Numbers of Broods Produced by the Crab Spider Misumena vatia (Araneae, Thomisidae)

5 Pages·1994·5.4 MB·English

by  Douglass H Morse

1994. TheJournal ofArachnology 22:195-199
NUMBERS OF BROODS PRODUCED BY THE CRAB SPIDER
MISUMENA VATIA (ARANEAE, THOMISIDAE)
Douglass H. Morse; Department ofEcology and Evolutionary Biology, Box G-W,
Brown University, Providence, Rhode Island 02912 USA
ABSTRACT. Incoastal Mainethecrab spiderMisumena vatiaproducesasinglebroodofeggs, butincipient
signsofdouble-broodednessoccasionallyappear: 1)huntingafterguardingnestoffirstbrood;2)apparentlaying
ofsecond brood by artificially provisioned individuals during an unusually warm summer; 3) and occasional
production ofsecond nests without eggs, accompanied by guarding. To determine whether these spiders are
capable ofproducing a successful second brood, I provisioned adult females to enhance early laying ofa first
brood, removedthem fromtheirbroodafter 10 days, matedhalfofthema secondtime, andthenprovisioned
themallagain. Nearlytwo-thirdslaidasecondbrood, whose successdidnotdifferfromthatofunmanipulated
Misumena firstbroods in the study area. Numbers ofremated and non-remated females producingyoungdid
notdiffer, indicatingthatrematingisnotnecessaryforasuccessfulsecondbrood. However, fivebroodsofnon-
remated spiders had low hatching success, suggesting that sperm were sometimes limiting. Semelparity in this
population is thus apparentlynormally maintained indirectlybythe length ofthe season.
Most temperate-zone spiders are reproduc- notclearinMisumena,noristhedegreetowhich
tively active for a single year, probably a con- its semelparity is genetically programmed.
sequence ofthe adults’ inability to survive the Over this study (1977-present) I have ob-
winter (Gertsch 1979). The reproductive effort tainedsomesuggestionsthatthesemelparityob-
itselfmay be divided into one or more broods, served is environmentally determined. 1) Some
the number varying with the species and, at an individuals resume hunting after leaving their
intraspecific level, often with hunting success broods and gain considerable biomass, which
(Turnbull 1962; Kessler 1971; Schaefer 1976). would be necessary to produce a second brood.
Somespeciesguardtheirbroods(e.g.,Fink 1986), 2) In 1991, an unusually warm summer, two
thereby facilitating success, but lowering their individuals I had provisioned in the laboratory
opportunity for producing extra broods. Single- priortoegg-laying(firstbrood)inthefieldalmost
broodedness (semelparity) would be most likely certainly produced second broods: nestbuilding
expected among such species. In this context I (Morse 1985) was followed by a striking loss of
define semelparity as the production ofa single biomass like thataccompanyingegg-laying. The
brood (one egg mass), as opposed to producing artificial provisioningpermittedthese spiders to
two or more broods at different times during a complete their first brood earlier than they oth-
season (Fritz et al. 1982). erwise would have, facilitatingthe possibility of
The crab spider Misumena vatia is generally laying second broods generated from naturally-
considered to be semelparous (Gertsch 1939), gainedbiomass. However, Iwasunabletoverify
andIhavenotobservedittoproducemorethan thattheseputativebroodsproducedyoung. One
one successful, natural brood at a northerly site waspreyedon, andtheleafonwhich the second
alongtheMainecoast(Morse 1979, 1988). Since nest was located fell offthe plant and could not
members ofthis population have a short repro- befound. 3)I havealso occasionallyfoundnests
ductiveseason,andtheireggmassesaverage65% without eggs (“pseudonests”) built by individu-
ofthematernalprelayingbiomass(Fritz&Morse als that had already fledged a brood (12 out of
1985), the questionarises aboutwhatfactors re- 1434egg-layersobservedovernineyears=0.8%).
strain these spiders from laying a second brood. This behavior demonstrates that previous egg-
Either the season might be too short for more layersretainthebehavioraltraitsassociatedwith
than one brood (Fink 1986), orthe brood might nestbuilding, although it need not be associated
be too large to permit recovery fora second one with laying eggs.
