Ecology Article summary and critique

Journal of the Tennessee Academy of Science 89(2): 51-58 August 2014

The Giant Water Bug, Belostoma lutarium (Stal): An Ideal System for Studies of Ecology,
Evolution, and Behavior

Hope Klug* and Patrick Hicks

Department o f Biological and Environmental Sciences, University o f Tennessee at Chattanooga, 215 Holt Hall, Dept 2653 615 McCallie Avenue,
Chattanooga, T N 37403 USA

Abstract— Parental care, sexual selection, and life history are major areas of research in evolutionary ecology.
Recent theoretical work has suggested that parental care, sexually-selected traits, and life-history characteristics are
expected to co-evolve with one another, and such research has highlighted a need for more studies that focus on the
interactions among these traits. We begin by identifying and reviewing key directions in the field o f evolutionary ecology in
relation to parental care, sexual selection, and life history. We then describe a newly-documented southeastern Tennessee
population o f the giant water bug, Belostoma lutarium (Stal), that is ideal for addressing timely questions related to parental
care, sexual selection, and life history. Belostoma lutarium is one o f a relatively few species that provides exclusive paternal
care, which makes it particularly ideal for studies focused on the evolution o f male care. Surprisingly, the behavior o f this
species has not previously been studied. We describe mating and parental care in this species and provide details of adult
body size and laboratory housing conditions. We then outline how B. lutarium can be used to address specific questions
related to evolution, ecology and behavior.

Introduction
Understanding diversity in parental care behavior and

patterns of sexual selection is a major focus in current studies
of evolutionary ecology (Clutton-Brock, 2007; Kokko and
Jennions, 2008; Kokko et al., 2012; Royle et al., 2012). In
particular, recent research has suggested that the evolution of
parental care is influenced by mate competition and choice
(Alonzo, 2012; Kokko and Jennions, 2012), mate availability
(Kokko and Jennions, 2008, 2012), and general life-history
traits (Klug and Bonsall, 2010; Klug et al., 2013 a, b).
Likewise, sex-specific patterns of parental investment are
expected to affect the strength and direction of sexual selection
(Emlen and Oring, 1977; Ahnesjo et al., 2001; Shuster and
Wade, 2003; Kokko and Jennions, 2008, 2012; Jennions and
Kokko, 2010). As such, understanding the evolution of
parental care and sexual selection requires that we examine
the relationship between mate choice, mate competition, and
parental care in organisms that exhibit care and are likely to
experience sexual selection.

In the present work, we identify and review key directions
of research that are critical for broadening our understanding
of the evolution of parental care and sexual selection. We then
describe a newly-documented population of the giant water
bug Belostoma lutarium (Stal) (Insecta: Hemiptera) in Tennes­
see, and outline several ways in which B. lutarium could be
used to address timely questions in evolutionary ecology
related to parental care and sexual selection.

* Corresponding author: H. Klug, [email protected]

Key Directions in the Study o f Parental Care and
Sexual Selection

Parental care and sexual selection are intimately linked
and expected to co-evolve with one another (Kokko and
Jennions, 2008; Alonzo, 2012; Kokko et al., 2012; Royle et al.,
2012; Kokko and Jennions, 2012). From an evolutionary
perspective, parental care is only expected to evolve and be
maintained if the fitness benefits to the caring parent outweigh
the costs of care (reviewed in Klug et al., 2012 and Klug and
Bonsall, 2014). Parental care is typically associated with
increased offspring survival and/or quality (e.g. size). However,
care is also costly to parents when it decreases survival and/or
reduces future reproductive opportunities (Klug et al., 2012).
In particular, parental care often decreases time and energy
that individuals can invest into future mating (Royle et al.,
2012). The benefits and costs of parental care can be affected
by basic life-history characteristics such as offspring need,
stage-specific mortality, and maturation rates (Klug and
Bonsall, 2010; Klug et al., 2013 a, b). For example, if adults
have relatively high mortality, and hence reduced future
reproductive opportunities, the fitness benefits of care are
expected to be relatively high (Klug and Bonsall, 2010).
Likewise, the benefits of care are expected to be greatest when
offspring need care the most (Klug and Bonsall, 2010; Klug
et al., 2013 a, b).

When males and females differ in the potential costs of
parental care, we expect sex differences in parental care to
evolve (reviewed in Kokko and Jennions, 2012), which can, in
turn, affect mating dynamics and sexual selection (Kokko and
Jennions, 2008; Kokko and Jennions, 2012). Likewise, when
males and females differ in the sexual selection that they
experience, this can affect the evolution of parental care

52 Journal o f the Tennessee Academy o f Science vol. 89, no. 2

TABLE 1. Key questions in the field of evolutionary ecology and examples of specific related questions that could be addressed
in B. lutarium to enhance our general understanding o f the evolution of parental care, sexual selection, and life-history evolution.

