Research Article

Journal of Orthoptera Research 2023, 32(2): 119-126

Sexual dimorphism in the badlands cricket (Orthoptera, Gryllinae,

Gryllus personatus)

EsPERANCE M. Mapbera!, Kevin A. JUDGE!

1 Department of Biological Sciences, MacEwan University, Edmonton, Alberta, T5J 482, Canada.

Corresponding author: Kevin A. Judge (judgek3 @macewan.ca)

Academic editor: Diptarup Nandi | Received 15 August 2022 | Accepted 3 December 2022 | Published 12 June 2023

https://zoobank. org/F7C819F9-594F-4472-841 C-2D85A867C41A

Citation: Madera EM, Judge KA (2023) Sexual dimorphism in the badlands cricket (Orthoptera, Gryllinae, Gryllus personatus). Journal of Orthoptera

Research 32(2): 119-126. https://doi.org/10.3897/jor.32.93513

Abstract

Sexual dimorphism (SD) is a common phenomenon in sexual species
and can manifest in a variety of ways. Sexual size dimorphism (SSD) is
commonly investigated, but it can be confounded with sexual shape di-
morphism (SShD) if multivariate measures of size are not used. Univariate
studies may also overestimate the prevalence or direction of SSD when the
sexes are strikingly different in shape, which may be an issue in taxa such
as Orthoptera and other terrestrial arthropods where maximum body size
is strongly constrained. Here we tested for the occurrence of both SSD and
SShD in the badlands cricket Gryllus personatus (Orthoptera, Gryllinae). We
measured four body size dimensions—maxillae span, head width, prono-
tum length, and mean hind femur length—and used multivariate methods
to test whether male and female adult badlands crickets were sexually di-
morphic in size and/or shape. All the univariate dimensions were sexually
dimorphic, with males having wider heads and maxillae than females and
females having longer pronota and hind femora than males, which indi-
cates SShD. However, multivariate methods failed to detect SSD, instead
confirming that the sexes primarily differ in body shape. We show how a
simple ratio of head width to pronotum length captures SShD in badlands
crickets and apply it to iNaturalist, a citizen science platform, to broaden
our findings. We propose that orthopterists studying SD minimally meas-
ure head width, pronotum length, and hind femur length as a standard
that will allow a more repeatable and generalizable assessment of the
prevalence and direction of both SSD and SShD.

Keywords

body size, geometric mean size, Gryllinae, sexual shape dimorphism,
sexual size dimorphism

Introduction

Intraspecific differences between males and females, or sexual
dimorphism (SD), are common in sexually reproducing organisms
(Darwin 1871, Andersson 1994, Fairbairn et al. 2007, Stillwell et al.
2010) and are thought to be caused by either intersexual competition
for resources (Selander 1966), sex-specific equilibria (Blanckenhorn
2005), or some combination thereof. SD can take a variety of forms,

from differences in behavior (e.g., parental care, reviewed in Kokko
and Jennions 2008), development (e.g., Esperk et al. 2007, reviewed
in Hopkins and Kopp 2021), and immunity (e.g., Bagchi et al. 2021,
reviewed in Kelly et al. 2018) to differences in overall body size (sex-
ual size dimorphism, SSD; reviewed in Fairbairn et al. 2007) and
body shape (sexual shape dimorphism [SShD], e.g., Table 1). These
latter two are of special interest because they: 1) are relatively easy to
measure, 2) can impact other dimorphisms (e.g., sex differences in
mobility, reviewed in Herberstein et al. 2017) as well as important
life history traits (e.g., fecundity, reviewed for spiders in Foellmer
and Moya-Larano 2007), and 3) unlike other dimorphisms, SSD
and SShD are preserved in the fossil record making it possible to
study their long-term evolution (e.g., Martins et al. 2020). In organ-
isms such as arthropods that have an exoskeleton, maximum body
size and therefore SSD may be evolutionarily constrained (reviewed
in Whitman 2008 and references therein), placing greater selection
pressure on the evolution of body shape and thus SShD.