(see Roff 1992; Steams 1992). The cause-and- Thus, the question of facultative iteroparity
effect relationship between these two factors is remained:eventhoughitishighlylikelythattwo
195
1
196 THEJOURNALOFARACHNOLOGY
spiders laid a second set ofeggs, I do not know tercollection,one-halfofthesespidersweremat-
whether the eggs were fertile. Although female ed with males thathad been retained in the lab-
spiders may retain sperm for considerable peri- oratory for unrelated breeding experiments. All
ods in viable form (Foelix 1982), it remains to the females were then provisioned further until
bedeterminedwhetherthisholdsforMisumena, they again began to refuse prey. They were then
orwhethertheyretainadequate spermfora sec- weighed and placed, as before, in screen cages,
ond mating. These concerns may be important, in the fieldto lay theireggs iftheywere inclined
because numbers ofadult males decline rapidly to do so. Those that laid a second brood were
between the first mating of females and when again weighed and then returned to their nests.
theycompletecaringfortheirbrood(Morse, un- At the end ofthe season all nests were collected
published data). for analysis. Offspring emerge from their nests
An opportunity to test several aspects ofthis in the second instar, leaving behind their first-
problem arose inthe process ofan unrelatedex- instarcast skins, which provide an accurate rec-
periment that required removal ofbroods from ord ofsuccess (Morse 1988).
provisioned guarding female Misumena. I fed Weighingspidersimmediatelybeforeandafter
theseindividualsbothbeforeandaftertheirfirst theylaypermitscalculationofthe size oftheegg
broods, sotheresultswillnotdeterminewhether mass, and in turn, the reproductive effort (bio-
Misumena can successfully produce more than massofeggs/biomassoffemaleimmediatelybe-
onebroodinthestudyarea, buttheycananswer fore laying). Loss of biomass to production of
%
several questions about whether iteroparity is silkandotherfactorsatlayingis 1 orless(Fritz
possible or likely. & Morse 1985), and thus is not further treated
in these analyses.
METHODS
RESULTS
Forty adult female Misumena were captured
frommilkweed{Asdepiassyriaca)flowersduring The experiment demonstrated unequivocally
early July of 1993 and provisioned in the labo- thatthespiderscanproduceaviablesecondbrood
ratory with large flies (Syrphidae, Sarcophagi- (Table 1), as 23 of the 36 individuals (63.9%)
dae), moths (Noctuidae, Geometridae), and reared at least a few young in a second brood.
bumblebees (Apidae). These individuals had al- Success ofthose that laid eggs (23 of26: 88.5%)
mostcertainlynotlaidbefore. Individualsinthe didnotdifferfromthatofunmanipulatedspiders
study area only rarely produce broods before 1 thatlaideggs a firsttime in the same field(27 of
July (5 of 1615 broods from 1982-93: Morse, 33: 81.8%) (G - 0.51, F > 0.8 in a G-test). It
unpublisheddata), andthoseoccasionalindivid- must be emphasized, however, that the second-
uals, easilyidentifiedbytheirextremelyshrunk- nesters had in each instance already produced a
en abdomens, still guard theirnests atthis time. successful first brood.
I also have no record ofindividuals that lay in Remated individuals did not differfrom non-
one year surviving until the next (Morse, un- rematedonesinnumbersofnestsproducingsome
published).Aftertheycommencedtorefuseprey, young (G = 1.09, P > 0.2, G-test: Table 1), in-
the spiders were weighed and placed in screen dicating that many ofthem retain viable sperm
cages (1.5 m X 1.5 m x 1.5 m, covered with from earlier matings. A partial exception is that
standard metal window screening, open at the fivebroodsofnon-rematedfemaleshadlowsuc-
bottom) in the field that covered a single milk- cess (7.8-37.4%, X = 21.0% ofthe eggs hatched)
weed stem. Gravid females routinelyplace their (see Table 1), but none of those in which re-
egg-sacs in nests fashioned from the enclosed matingtookplaceshowedthispattern(F=0.03
vegetation when placed in these cages (Morse inaone-tailedBinomialTest). [Forcomparison,
1985, 1990). All ofthe spiders laid on the milk- the four individuals with high but not complete
weed after one to seven days. Screens were then successaveraged 88.4%(79.8-96.9%)(Table 1)].
