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Sistema de Información Científica
Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
Rcv. Int. Contam. Ambient.
5,
65-70,
1989.
STUDIES OF SiBLING
Drosophila
SPECIES FROM LAGUNA VERDE,
VERACRUZ, MEXICO. 111. EFFECTS OF RADIATION ON VIABILITY
M. E. de la ROSA', J. GUZMAN', L. LEVINE',
O. OLVERA' and R. F.
ROCKWELL~
l Departamento de Radiobiología y GenCtica, Instituto Nacional de Investigaciones Nucleares, Sierra
Mojada
447-20.
Piso,
Lomas Bamlaco
11010
D.F., MCxico.
Department of Biology, City College of New York, New York, N.Y.
10031,
USA.
(Recibido abril
1989,
aceptado noviembre
1989)
ABSTRACT
The sibliig specics
Drosopl~ila
ntelanogaster
and
D. simulans
were collected from
two sites at Laguna Verde, Veracruz, Mexico. Isofemale lines were established
from each species from both sites. Eggs of each isofemale line were exposed to
acute y-radiation doses of 4.0, 6.0 or 8.0 Gy from an externa1 source, and then
placed in vials. Non-irradiated eggs served as a control. Each vial was scored for
the number of adults produced. For the flies collected at Site-1,
D. melanogaster
was superior in viability to
D. simulans.
However, for the flies coiiected at Site-11,
there was no significant difference
in
egg to adult survival between the species. A
comparison of irradiated and control groups of each species from the various
collections showed that in both collections made in July there was a significant
reduced viability of irradiated groups, but this difference was completely absent
in
the collection madc in January. A comparison of the control groups of each species
from the various col-lections showed that Site-1 D.
melanogaster
were superior to
those fromsite-11. For
D.simularts
collected in July, Site-1 flies showed significant-
ly greater viability than Site-11 flies. However, this difference disappears when one
compares collections made at opposite seasons of the year. This complex situation
involving both populational and seasonal differences in viability is discussed.
RESUMEN
En la localidad de Laguna Verde, Veracruz, México, se colectaron las especies
fraternas
Drosopliila melariogaster
y
D. simulans
en dos sitios. A partir de las
hembras colectadas se establecieron isolíneas, los huevos de cada una de ellas
fueron expuestos a dosis agudas de radiación gamma 4.0,6.0 y 8.0 Gy en una fuente
externa. Se sembraron en frascos homeopáticos y posteriormente se contó el
número de descendientes. De las moscas colectadas en el Sitio 1 la viabilidad fue
M.
E.
de
la Rosa
el
aL
superior en D. nrelanogmter, mientras que en el 11 no hubo diferencia significativa
entre las dos especies. Cuando se compararon los grupos irradiados de cada una
de las especies con el testigo en las diferentes colectas, se encontró que en las
realizadas en julio hubo una reducción significativa de la viabilidad en los grupos
irradiados, mientras que en la muestra de enero no se observó esa diferencia. Al
comparar los grupos testigo de cada especie de las diferentes muestras se observó
que D. melanogaster del Sitio 1 presentó mayor viabilidad que la del 11. Para D.
sitnulaiis, colectada en julio la viabilidad fue significativamente más alta en el Sitio
1. Sin embargo, esta diferencia desapareció cuando se compararon las colectas
hechas en las estaciones opuestas del año. Se discute esta compleja situación que
involucra diferencias poblacionales y estacionales en la viabilidad.
INTRODUCTION
Those species that are reproductively isolated from one another but are morphologically
very similar, namely, sibling species, are of great interest to many population gcneticists.
A number of investigations have been conducted to determine whether they are alsovery
similar in their biochemistry (Choudhary and Singh 198?), physiology (McKenzie and
Parsons 1974), or behavior (Hoffman 1987). The findings of such studies often help
explain differences in species' frequencies associated with particular localities and with
seasonal or other environmental changes. One pair of sibling species Drosophila
melanogaster and D. simlans, has been widely studied due, at lepst in part, to the fact
that they are cosmopolitan in distribution and comrnensal with humans. These species
are the focus of
this
project as weil.
