus rubrithorax in the grassland. The central core of cold climate ant species in the oak forest was replaced by a central core of subordinate Camponotini and tropical specialists in the induced grassland. These results suggest that the increase in nestedness and generalization in the grassland may be related to the loss of the cold climate specialists from the core of the oak forest network. Our findings provide evidence that land-use change increases the level of generalization in the ant-plant interaction networks of temperate forests.

Tree Preference and Temporal Activity Patterns for a Native Ant Community in an Urbanized California Woodland

Anthropogenic disturbances, including land use change and exotic species, can alter the diversity and dynamics of ant communities. To examine foraging behavior in an urbanized habitat in northern California, we surveyed the presence of 9 ant species on 876 trees across 4 seasons during both day and night in a 9.5-hectare urbanized oak-exotic woodland. Ants were more likely to be observed on native, evergreen trees, suggesting that native evergreen species may help maintain ant diversity. Species showed clear patterns of temporal partitioning of foraging activity. Ant species varied in their use of native evergreen Quercus agrifolia trees across season and day/night axes. Of the 3 ant species most frequently observed, Camponotus semitestaceus was most active during spring and summer nights, Formica moki was most active during spring and summer days, and Prenolepis imparis was most active during both day and night during fall and winter. Liometopum occidentale was the second most active species during summer day and night, and winter day. Our findings demonstrate that an oak-exotic urban woodland in Northern California was able to maintain a native ant community, and strong temporal partitioning within that community.

Neither ant dominance nor abundance explain ant-plant network structure in Mexican temperate forests.

BackgroundAnt-plant mutualistic networks tend to have a nested structure that contributes to their stability, but the ecological factors that give rise to this structure are not fully understood. Here, we evaluate whether ant abundance and dominance hierarchy determine the structure of the ant-plant networks in two types of vegetation: oak and grassland, in two temperate environments of Mexico: Flor del Bosque State Park (FBSP) and La Malinche National Park (MNP). We predicted that dominant and abundant ant species make up the core, and submissives, the periphery of the network. We also expected a higher specialization level in the ant trophic level than in plant trophic level due to competition among the ant species for the plant-derived resources.MethodsThe ant-plant interaction network was obtained from the frequency of ant-plant interactions. We calculated a dominance hierarchy index for the ants using sampling with baits and evaluated their abundance using pitfall traps.ResultsIn MNP, the Formica spp. species complex formed the core of the network (in both the oak forest and the grassland), while in FBSP, the core species were Prenolepis imparis (oak forest) and Camponotus rubrithorax (grassland). Although these core species were dominant in their respective sites, they were not necessarily the most dominant ant species. Three of the four networks (oak forest and grassland in FBSP, and oak forest in MNP) were nested and had a higher number of plant species than ant species. Although greater specialization was observed in the ant trophic level in the two sites and vegetations, possibly due to competition with the more dominant ant species, this was not statistically significant. In three of these networks (grassland and oak forest of MNP and oak forest of FBSP), we found no correlation between the dominance hierarchy and abundance of the ant species and their position within the network. However, a positive correlation was found between the nestedness contribution value and ant dominance hierarchy in the grassland of the site FBSP, which could be due to the richer ant-plant network and higher dominance index of this community.ConclusionsOur evidence suggests that ant abundance and dominance hierarchy have little influence on network structure in temperate ecosystems, probably due to the species-poor ant-plant network and a dominance hierarchy formed only by the presence of dominant and submissive species with no intermediate dominant species between them (absence of gradient in hierarchy) in these ecosystems.

Transcriptomic signatures of cold adaptation and heat stress in the winter ant (Prenolepis imparis).

