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Mate quality, not aggressive spillover, explains sexual cannibalism in a size-dimorphic spider

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Sexual cannibalism particularly before mating is costly for the male victim but also for the female aggressor if she risks remaining unmated. The aggressive spillover hypothesis explains the persistence of this behavior as a maladaptive side effect of positive selection on aggressiveness in a foraging context. The hypothesis predicts that the occurrence of sexual cannibalism is explained by female aggressiveness but is not related to male phenotype or behavioral type. An alternative hypothesis invokes sexual selection and makes the opposite prediction namely that sexual cannibalism is an expression of female choice and should hence mainly target males of low quality. We tested the above hypotheses on a sexually dimorphic nephilid spider Nephilengys lívida, known for male monopolization of females via genital damage, female genital plugging, and mate guarding, by staging mating trials during which we recorded mating behaviors and occurrences of pre-and postcopulatory cannibalism. We did not restrict assessment of aggressiveness to the mating and foraging context but also included aggression against same sex conspecifics. To assess female personalities, i.e., consistent individual differences in behavior including aggressiveness, we repeatedly tested them for intra-sex aggression, voracity towards prey, locomotory activity, and boldness. Females exhibited consistent differences in intra-sex aggressiveness, latency to attack prey, and boldness. Aggressive females had shorter latencies to attack prey and were more active than nonaggressive ones. In contrast to the predictions of the aggressive spillover hypothesis, females that were aggressive towards prey and towards other females were not more likely to attack a male than non-aggressive females. In support of the mate choice hypothesis, less aggressive males were more likely attacked and cannibalized than more aggressive ones. This hints at sexual selection for aggressiveness in males and raises the question of mechanisms that maintain variation in male aggressiveness.
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ORIGINAL PAPER
Mate quality, not aggressive spillover, explains sexual
cannibalism in a size-dimorphic spider
Simona Kralj-Fišer &Jutta M. Schneider &
Živa Justinek &Sabina Kalin &MatjažGregorič&
Stano Pekár &MatjažKuntner
Received: 24 April 2011 / Revised: 12 September 2011 / Accepted: 13 September 2011
#Springer-Verlag 2011
Abstract Sexual cannibalism particularly before mating is
costly for the male victim but also for the female aggressor if
she risks remaining unmated. The aggressive spillover
hypothesis explains the persistence of this behavior as a
maladaptive side effect of positive selection on aggressiveness
in a foraging context. The hypothesis predicts that the
occurrence of sexual cannibalism is explained by female
aggressiveness but is not related to male phenotype or
behavioral type. An alternative hypothesis invokes sexual
selection and makes the opposite prediction namely that
sexual cannibalism is an expression of female choice and
should hence mainly target males of low quality. We tested the
above hypotheses on a sexually dimorphic nephilid spider
Nephilengys livida, known for male monopolization of
females via genital damage, female genital plugging, and
mate guarding, by staging mating trials during which we
recorded mating behaviors and occurrences of pre- and
postcopulatory cannibalism. We did not restrict assessment
of aggressiveness to the mating and foraging context but also
included aggression against same sex conspecifics. To assess
female personalities, i.e., consistent individual differences in
behavior including aggressiveness, we repeatedly tested
them for intra-sex aggression, voracity towards prey,
locomotory activity, and boldness. Females exhibited con-
sistent differences in intra-sex aggressiveness, latency to
attack prey, and boldness. Aggressive females had shorter
latencies to attack prey and were more active than non-
aggressive ones. In contrast to the predictions of the
aggressive spillover hypothesis, females that were aggressive
towards prey and towards other females were not more likely
to attack a male than non-aggressive females. In support of
the mate choice hypothesis, less aggressive males were more
likely attacked and cannibalized than more aggressive ones.
This hints at sexual selection for aggressiveness in males and
raises the question of mechanisms that maintain variation in
male aggressiveness.
Keywords Personality .Mate choice .Sexual conflict .