The order Orthoptera (crickets, katydids, grasshoppers, and
allies) display one of the highest degrees of SSD among insects
(Stillwell et al. 2010), with most species displaying female-biased
SSD (Hochkirch and Groning 2008). Most of these instances of
SSD are based on total body length as an index of body size, be-
cause it is a commonly reported metric of size in the taxonomic
literature from which the bulk of these data were gleaned (Hoch-
kirch and Gréning 2008). However, because total body length in-
cludes the relatively soft and flexible abdomen that can fluctuate
in size, the rate of SSD should be interpreted with caution (Hoch-
kirch and Groning 2008). Furthermore, because these data rely on
a single morphological dimension, conclusions about the extent
and direction of SSD are confounded with SShD.

The badlands cricket, Gryllus personatus (Uhler 1864), is a mid-
sized field cricket (Orthoptera, Gryllinae) inhabiting clay-type bad-
lands in the southwest United States (Weissman and Gray 2019).
As typical for most field crickets, males have specialized forewings
(tegmina) that they rub together to produce song, and females
have a long, thin ovipositor that they use to deposit fertilized eggs
into soil (Weissman and Gray 2019). Beyond these sex-limited

Copyright Esperance M. Madera and Kevin A. Judge. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which
permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

JOURNAL OF ORTHOPTERA RESEARCH 2023, 32(2)

120

E.M. MADERA AND K.A. JUDGE

Table 1. Selected published descriptions of sexual shape dimorphism in the Orthoptera. Choice of what morphological dimension is
considered the focal shape variable and what is considered a reference trait reflects the original publication and is presumably chosen to
reflect a functional hypothesis. Obviously, this polarity can be reversed, in which case the direction of dimorphism would be reversed
(e.g., female G. pennsylvanicus have longer hind femora than males for a given head width; see also figure S2 in Judge and Bonanno 2008).

Taxon Shape Variable
Caelifera
Elasmoderus wagenknechti forewing length, hindwing length
foretibia girth
tegmen length
body length

Gomphocerus sibiricus
Temnomastax spp.

Ensifera
head width
not specified

Acheta domesticus
Gryllacropsis sp.

Gryllus pennsylvanicus multiple mouthpart dimensions and

head width
Hemideina crassidens head length, head width
H. maori head width
Pachyrhamma spp. length of several antennal sensillae

P. waitomoensis hind leg length

Zaprochiline katydid auditory bulla size

characteristics, there is no published account of any other sexu-
ally dimorphic morphology in the badlands cricket. Our main goal
with this study is to test the hypotheses that male and female bad-
lands crickets differ in body size and/or body shape (i.e., display
SSD and/or SShD, respectively). We measured four morphological
dimensions that are predicted to be sexually dimorphic and then
used multivariate statistical methods to assess both SSD and SShD.

Methods

Study animals and care.—Individuals used in this study were the
offspring of approximately 60 late instar nymphs (30 males, 30
females) supplied by David Gray (California State University,
Northridge) from his laboratory colony of badlands crickets, origi-
nally collected from Winslow, Arizona, USA. Crickets were housed
in conditions like those described in Judge and Bonanno (2008)
at the Department of Biological Sciences, University of Lethbridge.
Briefly, hatchlings were added to a large plastic bin (48 cm long,
35 cm wide, 31 cm high) containing layers of egg cartons for shel-
ter, glass shell vials filled with water and stoppered with cotton
for moisture, and ground cat food (Iams Original with Chicken;
Iams, Mason, Ohio, USA) and ground rabbit food (Martin Little
Friends; Martin Mills Inc., Elmira, Ontario, Canada) to provide a
variety of food choice (cat food is high in protein, whereas rabbit
food is high in fiber). Environmental conditions in the lab during
rearing were 25°C, 70% relative humidity, and 12 hours light:12
hours dark daily light cycle. The badlands cricket was to be in-
cluded in a larger comparative study of aggressive behavior, but
this colony had to be euthanized (-20°C for 24 hours) when the
study was ended because the second author accepted a fulltime
faculty position at MacEwan University. All individuals that were
in the colony were preserved separately in 70% ethanol for later
measurement.

