ОБЩАЯ ГЕНЕТИКА
УДК 575.224.232.4
INVERSION POLYMORPHISM IN TWO SERBIAN NATURAL POPULATIONS OF Drosophila subobscura: ANALYSIS OF LONG-TERM CHANGES © 2014 G. Zivanovic1, C. Arenas2, and F. Mestres3
department of Genetics, Institute for Biological Research "Sinisa Stankovic" University of Belgrade, Belgrade, 11000 Serbia e-mail: goranziv@ibiss.bg.ac.rs 2Departament d'Estadística, Universidad de Barcelona, Barcelona, 08028Spain 3Departament de Genética, Universidad de Barcelona, Barcelona, 08028 Spain Received Oktober 07, 2013
To study whether inversions (or arrangements) by themselves or karyotypes are the main global warming adaptive target of natural selection, two Drosophila subobscura Serbian populations (Apatin and Petnica) were re-analyzed using different statistical approaches. Both populations were sampled in an approximately 15 years period: Apatin in 1994 and 2008 + 2009 and Petnica in 1995 and 2010. For all chromosomes, the four collections studied were in Hardy—Weinberg equilibrium. Thus, it seems that inversions (or arrangements) combined at random to constitute populations' karyotypes. However, there were differences in karyotypic frequencies along the years, although they were significant only for Apatin population. It is possible to conclude that inversions (or arrangements) are likely the target of natural selection, because they presented long-term changes, but combine at random to generate the corresponding karyotypic combinations. As a consequence, the frequencies of karyotypes also change along time.
DOI: 10.7868/S0016675814060150
In Drosophila genus, the chromosomal inversion polymorphism seems to be adaptive and it is subject to strong selection, because their frequencies change in time. For instance, short- (seasonal variation) and long-term changes (according to environmental variations) were reported in different species of this genus [1—5]. In this context, studies in the model species Drosophila subobscura, due to its rich chromosomal polymorphism for inversions, gave new insights on this adaptive process and the role of natural selection. Seasonal variation in chromosomal polymorphism frequencies was observed and interpreted as an adaptive process [6—9]. Furthermore, variations in the chromosomal polymorphism in time (long-term changes) were considered a key element to monitor the global climate change (for a review see [10]). The role of natural selection was also observed in the latitudinal clinal variation of the inversion frequencies, both in Palearc-tic and American colonizing populations [11—14]. Finally, in American populations of D. subobscura, the effect of natural selection on several inversions (O5 and O3 + 4 + 7) could be measured [15].
However, although short- and long-term changes in the composition and frequencies for chromosomal inversions or arrangements (overlapped inversions) have been intensively analyzed, this is not the case with regard to inversion karyotypes. Few studies have been carried out and limited information has been obtained [9, 16—20]. Inversions on one chromosome could not act independently, because the genome is an
integrated functional system. The genetic information carried by both homologous chromosomes could have an important effect on the adaptive capacity. For instance, some inversions (or arrangements) in one homologous chromosome combined with those of the other homologous of the same pair could provide a better adaptation to certain environmental or climatic conditions. For this reason, the information provided by karyotypes could generate new insights in the adaptive changes along time. Our aim has been to re-analyze — using different statistical approaches data on chromosomal karyotypes from two Serbian populations, which were sampled two times each one in a 15 years period and to study the variation in their karyo-typic frequencies.
MATERIALS AND METHODS
We have re-analyzed data from a couple of Serbian populations: Apatin (sampled in 1994 and 2008 + + 2009) and Petnica (collected in 1995 and 2010). Detailed information regarding both populations can be found in [19] and [20]. Meteorological data for both sites were obtained from the Serbian Republic Hy-drometeorological Service, previously published [19, 20], are also presented in Table 1 of this study (for maximum, minimum and mean temperatures). Samples of different years were strictly collected in the same place, month and equivalent day. Males, and in some collections sons of wild females to increase the
Table 1. Meteorological data for the Apatin population for the month of June from 1994 to 2009 and the Petnica population for the month of May from 1995 to 2010
Year Max. T (°C) Min. T (°C) Mean T (°C)
Apatin Petnica Apatin Petnica Apatin Petnica
1994 26.3 - 13.8 - 20.3 -
1995 25.2 21.4 13.5 10.2 19.1 15.7
1996 27.5 23.8 13.6 11.4 21.0 17.5
1997 26.7 23.8 13.6 9.9 20.4 16.9
1998 27.9 21.2 15.1 10.3 21.7 15.5
1999 26.0 22.3 13.9 10.7 20.1 16.8
2000 29.4 25.2 13.4 11.1 22.6 18.3
2001 23.7 23.6 12.3 10.9 18.1 17.4
2002 28.5 24.1 14.6 11.7 21.9 18.1
2003 31.6 26.4 16.5 12.5 24.6 19.7
2004 25.7 20.6 13.6 9.4 19.5 14.9
2005 25.3 22.4 13.3 10.3 19.8 16.6
2006 25.7 22.3 14.3 10.1 20.0 16.2
2007 28.8 23.9 15.4 12.6 22.3 18.0
2008 27.3 24.5 15.7 11.5 21.8 18.0
2009 25.5 25.1 13.0 12.0 19.4 18.5
2010 - 22.1 - 11.9 - 16.7
Note: Max. T and Min. T stand for maximum and minimum temperatures, respectively.
sample size, were crossed individually with virgin females of the Kussnacht strain that were homokaryo-typic for standard chromosomal arrangements in all five chromosomes (A (X), E, J, U and O). Once dissected from third instar larvae, polytene chromosomes were stained and squashed in aceto-orcein solution. At least eight larvae from the progeny of each cross were examined in order to know the inversion pattern of both homologous chromosomes with a probability higher than 0.99. The chromosomal map of KunzeMühl and Müller [21] and Krimbas [22] was used for cytological analysis of the chromosomal inversions and arrangements and their nomenclature that of Kunze-Mühl and Sperlich [23]. Departure of chromosomal karyotypes from Hardy—Weinberg equilibrium and comparisons between samples were analyzed using Fisher's exact test (statistically significant Rvalue <0.05), as it is considered the best procedure in the case of multiple alleles per locus [24], in our case, different inversions (or arrangements) per chromosome. The corresponding p-values were obtained using the bootstrap procedure (100000 runs). These computations were carried out with R packages (http:// CRAN.R-project.org). Confidence intervals (CI) of karyotypic frequencies were estimated according to the binomial distribution.