removed, and parents were again weighed and However, three remated individuals produced
then allowed to guard their broods until the completely unsuccessful broods, for unknown
broods were collected 10 days later. reasons, although they all had apparently suc-
At this time parents were again removed to cessful first broods (normal embryonic devel-
the laboratory. As a result of losses from pre- opmenttookplace). Additionally,afewindivid-
dationandhandling, 36adultswereavailablefor ualsfrombothgroupsdidnotlaysecondbroods,
the experiment on semelparity. Within a dayaf- and a few from both groups died during provi-
MORSE-CRAB SPIDER BROODNUMBER 197
Table L—Success ofremated and not-rematedspi- DISCUSSION
ders{Misumenavatia)inproducingandrearingsecond Facultative semelparity.—Any change in fe-
broodsto emergence from the nest.
cundity,ageatmaturity,orage-specificmortality
thatreducesthevalueofadultsandincreasesthe
Remat- Not
Success ed remated value ofjuvenileswill select forsemelparity and
against iteroparity (Young 1990; Steams 1992).
100% successful eggs 7 7 Forinstance,failureofanadulttoacquireenough
>50% successful eggs 3 1 resourcestobreedinaparticularyearwouldforce
<50% successful eggs 0 5
Eggscompletely unsuccessful 3 0 it to endure an additional winter, entailing high
Did not layagain 3 3 mortalityand strongselectionto shorten thelife
Diedbefore layingagain 2 2 cycle. However,theinvestmentbyMisumenain
a brood is extreme. Its extremely high repro-
ductive effort, about two-thirds of body mass
sioning for a second brood (Table 1). Overall, priortoegg-laying(Fritz&Morse 1985),exceeds
similarities between the two groups greatly ex- that ofcoexisting hunting and sit-and-wait spi-
ceededdifferences.Theprincipalpointofinterest ders [Xysticus emertoni, 45.0%; Metaphidippus
is that the majority of these provisioned indi- insignis, 55.3%;Phidippusdarns, 63.5%(Morse,
viduals laid second broods, and most of their unpublished data)]. Further, a substantial per-
broods produced young. centageofguardingparentsdiebeforetheiryoung
Although body mass ofthe spiders averaged emerge from their nests slightly less than four
slightly larger after laying the first brood than weeks later (Morse 1987).
after the second, this difference was not signifi- Ontheotherhand,remainingresourcespermit
cant (P > 0.05 forboth remated and unremated survival for guarding a short time, and many
ones:one-tailedWilcoxonmatched-pairs,signed- individuals do live until their young emerge
ranks tests: Table 2). Assumingthat the average (Morse 1987). It may be that all the resources
differencebetweenbodymassfollowingfirstand that can be exploited from the body at these
secondbroodsrepresentedtheproportionofbody times are used, and that the spiders’ remaining
mass not used for the first brood that was used resourcesmerelyhappentobeadequateforthem
forthe secondbrood, over 95% ofthe resources to survive. Aperhapsrevealingresultrelativeto
usedforthe secondbrood must have been gath- theargumentaboutmaximizingreproductiveef-
ered between the two layings (Table 2). fortisthatindividualslayingtwoclutchesunder
No relationship occurred between the repro- provisioned conditions registered a higher re-
ductive effort ofthe first brood and whether a productive effort in the first brood than in the
spider laid a second brood (P > 0.2 in a one- second, with over 95% ofthe resources for the
tailedMann-Whitney UTest).Spidersproducing second brood coming from new food captured
asecondbroodaveragedareproductiveeffortof after laying the first brood. Thus, the initial re-
65.6 ± 4.6%, n = 26, during their first brood; productive effort ofthese spiders appears to be
those that did not lay a second brood, the pu- as high as possiblewithin theircurrent morpho-
tative obligate semelparous individuals, aver- logical and ecological constraints; as noted, it
aged 66.7 ± 4.7%, n= \0. Withinthe nonlaying exceeds that ofcoexisting spiders with compa-
group, reproductiveeffortdidnotdifferbetween rable life styles. All ofthis information suggests
those dying before others laid a second brood that it would require a major evolutionary in-
(66.2 ± 2.7%, n = 4)andthose survivingaslong novation in Misumena to increase its reproduc-
asthoselayingasecondbroodbutnotproducing tiveeffortsubstantively.Themachineryrequired
one themselves (67.0 ± 5.8%, n = 6), forpredation, plusthelowmetabolicrateofspi-
Table 2.—Biomass in mg, ±SD, (mg) ofspiders {Misumena vatia) followingfirstand secondclutches.