Aggressiveness .Behavioral syndromes .Boldness
Introduction
Females attack, kill, and consume males during, after, or even
before copulation in a wide range of species, but this is most
prevalent in praying mantids and spiders (Elgar 1992;Barryet
Communicated by M. Hauber
S. Kralj-Fišer :M. Gregorič:M. Kuntner
Institute of Biology, Scientific Research Centre,
Slovenian Academy of Sciences and Arts,
Novi trg 2, P.O. Box 306, SI-1001 Ljubljana, Slovenia
S. Kralj-Fišer (*):J. M. Schneider
Biozentrum Grindel, University of Hamburg,
Martin-Luther-King Platz 3,
20146 Hamburg, Germany
e-mail: simonakf@gmail.com
Ž. Justinek :S. Kalin
Department of Biology, Biotechnical faculty,
University of Ljubljana,
Večna pot 111,
SI-1001 Ljubljana, Slovenia
S. Pekár
Department of Botany and Zoology, Faculty of Sciences,
Masaryk University,
Kotlářska 2,
611 37 Brno, Czech Republic
M. Kuntner
National Museum of Natural History, Smithsonian Institution,
Washington, DC, USA
Behav Ecol Sociobiol
DOI 10.1007/s00265-011-1262-7
al. 2008). This phenomenon, referred to as sexual cannibal-
ism, is often viewed as an extreme form of sexual conflict
especially if females consume males prior to mating (Elgar
1992; Elgar and Schneider 2004; Wilder et al. 2009).
Costs and benefits of sexual cannibalism for both sexes
depend on the timing of sexual cannibalism (Elgar and
Schneider 2004). While females may profit from precopula-
tory sexual cannibalism through weight gain and increased
fecundity (Birkhead et al. 1988;ElgarandNash1988;Elgar
1998;Johnson2001;Moya-Laranoetal.2003;Barryetal.
2008), postcopulatory cannibalism may be advantageous for
males if they benefit through parental investment and reduced
sperm competition (Andrade 1996;ProkopandVaclav2005).
Precopulatory sexual cannibalism may be a result of any of
the following mechanisms: failingrecognitionofaprospective
mate by voracious females (Gould 1984); spillover of female
aggressiveness towards prey (Arnqvist and Henriksson 1997;
Johnson and Sih 2005); mate choice, when females reject
unwanted mates (Elgar and Nash 1988;Elgar1992;Persons
and Uetz 2005;Prenteretal.2006); or hunger, when females
benefit from the energy and nutrient intake by devouring the
male (adaptive foraging hypothesis) (Newman and Elgar
1991;Snyderetal.2000 but see Wilder and Rypstra 2010).
Frequency and occurrence of sexual cannibalism often
positively correlate to low foodandperhapsmateavailability,
as well as high sexual size dimorphism (reviewed in Wilder
and Rypstra 2008;Wilderetal.2009;Roggenbucketal.
2011). Females may cannibalize males in the context of
mating due to any combination of these factors, as the various
hypotheses are not mutually exclusive. Here, we test
predictions of the aggressive spillover and the mate choice
hypothesis.
The aggressive spillover hypothesis predicts that sexual
cannibalism represents a spillover of aggression from the
juvenile foraging context, where high levels of aggression
might be selectively favorable, to the adult mating context
(Johnson and Sih 2005). The proposed mechanism is that
genetic constraints limit behavioral plasticity (Sih et al. 2004).
In the view of personalities, i.e., consistent individual
differences in behavior (Bell et al. 2009), positive behavioral
correlations for aggression levels across ontogenetic stages
(juvenile, adult), and across contexts (foraging, mating), are
predicted (Johnson and Sih 2005). Indeed, aggressive
carryover across multiple contexts was found in several
spider species, e.g., Dolomedes fimbriatus,Dolomedes triton,
Agelenopsis aperta,andAnelosimus studiosus (Hedrick and
Riechert 1989; Riechert and Hedrick 1993; Arnqvist and
Henriksson 1997; Riechert and Johns 2003; Johnson and Sih
2007;Pruittetal.2008). Aggression positively correlates to
other personality traits, such as boldness in A. aperta and D.
triton and activity in A. aperta (Hedrick and Riechert 1989;
Riechert and Johns 2003; Johnson and Sih 2007). However,
no study tested if female high voracity towards prey and
aggression towards same sex conspecifics are also correlated
to postcopulatory sexual cannibalism, when females do not
compromise their reproductive future. Aggressiveness in the
context of same sex interaction could be adaptive through
winning competition or maladaptive, for example through
unnecessary wasting of energy.
