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Faking death to avoid male coercion: Extreme sexual conflict resolution in a dragonfly

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1
Faking death to avoid male coercion:
extreme sexual conflict resolution in a
dragonfly
I spent the summers of 2014 and 2015 in the Swiss Alps,
collecting the eggs of odonates (dragonflies and damsel-
flies) for laboratory experiments on larval responses to
temperature. This involved many hours spent waiting
beside ponds to capture females as they came to the water
to lay eggs. On 5 July 2015, while I was waiting at a pond
near Arosa, at about 2000 m elevation, I witnessed a drag-
onfly dive to the ground while being pursued by another
dragonfly. I grabbed my camera and started filming
(Video S1). As I approached the two insects, I realized
that they were Aeshna juncea (moorland hawker or sedge
darner), that the individual that crashed was a female,
and that she was lying motionless and upside down on
the ground. Upside down is an atypical posture for a
dragonfly. The male hovered above the female for a
couple seconds and then left. I expected that the female
could be unconscious or even dead after her crash landing,
but she surprised me by flying away quickly as I
approached. The question arose: did she just trick that
male? Did she fake death to avoid male harassment? If
so, this would be the first record of sexual death feigning
in odonates and probably the fifth in the animal kingdom
after a nuptial gift- giving spider (Bilde et al. 2006, Hansen
et al. 2008), two species of robber fly (Dennis and Lavigne
1976), and a European mantis (Lawrence 1992). Kaiser
(1985) described motionless hiding by females in another
dragonfly (A. cyanea; blue hawker), but did not indicate
that they were faking death. I also wondered how common
this behavior might be. The observation near Arosa
prompted me to remember several other instances during
the previous season in which I had seen dragonflies diving
into the ground or vegetation. Aeshna juncea is common
at each of the ponds where those observations occurred;
could sexual death feigning occur regularly in this species?
To answer these questions, I studied the reproductive
behavior of A. juncea for 72 h in July and August 2015 at
two sites (the Arosa pond, 46.80°N, 9.67°E and another
pond near Lenzerheide, 46.73°N, 9.55°E) from 10:00 to
16:00. In both ponds, the bank vegetation, where most
egg laying takes place, was relatively dense with most
patches not exceeding 60 cm height. As for many other
dragonflies, the female reproductive episode of the
moorland hawker may be divided into four important
sequential events: female arrival at reproductive site, cop-
ulation, oviposition, and departure from reproductive site.
To summarize, mature males remained close to the water
waiting for females. When the female came to the pond,
the male intercepted her in the air and both formed the
copulatory wheel. Copulation took place near the pond,
often perched on a plant support (Fig. 1a). After copu-
lation, the male detached himself from the female and flew
away. The female laid eggs (oviposition) solitarily without
male protection (Fig. 1b), unlike many other dragonflies
(Corbet 1999). Female became vulnerable to male coercion
at that time because conspecific males were constantly
patrolling each corner of the pond looking for a mate. To
overcome this pressure, females showed both preventive
and protective behavioral strategies to avoid coercion
during oviposition and departure from reproductive sites.
To reveal potential preventive behavioral strategies of
females, I estimated the vegetation density (percentage
of 1 m2 water area covered by vegetation) around ovi-
position sites of 56 and 46 ovipositing females during five
days in Arosa and Lenzerheide, respectively (Appendix
S1). I hypothesized that females choose sheltered areas
Ecology, 0(0), 2017, pp. 1–3
© 2017 by the Ecological Society of America
The Scientific Naturalist
Fig. 1. Moorland hawker (Aeshna juncea). (a) Reproductive pair; (b) oviposition of a single female.
2Ecology, Vol. 0, No. 0
of the pond to reduce its visibility to coercive males. On
average, females laid eggs in sites with high vegetation
density of 70.9% in Arosa (n = 56) and 69.2% in
Lenzerheide (n = 46). I conducted an experiment in which
I reduced male density by 50% in the two sites during
one day (Appendix S1), which reduced of the average
density of oviposition sites in vegetation (Appendix S1:
Fig. S1a) and decreased the number of male coercion
events (Appendix S1: Fig. S1b). These results suggest that
males shape habitat selection of females, and thus the
occupancy of densely vegetated parts of the pond during
oviposition could be a behavior to reduce male coercion.