Measurement of morphology.—We measured five morphological di-
mensions in all individuals: head width, maxillae span, pronotum
length, and both left and right femur length using a methodology
similar to that of Judge and Bonanno (2008). Briefly, each indi-
vidual was removed from their container and dissected to remove

Reference Trait Direction References
abdomen length M>F Cepeda-Pizarro et al. 2003
not specified M>F Valverde et al. 2018
hind femur length F>M da Silva Olivier and
tegmen length F>M Aranda 2018
pronotum width M>F Walker et al. 2008
not specified Tomar and Diwakar 2020
pronotum length, hind M>F Judge and Bonanno 2008
femur length
hind femur length M>F Kelly 2006
hind tibia length M>F Gwynne and Jamieson
1998
not specified various Fea et al. 2019
pronotum width M>F Fea and Holwell 2018
not specified F>M Bailey and Simmons 1991

the head and both hind femora (at the juncture with the hind
coxae) and placed in a standardized position submerged in 70%
ethanol under a stereomicroscope (M5; Wild, Heerbrugg, Switzer-
land) with an attached phototube (Martin Microscope Company,
Easley, South Carolina, USA) and digital camera (INFINITY 1-3C;
Teledyne Lumenera, Ottawa, Ontario, Canada). We used INFIN-
ITY CAPTURE v5.0.2 (Teledyne Lumenera) to capture three im-
ages: 1) the ventral head perpendicular to the transverse plane, 2)
the dorsal thorax perpendicular to the frontal plane, and 3) the
lateral femora perpendicular to the sagittal plane. These photo-
graphs were used to place landmarks using the programs tpsUtil
and tpsDig2 (SB Morphometrics, https://sbmorphometrics.org/),
and the landmarks were converted to linear dimensions using
basic trigonometry in Excel (Microsoft Corporation, Redmond,
Washington, USA). The landmarks used for each linear dimension
are described in detail in Judge and Bonanno (2008, see Fig. 1
therein), and the image capture and morphological measurement
procedures are explained in more detail in Dupuis et al. (2020).
All photographs and the resulting measurement data used for our
analysis are freely available at Dryad (https://doi.org/10.5061/
dryad.qjq2bvqkw).

Statistical analysis.—We reduced the number of morphological
variables from five to four by using the mean of the left and right
femur lengths. Then we used a multivariate general linear model
with sex (male or female) as the independent variable and the four
morphological variables (head width, maxillae span, pronotum
length, and mean femur length) as dependent variables to test for
sex-related differences in morphology. Kolmogorov-Smirnov tests
were used to assess the normality of the residuals of all statistical
analyses. We used IBM SPSS Statistics Version 28.0 (IBM Corpora-
tion, Armonk, New York, USA) for all analyses, which were carried
out at a Type 1 error rate set at 5%.

Results
The head width, maxillae span, pronotum length, and

left and right femur lengths of 167 (71 males and 96 females)
adult G. personatus were measured. One male was excluded

JOURNAL OF ORTHOPTERA RESEARCH 2023, 32(2)

E.M. MADERA AND K.A. JUDGE

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ei
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oO
A
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oD
q
2.
=
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O
—_—
Lay)
a
2
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AY

Fig. 1. Average scores for adult male (filled circles) and adult fe-
male (open circles) badlands crickets (Gryllus personatus) on the
first two components from a principal components analysis of the
four measured variables: head width, maxillae span, pronotum
length, and mean femur length. Error bars represent standard er-
rors. See Table 3 for factor loadings.

from further analysis because he had deformed forewings, and
26 females were excluded using a random number generator to
even the sample sizes for males and females at 70 apiece (Table
2). Kolmogorov-Smirnov tests for normality revealed that the
residuals from the following statistical tests were normally
distributed (all p > 0.083). A multivariate GLM with sex as the
fixed factor and maxillae span, head width, pronotum length, and
mean femur length as dependent variables revealed overall sexual
dimorphism (F, ,,, = 81.894, p < 0.001), although post-hoc tests
showed that the direction of dimorphism depended on the trait
measured. Adult males had wider maxillae spans (F, ,,, = 54.506,
p < 0.001) and wider heads (F, ,,, = 10.492, p = 0.002), whereas
adult females had longer pronota (F, ,,, = 13.587, p < 0.001) and
longer femora (F, ,,, = 7.217, p = 0.008) (Table 2).

Given that the direction of sexual dimorphism varied across
linear dimensions, it was not clear whether males and females

Table 2. Means + standard deviations (range in parentheses) of
five measures of size in the badlands cricket (Gryllus personatus).
Mean femur length is the average of left and right femora, and geo-
metric mean size is the fourth root of the product of head width,
maxillae span, pronotum length, and mean femur length. N = 70
for both males and females.