Sexual cannibalism may be a radical form of mate choice if
females preferably cannibalize inferior males or if inferior
males are less capable of escaping female aggressiveness
(Elgar and Nash 1988; Elgar 1992; Persons and Uetz 2005;
Prenter et al. 2006). Sexual cannibalism during mating
allows females to control copulation duration, and if females
mate repeatedly, they may thereby exert control over relative
paternity of males (Elgar et al. 2000; Schneider et al. 2006;
Herberstein et al. 2011). Sexual cannibalism caused by
female choice may be particularly adaptive in species where
females are monopolized by males. In several nephilid
spiders, males plug female genitalia during copulation,
thereby reducing their chance of remating with other males
(Fromhage and Schneider 2006; Nessler et al. 2007; Kuntner
et al. 2009b; Uhl et al. 2009). Males that survive copulation
guard their mates, additionally reducing female polyandry
(Kuntner et al. 2009a, b; Kralj-Fišer et al. 2011). We propose
that in species where males plug female genitals and then
guard them, females may consume the mate to avoid being
monopolized, in particular after the first mating encounter
(Schneider et al. 2006; Kralj-Fišer et al. 2011). On the other
hand, if the (guarding) male is of superior quality (e.g., large,
aggressive), females may not oppose monopolization due to
heritable advantages of sired offspring in foraging and
mating contexts (Elgar 1998; Persons and Uetz 2005;
Kralj-Fišer et al. 2011).
Sexual selection can act directly through female aggression
targeting undesired suitors or indirectly if females are
indiscriminately aggressive towards mates, but only high-
quality males survive attacks. If the occurrence of sexual
cannibalism depends on the female's physical strength relative
to the male's ability to defend his life (Wilder and Rypstra
2008), size assortative mating can result. Studies in wolf
spiders Hogna helluo and Schizocosa ocreata as well as in
orb-web spider Araneus diadematus showed that size
difference between mating partners strongly affected the
success of female attacks (Persons and Uetz 2005; Wilder and
Rypstra 2008; Roggenbuck et al. 2011). These species are
sexually size monomorphic, while in extremely sexually size-
dimorphic spiders, small males have little chance to resist an
attack by their large female mates, and thus this mechanism is
unlikely to hold in, e.g., nephilids. However, if female
voracity towards prey correlates to female aggression towards
mates, cannibalistic females might be heavier and larger and
thus more fecund.
We studied the mating biology, in particular the occurrence
of precopulatory and postcopulatory cannibalism in relationto
Behav Ecol Sociobiol
female personalities and male behavior through malemale
contests in Nephilengys livida (Araneae: Nephilidae), noto-
rious for extreme sexual size dimorphism, genital plugging,
eunuchs (males with broken genitalspedipalps), sexual
cannibalism, and postcopulatory mate guarding (Kuntner
2007; Kuntner et al. 2009a). We tested (1) if female voracity
towards prey positively correlates to pre- and postcopulatory
cannibalism (which would be in support of aggressive
spillover), (2) whether females cannibalize males according
to their behavior in the web (supporting direct mate choice),
and (3) if female size correlates to their propensity to
cannibalize their mates (supporting indirect mate choice). In
addition, we investigated (4) if male behavior predicts their
mating success and (5) if female voracity towards prey
correlates with other behavioral traits such as aggressiveness
towards same sex conspecifics, activity, and boldness. To test
whether female behaviors can be referred to as personality
traits, we estimated temporal consistency of their behaviors.
While the aggressive spillover hypothesis proposes that
female-inherited personality predicts occurrences of sexual
cannibalism independently of male quality, the mate choice
and the mate size dimorphism hypotheses are not mutually
exclusive. Male size, important male quality characteristic
that we failed to measure, might be a significant factor in
mate size dimorphism predictions. Yet, N. livida females
are cca four times bigger than males (mean body length,
Kuntner and Coddington 2009); hence, female body sizes
generate the most of the mate size dimorphism variance.
The latter also implies that the male body sizes do not make
a difference in triggering female foraging behavior.
Materials and methods
Study animals
We co l lected N. livida spiders in Andasibe-Mantadia
(Toamasina Province) and Ranomafana (Fianarantsoa
Province) national parks in Madagascar, between 24
February 2010 and 4 April 2010. To examine personalities
in individuals with the same mating history, we collected
subadults and reared them to adulthood in the laboratory
(females = 25, males =23). We housed females in glass
frames (50×50×10 cm) and males in 250-ml plastic cups.
