The study compared population dynamics of M. minuta in different environments (reservoirs and rivers) in a semi-arid region of Brazil after rain. M. minuta was only present in the active form for a short period after rain, then disappeared, remaining only as diapause stages in ephippia. Results showed higher proportions of ephippial females and juveniles in populations with higher salt concentrations. Ephippia production appeared to be induced by crowding and chemical cues like ammonium and chloride. M. minuta disappeared from environments where water remained for longer periods, suggesting other factors also influence its population dynamics.

1. ~~
JosédaPaz;TakakoWatànabe.
}m~9iffer~nt.population dYn'Hni90f.Mqinaminu.taMtchedfTO~ '.
~l#]"}'enY~roIljnents(res,ervoirs andriver),afterr<in,inasenll~<lfidregi()n
, ' , ' .ia:litAll~he'ehVlrOn1ne1'ltswereleritic,b~cal1sethearnóliritÔfràiriWiÜer"
',Wa ',', ,ught6n~wthe'riVer,aÚd'üonly reli1aitiédwithállttlê lagóoti.I'~róentágeÓf
,~phippíâi'{ehi~lês,partp eti()getietic'~êrilalesiiri~l eS aridj uvêtiilês i'in' por ulatibns,wêrê
"âri ~1Y $ed: IJiomêtpc " m~~Sl,lt~sWete "aIs6de ve16pedicÓmp â:ririg body 1ength1tiiéphippial
'~~;pârt~~llo~en~tic~l fem~lêS,i*Wer~servoifsi ~lldJhyri~~tstudiyd ',Re~HltSóbtâined',in
çláq;pcêrai}popülatiór1sVeteÓop-êlatedwi th criviri)rrti}êtitalóhêll1ical'vària~lêS.In Solêdade
r~s~r'ii:>.ir'áhighpró),)()rti6ÚPfferilàlêsproducedêphippia,whilêln the()theTT~etvoitsand
tiv~rW~jJerceütagebfephippial fem.aleswasmuchlower. ,',' "
, ' ,
, l{eyiy()tds: é:ladôcera,testil1geggs,popl1IatiOI'ldyIià!I1~cs,senli-arid. '
JNTRODUCTI()N
", , ,,~~l .~aridregions ~swell asin extremely cola
.fêgfoti's; ",al$ ne,edto h~ve special adaptations to
's'urvi veéx treill.é êÍ1Virónrhents.InJ3 ranchiopoda
;,dhipat!~t-:Jiàs;pé~t1dbsetVédin fossils sinéegéological,,', '"d,,' .. ' ' , ' ',' ',,' ,
perió<;J~.°J'hê~eI;éstingéggs enabled',thetn to livein
'",: ,'o" I" ', ,'., d ", o
, tetnp~târypondsand Hiextremely cola habit;lts, thus
allowibgtb.em to counter adverse conditibns ind to
'act asdi~pets~l~gents (4). According Hairston &
:Cáceres{~), qr.u~~aceansfo4!ldininlando>yaterbodies,
:é ,"o", toc~sionallybecomedry,aremore
.. ..,' , )àpausingstage than:tbôse living
,.,irh)peh'00 o o', shápperisdqétóselectionpressúreo'i,exérte<fôp,~tiIsiacéàhspecies by lhe environments
'wberethey lfve:andas feSult aftheir phylogenetic
:historY:Stilll~cc()rding th~saI1le~uthors;resting egg
;,duratiÓIi)ih1é i$'véryyariable,depending imeach
;.sPt}Ciés',':bu(ili1íi~" ê,aIariqid Onychodidpt~mus
isa~guín~u/tbe 'd"";!;;ofdl~pause banbé7byeats.
