Breaking the rule: multiple patterns of scaling of sexual size dimorphism with body size in orthopteroid insects

Abstract

El dimorfismo sexual de tamaño (SSD por sus siglas en inglés) es un fenómeno ampliamente distribuido en los animales y sin embargo, enigmático en cuanto a sus causas últimas y próximas y a las relaciones alométricas entre el SSD y el tamaño corporal (regla de Rensch). Analizamos el SSD a niveles intra- e interes - pecíficos en un número de especies y géneros representativos de los órdenes or - topteroides mayores: Orthoptera, Phasmatodea, Mantodea, Blattodea, Dermaptera, Isoptera, y Mantophasmatodea. La vasta mayoría de las especies mostraron SSD sesgado hacia las hembras, pero numerosas excepciones ocurren en cucarachas y dermápteros. La regla de Rensch y su inversa no constituyeron patrones comunes, tanto a nivel intraespecífico como interespecífico, con la mayoría de las especies y géneros mostrando una relación isométrica entre los tamaños de macho y hembra. En algunos casos, los patrones alométricos hallados podrían relacionarse con la va - riación geográfica del tamaño corporal. También demostramos que no todos los es - timadores de tamaño corporal producen el mismo grado de SSD y que el dimorfismo puede estar influenciado por un gran número de condiciones de vida y patrones de desarrollo ninfal. Finalmente, discutimos nuestros resultados en relación a modelos actuales de la evolución del dimorfismo sexual de tamaño en animales.

Full text

11
Recibido: 14-I-2016; aceptado: 17-III-2016
Breaking the rule: multiple patterns of scaling of sexual size
dimorphism with body size in orthopteroid insects
1Paraná y Los Claveles, 3304 Garupá, Misiones, Argentina. E-mail: bidau50@gmail.com
2,3
Laboratorio de Genética Evolutiva. Instituto de Biología Subtropical (IBS) CONICET-Universi-
dad Nacional de Misiones. Félix de Azara 1552, Piso 6°. CP3300. Posadas, Misiones Argentina.
2,3Comité Ejecutivo de Desarrollo e Innovación Tecnológica (CEDIT) Felix de Azara 1890, Piso
5º, Posadas, Misiones 3300, Argentina.
Quebrando la regla: multiples patrones alométricos de dimorfismo sexual de tama-
ño en insectos ortopteroides
RESUMEN.
El dimorfismo sexual de tamaño (SSD por sus siglas en inglés) es un
fenómeno ampliamente distribuido en los animales y sin embargo, enigmático en
cuanto a sus causas últimas y próximas y a las relaciones alométricas entre el SSD
y el tamaño corporal (regla de Rensch). Analizamos el SSD a niveles intra- e interes-
pecíficos en un número de especies y géneros representativos de los órdenes or-
topteroides mayores: Orthoptera, Phasmatodea, Mantodea, Blattodea, Dermaptera,
Isoptera, y Mantophasmatodea. La vasta mayoría de las especies mostraron SSD
sesgado hacia las hembras, pero numerosas excepciones ocurren en cucarachas y
dermápteros. La regla de Rensch y su inversa no constituyeron patrones comunes,
tanto a nivel intraespecífico como interespecífico, con la mayoría de las especies y
géneros mostrando una relación isométrica entre los tamaños de macho y hembra.
En algunos casos, los patrones alométricos hallados podrían relacionarse con la va-
riación geográfica del tamaño corporal. También demostramos que no todos los es-
timadores de tamaño corporal producen el mismo grado de SSD y que el dimorfismo
puede estar influenciado por un gran número de condiciones de vida y patrones de
desarrollo ninfal. Finalmente, discutimos nuestros resultados en relación a modelos
actuales de la evolución del dimorfismo sexual de tamaño en animales.
PALABRAS CLAVE. Tamaño corporal. Blattodea. Dermaptera. Mantodea. Man-
tophasmatodea. Caracteres morfométricos. Orthoptera. Phasmatodea. Regla de
Rensch. Alometría.
ABSTRACT. Sexual size dimorphism (SSD) although a widespread phenomenon
among animals, is both enigmatic as to its proximate and ultimate causes and the
scaling relationships between SSD and body size (Rensch’s rule). We analyzed
SSD at the intra- and interspecific levels in a number of representative species and
genera of the major orthopteroid orders: Orthoptera, Phasmatodea, Mantodea, Blat-
todea, Dermaptera, Isoptera, and Mantophasmatodea. The vast majority of the spe-
cies showed female biased SSD but numerous exceptions occur in cockroaches
and earwigs. Rensch’s rule and its converse are not common patterns at both, intra-
and cross-species level, most species and genera showing an isometric relation-
ship between male and female body sizes. In some but not all cases, the demon-
strated allometric patterns could be related to geographic body size variation. We
also showed that not all body size estimators produce the same degree of SSD and
that dimorphism can be strongly influenced by a number of living conditions and
the patterns of nymphal development. Finally, we discuss our results in relation to
BIDAU, Claudio J.
1
, Alberto TAFFAREL
2,3
& Elio R. CASTILLO
2,3
ISSN 0373-5680 (impresa), ISSN 1851-7471 (en línea) Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2015
Trabajo Científico
Article

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Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
INTRODUCTION
The length range of living systems is aston-
ishing: it spans 17 orders of magnitude from
DNA molecules to ecosystems; while organisms
vary 7 orders of magnitude in length and 21 in
mass (Ellers, 2001). Insects have an impressive
body size range, from less than 0.2 mm in the
parasitic wasp Dicopomorpha echmepterygis
(Mymaridae) to ca. 360 mm in the stick-insect
Phobaeticus chani (Phasmatidae). Body mass
varies accordingly with females of the giant
weta, Deinacrida heteracantha (Anostostoma-
tidae) weighing more than 70 g (Björkman et
al., 2009). The enormous amount of scientific
literature relative to animal body size reflects
the importance of this trait in biology. Almost
every life history and ecological characteristic
of animals is correlated with body size (LaBar-
bera, 1986, 1989; Calder, 1996; Smith & Lyons,
2013) and in turn body size is strongly affected
by most ambient abiotic and biotic factors (Gas-
ton, 1991; Chown & Gaston, 2010, 2013; Price
et al., 2011). Thus, most physical, physiologi-
cal, ecological, and evolutionary processes are
highly dependent on size; these relationships
are called scale effects or scaling. As defined
by Barenblatt (2003), scaling “… describes a
seemingly very simple situation: the existence
of a power-law relationship between certain
variables y and x, y = Ax
α
, where A,
α
are con-
stants.” This so-called allometric equation is
usually expressed in logarithmic form as log y =
log A +
α
log x. The concept of allometric scal-
ing was initially developed by Otto Snell (1892),
D’Arcy Wentworth Thompson (1917), and Julian
Huxley (1932) and resulted in numerous theo-
retical and empirical investigations of the scal-
ing laws regulating the allometric relationship
of many organismic traits with body size (e.g.
Schmidt-Nielsen, 1975, 1984; Brown & West,
2005; Hoppeler & Weibel, 2005).
Differences in body size between sexes (sexu-
al size dimorphism, SSD) are pervasive in the ani-
mal kingdom and thus, a fundamental component
of body size variation (
e. g.
Darwin, 1871; Anders-
son, 1994; Fairbairn, 2013). SSD is a controversial
aspect of evolutionary biology for several reasons.
On one side, although sexual selection has tradi-
tionally been assumed as the key process behind
SSD, it is now well known that natural selection
can also produce size differences between males
and females and that both processes are not com-
pletely independent from one another (
e.g.
Isaac,
2005; Carranza, 2009). This problem includes
the study of the adaptive significance of SSD, the
genetic constraints to its evolution, and its proxi-
mate and ultimate causes (Fairbairn, 1997, 2007).
Secondly, a problem which has not received a
satisfactory explanation is that of the allometric
scaling of SSD with body size. Bernhard Rensch
(1950, 1960) proposed that in phylogenetically re-
lated species, SSD increases with general body
size when males are larger than females and
decreases when females are larger. This pattern
was termed Rensch´s rule by Abouheif & Fair-
bairn (1997) but despite numerous studies in very
diverse taxa (Fairbairn et al., 2007) there is little
evidence to support this rule and no convincing
mechanism for its operation has been proposed
(Reiss, 1989; Webb & Freckleton, 2007; Bidau &
Martí, 2008a; Martínez et al., 2014).
Further problems regarding the scaling of
SSD with body size remain. In the first place,
there is the question of the taxonomic level at
which it is studied, and if Rensch’s rule operates
(if it does) in any taxonomic entity. Most studies
of the scaling of SSD with body size either phylo-
genetically-based or not have been performed
across species at different levels (Fairbairn et
al., 2007), and only a few intraspecifically as for
example, in insects, some grasshoppers and
beetles (e.g. Bidau & Martí, 2008b; Stillwell &
Fox, 2009; Blanckenhorn et al., 2007a,b). An
additional problem is that of the appropriate
measurements for analyzing SSD (Fairbairn,
2007). Is it the same using body mass or body
length, or some other measurement (e.g. pro-
notum width, wing length) as a proxy for body
size? Are SSDs for different measurements sig-
nificantly correlated? (Martínez et al., 2014).
Orthopteroids do not only vary greatly in
current models of the evolution of sexual size dimorphism in animals.
KEY WORDS. Body size. Blattodea. Dermaptera. Mantodea. Mantophasmatodea.
Morphometric traits. Orthoptera. Phasmatodea. Rensch’s rule. Scaling.

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
13
size (Nasrecki, 2004; Bell et al., 2007; Whit-
man, 2008; Brock & Hasenpusch, 2009) but
also in the magnitude of SSD and in body
shape (Hochkirch & Gröning, 2008; Bidau et
al., 2013; Bidau, 2014). Furthermore, many
species are fairly common, easy to collect, and
have large geographic distributions that allow
the sampling of several populations inhabiting
different or even contrasting environments (Bi-
dau et al., 2012). The latter is relevant because
it has been suggested that in species showing
intraspecific geographic variation in body size
(e.g. Bergmann’s rule [Bergmann, 1847]) there
may exist a link between these patterns and the
scaling of SSD with body size (Blanckenhorn
et al., 2006). In this sense orthopterans are an
excellent model for the comparative analysis
of SSD and although a few studies have been
performed (Bidau & Martí, 2008b), virtually
nothing is known about patterns of SSD at the
intraspecific level regarding the points men-
tioned in this Introduction.
The aim of this investigation is to analyze the
magnitude of SSD, its scaling with body size,
the comparison between different estimates of
SSD, and the geographic variation of SSD in
several species of Orthoptera belonging to the
suborders Caelifera and Ensifera, as well as
species of Mantodea, Phasmatodea, Blattodea,
Isoptera and Dermaptera, using new data as
well as published information.
MATERIALS AND METHODS
1. Data collection
For the purposes of this paper we collected in-
formation from the published scientific literature on
geographic variation of body measurements of sev-
eral orthopteroid species from most of the orders
usually included in the orthopteroid assemblage
(Tables 1-9). We collected data for two purposes:
a. Intraspecific analyses. The criteria used for
including species were that at least 5 geographi-
cally separated populations were studied, and that
data on body size (either body length, body mass
or some adequate morphometric proxy) for both
sexes were available for each population or sam-
ple. Also, we included unpublished data on three
South American melanoplines (Orthoptera: Acridi-
dae: Melanoplinae), Dichroplus fuscus (Thunberg)
(17 populations, 193♂/133♀), Ronderosia bergii
(Stål) (19 populations, 152♂/108♀) and Scotussa
cliens (Stål) (6 populations, 56♂/58♀) (Table 1).
Most studies of geographic variation of body size
of orthopteroids are based on different linear mea-
surements. However, different authors use different
estimators of body size. For example, body length
and length of hind femur are commonly used mea-
surements but in some groups (e.g. Gryllidae and
Proscopiidae) researchers tend to favor measure-
ments of the head and the pronotum as proxies for
body size. Body mass measurements are extreme-
ly rare in these insect groups thus, few cases of
body mass SSD were included in this study. Some
studies included only one measurement of body
size while others, reported variation in male and
female size of up to 10-plus linear characters. The
latter were especially favorable because allowed
the comparison of degrees of SSD and Rensch’s
rule in different traits. Data were obtained from
published tables and, in a few cases, extrapolated
from graphs provided in the publication. The study
concentrates in species where data on a sufficient
number of populations were available for statisti-
cal analyses, although some cases included only
a few populations and this is indicated in the text.
Whenever the information was available, geo-
graphic data of each population (latitude, longitude
and elevation) were recorded. The raw data in all
analyses were male and female population means
for each trait. These values were log-transformed
for the purpose of statistics. Mean body length val-
ues for each species as shown in Tables 1, 6, 8,
and 9 were obtained from the published literature
usually averaging data from several populations. In
the case of those species reported here for the first
time, six linear measurements were obtained: body
length, hind femur length, hind tibia length, length
of tegmina, pronotum length and pronotum height.
b. Cross-species (interspecific analysis):
In
order to put each of the intraspecific analyses
within the context of the higher-order taxa to
which the species belong regarding body size
and sexual size dimorphism, we collected data
on body length of a large number of species
of Orthoptera, Phasmatodea, Mantodea, Blat-
todea, and Dermaptera to produce cross-spe-
cies analyses of the scaling of SSD with body
size, and graphs representing the variation of
SSD within each higher-order taxon (Tables 8,
9; Figs. 1, 2). A graph for the Orthoptera was
not included because a comprehensive one has
been recently published (Hochkirch & Gröning,
2008). Only data on male and female body