We watered all spiders daily and fed them Drosophila flies,
crickets, and mealworms twice per week.
Mating trials and personality tests
In trials, we observed malemale aggressiveness, occurrence
of mating, and pre- and postcopulatory sexual cannibalism. In
nine malemale contest trials (9 females, 15 males), we gently
placed two virgin males on the web of a virgin female. We
scored malemale antagonism as frequencies of being
stationary (score= 0), orienting, or walking towards conspe-
cific (score=1), shaking web (score=1), chasing (score= 2),
attacking (score= 2), and biting (score=3). We estimated
aggressiveness intensity levels as the sum of scores given in
the brackets (lowest to highest) (e.g., Kralj-Fišer et al. 2011).
Additionally, we recorded locomotory activity, scored as
frequency of moves, and frequency of web plucking
(courtship behavior). We also observed males' frequency of
touching the female and recorded malefemale distances
every 5 min. The former we used as a measure of risk taking
as females are highly cannibalistic (Kralj-Fišer et al.
unpublished). Contest trials were terminated after a copu-
lation occurred (N=8) or after 60 min. Due to the small
number of males, we additionally observed occurrences of
copulation and female sexual cannibalism in further nine
mating trials (nine females), where only one male was
introduced into the female web. We used six virgin males
from the above contests and three males, which were
previously not tested. Hence, we had a total of 18 females
that mated once either with or without competition. At the
end of the tests, ten of the above (once mated) females were
introduced to one male (previously mated or virgin) for the
second mating opportunity. We observed spiders for 60 min
to allow enough time for copulation.
We observed 12 of the 18 previously used females (from
the above experiment) and an additional 8 unmated females
(N=20) in a series of standardized tests for personality
characterization, i.e., contest (aggressiveness towards a
conspecific of the same sex, locomotor activity), feeding
(aggressiveness towards prey), and predatory test (antipre-
dator behavior). To test for behavioral repeatability, we
examined each individual twice in each test situation, with
510 days between repeats.
We observed the females' aggressiveness in two different
contexts: (1) we gently placed a female conspecific on the
web 5 cm from the observed female for 30 min, and 2) we
introduced prey on the web 10 cm from the observed
individual. Femalefemale aggression was scored as
explained above for males. We measured aggressiveness
towards prey as the latency to first reaction and latency to
bite prey. In predator tests, we touched the female's
abdomen with a paintbrush and scored boldness as follows:
spider feints death (score=0), spider runs away (score = 1),
spider does nothing (score= 2), spider shakes the web up to
65 s (score=3), spider shakes the web more than 65 s
(score=4), and spider attacksa predator (score = 5). We
chose a limit of 65 s, because duration of shaking varied
highly among individuals, and 65 s was the median.
At the end of the experiments,we weighed the females (N=
20) and measured their first patella+tibia and carapace
lengths (N=16). As many males were cannibalized during
copulation, we could not take their body measures.
Behav Ecol Sociobiol
Statistical analyses
Personality measures in both males (waving legs, touching
female, exploring, walking towards female, distance to female)
and females (boldness, latency to first reaction, latency to first
bite, and locomotor activity) and morphological traits in
females (mass, patella+tibia I length, carapace length) were
subjected separately to Principal Component Analysis. The
scores along the first axis were extracted and used as
explanatory variables. The effect of these trait variables and
the intra-sex aggressiveness on the probability of cannibalism
and mating success was studied using Generalized Linear
Models with binomial error structure (GLM-b) or Generalized
Estimating Equations with binomial error structure (GEE-b) if
males were used repeatedly. The correlation structure within
GEE was exchangeable (Hardin and Hilbe 2003). The analyses
were performed in R (R Development Core Team 2010)using
the geepack package (Yan and Fine 2004)andinPASW
version 18. We analyzed the repeatability of behaviors using
the parametric repeatability test (Falconer 1996). We trans-
formed (log (×+1)) not normally distributed data, thus
rendering them suitable for parametric statistics. Using data
from the first series of tests, we analyzed behavioral
correlations using Spearman's correlations.