Climate change is a serious threat to biodiversity; it is therefore important to understand how animals will react to this stress. Ectotherms, such as ants, are especially sensitive to the climate as the environmental temperature influences myriad aspects of their biology, from optimal foraging time to developmental rate. In this study, we conducted an RNA-seq analysis to identify stress-induced genes in the winter ant (Prenolepis imparis). We quantified gene expression during heat and cold stress relative to a control temperature. From each of our conditions, we sequenced the transcriptome of three individuals. Our de novo assembly included 13,324 contigs that were annotated against the nr and SwissProt databases. We performed gene ontology and enrichment analyses to gain insight into the physiological processes involved in the stress response. We identified a total of 643 differentially expressed genes across both treatments. Of these, only seven genes were differentially expressed in the cold-stressed ants, which could indicate that the temperature we chose for trials did not induce a strong stress response, perhaps due to the cold adaptations of this species. Conversely, we found a strong response to heat: 426 upregulated genes and 210 downregulated genes. Of these, ten were expressed at a greater than ten-fold change relative to the control. The transcripts we could identify included those encoding for protein folding genes, heat shock proteins, histones, and Ca2+ ion transport. One of these transcripts, hsc70-4L was found to be under positive selection. We also characterized the functional categories of differentially expressed genes. These candidate genes may be functionally conserved and relevant for related species that will deal with rapid climate change.

Intraspecific variation in thermal acclimation and tolerance between populations of the winter ant, Prenolepis imparis.

Thermal phenotypic plasticity, otherwise known as acclimation, plays an essential role in how organisms respond to short‐term temperature changes. Plasticity buffers the impact of harmful temperature changes; therefore, understanding variation in plasticity in natural populations is crucial for understanding how species will respond to the changing climate. However, very few studies have examined patterns of phenotypic plasticity among populations, especially among ant populations. Considering that this intraspecies variation can provide insight into adaptive variation in populations, the goal of this study was to quantify the short‐term acclimation ability and thermal tolerance of several populations of the winter ant, Prenolepis imparis. We tested for correlations between thermal plasticity and thermal tolerance, elevation, and body size. We characterized the thermal environment both above and below ground for several populations distributed across different elevations within California, USA. In addition, we measured the short‐term acclimation ability and thermal tolerance of those populations. To measure thermal tolerance, we used chill‐coma recovery time (CCRT) and knockdown time as indicators of cold and heat tolerance, respectively. Short‐term phenotypic plasticity was assessed by calculating acclimation capacity using CCRT and knockdown time after exposure to both high and low temperatures. We found that several populations displayed different chill‐coma recovery times and a few displayed different heat knockdown times, and that the acclimation capacities of cold and heat tolerance differed among most populations. The high‐elevation populations displayed increased tolerance to the cold (faster CCRT) and greater plasticity. For high‐temperature tolerance, we found heat tolerance was not associated with altitude; instead, greater tolerance to the heat was correlated with increased plasticity at higher temperatures. These current findings provide insight into thermal adaptation and factors that contribute to phenotypic diversity by revealing physiological variance among populations.

Facultative mutualism increases survival of an endangered ant-tended butterfly

Much of our understanding of mutualism is derived from pairwise obligate interactions between specialized participants. These observations may not adequately inform conservation efforts for facultative mutualist species, especially for areas in which invasive species are present and affect the mutualism. We evaluate the effects of ant attendance on larval survival for the endangered Fender’s blue butterfly (Icaricia icarioides fenderi Macy) in situ and examine the effects of biotic and abiotic factors—specifically ant community composition and microhabitat structure—on this mutualistic interaction in Oregon, USA. Fender’s blue larval survival was as much as three times higher in plots with a high proportion of ant attendance compared to plots in which larvae were rarely tended, and ant recruitment was reduced by dense, invasive European grasses. Thatch from these dense invasives, specifically tall oatgrass (Arrhenatherum elatius Beauv.) and tall fescue (Schedonorus arundinaceus Schreb.), are a threat to larval survival. In addition, variation in microhabitat structure determined which ant species occurred in our plots. Larvae were associated with ten ant species but primarily tended by only two: Prenolepis imparis Say and Aphaenogaster occidentalis Emery, and we observed no difference in butterfly larval survival between the two predominant ant species. Conservation efforts for this species would benefit from actions that reduce invasive grasses and facilitate ant tending interactions. Our study demonstrates how invasive grasses and forbs in degraded prairie systems can negatively impact the conservation of an at-risk species by disrupting an important mutualistic interaction.