General question: Example o f questions that B. lutarium is ideal for answering:

What are the costs and benefits
of parental care, and how do
these costs and benefits
influence the evolution of
parental care and mating
dynamics?

Which sex, if any, experiences
sexual selection, and if so,
which traits are under sexual
selection?

Which general life-history
characteristics are associated
with parental care?

Is there a relationship between male care behavior and future reproductive success?
Is there a relationship between female parental investment (egg size and number) and
future reproductive success?
Does care duration influence offspring hatching success, future survival, future
reproductive success, and/or size?
How long are males unavailable to mate while providing parental care?
Do females experience a mating ‘time-out’ period after producing eggs?
What is the relative abundance of males and females that are available to mate at a given
time?
Does female investment in eggs (i.e., egg size and number) influence male care behavior
and offspring abandonment?
Are male traits, such as size and backspace area, correlated with mating success?
Are female traits, such as size, correlated with mating success?
Do males and females differ in the strength of sexual selection experienced?
Does sexual selection change over the course of the breeding season?
Are males that exhibit relatively high levels of parental care more likely to get mates in the
future?
How well do offspring survive in the absence of care (i.e., what is offspring need)?
What is the average male and female survival during various life-history stages and how is
survival influenced by care and mating?
How long do individuals spend in various life-history stages?

(K okko and Jennions, 2008; Alonzo, 2010; K okko and
Jennions, 2012). Indeed, there is expected to be co-evolutionary
feedback between parental care and sexual selection, and, in
part, this feedback is related to mate availability (reviewed in
Kokko and Jennions, 2008).

If one sex provides parental care, that sex is often
unavailable to mate for some period o f time due to time spent
caring and/or time spent recouping resources that are required
for mating (reviewed in Kokko and Jennions, 2008). If one sex
is excluded from the mating pool due to this ‘time-out’ cost of
parental care, the other sex will potentially have reduced
mating opportunities because of the lack of opposite-sex
individuals currently ready to mate. This lack o f potential
mates, in turn, can lead to strong mate competition and sexual
selection on the sex that does not provide parental care
(Kokko and Jennions, 2008). Alternatively, a lack o f potential
opposite-sex mates can select for the sex that is more common
in the mating pool to provide parental care (Kokko and
Jennions, 2008).

Understanding the complex link between parental care
an d sexual selection requires th a t we have a detailed
understanding of 1) the costs and benefits of parental care
and investment by both males and females, 2) which sex (if
any) experiences sexual selection, 3) which traits (if any) are
under sexual selection, and 4) basic life-history characteristics
such as offspring need (e.g., survival in the absence of parental
care) and stage-specific m ortality and m aturation (Table 1).
While many studies have focused on parental care (reviewed in
Clutton-Brock, 1991 and Royle et ah, 2012), sexual selection
(reviewed in Andersson, 1994), or life history (reviewed in

Stearns, 1992), relatively few studies focus on quantifying
components of all three within the context o f a single species
and/or a single study. As such, there is a need for more
empirical studies that simultaneously focus on parental care,
sexual selection, and basic life-history characteristics (Clutton-
Brock, 1991; Alonso-Alvarez and Velando, 2012; Klug et ah,
2012; Klug and Bonsall, 2014). In particular, paternal care has
received substantially less empirical and theoretical attention
than m aternal care and has been more difficult to explain
theoretically (e.g., Kokko and Jennions, 2008). As a result,
more empirical studies are needed in systems in which males
alone provide parental care to enhance our understanding of
parental care and sexual selection (see e.g., discussion in
Kokko and Jennions, 2008 and Alonzo, 2010).

We recently discovered a population of the giant water
bug, Belostoma lutarium, in southeastern Tennessee. Based on
our initial behavioral and population-level measurements of B.
lutarium, we believe that this population could serve as an ideal
study system for biologists interested in the evolution of
parental care, sexual selection, and life history. Below we
outline why B. lutarium is ideal for such studies in evolutionary
ecology and provide suggestions for future avenues o f research
in this system.