)'el~dóéer~nr;can beviablefor 55years
,>r?)ándlho, S)Íéars(3) though this is not
:~:thhl.üe.,' i/'"" 'o "
i,;,:Árbaobserved that life
~~is:torytralt$o ."arthenogenetic;,gerieràtiorisdtJ:)/:l ,', " " ".Dáphniids
i:t11ai~hingfrom re~ting , their body
~
ABSTRACT:
gizesare.big;g#Jháh thqsepatcbingfrom subitafteous
eggs.B eeausê~i~ thfjy'Díatlireafew, d,ay#'~#li~fthll*
parthenogenetic females. Fecup.qtty'ç>ffheéphi ppi~l
gel]erâtionismatkedlyhigQ,~r, """;,, - " " ,,'
" , 'IIiteIIlperateregiQIÍs'th~ep.yifê>nwêriiálcueiq
pr~ducen~sti~geggs ',~stl*~~ê>!p'pê~i64(8;Q);'i~~'
púpulatiôn Mpsity'( 8;9);W~d~f~sêil1, f(jQ4g~~p~Hy
(5) anditi'iiibIl1e' ~lad6cêi~Ii~i~yihêptêsêiiç,ê59,fpredators(l1). '.',,' ,', ",' "", i ,'o;
lril1orthe!lst"i3hisil,'sêvêréral ',da.IIls,iW~~;ê
çQnstqlç t~d::' !Q '4~9Jêil$:~:~4ê ÜÂp~çJPf4fq4gttú'H:
ru~alis .:1?t1ri,pg'"riôrrIl ilí,i,yé~fs; ;tMs~" da.f1i,~,e~P8~t~Xt~'
H&'Btgg;êfÕl1 ês,k~ê'p w~t~f',d,uHrig'drY}~~~~9ftr
altho1lgh'Úieir 'Watêrlevêls ,strbhgl)'dêHf~ã§:~?!!~'
especiáHy,' 4iy 'yeái$, ':theseêl1'Yt1"oIl11lg~ts:~ê~Çi~~", '," '," , ", ..', ,,' , ",," ,..,cQinpl~1ydrY ,il1çll1dWg;soIJlí:rivei$. Litj1~' " "
aIways ,.hy6ut4ttl;ing thedraughotes
happênedcll11'ing'lQ98it1TaperoáJ.l~*lq
regiorl,innÓrtl1t';as(J3rá$il,V hereJd~]Q[l
qÓri)pIételfdried. "Afteffitst' raih,Mqi~â
th~first dadocerah'spêciestoJppê~t, ,ycôf1iPâredth~diffetent,populatlqp,' "Wt.
minlltq~IQd~ fram ephippialfj ,~tidin
one riY~r;;~11~tSp~9JSpmemQP .,,~(çlry.)n
tllostelivironrneI1ts Vátefre',. o" prqlQgical
cycle"aft~r.rainfal.l,qq .' 'áiri,itonly
feI1iainedforapproxiI1i~t' , ' 'i,e-Qetthel~ss in
33

2. ~
. .
.M.rhÜiuta disappeared from water
nly asdiapausestages,in epphippia.
. is work was to compare the different
densities, fecundities, percentage of male, juveniles,
ephhippial females andcorporallength of the different
populations and to detect which environmental cues
areresponsible for the formation of epphippial eggsin
M. minuta.
STUDYSITES
TaperoáRiver - ls atemporaryriver in asemi-arid
region in Paraíba state, in the northeast of Brazil. It
wasdry for more than a year. After the first rain, some
pools appeared on its sandy bed. As rain was not
abundant, the river waters did not mn and the
environment remained lentic. M. minuta wascollected
15daysafter.rain.This spéciesonly waspresentduring
2 weeks after the fitst sample. Later, only copepods
androtifers wen:;present. .' ,
Soledade Dam - Soledadeis alsolocqted in
TaperoáRiver Basin, but in a dryer region. This dali
tas maximum capacity of 27 058 000 m3. and was
completely dry for 3 years.The first sample wasdane
a week after rain falI. The next week this species'
disappearedandoneweekafterthedali wascompletely
dry again.
Taperoá Dam - This is a very large dali in the
saméBasin. Water remained in the dali during the dry
period until a month before the rain. After that, only a
litle pond remained with water, on the deepersite.This
water washypereutrophic with abloom ofEuglena sr.
and the only zooplankters present were 3 species of
rotifers, being Brachionus urceolaris the more
abundant. The rain was very abundant, and after 3
days the dali was full. The first sample was taken 2
weeks after rain, when M. minuta waspresent in high
densities, but one week later none were observed.