Asian needle ant (Brachyponera chinensis) and woodland ant responses to repeated applications of fuel reduction methods

AbstractAnts (Formicidae: Hymenoptera) are important components of forest ecosystems and can be affected by fuel reduction forest management practices. We assessed the impact of repeated applications of fuel reduction treatments on abundance and diversity of ants within upland mixed‐hardwood forests in the Southern Appalachian Mountains in North Carolina, USA. We established three replicate blocks (~56 ha each) and split each block into four fuel reduction treatments, which included prescribed burning (B), mechanical felling (M), a combination of prescribed burning and mechanical felling (MB), and a control (C; i.e., no treatment). We implemented treatments multiple times (two mechanical thinnings and four prescribed burns) over the course of a 15‐yr period. Due to tree mortality and resultant canopy gaps from high‐severity burns, forest structure was dramatically altered in MB. Over a 3‐yr period (2014–2016), we captured 54,219 ants comprised of 23 genera using pitfall and colored pan traps. Prenolepis imparis was the most common ant species collected, and it was significantly lower in abundance in MB than all other treatments. However, the non‐native species Brachyponera chinensis was more abundant in MB than all other treatments. Thus, some fuel reduction treatments may have consequences for invasive ant colonization in forests. Most ant taxa did not differ in abundance among treatments, suggesting that some fuel reduction practices may affect some, but not all ant species. Our results indicate that some fuel reduction treatments can alter forest ant communities, thus contributing to changing forest ecosystem dynamics. Monitoring of ants and other bioindicators after repeated rounds of fuel reduction treatments could provide useful knowledge that can be used to help balance forest management and biological diversity.

Foraging behavior and locomotion of the invasive Argentine ant from winter aggregations.

The collective behavior of ant colonies, and locomotion of individuals within a colony, both respond to changing conditions. The invasive Argentine ant (Linepithema humile) thrives in Mediterranean climates with hot, dry summers and colder, wet winters. However, its foraging behavior and locomotion has rarely been studied in the winter. We examined how the foraging behavior of three distinct L. humile colonies was related to environmental conditions and the locomotion of workers during winter in northern California. We found that colonies foraged most between 10 and 15°C, regardless of the maximum daily temperature. Worker walking speed was positively associated with temperature (range 6–24°C) and negatively associated with humidity (range 25–93%RH). All colonies foraged during all day and night hours in a predictable daily cycle, with a correlation between the rate of incoming and outgoing foragers. Foraging activity was unrelated to the activity of a competing native ant species, Prenolepis imparis, which was present in low abundance, and ceased only during heavy rain when ants left foraging trails and aggregated in small sheltered areas on trees.

Winter Ant, False Honey Ant Prenolepis imparis (Say) (Insecta: Hymenoptera: Formicidae: Formicinae)

This EDIS publication is an alternate version of a page published first on the Featured Creatures website. The Featured Creatures collection provides in-depth profiles of insects, nematodes, arachnids and other organisms relevant to Florida. These profiles are intended for the use of interested laypersons with some knowledge of biology as well as academic audiences. This 5-page fact sheet that discusses the winter ant was written by Jason L. Williams and Andrea Lucky, and published by the UF Entomology and Nematology Department, February 2017.
 EENY-675/IN1168: Winter Ant, False Honey Ant Prenolepis imparis (Say) (Insecta: Hymenoptera: Formicidae: Formicinae) (ufl.edu)

Winter activity of the European false honeypot ant, Prenolepis nitens (Mayr, 1853)

Cryophily, or negative thermotropism, is a poorly documented phenomenon in ants. Only a few species have been reported to be active at such extremely low temperatures that would incapacitate other ant species. In this study, the winter activity of the European false honeypot ant, Prenolepis nitens, was investigated in an oak forest in mid-western Hungary. The results suggest that P. nitens similar to its North American sister species, Prenolepis imparis, has no definite winter hibernation period and, unlike most temperate ant species, it remains active above-ground all winter and early spring, foraging whenever temperature allows movement, even when temperatures are near freezing.