The present paper deals with the effeds of radiation on viability, namely egg to adult
survival.
Our
interest in radiation
sedviiy
stems from the faa that not only are the long
term, multi-generation effeds of radiation a consequence of the indudion of mutations,
but even short ter-
life-time effeds are often the resdt of damage to the individual's
genome.
Vibility
is
used
as the criterion by
which
to measure radiation sensitivity
because egg to addt swival represents the sum of chailenges that must be overcome
before sexuai maturity and reproduction
can
be achieved.
We have colleded and studied
the
Dmsophila at two sites in the area of Laguna
Verde, Veracruz, Mexico. Laguna Verde
is
on the Gulf of Mexico, at longitude 96' 24'
30" W and latitude
19O
43'
24"
N, about 75 Km north of the city of Veracruz. It is the
location of the country's fust nuclear power plant. The prevailing wind flow
in
this area
is
from North to South. CoUection Site-1
is
located 1350 meters,
292'
WNW, from the
center of the nuclear reactors. Site-11
is
located 350meters, 21S0SSW, from the reactors.
Site-1 is 1320 meters, 309OWNW, from Site-11. At the time of the coilections, the power
plant had not yet gone "on-line". In addition to supplying us with information of
importance for an understanding of the radiation sensitivity of sibling species, it is
expected that thc data obtained through an exíended study of these populations will
I~I:l:l:<.'I'S
01:
RADIA'I'ION ON VIABILiTY OF Droaophil.
indicatc what, if any, arc thc viability cffccts of the operation of the nuclear reactors on
surrounding populations.
MATERIAL AND METHODS
Thc flics uscd in thc prcscnt cxperimcnts came from isofcmale lines, each line consisting
oí thc dcsccndants oí cithcr an individual D.
melanogaster
or
D. simulans
female that
hüd matcd in thc wild. Flics wcrc collcctcd at Sitc-1 in July, 1986 (hcreafter referrcd to
as collcction 1-W7) and tcstcd in Scptcmber, 1986. Onc group of flies was collectcd at
Sitc-11 in January, 1987 (11-8701) and tcstcd in March, 1987, whereas a sewnd group was
collcctcd in July, 1987 (11-8707) and tcstcd id August, 1987.
Cornmcal-agar mcciium plus ycast was used as food, and the flies wcre maintained
at 24
OC.
Twcnty males and 20 fcmalcs from each isofcmale linc were placed togethcr in
individual cmpty bottlcs. Thcsc wcrc thcn invcrtcd ovcr pctri dishes (4.8 cm diameter)
into which a thin laycr oí food mcdium containing powdcrcd charcoal had been poured.
Thc femalcs werc allowcd to oviposit for a pcriod of two hours. At thc cnd of that time,
the pctri dishcs wcrc rcmovcd, covcrcd, and carricd to the nearby radiation facilitywithin
the Nuclear Ccntcr oí Mcxico. Thcrc thc cggs wcre cxposcd to 4.0,ó.O or 8.0 Gy (1 Gy
=
100 Rads). A fourth sci oí cggs from cach isofcmalc line of both species was an
unirradiatcd transportation control.
Radiation was dclivcrcd by a ~icks-RU~
2000 (Vickers Radiation Company, Swin-
don, England) at a ratc oí 0.06 Gy of gamma rays pcr sccond. In thc Vicks-Rad 2000,
spccimens are placcd in a ccntral cylindcr anci lowcrcd into a ring-shagd "CO
source
for uniform irradiation. At the time of irradation, the activity of the
Co source was
2.785 x 1012 Bq (75 Ci).
After thc radiation procedurc was completed, the egg-containing petri dishes were
rcturncd to thc Iüboratory, and 80 cggs wcre transferred from cach pctri dish to a
scparate vial (9 cm x2.5 cm), containing2cm of food mediuin. Each test of each isofemale
linc was performcd three times, and each vial was scored for the numbcr of adults
produced.
