Table Of Content2007. The Journal of Arachnology 35:84-88
MATING FREQUENCIES OF MALE CRAB SPIDERS,
MISUMENA VATIA (ARANEAE, THOMISIDAE)
Douglass H. Morse: Department of Ecology & Evolutionary Biology, Box G-W,
Brown University, Providence, Rhode Island 02912 USA.
E-mail: [email protected]
ABSTRACT. The number of matings obtained by a male is likely to be a major component of his
lifetime fitness. Males that depend on finding mates before their competitors must allocate resources to
this effort, potentially at the expense oftheir reproductive rate. Male crab spiders Misumena vatia (Clerck
1757) often occurat low densities andexperience considerable difficulty infindingfemales. Thisconstraint
might select for their cursorial body form and high movement rates at the expense of their reproductive
rate. Male M. vatia will not mate more than once in rapid succession and typically no more than once
every other day, although they are capable of several matings over their lifetime. Males may rarely
encounter virgin females more often than once every other day and thus would experience little loss of
fitness from an inability to mate in rapid order.
Keywords: Male fitness, reproductive constraint, scramble competition
The key determinant of male lifetime fit- mate females in rapid succession, would pro-
ness often is the number of matings a male vide important benefits at a likely infrequent
obtains (Williams 1992). Under many circum- cost.
stances the difference in number of matings Adult male spiders are often assumed to be
among males is high, reaching its maximum less common than theirfemales (Foelix 1996),
in harem formers, and variance in male fitness primarily because of an assumed dispropor-
is generally taken to be higher than that of tionately high mortality incurred from search-
&
females, a consequence of differences be- ing for females (Vollrath Parker 1992;
tween the sexes in investment per offspring. Shuster & Wade 2003). However, females of
In high-density situations, males may achieve many species do not mature simultaneously,
such variance via a dominance hierarchy, with the result that overt competition may
which often is size-related (LeBouef 1974; nevertheless occur for access to females as
Clutton-Brock et al. 1982). Low-density situ- they molt into their adult stage, with conse-
ations in which male-male contact is the ex- quent guarding of penultimate females in
ception provide a situation in which different many instances. In spite of potential compe-
factors dictate success; here, the first male to tition, populations with a low number of
find a female may instead be the one to suc- males relative to females present the oppor-
ceed via scramble competition, accompanied tunity for males, on average, to mate several
by first-male sperm priority (Ghiselin 1974; times.
LeGrand & Morse 2000). My crab spider Misumena vatia (Clerck
A male should normally maximize the sit- 1757) populations exhibit a female-biased pri-
uations in which he can capitalize upon a re- mary sex ratio (1.5 females to 1 male), and
productive opportunity. However, factors oth- this ratio shifts to 2.5-5.1 females to 1 male
er than the ability to mate successively may by the adult stage (LeGrand & Morse 2000).
assume importance. For instance, males that Further, adults are not abundant (Holdsworth
must expend considerable energy and time in & Morse 2000) and the males experience con-
finding females may be unable to mate re- siderable difficulty in finding females, which
peatedly, but seldom find themselves in a sit- apparently do not emit pheromonal cues (An-
uation where that ability would provide an ad- derson & Morse 2001; Leonard & Morse
vantage. If so, extra allocation to effective 2006), as opposed to other spider species ex-
&
movement, even at the expense of failing to amined in this regard (Tietjen 1977; Elgar
84
MORSE—CRAB SPIDER MATING 85
Schneider 2004). Given this combination of (Holdsworth & Morse 2000). Five minutes af-
traits, male M. vatia should experience strong ter positioning the female, I released the male
selection to reproduce multiple times, but the onto the flower stem immediately below the
ability to mate in rapid succession would not flower. Since males almost inevitably move
be under equally strong selection. The number upward in this circumstance (Hu & Morse
of matings by individual males in my popu- 2004), they are well positioned to find the fe-
lations is open to question; nevertheless, adult male. I observed the male for 30 min after he
males on average must mate several times in climbed into the flower, or until he mated with
their lifetime, a consequence of the sex ratios the female. Previous experiments have dem-
of adults noted above (LeGrand & Morse onstrated that males not mating within 30 min
2000), the extremely high proportion of adult are unlikely to do so subsequently (Hu &
females that produce fertile egg masses Morse 2004). I ran 28 male-female pairs in
(Morse 1994), and the lack of any evidence this way. Matings usually took 3-10 min, and
to suggest that M. vatia ever reproduces par- the males then quickly dismounted the fe-
thenogenetically (D. H. Morse, unpublished males and retreated a minimum of several
data). The purpose ofthis study is to establish body lengths from them (Hu & Morse 2004).