Belostoma lutarium: Ideal fo r Studies o f Parental Care
and Sexual Selection

The giant water bug, Belostoma lutarium, is a small insect
in which males alone provide parental care o f eggs. After
mating, females adhere their eggs to the back o f their mate,

August 2014 Klug and Hicks—G iant W ater Bug: Ideal for Studies o f Evolution & Ecology 53

an d m ales are left to care for eggs fo r approxim ately tw o weeks
(described in detail below). B oth m ales a n d females have the
p o te n tia l to m a te m u ltip le tim es b o th d u rin g a given
reproductive b o u t an d th ro u g h o u t th e breeding season. M ale
m atin g success in giant w ater bugs is p o tentially lim ited by
female egg p ro d u ctio n , a n d female m atin g success is p o te n ­
tially lim ited by the availability o f m ale back space (K ruse,
1990). A s such, b o th m ale a n d female traits in this species have
the p o ten tial to be u n d e r sexual selection. Because B. lutarium
provides p a re n ta l care a n d likely experiences m ate lim itation, it
is an ideal organism for em pirical studies o f paren tal care and
sexual selection. Surprisingly, B. lutarium has never previously
been used in studies o f p a re n ta l care a n d sexual selection.

Below we describe characteristics o f B. lutarium th a t m ake
it well-suited to studies in evolution, ecology, a n d behavior,
p artic u la rly th o se focused on p a re n ta l care a n d m atin g
behavior. We begin by p roviding an overview o f previous
descriptive w ork on this species a n d som e relevant inform ation
on closely related species. W e th e n describe th e newly
docum ented p o p u la tio n o f B. lutarium fo u n d in southeastern
Tennessee. W e describe the collection, behavior, a n d m o r­
p h ology o f individuals in this p o p ulation.

Overview o f Previous Inform ation on B. lu tarium

Distribution and morphology!appearance— Belostoma lutar­
ium is pred o m in an tly fo u n d in the so u th eastern U n ited States,
b u t has been fo u n d as far n o rth as M ichigan a n d is fairly
co m m o n in n o rth e rn states alo n g the A tlan tic seab o ard
(L u ack , 1964). I t is a m edium -sized b e lo sto m a tid , w ith
previous research suggesting th a t m ale lengths range from
18.5-27.5 m m a n d fem ale lengths range fro m 19.5-26.0 m m
(L uack, 1964). W idths ranged from 9.4—13.5 m m fo r males,
an d 10.3-13.0 m m for females (L uack, 1964). T he ovate shape
o f th eir bodies an d their b row n co lo ratio n give them the
ap p earan ce o f decaying leaves a n d can m ake th em difficult to
distinguish from litter resting on th e substrate. T heir ventral
sides, including th eir legs, are often a lighter shade o f brow n.
T heir legs are ch aracterized by distinct a n d regular d a rk spots
an d bands; the m iddle an d hind lim bs are b ro ad en ed and
h irsute to facilitate sw im m ing (Sm ith, 1997). T hey have
pow erful ra p to ria l forelim bs used for grasping prey during
cap tu re a n d while feeding.

P redatory habits and diet— B elostom a lutarium is an
am b u sh p re d a to r. It grasps o n to vegetation using its hind-
lim bs, w hich leaves its ra p to ria l forelim bs available to seize
passing prey (personal o b servation in a la b o ra to ry setting). N o
studies have focused on determ ining th e com plete diet o f B.
lutarium; how ever, it is assum ed to be a generalist p red ato r.
Sm ith (1997) states th a t th e genus Belostom a is a know n
p re d a to r o f snails, crustaceans, insects, fish, a n d larval and
ad u lt am phibians. In a study on p red ato r-p rey relationships,
Sw art an d T ay lo r (2004) show ed th a t B. lutarium will readily
feed u p o n tadpoles o f th e frog A naxyrus fow leri.

Parental care— Like all know n m em bers o f the subfam ily
B elostom atinae, B. lutarium provides p a ren tal care o f eggs.
W hile p a re n ta l care in closely re la te d species has been
described, a n d is likely to be fairly sim ilar to th a t o f B.
lutarium, p a ren tal care beh av io r in B. lutarium has n o t been
previously described in detail, an d is a p rim ary goal o f this
study. Some species o f the subfam ily B elostom atinae, includ­
ing m em bers o f the genus Lethocerus, b ro o d th eir eggs on

FIG. 1. Study site, a m arsh adjacent to M o u n ta in C reek
R d, C h attan o o g a, T N , an d h a b ita t o f Belostom a lutarium.

em ergent vegetation. In co n trast, males o f th e genus Belostoma
b ro o d th eir eggs on their backs, w hich are deposited there by a
female after several b o u ts o f co p u latio n (see Sm ith, 1979 for
details o f repeated co p u latio n in a related species an d its role in
p atern ity assurance). W hile encum bered w ith eggs, Belostoma
m ales are assum ed to a d o p t several care behaviors w hich are
th o u g h t to prim arily provide oxygen to their eggs.