To assess the protective behavioral strategies of females
during coercion, I assessed female behavior during
departure from the reproductive site, which is probably
the phase where the female is most vulnerable to coercion.
Fig. 2 illustrates behavioral responses of females to male
coercion after oviposition and Appendix S1: Table S1
presents the respective statistics for both sites. When the
female tried to leave the oviposition site, males always
chased her on the air. Females (n = 35) usually crashed
on the ground (88.6%, n = 31), and rarely kept flying
(11.4%, n = 4; chi- square test, P < 0.0001; Appendix S1:
Table S1). Females who did not crash to the ground or
vegetation were all intercepted by a male. Females crash-
landed (n = 31) more often within vegetation such as
bushes and dense grasses (71%, n = 22), than on open
areas on the ground (29%, n = 9; chi- square test, P = 0.02).
Following the crash, death feigning was observed in 27
out of 31 cases (87%). Of the 27 motionless females, 21
(77.7%) were successful in deceiving the coercive male.
The high frequency of sexual death feigning in both sites
suggests that this behavior is common for the species. In
addition, that males could not detect the motionless
females highlights the importance of movement for males
to detect females, which is the case for many odonates
(e.g., Bick and Bick 1961, Ubukata 1984).
To test whether females are sensitive to touching
during death feigning, I performed an experiment in early
August 2015 at Arosa pond in which I attempted to catch
by hand females performing death feigning after male
harassment. Usually, it is impossible to catch an active
dragonfly by hand because they rapidly escape. Of 31
catching attempts, 27 females successfully escaped (87%).
Therefore, when females display death feigning they are
perfectly conscious and readily avoid disturbance and
probably predators.
So how did sexual death feigning evolve? On one hand,
this behavior could have resulted from exaptation. Since
death feigning already exists in the behavioral repertoire of
dragonflies (Corbet 1999), females of the moorland hawker
expanded the use of this antipredatory function to avoid
male coercion. On the other hand, the origin of this exap-
tation is probably sexual conflict where each sex adopts
reproductive strategies that best serve its own survival and
reproductive success (Parker 1979). The mating system of
the moorland hawker is predisposed to sexual conflict
because the vulnerability of solitary oviposition, the fitness
costs of male harassment (Rice 1996, Crudgington and
Siva- Jothy 2000), and the highly male- biased sex ratio in
oviposition sites (Wildermuth 1993) put the females under
extreme reproductive conditions that require effective
Fig. 2. Death feigning of female (in red) against male (in blue) coercion of the moorland hawker (Aeshna juncea). Numbers refer
to the succession of the events. Numbers in black and white are males and females, respectively. When the female leaves oviposition
site (red 1), a male usually chases her (blue 1), which induces the female to flee (red 2). The female either keep flying or crash on the
ground or vegetation (red 3). She performs death feigning right after crashing (red 4) while the male is searching for her (blue 2). The
male does not detect the female and leaves the crashing area (blue 3). The female, knowing that she is no longer coerced, flies away
(red 5).
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THE SCIENTIFIC NATURALIST
behavioral responses to overcome survival and repro-
ductive costs. Thus, females that perform death feigning
probably undergo less coercion, survive longer and produce
more offspring, hypotheses that warrant testing.
Sexual death feigning is one of the rarest behaviors in
nature, and due to its scarcity, it has received little attention
in behavioral ecology. Currently, it is restricted only to
arthropods. It would be interesting to know whether this
scarcity is true or just an artefact related to the lack of
behavioral investigations or difficulty in detecting this
behavior. Further studies should investigate how wide-
spread sexual death feigning is among arthropods and
whether it occurs in other phyla. Moreover, it is time to
develop an informative classification for death feigning
behavior that takes into account both behavioral and
physiological information because death feigning could
be strictly behavioral in which the animal is conscious and
sensitive to touching and handling (moorland hawk-
er- like), but could also include physiological changes
where the animal is “unconscious,” physiologically shut
down and unresponsive to physical contact (opos-
sum- like). Finally, the new case of sexual death feigning
reported here demonstrates discoveries even in common
species and well- studied areas of the world remain.
