INVERSION POLYMORPHISM IN A NATURAL POPULATION OF

Rev. Int. Contam. Ambient. 21 (Supl. 1) 31-34, 2005
INVERSION POLYMORPHISM IN A NATURAL POPULATION OF
Drosophila nebulosa. A TEN YEARS RECORD
Víctor M. SALCEDA
Departamento de Biología, Instituto Nacional de Investigaciones Nucleares. Salazar, Edo. de México. Apartado
Postal 18-1027. México, 11801, D.F. [email protected]
Keywords: Drosophila nebulosa, inversion polymorphism
ABSTRACT
A natural population of D. nebulosa from Arroyo Agrio in Veracruz, Mexico was sampled
over a 10 year period for its chromosomal polymorphism. A total of 616 third and X
chromosomes were analyzed. Of the17 different III chromosome inversions known to
occur in this species, we were able to detect 9, which is 52.94 % of the total. Most of the
inversions were less than 10 per cent in frequency. Inversions A and B attained higher
values, namely 19.96 and 14.28 per cent respectively. These values are in the range of
frequencies found in other populations studied elsewhere. Not all the inversions were
present in all the collections and one inversion, H, was detected only in a single collection. Also rare were inversions C and F that appeared three times and H/h four times. As
for the inversion in the XL chromosome arm, it was observed in all collections with
variable frequency. It had an average frequency for the whole period of study of 14.33
per cent. The average number of heterozygous inversions per individual was 1.57, a
value included in the range previously reported. The data did not allow a seasonal
analysis.
Palabras clave: Drosophila nebulosa, polimorfismo, inversiones
RESUMEN
Una población de Drosophilae nebulosa originaria de Arroyo Agrio en el estado de
Veracruz, México, fue muestreada por un período de 10 años a fin de analizar el grado del
polimorfismo cromosómico presente en la misma. Se analizaron un total de 616
cromosomas tanto sexuales como del tercer par cromosómico. De las 17 diferentes
inversiones conocidas para el cromosoma III de esta especie pudimos detectar la presencia de 9 de ellas lo que corresponde al 52.94 por ciento del total. La mayoría de las
inversiones presentaron frecuencias menores al 10 por ciento, sin embargo las inversiones A y B alcanzaron valores superiores, a saber, 19.96% y 14.28% respectivamente.
Estos valores están comprendidos dentro del rango de frecuencias encontrado por
otros investigadores en las poblaciones por ellos estudiadas. No todas las inversiones
estuvieron presentes en todas las colectas y una de ellas la H se detectó en solo una
muestra. Las inversiones C y F se encontraron en tres ocasiones y la configuración H/
h cuatro veces. En cuanto a la inversión XL del cromosoma sexual, se observó en todas
las colectas con frecuencias variables, pero con una frecuencia promedio para el período de estudio de14.33%. El número promedio de inversiones heterocigotas por individuo fue de 1.57 valor que queda incluido dentro del rango de frecuencias publicado. Los
datos obtenidos no permitieron un análisis estacional.
32
V.M. Salceda
INTRODUCTION
Inspired by the work of Painter (1934) and Bridges
(1935) on the use of the chromosomes in the salivary
gland cells of flies of the genus Drosophila to build
chromosome maps, a goodly number of species have
been studied. Among the widely studied species inhabiting North America is the species Drosophila
pseudoobscura. This work initially summarized by
Dobzhansky and Epling (1944) has continued for decades with a further summary by Anderson et al.
(1991). In Mexico studies of this species have been
summarized by Olvera et al. (1979). In South America
this kind of analysis has been done in Argentina, Bolivia, Brazil and Uruguay for D. willistoni and some
of its sibling species (Burla et al. 1949; Dobzhansky et
al. 1950; da Cunha et al. 1953), including D. nebulosa.
D. nebulosa has a broad geographical distribution
extending from Buenos Aires, Argentina in the South up
to Central Mexico and Texas (Paterson and Wagner
1943). This species is the most common member of the
willistoni group found in Mexico, occupying the eastern
part of the country (Paterson and Mainland 1944).
This species has not been well analyzed with respect
to its inversion polymorphism (Pavan 1946; da Cunha et
al. 1953) and no information is available from Mexico.
The chromosome map of D. nebulosa was first
described by Pavan (1946), who reported the presence of polymorphisms in two of the chromosome arms
of this species, namely the left arm of the sex or X
chromosome (XL) and the third chromosome (III). In
that study Pavan found a single inversion in the tip of
the XL chromosome arm, and 17 different inversions
in chromosome III.