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Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
Table 1.
Orthopteroid species for which scaling of sexual size dimorphism (SSD) was analyzed in this
paper. In the column corresponding to Rensch’s rule, values in parentheses are the slopes of RMA re-
gressions (see text). All measurements correspond to adult individuals. In the case of the two Isoptera
species, measurements correspond to alates.
Higher order
taxa
Species Location Body
length
(mm)
Body size
trend
SSD
trend
Rensch’s
rule
References
Acrididae,
Melanoplinae
Dichroplus fuscus
(Thunberg)
Argentina,
Paraguay
M: 18.0
F: 20.1
LON (+M.+F) LON (↓) Is (1.04) This paper
Dichroplus pratensis
Bruner
Argentina M: 22.3
F: 25.2
LAT (-M,-F) NP R (1.38) Bidau & Martí,
2007a, 2008b
Dichroplus pratensis
hybrid zone
Argentina M: 22.3
F: 25.2
ELE (+M) ELE (↓) Is (1.04) Miño et al.,
2011
Dichroplus vittatus
Bruner
Argentina M: 15.0
F: 21.5
LAT (-M,-F) NP IR (0.77) Bidau & Martí,
2007b, 2008b
Melanoplus
boulderensis Otte
U.S.A. M: 19.0
F: 23.0
ELE (-M. –F) ELE () IR Levy & Nufio,
2014
Melanoplus
devastator Scudder/
M. sanguinipes
(Fabriicius)
U.S.A. M: 20.8
F: 23.0
--- --- IR (0.78) Orr, 1996
Melanoplus
femurrubrum (DeGeer)
U.S.A. M: 19.8
F: 26.0
LAT (-M, -F) LAT (↑) Is (1.10) Parsons &
Joern, 2014
Melanoplus
sanguinipes (Fabricius)
U.S.A. M: 21.3
F: 24.2
LAT (-M,-F)
ELE (-M, -F)
NP R (1.28) Orr, 1996; Roff
& Mousseau,
2005
Neopedies brunneri
(Giglio-Tos)
Argentina M: 17.8
F: 21.4
LON (-M, -F)
ELE (-M, -F)
NP Is (0.87) Romero et al.,
2014
Podisma sapporensis
Shiraki
Japan M: 19.1
F: 25.2
?? ?? Is (0.89) Tatsuta &
Akimoto, 1998
Ronderosia bergii (Stål) Argentina,
Paraguay
M: 18.2
F: 23.4
LON (-F)
ELE (-F)
LAT (↑) Is (1.02) This paper
Scotussa cliens (Stål) Argentina M: 24.3
F: 31.2
LON (+F) LAT (↑) IR (0.58) This paper
Acrididae,
Leptysminae
Cornops aquaticum
Bruner
Argentina,
Brazil,
Uruguay,
Trinidad,
South
Africa
M: 25.6
F: 31.1
NP LON (↑) R (1.25) Adis et al.,
2008
Acrididae,
Gomphocerinae
Aeropedellus clavatus
(Thomas)
U.S.A. M: 17.3
F: 20.3
ELE (-M. –F) ELE (↓) IR Levy & Nufio,
2014
Chorthippus cazurroi
(Bolivar)
Spain M: 13.0
F: 18.0
ELE (-M, -F) NP Is (0.98) Laiolo et al.,
2013
Chorthippus vagans
(Eversmann)
Turkey M: 16.6
F: 22.4
?? NP Is (1.01) Ciplak et al.,
2008
Chorthippus yersini
Harz
Spain M: 19.0
F: 25.0
ELE (-F) ELE (↓) Is (0.92) Laiolo et al.,
2013

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
15
Omocestus viridulus
(Linnaeus)
Switzerland
M: 15.8
F: 20.5
LAT (+M, +F)
LON (-M, -F)
ELE (-M, -F)
LON (↓)
ALR (↓)
Is (0.81/0.98) Berner &
Blanckenhorn,
2006
Pseudochorthippus
parallelus parallelus
(Zetterstedt)
Spain,
France
M: 15.0
F: 20.0
NP* NP R (1.57) Laiolo et al.,
2013
Psudochorthippus
parallelus erythropus
(Faber)/ P.p. parallelus
France M: 13.0
F: 17.5
--- --- R (1.36) Butlin &
Hewitt, 1985
Acrididae,
Acridinae
Caledia captiva
(Fabricius)
Australia M: 24.5
F: 30.0
LAT (+F) LAT (↑) Is (1.06) Groeters &
Shaw, 1996
Acrididae,
Catantopinae
Phaulacridium vittatum
(Sjösted)
Australia M: 12.0
F: 16.0
NP NP Is (0.94) Harris et al.,
2012
Acrididae,
Cyrtacanthacridinae
Schistocerca alutacea
(Harris)
North
America
M: 47.0
F: 59.0
--- --- R (1.27) Hubbell, 1960
Acrididae,
Oedipodinae
Oedipoda miniata
(Pallas)
Turkey M: 19.5
F: 24.3
--- --- NR Ciplak et al.,
2008
Xanthippus corallipes
(Haldeman)
U.S.A. M: 43.0
F: 62.0
ELE (-M, -F) ELE (↑) R (1.40) Ashby, 1997
Romaleidae,
Romaleinae
Romalea microptera
(Palisot de Beauvois)
U.S.A. M: 55.0
F: 65.0
LON (-M, -F)
LAT (-M,-F)*
NP Is (0.88) Huizenga et
al., 2008
Pyrgomorphidae,
Pyrgomorphinae
Zonocerus variegatus
(Linnaeus)
Nigeria M: 34.8
F: 38.3
LAT (+M) ELE (↑) Is (0.84) Bamidele &
Muse, 2012
Tettigoniidae,
Tettigoniinae
Metrioptera roeselii
(Hagenbach)
Sweden M: 20.0
F: 22.0
LAT (+F) LAT (↑) Is (0.97) Holma, 2009
Eobiana engelhardti
(Uvarov)
Japan M: 26.0
F: 29.0
LAT (-M, -F) LAT (↑) R (1.30) Higaki &
Ando, 2002
Tettigoniidae,
Phaneropterinae
Poecilimon luschani
birandi Karabag
Turkey M: 20.8
F: 22.5
ELE (-M. –F) ELE (↑) IR? Ciplak et al.,
2008
Poecilimon thessalicus
Brunner von Wattenwyl
Greece M: 19.0
F: 20.0
NP* LAT (↓) R (1.64) Lehmann
&Lehmann,
2008
Poecilimon veluchianus
veluchianus Ramme
Greece M: 17.0
F: 19.0
ELE (-M, -F) NP Is (1.09) Eweleit &
Reinhold,
2014
Poecilimon veluchianus
minor Heller & Reinhold
Greece M: 16.3
F: 17.1
ELE (-F) ELE (↑) Is (0.90) Eweleit &
Reinhold,
2014
Poecilimon veluchianus
Ramme (both
subspecies)
Greece --- NP NP Is (1.10) Eweleit &
Reinhold,
2014
Tettigoniidae,
Conocephalinae
Conocephalus
spartinae (Fox)
U.S.A: M: 12.1
F: 13.0
LAT (-M. –F) NP Is (0.90)
Wason &
Pennings, 2008
Orchelimum fidicinium
Rehn & Hebard
U.S.A. M: 18.0
F: 16.5
LAT (-M. –F) NP Is (0.88)
Wason &
Pennings, 2008
Gryllidae,
Gryllinae
Teleogryllus emma
(Ohmachi & Matsuura)
Japan M: 24.3
F: 21.4
LAT (-M, -F) NP Is (1.04) Masaki, 1967
Higher order
taxa
Species Location Body
length
(mm)
Body size
trend
SSD
trend
Rensch’s
rule
References

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Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
Velarifictorus micado
(Saussure)
Japan M: 15.3
F: 20.0
LAT (-M, -F) NP R (1.25) Zeng & Zhu,
2014
Gryllidae,
Nemobiinae
Polionemobius
taprobanensis (Walker)
Japan M: 6.7
F: 6.8
LAT (+M, +F) LAT (↑) IR (0.69) Masaki, 1978
Gryllotalpidae,
Scapteriscinae
Neoscapteriscus
borellii Giglio-Tos
U.S.A. M: 30.4
F: 31.0
---- --- R (1.84)* Forrest, 1987
Anostostomatidae
Hemiandrus pallitarsis
(Walker)
New
Zealand
M: 22.0
F: 23.0
LAT (-M,-F) LAT (↑) R (1.76) Chappell,
2008
Blattodea-
Corydiidae
Eupolyphaga sinensis
(Walker)
China M: 22.6
F: 29.0
LAT(+M) LAT (↓) Is (0.96) Hu et al., 2011
Mantodea,
Mantidae
Tenodera
angustipennis
(Saussure)
Japan M: 73.0
F: 79.0
--- --- IR* Matsura et al.,
1975
Isoptera,
Rhinotermitidae
Reticulitermes speratus
Kolbe
Japan M: 3.8
F: 5.5
--- --- Is (0.88) Matsuura,
2006
Isoptera,
Termitidae
Nasutitermes corniger
(Motschulsky)
Panama M: 6.8
F: 6.9
--- --- Is (1.07) Thorne, 1983
length of each species were considered, and
only length measurements from tip of head to
tip of abdomen were included. Measurements
were obtained from primary and secondary
published sources on the basis of availability
and the meeting of our standard criterium for
length measurement.
2. The analysis of sexual size dimorphism
and testing of Rensch’s rule
Because SSD is practically always female-
sex biased in the studied species as is the rule
in most orthopteroids, we used the simplest
SSD estimator which is the ratio of the arith-
metic means of female size and male size that
produces SSD indices higher than 1.0. Three
exceptions occurred within our sample: length
of pronotum and wing length SSD are male-
biased in the mole-cricket Scapteriscus borelli
and the katydid Metrioptera roeselii (it could be
possible that, in the last case, sampling bias
is the cause of the observation), respectively,
and head width in the cricket Velarifictorus mi-
cado (Table 2). The scaling of SSD with body
size was analyzed using a Model II regression
method: Reduced Major Axis (RMA) regression;
ordinary least-squares (OLS) regression is inad-
equate for this type of analysis. The use of RMA
regression of log10 (male size) on log10 (female
size) is also justified because RMA is symmetric
which means that a single regression line de-
fines the bivariate relationship independently of
which variable is X and which is Y, and this is
the case for SSD comparisons: Rensch’s rule is
supported when the slope βRMA is significantly
> 1.0, while slopes < 1.0 signal its reversion.
Slopes not significantly different from 1.0 indi-
cate sexual isometry. We run the regressions
using the software of Bohonak & van der Linde
(2004). One-delete Jacknife estimates of a, β
and r2 were obtained and 95% confidence in-
tervals were calculated by bootstrapping 10000
times over cases. The RMA slope is significantly
different from 1.0 when the former value is not
included within the calculated 95% confidence
intervals. In a few cases although the 1.0 values
were included in the CI but so close to one of the
limits, the difference of the slope was consid-
ered significant. RMA regression was also em-
ployed to investigate allometries between body
parts. Simultaneous autoregressions (SARs)
between body size and SSD variables (different
SSD indexes using various body size estima-
Higher order
taxa
Species Location Body
length
(mm)
Body size
trend
SSD
trend
Rensch’s
rule
References
M: male; F: female. LAT: latitude; LON: longitude; ELE: elevation. NP: no discernible pattern. -/+: indicate the sign of the cor-
relation between male and female body size, and geographic coordinates and elevation. Arrows indicate if SSD increases or
decreases with LAT, LON and ELE. R: Rensch’s rule; IR: converse Rensch’s rule; Is: Isometry.