Results
Mating success, precopulatory and postcopulatory sexual
cannibalism
Seventeen out of 18 virgin females copulated (94.44%). In
8 out of 17 copulations (47.06%), females cannibalized their
mates during the first copulation, but never prior to mating.
Six out of ten females that had mated in one copulatory
opening (CO) copulated in the other CO with another male.
During second copulations, sexual cannibalism occurred in
83.33% of the cases (five of six copulations) precluding
further analysis.
The probability of cannibalism during first copulation
decreased significantly with increasing male aggressiveness
(GLM-b, X
1
2
=5.9, P=0.002, Fig. 1a, Table 1) and was
independent of other male personality traits (GLM-b, X
1
2
<
0.1, P=0.98). Probability of mating success increased
significantly with increasing male aggressiveness (GEE-b,
X
1
2
=10.4, P=0.0012, Fig. 1b) and was independent of
other male personality traits (GEE-b, X
1
2
=3.2, P=0.08).
Female attacks always resulted in cannibalism.
Consistency of individual behavioral differences
and behavioral correlates
Females exhibited consistent individual differences in aggres-
siveness towards prey (Table 2, latency to first reaction: r=
0.771, N=18, P=0.002; latency to first bite: r=0.59, N=18,
P=0.042) and consistent differences in antipredator behavior
(boldness) (r=0.661, N=20, P=0.011). Females showed
consistent individual differences in their aggressiveness
towards same sex conspecifics, though these were not
significant (repeatability: r=0.52, N=19, P= 0.064), whereas
female locomotory activity was inconsistent between the
repeats (r=0.467, N=19, P=0.788).
Female voracity towards prey correlated with their aggres-
siveness towards same sex conspecifics: we found the latency
to first bite to be negatively correlated with aggression
towards same sex conspecifics (r=0.487, N=18, P=0.04).
Aggressive females were locomotively more active (r=
0.457, N=19, P=0.049). The probability of sexual cannibal-
ism was independent of female personality traits (GLM-b,
X
1
2
=0.8, P=0.31), aggressiveness towards conspecifics
(GLM-b, X
1
2
=1.5, P=0.22), and morphological traits
(GLM-b, X
1
2
=0.3, P=0.57). In males, aggression frequency
correlated positively with boldness while approaching a
female (distance to the female: r=0.54, N=15, P=0.037).
5 10 15 20
0.0 0.2 0.4 0.6 0.8 1.0
Aggression scores
m
s
i
l
a
b
i
n
n
a
c
f
o
y
t
i
l
i
b
a
b
o
r
P
A
0 5 10 15 20
0.0 0.2 0.4 0.6 0.8 1.0
Aggression scores
g
n
i
t
a
m
f
o
y
t
i
l
i
b
a
b
o
r
P
B
Fig. 1 Relationship between the
probability of cannibalism (a) and
probability of mating (b) and the
aggression of males. Estimated
logit models are displayed
Behav Ecol Sociobiol
Discussion
Our study does not support the aggressive spillover hypothesis
as an explanation for post-copulatory sexual cannibalism in
the nephilid spider N. livida. Forty-seven percent of females
cannibalized their males during the first copulation, and
female personality did not affect sexual cannibalism, while
the male behavior in the malemale contest in the female
web was important. Aggressive males were less likely to be
attacked and killed after their first copulation than were less
aggressive males. Our results suggest that sexual (postcop-
ulatory) cannibalism in N. livida probably results from
sexual selection rather than from low plasticity in the female
aggressive personality type (aggressive spillover). The direct
mate choice model fits the data better than the indirect model
as females did not attack every male.
Even though aggressive spillover was proposed to explain
sexual cannibalism in several spider species (Arnqvist and
Henriksson 1997;JohnsonandSih2005), this mechanism is
not applicable for N. livida,wheresexualcannibalismis
independent of general aggressiveness. However, we showed
that aggression towards the same sex conspecifics, voracity
towards prey, and boldness are repeatable and correlated and
thus part of female N. livida personality. This is in accordance
with other studies suggesting that these traits are inherited
components of spider personalities (Riechert and Hedrick
1993;ArnqvistandHenriksson1997;JohnsonandSih2005,
2007;Pruittetal.2008). According to the above studies, intra-
sex aggressiveness positively correlates to voracity towards
prey and activity (Riechert and Hedrick 1993;Arnqvistand
Henriksson 1997;JohnsonandSih2005,2007;Pruittetal.