The inversion in the tip of the XL chromosome looks
very similar to the “sex-ratio” inversion found in D.
pseudoobscura (Dobzhansky and Epling 1944) but
does not carry the same consequences. There is no
change in the expected equal proportion of the sexes
in the progeny of its carriers. The inversions in the
third chromosome are paracentric and in general of
small size, as represented in the cytological map determined by Pavan (1946). The 17 inversions are the result of combinations of 8 different inverted sections. In
a pioneering work, da Cunha et al. (1953) analyzed
the relative frequencies of the different heterozygous
inversions of D nebulosa in 10 natural populations from
Brazil, as well as the average number of heterozygous
inversions per individual.
MATERIAL AND METHODS
The population under study is from Arroyo Agrio
located 75 Km North of the city of Veracruz, and
was sampled on 10 occasions from January, 1991 to
January, 2001. Flies were trapped in morning collections from 8-10 a.m. on three sucesive days.
Flies were attracted to traps using as bait fermenting bananas contained in 25 plastic buckets which
were distributed every 5-7 meters in the site in order
to cover a large area. Traps were visited at intervals
of 10-15 minutes during the collection and, using a
net, the traps were swept and the flies captured. Captured flies were separated by species and D.
nebulosa females were placed in a vial with fresh
food in groups of 15-20 individuals to be carried to
the laboratory in Mexico City.
Once in the laboratory, each female was transfered
into an individual half-pint bottle with fresh food initiating an isofemale line, and incubated at 25° + 1C.
When larvae started to crawl, cultures were transfered
to a cooler area which was kept between 15-20°C
and supplied with a heavy solution of live yeast to
provide maximum nourishment for the larvae.
From each isofemale line a single larva was taken,
dissected and the salivary glands extracted. They were
stained with a regular lacto-aceto orcein solution and
a smear was done. The smear was analyzed using a
light microscope and the karyotypes determined using as a guide the figures published by Pavan (1946).
The different heterozygous inversions found in each
isofemale line were recorded, their relative frequencies calculated, and the respective tables containing
the information prepared.
RESULTS
The 10 collections yielded 308 isofemale lines and
from them we were able to determine the banding
patterns of 616 XL and III chromosomes. Due to the
fact that some times more than two inversions were
detected in a particular chromosome the total number of banding patterns analyzed gave a theoretically
higher number of chromosomes, in this case 626 XL
and 644 III.
In 5 out of the 10 collections the sample size was
very low yielding only 8 chromosomes.
Of the 17 different third chromosome heterozygous inversions known for D. nebulosa we detected
9 of them. This is equivalent to a 52.94 per cent of
the total. All together the number of heterozygous
inversions found was 486 which corresponds to 1.57
inversions per analyzed female.
DISCUSSION
Some species of Drosophila are uniform with re-
33
INVERSIONS IN D. nebulosa FROM MÉXICO
TABLE I. FREQUENCIES (IN PER CENT) OF VARIOUS INVERSIONS IN THE XL CHROMOSOME ARM OF Drosophila
nebulosa FOUND IN HETEROZYGOUS CONDITION IN TEN COLLECTIONS OF A NATURAL POPULATION IN
VERACRUZ, MEXICO
XL none
Inverted
n
July
1991
Jan.
1994
212
88.33
28
11.66
240
86
91.49
8
8.51
94
July
1995
68
89.47
8
10.53
76
July
1996
11
91.66
1
8.33
12
Oct.
1996
81
96.43
3
3.57
84
spect to the distribution of gene arrangements in their
chromosomes. Such is the case of D. willistoni with
70 different inversions (Valente and Morales 1985).
In other species the inversions are concentrated in a
single chromosome as in D. pseudoobscura and D.
persimilis with up to 52 different inversions within
both species in the third chromosome (Powell 1992).
D. nebulosa is included in this category with 17 different gene arrangements in its third chromosome as
previously indicated.
In their study da Cunha et al. (1953) mentioned
that among the 12 different inversions found in 10
natural populations, 5 were present in all the localities with variable relative frequencies depending on
the locality. The remaining 7 were less common.
In our case, among the 10 inversions recorded,
one was found in the XL chromosome arm and 9 in
the III chromosome. Inversion H appeared in a single
Nov.
1996
Jan.