Intermediate disturbance promotes invasive ant abundance

Urban habitats are undergoing a faunal and floral homogenization process worldwide. We investigated how such homogenization influences ant communities. We monitored ant species richness and abundance in natural, semi-natural, urban, and agricultural habitats for one year, along an urban–rural gradient in the San Francisco Bay Area, and examined which human-related and other environmental variables most affect ant distribution. We investigated whether alien ant species have an advantage in human-modified habitats. We found that distance from buildings was the most important factor affecting ant distribution. In total, we recorded 17 ant species, of which four were non-native. Native ant species richness was highest in natural habitats, and alien species richness was highest in urban habitats. Remarkably, in a sample of 19,450 ant workers at food baits, the highest ant abundance across all seasons was in the semi-natural habitat where usually only the invasive Argentine ant (Linepithema humile), representing 81% of all ants seen at baits, and the native winter ant (Prenolepis imparis) were present. Agricultural habitats had a surprisingly high number of native and alien species. It appears that the invasive Argentine ant creates a favorable ecological community in semi-natural environments, where they compete successfully with the native species, and do not face the increased competition with other alien species that they encounter in urban habitats. Even well protected natural habitat may be favorable for invasive species, due to its proximity to human disturbance.

Corrected Identification of a Cold-Foraging Ant,Nylanderiasp.1, in Saltillo, Mexico

Sanchez-Peña (2013) reported an ant species foraging at remarkably low temperature (5°C) in Saltillo, Mexico. The ant was reported to be the known cryophilic formicine ant, Prenolepis imparis Say. However, further revision of these worker ants by Sergio R. Sánchez-Peña and Joe A. MacGown indicated that the ants were a species of the closely related and recently redefined genus Nylanderia (Kallal and LaPolla 2012, MacGown 2013). LaPolla et al. (2010) reviewed the species of the Prenolepis group of ants that includes Nylanderia; Kallal and LaPolla (2012) transferred most Nearctic Paratrechina species to Nylanderia and resurrected and redefined this last genus. Foraging activity at low temperature has rarely been reported for Nylanderia. Thus, the corrected observation indicated that this species of Nylanderia is capable of foraging at low temperatures (5°C), matching the temperature threshold for foraging reported several times for P. imparis (see references in Sanchez-Peña 2013). Further identification of this Nylanderia species is ongoing.

Parasitic Beechdrops (Epifagus virginiana): A Possible Ant-Pollinated Plant

Abstract Epifagus virginiana (Beechdrop) is an annual flowering plant that parasitizes Fagus grandifolia (American Beech) roots. The pollination biology of the chasmogamous flowers of E. virginiana is unknown. In September 2011–2012, we observed insect visitors to E. virginiana flowers. Insect visitors included Bombus impatiens, Crematogaster spp., and Prenolepis imparis, but were dominated by P. imparis (over 96% of insect visits). In September 2012, we captured ants (Crematogaster and P. imparis) on E. virginiana flowers in three different areas found in the Coastal Plain and Piedmont physiographic provinces. With the use of 2,5-diphenyl tetrazolium bromide (MTT), we tested E. virginiana pollen from flowers and ant integuments for viability. We observed no significant difference (P > 0.05) between the viability of pollen taken directly from E. virginiana flowers and pollen removed from the ants. Our data suggests that ants can be playing an important role in the pollination of E. virginiana.

Precision Rescue Behavior in North American Ants

Altruistic behavior, in which one individual provides aid to another at some cost to itself, is well documented. However, some species engage in a form of altruism, called rescue, that places the altruist in immediate danger. Here we investigate one such example, namely rescuing victims captured by predators. In a field experiment with two North American ant species, Tetramorium sp. E and Prenolepis imparis, individuals were held in artificial snares simulating capture. T. sp. E, but not P. imparis, exhibited digging, pulling, and snare biting, the latter precisely targeted to the object binding the victim. These results are the first to document precision rescue in a North American ant species; moreover, unlike rescue in other ants, T. sp. E rescues conspecifics from different colonies, mirroring their atypical social behavior, namely the lack of aggression between non-nestmate (heterocolonial) conspecifics. In a second, observational study designed to demonstrate rescue from an actual predator, T. sp. E victims were dropped into an antlion's pit and the behavior of a single rescuer was observed. Results showed that T. sp. E not only attempted to release the victim, but also risked attacking the predator, suggesting that precision rescue may play an important role in this species' antipredator behavior.

