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The expression of aggression in the dobsonflies Corydalus
magnus Contreras-Ramos, 1998 and Platyneuromus soror
(Hagen, 1861) (Megaloptera: Corydalidae)
Hugo Alejandro
Alvarez
a,b
, Jos
e Manuel Tierno de Figueroa
b
and
Jorge Alejandro Cebada-Ruiz
c
a
Departamento de Biolog
ıa, Instituto de Investigaci
on en Ciencias-Naturales y Humanidades AC,
Puebla, Mexico;
b
Departamento de Zoolog
ıa, Facultad de Ciencias, Universidad de Granada, Granada,
Spain;
c
Laboratorio de Biociencias, Facultad de Medicina, Benem
erita Universidad Aut
onoma de
Puebla, Puebla, Mexico
ABSTRACT
The expression of aggression in Megaloptera has received little
attention, specifically for the adults of the subfamily Corydalinae.
Among the New World species of Corydalinae, it is not known if
aggression is triggered and expressed in the same way. Since two
genera, Corydalus Latreille, 1802 and Platyneuromus Weele, 1909
have different courtship strategies, the effect of the social envir-
onment in the expression of aggression in two species of those
genera, Corydalus magnus Contreras-Ramos, 1998 and
Platyneuromus soror (Hagen, 1861), is examined here and com-
pared with the known data in Corydalus bidenticulatus Contreras-
Ramos, 1998. Our results suggest that the triggering of aggressive
behaviours in the three species is similar. The decision of whether
or not to fight is affected by their social environment: a male is
aggressive against other males only when a female is present.
Furthermore, the intensity of aggression does not differ among
the three species. The behavioural observations support the idea
that the mandibles of Corydalus males are used as weapons in
male-male competition and during the courtship, but the post-
ocular flanges of P. soror males are not involved in male-male
competition (they use their short mandibles to bite). Conversely,
data show that such a feature might act as a signal trait for
female choice.
ARTICLE HISTORY
Received 18 September 2018
Accepted 19 December 2018
KEYWORDS
Megaloptera; Corydalidae;
aggressive behaviour;
male–male interactions;
Mexico
Introduction
Among animals, males commonly compete for female access (Andersson 1994;
Clutton-Brock 2007). However, it is known that social environments affect the per-
formance of males in competition over female access (Cox and Le Boeuf 1977; Hand
1986). For example, the males of the leaf-footed cactus bug, Narnia femorata Stål,
1862, defend territories from other males regardless of whether females are present or
not, but they become highly aggressive when females are present (Procter, Moore,
CONTACT Hugo Alejandro
Alvarez hugoalvarez01@gmail.com Departamento de Zoolog
ıa, Facultad de
Ciencias, Universidad de Granada, Avenida Fuente Nueva S/N C.P. 18071, Granada, Spain
ß2019 Informa UK Limited, trading as Taylor & Francis Group
AQUATIC INSECTS
https://doi.org/10.1080/01650424.2018.1564332
Published online 11 Mar 2019
and Miller 2012). Liu, Wei, Tian, and Hao (2017) demonstrated that male fight inten-
sity in the parasitoid Eupelmid wasp, Anastatus disparis (Ruschka, 1920), was posi-
tively influenced by competitor density and female presence. In the stonefly, Leuctra
fusca (Linnaeus, 1758), the duration of a male mating position (a contact mate guard-
ing strategy) is significantly increased when other males are close and there are dis-
placement attempts by such males (Tierno de Figueroa 2003). Adult males of the
dobsonfly genus Corydalus Latreille, 1802 are another example. Recently, it has been
shown that males of Corydalus bidenticulatus Contreras-Ramos, 1998 are highly
aggressive with other males only when female presence is detected, if not, males are
peaceful (
Alvarez, Garc
ıa-Ch
avez, and Cebada-Ruiz 2017a).