Life-history stages— G ia n t w ater bugs have distinct life-
history stages w hich m akes them ideal to test predictions o f
basic life-history theory. Belostoma lutarium develops from an
egg th ro u g h five n y m p h a l in sta rs (see M c P h e rso n an d
Packauskas, 1986 fo r a description o f each instar), before
m olting to an adult.

A s stated above, o u r goal is to provide m ore inform ation
on the behavior an d possible utility o f B. lutarium fo r studies
o f ecology, evolution, and behavior. Below, we provide basic
behav io ral a n d population-level in fo rm a tio n fo r a newly
described p o p u la tio n in south eastern Tennessee. Specifically,
we focused on identifying th e breeding season o f B. lutarium in
the p o p u latio n , quantifying the a b u n d an ce an d sex ra tio o f B.
lutarium in the wild, an d providing details o f la b o rato ry
housing an d rearing, behavioral observations o f m atin g a n d
p a re n ta l care, a n d m o rp h o lo g ic a l m easu rem en ts o f this
p o p ulation.

M aterials a n d m eth o d s

Beginning in June 2012, we identified a p o p u la tio n o f B.
lutarium in a m arsh connected to M o u n ta in C reek located to
th e west o f M o u n ta in C reek R o a d in C h a tta n o o g a , T N . This
perm an en t m arsh, roughly th e size o f a football field, is fed by
M o u n ta in C reek (Figure 1). T he m arsh is characterized by rich
vegetation w ithin and a ro u n d th e w ater du rin g spring and
sum m er. T he edge o f the m arsh is p o p u lated w ith large grasses,
a n d the w ater bugs were typically observed a n d cap tu red
w ithin 1 m o f these grasses in w ater less th a n 1 m deep. T he
shallows are inh ab ited by poten tial prey species such as
m innow s, tadpoles, a n d m acroinvertebrates.

W e sam pled this m arsh fo r B. lutarium betw een June 17
an d July 15, 2012 an d from M arch 19 to July 26, 2013. We
m oved dip nets th ro u g h the vegetation a n d along th e su bstrate

54 Journal o f the Tennessee Academy o f Science vol. 89, no. 2

FIG. 2 a -b . G eneral ap p earan ce o f th e giant w ater bug, Belostoma lutarium (dorsal view) (2a) an d (ventral view) (2b).

to cap tu re adult w ater bugs. Each sam pling p eriod lasted for
approxim ately 90 min. A d u lt bugs were stored in plastic
bottles a n d transferred to a lab o ra to ry a t the University o f
Tennessee a t C h attan o o g a. C annibalism w as never observed
am ong adu lts during transfer. W e recorded the ab u n d an ce o f
adult m ales a n d females an d the n u m b er o f cap tu red males
th a t h ad eggs on their backs during each collecting trip.

In the lab o rato ry , w ater bugs were housed in aerated 10-
20 gal a q u a ria a n d /o r approxim ately 450-m L plastic cups filled
w ith aged ta p w ater. A q u aria were o u tfitted w ith artificial
p lan ts and an air stone. C om plete o r p a rtial w ater changes
were im plem ented approxim ately every two weeks. A fter
com pletion o f the study, bugs were used in o th er behavioral
studies in the laboratory.

U sing dial calipers, we m easured the w idth a n d length o f
the back for a sam ple o f male an d female adults collected in

2013. M easurem ents tak en include the back length from the
m ost a n terio r po in t o f th e scutellum to th e m ost p o sterio r
po in t o f th o rax , and the w idth o f the back at its w idest point.
D escription an d diagram s o f h em ipteran anatom y, including
Belostoma, can be found in M erritt an d C um m ins (1995), an d
the general appearance o f B. lutarium is provided in Figs. 2a
an d b. T o determ ine w hether males an d females were sexually
dim orphic in size, we used a tw o-tailed stu d e n t’s f-test to
determ ine w hether there were significant differences between
m ales an d females in back w idth a n d /o r back length.

W e recorded the sex ratio (males/females) o f a sam ple o f
a d u lt w a te r bugs c a p tu re d each m o n th in b o th years.
Specimens were sexed using a dissecting m icroscope (Fisher
Scientific Stereoscope M odel 1256214). T h e genital plate,
found on the m ost p o sterio r p o rtio n o f the abd o m en , has a few
distinct differences am ong males (Figure 3a) an d females

FIG. 3 a-3 b . G en ital p late o f a male Belostom a lutarium (3a). N o te the lack o f setal tufts. G enital plate o f a fem ale Belostoma
lutarium (3b).

August 2014 Klug and Hicks—Giant Water Bug: Ideal for Studies of Evolution & Ecology 55

TABLE 2. Abundance of male and female B. lutariwn
collected in the M ountain Creek m arsh June 17-July 15, 2012.
The num ber o f males found with eggs on their back(s) is shown
in parentheses.