Modeling the spread of the Argentine ant into natural areas: Habitat suitability and spread from neighboring sites

To predict a fine-scale invasion of Argentine ants (Linepithema humile) into a natural area from the surrounding suburban matrix, we introduce a grid-based invasion model, similar to a cellular automaton model. Our model was based on observations of ant presence and absence but, unlike other models based on presence–absence data, it incorporated the process of invasion by spread from neighboring areas. Simulations were parameterized from a statistical analysis of a 17-year survey of ant distributions in the Jasper Ridge Biological Preserve in northern California. We simulated the effects of Argentine ant presence at neighboring grid squares, distance to development, presence of the native winter ant Prenolepis imparis, and other habitat and climate variables, and used these models to simulate invasion over many decades. The best predictions of the extent of Argentine ant invasion were based on the distance of each site to developed areas. Adding the effect of neighbors improved the predictions of the time at which sites would be invaded. Winter ants responded mainly to vegetation cover. Our results suggest that Argentine ants may reach their potential distribution in insular urban reserves rapidly, perhaps within 10 years, and that reserve size determines whether the reserve is likely to become fully invaded.

Effects of Vegetation Cover, Presence of a Native Ant Species, and Human Disturbance on Colonization by Argentine Ants

The spread of non-native invasive species is affected by human activity, vegetation cover, weather, and interaction with native species. We analyzed data from a 17-year study of the distribution of the non-native Argentine ant (Linepithema humile) and the native winter ant (Prenolepis imparis) in a preserve in northern California (U.S.A.). We conducted logistic regressions and used model selection to determine whether the following variables were associated with changes in the distribution of each species: presence of conspecifics at neighboring sites, distance to development (e.g., roads, buildings, and landscaped areas), proportion of vegetation cover taller than 0.75 m, elevation, distance to water, presence of both species at a site, temperature, and rainfall. Argentine ants colonized unoccupied sites from neighboring sites, but the probability of appearance and persistence decreased as distance to development, vegetation cover, and elevation increased. Winter ants appeared and persisted in sites with relatively high vegetation cover (i.e., highly shaded sites). Presence of the 2 species was negatively associated in sites with high vegetation cover (more winter ants) and sites near development (more Argentine ants). Probability of colonization of Argentine ants decreased where winter ants were most persistent. At sites near development within the preserve, abundant Argentine ant populations may be excluding winter ants. The high abundance of Argentine ants at these sites may be due to immigration from suburban areas outside the preserve, which are high-quality habitat for Argentine ants. In the interior of the preserve, distance from development, low-quality habitat, and interaction with winter ants may in combination exclude Argentine ants. Interactions among the variables we examined were associated with low probabilities of Argentine ant colonization in the preserve.

Interactions Between Aphaenogaster carolinensis (Hymenoptera: Formicidae) and Four Sympatric Ant Species

Individual ants of Aphaenogaster carolinensis Wheeler were placed in two way combinations with four sympatric ant species (Aphaenogaster lamellidens Mayr, Crematogaster lineolata Say, Pachycondyla chinensis Emery and Prenolepis imparis Say) to determine whether their interspecific behavior was dependent upon the ant species they were confronted with. The tendency of A. carolinensis to initiate and terminate interactions, and the durations of those interactions, were measured for all combinations. There was no significant effect of species on initiation or termination. There was a significant effect of species on the duration of interactions that were both initiated and terminated by A. carolinensis. Durations of interactions with A. lamellidens were significantly longer than with other species. The conclusion is that the interspecific behavior of A. carolinensis is dependent in part on the species it is interacting with.

Chemical defense by the native winter ant (Prenolepis imparis) against the invasive Argentine ant (Linepithema humile).

The invasive Argentine ant (Linepithema humile) is established worldwide and displaces native ant species. In northern California, however, the native winter ant (Prenolepis imparis) persists in invaded areas. We found that in aggressive interactions between the two species, P. imparis employs a potent defensive secretion. Field observations were conducted at P. imparis nest sites both in the presence and absence of L. humile. These observations suggested and laboratory assays confirmed that P. imparis workers are more likely to secrete when outnumbered by L. humile. Workers of P. imparis were also more likely to secrete near their nest entrances than when foraging on trees. One-on-one laboratory trials showed that the P. imparis secretion is highly lethal to L. humile, causing 79% mortality. The nonpolar fraction of the secretion was chemically analyzed with gas chromatography/mass spectrometry, and found to be composed of long-chain and cyclic hydrocarbons. Chemical analysis of dissected P. imparis workers showed that the nonpolar fraction is derived from the Dufour's gland. Based on these conclusions, we hypothesize that this chemical defense may help P. imparis to resist displacement by L. humile.