Although the diversity of sizes, shapes, structures and col-
orations of organisms on earth is astonishingly high, the
diversity of behaviors might be surprisingly comparable.
Acknowledgments
Funded by the Swiss Government Scholarship for Excellence
2013.0051 and a Forschungskredit der Universität Zürich (Nr.
FK- 16- 087). Thanks to Brad Taylor and John Pastor for helpful
comments on the manuscript. I am grateful to Gregory
Goldsmith, Josh Van Buskirk, and the Lukas Keller group for
constructive discussion and advice.
literAture cited
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Corbet, P. 1999. Dragonflies: behaviour and ecology of
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Crudgington, H. S., and M. T. Siva-Jothy. 2000. Genital dam-
age, kicking and early death. Nature 407:855–856.
Dennis, D. S., and R. J. Lavigne. 1976. Ethology of Efferia
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Mantis religiosa: a field study. Animal Behaviour 43:
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Parker, G. A. 1979. Sexual selection and sexual conflict. Pages
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Rice, W. R. 1996. Sexually antagonistic male adaptation trig-
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381:232–234.
Ubukata, H. 1984. Oviposition site selection and avoidance of
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amurensis Selys (Corduliidae). Researches on Population
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rAssim kheliFA
Department of Evolutionary Biology and Environmental Studies,
University of Zurich
Winterthurerstrasse 190, CH-8057, Zurich, Switzerland
E-mail: rassimkhelifa@gmail.com
Manuscript received 2 November 2016; revised 24 January
2017; accepted 30 January 2017. Corresponding Editor: John
Pastor.
Additional supporting information may be found in the
online version of this article at http://onlinelibrary.wiley.com/
doi/10.1002/ecy.1781/suppinfo

Supplementary resource (1)

... Death feigning (or thanatosis, tonic immobility, playing possum, playing dead, post-contact immobility, and so on) that have recently received special attention is one way to avoid enemy attack 3,4,5,6 . It has also been considered an adaptive behavior for females to avoid male harassment 7,8,9,10,11 and for individuals to avoid worker aggressions in social insects 12 . Although the adaptive signi cance of death-feigning behavior has become widely recognized, very little research has been done on its molecular mechanisms. ...
Preprint
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Predator avoidance is an important behavior that affects the degree of adaptation of organisms. We compared the DNA variation of one of the predator-avoidance behaviors, the recently extensively studied "death-feigning behavior," between the long strain bred for feigning death for a long time and the short strain bred for feigning death for a short time. To clarify how the difference in DNA sequences between the long and short strains corresponds to the physiological characteristics of the death-feigning duration at the transcriptome level, we performed comprehensive and comparative analyses of gene variants in Tribolium castaneum strains using DNA-re-sequence. The duration of death feigning involves many gene pathways, including caffeine metabolism, tyrosine metabolism, tryptophan metabolism, metabolism of xenobiotics by cytochrome P450, longevity regulating pathways, and circadian rhythm. Artificial selection based on the duration of death feigning results in the preservation of variants of genes in these pathways in the long strain. When an animal wake up from a near-death experience is closely related to its success in avoiding predation. This study suggests that many metabolic pathways and related genes may be involved in the decision-making process of anti-predator animal behavior by forming a network in addition to the tyrosine metabolic system, including dopamine, revealed in previous studies.
... In many animal species, TI behaviors have been examined for their adaptability (e.g., Ruxton et al. 2004, Miyatake et al. 2004, Cassill et al. 2008, Rogers and Simpson 2014, Humphreys and Ruxton 2018, Skelhorn 2018. This behavior has some varied function on survival of prey including an adaptive defense against predators (Miyatake et al. 2004, Honma et al. 2006, Ohno and Miyatake 2007, a tactic to avoid sexual harassment (Khelifa 2017), and a strategy to avoid individuals of conspecific species in a social ant species (Cassill et al. 2008), or of predator to attack and approach the bait without moving (McKaye 1981). ...