Date
Total number of males

(number with eggs)
Total number of

females

June 17 8 (2) 2
June 27 1 (1) 3
June 30 1 (0) 9
July 4 2 (1 ) 6
July 10 2 (0 ) 1
July 15 1 (0) 11

Total 15(4) 32

(Figure 3b). The most conspicuous difference is the numerous
setae present on the female genital plate, especially along the
posterior tip of the plate (Fig. 3a and 3b). The setae may
appear in two small patches on either side o f the midline.
Males usually lack setae in this area or may display a few setae.
The tip of the genital plate in males is rounded, whereas
females may have a notched or split tip. To determine whether
sex ratio o f captured individual was significantly biased, we
calculated sex ratio (males/females) for each m onth and
categorized each month as male-biased, female-biased, or
unbiased. We then used a one-sample t-test to determine if sex
ratio was on average biased across months.

To observe m ating and parental care behavior, various
male-female combinations were each placed in a 10-gallon
aquarium and observed for 20 min per day for five days. These
included pairs (N = 5), two male and four female com­
binations (N = 5), and four male and two female combinations
(N = 5). We describe mating and parental care behavior
below.

TABLE 3. Abundance of male and female B. lutarium
collected in the M ountain Creek m arsh M arch 19-July 26,
2013. The number of males found with eggs on their back(s) is
shown in parentheses.

Total number of males Total number of
Date (number with eggs) females

March 19 0 0
April 12 1 (0) 1
April 30 5(?) 7
May 2 0 0
May 7 2(1) 0
May 20 3(3 ) 0
May 24 0 0
May 31 1 (1) 1
June 8 4 (1 ) 6
June 28 1(0) 4
July 13 3(2) 5
July 26 KD 1

Total 21(9) 25

TABLE 4. Adult sex ratio (males/females) of collected B.
lutarium during June and July o f 2012 and A pril-July 2013.

Year Month
Sex ratio

(males/females) Bias

2012 June 0.71 Female
July 0.28 Female

2013 April 0.75 Female
May 6 Male
June 0.5 Female
July 0.67 Female

Results

Abundance and sex ratio o f adult B. lutarium in 2012
and 2013—We first identified the M ountain Creek population
of B. lutarium on June 17, 2012. Adults and nymphs were
captured regularly until July 15, 2012 (Table 2), after which no
B. lutarium individuals were found in 2012. In 2013, adults of
B. lutarium were first observed on April 12, 2013 (Table 3) and
captured regularly until July 26, 2013, after which no adults
were observed. Nymphs were first observed in early May 2013.
Thus, the breeding season of this B. lutarium population
appears to span April through July. During four out o f the six
m onths that B. lutarium individuals were found in the marsh,
the sex-ratio was female biased (Table 4). Indeed, across
months, the sex ratio was significantly female-biased (two-
tailed student’s t-test, t = 7.0, d f = 5, P = 0.001).

Morphological measurements—Males captured in 2013
had back widths o f 11.32 ± 0.34 mm (mean ± SD) and back
lengths o f 16.21 ± 0.73 mm (mean ± SD). Females had back
widths of 11.44 ± 0.51 mm (mean ± SD) and back lengths of
16.35 ± 0.82 mm (mean ± SD). There was no significant
difference between male and female back widths (FJ22 — 0.49,
P = 0.49) or between male and female back lengths ( F , 32 =
0.29, P = 0.59), suggesting no sexual dimorphism in back size
in this population.

Mating behavior—Adult B. lutarium readily bred in the
laboratory in all male-female combinations described above.
Prior to mating, males were often seen display-pumping at the
surface, and we hypothesize that this pumping behavior might
be used to attract female mates or function as a form of
communication between individuals. Pumping involves a
longitudinal up-and-down body movement, like a push-up
(see also Smith, 1997). After courtship, multiple bouts o f
ovipositing occurred over a span o f several hours (e.g., in
Fig. 4 a female is depositing eggs on the back of a male shortly
after copulating; for a description o f breeding behavior in a
closely related species, see Smith, 1979). When breeding was
successful and eggs were deposited on the back of a male in the
laboratory, the number of eggs deposited ranged from 44 to
87. Egg-encumbered males in nature were never found with
fewer than 83 eggs. If females were kept in isolation without
males, a small number o f females deposited eggs on the
artificial vegetation in the aquarium.