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
17
Table 2. Mean índices of sexual size dimorphism (SSD= female size/male size) of different traits for
all taxa shown in Table 1. References as in Table 1 except *.
Species Trait (mean SSD)
D. fuscus BL (1.27): F3L (1.28); T3L (1.30); TEL (1.22); PL (1.30); PH (1.30)
D. pratensis BL (1.08); F3L (1.11); T3L (1.12); TEL (1.03); PL (1.11); PH (1.14)
D. pratensis hybrid zoneBL (1.04); F3L (1.06); T3L (1.10); TEL (0.99); PL (1.06); PH (1.08)
D. vittatus BL (1.27); F3L (1.27); T3L (1.28); TEL (1.22); PL (1.41); PH (1.33)
M. devastator /M. sanguinipes BL (1.03)
M. femurrubrum F3L (1.14)
M. sanguinipes F3L (1.06); TEL (1.03); PL (1.04)
N. brunneri F3L (1.18); T3L (1.15); PL (1.15); TEL (1.11)
P. sapporensis BL: (1.32); HL (1.41); HW (1.27); ED (2.08); F1L (1.16); F2L (1.23); F3L (1.52); T3L
(1.59); PL (1.61); EL (1.22); TAT (0.85)
R. bergii BL (1.23); F3L (1.25); T3L (1.28); TEL (1.16); PL (1.32); PH (1.33)
S. cliens BL (1.22); F3L (1.23); T3L (1.23); TEL (1.14); PL (1.32); PH (1.28)
C. aquaticum TL (1.20); BL (1.39); TEL (1.20)
C. cazurroi BL (1.35)
C. vagans BL (1.37); TEL (1.25); F3L (1.28)
C. yersini BL (1.33)
O. viridulus F3L (1.27/1.22);
P. parallelus parallelus BL (1.37)
P. parallelus erythropus/ P.p. parallelus F3L (1.06)
C. captiva PL (1.33)
P. vittatum F3L (1.27)
S. alutacea PW (1.43)
O. miniata BL (1.25); F3L (1.27); TEL (1.23)
X. corallipes BM (3.33)
R. microptera F3L (1.08); PL (1.15)
Z. variegatus Bl (1.10)
E. wagenknetchi* BL (1.53); F3L (1.34); F3W (1.31); TEL (1.28); TEW (1.51); HW (1.36); PL (1.52);
PH (1.34); BM (3.13); DW (3.07)
M. roeselii BL (1.20); F3L (1.09); T3L (1.12); F3W (1.04); TEL (0.67); HL (1.12); HW (1.15); PW
(1.10); BM (1.47)
E. engelhardti HW (1.08)
P. luschani birandi BL (1.09)
P. thessalicus F3L (1.09); T1L (1.05); PL (1.04)
P. veluchianus veluchianus F3L (1.10)
P. veluchianus minor F3L (1.12)
P. veluchianus (both subspecies) F3L (1.11)
C. spartinae T3L (1.09)
O. fidicinium T3L (1.09)
T. emma HW (1.00)
V. micado HW (0.96); BW (1.11)
P. taprobanensis HW (1.06)
S. borellii PL (0.83)

18
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
tors), and geographic coordinates and eleva-
tion, were performed in SAM v.4.0 (Rangel et
al., 2010). Taxonomy follows Beccaloni (2015),
Brock (2015), Eades et al. (2015), Hopkins et
al. (2015), and Otte et al. (2015). Final retrieval
dates are indicated.
3. A test of the differential variability hy-
pothesis for Rensch’s rule
An expected condition for the operation of
Rensch’s rule is that males are more variable in
body size than females. If this condition holds,
we expect that in those species showing the con-
verse Rensch’s rule, females should display the
highest variability while in those cases where the
relationship between male and female body size
is isometric, both sexes should be equally vari-
able. In order to test this hypothesis, we calculat-
ed male and female coefficients of variation (CV
= s/
⨰
*100 where s= standard deviation, and
⨰
=
arithmetic mean) of body size to produce a mea-
sure of the differential inter-sex variability (∆CD).
4. SSD and Rensch’s rule in different traits
We tested Rensch’s rule for different linear
morphometric characters using the above de-
scribed methodology in 7 species in order to
test if differences of SSD for each character
affected the scaling of sexual dimorphism with
body size. Also, a large scale comparison was
performed in our Dermaptera sample to high-
light a higher-order pattern of sexual dimor-
phism divergence comparing body length and
forceps length sexual dimorphism.
5. Intraspecific allometric scaling
Because differences in static allometry within
species are important factors in determining
SSD when different traits are used, we explored
these allometric patterns within four melano-
pline grasshopper species using Ordinary Least
Squares (OLS) regressions and paired-samples
t-test comparisons.
6. Testing the effects of different rearing
and ecological conditions on SSD
Since it is well-known that body size is highly
affected by environmental conditions (e.g. Whit-
man, 2008) it is only reasonable to expect that
SSD will be similary affected. To test this hypoth-
esis we obtained body size data of males and
females of several orthopteroid species that
were laboratory-reared in different ambient con-
ditions or that were studied in different ecologi-
cal scenarios
7. Testing the effects of ontogenetic allom-
etry on final SSD
Assuming that differential rates of develop-
ment and number of nymphal stages affect the
degree of adult SSD, we performed compari-
sons of SSD during nymphal development of 10
species of orthopteroid insects for which accu-
rate measurements of different traits were per-
formed at each nymphal instar and adult stage.
RESULTS
1. Body size and sexual size dimorphism in
the studied species
Because SSD could be influenced by body
size (see below) we tried to cover the widest
possible range of sizes among the study species
(Table 1). Within our sample, the smallest caelif-
erans were Phaulacridium vittatum (Sjöstedt)
(Catantopinae) and Myrmeleotettix maculates
(Thunberg) (Gomphocerinae), and the smallest
ensiferans, the tettigoniid Conocephalus spar-
tinae (Fox) (Conocephalinae) and the cricket
Polionemobius taprobanensis (Walker) (Nemo-
biinae) (Tables1, 4). The smallest species were
the termites Reticulitermes speratus Kolbe and
Nasutitermes corniger (Motschulsky) (Table 1).
The largest species are represented by Roma-
lea microptera (Palisot de Beauvois) (Roma-
H. pallitarsis BL (1.06); F3L (1.04); HL (1.11); HW (1.12); FaL (1.14)
E. sinensis BL (1.28); BW (1.72); PW (1.56)
P. angustipenns BL (1.09)
R. speratus DW (1.13)
N. corniger DW (1.28)
Species Trait (mean SSD)
BL: body length; TL: total length; BM: body mass; DW: dry weight; F1L: fore femur length; F2L: mid femur length; F3L: hind femur
length; T3L: hind tibia length; TEL: tegmina length; TEW: tegmina width; PL: pronotum length; PH: prontum height; PW: prono-
tum width; PH: pronotum height; HW: head width; HL: head length; ED: eye distance; EL: epiproct length; TAT: tenth abdominal
tergum; FaL: fastigium length. *Elasmoderus wagenknetchi (Liebermann, 1942). Ref.: Cepeda-Pizarro et al., 2003.

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
19
leidae) and the acridids Xanthippus corallipes
(Haldeman) (Oedipodinae) and Ornithacris tur-
bida (Walker) (Cyrtacanthacridinae) within the
Orthoptera, and the Japanese mantid Tenodera
angustipennis Saussure (Tables 1, 6). It must be
kept in mind that the mean lengths are averages
of many individuals and populations; most spe-
cies and especially those with large geographic
distributions, show high variability in body length.
SSD was calculated for all available measure-
ments of each species. Most measurements are
linear and in only a few cases, body mass or dry
weight were available for male/female compari-
son (Table 2). For the Orthoptera, female/male
size ratios were in general higher in caeliferans
than in ensiferans as it has been previously re-
ported (see discussion). However, interspecies
variation is high even between closely related
species. For example, within the genus Dichro-
plus, D. pratensis Bruner shows a body length
SSD of 1.04-1.08 while its sister species D. vit-
tatus Bruner and other congener, D. fuscus
(Thunberg) are much more dimorphic (SSD=
1.27) (Table 2). Within the melanoplines stud-
ied here, the most dimorphic species was Po-
disma sapporensis Shiraki (Table 2). While the
Melanoplinae show low to moderate SSD (see
discussion) other caeliferans are characterized
by higher levels of dimorphism as is the case
of the Gomphocerinae represented in this work
by several truxaline species all of them showing
relatively high SSD values (Tables 1, 2, 6).
In the few cases where body mass was
available for calculating SSD, values were sig-
nificantly higher than those for linear measure-
ments (Tables 2, 6). For example, the oedipo-
dine Xanthippus corallipes has a mean SSD
index of 1.44 when body length is considered,
but SSD= 3.33 for body mass (Table 2) reflect-
ing the different dimensionality of the employed
measurements. However, the difference beween
both indexes are not always as high: in the katy-
did Metrioptera roeselii (Hagenbach) BL SSD=
1.20 and BM SSD= 1.47, and in the cockroach
Eupolyphaga sinensis (Walker) 1.28 and 1.76,
respectively (Table 2). In one case, the cricket
Velarifictorus micado (Saussure), SSD for head
width and body mass showed opposite direc-
tions (Table 2 and see Discussion).
In order to illustrate the wide variation in SSD
in our study organisms, we contructed Figs. 1
and 2. The bar graphs clearly show the extent
Fig. 2.
Distribution of sexual size dimorphism for body size
(female body length/male body length) in a. Blattodea. b.
Dermaptera. In b. White columns represent the distribution of
sexual dimorphism for forceps length. Arrows mark mean values.
Fig. 1.
Distribution of sexual size dimorphism for body size
(female body length/male body length) in a. Phasmatodea.
b. Mantodea. Arrows mark mean values.

