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2011 SOUTHEASTERN NATURALIST 10(2):357–364
Correlated Morphological, Ecological, and Behavioral
Aspects of the Microhabitat Associations in Geolycosa Wolf
Spiders of Florida (Araneae, Lycosidae)
Samuel D. Marshall1,* and Katherine A. Martin1
Abstract - Species of Geolycosa (burrowing wolf spider) found in the eastern USA
exhibit one of two species-specific microhabitat associations with associated burrow
architectures: “turricolous” species burrow in areas covered in leaf litter and construct a
distinct turret of silk and debris at the burrow mouth, while “aturricolous” species locate
their burrows in more barren areas and do not construct a turret. Our research goal was to
document the relationship between spider coloration, burrow-site selection, and burrowconstruction
behaviors in five Geolycosa species in Florida (G. micanopy, G. hubbelli,
G. xera, G. patellonigra, and G. escambiensis). Discriminant analysis of morphological
data supports our contention that each ecomorph has a distinct pattern of pigmentation,
with the barren-substrata species being paler. Field studies of species pairs at three sites
in Florida (Archbold Biological Station, Ocala National Forest, and the Panhandle)
documented the species-specific association with one of the two microhabitats. Field
enclosure tests with five of these species demonstrated that the observed microhabitat
association was due to active burrow-site choice. Finally, tests we conducted in the laboratory
documented that these species will build the predicted species-specific burrow
types under controlled conditions.
Habitat selection is the behavioral process by which dispersing animals identify
and settle in a location meeting their resource needs (e.g., food, nest sites,
moisture). Spiders have been the subject of extensive research in habitat selection
(Uetz 1991, Wise 1993) in part because most are sedentary, even sessile, building
webs and/or silk-lined retreats. Because of the investment in site choice implicit
in investing resources in a trap or retreat, habitat choice is unambiguous (Uetz
1991). The “ecomorph” concept (short for ecological morphology) proposes an
adaptive correlation of habitat use and functional characteristics of an organism’s
phenotype. Ecomorphs are suites of developmentally stable species-specific
traits functionally linked to the organism’s niche (Losos 1990, Schulte et al.
2004). This study examines the correlation of the state of each of three ecological
traits in a suite of Geolycosa (burrowing wolf spiders): habitat selection, burrow
construction, and color pattern. The specific combinations of the trait states
should be consistent between the two ecomorphs we propose.
Geolycosa wolf spider species, unlike most other burrowing lycosids, are
obligate burrowers and spend their entire lives in and around a burrow they
construct themselves. All foraging activity is centered on the burrow mouth, and
1Northwestern State University of Louisiana, Department of Biological Sciences, 317
Bienvenu Hall, Natchitoches, LA 71497. *Corresponding author - firstname.lastname@example.org.
358 Southeastern Naturalist Vol. 10, No. 2
the spiders only leave their burrow to make strikes at passing prey. An exception
to this rule is when males become vagrant upon molting into their terminal
instar. The burrows of North American Geolycosa are similar to each other in
structure: a circular, vertical tube terminating in an enlarged chamber (Wallace
1942). Burrow depths vary with species, soil, and latitude, but can range from
15–100 cm (S.D. Marshall, pers. observ.). Most North American Geolycosa species
exhibit a highly localized pattern of distribution and dispersion (Marshall
1995a, b; Marshall et al. 2000). Geolycosa from the eastern US appear to exhibit
clear microhabitat preferences; some species burrow in barren areas, while others
are found associated with soil covered with a litter layer (Carrel 2003, Edwards
and Edwards 1989, Marshall 1997, Marshall et al. 2000, Wallace 1942). “Turricolous”
Geolycosa species are those that construct their burrows in microhabitats
in which the soil surface is covered in leaf litter or other vegetative debris. They
construct a turret around the burrow mouth by binding leaves, stems, and other
plant debris together with silk. The turret is an unambiguous feature that entails
specific behaviors to construct and can exceed 2 cm in height. In contrast, “aturricolous”
Geolycosa species build no turret at the burrow mouth, and are restricted
to microhabitats in which the soil surface is barren (Carrel 2003, Marshall et al.
2000). The goal of this research was to document the morphological, ecological,
and behavioral attributes correlated with the species-specific microhabitat associations
in three Geolycosa species pairs across Florida.
All spiders used in the research below were collected in the field by digging
them from their burrows. Because it is not possible to determine the sex of these
spiders before the penultimate instar (when males begin to show an enlargement
of the pedipalps prior to maturity), all research detailed here was conducted with
either adult females or immature males and females.