Parental care behavior— After egg deposition, several
parental care behaviors were observed. First, males with eggs
positioned themselves at the surface. While at the surface, the
eggs are partially exposed to the air (Fig. 5). This likely allows

56 Journal o f the Tennessee Academy o f Science vol. 89, no. 2

FIG. 4. A pair of Belostoma lutarium mating. The female is
seen ovipositing on the male’s back.

sufficient oxygen exchange while also keeping the eggs moist
(Smith, 1997). Second, brood pumping was commonly
observed. Brood pumping is similar to the display pumping
described above except that it occurs frequently under the
surface and at a slower rate than display pumping (Smith,
1997). Third, males were also observed engaging in a behavior
which involved stroking their eggs using their hind legs. In B.
flumineum, this behavior may aid nymphs in freeing themselves
from their eggs (Smith, 1979). We hypothesize that egg
stroking in B. lutarium might also function to clean the eggs
of debris or other material and/or provide stimulation that
could improve development. No egg predators were present in
our laboratory set-up, but in the wild, males also likely protect
their eggs from predators. Fish, which are a likely egg predator
(Smith and Horton, 1998), were commonly observed near
water bugs in the marsh.

Egg abandonment was also frequently observed. Egg pads
were commonly scraped off by parental males; this typically
occurred within the first day or two of care. Additionally, two
cases of filial cannibalism (i.e., the consumption of one’s own
offspring) were observed. After removing small egg pads from
their backs, two males were seen cannibalizing their eggs.
Similar behaviors were also observed in a study of B.
flumineum (Smith, 1976). Hatching occurred roughly 17 days
after deposition.

Discussion

Here, we have provided basic behavioral and population-
level information for a newly-described population of Belo­
stoma lutarium in southeastern Tennessee. Specifically, we
found that the breeding season of the Mountain Creek
population of B. lutarium extends from April through July,
the sex ratio is typically female-biased across months in the
wild, and males and females were not sexually dimorphic with
respect to back size. In a laboratory setting, B. lutarium mated
in pairings that included one male and one female, two males
and four females, and four females and two males, suggesting
that individuals breed readily in aquaria. Behaviorally, prior to
mating males exhibited display pumping, and after mating,
their parental care behavior included brood pumping, remain­
ing at the surface such that eggs were exposed to the air, and

FIG. 5. Male Belostoma lutarium with eggs at water
surface.

egg stroking behavior. Egg abandonment and filial cannibal­
ism by males were also observed.

Belostoma lutarium is ideal for studies of ecology,
evolution, and behavior (outlined in Table 1). Adults are
easily maintained and observed in a laboratory setting, which
will allow for future experimental studies. Additionally, they
exhibit exclusive paternal care, which is relatively uncommon
(Clutton-Brock, 1991; Royle et al., 2012; Kokko and Jennions,
2008) and remains an evolutionary conundrum (reviewed in
Kokko and Jennions, 2008, 2012). Recent reviews have
highlighted the need for more studies that focus on under­
standing the evolution of paternal care (e.g. Kokko and
Jennions, 2008; Alonzo, 2010; Klug et ah, 2012). Belostoma
lutarium is well-suited for determining what selective factors
play a role in maintaining paternal care (outlined in Table 1).
Smith (1997) hypothesized that selection for larger body size,
and hence, larger eggs, is the driving force maintaining
paternal care within giant water bugs in general. Specifically,
he argues that larger eggs require brooding because brooding
provides sufficient 0 2 which allows larger eggs to survive and
develop (Smith, 1997). In the future, it would be interesting to
explicitly examine the costs and benefits of brooding behavior
in relation to oxygen availability and size at hatching in B.
lutarium (Table 1). Such a study would provide insight into
whether brooding and oxygen availability influence body size,
and whether larger body size is a likely driver of paternal care.

Sexual selection might also play a role in maintaining
paternal care. The operational sex ratio (i.e., ratio of males and
females that are prepared to mate at a given point in time,
OSR; Emlen and Oring, 1977) likely shifts throughout the
breeding season in giant water bugs. In a study on the related
species B. flumineum in Illinois, Kruse (1990) found that male
back space is limited only during early spring when animal
density is low and the sex ratio is female biased. During this
time period, one would expect females to compete for males,
and as a result sexual selection will potentially favor female
traits that improve their access to male mates. Similarly, in the
giant water bug, Abedus indentatus, in California, male back
space was found to limit female mating at certain points during
the breeding season (Kraus, 1989). In our study, the adult sex
ratio of B. lutarium was female biased, which might lead to
male mate choice and female competition for mates in this
population. In B. lutarium, it will be key for future studies to
examine whether males or females are mate limited and
identify potential traits (e.g., body size in males or females,

August 2014 Klug and Hicks—Giant Water Bug: Ideal for Studies of Evolution & Ecology 57

parental care in males) that are under sexual selection
(Table 1). Additionally, examining any shift in the operational
sex ratio throughout the breeding season is an ideal avenue of
future research. Such work could provide insight into plasticity
in sex roles and examine the link between paternal care, sexual
selection, and OSR.