20
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
and range of variation of SSD in the different
polyneopteran orders discussed in this paper.
2. Scaling of SSD with body size follows dif-
ferent patterns
Table 1 shows the results of RMA regressions
between log10 (male size) and log10 (female
size) for several orthopteran species, a cock-
roach, a praying mantis, and two termites. For
each species, the regression slope (
β
RMA) and
the 95% confidence intervals are shown. In all
cases when it was possible, the slope for the
regression of male body length on female body
length is shown; in the rest of cases, the slope
corresponds to the regression using the first
measurement shown in Table 2. Of the 45 ana-
lyzed cases, Rensch’s rule (as indicated by a
slope significantly > 1.0) occurred in 12 (26.7%)
thus, SSD decreases as body size increases. In
eight cases (17.8%) scaling of SSD with body
size followed a converse trend (
β
RMA<1.0) in
which dimorphism increases with body size. In
the rest (55.5%), male and female body sizes
scaled isometrically (
β
RMA =1.0). Interestingly
enough, all three patterns were observed in
three closely related species of a single genus,
Dichroplus Stål (Tables 1, 2).
A further interesting observation pertains to
the scaling of SSD with body size within hybrid
zones. As a whole, D. pratensis follows Rensch’s
rule but the rule was not verified within a hybrid
zone between two chromosomal races which dif-
fer in body size and the degree of SSD (Table
1). Melanoplus sanguinipes (Fabricius) also fol-
lows Rensch’s rule but the analysis of a hybrid
zone between this species and M. devastator
showed the converse pattern (Table 1). Finally,
Pseudochorthippus parallelus parallelus (Zetter-
stedt) complies with Rensch’s rule and the same
pattern was observed among populations of a
hybrid zone with the subspecies Pseudochor-
thippus parallelus erythropus (Faber) (Table 1).
3. SSD scaling and morphometric variability
Because it has been considered that one of
the preconditions for Rensch’s rule is a higher
variability of body size in males with respect to fe-
males, we calculated the coefficients of variation
Table 3. Male and female coefficients of variation (CV= s/
⨰
*100) for morphometric traits used in the
calculation of RMA regression slopes in species that follow Rensch’s rule, its converse, or show iso-
metric scaling. M= male; F= female; ∆CV= male CV – female CV. References as in Table 1.
Rensch’s rule Converse Rensch’s rule Isometry
Coefficient
of variation
Coefficient
of variation
Coefficient
of variation
Species M F ∆CV Species M F ∆CV Species M F ∆CV
D. pratensis 8.86 6.17 2.69 D. vittatus 6.84 9.04 -2.20 D. fuscus 4.27 3.40 0.87
M. sanguinipes 7.60 6.20 1.40 M. boulderensis 5.71 7.79 -2.08 R. bergii 6.91 6.57 0.34
C. aquaticum 5.69 4.60 1.09 M. devastator 7.78 5.79 1.99 C. cazurroi 5.66 6.56 -0.90
P. p. parallelus 8.46 5.30 3.16 S. cliens 3.13 4.42 -1.29 C. yersini 3.78 3.94 -0.16
P. p. erythropus
3.82 2.58 1.24 A. clavatus 9.82 9.05 0.77 C. captiva 3.78 3.47 0.31
S. alutacea 10.79 8.72 2.07 P. luschani 14.8 12.3 2.50 P. vittatum 3.87 4.35 -0,48
X. corallipes 5.41 3.77 1.64 P. taprobanensis 1.52 2.18 -0,66 R. microptera 8.97 10.07 -1.10
E. engelhardti 7.31 5.61 1.70 T. angustipennis 4.35 8.37 -4.02 Z. variegatus 3.30 3.84 -0,54
P. thessalicus 6.60 3.98 2.62 -------------------- ------ ------ ------
P. v. veluchianus
4.88 4.44 0.44
V. micado 6.32 4.44 1.88 -------------------- ------ ------ ------ P. v. minor 5.56 4.91 0.65
N. borellii 3.66 1.99 1.67 -------------------- ------ ------ ------ C. spar tinae 9.62 10.1 -0,48
H. pallitarsis 7.14 4.67 2.47 -------------------- ------ ------ ------ O. fidicidium 6.92 7.88 -0,96
-------------------- ------ ------ ------ -------------------- ------ ------ ------ T. emma 6.84 6.73 0.11
-------------------- ------ ------ ------ -------------------- ------ ------ ------ E. sinensis 3.17 3.22 -0.05
-------------------- ------ ------ ------ -------------------- ------ ------ ------ R. speratus 9.7 11.4 -1.70
-------------------- ------ ------ ------ -------------------- ------ ------ ------ N. corniger 8.4 8.0 0.40

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
21
(CV) of the body size estimators of both sexes
(Table 3). In all cases where Rensch´s rule was
verified, males were more variable than females.
In the case of those taxa following the con-
verse to Rensch’s rule, females were more vari-
able than males in five species. Those cases in
which a higher CV was observed in males could
be attributed to low sample size (Aeropedellus
clavatus (Thomas) and Poecilimon luschani bi-
randi Karabag) or to the fact that measurements
were taken from populations within a hybrid
zone (Melanoplus devastator Scudder). Those
species where the scaling of SSD with body size
was isometric did not show any consistent pat-
tern of body size variation in males and females.
Furthermore, both sexes of these taxa showed
very similar levels of variability (Table 3).
4. The use of different measurements may pro-
duce different estimates of SSD and scaling patterns
The vast majority of measurements employed
in this study are linear since these are the most
frequently used by biologists when analyzing
body size variation in orthopteroid insects. Body
mass measurements are rare and for reasons
that will be discussed later, probably not the
best for studying SSD (however see below). We
calculated SSD for all available measurements
in all taxa and the results are shown in Table 2. It
can be seen that, considering that all SSD esti-
mates were calculated using the same individu-
als and populations, a considerable variation
in SSD indices occur in many of the species.
For example, although in some species differ-
ent linear measurements produced practically
identical SSD estimates (e. g. Melanoplus san-
guinipes (Fabricius), Dichroplus pratensis), in
others strikingly different indexes were obtained.
One clear case is that of Podisma sapporensis
where SSD ranges from a male biased 0.85 for
the length of the tenth abdominal tergum, to
1.61 in the case of pronotum length while body
length produced 1.31 (Table 2).
Furthermore, variation in the scaling patterns
of SSD with body size also occurs when different
measurements are used in regression analyses.
Table 4 shows values of
β
RMA in seven melano-
pline species for which several linear measure-
ments were available in a variable number of
populations. It is evident that while some spe-
cies show a remarkable consistency regarding
the scaling pattern (e.g. D. fuscus, D. vittatus,
D. pratensis, R. bergii, and S. cliens) others do
not (e.g. P. sapporensis and Neopedies brun-
neri (Giglio-Tos)) (Table 4).
It is worth noting that despite the fact that dif-
ferent linear traits may show different degrees
of sexual dimorphism, SSD tends to be highly
correlated although exceptions do occur. How-
ever, the distribution of SSD values of different
traits are usually significantly different as dem-
Table 4. Scaling of sexual size dimorphism for several traits of seven species of melanopline grass-
hoppers. References as in Table 1.
βRMA (95% Confidence Interval)
SPECIES N BL F3L T3L TEL PL PH HL HW
D. fuscus 17
1.04 (0.60-
1.45)
0.89
(0.58-1.03)
0.98
(0.56-1.32)
0.81
(-1.06-1.35)
1.04
(0.64-1.46)
1.15
(0.52-1.79)
--- ---
D. pratensis 25
1.33
(0.98-1.68)
1.77
(1.19-2.35)
1.89
(1.17-2.60)
1.46
(1.12-1.80)
1.62
(1.13-2.11)
1.74
(1.17-2.309
--- ---
D. vittatus 19
0.77
(0.55-0.99)
0.75
(0.53-0.98)
0.70
(0.48-0.92)
0.71 (0.44-
0.98)
0.88
(0.59-1.16)
0.66 (0.44-
0.88)
--- ---
R. bergii 17
1.02
(0.68-1.66)
1.10
(0.75-1.80)
1.11
0.77-1.74)
0.98
(0.90-1.19)
1.13
(0.77-1.77)
1.06
(-0.95-1.78)
--- ---
P. sapporensis
14
--- 0.89
(0.79-1.09)
0.96
(0.74-1.46)
--- 0.63
(0.33-0.94)
--- 0.83
(0.50-1.239
0.89
(0.63-0.98)
S. cliens 6
0.58
(0.31-1.109
0.57
(0.30-0.99)
0.66
(0.34-1.00)
0.60
(0.35-1.44)
0.58
(0.37-1.17)
0.77
(0.09-1.23)
--- ---
N. brunneri 5
--- 0.86
(0.21-1.22)
0.39
(0.29-1.56)
0.97
(0.66-1.29)
0.57
(-0.35-0.81)
--- --- ---
N: number of populations; BL: body length; F3L: hind femur length: T3L: hind tibia length; TEL: tegmina length; PL: pronotum
length; PH: pronotum height; HL: head length; HW: head width.

22
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
onstrated by paired t-test comparison (Table 5).
If the growth of different body organs were iso-
metric in both sexes we would not expect differ-
ences in SSD for different linear traits. However,
most structures show allometric growth and, if
differential sexual allometry occurs, then unequal
SSD estimates could be obtained for different
body parts. To analyze this problem we studied
static allometry in relation to SSD of six linear mor-
phometric characters in 4 grasshopper species
using individual (not population averages) mea-
surements. Results are shown in Table 5. It can be
seen that for most traits, males and females have
different patterns of allometric growth (as shown
by significant differences between the slopes of
OLS regressions of log10 [trait] on log10 [body
length]) and the degree of variation in SSD esti-
mates is associated with these differences.
A more dramatic case of the disparity be-
tween sexual dimorphism for body size and
specific body parts is found in earwigs. Differ-
ently from other orthopteroid orders, the Der-
maptera show a large number of species with
little or no SSD with respect to body length and
almost equivalent numbers of species with
male-biased and female-biased SSD (see Dis-
cussion and Fig. 2b). However, earwigs have
conspicuous forceps-like cerci which can be
extremely dimorphic in size and form. As shown
in Fig. 2b sexual dimorphism of forceps length
follows a completely different distribution from
that of SSD for body length. Furthermore, aver-
age body length SSD is, in our sample, 1.04,
and sexual dimorphism for forceps length, 0.85.
Both SSDs are not significantly correlated (R2=
0.005; p= 0.235). A second selected example
of this situation is that of the bark mantid genus
Liturgusa Saussure, which as all Mantodea pos-
sesses highly specialized hunting forelegs (see
Table 9). Mean SSD (range) for six morphomet-
ric characters (data from Svenson, 2014) were:
body length, 1.29 (1.14-1.63); prothoracic femur
(F1) length, 1.26 (1.12-1.55); mesothoracic fe-
mur (F2) length, 1.15 (1.04-1.27); metathoracic
Table 5. A. Allometric scaling of 5 morphometric traits with body length in four species of melano-
pline grasshoppers. B. Correlations between SSD for body length and SSD for six linear traits, and
the respective paired t-tests in the same species.
Trait
A.
F3L T3L TeL PL PH
Species
nM/F
bM bF t ; p bM bF t ; p bM bF t ; p bM bF t ; p bM bF t ; p
Dichroplus
fuscus
193/121
0.890
0.868 5.41;
<0.001
0.695 0.772 6.21;
<0.001
0.766 0.807 2.34;
<0.05
0.786 0.974 31.4;
<0.001
0.757 0.624 2.96;
<0.005
Ronderosia
bergii
155/93
0.687
0.948 27.99;
<0.001
0.694 0.948 33.81;
<0.001
0.865 1.277 17.72;
<0.001
0.744 0.835 40.53;
<0.001
0.696 0.838 25.02;
<0.001
Scotussa
cliens
95/53
0.835
0.901 1-44; ns 0.844 0.866 0.94;
ns
0.724 0.662 11.77;
>0.001
0.927 0.906 3.74;
<0.001
0.906 0.860 3.84;
<0.001
Dichromatos
lilloanus
40/57
0.871
0.739 3.38;
=0.001
0.809 0.823 0.23; ns 1-358 1.226 2-56;
<0.05
0.859 0.860 ≅0;
ns
1-190 0.617 13.51;
<0.001
SSD BL/F3L SSD BL/T3L SSD BL/TeL SSD BL/PL SSD BL/PH
B.
R2Pair. t p R2Pair.t p R2Pair.t p R2Pair. t p R2
Pair. t
p
Dichroplus
fuscus
0.68**
3.29
<0.05
0.49* 5.44
<0.001 0.14ns
2.67
<0.05
0.20ns
3.53
<0.05
0.70** 3.62
<0.05
Ronderosia
bergii
0.84**
1.97 ns 0.87** 5.43
<0.001
0.37* 4.94
<0.001
0.79** 6.12
<0.001
0.59** 4.65
<0.001
Scotussa
cliens
0.74*
1.40 ns 0.84* 1.52 ns
0.52ns
4.82
<0.001
0.67* 5.50
<0.001 0.41ns
3.11
<0.05
Dichromatos
lilloanus
0.41ns
1.25 ns
0.44ns
3.31
<0.05
0.13ns
1.66 ns 0.69* 3.99
<0.005 0.19ns
2.42
<0.05
F3L: femur 3 length; T3L: tibia 3 length; TeL: tegmina length; PL: pronotum length; PH: pronotum height; nM/F: number of males
and females measured; bM, bF: slopes of OLS regressions between log10 (trait) and log10 (body length); t,p: Student´s t-statistic
for the difference between male and female slopes and its significance; R2: coefficient of determination; Pair.t: t-statistic for the
paired t-tests between SSDs; p: statistical significance.