Chapter
This chapter first touches on the taxonomic groups of insects that have been observed to tonic immobility. Although I have used the word “death feigning” in many of my previous papers, I used “tonic immobility (TI)” here as the same meaning as death feigning. Next, the two modes of insects the author discovered in our experiments with beetles, stationary and activity, are described. Individuals in the active mode do not TI, while individuals in the stationary mode TI. In other words, TI is a behavior with phenotypic plasticity. Eight factors are outlined as to what conditions cause this plasticity. Finally, I outline the results of direct and correlated responses in artificial selection for duration of TI on beetles as model materials. Using the selected strains, I will also present the results of experiments approaching a group of genes that control duration of TI and the stimuli that arouse from TI.
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In meiner Dissertation untersuche ich das Paarungs- und Fortpflanzungsverhalten des Europäischen Grasfrosches (Rana temporaria) in einem evolutionären Kontext. Mein Ziel ist es zu verstehen, welche Mechanismen zur Bildung von Paaren führen, ob die Partnerwahl die Paarungsmuster erklärt, die wir beobachten können, und ob es evolutive Vorteile gibt, die sich aus der Paarung mit einem bestimmten Partner ergeben. Die Suche nach und die Konkurrenz um Paarungspartner führt zur Entwicklung verschiedener Paarungssysteme, Strategien und Taktiken, um den Reproduktionserfolg während der gesamten Lebensdauer zu erhöhen. Das Paarungsverhalten wird durch natürliche und sexuelle Selektion beeinflusst, wobei beide in unterschiedliche Richtungen wirken können. Für die meisten Individuen ist das Überleben unerlässlich, um sich so oft wie möglich zu reproduzieren, und dadurch die reproduktive Gesamtfitness zu erhöhen. Andererseits könnte ein auffälliges Verhalten bei der Fortpflanzung das Prädationsrisiko erhöhen. Der Akt der Paarung selbst kann bereits mit Risiken verbunden sein, welche sich auf die Überlebensraten auswirken können. Durch sexuelle Selektion könnten bestimmte sekundäre Geschlechtsmerkmale begünstigt werden, entweder aufgrund von Vorteilen im Wettbewerb innerhalb eines Geschlechts (intrasexuell), oder aufgrund spezifischer Präferenzen zwischen den Geschlechtern (intersexuelle Selektion). Damit sich die Partnerwahl entwickeln kann, muss der gewählte Paarungspartner Vorteile aufweisen, von denen der wählende Partner profitiert, denn die Wahl ist mit energetischen Kosten und zeitlichem Aufwand verbunden. Als Frühlaicher muss der Europäische Grasfrosch mit einem eingeschränktem Paarungszeitraum umgehen. Die Männchen konkurrieren um den Zugang zu Weibchen und es wird angenommen, dass sich Weibchen während der Paarung und Reproduktion passiv verhalten, da der hohe "Männchen-Überschuss" keine Wahl zulassen würde. Aus evolutionärer Sicht sollten Weibchen jedoch das wählerische Geschlecht sein und entscheiden mit wem sie sich paaren, da sie mehr Energie in die Eierproduktion investieren.
... Male mating harassment can reduce female fitness (Helinski and Harrington 2012), fecundity (Gosden and Svensson 2009;Rossi et al. 2010), and longevity (Mühlhäuser and Blanckenhorn 2002). Selection has favored multiple female phenotypic traits that reduce male mating harassment, such as female-limited polymorphism (Takahashi et al. 2014), male mimicry (Takahashi and Watanabe 2011;Huang and Reinhard 2012;Iserbyt et al. 2013), cryptic female coloration (Fincke 2015), and behaviors such as death feigning (Khelifa 2017) and mating refusal displays (Chan et al. 2009;Ide 2011). Female-limited color polymorphism reduces mating harassment by not conforming to the male mate search image. ...