RESU LTS
Thc data obtaincd for al1 threc collections are shown in Table 1 and Figure 1. Also shown
in Table 1 are thc resulis of painvise comparisons, using Studcnt's t-test, of the two
species for each experimental condition. It was found that in collection
1-8607,
D.
melanogaster
was significantly superior to D.
siniulatts
in viability in al1 four experimental
situations. By wntrast, there werc no significant differences in egg to adult survival
bctween the species of flies from collections 11-8701 and 11-8707.
Radiation sensitivity was measured by comparing the viability of the various ir-
TABLE 1.
EGG
TO ADULT SURVIVAL
Proportion Eclosing
(f
S.E.)
Collection
Tieat-
ment
D. Melonogaster
n
D. Stmukma
n
P(t
-
test)
(GY)
1-
8607 0.0
0.607 f0.021
1 O
0.457 f 0.026
10
<0.001
4.0
0.597 f 0.023
10
0.346 k0.050
1 O
<
0.001
6 .O
0.520 f0.045
1 O
0.345 f 0.044
1 O
<
0.02
8.0
0.498 f 0.034
1 O
0.278 f 0.046
1 O
<
0.005
11
-
8701
0.0
0.391 10.061
8
0.390 f 0.061
7
>
0.9
4.0
0.392 f 0.040
i
0.325 f 0.072
6
>
0.4
6.0
0.322 f 0.046
8
0.250 f0.066
6
>
0.3
8.0
0.391 f 0.052
7
0.297 f 0.037
6
>
0.1
11
-
8707 0.0
0.310 f 0.062
10
0.260 f 0.064
9
,
>
0.5
4.0
0.093 f 0.017
1 O
0.073 f 0.019
10
>
0.4
6 .O
0.077 f 0.023
8
0.092 f 0.023
10
>
0.6
8.0
0.048 f 0.017
8
0.069 f0.019
9
>
0.4
"
number of isofemale
lines
radiated groups with their respective control groups (0.0 Gy exposure). Usiiig the t-test,
it
was
found that, in collection 1-8607, a significant reduction
in
egg to adult survival
occurrcd in D. tnelanogaster at 8.0 Gy (Pc 0.02), whereas D. simulans showed a sig-
Diñcant reduction
in
viability at both 6.0 Gy (P 0.05) and 8.0 Gy (P c 0.005). Collection
11-8701 showed no significant reduction in viability at any of the levels of irradiation for
either species. However, in collection 11-8707, there was a significant reduction
m
egg to
adult survival for both species in al1 experimental situations (Pc0.005 for D.
melanogaster, P c 0.05 for D. simulans).
In order to further detect populational as well as seasonal differences within each
of these sibling species, comparisons were made of the control groups from the three
coiiections of each species. For D. nielanogaster it was found that 1-8607 control group
flies demonstrated significantly greater viability than both 11-8701 and 11-8707
ílies
(P c 0.005). In the
case
of D. simulans, there was no significant difference
in
egg to adult
survhal between 1-8607 and 11-8701 control group (P
>
0.3), but 1-8607 flies showed
significantly greater viability than 11-8707 flies (P c 0.02). For both species, there
wx
no
significant difference
in
egg to adult survival between the control groups of the two Site-iI
collections (P
>
0.1).
DISCUSSION
AND
CONCLUSImS
The flies from the three collections reported here have also been studied for other
charactcristics (Rosa et al. '1989; unpub!ished data). One characteristic closeiy
as-
Drosophila melanogaster
Drosophila simulans
Fig. 1. Egg to adult survival of irradiated and non-irradiated Dwphila melanogasíer and D. simuians
collected at Laguna Verde, Veracruz, Mexico
sociated with viability is species frequencies. The frequencies of D.
naelanogaster
and
D.
siinulans
males at Site-1, relative to one another, were respectively 83
%
and 17
%.
