The Pheidole ( Hymenoptera : Formicidae ) of Oklahoma : new species records and distributional notes

Big-headed ants from the genus Pheidole (Hy men optera: Formicidae) are diverse and ecologically important world-wide. Here we report the first record in Oklahoma for two species, Pheidole pelor and Pheidole tysoni, increasing the number of known Pheidole species in Oklahoma to twelve. We highlight two areas, northwestern and southeastern Oklahoma, that may contain undocumented species based on their unique habitat, and stress the importance of surveying the regional fauna of these areas to create a proper baseline for monitoring the effects of environmental change.

Ants (Hymenoptera: Formicidae) are a conspicuous and important group of terrestrial arthropods (Hölldobler & Wilson 1990;Lach et al. 2010).They perform a variety of ecosystem services (Del Toro et al. 2012), invade novel habitats (Tschinkel 2006;Roeder & Kaspari 2017), form nomadic armies (Kaspari & O'Donnell 2003), and have been used as bioindicators of ecosystems (Andersen & Majer 2004).Within the ants, the genus Pheidole ranks as one of the most speciose, morphologically diverse, and geographically distributed clades (Wilson 2003;Economo et al. 2015).Workforces are comprised of two castes: minor and major workers.The latter have enlarged heads giving rise to their common name, the big-headed ants.Presently, there are over 1000 recognized Pheidole species (Wilson 2003) making up almost 8% of the approximate 15000 described ant species (Economo et al. 2015; Bolton 2016).However, few records exist for Pheidole in Oklahoma despite the state's numerous environmental gradients and potential for ant biodiversity (Roeder & Roeder 2016).
Here we combine personal collections with literature and natural history museum records towards a better understanding of the genus' distribution.
New locality records for both Pheidole pelor Wilson 2003 andPheidole tysoni Forel 1901 were found at the University of Oklahoma Biological Station (UOBS), which was initially established in 1949 on the northern border of Lake Texoma (Figure 1).At the UOBS, approximately 131 ha of forest comprised of American elm (Ulmus americana L.), hackberry (Celtis occidentalis L.), and pecan (Carya illinoinensis (Wangenh.)K. Koch) are located both west and north of the main lawn of the station grounds and surround 36 ha of fields that contain Indiangrass (Sorghastrum nutans (L.) Nash), Johnsongrass (Sorghum halepense (L.) Pers.), and little bluestem (Schizachyrium scoparium (Michx.)Nash).For P. pelor, workers were collected in the leaf litter of the woods, 200 m directly west of the main lawn of the station grounds on 10% sucrose and cricket baits (Figure 1; Table 1).For P. tysoni, workers were collected in a pitfall trap that was placed 15 cm underground in an old agricultural field (Figure 1; Table 1).

Notes oN GeoGraphic DistributioN
Specimens were identified using Wilson (2003).A series of measurements were taken for minor and major workers for the new species records using a Leica S8 APO stereo microscope.All measurements are in millimeters and reflect a set of standard measurements for morphological traits listed in the Global Ants Database (Parr et al. 2017).These include head width (HW), head length (HL), clypeus length (CL), mandible length (ML), femur length (FL), scape length (SL), Weber's length (WL), pronotum width (PW), inter-ocular width (IOW), eye width (EW), and eye length (EL).All available specimens for each species were measured which included one major and ten minor workers for P. pelor, and one major and six minor workers for P. tysoni.Measurement values are reported for minors as a mean with the range listed in parentheses and as a single value for majors.Digital color images were then taken using a Leica EC3 digital camera with FireCam software version 3.4.1 (Leica Microsystems Inc., Wetzlar, Germany).Images were compiled using Helicon Focus version 4.2.7 (Helicon Soft Ltd.) with scale bars added in Adobe Photoshop CS3 version 10.0.1 (Adobe Systems Inc., San Jose, CA, USA).One major and minor worker of each species are deposited as vouchers in the Sam Noble Oklahoma Museum of Natural History, while the others remain in the K.A. Roeder collection at the University of Oklahoma.Wilson, 2003 Pheidole pelor Wilson 2003: 547.Material examined: OMNH-210930, KAR186 and OMNH-210931, KAR187; Figures 2-7.

Distribution of Pheidole in Oklahoma by county
Below we list distribution records for other Pheidole species in Oklahoma counties from literature sources (Smith 1935;Young & Howell 1964;Smith 1979;Wheeler & Wheeler 1989;Albrecht 1995;Roeder & Roeder 2016), the Sam Noble Oklahoma Museum of Natural History    The number of known species of the ant genus Pheidole is now twelve in Oklahoma.However, for 88% of the counties, only two or fewer Pheidole species have been reported (Figure 14).With the majority of these belonging to P. bicarinata and P. dentata, the remaining 10 species are found on average in less than 5% of Oklahoma's counties.This lack of information is troubling, especially if ants are to be used to their fullest potential as bioindicators of ecosystems (Andersen & Majer 2004).
Across Oklahoma there are 32 state parks, 12 level III ecoregions, 10 nature conservancy preserves, and nine wildlife refuges.Many of these are in counties where low Pheidole species richness has been reported.For example, Beaver, Cimarron, and Texas Counties in northwestern Oklahoma are primarily High Plains or Southwestern Tablelands, which are elevated subhumid grasslands or semiarid grazing lands.Despite the potential for biodiversity in these two ecoregions, only three Pheidole species have been collected from these areas.Cimarron County specifically contains the only reported record for P. desertorum in Oklahoma.On the opposite side of Oklahoma, the counties of Love, Marshall, Bryan, Choctaw, and McCurtain make up the southeastern portion of the state as well as a fraction of the Cross Timbers, East Central Texas Plains, and South Central Plains ecoregions.These ecoregions originally contained both post oak savannas and oak-hickory-pine forests, however much of the Cross Timbers and East Central Texas Plains are now used as rangeland or pastures.Excluding Marshall County which is home to the UOBS, only a single species, the common P. dentata, has been found.As recent ant records have started to emerge from this area (Roeder & Roeder 2015;Roeder et al. 2015), future discoveries undoubtedly await and will increase the most recently published estimate of 124 ant species in Oklahoma (Roeder & Roeder 2016).We suggest a greater focus should be placed on creating baseline data of native biodiversity in these potentially species rich regions.With such data, we could then monitor for shifts in species distributions that will help us better understand the impacts of climate change and habitat modification in this region of the USA.

Figure 1 .
Figure 1.Map of the University of Oklahoma Biological Station (UOBS).Collection areas are denoted by grey points.The inset shows the location of the UOBS in North America.

Figure 14 .
Figure 14.Species richness of Pheidole across the 77 counties of Oklahoma.

Table 1 .
New locality records for Pheidole species at the University of Oklahoma Biological Station.