The Megaloptera are an interesting, but relatively poorly studied group of insects
composed of two families, Sialidae (alderflies) and Corydalidae. The latter including
the subfamilies Corydalinae (dobsonflies) and Chauliodinae (fishflies). This insect
order is composed of less than 350 species (Cover and Resh 2008; Cover and Bogan
2015). Megaloptera are holometabolous, with aquatic larvae and terrestrial pupae and
adults (Cover and Bogan 2015). The life cycle of most species ranges from one to two
years, though some species live up to five years (Elliott 1996; Contreras-Ramos 1998;
Cover and Resh 2008;
Alvarez 2012). Nevertheless, the adult lifespan is short, only
one to two weeks (Hayashi 1999;
Alvarez 2012,2014; Cover and Bogan 2015). Adult
dobsonflies are typically nocturnal (Contreras-Ramos 1998;
Alvarez 2014;
Alvarez
et al. 2017a;
Alvarez, Carrillo-Ruiz, and Cebada-Ruiz 2017b), while many alderflies
and fishflies are diurnal (Stange 1990; Elliott 1996; Anderson 2009).
The male behaviour, including mating behaviour, of the New World species of
the subfamily Corydalinae has been studied in few species (Parfin 1952;Contreras-
Ramos 1999;
Alvarez et al. 2017a). However, the expression of aggression has
received even less attention (see
Alvarez et al. 2017a). For example, the genera
Corydalus and Platyneuromus Weele, 1909 show different courtship strategies, and
literature data suggest that in the genus Corydalus, males fight intensively with other
males using their elongated mandibles to gain access to females (Parfin 1952;
Sublett 2012;
Alvarez et al. 2017a). Conversely, in the genus Platyneuromus,males
have elongated post-ocular flanges (and not elongated mandibles) and show face to
face behaviour that may be intended to intimidate other males (Contreras-Ramos
1999), although there is no evidence of agonistic encounters between males of
this genus.
This leads to some questions: among New World species of Corydalinae, is aggres-
sion triggered in the same manner as in the previously studied C. bidenticulatus?If
so, is the intensity of aggression diverse among genera and species? We hypothesise
that agonistic behaviours will be triggered and expressed in the same manner among
related species within a genus but not between genera. The aim of the present study
is to examine the effect of social environments on the expression of aggression in two
species of New World Corydalinae. First, we investigate how male–male interactions
are carried out by exploring whether the presence of a female triggers agonistic
encounters between males of Corydalus magnus Contreras-Ramos, 1998 and
Platyneuromus soror (Hagen, 1861). Then, we describe how males of both species
use secondary sexual traits in male–male and courtship interactions. Finally, we
2 H.A.
ALVAREZ ET AL.
measure the duration of agonistic encounters as an indicator of the intensity of
aggression between C. magnus and P. soror, in order to compare this parameter with
that of C. bidenticulatus.
Material and methods
Research organisms
Corydalus magnus and Platyneuromus soror have different secondary sexual morpho-
logical characteristics. Adults of the genus Corydalus typically show sexual dimorph-
ism in mandibles and antennae: males have large mandibles with no dentition and
long, thick antennae, whereas females have short mandibles with large dentition and
short, thin antennae (Contreras-Ramos 1998;
Alvarez et al. 2017a). The studied spe-
cies, C. magnus (Figure 1a), is characterised by a medium to very large body size,
very long antennae (sinuate or subserrate), a pallid brown colour with big moderately
dark spots at the edge of the wings, small white spots on the wings, and very slightly
to moderately patterned heads (Contreras-Ramos 1998). Adults of the genus
Platyneuromus typically show sexual dimorphism in post-ocular flanges: males
have large (elongated) acuminate to courved post-ocular flanges, whereas females
have short (sometimes elongated) sharp post-ocular flanges (Glorioso and Flint 1984).
The studied species, P. soror (Figure 1c), is characterised by a small to medium body
size, thin antennae, a pale yellow colour with lateral margin of prothorax, brown
post-ocular flanges, and pale brown medium size spots on the wings (Glorioso 1981;
Glorioso and Flint 1984).
Specimen collection
Adult specimens were collected near the street lights located along the pedestrian
paths of the residual water treatment plant of the city of Zacatl
an, located in the
Figure 1. Male heads indicating secondary sexual traits of the three dobsonfly species studied.
Elongated mandibles: (a) Corydalus magnus Contreras-Ramos,1998; (b) Corydalus bidenticulatus
Contreras-Ramos, 1998. Postocular flanges: (c) Platyneuromus soror (Hagen, 1861) (modified from
Thouvenot 2008).