We measured 10 morphological attributes on each preserved specimen of Geolycosa.
Carapace width was recorded and used to scale the following 3 features:
carapace height (measured at the anterior edge), and the lengths of patella-tibia
I and IV. We also quantified the degree of black pigmentation on ventral body
segment surfaces: sternum, venter, coxa I, femur I, patella I, and tibia I. Pigmentation
was noted as lacking on the anatomical feature (0), partially covering the
feature (0.5), or entirely covering the feature (1.0). We used ventral color pattern
as a proxy for overall degree of pigmentation because these ventral pigmentation
marks remain distinct, even after the specimen has been preserved in alcohol for
decades (S.D. Marshall, pers. osberv.). The more subtle dorsal patterns become
difficult to quantify after a similar period of preservation as the specimens fade.
We further justify the use of ventral pigmentation noting that Wallace in his 1942
revision of the genus relied heavily on ventral pigmentation as a key character,
indicating its stability as a species-specific trait. A total of 51 subadult male and
2011 S.D. Marshall and K.A. Martin 359
female and adult female specimens were measured, including aturricolous species:
G. escambiensis Wallace (n = 12), G. patellonigra Wallace (n = 13), G. xera
xera McCrone (n = 12), and G. xera archboldi McCrone (n = 2); and turricolous
species: G. hubbelli Wallace (n = 2) and G. micanopy Wallace (n = 10). Discriminant
analysis (SPSS ver. 14.0) was used with “turricolous” or “aturricolous”
being used as categories.
We used a line-intercept method to study the soil-surface conditions in the vicinity
of Geolycosa burrows. In all cases, burrows were located by walking, head
down, scanning the soil surface for burrows during daylight hours. At Archbold
Biological Station, data were collected on the burrows of 24 G. x archboldi and
29 G. hubbelli. At Ocala National Forest, data were collected in the Big Scrub
area on the burrows of 25 G. patellonigra and 21 G. hubbelli. In the Florida
Panhandle, data were collected in coastal scrubs west of Apalachicola and east of
Pensacola on the burrows of 20 G. escambiensis and 15 G. micanopy.
Habitat was quantified by laying a 1-m transect in a north–south direction to
standardize data collection across sites. At each site, the meter stick was centered
on the burrow (i.e., at the 50-cm mark) and substratum type was recorded for each
10-cm interval as: (1) barren, (2) sparse litter, or (3) completely litter covered.
These determinations were made by visual inspection. We collected spiders from
all burrows surveyed to confirm species identity. These data were analyzed using
a MANOVA of counts of the categories of substratum cover along each transect
(leaf litter, leaf litter + sand, barren sand). These data were analyzed with SPSS
(ver. 14.0) using locality and species as factors.
We conducted microhabitat choice experiments in field enclosures in which recently
collected spiders were offered a choice of barren or litter-covered substrata
for settlement. Geolycosa movement is restricted to relocation after burrow abandonment.
Research has documented that Geolycosa do settle in self-constructed
burrows immediately upon dispersing from the maternal burrow (Marshall
1995a, b). We have never observed Geolycosa wandering or captured them in
pitfall traps, apart from sexually mature males. It is assumed that these spiders
quickly construct a new burrow if they find themselves without a burrow. Observed
causes for burrow abandonment in the field include invasion by ants, territorial
conflicts, and movement of litter (Marshall 1995a, b). The enclosures were built of
30-cm-wide aluminum sheeting (wolf spiders lack adhesive tarsi and so are unable
to climb smooth surfaces). Each enclosure was 0.5 by 1.0 m. Prior to each trial, we
would randomly select (by coin toss) which half of the enclosure would be litter
covered, with the other half of the enclosure remaining barren. We would then cover
the sand in the selected end with leaf litter collected in the vicinity. A 5-cm wide
strip of mesh plastic of the type used to prevent leaves from clogging household
rain gutters was used to contain the leaf litter. This strip was necessary as otherwise
wind would move the litter around the enclosure. Spiders were collected from burrows
in the area and used within 5 days. The open vial containing the spider was
360 Southeastern Naturalist Vol. 10, No. 2
placed along the middle of the enclosure next to the plastic mesh. The side of the
mesh for release was selected randomly, by coin toss. The spider was allowed to
exit the vial on its own. Because the leaf litter barrier material was low (5 cm) and
perforated, it presented no barrier to movement by the spiders. We would note the
location of the spider the next morning. Where it was found, with or without a burrow,
was considered a choice. Between trials, the leaf litter was replaced and the
sand was thoroughly mixed. Each spider was used only once.
