Study site and field methods
Trachymyrmex septentrionalis colonies were found in Florida, USA.
Florida is located entirely within the North American Coastal Plain,
which is a global biodiversity hotspot owing to its unique geologic
history and diverse ecosystems (Griffith,
1994; Noss, 2012;
Noss et al., 2015). Samples were
collected across two primary regions in Florida that correspond with
known biogeographic breaks in the state (e.g.,
(Seal et al., 2015)); the panhandle
(which included two distinct ranger districts within the Apalachicola
National Forest and a nearby barrier island) and the peninsula,
represented by samples collected in North Central Florida near
Gainesville and in Central Florida near Orlando (Figure 1).
In the panhandle, the Apalachicola National Forest (ANF) is divided into
two ranger districts that occur on either side of the Ochlockonee River:
the Apalachicola Ranger District on the west and the Wakulla Ranger
District on the east. The Apalachicola Ranger District (ARD) is
comprised mainly of pine flatwood forest with high herbaceous cover,
little relief, and a high water table
(Abrahamson & Harnett, 1990).Trachymyrmex septentrionalis colonies in pine flatwoods are
restricted to ‘habitat islands’ of somewhat higher elevation (relative
to the water table) and population sizes likely vary temporally as
annual rainfall varies from drought to very wet
(Seal & Tschinkel, 2010). On the other
hand, the Wakulla Ranger District (WRD) contains significant stands of
sandhill forest (i.e., remnants of Pleistocene sand dunes;
(Myers, 1990)) that are excessively
drained and support many species associated with deserts
(Brown, Stone, & Carlisle, 1990).T. septentrionalis colonies are found throughout the sandhills,
absent only from frequently inundated areas near ephemeral ponds. Unlike
flatwoods populations, those found in sandhills do not likely fluctuate
very much in size, at least with respect to rainfall
(Seal & Tschinkel, 2006,
2010). Both ranger districts are
dominated and characterized by longleaf pine (Pinus palustris )
and sandy soils. Located just south of the ANF, St. George Island is a
sandy barrier island approximately 6km from the mainland. Despite its
low relief and susceptibility to hurricanes, the island contains several
stands of pine forest on elevated regions
(Gornish & Miller, 2010;
Huffman, Platt, & Grissino-Mayer, 2004)
which harbor several species typical of sandhills further inland, such
as T. septentrionalis and the seed-harvesting antPogonomyrmex badius . The Florida peninsula is separated from the
panhandle by the Suwanee River, a known biogeographic barrier to many
species (including ants), owing to different soils and geological
history (Brown et al., 1990;
Richter et al., 2014;
Strehl & Gadau, 2004). Thus, the
collections were made across multiple ecological gradients and potential
dispersal barriers.
Trachymyrmex septentrionalis colonies were identified in the
field by their distinctive and steep crescent-shaped mounds, which are
built up by ants piling excavated chamber soil
(Seal & Tschinkel, 2006). Individual
worker ants were collected directly from colonies in 2013 and 2018. All
workers were preserved in 95% ethanol at -20ºC until DNA extraction.
Only one individual worker per colony was used for sequencing. All
relevant specimen information (e.g., collection date, region/location)
can be found in Table S1.