whether male M. vatia will mate in rapid suc- Following these initial runs I presented 14
cession and if not, with what frequency they of the successful males with a second virgin
do successfully mate. The results will provide female to determine if they would mate twice
insight into the evolution ofthis breeding sys- in succession. As before I placed the female
tem. on a fresh daisy and released the male on the
METHODS stem of this flower five min later. All second
presentations were made within 10 min ofthe
Spiders were collected from flowers in termination of the initial mating.
fields and along roadsides in South Bristol, Any females that these males refused to
Lincoln County, Maine, USA (43.96°N, mate in the first run were then paired with
69.56°W) during June 1998-2006 and subse- other males that had not mated within the past
quently maintained in 7-dram vials (—26 ml; two days. Any of these males that did not
5 cm long X 3 cm diameter) until testing. mate with the female presented them in the
They were fed small moths and flies every first run were tested in the same way with a
other day. All females were collected as pen- second virgin female, and if they mated with
ultimates and used as adults within a week the second female, they were then paired with
after their final molt. Males were collected ei- a third virgin female. Thus all males were giv-
ther as penultimates or adults. Adult males en the opportunity to mate twice in succes-
were not mated for the first two days after sion, and all females that did not mate in their
collection. In all but one experiment individ- first run were given the opportunity to mate
uals were tested within the first week after with a second male.
capture, or the first week after final molt in I also further investigated how frequently
the case of the penultimates, to insure that and how many times males would mate over
their behavior matched that of individuals in their adult lifetime. To test frequency, I ran 10
the field (Leonard & Morse 2006). In the sin- males in the same way as noted above and
gle exception I repeatedly paired nine males then repeated the procedure on the following
over periods as long as two months to estab- day. I also mated nine other males with virgin
lish how many times they would mate. Mat- females at two-day intervals five to 20 times.
ings of M. vatia are described in detail in Voucher specimens of Misumena vatia have
Morse (2007). been deposited in the American Museum of
To test the ability of an adult male to mate Natural History, New York.
more than once in succession, I first presented
RESULTS
him with arecently molted virgin adultfemale
perched on an ox-eye daisy Chrysanthemum Twenty-three of 28 males (82.1%) mated
leucanthemum flower, a frequent hunting site with the first virgin female presented them
at the time that females molt into the adult within the 30 min period. All the males that
stage. Female M. vatia readily mate as soon mated inserted both pedipalps one or more
as they have completed their final molt times. Of the remaining males, one individual
86 THE JOURNAL OF ARACHNOLOGY
had still not contacted the female after 30 min, of males to mate with them resulted from the
and the remaining four contacted the female males’ inability to mate twice in rapid suc-
but did not mate. cession. The females eschewed by the males
When 14 of the males that mated with the in this first test were for some unknown rea-
hrst female were presented with a second vir- son unacceptable to all males tested, but the
gin female, none of these males would mate third set of females were likely eschewed by
with the second females. The difference in the latter males only because oftheir apparent
their performance in the first and second runs inability to mate twice in rapid succession.
is highly significant (one-tailed sign test, P < Thus, the four males that eschewed the first
0.001). The 14 females used for these second female but mated with the second one should
matings were then tested with a new set of probably be treated as performers rather than
adult males. These males mated with all 14 of nonperformers in this analysis; that is, they
the females. The performance of the two mated when presented with the first accept-
groups of males with this set of females was able female. If so, this correction would
highly significantly different {P < 0.001, change the proportion of male performers to
same test). 96.4% (27 of 28).
Four of the five males that did not mate Mate-choice theory suggests that males
with the first virgin female presented to them should be choosy if presented with an excess
proceeded to mate with another virgin female of females (see Andersson 1994). Since the
presented to them immediately after the first average male M. vatia in these populations re-
one, but all five of them refused to mate with produces several times in his lifetime (Le-
a third virgin female that was presented im- Grand & Morse 2000), one might predict a
mediately after their second run. The five ini- tendency for choosiness, especially since they
tially rejected females were eschewed by a do not mate in rapid succession. However, the
subsequent set of males as well, but these last tendency for males to mate with any available
males mated with another set of virgin fe-
virgin female after a sufficient hiatus bolsters
males presented to them.
the argument that they do not frequently meet
All 10 males tested on successive days
adult virgin females.