2008). Thus, individual aggressiveness carries over from
territory defense to foraging context (probably sharing the
same proximate mechanism), whereas individual aggressive-
ness does not spillover into the mating context.
The discrepancy between these studies may be explained by
different species' mating biology. Aggressive spillover
explains sexual cannibalism in species with a polygamous
mating system and moderate sexual size dimorphism (D.
fimbriatus,D. triton,A. aperta, and A. studiosus; Hedrick and
Riechert 1989; Riechert and Hedrick 1993; Arnqvist and
Henriksson 1997; Riechert and Johns 2003; Johnson and Sih
2007; Pruitt et al. 2008). In extremely sexually size-
dimorphic N. livida, males obligatorily damage their palps
during copulation and thereby plug female copulatory open-
ings (CO, Kuntner et al. 2009a). Thus, males are monoga-
mous or bigamous (two palps) by default. In nephilids where
males emasculate their palps during mating, the plugs prevent
remating into the used female CO by the rival males in
approximately 70% of the cases (Kuntner et al. 2009b; Kralj-
Fišer et al. 2011). Mate plugging will thus limit female
mating to a single male if both of her genital openings get
plugged. Females, however, may benefit from polyandry and
may control the number of their mates through sexual
cannibalism during or after copulation (Schneider et al.
2006). Under a high risk of monopolization, selection may
favor females that are selective and only allow high-quality
males two copulations. If male quality is reflected in high
aggressiveness (and boldness), this can explain why female
N. livida more readily cannibalize less aggressive (and shy)
males and prevent them from inseminating both of her
spermathecae (Schneider et al. 2006), while aggressive (and
bold) males are allowed to monopolize both of them. Females
might prefer monopolization by an aggressive (and bold)
male if they can gain genetic benefits. Thus, sexual
cannibalism in N. livida may be a female mechanism to
select her offspring's behavioral phenotypes (Riechert and
Johns 2003); her offspring may benefit from aggressiveness
(and boldness) in the foraging and mating contexts. Our
explanation assumes that high male aggressiveness equals
high quality, but in reality, more features may define male
quality. For example, in a study on a wolf spider, sexual
cannibalism depended on male size and relative size of their
secondary sexual ornaments (Prenter et al. 2006). Neverthe-
less, aggressiveness often correlates with other traits, e.g.,
body size, boldness, mating and foraging success, which
reflect mate quality (this study, Riechert and Tracy 1975;
Riechert and Johns 2003).
Table 2 Summary of the measured personality and morphological
traits in females
Trait Median Q25/Q75
Latency to first reaction (s) 15 5.5/43.5
Latency to first bite (s) 37 12.5/109.5
Boldness 3 1.5/4
Locomotory activity 4 2.5/4.5
Intra-sex aggression 6 3.5/7
Mass (g) 0.73 0.65/0.81
Patella+ tibia I length (mm) 10.94 10.24/11.56
Carapace length (mm) 7.54 7.28/8.47
Median and quartiles are presented
Table 1 Summary of the measured behaviors (frequency of occur-
rence) in males
Behavior Median Q25/Q75
Waving legs during courtship 8 6/12.75
Touch female 1.5 0/7.5
Explore 5.5 2/11
Walk towards female 2.5 1/7.25
Distance to female (mm) 6.46 4.13/11.71
Aggression intensity 6 1/10.75
Median and quartiles are presented
Behav Ecol Sociobiol
However, despite selection seemingly favoring aggressive
and bold males in N. livida, males of this species are not
overly aggressive and are rather cautious when approaching
a female (e.g., Kralj-Fišer et al. 2011). Theoretically, males
with intact palps are expected to avoid contests and potential
injuries prior to mating, thus not risking their future mating
opportunities (Fromhage and Schneider 2005). A relatively
low aggressiveness in males may relate to their residual
reproductive value. Thus, the low levels of precopulatory
cannibalism in nephilids may also be the result of male
behavioral adaptations, i.e., cautious behavior in a female
web (Uhl and Vollrath 1998). Nevertheless, more aggressive
males had higher chances to achieve copulation in N. livida.