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Conspicuous female colouration can evolve through male mate choice or via female‐female competition thereby increasing female mating success. However, when mating is not beneficial, such as in pre‐reproductive females, selection should favour cryptic rather than conspicuous colouration to avoid male detection and the associated harassment. Nevertheless, conspicuous female colouration occurs in many pre‐reproductive animals, and its evolution remains an enigma. Here, I studied conspicuous female colouration in Agriocnemis femina damselflies, in which the conspicuous red colour of the immature females changes to a less conspicuous green approximately a week after their emergence. I measured body size, weight and egg numbers of the female morphs and found that red females are smaller, lighter and do not carry developed eggs. Finally, I calculated the occurrence frequency and mating frequency of red and green females in several populations over a three‐year period. The results demonstrate that red females mated less frequently than green females even when red females were the abundant morph in the populations. I concluded that conspicuous female colouration is likely to function as a warning signal of sexual unprofitability, thereby reducing sexual harassment for females and unprofitable mating for males. This article is protected by copyright. All rights reserved
... It is also considered an adaptive behaviour for females to avoid male harassment (e.g. Bilde, Tuni, Elsayed, Pekár, & Toft, 2006;Dennis & Lavigne, 1976;Khelifa, 2017;Lawrence, 1992;Shreeve, Dennis, & Wakeham-Dawson, 2006) and for individuals to avoid worker aggressions in social insects ( van Veen, Sommeijer, & Aguilar Monge, 1999). Although the adaptive significance of death-feigning behaviour has become widely recognized, it is still partially in dispute due to a lack of evidence on what drives its evolution (See Honma, Oku, & Nishida, 2006;Humphreys & Ruxton, 2018;Rogers & Simpson, 2014). ...
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Death feigning is considered to be an adaptive anti-predator behavior. Previous studies on Tribolium castaneum have shown that prey which death feign have a fitness advantage over those that do not when using a jumping spider as the predator. Whether these effects are repeatable across species or whether they can be seen in nature is, however, unknown. Therefore, the present study involved two experiments: 1) divergent artificial selection for the duration of death feigning using a related species T. freemani as prey and a predatory bug as predator, demonstrating that previous results are repeatable across both prey and predator species, and 2) comparison of the death-feigning duration of T. castaneum populations collected from field sites with and without predatory bugs. In the first experiment, T. freemani adults from established selection regimes with longer durations of death feigning had higher survival rates and longer latency to being preyed on when they were placed with predatory bugs than the adults from regimes selected for shorter durations of death feigning. As a result, the adaptive significance of death-feigning behavior was demonstrated in another prey-predator system. In the second experiment, wild T. castaneum beetles from populations with predators feigned death longer than wild beetles from predator- free populations. Combining the results from these two experiments with those from previous studies provided strong evidence that predators drive the evolution of longer death feigning.
Chapter
Lower invertebrates exhibit both morphological and behavioral defensive responses to aversive stimuli, characterized by withdrawal. Typical immobility responses are “sinking” in Rotifers and “crumpling” in Cnidaria. They also display individual adaptation and phenotypic plasticity but not tonic immobility (TI). The higher phyla with a more organized nervous system have developed morphological and behavioral defensive strategies including TI, occurring both in natural and laboratory conditions. There are general but also specific prey-predator mechanisms, that have coevolved leading to reciprocal phenotypic plasticity. The evolution of traits differentiated in subpopulations has been described in many species (animal personality). In insects the variability in TI is heritable and inversely related to boldness. In two genetic lines of beetles with long and short TI duration, the long duration line has higher survival rate but lower mating success (behavioral syndromes). TI may have an adaptive significance also in intraspecific interactions in the context of sexual selection.
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Dragonflies never cease surprising me. I thought the most astonishing observation was the apparent “death feigning” (tonic immobility) of females to avoid male harassment. I observed this behavior during my PhD studies in the Swiss Alps in the holarctic Moorland Hawker (Sedge Darner) Aeshna juncea (Linnaeus) (Khelifa 2017). Ever since then, I have wondered whether this behavior occurs in other closely dragonfly species.