Burrowing construction behavior
The use of debris in turret construction under standardized conditions was
tested in a greenhouse at Northwestern State University of Louisiana using spiders
collected in Florida and transported to Louisiana in 85- by 30-mm cylindrical
plastic vials. The length of time these spiders were held in the vials varied from
one to several weeks. During this holding period, all spiders were given moist
sand as a substratum and fed crickets. Prior to the test, spiders were allowed to
establish burrows in 592-ml plastic drink cups filled to a depth of approximately
10 cm with sand. The test consisted of offering each spider ten 1.0-cm sections
of pine needle, placed 1.0 cm from the burrow mouth for turret construction. Pine
needles were used because it was relatively easy to standardize the size and shape
of the material offered. We have observed Geolycosa using pine needles for turret
construction in the field. We examined the containers 48 h later, checking for the
incorporation of the pine needle sections into the silk collar at the mouth of the
burrow. A spider was scored as turret building if they incorporated more than one
pine needle section into the burrow mouth.
The discriminant function was able to separate the two classes of Geolycosa
species (turricolous and aturricolous) primarily based on the amount of black
pigmentation on the ventral body surfaces (Wilk’s Lambda = 0.015; with sternum,
venter, coxa I, femur I, and patella I color being the most important).
When these data were summarized, there were clear differences between
the burrow sites of turricolous and aturricolous species in the prevalence of
barren sand versus complete litter cover (Fig. 1). The differences between the
number of barren intervals and litter-covered intervals at aturricolous burrows
vs. turricolous burrows were significant; the difference between the number of
mixed-substratum intervals was not (MANOVA: F3, 129 = 40.9, P < 0.001). These
results indicate a clear separation based on the extremes of substratum condition
(i.e., barren vs. litter) but ambiguity when there are elements of both (scattered
litter on barren sand).
We found a strong preference for the predicted substrata for all species except
the aturricolous G. patellonigra, which settled randomly (Table 1).
2011 S.D. Marshall and K.A. Martin 361
A total of 27 turricolous and 63 aturricolous spiders were tested. Virtually
all spiders constructed or did not construct turrets as predicted by their species
(Table 2). Based on a binomial test for each species/locality tested, all P < 0.01.
Figure 1. Results of 1-m transect studies of soil-surface conditions around Geolycosa
wolf spider burrows at three localities in Florida. “Archbold” represents data collected at
Archbold Biological Station, Highlands County; “Ocala NF” represents Ocala National
Forest, Marion County; “Port St. Joe” represents coastal scrubs in the vicinity of Port St.
Joe, Gulf County. Soil-surface conditions were recorded for each of ten 10-cm intervals
along the 1-m transect as barren (no leaf litter present), light leaf litter/debris (litter present
and sand visible) and leaf litter/debris (no barren sand visible).
Table 1. Results of habitat choice test. Number of Geolycosa selecting the two different substratum
types in field enclosures. Significance levels based on a binomial test with an expectation of random
(50/50) settlement. Archbold = Archbold Biological Station, Ocala = Ocala National Forest, and St.
Joseph’s = St. Joseph’s Peninsula State Park.
Turricolous/ n settle n settle
Taxon aturricolous Locality n tested in litter in sand P
G. hubbelli Turricolous Archbold 15* 11 2 0.0095
G. xera archboldi Aturricolous Archbold 15 0 13 0.0001
G. hubbelli Turricolous Ocala 10 9 1 0.0092
G. patellonigra Aturricolous Ocala 10 5 4 0.2461
G. escambiensis Aturricolous St. Joseph’s 10 0 10 0.0001
*Differences between the number tested and the number scored represents missing spiders.
362 Southeastern Naturalist Vol. 10, No. 2
Our results support our hypothesis that Geolycosa wolf spiders actively select
burrow sites based on the presence or absence of a litter layer covering the
soil surface and that this choice is correlated with degree of pigmentation and
burrow-construction behavior. Thus, there are two alternative species-specific
ecomorphs in the eastern US. Geolycosa species which primarily exploit areas
where the soil is covered in leaf litter are dark in color and construct turrets at
the burrow mouth, whereas those species that are restricted to barren areas tend
to be paler in color and do not build a turret.