failed to mate with virgin females on the fol-
oltohweirngsetdayo.f mWahleens {Insu=bs9e)queevnetrlyy ottehsetreddaany-, woTulhde bfeailcuoruentteorprmoadtuectiivneriafpitdhesmuaclceesssieon-n
countered more than one virgin female within
they mated in 82.5% of the pairings with vir-
a brief period of time. The low population
gin females (5-20 matings per male, 80 in- density of these spiders (LeGrand & Morse
dividual runs, 73.7-90.9% acceptance rate),
significantly different from the results on suc- 2000), combined with the failure of the fe-
crfe/e-sftsueissvetedfotdoraymisantd(eePpoe<nndse0un.ct0c0e1ssasmiipnvleeasd)Ma.yasnSnib-nuctWehuismutaanlleelysy Ltmheaeloienrsarctdoon&dmiotMliotornssie(mAu2nl0dt0ae6nr)es,ooumnsalky&esorMitotrofsuraetdhvee2rr0t0ui1ns;-e
mated every other day, I conclude that they likely that the failure to mate in rapid se-
require a two-day interval between matings. quence constitutes a significant constraint for
the males. The average female in this popu-
DISCUSSION lation was not mated until approximately 1.5
Clearly these male M. vatia will not mate days after molting into the adult stage (Le-
twice in rapid succession, or on successive Grand & Morse 2000), although females will
days (but see below), although they will rou- readily mate immediately after their last molt
tinely mate every other day. I did not attempt (Holdsworth & Morse 2000). Males capable
to test them at various intervals between one of mating on an every-other-day basis should
and two days, but since they are usually di- thus easily account for insemination of all of
urnal (Morse 1981), even if they could mate the females in the population (Morse 1994).
at, say, 1.5-day intervals, they would be un- However, at this point I do not know whether
likely to do so in the field. mating slows a male’s subsequent searching
The second females presented to the males rate, nor whether such a slowdown would sig-
were apparently in no way deficient as mates, nificantly affect the frequency with which it
so I conclude that the failure of the first set finds a new female. I also do not know wheth-
MORSE—CRAB SPIDER MATING 87
er a male needs to recharge his palps before virgin females used for other studies with
mating a second time. males that have not mated the previous day,
In spite of the attention paid to the repro- because I have so seldom obtained matings
ductive behavior of spiders, relatively little is with males that mated the previous day (D. H.
known about either the frequency with which Morse unpubl. data). The males that I ran the
males recharge their pedipalps or the mating largest number of times usually mated on al-
rates of species that can mate several times. ternate days as long as we could find virgin
The effect of sperm depletion for multiply females for them. Several of these matings
mating males is rarely explicitly considered in produced viable clutches, though in other cir-
the literature (Jones et aL 2006). Quantitative cumstances I was unable to rear the females
data on rates of pedipalp recharging and mat- to their egg-laying stage before the season
ing frequencies of spiders appear to be non- ended (D. H. Morse unpubl. data).
existent. Neither subject is discussed in stan- It must be reiterated that these males were
dard treatises on spider biology such as confined, so that their responses may differ
Savory (1928), Bristowe (1958), Gertsch somewhat from individuals in the field. How-
(1979) and Foelix (1996), though Gertsch ever, I attempted to minimize this effect by
(1979) notes without attribution that some testing individuals soon after collecting them.
species can mate multiple times without re- With the exception of the males run multiple
charging their pedipalps, while others have to times, all males were run within a week of
recharge during mating. Most recent attention their capture, a period during which confined
to mating rates ofmale spiders focuses on ex- individuals perform several other acts [forag-
treme adaptations in which a male is physio- ing (Morse 2000, 2005), line running (Leon-
logically or anatomically incapable of mating ard & Morse 2006), orientation and activity
more than once or twice in its lifetime (e.g., (Sullivan & Morse 2004)] similarly to unre-
&
Tidarren argo, Theridiidae: Knoflach van strained individuals in the field.
Harten 2001; Lacrodectus hasselti, Theridi- These males thus form an extreme opposite
idae: Andrade and Kasumovic 2005; Argiope pole to harem formers (Andersson 1994), al-
keyseriingi, Araneidae: Herberstein et al. though many of them also mate several times
2005). under natural circumstances. Harem formers
Although it is possible that males failed to exhibit some ofthe most extreme examples of
mate in rapid succession because they did not sexual dimorphism favoring large males, but
have time to recharge their pedipalps with these crab spiders are among the mostextreme
sperm during the experimental period, several examples of sexual dimorphism favoring
lines of evidence suggest that this factor does small males; although both exhibit a female-
not explain the failure of these males to mate biased sex ratio at reproduction (Morse 2007).
with a second female in the experiments. First, ACKNOWLEDGMENTS
males almost inevitably refuse to mate again
on the day following a mating (no observa- I thank J. K. Waage for discussion and
tions in this study and only rare instances in K. J. Eckelbarger, T C. Miller and other staff
other observations: D. H. Morse pers. obs.). members of the Darling Marine Center of the
Second, I observed no efforts by the spiders University of Maine for facilitating work on
to recharge their pedipalps shortly following the premises. This work was partially sup-
a mating in this study. Finally, the males in- ported by the National Science Foundation
serted their pedipalps into the females' genital (IBN-98-16692).
apertures a variable number of times during a
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