Measurement (mm) Males Females
Maxillae Span 4.87+0.47 (3.87-5.95) 4.38+0.30 (3.58-5.05)
Head Width 5.18+0.39 (4.21-6.06) 4.99+0.33 (4.11-5.85)

Pronotum Length
Mean Femur Length

3.29+0.26 (2.49-3.78) 3.4540.27 (2.66-3.98)
9.9040.68 (8.30-11.68) 10.22+0.73 (8.45-12.02)

Geometric Mean Size 5.35+40.40 (4.28-6.26) 5.2740.36 (4.27-6.13)

121

Table 3. Results of the principal components analyses for adult
badlands crickets (Gryllus personatus) including factor loadings, ei-
genvalues, and percent variance explained for PC1 and PC2.

Dimension PCl1 PC2
Maxillae Span 0.823 0.554
Head Width 0.955 0.247
Pronotum Length 0.843 -0.486
Mean Femur Length 0.912 -0.309
Eigenvalue 55832 0.699
% Variance Explained 78.311 17.471

were dimorphic in just body shape or in both body shape and
overall body size. We investigated sexual dimorphism in overall
size by conducting two separate analyses. First, we calculated the
geometric mean of the four morphological measures as an index
of overall size (Mosimann 1970) and compared males and females
using a t-test. Adult G. personatus were not sexually dimorphic in
geometric mean size (adults: f,,, = 1.318, p = 0.190). Second, we
conducted a principal components analysis (PCA) to reduce the
four measured variables to a limited number of uncorrelated prin-
cipal components (PCs), where PC1 represents overall size and
other PCs represent latent shape variables (Jolicoeur 1963, Cadi-
ma and Jolliffe 1996). Although only PC1 had an eigenvalue over
1, we also extracted PC2 (Table 3) because we had an a priori hy-
pothesis regarding shape difference between the sexes. We tested
for size and shape sexual dimorphism using separate t-tests. Adult
G. personatus were dimorphic in PC2 (t,,, = 16.961, p < 0.001) but
not PC1 (t,,, = 0.888, p = 0.376; Fig. 1).

To further explore adult sexual dimorphism, we conducted a
discriminant function analysis (DFA) to find out whether there
was a linear combination of our measured variables that could
accurately predict the sex of individual adult G. personatus. The
DFA resulted in a significant linear combination of measurements
(x?, = 167.489, p < 0.001) that successfully identified the sex of
adult G. personatus 94.3% (66/70) of the time for females and
91.4% (64/70) of the time for males. The resulting canonical dis-

Table 4. Structure matrix from a discriminant function analysis
distinguishing adult male and adult female badlands crickets
(Gryllus personatus). Values represent the pooled within-groups
correlations between discriminating variables and the standard-
ized canonical discriminant function.

Variable Function
Maxillae Span 0.403
Head Width 0.177
Pronotum Length -0.201
Mean Femur Length -0.147

criminant function was positively correlated with head width and
maxillae span and negatively correlated with pronotum length
and mean femur length (Table 4).

Finally, we wanted to test whether the SShD we detected in lab-
reared badlands crickets was generalizable to the species. First, we
calculated the ratio of head width to pronotum length. This ratio
variable was sexually dimorphic in adults (¢,,, = 11.520, p < 0.001)
and was highly positively correlated with both PC2 (r = 0.917, p<
0.001) and the discriminant function (r = 0.821, p < 0.001). To
assess the generalizability of this ratio, we used the online natural
history website iNaturalist to collect images of wild adult G. per-

JOURNAL OF ORTHOPTERA RESEARCH 2023, 32(2)

122

sonatus and measured the ratio of head width to pronotum length
using the same procedure as above. We chose only observations
that had 1) at least one photo taken from above and perpendicu-
lar to the frontal plane and 2) attained the status of “Research
Grade”, which meant that at least two people had agreed on the
species-level identification with no dissenting opinions. This se-
lection procedure resulted in 10 useable observations (9 females
and 1 male). Because of the small sample size, we did not perform
a statistical analysis comparing the head width:pronotum length
ratios of wild crickets to lab-reared crickets. In wild crickets, as in
lab-reared crickets, the male had a bigger ratio than females, and
the ratios of wild crickets were less than the ratios of lab-reared
crickets, although this difference was less than 5% (Fig. 2).