Alternative to the mate choice hypothesis, aggressive males
may have better chances to survive copulation due to their
greater ability to evade female attacks. However, this
explanation seems unlikely as we never observed successful
escapes from cannibalism in this species, while escapes seem
possible in other nephilids, but in very few cases (Kralj-Fišer
et al. 2011). Apparently, the mating position in N. livida
allows females to fully control male survival as is the case in
the brown widow Latrodectus hasselti (Andrade 1998). In
other words, female aggressive attempts in N. livida appear
to be always successful regardless of her or male size. The
extreme sexual size dimorphism in N. livida (as Nephilengys
borbonica in Kuntner and Coddington 2009) also speaks
against the adaptive foraging explanation for sexual canni-
balism because small males are a poorly nutritious meal
compared with their usual prey (e.g., Barry et al. 2008;
Wilder and Rypstra 2010).
To co nclu de, ou r stud y s how s t hat f emal e g ener al
aggressiveness, measures of body size, and rates of sexual
cannibalism are independent and thus provide no support
for the aggressive spillover hypothesis in N. livida.We
showed that the mate choice hypothesis with a mechanism
of direct choice best explained N. livida sexual cannibalism,
where females preferentially cannibalize non-aggressive
(and shy) males.
Acknowledgments We thank two anonymous reviewers for their
helpful comments. We thank Ingi Agnarsson, Sahondra Lalao Rahani-
triniaina, and Honore Rabarison for their help in the field. This work was
funded by theSlovenian Research Agency (grant J1-2063 to MK) and the
National Geographic Society (grant 8655-09 toI. Agnarsson, M. Kuntner,
and T. Blackledge). SKF was supported by a Humboldt fellowship for
postdoctoral researchers and a Humboldtian Return Fellowship. SP was
supported by grant no. 0021622416 from the Ministry of Education,
Youth and Sports of the Czech Republic.
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Plugging of female genitals via male sexual mutilation is a common sexual repertoire in some nephilid spiders (Herennia, Nephila, Nephilengys), but the behavioral pathways leading to emasculation are poorly understood. Recent work suggests that copulating Herennia males damage their reproductive organs during copulation and then voluntarily, and stereotypically, remove their pedipalps to become eunuchs. Presumably, such emasculation increases agility allowing the male to better fend off rival males. However, through our observation of male antagonism in Nephilengys borbonica (Vinson 1863) in La Reunion (Indian Ocean), we discovered that genital severance involving the entire male palp is induced by a rival eunuch. Additionally, laboratory matings of the same species from Mayotte provide the first observations of female sexual cannibalism in this species, one such forceful copulation termination leading to emasculation of the entire palp. These novel behaviors suggest that mate plugging and the eunuch phenomenon are more plastic repertoires than hitherto thought, and thus our observations add to possible pathways leading to them. Based on our examination of 791 samples of Nephilengys spp. from museum collections and of a freshly collected representative sample of N. borbonica, we conclude that i) palpal severance is common (50% of males from the wild were eunuchs lacking both palps), but ii) the females (or perhaps subsequent males) must possess a mechanism for removing severed palps from the epigyna (none had a whole palpal bulb), leaving behind only partial, embolic plugs, and iii) the disparity between male palpal damage (50%) and visible mating plugs in females (21%) merits further research as the relative numbers of severed males and plugged females can offer insight into which sex may have the upper hand in an evolutionary arms race.
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During copulation, male redback spiders (Latrodectus hasselti: Theridiidae) position themselves above the female's jaws. This apparent male complicity in sexual cannibalism is favored by sexual selection because cannibalized spiders receive two paternity advantages. First, cannibalized males copulated longer and fertilized more eggs than those that survived copulation. Second, females were more likely to reject subsequent suitors after consuming their first mate. These results represent empirical evidence for male copulatory suicide as an adaptive behavior.