The repeated pattern of pair-wise co-distribution of the ecomorphs suggests
that competitive interactions may explain why only one of each ecomorph species
may be found at a given site. Geolycosa is unusual among spiders in that
most species have a very restricted geographical range, and that historical biogeography
has led to the accumulation of endemic species in Florida (Marshall
et al. 2000). In contrast, in more northern regions with a shorter post-glacial
history, only single-pairs of species may be found across a large geographical
area (e.g., G. missiouriensis and G. wrightii in the Midwest and Great Lakes
region, G. turricola and G. pikei along the Atlantic coastal plain to Georgia).
The repeated co-occurrence of these contrasting ecomorph species pairs raises
the question of their origin. In Florida, the high rates of endemism of plants
and invertebrates on the inland sand ridges is generally attributed to vicariance
biogeography (Marshall et al. 2000). To date, there is no definitive answer to the
question of evolutionary origins. Unpublished phylogenetic analyses based on
mtDNA sequence data (S.D. Marshall et al., unpubl. data) indicate that the aturricolous
ecomorph has evolved several times, and that ecomorph status reflects
adaptation rather than common descent.
The adaptive significance of the turret constructed by Florida’s Geolycosa is
untested. Research into the turret-construction behavior of other burrowing lycosids
has provided differing hypotheses for the function of the turret. Framenau
and Baehr (2007) propose that the turret may function as a “look out” for Dingosa
species wolf spiders in Australia by providing them with an elevated perch to sit
and wait for prey. Williams et al. (2006) found experimental evidence that the
turret of Lycosa tarantula (L.) (Spanish Wolf Spider) functions to deter burrow
Table 2. Results of a laboratory test of burrow-construction behavior in which Geolycosa inhabiting
self-constructed burrows in laboratory containers were offered turret-building material (ten 1-cm
lengths of pine needle). Predictions are based on species identity. Ocala = Ocala National Forest,
Archbold = Archbold Biological Station, and Panhandle = Central Panhandle
Collecting Turricolous/ Number building expected to Binomial
Species locale aturricolous tested turrets build turrets probability
G. hubbelli Ocala Turricolous 11 0.8 1.0 P = 0.0
G. hubbelli Archbold Turricolous 16 1.0 1.0 P = 0.0
G. xera Archbold Aturricolous 24 0.0 0.0 P = 0.0
G. patellonigra Ocala Aturricolous 15 0.2 0.0 P = 0.0
G. escambiensis Panhandle Aturricolous 24 0.0 0.0 P = 0.0
2011 S.D. Marshall and K.A. Martin 363
invasion by scorpions. We did not test for turret function. However, the observation
that these turricolous-aturricolous species pairs are often found within
meters of each other segregated by microhabitat may indicate that the turret (or
lack thereof) is specifically related to microhabitat structure rather than foraging
or anti-predator behavior. Of course, none of these hypothesized functions are
Geolycosa wolf spiders are a peculiar component of the fauna of scrubs and
barrens across the eastern half of the US. It seems that where there is sand, there
will be Geolycosa. We have even discovered Geolycosa in small, isolated barrens
in the Midwest and Mid-Atlantic states. As is true with many sand-barrens
endemics (e.g., Lycaeides melissa samuelis Nabokov [Karner Blue Butterfly]),
fire plays a significant role in the ecology of Geolycosa (Carrel 2008). Fire and
post-fire succession in part determines the local distribution and abundance
of Geolycosa species pairs. Long-term fire suppression can lead to the local
extinction of aturricolous Geolycosa species as a litter layer develops—one
way that development pressures in Florida have impacted local species, such
as G. escambiensis. Geolycosa escambiensis is only known from the central
Panhandle west into Alabama. Much of its habitat has been compromised by
development, and there are no protected populations in Florida. We consider it to
be the only recognized Geolycosa species at risk.
We thank Archbold Biological Station for allowing one of us (S.D. Marshall) to
conduct research into the ecology of Geolycosa over the years. We thank the Florida
Department of Environmental Protection for permission to collect spiders and conduct
research at St. Joseph Peninsula State Park (Permit # 07060711). We thank the United
States Department of Agriculture for a special use permit to conduct research at Ocala
National Forest (Authorization ID LAK198). This research was funded in part by Northwestern
State University’s Enrichment Fund (NEF Agreement #PS 06-07 002). Finally,
we thank the students in S.D. Marshall’s summer 2007 Introductory Biology Laboratory
for their enthusiastic contribution to the laboratory studies of turret-construction behavior.
We also thank E. Hebets for her editorial improvements to the writing and C. Morrison
for comments on an early draft of the manuscript. We especially thank L. Campbell
for her critical review of grammar and style.
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