Discussion

In this study, we tested whether the badlands cricket, Gryllus
personatus, displayed SSD, SShD, or both. Of the four morpho-
logical dimensions that we measured, all were highly positively
correlated, and all were sexually dimorphic in adults but in con-
trasting directions. Adult females had longer hind femora and
longer pronota but narrower heads and smaller maxillae spans
than adult males (Table 2, Fig. 3), clearly indicating SShD. Be-
cause the direction of sexual dimorphism varied by morphologi-
cal dimension, it was unclear whether badlands crickets were
sexually dimorphic in overall body size. We addressed this ques-
tion in two ways: 1) we compared adult males and females on
the geometric mean of all measured variables (GMS), and 2) we
used principal components analysis (PCA) to extract a multivari-
ate measure of size (principal component 1, PC1) and an un-
correlated PC2, which can be interpreted as a measure of shape
(Jolicoeur 1963). Adult males and females differed on PC2 but
not PC1 or GMS, indicating that adult badlands crickets are sexu-
ally dimorphic for shape but not size. To further explore SD in
the badlands cricket, we conducted a DFA that extracted a linear
combination of the measured variables that accurately identified
the sex of adult crickets at least 91% of the time. The resulting
discriminant function had factor loadings that closely mirrored
those of PC2, namely that head width and maxillae span loaded
in the opposite direction as pronotum length and mean femur
length. These patterns are consistent with the divergent univari-
ate patterns of sexual dimorphism (Table 2) and describe a pat-
tern of SShD whereby adult males have larger heads and mouth-
parts and adult females have larger thoraxes and hind legs.

Males of many animals have relatively bigger heads and
mouthparts than females, including lizards and snakes (e.g.,
Becker and Paulissen 2012, King et al. 1999, Kratochvil and Frynta
2002), amphibians (e.g., Katsikaros and Shine 1997, Zhang et al.
2020), fish (e.g., Laporte et al. 2018), mammalian carnivores (e.g.,
Gittlkeman and Van Valkenburgh 1997), beetles (e.g., Marlowe et
al. 2015). and orthopterans (e.g., Kelly 2006, Walker et al. 2008,
Judge and Bonanno 2008) (see Shine 1989 for a review of sexually
dimorphic trophic structures). Amongst orthopterans, larger head
size in males is thought to be the result of sexual selection because
males compete for access to female mates by grappling with their
mouthparts (Kelly 2006, Judge and Bonanno 2008). In the fall
field cricket, G. pennsylvanicus, males with proportionately larger
heads were more likely to win aggressive contests, but only if
those contests escalated to grappling with mouthparts (Judge and
Bonanno 2008). Like most Gryllus species (Jang et al. 2008, Ber-
tram et al. 2011), adult male badlands crickets compete aggressive-
ly with each other for females using their heads and mouthparts

E.M. MADERA AND K.A. JUDGE

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Males Females

Fig. 2. Average values for the ratio of head width to pronotum
length for lab reared (open squares, N = 70 for both sexes) and
wild (filled squares, N = 1 male and 9 females) badlands crickets
(Gryllus personatus). Error bars represent 95% confidence limits for
lab reared crickets and + one standard deviation for wild females.

Fig. 3. Matrix scatterplot of the four measured variables: maxillae
span (MS), head width (HW), pronotum length (PL) and mean fe-
mur length (MFL), and geometric mean size (GMS) for male (filled
circles, N = 70) and female (open circles, N = 70) badlands crickets
(Gryllus personatus). All variables have been log transformed (LG)
to facilitate comparison of scaling relationships. Note that the axis
labels are all contained along the diagonal so that each is both an
x-axis label for any plots above and below and a y-axis label for
any plots to the left and right. Thus, every pairwise combination
of variables is plotted twice, with each variable appearing on the
x-axis on one side of the diagonal and on the y-axis on the other.

JOURNAL OF ORTHOPTERA RESEARCH 2023, 32(2)

E.M. MADERA AND K.A. JUDGE

123

Table 5. Studies from a special issue on body size in Orthoptera that measured multiple homologous morphological dimensions in
both males and females, where, in principle, it would have been possible to evaluate both SSD and SShD. Columns indicate the taxa
studied, the number of morphological dimensions measured, whether SSD was evaluated (and if so whether a univariate or multivari-
ate measure of body size was used), conclusions regarding the direction of SSD, and whether SShD was evaluated.