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Females of an odonate species in which oviposition sites overlap with mating sites may adopt one or more of the following strategies when they lay eggs except when they ‘trade’ mating for access to suitable oviposition sites or for services (guarding, etc.) provided by males: (1) ovipositing at hidden places; (2) ovipositing at a time when males are neither patrolling nor watching; (3) indicating non-receptivity by a behavioral display. The density of ovipositing females of the dragonfly,Cordulia aenea amurensis Selys which was studied between 1970 and 1983 at a pond (Hôrai-numa, Sapporo, Hokkaido) had a high negative correlation with the distance from ‘entrance’ (a part of shore at which the arrival of most adults seems to have occurred). On the other hand, oviposition was rarely observed at a sector being distant from entrance in spite of the inference that larval survivorship was probably high at this sector. Most females oviposited among emergent vegetation in which approach of males to them was difficult, and they scarcely traveled across the open water in search of oviposition sites. Therefore, most females of the population studied were considered to adopt the first strategy. The second and third strategy were not adopted by the population studied. Finally, the influences of some environmental factors and traits possessed by a species on the adoption of these tactics or on the execution of the ‘trades’ were discussed.
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An isolated population of Lestes disjunctus australis Walker was studied in the adult stage during 2 summers by counting and observing marked and unmarked individuals at water during all daylight hours on 12 days and between 1600 and 1800 on 32 days, 9 of which were successive. Peak emergence was in early June and maximum number of mature individuals in late July. Newly-emerged adults left water for a mean of 13 dyas and were reproductive on the day of return. Mean reproductive span was 10 days, maximum 50. Recoveries of matures and of males were much higher than of tenerals and of females. In spite of an approximately 1:1 sex ratio at emergence, 86% of all individuals at water were paired and unpaired males; unpaired females were never more than 1%. Females came to water on fewer hours of any one day than males and on fewer days during their total reproductive spans. Movements of males to and from water were more complex than mass morning arrivals and late evening departures as is commonly presented for the Order. Thirty-three per cent of the males were present for the entire day, 32% left by noon but returned in the afternoon, and 7% were present in the morning only. By 0800, 72% of the males in the vicinity of the pond were at water. In the afternoon an additional group of males (20%) and 78% of the females arrived, resulting in maximum numbers and mating around 1700. These movements could not be correlated satisfactorily with temperature, light intensity, relative humidity, or wind velocity. Males visited the pond quite regularly but seldom mated. Females came more infrequently but usually mated. Because of this reciprocal relationship mean number of mating days per reproductive span in males (1.2) and females (1.7) was similar. Mean time in tandem for 81 marked individuals was 60.2 minutes. Duration of actual copulo was 6-19 minutes. Moderate sector localization occurred. Intraspecific interactions between males were infrequent and each male usually maintained a single Eleocharis stem by passive occupancy. Brief notes were recorded on distance from water, under-water oviposition, predation, and feeding.
Article
The frequency of sexual cannibalism, mating behaviour and general biology of a wild population of the mantid, Mantis religiosa, were examined. Mating behaviour of wild mantids was similar to that of captive individuals: males were always ‘cautious’ towards females and performed no display in their precopula approach. Sexual cannibalism occurred in 31% of matings observed in the wild. Growth (weight gain/age) was restricted in wild females. Males were attracted more to heavier females which oviposited sooner after mating. The sex ratio became progressively female biased as the breeding season progressed and it is suggested that sexual cannibalism may have contributed to this bias.
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The females of the dragonfly Aeschna cyanea visiting ponds vary in their receptiveness to males waiting there. Individual males pay several short visits to a mating place in the course of a day, searching for receptive females. Non-receptive females prefer to oviposit at the pond in the evening, whereas receptive females arrive throughout the day. The highest number of receptive females is found on warm days during the afternoon at which time the greatest number of copulations occur. However, as the number of males and, therefore, the competition between males is also highest during these periods, the mating chances of a particular male are constant throughout the day.