Second clutch as
a proportion of
Treatment n Firstclutch Second clutch firstclutch
Remated 11 71.6 ± 8.8 67.3 ± 7.0 94.0%
Notremated 10 77.7 ± 17.7 74.9 ± 13.4 96.4%
THEJOURNALOFARACHNOLOGY
198
ders (Foelix 1982), may account for the ability yopidae) exhibits increasing tendencies toward
ofmost individuals to survive past this prodi- double-broodedness southward across central
gious reproductive effort. Given these condi- Florida (Fink 1986). However, its behavior, in-
tions, any opportunities that exist after the first cludinghuntingandconstructingsecondeggsacs
brood are a bonus. There is no clear evidence while still guarding, changes concurrently, and
thatthespidershavecompromisedthefirstbrood thusdiffersfromanytendenciesseeninguarding
for the second; in fact, the relative reproductive Misumena.Althoughguarding some-
efforts of the two broods counter the common times capture prey that visit their nest-sites, the
prediction(Williams 1957)thatreproductiveef- sites at which they prefer to place their nests do
fortwillincreasewithbrood,asreproductiveval- not attract many prey, and this food never sub-
ue (potential volume offuture reproductiveout- stantially increases theirbiomass (Morse 1987).
put) decreases. The strength of the egg-laying The lynx spider’s strategy would favor building
response obtained in the experiment was there- nestsat sitesofactive flowers. The favorednest-
fore somewhat surprising. ingsitesofMisumenaareonmilkweed,wellafter
The presence ofthe machinery for iteroparity ithasceasedtoflower;further,theyusuallyselect
wheretherehasbeenalmostcontinuousselection nonflowering stems (Morse 1985). Goldenrods
for semelparity raises an interesting question (Solidago spp.) are the principal field flowers in
about the retention ofvariability in life history bloomduringtheheightoftheMisumenaguard-
traits. Heritability oflife history traits is on av- ingperiod,andmostofthelocalgoldenrodshave
erage lower than that of most other traits, al- lanceolate leaves that would not provide satis-
though some variance usually remains (Mous- factory nesting sites. Thus, a foraging and nest-
seau & Roff1987). The retention ofvariation in productionshiftsimilartothatofdouble-brood-
lifehistorytraitsshoulddependontheageofthe ed lynx spiders would additionally require a si-
relationship, as well as the level ofongoing se- multaneousshiftinnest-siteselection(seeMorse
lection. If the trait exacted little cost, at some 1990).
pointselectiontowardobligatesemelparitywould
beslowed, andvestigesofabilitiesforproducing ACKNOWLEDGMENTS
second broods might remain. Although semel-
I thankJ. D. Parrishforreadinga draftofthis
parity is usually associated with big-bang repro- manuscript. Partially supportedby the National
duction, iforganisms are often prevented from Science Foundation (BSR90-07722). I thank S.
pfrooodduscuipnpglya:nFerxittrzem&elMyolrasrege1b9r8o5o)d,(see.lge.,ctliiomnitfeodr CahnidenJ.,OKl.soEnrifcokrsaosns,isAt.ancHeolidnstwhoerftihe,ld,Ea.nMdoEr.seB,.
an extreme condition should decline.
Noyce for permitting use ofthe study site.
Predictions about neighboring populations.--
Theconditionfoundandthebehaviorassociated LITERATURECITED
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