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
23
Table 6. Effects on sexual size dimorphism (SSD= female size/male size) of different living and rear-
ing conditions in twelve species of orthopteroid insects.
M: male; F: female; F3L: hind femur length; TEL: tegmina length; PL: pronotum length; HW: head width; BM: body mass. G:
generation; ISO: isolated population.
SPECIES LOCATION BODY SIZE
(mm)
CONDITION F3L TEL PL HW BM References
Schistocerca
pallens (Thunberg)
Barbados
M.: 42
F: 52
ISOLATED 1.25 1.23 1.27 1.19 1.92 Antoniou &
Robinson, 1974
CROWDED 1.20 1.20 1.22 1.20 1.67
Ornithacris turbida
(Walker)
Africa
M.: 50
F: 61
ISOLATED 1.19 1.19 --- 1.15 1.69 Antoniou, 1973
CROWDED 1.23 1.23 1.18 1.89
Melanoplus
differentialis
(Thomas)
U.S.A.
M.: 31.5
F: 36.5
ISOLATED 1.27 1.17 1.29 1.25 --- Dingle & Haskell,
1967
CROWDED 1.20 1.14 1.14 1.17
Acheta domesticus
(Linnaeus)
Canada
M.: 25.0
F: 30.0
ISOLATED --- --- --- --- 1.06 McFarlane, 1962
CROWDED --- --- --- --- 1.06
Locusta migratoria
(Linnaeus)
Africa, Asia
M.: 37.5
F: 50.0
ALBINO ISOLATED 1.19 1.22 1.19 1.22 -- Hoste et al.,
2002
ALBINO CROWDED 1.11 1.14 1.14 1.15 ---
NORMAL ISOLATED 1.16 1.23 1.16 1.23 ---
NORMAL
CROWDED
1.06 1.08 1.09 1.11 ---
Anabrus simplex
Haldeman
U.S.A.
Greystone
M: 41.0
F: 45.0
HIGH DENSITY --- --- 1.013 --- 1.48 Gwynne, 1984
U.S.A., Indian
Meadows
LOW DENSITY --- --- 1.008 --- 1.26
Schistocerca
shoshone (Thomas)
U.S.A., Portal
M: 41.5
F: 58.0
Prosopis
Simmondsia
--- --- --- --- 1.41
1.49
Sword &
Chapman, 1994
U.S.A., Tacna Prosopis
Simmondsia
--- --- --- --- 1.67
1.49
Chorthippus
brunneus
(Thunberg)
England
M.:15.5
F: 20.0
25°C
30°C
35°C
1.16
1.22
1.28
--- --- --- 1.45
1.67
1.92
Willott & Hassall,
1998
Omocestus
viridulus (Linnaeus)
England
M.:15.8
F: 20.5
25°C
30°C
35°C
1-11
1.25
1.25
--- --- --- 1.27
1.67
1.72
Willott & Hassall,
1998
Myrmeleotettix
maculatus
(Thunberg)
England
M.:11.5
F: 13.5
30°C
35°C
1.15
1.16
--- ------ --- 1.35
1.43
Willott & Hassall,
1998
Stenobothrus
lineatus (Panzer)
England
M: 16.5
F: 23.0
30°C
35°C
1.10
1.15
--- --- --- 1.41
1.54
Willott & Hassall,
1998
Blatella germanica
(Linnaeus)
Germany
M.:13.5
F: 20.0
24°C
27°C
33°C
1.02
1.06
1.09
1.10
1.12
1.12
--- --- 1.30
1.25
1.28
Reinhard, 2007
Chorthippus
brunneus
(Thunberg)
Belgium
M.:15.5
F: 20.0
URBAN
RURAL
1.20
1.19
1.18
1.16
--- --- 2.44
2.44
San Martin y
Gomez & Van
Dyck, 2002
Pholidoptera
fryvaldszkyi
(Herman)
Slovakia
M.:15.5
F: 20.0
ISO1
ISO2
ISO3
1.08
0.99
1.11
--- 1.07
0.97
1.08
--- 1.25
1.00
1.43
Fabriciusová et
al., 2008
Oedaleus
senegalensis
(Krauss)
Africa
M.:29-0
F: 38.6
G1
G2
1.24
1.26
1.30
1.31
1.25
1.27
1.32
1.33
--- Ritchie, 1981

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Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
femur (F3) length, 1.14 (1.02-1.29); and prono-
tum (P) length, 1.24 (1.15-1.44). The converse
Rensch’s rule was verified for body length
(
β
RMA= 0.70 [0.51-0.94]), and F1 (
β
RMA=
0.59 [0.49-0.81]) while the other three charac-
ters showed sexual isometry; F2 (
β
RMA= 0.85
[0.69-1.01]), F3 (
β
RMA= 0.999 [0.76-1.14]), and
P (
β
RMA= 0.91 [0.74-1.08])
5. Geographic variation of SSD within species
Many of the species studied by us showed
significant clinal variation in body size along
latitudinal, elevational and/or longitudinal geo-
graphic gradients (Table 1). The most frequent
trends involved a decrease in size towards high-
er latitudes or elevations although other patterns
or the lack of a pattern, were observed (Table
1). Because SSD could be affected by these
body size clines, we analyzed if significant SSD
geographic clines also existed. As shown in
Table 1, in at least 19 cases, SSD clines along
the geographic coordinates and elevation were
observed usually in coincidence with body size
clines although the existence of the latter did not
always imply SSD clines.
6. Temporal Variation of SSD
The vast majority of species analyzed by us
are univoltine. However, there is an exception
represented by the mole cricket Neoscapter-
iscus borellii (Giglio-Tos) which has more than
one generation per year. It is most interesting
that this species follows Rensch’s rule not spa-
tially (data used in this study come from the
same population at different times of the year)
but temporally since different generations show
different body sizes and SSDs (Table 1). Many
bi- or multivoltine grasshoppers also show dif-
ferences in size and SSD between genera-
tions as is the case of Oedaleus senegalensis
(Krauss) in which two consecutive adult gen-
erations showed a 12% increase in body size of
both sexes and a slight but significant increase
of SSD in all studied characters (Table 6).
7. Different ecological and/or rearing con-
ditions can change SSD
Different living conditions such as different
diets or rearing temperatures can modify adult
body size of insects, thus potentially altering
SSD. We analyzed different situations in which
orthopteroid populations experienced divergent
living conditions (Table 6). In almost all studied
cases, changes in diet, rearing temperature or
environment produced modifications of final
adult size of males and females and changes
in the degree of SSD. However, these changes
seem to be species specific as shown by the
effects of rearing in isolation or crowded condi-
tions in four orthopteran species. While SSD de-
creases in crowded conditions in Schistocerca
pallens (Thunberg) and two strains of Locusta
migratoria (Linnaeus), it has the opposite ef-
fect in Ornithacris turbida while no differences
in SSD were observed in a study of Acheta do-
mesticus (Linnaeus). Regarding diet, opposite
effects were obtained when locusts, Schisto-
cerca shoshone (Thomas) from two different
populations were made to feed on two different
plant species (Table 6). Increasing rearing tem-
perature produced parallel effects in four spe-
cies of gomphocerine grasshoppers, that is, an
increase of SSD while no significant differences
were observed in the cockroach Blatella ger-
manica (Linnaeus) (Table 6).
8. SSD and nymphal development
Final adult size of insects, and thus SSD, is
determined during development. As hemime-
tabolus insects, orthopteroids reach adulthood
after a number of nymphal stages which var-
ies among species. We studied SSD for sev-
eral characters during nymphal development of
seven orthopteran species (Table 7). The num-
ber of nymphal stages varied widely (4-11) in
the studied species. What all analyzed cases
have in common is that during a large part of
development nymphs show no SSD or reversed
SSD and that final female-biased dimorphism is
reached during the final developmental stages.
In some species, this occurs mainly because fe-
males add a further instar (e.g. Bryophyma deb-
lis (Karsch), Chorthippus brunneus (Thunberg),
Eyprepocnemis plorans meridionalis Uvarov,
and Atractomorpha sinensis sinensis Bolívar)
not present in males, while in other species
where males and females share the same num-
ber of nymphal stages (e.g. Phymateus lepro-
sus (Fabricius), Deinacrida White spp.), there is
a fixed moment when female-biased SSD starts
to incresase until reaching the adult value (Table
7). The situation is further complicated in cases
such as the mantid Psudomantis albofimbriata
Stål where although males experience one extra
nymphal stage adults nevertheless reach high
female-biased SSD (Table 7). In another pray-
ing mantis the developmental outcome is even
more complicated because nymphs of both

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
25
Table 7. Sexual size dimorphism (SSD) of different traits in seven orthopteran species. SSD calcu-
lated as female size/male size is shown for each instar. Final (adult) SSD is indicated in bold type.
Instar number
Species
N of
Instars
Trait12345678910 11 Ref.
Phymateus leprosus
(Fabricius)
M: 10
F: 10
BL 0.95 0.90 0.90 1.03 1.00 0.93 1.11 1.18 1.23 1.20 1
F3L 1.02 1.05 0.97 1.06 1.05 1.01 1.05 0.99 1.06 1.05
Bryophyma debilis
(Karsch)
M: 5
F: 6
BL 0.96 0.99 1.04 0.97 0.99 1.45 2
BM 1.00 0.94 1.09 1.11 0.93 1.19
PL 0.89 1.03 1.00 0.89 1.01 1.30
F3L 0.92 1.04 1.03 0.96 0.94 1.30
Chorthippus
brunneus
(Thunberg)
M: 4
F: 4, 5
F3l 1.01 1.05 1.23 1.28 3
BM 0.87 0.76 1.46 1.72
Eyprepocnemis
plorans meridionalis
Uvarov
M: 7
F: 7, 8
HW1 1.07 1.05 1.05 1.1 1.14 1.16 1.19 4
HW2 1.04 0.97 1.02 1.02 1.01 1.05 1.13 1.31
Atractomorpha
sinensis sinensis
Bolívar
M: 6
F: 7
A0.97 1.03 1.02 0.81 0.81 0.88 0.99 5
PL 0.91 1.03 0.98 0.88 0.98 1.22 1.30
HWP 1.00 0.93 1.08 0.38 0.56 1.05 1.16
F3L 1.04 1.06 1.01 0.88 0.95 1.06 1.22
Deinacrida fallai
Salmon
M: 10
F: 10
F3L 1.00 1.00 1.00 1.00 1.00 1.19 1.15 1.36 1.23 1.26 6
BM 1.00 1.00 1.00 1.00 1.08 1.07 1.06 2.00 2.50 2.22
Deinacrida
heteracantha White
M: 11
F: 11
F3L 1.00 1.00 1.00 1.13 0.88 0.84 0.97 0.98 1.04 1.17 1.14 6
BM 1.00 1.00 1.00 1.00 1.14 1.20 1.00 1.00 1.17 1.73 1.73
Pseudomantis
albofimbriata Stål
M: 7
F: 6
PL 1.05 1.40 1.45 1.49 1.42 1.38 1.20 7
Hierodula majuscula
Tindale
M: 9
F: 10
PL 1.00 1.00 1.00 1.00 1.00 0.95 0.96 0.97 1.08 1.39 7
Stagmomantis
limbata Hahn
M: 6,7
F: 7,8
PL --- --- --- --- 0.98 1.36 1.43 8
PL --- --- --- --- 1.10 1.18 1.28
PL --- --- --- --- 0.88 1.21 1.57 1.62
PL --- --- --- --- 0.99 1.05 1.36 1.47
Higher order taxonomy of species: P. leprosus (Pyromorphidae: Pyrgomorphinae); B. debilis (Acrididae: Cyrtacanthacridinae);C.
brunneus (Acrididae: Gomphocerinae); E. plorans (Acrididae: Eyprepocnemidinae); A. sinensis (Pyromorphidae: Pyrgomorphi-
nae); D. fallai, D. heteracantha (Anostostomatidae: Deinacridinae); P. albofimbriata, H. majuscule, S. limbata (Mantidae, Man-
tinae): References: 1. Kohler et al., 2008; 2. Luong-Skovmand & Balança, 1999; 3. Hassall & Grayson, 1987; 4. Jago, 1963; 5.
Kevan & Lee, 1974; 6. Richards, 1973; 7. Allen et al., 2013; 8. Maxwell, 2014. Abbreviations: BL, body length; BM, body mass;
F3L, hind femur length; HW, head width; A, antenna; PL, pronotum length; HWP, hind wing pad.