Taxa Measurements SSD?
Caelifera
Chorthippus vagans 4 Yes (U)
Cornops aquaticum 3 Yes (U)
Dactylotum variegatum 2 Yes (U)
Dichroplus pratensis 6 No
6 Yes (U)
D. vittatus 6 Yes (U)
Gomphocerinae (8 spp.) 10 Yes (U)
Oedipoda miniata 4 Yes (U)
Oedipodinae (4 spp.) 10 Yes (U)
Podisma sapporensis 8 No
Romalea microptera Yes (U)
10 Yes (U)
Ensifera
Pholidoptera frivaldskyi 5 Yes (U)
Poecilimon birandi 4 Yes (U)
P. thessalicus 3 Yes (U)
Roeseliana roeselii 5 No
Stenopelmatus sp. 4 Yes (U)

(D. Gray, pers. comm.), suggesting that the sexual dimorphism
in head size relative to pronotum length may also be influenced
by sexual selection through male-male competition. Conversely,
the observed SShD may also reflect differences between the sexes
in mobility, with females evolving longer legs and larger thorax-
es (i.e., increase stride length and leg muscle mass, respectively)
because sexually active female field crickets search for sedentary
singing males (Alexander 1961) all the while attempting to avoid
predation, which may be strongly influenced by jumping ability
(e.g., Ercit et al. 2014). There are several mechanisms which may
result in sex-specific optima for morphological (or other) traits
(Shine 1989, Blanckenhorn 2005), and future research should in-
vestigate sex-specific mobility patterns, diet, burrow digging, and
aggression and the adaptiveness of variation in head and mouth-
part size versus thorax and leg size.

Even though every morphological trait we measured in adult
badlands crickets was sexually dimorphic in univariate analyses,
our multivariate analysis failed to detect any evidence of SSD.
This contrasts with the almost universal female-biased SSD in
over 1500 species of Orthoptera reported in a recent review
(Hochkirch and Gréning 2008). This difference is not surpris-
ing given that we used a multivariate approach to measuring
body size, whereas, by necessity, Hochkirch and Gréning were
constrained to use total body length, a univariate measure of
body size that is widely reported in the taxonomic literature
that formed the basis of their dataset (Hochkirch and Groning
2008). We did not measure total body length because of the
inherent variability in this measurement due to the effects on
abdomen size of nutritional status, oocyte growth, and preserva-
tion artefacts (Hochkirch and Gréning 2008), and so our results
are not directly comparable. However, our study raises ques-
tions as to the true extent of SSD and how often SSD is conflated
with SShD. In a recent special issue on body size in Orthoptera
(Whitman and Vincent 2008), of 13 studies that measured mul-
tiple homologous morphological variables in both males and
females (representing 27 species), only 5 evaluated SShD, and

SSD Pattern SShD? Reference

F>M - Ciplak et al. 2008
F>M Yes Adis et al. 2008
F>M Yes DeBano et al. 2008

- Yes Bidau and Marti 2008b
F>M - Bidau and Marti 2008a
F>M - Bidau and Marti 2008a
F>M - Picaud and Petit 2008
F>M - Ciplak et al. 2008
F>M - Picaud and Petit 2008

- - Sugano et al. 2008
F>M - Huizenga et al. 2008
F>M Yes Vincent and Lailvaux 2008
F>M - Fabriciusova et al. 2008
F>M - Ciplak et al. 2008
F>M - Lehmann and Lehmann 2008

- - Berggren 2008
No Yes Weissman et al. 2008

all 5 found evidence supporting sex differences in body shape
(Adis et al. 2008, Bidau and Marti 2008b, DeBano 2008, Vincent
and Lailvaux 2008, Weissman et al. 2008). Furthermore, of the
9 studies that evaluated SSD, all but one concluded that females
were larger than males; none used a multivariate measure of size
but instead evaluated SSD separately for one or more individual
measurements (Table 5). It is unclear whether a multivariate
measure of body size would have changed the conclusions of
these studies, but until more studies assess both SSD and SShD,
we will not know how often these two sexual dimorphisms con-
found or complement each other.