StateDam - This dali is about3Km fiom Taperoá
Dam,andis verysmall (l00mx 30m). Itwas completely
dry before therain, andreceivedwater when the others
did. Nevertheless, as this dali is located downstream
of the other, received less water. ln this dali the first
sample was collected two weks after the rain and M.
minuta remained tere one week more than in Taperoá
Dam.
~
colIected 7 and 15daysafter
occurredbecause
in alI environrnents.
40 liters oflitoral
sugar.
34
~
Data analysis: .j'
One way ANO V A was used to comp').re.,
measurementsofbody length in adults andjuvenile àf
M. minuta. Males were not included. To discriminate/j
between juveniles and adults, we measured adule('
ovigerous females's length and considered allloweni
values asjuveniles. .
Densities representthe mean of 3 replicates.
Pearsoncorrelationwasusedto corre(ate'.,
densities, andpercentageof stagesand sexproportioll;
in populations with physical andchemical parameters...
in the environments. Only the first samplewassuitable..
for correlation analysis asin later samplesM. minuta,'
was not found in SoledadeDam and TaperoáDam.
Analysis offecundity andgrowth rateswere also'
performed.Fecundity wasestimatedfram thefollowing '"
equation, F= E x (A+), whereE is medium number of '
A ..;
eggs,A is adult femalesand(A+) is adult femaleswith;.
eggs/embryos. Growth rate was obtained by the.'
equation: r =Ln NI - Ln NO,where NI is the final
ti-tO
~
RESULTS
After the start of the rain in the semi arid region .
studied, water remainedin ponds andin the river, until..
the rest of the season,except in SoledadeDam, where.
therainfall waslessandabout20 daysafter rain falI, alI .
water disappeared.
The active life-cyc1es of M. minuta were very
short. In the falir environments analysed, supposing .
that this specieshatched as soon as it rained, M. mi-
nuta was present in the water column less than 40
days. 12 days after ephippial eggs be produced, M. .
minuta was not seen again. In Soledade Dam and
TaperoáDam, epphippiawereproducedapproximately .
7 and 15daysrespectively after rain falI. In StateDam
and Taperoá River, ephippia were produced
aproximately onday 27. . .
In State Dam, M. minuta population dynamics
changed during the time this species was actively
presentin water column. Fecundity values,percentage
of juveniles and percentageof males decreasedfram
day 15to day 27. Ephippial eggs were observed only
on day 27 (Table I). Density sl~ghtly increased fram
~

3. ~
in M. minuta in
In TaperoáRiver lhe fecundity value on lhe first
ewaslhe highestin alI study,F =10.63, resulting
percentage of juvenile of lhe second sample
ighest of alI samples in lhe study. Male
agewas similar to thosein SoledadeDam, and
than that observed at State Dam. Densities
. here lhe highest values on dar 27, although
centage of this speciesin lhe community was
is is due to lhe presenceof lhe colonial rotifer
llus sp., present in high densities. M. minuta
second most abundant species.
alysing lhe body length of M. minuta in lhe
ronrnentsby ANOV A, wedetectedsignificant
betweenadult femalesofTaperoá Dam and
therf1nvironrnents(p<O,OOl)(Table11),being
th alwaysshorterinTaperoáDam. Significant
swere alsoobservedbetweenSoledadeDam
eroáRiver (FI, 107= 12.81,p<O,OOI),beingM.
~~
minuta bodies larger in Taperoá River. In the two
environments where was possible to compare body
length over time (Taperoá River and Taperoá Dam),
there were no signifficant differences among
populations. Juveniles showed different patterns in
body length. The only environments that showed no
significant differences injuveniles's body lengtl1were
Taperoá River and Taperoá Dam, alI other pairs of
environments presentedsignificant differerices (Table
11).The mean body length values of juveniles were
higher in StateDam (0.534mm), followéd by valuesof
SoledadeDamjuveniles (0.495 mm). The lower mean
value was obtained at Taperoá Dam (0.438 mm).