The distinct life-history stages of giant water bugs could
be used to answer timely questions related to life-history
evolution. For example, classic life-history theory predicts
that an increase in predation risk should select for nymphs
that have increased size at hatching. Whether there are
differences in the size of offspring from a single pad or across
egg pads, and whether such size differences influence
predation risk is an interesting focus for future studies. If
larger nymphs have a higher chance of survival, this could
play a part in maintaining paternal care (see also Smith,
1997). In addition, recent studies have suggested that stage-
specific maturation and mortality rates will influence the
evolution of parental care (Klug and Bonsall, 2010; Klug
et al., 2013 a, b). The fact that B. lutarium has distinct life-
history stages makes this species well-suited for examining the
link between life-history characteristics (e.g., maturation rate
and egg, juvenile and adult mortality) and parental care.
Characterizing stage-specific mortality and maturation rates
would provide insight into the characteristics that are likely to
be associated with paternal care (Table 1).

Belostoma lutarium is also ideal for studies of offspring
abandonment. As mentioned above, egg pad removal by the
encumbered males was common. Anecdotally, it appeared that
the smaller egg pads were more commonly discarded than
larger pads. This possibly allows the male to breed again and
obtain a larger egg pad, potentially increasing his fitness.
Consistent with this idea, Kight and Kruse (1992) found that
B. flumineum males are more likely to discard smaller egg pads
prior to hatching. However, they also determined that the
likelihood of discarding eggs decreases as eggs age. In the
future, it would be interesting to examine the relationship
between egg pad size and discarding behavior in B. lutarium. In
particular, if males discard pads in order to increase their
chances of receiving a larger egg pad in the future, one might
expect OSR to influence discarding. For example, males may
be less likely to discard small egg pads during times when
females are scarcer.

In summary, B. lutarium is an ideal system for ecological,
evolutionary, and behavioral studies. There is limited research
on B. lutarium and other giant water bugs. Paternal care is a
key life-history trait and a major focus in studies of behavior of
behavior and evolution. The fact that B. lutarium provides
parental care, likely experiences sexual selection, and is easily
housed and studied in the lab makes this species ideal for a
range of future studies.

Acknowledgments

We are grateful for the assistance provided by S.
Chatzimanolis (University of Tennessee at Chattanooga) in
identifying and sexing B. lutarium. We are also appreciative of
E. Reyes (University of Tennessee at Chattanooga) and P.
Thrasher (University of Tennessee at Chattanooga) for their
assistance in the laboratory and T. Gaudin (University of
Tennessee at Chattanooga) for his help photographing the

water bugs. We also appreciate the detailed comments from
the referees which greatly improved this manuscript.

Literature Cited

Ahnesjo, I., C. Kvamemo, and S. Merilaita. 2001. Using
potential reproductive rates to predict mating competition
among individuals prepared to mate. Behavioral Ecology,
12:397—401.

Alonzo, S. H. 2010. Social and coevolutionary feedbacks
between mating and parental investment. Trends in
Ecology and Evolution, 25:99-108.

Alonzo, S. H. 2012. Sexual selection favours male parental
care, when females can choose. Proceedings o f the Royal
Society o f London Series B-Biological Sciences, 279:
1784-90.

Alonso-Alvarez, C., and A. Velando. 2012. Benefits and costs
of parental care. Pp. 40-61 in The Evolution o f Parental
Care (N. J. Royle, P. T. Smiseth, and M. Kolliker, eds.).
Oxford University Press, Oxford, United Kingdom.

Andersson, M. 1994. Sexual Selection. Princeton University
Press, Princeton, New Jersey.

Clutton-Brock, T. H. 1991. The Evolution o f Parental Care.
Princeton University Press, Princeton, New Jersey.

Clutton-Brock, T. H. 2007. Sexual selection in males and
females. Science, 318:1882-1885.

Emlen, S. T., and L. W. Oring. 1977. Ecology, sexual selection,
and the evolution of mating systems. Science, 197:
215-223.

Jennions, M. D., and H. Kokko. 2010. Sexual selection.
Pp. 343-364 in Evolutionary Behavioral Ecology (D. F.
Westneat, and C. W. Fox, eds.). Oxford University Press,
New York, New York.

Kight, S. L., and K. C. Kruse. 1992. Factors affecting the
allocation of paternal care in waterbugs (Belostoma
flumineum Say). Behavioral Ecology and Sociobiology,
30:409-A14.