26
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
sexes may experience a variable number of in-
stars in the same population; thus, the degree of
SSD depends on what categories of males and
females are compared (Table 7).
DISCUSSION
Sexual dimorphism is arguably the most per-
vasive characteristic of bisexual organisms and
was the main inspiration of Darwin’s (1871) the-
ory of sexual selection. Sexual dimorphism has
multiple manifestations as differences between
males and females in secondary sexual charac-
ters. Although the latter have been difficult to de-
fine precisely (e.g. Darwin, 1871; Cunningham,
1900; Morgan, 1919) a simple definition would
be “Differences between males and females of
a species in size, structure, color, ornament, or
other morphological trait(s), not including the
sex organs” (Broughman, 2014), although di-
morphism is also manifested in behavioral or
biochemical traits. One of the most conspicu-
ous types of sex dimorphism is constituted by
differences in size between males and females.
Sexual size dimorphism (SSD) can be slight and
barely perceptible, or spectacular with members
of one sex many times larger or heavier than the
other (Fairbairn, 2013). Additionally, both sexes
frequently differ in the size of specific body parts
(sexual body component dimorphism or SBCD)
which are sometimes used to estimate the de-
gree of SSD (Fox et al., 2015): SSD may be male-
biased or female-biased which is the case of
the majority of invertebrates including insects
(although exceptions do occur; see below) (e.g.
Andersson, 1994; Faibairn et al., 2007; Fairbairn,
2013), while SBCD may not always follow the
same direction as SSD (Fox et al., 2015).
Despite the enormous quantity of studies of
SSD in all kinds of species since Darwin´s time,
the phenomenon remains largely an enigma
(Fairbairn, 2007, 2013). The studies of SSD
roughly involve two main problems (Reiss, 1986,
1989; Andersson, 1994; Fairbairn et al., 2007).
One is that of the ultimate causes of SSD where
both sexual selection and natural selection have
been variously favored since Darwin’s time.
While Darwin (1871) proposed sexual selection
as the main (but not unique) mechanism behind
SSD and other forms of sexual dimorphism,
Wallace (1889) considered that the vast majority
of cases could be explained essentially by clas-
sic natural selection. Sexual selection operates
via two processes: intrasexual selection where
individuals of one sex compete in various ways
for the access to individuals of the opposite
sex, and intersexual or epigamic selection that
involves choice of the members of one sex by
members of the other sex (Darwin, 1871; Ander-
sson, 1994; Kokko et al., 2006; Clutton-Brock,
2009). A further proposed cause for SSD espe-
cially apt for female-biased SSD is fecundity se-
lection (Honek, 1993; Reeve & Fairbairn, 1999)
although a positive relationship between body
size and fertility has also been documented for
male insects (e.g. bush crickets; Wedell, 1997).
Natural selection could be the cause of SSD
in cases of niche partitioning between males
and females (sexual segregation) (Shine, 1989;
Isaac, 2005). However, the effects of sexual and
natural selection are frequently very difficult to
discriminate, hence, some authors have pro-
posed to eliminate the distinction between both
forms of selection and concentrate on “con-
trasts in the components, intensity and targets
of selection between males and females’’ (Clut-
ton-Brock, 2010). In this sense, the “differential
equilibrium hypothesis” of SSD proposes that
males and females are differential targets of op-
posing selective forces that shape SSD (Blanck-
enhorn, 2005; Hochkirch & Grõning, 2008). A
further complication is represented by the mul-
tiple proximate mechanisms that can determine
differences in size between the sexes: in insects
for instance protandry may favor smaller males
(
e.g.
Morbey & Ydenberg, 2001; Bidau & Martí,
2007a, b; Blanckenhorn et al., 2007a, b) while
a greater number of larval or nymphal stages
and longer development may produce larger
females (
e.g.
Teder & Tammaru, 2005; Esperk
et al., 2007; Tammaru et al., 2010; Teder, 2014).
The other problem that has generated a prof-
fuse literature is that of the scaling of SSD with
body size essentially derived from Rensch’s
hypothesis (Rensch, 1950, 1960) later termed
Rensch’s rule (Abouheif & Fairbairn, 1997).
However, as Reiss (1986, 1989) has pointed
out, Rensch’s original data are not statistically
significant. Furthermore, many studies have
failed to prove an allometric scaling of SSD with
body size in the sense of Rensch’s rule espe-
cially when females are larger than males (
e.g.
Webb & Freckleton, 2007; Bidau et al., 2013)
but also when SSD is male-biased (Lindenfors

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
27
et al., 2007; Martínez et al., 2014; Martínez &
Bidau, 2016). This is particularly true for insects
(Blanckenhorn et al., 2007b). Thus far, no con-
vincing explanatory mechanism for Rensch’s
rule (at least in the cases in which it seems to
operate) has been postulated (Reiss, 1986,
1989; Martínez et al., 2014).
The large assemblage of Neopteran insects
referred to as “orthopteroids” shows a striking
amplitude of body sizes from tiny (less than 5
mm long) ant-inquiline crickets and termites to
giant stick insects exceeding 300 mm in total
body length (e.g. Prete et al., 1999; Bell et al.,
2007; Whitman, 2008; Brock & Hasenpusch,
2009; Bignell et al., 2011). Also, the vast major-
ity of species in all orthopteroid orders shows
SSD. As in most insects, SSD is frequently fe-
male-biased but cases of male-biased SSD also
occur in some orders (e.g. Blanckenhorn et al.,
2007a, b; Hochkirch & Gröning, 2008; Chown
& Gaston, 2010). The distribution of SSD within
orthopteroid orders has seldom been analyzed
(Sivinski, 1978; Hochkirch & Gröning, 2008; Bi-
dau et al., 2013). In the Orthoptera the Caelifera
Table 8.
Scaling of sexual size dimorphism with body size in assorted families and subfamilies of
orthopteran insects. In columns 5, 6 and 7 mean male and female body lengths (BL) and average SSD
are given. Values in parentheses represent the respective ranges. In the last column, the slope (
β
)
of the RMA regression of log10 (male BL) on log10 (femaleBL) and the 95% confidence intervals (in
parentheses) are shown. In bold type, taxa that follow Rensch’s rule or its converse. The extensive bib-
liography consulted for the construction of this Table is readily available from the corresponding author.
ORDER FAMILY SUBFAMILY N° OF
TAXA
MALE BL FEMALE BL BL SSD
[F/M]
βRMA
Orthoptera
(Caelifera)
Tristiridae 22 18.8
(6.9-34.9)
23.8
(10.0-39.6)
1.29
(1.00-1.69)
1.105
(0.93-1.28)
Ommexechidae 24 15.9
(5.2-25.8)
22.6
(8.6-36.6)
1.46
(1.19-2.73)
1.075
(0.95-1.24)
Proscopiidae* 60 --- --- 1.33
(0.79-1.70)
0.967
(0.90-1.05)
Tetrigidae 89 8.2
(5.3-13.3)
10.2
(7.0-14.7)
1.25
(0.97-1.57)
1.053
(0.92-1.19)
Romaleidae 195 30.1
(11.9-87.5)
42.9
(14.1-109.3)
1.43
(1.03-1.95)
0.953
(0.91-0.99)
Pamphagidae 43 28.9
(16.5-55.0)
43.4
(25.5-77.0)
1.52
(1.12-2.20)
1.024
(0.87-1.20)
Acrididae Catantopinae 140 17.9
(10.2-46.9)
23.7
(13.1-59.0)
1.33
(1.07-2.00)
0.980
(0.92-1.04)
Oedipodinae 221 21.1
(13.0-42.0)
28.1
(17.8-53.0)
1.35
(0.96-2.52)
1.092
(1.01-1.18)
Gomphocerinae 206 15.7
(8.2-28.0)
21.1
(12.5-36.0)
1.35
(1.00-2.12)
0.965
(0.90-1.05)
Melanoplinae 798 18.8
(9.0-34.5)
23.8
(12.8-44.0)
1.27
(1.01-1.83)
0.968
(0.94-1.01)
Orthoptera
(Ensifera)
Tettigoniidae Phaneropterinae 115 19.2
(7.3-37.0)
20.9
(7.8-36.5)
1.10
(0.90-1.63)
1.042
(0.96-1.11)
Decticinae 163 20.5
(9.3-47.5)
22.5
(9.8-50.3)
1.10
(0.92-1.43)
1.001
(0.96-1.04)
Ephippigerinae 62 26.4
(15.3-43.5)
28.0
(16.2-41)
1.06
(0.85-1.22)
1.023
(0.92-1.14)
Rhaphidiophoridae 27 17.9
(12.5-34.0)
18.3
(12.5-31.5)
1.03
(0.76-1.24)
1.085
(0.85-1.26)
Gryllidae 65 11.5
(2.2-34.5)
12.1
(2.2-36.5)
1.07
(0.86-1.39)
1.041
(1.01-1.09)
*SSD was calculated using pronotum length and not total body length.