RESULTS AND DISCUSSION
The observed and expected frequencies of chromosomal karyotypes from Apatin and Petnica are presented in Table 2. With regard to the Apatin population (1994), all chromosomes were in H—W equilibrium: J (-value = 0.8956), U (p-value = 0.8892), E (p-value = = 0.4909) and O (p-value = 0.6626). For the same population, but analyzing the 2008 + 2009 sample, for all chromosomes not significant deviations from H—W equilibrium were detected: J (p-value = 0.8294), U (p-value = 0.9558), E (p-value = 0.9059) and O (p-value = = 0.9288). In the case of Petnica population, for the sample of 1995 all chromosomes were in H—W equilibrium: J (p-value = 0.8973), U (p-value = 0.9311), E (p-value = 0.9967) and O (p-value = 0.8980). Finally, for the same population, but sampled in 2010, H—W equilibrium was observed for all chromosomes: J (p-value = 1), U (p-value = 1), E (p-value = 0.9337) and O (p-value = 0.6089).
In the comparisons between the karyotypic frequencies of both samples of Apatin (1994 and 2008 + + 2009), all chromosomes presented significant differences for karyotypic frequencies with the exception of J chromosome: J (p-value = 0.6376), U (p-value = = 0.0026), E (p-value = 0.0148) and O (p-value = = 0.0007). In 2008 + 2009 sample, karyotypes containing the arrangements U and U1 + 8 + 2 increased in frequencies, whereas karyotypes with Ust tended to
Table 2. Frequencies (in %) of the observed (Obs.) and expected (Exp.) karyotypes from Apatin (1994 and 2008 + 2009) and Petnica (1995 and 2010) populations
APATIN PETNICA
Karyotype 1994 2008 + 2009 1995 2010
Obs. Exp. Obs. Exp. Obs. Exp. Obs. Exp.
Jst/Jst 18.0 15.21 10.0 14.06 5.7 7.51 - 2.56
VJ1 42.0 47.58 55.0 46.88 43.4 39.78 32.0 26.88
J1/J1 40.0 37.21 35.0 39.06 50.9 52.71 68.0 70.56
n 50 50 20 20 53 53 25 25
Ust/Ust 34.0 27.04 - 7.65 - 1.69 - 1.44
Ust/U1 + 2 20.0 23.92 35.0 26.13 15.1 9.80 16.0 11.52
Ust/U1 + 2 + 6 16.0 24.96 10.0 9.63 11.3 12.77 8.0 7.68
Ust/U1 + 8 + 2 - - 10.0 4.13 - - - 1.92
U1/U1 + 2 2.0 0.46 - - - - - -
U1+ 2/U1 + 2 6.0 5.29 20.0 22.56 13.2 14.21 20.0 23.04
U1 + 2/U1 + 2 + 6 12.0 11.04 15.0 16.63 34.0 37.02 32.0 30.72
U1+ 2/U1 + 8 + 2 - - 5.0 7.13 - - 8.0 7.68
U1 + 2 + 6/U1 + 2 + 6 10.0 5.76 5.0 3.06 26.4 24.11 8.0 10.24
U1 + 2 + 6/U1 + 8 + 2 - - - - - - 8.0 5.12
U1 + 8 + 2/U1 + 8 + 2 - - - - - - - 0.64
Other 1.53 3.08 0.4 -
n 50 50 20 20 53 53 25 25
Est/Est 58.0 49.0 30.0 39.06 17.0 16.48 4.0 9.0
Est/E1 + 2 2.0 2.8 - - 3.8 3.09 12.0 3.6
Est/E1 + 2 + 9 16.0 23.8 30.0 18.75 30.1 31.42 24.0 20.4
Est/E1 + 2 + 9 + 12 - - 10.0 6.25 - - 8.0 3.6
Est/E8 6.0 15.4 25.0 22.88 13.2 13.80 8.0 14.4
E1 + 2/E1 + 2 + 9 - - - - 1.9 2.94 - 4.08
E1 + 2 + 9/E1 + 2 + 9 4.0 2.89 - 2.25 17.0 14.98 8.0 11.56
E8/E8 2.0 1.21 5.0 3.06 3.8 2.89 4.0 5.76
E8/E1 + 2 2.0 0.44 - - 1.9 1.29 - 2.88
E8/E1 + 2 + 9 10.0 3.74 - 5.25 11.3 13.16 28.0 16.32
E8/E1 + 2 + 9 + 12 - - - - - - 4.0 2.88
Other 0.72 2.5 - 5.52
n 50 50 20 20 53 53 25 25
Ost/Ost 44.0 37.41 10.0 16.0 15.1 12.82 3.7 4.93
Ost/O6 8.0 7.32 - - - 0.64 - -
Ost/O22 - - 5.0 2.0 1.9 0.64 - -
Ost/O3+4 14.0 28.06 45.0 32.0 30.1 28.35 29.7 18.91
Ost/O3 + 4 + 1 8.0 9.76 5.0 4.0 7.5 10.17 3.7 4.93
Ost/O3 + 4 + 2 4.
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.