Klug, H., and M. B. Bonsall. 2010. Life history and the
evolution of parental care. Evolution, 64:823-835.

Klug, H., M. B. Bonsall, and S. H. Alonzo. 2013 a. The origin
of parental care in relation to male and female life-history.
Ecology and Evolution, 3:779-791.

Klug, H., M. B. Bonsall, and S. H. Alonzo. 2013 b. Sex
differences in life history drive transitions between
maternal, paternal and bi-parental care. Ecology and
Evolution, 3:792-806.

Klug, H., and M. B. Bonsall. 2014. The benefits of par­
ental care in relation to increased offspring survival
and parental effects on developmental rate. Ecology
and Evolution. Published online early: DOI: 10.1002/
ece3.1083

Klug, H., S. H. Alonzo, and M. B. Bonsall. 2012. Theoretical
foundations of parental care. Pp. 21-39 in The Evolution o f
Parental Care (N. J. Royle, P. T. Smiseth, and M. Kolliker,
eds.). Oxford University Press, Oxford, United Kingdom.

Kokko, H., and M. D. Jennions. 2008. Parental investment,
sexual selection and sex ratios. Journal of Evolutionary
Biology, 21:919-948.

Kokko, H., and M. D. Jennions. 2012. Sex differences in
parental care. Pp. 101-116 in The Evolution o f Parental
Care (N. J. Royle, P. T. Smiseth, and M. Kolliker, eds.).
Oxford University Press, Oxford, United Kingdom.

58 Journal o f the Tennessee Academy o f Science vol. 89, no. 2

Kokko, H., H. Klug, and M. D. Jennions. 2012. Unifying
cornerstones of sexual selection: operational sex ratio,
Bateman gradient, and the scope for competitive invest­
ment. Ecology Letters, 15:1340-1351.

Kraus, W. F. 1989. Is male back space limiting? An
investigation into the reproductive demography of the
giant water bug, Abedus indentatus (Heteroptera: Belosto-
matidae). Journal o f Insect Behavior, 2:623-648.

Kruse, K. C. 1990. Male backspace availability in the giant
waterbug (Belostoma flumineum Say). Behavioral Ecology
and Sociobiology, 26:281-289.

Lauck, D. R. 1964. A monograph of the genus Belostoma
(Hemiptera) Part III. Bulletin o f the Chicago Academy o f
Sciences, 11 (5): 102-154.

McPherson, J. E., and R. J. Packauskas. 1986. Life history and
laboratory rearing of Belostoma lutarium (Heteroptera:
Belostomatidae) with descriptions of immature stages.
Journal o f the New York Entomological Society, 94:
154-162.

Merritt, R. W., and K. W. Cummins. 1995. An Introduction to
the Aquatic Insects o f North America, 3rd Edition. Kendall/
Hunt, Dubuque, Iowa.

Royle, N. J., P. T. Smiseth, and M. Kolliker. 2012. The
Evolution o f Parental Care. Oxford University Press,
Oxford, United Kingdom.

Shuster, S. M., and M. J. Wade. 2003. Mating Systems and Stra­
tegies. Princeton University Press, Princeton, New Jersey.

Smith, R. L. 1976. Brooding behavior of a male water bug
Belostoma flumineum (Hemiptera: Belostomatidae). Jour­
nal o f the Kansas Entomological Society, 49:333-343.

Smith, R. L. 1979. Paternity assurance and altered roles in
the mating behavior of a giant water bug Abedus
herberti (Heteroptera: Belostomidae). Animal Behaviour,
27:716-725.

Smith, R. L. 1997. Evolution of paternal care in the giant
water bugs (Heteroptera: Belostomatidae). Pp. 116-149 in
Social Behavior in Insects and Arachnids (J. C. Choe, and
B. J. Crespi, eds.). Cambridge University Press, London,
United Kingdom.

Smith, R. L., and C. Horton. 1998. Fish predation on giant
water bug (Heteroptera: Belostomatidae) eggs in an
Arizona stream. Great Basin Naturalist, 58:292-293.

Stearns, S. 1992. The Evolution o f Life Histories. Oxford
University Press, Oxford, United Kingdom.

Swart, C., and R. Taylor. 2004. Behavioral interactions between
the Giant Water Bug (Belostoma lutarium) and tadpoles of
Bufo woodhousii. Southeastern Naturalist, 3:13-24.

Manuscript received 9 October, 2013; Manuscript accepted 1 August,
2014.

Copyright of Journal of the Tennessee Academy of Science is the property of Tennessee
Academy of Sciences and its content may not be copied or emailed to multiple sites or posted
to a listserv without the copyright holder’s express written permission. However, users may
print, download, or email articles for individual use.