Comparing body length of erous females and
ephippial females in Soledad. fi (the only one with
both kind of females in sufficient quantity to compa-
re), ovigerous femaleswérel>ignificantly larger (Table
m.
35

4. ~~
Tabela 2. Coeficientes decorrelação entre os seisprimeiros eixos da ordenaçãopor
pais e os descritores ambientais.
~
Table 111- Pearson'scorrelation analysis amongM.
meansp < 0.05. ** meansp< 0.01.
Total P (mg!1) 0.09
94.83
18.88
~~~~~~~

5. d .in th~ Tiver). To know which
logical factors were respàl1sible
rence of lhe organisms from lhe
t. we correlated biological with
ental parameters. This shows that lhe
af sexualeggswaspositively correlatedwith
monium andchloride concentrations.Density
Iso positively correlated with ephippia
tage, showing that crowding induced ephippia
tion as welI as occurs in Daphnia (9). aTIce
pia were produced, popula~ion densities began
chile and about 10 days later lhe populations
letely disappeared.
As in Soledade Dam, lhe water remained less
han in lhe other environments analysed,andlhe
presentedmore salts lhe induction of ephippia
uction in lhe females in lhe population was high.
ertheless, in this dam were produced lhe higher
ut of juveniles andlhe population reachedhigher
sities on first sample. This show that lhe
onmental condition can induce more ar less lhe
er of M. minuta dynamics. AlI lhe environments
oledadeDam remained with water andM. minuta
ppeared from lhe water column, so other factors
ond chemical parameters must be involved in.
bably food, ar other biotic factors can be involved
M. minuta disappearence. Decreases in food
ntity induces resting egg formation in rotifers (5),
s could happen in lhe study sites after rain.
toplankton populations probably highly increased
. m diapause stages,allowed M. minuta to increase
population densities, andcollapseddueto overgrazing
by cladocerans and other organisms in lhe
environments. When densities of M. minuta reached
high values lhe kind of eggs were changed from
parthenogenetical to ephippia. We will do further
r.esearchtofindanswers. .
. When body length of ovigerous and ephippial
females was compared, significantly differences
.wereobtained, being ephippial females smalIer than
the others. This could mean that lhe females spent
more energy producing ephippia than producing
normal eggsar that ephippial females were youngers
than lhe others. As comparations were dane in lhe
same dam and at lhe same time, food did not
influenced this body length. Experimental testsmust
be developed to find out why ephippial females were
shorter, than lhe others.
To conclude, when ephippia began to be
producedasexualfecundity valuesstrongly decreased
in alI sites and consequently lhe percentage of
juveniles, resulting in lhe complete disappearenceof
lhe species few days later. This speciespresented a
short active life cycle in alI study sites and was
negatively affected by population densities,amonium,
nitrate and chloride concentrations.
~~
Compa
de Moin ,
semi-árida do
rentes dinâmicas po "
ec1odidasde efípiosem di
(açudese rio), apóso iníci
semi-áridadaParaíba-Brasil.Tod
ram lênticos porque a quantidade de.
não foi o suficiente parao rio correr, produz
nas uma pequena lagoa. A percentagem.
efipiais, fêmeas partenogenéticas, machos e juv s'..
napopulação foram analisados.Medidas biométricas
tambémforam realizadas,comparandoo comprimento
do corpo em fêmeas afipiais e partenogenéticasnos
açudese no rio analisados.Os resultados obtidos nas
populaçõesdec1adócerosforam correlacionadoscom
parâmetros químicos ambientais. No Açude de
Soledade uma maior proporção de fêmeas produziu
efípios, enquantonos outros açudese no rio essaper-
centagemfoi menor.
Palavras chave: cladocera,ovos deresistência,dinâ-
mica populacional, semi-árido
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~
FreshwaterBiology,
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~

6. ãceres,1996.Distribution
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~~
38
~~~~