28
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
Table 9.
Scaling of sexual size dimorphism with body size in assorted genera of orthopteroid insects.
In columns 5, 6 and 7 mean male and female body lengths (BL) and average SSD are given. Values in
parentheses represent the respective ranges. In the last column, the slope (
β
) of the RMA regression
of log10 (male BL) on log10 (femaleBL) and the 95% confidence intervals (in parentheses) are shown.
In bold type, genera that follow Rensch’s rule or its converse. The extensive bibliography consulted for
the construction of this Table is readily available from the corresponding author.
ORDER FAMILY GENUS N° OF
TAXA
MALE BL FEMALE BL BL SSD [F/M]
β
RMA
Orthoptera
(Caelifera)
Pyrgomorphidae Atractomorpha
Saussure, 1862
21 20.0
(16.0-24.5)
30.2
(24.0-36.0)
1.52
(1.35-2.08)
0.997
(0.80-1.27)
Pamphagidae Acinipe Rambur, 1838 633.3
(29.0-41.0)
48.9
(37.5-69.5)
1.45
(1.29-1.70)
0.571
(0.42-0.68)
Pamphagidae Asiotmethis Uvarov,
1943
727.5
(25.0-31.5)
35.5
(31.7-41.0)
1.29
(1.20-1.36)
1.064
(0.76-1.53)
Acrididae Calliptamus Serville,
1831
717.6
(14.0-19.5)
26.9
(22.5-29.0)
1.53
(1.41-1.68)
1.287
(0.84-2.34)
Acrididae Sphingonotus Fieber,
1852
12 17.6
(13.5-22.0)
24.5
(17.8-31.0)
1.39
(1.16-1.70)
0.941
(0.65-1.22)
Acrididae Oedaleus Fieber,
1853
33 26.2
(19.0-38.2)
34.7
(24.2-46.1)
1.32
(1.10-2.04)
0.897
(0.71-1.07)
Acrididae Chorthippus Fieber,
1852
99 15.4
(10.0-24.0)
20.5
(13.3-34.5)
1.34
(1.07-1.58)
0.981
(0.83-1.45)
Acrididae Arcyptera Serville,
1838
12 23.1
(21.0-28.0)
30.4
(25.5-35.5)
1.32
(1.09-1.38)
0.880
(0.40-1.68)
Acrididae Dociostaurus Fieber,
1853
10 15.3
(9.0-23.0)
22.3
(12.5-33.5)
1.46
(1.30-1.86)
0.902
(0.63-1.17)
Acrididae Omocestus Serville,
1838
17 13.1
(10.3-17.2)
16.9
(13.8-21.5)
1.29
(1.12-1.41)
0.851
(0.65-1.07)
Acrididae Stenobothrus Fischer,
1853
20 16.5
(11.0-22.0)
21.5
(14.5-34.0)
1.32
(1.16-1.53)
0.852
(0.67-1.13)
Acrididae Melanoplus Stål, 1873 293 19.0
(9.5-33.0)
23.4
(14.5-48.0)
1.22
(0.84-1.82)
1.010
(0.95-1.10)
Acrididae Conophyma
Zubovski, 1898
78 14.9
(10.2-19.8)
19.4
(13.1-27.6)
1.30
(1.01-1.56)
0.858
(0.76-0.97)
Acrididae Pseudoceles Bolívar,
1899
11 17.6
(16.0-20.0)
23.9
(21.0-27.0)
1.35
(1.25-1.49)
0.959
(0.62-1.67)
Acrididae Thalpomena
Saussure, 1884
916.5
(14.5-18.5)
22.9
(20.5-25.0)
1.39
(1.22-1.56)
1.190
(0.20-2.18)
Acrididae Diexis Zubovski, 1899 813.2
(10.9-15.3)
21.9
(17.8-27.5)
1.65
(1.48-2.00)
0.702
(0.32-1.11)
Acrididae Oxya Serville, 1831 16 22.3
(17.7-29.8)
28.2
(21.5-32.2)
1.28
(1.04-1.58)
1.304
(0.92-2.17)
Dericorythidae Dericorys Serville,
1838
826.3
(18.4-46.99
37.7
(26.5-53.4)
1.50
(1.14-1.18)
1.522
(1.06-2.03)
Lentulidae Usambilla Sjöstedt,
1910
12 7.7
(7.0-8.3)
9.3
(8.5-10.9)
1.21
(1.13-1.39)
0.956
(0.74-1.25)
Romaleidae Xyleus Gistel, 1848 17 32.3
(29.2-36.4)
44.3
(38.5-52.6)
1.37
(0.67-0.80)
0.807
(0.63-1.06)
Romaleidae Zoniopoda Stål, 1873 10 32.3
(28.8-39.4)
43.0
(36.0-48.9)
1.33
(1.23-1.45)
1.025
(0.63-1.46)
Romaleidae Argiacris Walker,
1870
11 33.9
(29.8-37.6)
52.9
(38.6-63.1)
1.54
(1.14-1.85)
0.440
(0.17-0.99)

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
29
Romaleidae Staleochlora Roberts
& Carbonell, 1992
12 33.8
(25.9-38.9)
51.2
(43.7-58.7)
1.52
(1.33-1.92)
1.34
(-1.12-1.72)
Romaleidae Phaeoparia Stål, 1873 14 24.5
(15.6-32.2)
35.3
(22.4-42.6)
1.45
(1.30-1.56)
1.049
(0.94-1.28)
Romaleidae Maculiparia Jago,
1980
15 21-4
(18-6-25.0)
31.9
(27.8-38-2)
1.49
(0.60-0.72)
0.924
(0.65-1.45)
Romaleidae Taeniophora Stål,
1873
11 14.4
(11.9-16.9)
18.4
(14.1-21-7)
1.27
(1.19-1.33)
0.919
(0.79-1.20)
Romaleidae Phrynotettix Glover,
1872
10 27.7
19-9-34.5)
38.7
(28.6-47.0)
1.41
(1.25-1.59)
1.154
(0.83-1.61)
Orthoptera
(Ensifera)
Tettigoniidae Isophya Brunner von
Wattewyl, 1878
31 22.3
(16.5-31.5)
23.1
(17.3-32.5)
1.04
(0.90-1.30)
1.057
(0.87-1.36)
Tettigoniidae Poecilimon Fischer,
1853
55 17.9
(12.5-28.8)
19.7
(14-0-32.00)
1.10
(0.93-1.63)
0.949
(0.82-1.10)
Tettigoniidae Platycleis Fieber, 1853 37 18.2
(13.0-28.0)
19.6
(14.5-30.3)
1.08
(0.95-1.31)
1.010
(0.89-1.20)
Tettigoniidae Metrioptera Wesmäel,
1838
21 17.5
(14.3-25.0)
20.0
(15.5-34.0)
1.13
(1.00-1.34)
0.701
(0.61-0.96)
Tettigoniidae Pholidoptera
Wesmäel, 1838
22 21.2
(14.0-26.5)
24.1
(18.0-31.0)
1.14
(0.99-1.43)
1.05
(0.74-1.41)
Tettigoniidae Eupholidoptera
Maran, 1953
13 22.0
(18.0-26.5)
23.8
(18.0-28.5)
1.04
(0.92-1.13)
0.85
(0.30-1.12)
Tettigoniidae Rhacocleis Fieber,
1853
11 18.6
(14.5-22.1)
21.0
(14.3-28.4)
1.13
(0.98-1.28)
0.706
(0.63-1.49)
Tettigoniidae Antaxius Brunner von
Wattenwyl,
10 17.4
(14.5-19.5)
19.5
(16.3-21.8)
1.12
(1.02-1.32)
0.991
(0.41-1.59)
Tettigoniidae Ephippiger Berthold,
1827
16 25.6
(21.0-34.5)
27.5
(22.2-36.5)
1.08
(0.98-1.19)
0.958
)0.68-1.19)
Tettigoniidae Ephippigerida Bolivar,
1903
10 26.8
(15.3-46.5)
28.5
(16.2-41.0)
1.07
(0.94-1.17)
1.054
(0.82-1.35)
Tettigoniidae Uromenus Bolívar,
1878
25 25.4
(18.3-36.0)
26.8
(17.3-36.5)
1.06
(0.85-1.19)
0.937
(0.80-1.16)
Raphidiophoridae Dolichopoda Bolívar,
1880
19 13.6
(13.0-34.0)
18.8
(13.0-31.5)
1.02
(0.76-1.21)
1.118
(0.83-1.42)
Gryllidae Eugryllodes Chopard,
1927
13 13.9
(12.0-17.0)
13.5
(11.0-18.5)
0.97
(0.87-1.12)
0.711
(0.61-0.99)
Myrmecophilidae Mrmecophilus
Berthold, 1827
93.0
(2.2-4.5)
3.4
(2.2-4.7)
1.11
(1.00-1.34)
0.897
(0.49-1.21)
Phasmatodea Diapheromeridae Asceles
Redtenbacher, 1908
10 58.2
(32.0-80.0)
75.3
(60.0-98.0)
1.34
(1.13.2.00)
1.591
(1.04.2.35)
Diapheromeridae Candovia Stål, 1875 954.0
(41.0-79.0)
73.8
(57-0-109.0)
1.37
(1.20-1.56)
0.976
(0.72-1.31)
Diapheromeridae Clonaria Stål, 1875 15 54.4
(35.0-68.0)
70.3
(42.0-108.0)
1.29
(0.87-1.71)
0.77
(0.49.1.27)
Diapheromeridae Necroscia Serville,
1838
33 51.9
(35.0-75.0)
69.2
(42.5-90.0)
1-34
(1.06-1.63)
1.037
(0.91-1.21)
Diapheromeridae Sipyloidea Brunner
von Wattenwyl, 1893
24 59.4
(48.0-85.0)
81.6
(59.5-116.0)
1.38
(1.12-2.03)
0.959
(0.78-1.20)
Pseudophasmatidae
Anisomorpha Gray,
1835
11 34.1
(24.0-46.5)
48.7
(30.0-62.5)
1.46
(1.04-2.16)
1.046
(0.39-1.70)
ORDER FAMILY GENUS N° OF
TAXA
MALE BL FEMALE BL BL SSD [F/M]
β
RMA

30
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
Phasmatidae Phasma Lichtenstein,
1796
14 49.1
(38.0-59.0)
70.2
(61.0-80.0)
1.44
(1.29-1.84)
1.320
(0.84-2.06)
Phasmatidae Phobaeticus Brunner
von Wattenwyl, 1907
11 139.4
(118.1-165.5)
241.3
(163.0-343.3)
1.69
(1.30-2.56)
0.533
(0.32-1.17)
Phasmatidae Carausius Stål, 1875 10 75.5
(47.0-110.0)
101.9
(54.0-165.0)
1.35
(1.04-1.60)
0.81
(0.74-1.38)
Lonchodinae Promachus Stål, 1875 16 44.3
(21.0-53.0)
65.0
(29.0-88.0)
1.46
(1.10-1.76)
0.86
(0.52-0.97)
Mantodea Mantidae Rhodomantis Gilgio-
Tos, 1917
845.5
(37.3-57.7)
61.5
(50.8-81.5)
1.35
(1.20-1.61)
0.840
(-1.36-1.98)
Mantidae Hierodula Burmeister,
1839
10 64.8
(52.0-83.5)
72.6
(57.0-98.0)
1.12
(1.01-1.17)
0.945
(0.87-1.41)
Hymenopodidae Oxypiloidea
Schulthess, 1898
12 21.2
(19.0-22.5)
26.2
(22.0-35.0)
1.23
(1.09-1.46)
0.649
(0.33-0.96)
Liturgusidae Liturgusa Saussure,
1869
20 22.8
(18.7-30.7)
29.4
(23.8-42.1)
1.29
(1.14-1.63)
0.698
(0.51-0.94)
Blattodea Ectobiidae Ischnoptera
Burmeister, 1838
14 15.2
(10.3-21.0)
13.5
(9.3-19.0)
0.89
(0.72-1.03)
1.033
(0.76-1.56)
Ectobiidae Ectobius Stephens,
1835
24 8.3
(6.3-10.5)
7.6
(5.8-9.5)
0.92
(0.75-1.17)
1.037
(0.77-1.41)
Ectobiidae Neoblattella Shelford,
1911
10 11.6
(9.2-14.2)
12.4
(9.3-14.7)
1.07
(0.89-1.30)
0.955
(0.69-1.69)
Ectobiidae Phyllodromica Fieber,
1853
26 6.5
(4.5-8.2)
7.0
(5.7-8.5)
1.10
(0.90-1.50)
1.518
(1.14-2.46)
Dermaptera Forficulidae Forficula Linnaeus,
1758
22 11.2
(7.5-15.5)
10.6
(6.8-13.3)
0.95
(0.78-1.31)
1.085
(0.96-1.32)
Labiduridae Forcipula Bolívar,
1897
12 18.9
(13.5-25.5)
|8.8
(13.5-25.5)
0.99
(0.81-1.18)
1.019
(0.94-1.19)
Mantophasmatodea
several several 814.0
(9.4-23.6)
16.5
(11.7-22.5)
1.27
(1.01-1.54)
1.885
(0.90-4.13)
ORDER FAMILY GENUS N° OF
TAXA
MALE BL FEMALE BL BL SSD [F/M]
β
RMA
are generally more dimorphic than Ensifera: the
former average 1.37 SSD in body length ranging
from 0.83 to 2.45, while the latter show a mean
SSD of 1.09 (0.77-1.44) (Hochkirch & Gröning,
2008). However, different families and subfami-
lies within each suborder show marked differ-
ences in degrees of SSD (Table 8). The same is
true for different related genera (Table 9 and Bi-
dau et al., 2013). Sometimes, extreme differenc-
es in SSD occur in very closely related species
as is the case of two recently evolved species
of the pamphagid genus Purpuraria Enderlein
from the Canary Islands that, despite their very
close relationship and morphological similarity,
show a dramatic difference in SSD: while Purpu-
raria magna López & Oromi and Purpuraria erna
Enderlein show females of similar size (average
body lengths, 42.41 and 43.48 mm respective-
ly) males of the first species average 25.2 mm in
length and those of the second species, 16.17
mm producing SSDs of 1.68 and 2.79 respec-
tively (López et al., 2013) which largely exceeds
the range observed in many genera containing
large numbers of species (Table 9).
Very few studies of Rensch’s rule have been
performed in orthopteroid insects either at the
interspecific (Bidau et al., 2013) or intraspecific
(Bidau & Martí, 2007a, 2008a, b) levels. From
Tables 8 and 9 it can be seen that the vast
majority of orthopteroid taxa analyzed show
isometric scaling of SSD with body size dem-
onstrated by RMA slopes not different from 1.
Of course, these results could be different if a
phylogenetic approach is used but compre-
hensive phylogenies for these groups are not
available. However, in a number of non-orthop-
teroid cases, SSD has been shown to lack phy-
logenetic signal and Rensch’s rule is not veri-