Although we failed to detect SSD using multivariate methods,
the conclusion that adult badlands crickets are not sexually dimor-
phic for body size should be viewed with some caution as it may
depend on the choice of measured dimensions. Choosing an ap-
propriate index of body size is no simple task (Fairbairn 2007),
and this is precisely because of shape variation within species, in-
cluding 1) SShD, 2) polymorphisms (e.g., alternative male morphs
in isopods, Shuster 1987), 3) age-related changes in body shape,
and 4) condition-dependent effects on body shape (e.g., parasite
effects). Many researchers use a single morphological dimension
as an index of size (Fairbairn 2007). This practice has the advan-
tage of convenience, standardization, and comparability, whereas
multivariate measures of size may not be convenient and can be
sample-dependent and therefore not comparable between studies
(e.g., principal components). In insects, head width is often used
as an index of size (Fairbairn 2007). Because of mounting evidence
of relative head size difference between males and females in Or-
thoptera (e.g., Kelly 2006, Walker et al. 2008, Judge and Bonanno
2008, this study, KAJ unpubl. data) it is becoming increasingly
obvious that, for studies of orthopterans where sex is a factor of
interest, using head width as an index of body size is no longer
appropriate. Failing any consensus on a single measure of size, we
recommend a geometric mean of head width, pronotum length,
and hind femur length. This measure is 1) multivariate, 2) repre-
sentative (i.e., the three dimensions represent two body regions

JOURNAL OF ORTHOPTERA RESEARCH 2023, 32(2)

124

and three morphological axes), 3) convenient (i.e., only three di-
mensions per individual that can be measured on both live and
preserved specimens), 4) universal (i.e., all Orthoptera have these
three structures, which is not the case for wings), 5) comparable
(i.e., not sample dependent like PC-based size measures), and 6)
insensitive to variation in individual condition and damage/pres-
ervation artifacts (i.e., does not include weight or dimensions of
the abdomen, and component dimensions are rigid and shrink
little with drying). Even if individual studies chose to base their
analyses on a different index of size, widespread measurement of
head width, pronotum length, and hind femur length would great-
ly facilitate comparative analyses of both SSD and SShD.

SShD variation can be measured in a variety of ways, includ-
ing intersexual comparisons of 1) regression slopes, 2) second and
higher order principal components, 3) values on a discriminant
function separating males and females, and 4) ratios of different
dimensions to an index of body size (e.g., shape ratios; Mosimann
1970). Ideally SShD studies should incorporate more than one of
these methods, and to the extent that different methods result in
similar conclusions, shape ratios offer a useful comparative func-
tion that is absent from the other multivariate, sample-dependent
methods. Ratios are scale-independent and so can be calculated
from any image regardless of magnification. In the badlands crick-
et, results from PCA, DFA, and a simple comparison of the ratio
of head width to pronotum length all suggested the same conclu-
sion: that males have relatively wider heads than females. We then
used the simple ratio method to measure SShD in a sample of im-
ages of badlands crickets posted by citizen scientists to iNaturalist.
The head width/pronotum length ratios of these wild crickets were
within 5% of the averages of our lab-reared individuals, and the
degree of SShD was similar in wild and lab-reared badlands crick-
ets. It is worth noting that machine learning methods for image
recognition, such as the one used by iNaturalist to suggest species
identification, rely on scale-independent characteristics such as ra-
tios of different dimensions.

In conclusion, we found evidence of SShD in adult badlands
crickets: females had relatively longer hind legs and pronota than
males, who had relatively wider heads and maxillae spans than
females. A variety of multivariate methods failed to detect SSD,
and although we cannot (nor wish to) claim that male and fe-
male adult badlands crickets are the same size, we do suggest that
our results are cause to revise how body size is typically mea-
sured in arthropods in general and Orthoptera in particular. The
geometric mean of three body dimensions—head capsule width,
pronotum length, and hind femur length—has both the proper-
ties of universality, sample independence, comparability, and is
multivariate. The widespread adoption of this body size measure-
ment by orthopterists would open up enormous possibilities for
comparative assessments of the prevalence and direction of both
SSD and SShD.

Acknowledgements

We thank W. Cade for logistical support at the University of
Lethbridge, D. Gray for both supplying G. personatus nymphs and
comments on a previous draft, B. Smith for help with rearing the
crickets, D. Sanderson for assistance with lab equipment, and A.
Hochkirch, D. Nandi, and D. Whitman for helpful comments dur-
ing the review process. This research was supported by Natural
Sciences and Engineering Research Council Discovery Grant RG-
PIN-2017-04674 to KAJ. Lastly, thanks to the crickets for giving up
their lives for research.

E.M. MADERA AND K.A. JUDGE

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