However, at Site-11 there was a complete reversal in the relative frequencies of D.
nielanogaster
and
D. sinaulaiis
males: 16
%
vs
84
%
(8701) and 13
%
vs
87
%
(8707).
The superior viability of the non-irradiated D.
ntelanogaster
from the Site-1 collec-
tion is in concordante with its significantly greater relative frequency in the population.
Although one would have liked to see a superior viability of the non-irradiated D.
sinaulans
from the Site-11 collections, corresponding to its significantly greater reiative
frequency in that population, it did not occur. However, the absence of any superiority
of D.
melanogaster
in egg to adult survivai indicates the important contribution that
viability makes
in
determining species' frequency but does leave unanswered the ques-
tion of what other factors in the life cycles of the
two
species accounts for the signifícantly
greater relative frequency of D.
simulans
in the Site-11 coilections.
In examining the results for populationai as well as seasonai differences, one
fmds
a complex situation. If one compares the viabiities of the sibling species in
ail
four
experimental conditions, it
is
clear that there
is
a populational difference between flies
from Site-l and those from Site-11. However, there is no seasonal difference between the
rcsults from thc two Site-11 collections. lf one examines radiation sensitivity by comparing
thc viability of the various irradiated groups with their respective control groups, one
docs not find a distinct populational difference, but one does find a seasonal cffect for
thc Site-11 collcctions.
Finally, if one compares control groups within each species, one finds that
D.
melanogaster
shows a populational but no seasonal difference. By contrast,
D. siniulans
does not show a populational diffcrence but does show a seasonal difference when
comparing Site-1 flies with the two collections of Site-11 flies. However, there is no
seasonal differencc between Site-11 flies. It is clear that the types and degrees of
differences in the viability results obtained for these sibling species varies with the focus
of the particular analysis. We plan to continue collecting and tcsting the flies from both
sitcs at opposite seasons of the year in order to develop a body of information on the
p~pulational and seasonal characteristics of these species and, simultaneously, to
mo!nitor the effects, if any, of the operation of the nuclear power plant on surrounding
populations.
ACKYOWLEDGEMENTS
This paper is a contribution from a binational cooperativc rescarch program on
Mcxican
Drosophila,
involving the Departamento of Radiobiología y Genética, ININ,
México, and the Dcpartmcnt of Biology, City Collcgc of New York. The authors are
pleascd to acknowledge their indcbtedncss to thc authorities of ININ for their
wholchcartcd support of this rescarch. This rescarch was also supported in part by
U.$.
Dcpartment of Health and Human Service Grant No. 2-S07-RR07132 and by a grant
from Thc City University of New York PSC-CUNY Rcscarch Award Program to Louis
Lcvine. This papcr is dcdicatcd to Dr. Alfonso L. de Garay and to the memory of
Profcssor Th. Dobzhansky, initiators and guiding spirits of this program.
REFERENCES
Choudhary M. and Singh R. S. (1987). A comprchensive study of genetic variation in
natural popula:ions of
Drosopliila melanogaster.
111. Variations in genetic structure
and their causes between
Drosophila nielariogaster
and its sibling species
Drosophila sitriulans.
Genetics 117,697-710.
Hoffman A. A. (1987). A laboratory study of male territoriality in the sibling species
Drosophila meiartogaster
and
D. sirriiilaris.
Anim. Behav. 35,807-818.
McKenzie J. A. and Parsons P. A. (1974). The gcnetic architecture of resistance to
desiccat ion of populations of
Drosophila melariogaster
and
Drosophila sintulatis.
Austr.
J.
Biol. Sci. 27, 441-456.
Rosa M. E. de la, Guzmán J., Levine L., Olvera 0. and Rockwell R. F. (1989). Studies
of sibling
Drosophila
species from bguna Verde, .Veracrul, Mexico.
l.
Species
frequencies, viability, desiccatlon resistance, and vagility. J. Hcred. 80,44-47.
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