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
31
fied with or without the phylogenetic approach
(e.g. Martínez & Bidau, 2014; Martínez et al.,
2014) while in others hyperallometry has been
unquestionably demonstrated (e.g. Frýdlová &
Frynta, 2015). At the intraspecific level, howev-
er, orthopteroids showed a variety of responses
when scaling of SSD was analyzed (Table 1).
Only a fourth of the cases showed a response
consistent with Rensch’s rule (SSD decreas-
ing with increasing body size) and interestingly
enough, 17% of the species showed the con-
verse trend which according to Rensch’s rule
original formulation should be expected when
males are larger, not smaller, than females. Fur-
thermore, more than half the species displayed
isometric scaling indicating that Rensch’s rule
is not a common pattern in orthopteroids at the
intraspecific level. In fact, these results suggest
that the scaling of SSD with body size is a rather
idiosyncratic phenomenon in these insects with
each species following its particular trend. The
latter is reflected in cases such as the five close-
ly allied grasshopper species belonging to the
tribe Dichroplini of the Melanoplinae (Dichrop-
lus fuscus, D. pratensis, D. vittatus, Ronderosia
bergii, and Scotussa cliens) one of which fol-
lows Rensch’s rule, two its converse and two,
isometric scaling (Table 1). Nevertheless, one
thing seems to be true: it has been considered
a precondition for Rensch’s rule that male size
variability is higher than that of females (Fair-
bairn, 1997) which was substantiated by our re-
sults. As a confirmation, in most species show-
ing converse Rensch’s rule, females were more
variable in size than males while those species
with isometric scaling showed practically the
same degree of variability in both sexes.
However, this kind of results must be evalu-
ated cautiously. This is because different char-
acters used to evaluate SSD could yield dif-
ferent estimations of dimorphism and produce
discordant scaling patterns, thus the election
of such characters is of utmost relevance (Fair-
bairn, 2007; Fox et al., 2015). In insects, body
mass data are hard to come by, so that in most
cases, size and SSD are analyzed using linear
measurements of body length or other body
structures such as legs, wings, pronotum, head,
etc. The election of such a character would not
be problematic if the length of these different
structures scaled isometrically with general size
but this is rarely the case: most structures show
allometry and the allometric scaling is frequent-
ly different in males and females (see Table 5).
Many examples are clear from our results: in
Dichroplus pratensis which follows Rensch’s
rule independently of the character used for
its testing, SSD for body length (1.33) is much
lower than that estimated for all other five lin-
ear characters. This is a direct consequence
of the different degrees of male and female al-
lometry of these structures (allometric equations
not shown in this paper; see Table 4 in Bidau
& Martí, 2008b). Dichroplus vittatus that also
showed a considerable variation in SSD for dif-
ferent characters, produced converse Rensch’s
patterns in all cases except for pronotum length
which is, significantly, a structure frequently
used in orthopteroid insects as a proxy for body
size. Conversely, Podisma sapporensis exhib-
ited a converse pattern for pronotum length but
isometry for all other traits (see Table 4). Even
the length of the third femur, also used frequent-
ly to estimate size in orthopteroid insects, can
produce discordant results: the four species of
the romaleid genus Brachystola Scudder show
moderate (for the family) female-biased SSD for
body length (1.1-1.2) and pronotum length (1.1-
1.3) but surprisingly (and uniquely) the larger
females have shorter – in absolute length- hind
legs than males producing male-biased SSDs
ranging from 0.77 to 0.88. However, allometries
are not inevitable (Clutton-Brock et al., 1977)
but when they occur differentially in both sexes
it is not unreasonable to infer different selective
pressures on the same structure in males and
females. This is probably the case in to exam-
ples described in the Results section. The dra-
matic difference between the degree of SSD for
body length and SBCD for cerci (forceps) in ear-
wigs could be a result of the multiple functions
that these structures perform in males, such as:
male-male aggressive interactions, weapons,
sexual display, and clasping of females (Brice-
ño & Eberhard, 1995). In the other example,
that of the bark mantises of the genus Liturgusa
(Svenson, 2014) femurs of the forelegs show
a degree of sexual dimorphism comparable to
that of body length, which largely exceeds that
of the femurs of meso- and metathoracic legs,
and also exhibit differential allometry respect to
body length. It is worth noting that size of fore-
leg femurs and tibiae are essential in determin-
ing optimum prey size in mantids (Holling et al.,

32
Revista de la Sociedad Entomológica Argentina 75 (1-2): 11-36, 2016
1976). Interestingly in this genus, a converse
Rensch pattern is obtained when using body
length and prothoracic femur length as estima-
tors of body size, while sexual dimorphism for
second and third femur length and pronotum
length display sexual isometry.
Latitudinal, elevational, and longitudinal size
clines related to variation in biotic and abiotic
factors are frequent in insects and have been
relatively well studied in orthopteroid insects.
The most frequent pattern is one in which body
size decreases towards higher latitudes or el-
evations (the converse Bergmann’s rule) and it
is most satisfactorily explained by a shortening
of the developmental time as seasonality in-
creases and temperature decreases. Because
SSD has been also shown to vary geographi-
cally in many species, it has been suggested
that Bergmann’s (or converse Bergamnn’s) rule
and Rensch´s rule may overlap in the analysis of
body size variation (Blanckenhorn et al., 2006;
Bidau & Martí, 2007a). The possible correlation
is a logical one since Rensch’s rule depends
on body size which in turn shows geographic
clinal variation. The majority of species shown in
Table 1 presented clinal patterns of geographic
body size variation mainly of the converse Berg-
mannian type. In most cases, body size varia-
tion is accompanied by a corresponding clinal
change in the degree of SSD along the same
spatial coordinates. In some cases (
e.g.
Dichro-
plus pratensis and D. vittatus) that show strong
latitudinal and altitudinal patterns this correla-
tion, although expected, was not found but this
is due to confounding effects of elevation within
the latitudinal patterns that span many degrees
of latitude (Bidau & Martí, 2008b).
Since in most insects larger sizes occur in
more favorable conditions, an explanation of
Rensch’s rule and its converse could be pro-
duced if we assume differential sensitivity of
males and females to environmental factors as
suggested by Teder &Tammaru (2005).
If females are more sensitive, as conditions
improve, they could achieve their optimal size
more readily than in poorer conditions produc-
ing an increase in SSD (converse Rensch’s rule).
The reverse would occur if males are the most
sensitive sex. Thus, in this hypothetical scenario
Rensch’s rule and its converse (not SSD per se)
would be subproducts of body size variations
related to environmental conditions, specially in
species with large geographic distributions.
The effects of external conditions on adult
body size and SSD of orthopteroid insects have
been extensively studied experimentally. Again,
as shown by the examples summarized in table
6 responses to variation in living conditions, diet,
temperature, etc. are largely idiosyncratic. In-
crease or decrease of body size may be accom-
panied by different and contrasting responses of
SSD. For example, the effects of crowding may
produce increased SSD (e.g. Ornithacris turbida),
decreased size and SSD (e.g. Schistocerca pal-
lens, Melanoplus differentialis (Thomas), and dif-
ferent strains of Locusta migratoria), while no size
or SSD changes were observed in similar experi-
ments with the common cricket Acheta domesti-
cus. These and other experiments with varying liv-
ing conditions strongly suggest species-specific
responses of body size to external factors which,
if translated to nature could explain the diversity
of SSD patterns observed in orthopteroid insects.
Furthermore, while estimations of SSD are usually
performed at the adult stage, external factors act
during the whole period of development. One of
the proximate causes that have been invoked to
explain size differences between males and fe-
males in insects is the higher number of larval in-
stars shown by females of most species (Esperk
et al., 2007). Although this phenomenon occurs
frequently in orthopteroid insects (see Table 7), it
cannot be the sole cause of female-biased SSD.
For example, both giant weta Deinacrida spe-
cies and the pyrgomorphid Phymateus leprosus
showh high female-biased SSD but equal num-
ber of instars for both sexes, and in the praying
mantis Pseudomantis albofimbriata males, not
females, undergo an additional nymphal stage
(Table 7). The problem is further complicated in
that most species do not show significant SSD
until the more advanced developmental stages or
even only after the final moult (Stilwell et al., 2010;
Table 7). Furthermore, other factors such as size
at hatching, growth rate, size-dependent survival,
and phenotypic plasticity of the characters under
study greatly influence adult SSD (Stilwell et al.,
2010). Sex differences in plasticity resulting from
varying degrees of stabilizing and directional se-
lection on body size or the size of specific char-
acters, are probably the source of much of the
observed variation of SSD and is a promising field
of study to start disentagling the proximate and
ultimate causes of SSD (Stilwell et al., 2010).

BIDAU, C. J. et al. Sexual size dimorphism in orthopteroid insects
33
CONCLUSIONS
1. Orthopteroid insects show several different
scaling patterns of SSD with body size and this
is expressed at intra and interspecific levels.
2. Scaling patterns may differ significantly
within taxa depending on the body size estima-
tors considered for analysis and even closely
related species may show completely contrast-
ing patterns.
3. Rensch’s rule is just one of the possible
modes of scaling of SSD with body size and it
can hardly be regarded as a proper “rule”.
4. Numerous environmental factors affect
SSD both in nature and experimental studies
suggesting the role of differential plasticity be-
tween males and females in shaping SSD and
its variation.
5. The study of plasticity and the comparison
of sexual dimorphism for different characters
that may be under different selective pressures
are needed in the future for an understanding of
the proximate and ultimate causes of SSD.
General conclusion: Despite the pervasive
nature of sexual size dimorphism and the enor-
mous wealth of studies devoted to understand
its evolutionary significance and the mecha-
nisms responsible for its enormous variation
among widely different organisms as shown in
this paper, we still remain confronted with the
enigma of inter-sex size differences. One of the
multiple intriguing problems is the relationship
between SSD and body size and why in com-
parative studies, the latter usually shows strong
phylogenetic signal while SSD usually does not.
This may in part reflect the fact that SSD is not a
classic organismal property such as body mass
or form, but an adimensional measurement of
a difference. This special characteristic of SSD
strongly suggests that novel methods for its
study must be developed in the future.
ACKNOWLEDGMENTS
This paper honors Prof. Dr. Axel O. Bach-
mann, superb entomologist and excellent
teacher on the occasion of his 89th birthday.
Alberto Taffarel and Elio Rodrigo Castillo ac-
knowledge the continuous support of CONICET
(Argentina). We are grateful to two anonymous
reviewers and the section editor for suggestions
that improved the original manuscript.
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