AQUATIC INSECTS 3
municipality of Zacatl
an (1956008.4200N, 9757038.2100 W), in the Northern Sierra of
Puebla, Mexico. During May 2017, eight males and 10 females of C. magnus and 10
males and 22 females of P. soror were collected at night using entomological aerial
nets. Previous behavioural studies have been conducted on dobsonflies using similar
sample sizes (Parfin 1952; Hayashi 1992,1993; Contreras-Ramos 1999; Simonsen,
Dombroskie, and Lawrie 2008;
Alvarez et al. 2017a). Specimens were individually
placed in plastic containers and kept alive for the behavioural study.
Observational experiments and measurements
Observations were conducted at night in artificial enclosures (hereafter referred to as
arenas) with the help of a night vision camera First Alert model D575. Arenas con-
sisted of wood terrariums (30 cm length 15 cm width 25 cm height) with peat
moss and sticks (approximately 20 cm). Two types of experiments were designed to
avoid pseudoreplication following the approach of
Alvarez et al. (2017a). In experi-
ment A, a pair of males of the same species was placed in the arena for 45 min, then
a female was introduced into the arena and male interactions were observed for add-
itional 45 min. After this trial, the specimens were returned to the plastic containers.
In experiment B, a different pair of males and a female were placed in the arena for
45 min, then the female was removed from the arena and male interactions were
observed for additional 45 min. After this trial, specimens were returned to the plastic
containers. Individuals were never employed for more than one experiment. Overall,
four and five experiments were carried out for C. magnus and P. soror, respectively.
Observational data of C. bidenticulatus (Figure 1b) was obtained from the video
recording of
Alvarez et al. (2017a).
If agonistic behaviours were observed, then we timed the duration of the agonistic
interaction with the help of a digital chronometer (chronometer application, android
4.4.2) to quantify the intensity of aggression between males. Because the sample size
is low, instead of hypothesis testing, we used the overlap rule for 95% confident inter-
val (CI) bars (see Cumming, Fidler, and Vaux 2007) to search for differences in the
time of fighting between C. magnus,P. soror, and C. bidenticulatus from
Alvarez
et al. (2017a). Calculation of CIs was performed using R statistical software v3.4.0 (R
Development Core Team 2017).
Results
Typical behaviours were commonly observed among males of C. magnus (n¼8) and
P. soror (n¼10) involved in the interactions. In the absence of females, males stayed
on the floor and walls of the arena, touched each other with the antennae, but did
not engage in aggressive behaviour. When the presence of a female was detected,
males touched the female with their antennae. Furthermore, an aggressive stance dis-
played by males against other males was triggered by the presence of a female. When
males faced each other, they used their mandibles to attack rivals and fought each
other by biting or grasping until the winner drove the loser away. Aggressive behav-
iour ceased entirely when the female was taken away from fighting males. Differences
4 H.A.
ALVAREZ ET AL.
in aggressive behaviours were seen. Corydalus magnus males used their mandibles
primarily for grasping each other. Platyneuromus soror males quickly bit each other
and did not exhibit grasping behaviour.
Male courtship behaviour of C. magnus occurred in succeeding stages; (i) the male
positioned the mandibles above the female’s wings; (ii) the male remained still with-
out further movement for about 10–15 s; (iii) subsequently, the male abruptly moved
its head and thorax back and forth; and (iv) the male bent its abdomen horizontally
to position it under the female’s wings. Copulation was not observed.
Male courtship behaviour of P. soror occurred in a single stance. The male
approached the female and positioned his head besides hers, then the female turned
to look at the male’s head, and the male began to bend his abdomen horizontally to
position it under the female’s wings. Copulation was not observed.
Figure 2 shows the mean and the 95% CI of the time (duration) of the agonistic
interactions for C. magnus,P. soror, and C. bidenticulatus from
Alvarez et al. (2017a).
As they overlap completely (overlap: fraction of the average CI error bar arm 1),
this suggests that there are no significant differences in the duration of agonistic
interactions among the species.
Figure 2. Mean and 95% CI for time (duration) of agonistic interactions (AI) between males of
Corydalus magnus Contreras-Ramos,1998 (n¼4), Corydalus bidenticulatus Contreras-Ramos,1998
(n¼4; data from
Alvarez et al.2017a), and Platyneuromus soror (Hagen,1861)(n¼5).