Chapter
The chapter focuses on Polyandry, which sets the stage for sperm competition, and may provide female spiders with both material and genetic benefits. The material benefits include a reduction in the costs of male harassment and, perhaps, an increase in fecundity through the provision of nuptial gifts, including the body of the male. The genetic benefits, which are modified by the patterns of sperm precedence, are less apparent in females among species with a predominantly first-male sperm priority. However, for male spiders, most of the opportunities for securing paternity appear to be related to the timing of mating, physically guarding females from rival males and blocking the genital region of the female with a plug, or increasing the duration of copulation. Moreover, the latter reduces female receptivity and increases fertilization success in competition with other males, although the mechanisms remain unknown. Therefore, the studies of sperm competition also benefit by examining precedence patterns involving more than two males. The clear sexual dimorphism and often elaborate courtship behavior of many cursorial spiders provide a rich seam of model systems to investigate the evolutionary significance of both overt and cryptic female choice.
Article
Male Australian redback spiders (Latrodectus hasselti Thorell: Theridiidae) place their abdomens directly over their mate's mouthparts during copulation, increasing the likelihood of sexual cannibalism. Male sacrifice may be adaptive because cannibalized males increase their paternity relative to those that are not eaten. Despite male sacrifice behavior, however, up to 50% of laboratory matings may end without sexual cannibalism. Here, I report a similar pattern in the field, where males were not cannibalized in 35% of observed matings (6/17). I examined variation in female cannibalistic behavior by evaluating the following three hypotheses for the occurrence of cannibalism from the female perspective: (1) the mistaken identity hypothesis proposes that females sometimes cannibalize males because they mistake them for prey, (2) the mate rejection hypothesis predicts that females cannibalize males who are unacceptable as mates, and (3) the feeding opportunism hypothesis predicts that hungry females are more likely to be cannibalistic. Field observations refuted the first two hypotheses: females recognized males as potential mates (i.e., nonprey), and cannibalized and noncannibalized males were not phenotypically different. The feeding opportunism hypothesis was supported. In staged field matings, cannibalistic females were hungrier than their noncannibalistic counter-parts. Moreover, a logistic regression analysis indicated that hunger was a significant predictor of cannibalism. Because redback males are below the typical prey size that females accept, well-fed females are less likely to consume their mates, despite the vulnerable mating posture. These results indicate that, although males facilitate sexual cannibalism, their fate may depend on the female's physical condition.
Article
Sexual cannibalism, where a female kills and consumes a courting male, represents an extreme form of sexual conflict and has been proposed as a mechanism of mate choice. We evaluate the evidence for mate choice through premating sexual cannibalism via mate rejection, other indirect mechanisms of mate ‘choice’ and choice in postmating sexual cannibalism. We highlight a paucity of investigations, particularly of field studies, and note gaps in our knowledge. There is empirical support for the size-dependent sexual cannibalism predicted by mate choice through premating sexual cannibalism. This may represent mate choice operating on absolute male size but it could be a by-product of female foraging behaviour and greater vulnerability of relatively smaller males. Thus, indirect mate choice is as plausible an explanation of size-dependent sexual cannibalism as is direct mate choice based on discrimination of male traits. Direct female choice, mediated through premating sexual cannibalism, has yet to be demonstrated. We suggest a framework for distinguishing direct and indirect choice and note an absence of information on which to test it. There is evidence for sequential mate choice in postmating sexual cannibalism, but the nature or basis of the female's discriminatory behaviour remains unclear. Costs and long-term fitness benefits of the putative mate choice have been largely ignored. Reversed sexual cannibalism, in which the male eats the female, presumably occurs when the gain from food is high and potential gain from mating low and probably has little to do with mate choice.
Article
We tested the idea that sexual cannibalism increases male and female fecundity in the mantid Hierodula membranacea. Two experiments were performed, in the first we maintained females on one of three nutritional planes; high medium or low. Food intake was positively and significantly associated with: maximum mass attained, the mass of first and subsequent oothecae, and the rate at which oothecae were produced. Ootheca mass was positively correlated with maximum female mass, and the number of young hatching from oothecae was positively correlated with ootheca mass. In the second experiment we maintained females on low diets and allowed some to eat the male during mating and prevented others from doing so. Females which ate the male produced significantly heavier oothecae than those which did not. The female's nutritional state influenced her likelihood of eating the male; well fed females rarely ate males. These results confirm that under certain food regimes male and female fecundity are increased by sexual cannibalism. However, our observations indicate that males do not sacrifice themselves at mating, but attempt to avoid being eaten, suggesting that while sexual cannibalism may be adaptive for females it is unlikely to be so for male H. membranacea.