1997
59
89.39
7
10.60
66
July
1998
14
87.50
2
12.50
16
12
75.00
4
25.00
16
Oct.
1998
8
88.89
1
11.11
9
Jan.
2001
Avr.
Freq.
Tot.
10
76.92
3
23.08
13
87.51
561
12.49
65
626
collection. Two of them , C and F in three and inversion H/h in four samples. The remaining 6, including
XL, appeared more frequently.
Their relative frequency in any particular collection varied greatly, which was probably due to small
sample size.
Among the 616 chromosome arms analyzed, the
relative frequency of each heterozygous inversion in
decreasing order for chromosome III is: A= 19.96;
B= 14.28; D= 9.41; G= 9.25; E= 6.33; F= 2.69; C=
2.11; H= 1.94 and H/h= 1.46. In the case of the one
XL inversion the corresponding value is 10.55. All
the pertinent information is shown in tables I and II.
Inversions A and B attained relative frequencies
which are similar to those found by da Cunha et al.
(1953).
The inversion in XL, was present in an average
relative frequency of 14.33 per cent in the whole
TABLE II. FREQUENCIES (IN PER CENT) OF VARIOUS INVERSIONS OF THE III CHROMOSOME OF Drosophila
nebulosa FOUND IN HETEROZYGOUS CONDITION IN TEN COLLECTIONS OF A NATURAL
POPULATION IN VERACRUZ, MÉXICO
July
1991
none
A
B
C
D
E
F
G
H
H/h
n
63
24.61
62
24.22
41
16.02
11
4.30
17
6.64
15
5.86
14
5.47
17
6.64
12
4.69
4
1.56
256
Jan.
1994
47
48.96
15
15.63
16
16.66
_
6
6.25
3
3.13
1
1.04
8
8.33
_
July
1995
July
1996
Oct.
1996
Nov.
1996
Jan.
1997
35
40.70
13
15.12
7
8.14
_
24
34.78
9
13.04
9
13.04
_
5
35.71
1
7.14
_
11
15.94
6
8.70
_
1
7.14
3
21.43
2
14.29
_
July
1998
Oct.
1998
Jan.
2001
Avr.
Freq.
Tot.
2
16.66
3
25.0
1
8.33
_
2
25.0
3
37.5
2
25.0
_
5
50.0
2
20.0
1
10.0
_
35.45
229
19.04
123
14.67
88
4.22
13
4
33.33
1
8.33
1
8.33
_
_
_
14.83
58
_
_
8.61
39
_
_
4.95
16
_
2
20.0
_
12.36
57
4.69
12
_
4.82
9
43
53.08
13
16.05
8
9.88
1
1.23
6
7.41
4
4.94
_
3
25.0
2
16.66
3
25.0
_
2
16.66
_
11
12.79
6
6.98
_
6
7.41
_
2
16.66
_
12
13.95
_
8
11.59
_
2
14.29
_
2
2.33
86
2
2.90
69
_
_
14
12
_
_
_
_
96
81
12
_
_
1
12.50
8
10
644
34
V.M. Salceda
sampling period. It is remarkable to have found it
repeatedly since da Cunha et al. (1953) did not find
it in any of his 10 collecting sites, and Pavan (1946)
suggested the possibility that it may have arisen in
the laboratory.
The average number of inversions per individual
observed by us was 1.57 per cent ranging from 1.21
up to 2.33. In their study da Cunha et al. (1953) found
values from 0.62 up to 2.36. It is clear that our population is included in the same range of variation.
We plan to conduct similar studies in other localities, so as to cover most of the distribution of the
species in Mexico. This will allow us to have a better
understanding of the chromosomal polymorphism of
this species in the country.
ACKNOWLEDGMENTS
The author wishes to express his gratitude to Prof.
Louis Levine for reviewing the first typescript, as well
as for his suggestions. The work was partially supported by CONACyT under contract 31736-N. In dedicating this work to the memory of Dr. Alfonso León
de Garay, I should mention some aspects of his influence on my professional development. Been an undergraduate he kindly hired me to participate in his just
established Programa de Genética y Radiobiología, introducing me to the wonderful world of research in
Drosophila genetics. Along the years encouraged me
to continue studies up to obtain a doctor´s degree as
well as a full support to get international training. When
I moved to other institutions always follow with interest my progress in the several new Drosophila laboratories that I established as well as in the research there
conducted. During all that time he always showed interest in my professional and personal development
and was at the same time teacher and friend.
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