AQUATIC INSECTS 5
Discussion
Differences were seen in courtship behaviour between C. magnus and P. soror. For
example, males of C. magnus showed their characteristic behaviour of positioning the
elongated mandibles above the wings of females (see Parfin 1952; Evans 1972;
Contreras-Ramos 1999; Azev^
edo and Hamada 2007;
Alvarez et al. 2017a) and making
abrupt movements of the head in a back and forth motion (
Alvarez et al. 2017a). In
contrast, males of P. soror always tried to position themselves side-by-side with the
females, this allowed the females to turn to see the male’s head. Interestingly, it was
observed every time that Platyneuromus females turned to see a male’s head. This is a
behaviour that has never been seen in Platyneuromus nor Corydalus species before.
However, our results suggest that the trigger of aggressive behaviours in C. magnus
and P. soror is similar. As previously described for C. bidenticulatus (see
Alvarez
et al. 2017a), males are not indiscriminately aggressive. The decision of whether or
not to fight is affected by their social environment. Males are aggressive against other
males only when the presence of a female is detected. This behaviour can save energy
expenditure and potential body damage due to sparring (Reinhold 1999; Liu et al.
2017), which can be explained by game theory (Dugatkin and Reeve 1998) i.e.,
whole-organism performance capacity and an organism’s physiological state frame-
works (reviewed by Lailvaux and Irschick 2006). For C. magnus, fighting behaviour
was the same as seen in other Corydalus species (Parfin 1952; Simonsen et al. 2008;
Sublett 2012;
Alvarez et al. 2017a). Interestingly for P. soror, males fought using their
mandibles to bite, similar to what had been seen in Corydalus. In contrast, they only
bit quickly instead of engaging in grasping. Thus, Corydalus and Platyneuromus fol-
low the sequence pattern of behaviour suggested by
Alvarez et al. (2017a) for mal-
e–male interactions, which shows that there are two possible sequences in which two
males can engage in a fight. The first possibility is when a solitary male comes across
a female and identifies her as a possible mate, ushering a harassing behaviour against
the female. Then, another male comes toward the male accompanied by a female.
The first male identifies the second male as a rival and takes an aggressive position
and, finally, the rival males fight each other by biting or grasping with their mandi-
bles until the winner drives the loser away and stays with the female. The second pos-
sibility is when a solitary male comes across another male without showing any
apparent aggression. Then, a female encounters the two peaceful males which causes
both males to identify each other as rivals and take aggressive positions. Finally, rival
males fight each other by biting or grasping with their mandibles until the winner
drives the loser away and stays with the female.
Results also suggested that the intensity of aggression does not differ among C.
magnus,P. soror, and C. bidenticulatus from
Alvarez et al. (2017a) (although one fight
between two males of C. magnus lasted 25 s). If aggression is not different among
species of these two genera, and male-male interactions are similar, the question
arises as to why there are different secondary sexual traits i.e., elongated mandibles
vs. post-ocular flanges. Our behavioural experiments support the idea that the post-
ocular flanges of the males of P. soror could be used as a signal trait in female choice
i.e., females would prefer males with large post-ocular flanges (see Contreras-Ramos
1999). Thus, even when Platyneuromus males use mandibles to drive away other
6 H.A.
ALVAREZ ET AL.
males when females are present (resembling Corydalus males), mandibles are not
elongated because of constraints caused by possible sexual pressures on post-ocular
flange (see Shuster 2009).
It is important to note that our low sample size could mask some potential behav-
ioural patterns. However, the obtained results are consistent within each species and
allow insight into understanding aggression in such a primitive group of insects.
Further research on sexual selection is needed for the Corydalus and Platyneuromus
species, especially in Platyneuromus, to clarify how sexual pressures are driving the
development of aggression and secondary sexual traits.
Acknowledgements
The authors thank the directors and working personnel of ‘Planta de Tratamiento de Aguas
Residuales SOSAPAZ’for providing the facilities for fieldwork and the anonymous reviewers
for their comments on an earlier version of the manuscript. The authors also thank Daniel
Rougon, director of the journal L’Entomologiste, for authorising us to use the photo shown in
Figure 1c and the ‘Centre for International Education BUAP’for proofreading and style revi-
sion. H. A.
Alvarez thanks Marisol Rodr
ıguez for her help during fieldwork.
Disclosure statement
The authors are not aware of any affiliations, memberships, funding, or financial holdings that
might be perceived as constituting a conflict of interest.
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AQUATIC INSECTS 9
