Sep 10, 2018 - peregrina, Psylla ledi, Bactericera ciirvatinervis,. Trioza apicalis) B-chromosomes were described always as a single supernumerary element in ...
Folia biologica (Krakow), vol. 47 (1999), No 3-4
B-chromosome Polymorphism in Rhinocola aceris (L.) (Psylloidea, Homoptera) Anna
MARYANSKA-NADACHOWSKA
Accepted September 10. 1999
M A R Y A N S K A - N A D A C H O W S K A A. 1999. B-chromosome polymorphism in Rhinocola aceris (L.) (Psylloidea, Homoptera). Folia biologica 47: 115-121. DilTerent morphological types of B-chromosomes in Rhinocola aceris from Katowice (southern Poland) were found for the first time in Psylloidea. Four types of supernumerary chromosomes: B|, Bi, B,, and B4 were described on the basis of their morphology and heterochromalin pattern. Their behaviour during meiosis suggests a high tolerance of this species for different numbers of B-ehromosomes. Key words: Psylloidea, B-chromosomes. polymorphism, C-bands. Anna MARYA^ISKA-NADACHOWSKA, Department of Experimental Zoology. Institute ofSystematics and Evolution oj Animals. Polish Academy of Sciences, Slawkowska 17, 31-016 Krakow. Poland. E-mail: maryanska(aiisez.pan.krakow.pl
B-chromosomes (Bs) have been reported in numerous species o f plants and animals ( J O N E S & R E E S 1 9 8 2 ) . They can occur in various number and show a different morphological pattern in particular specimens o f a species. Usually, they are not homological with chromosomes o f a given karyotype ( S H A W & H E W I T T 1 9 9 0 ) . Their origin and importance is still not clear. It is generally assumed, however, that they appear as a result o f structural rearrangements of autosomes or sex chromosomes ( H E W I T T 1 9 7 9 ) . The occurrence of Bs is believed to be correlated with changes in environmental factors. It seems that the tolerance for B chromosomes is higher in optimal conditions and lower in a less suitable environment ( H E N R I Q U E S G\LetaL
1984).
In Homoptera B-chromosomes are relatively rare and up to now have been found only in single species o f Aphidoidea, Coccoidea and Cicadoidea (BLACKMAN
1976; N U R& B R E T T
1988; KlRIL-
In six species o f Psylloidea (Cacopsylla crataegi, C. nehiilosa, C. peregrina, Psylla ledi, Bactericera ciirvatinervis, Trioza apicalis) B-chromosomes were described always as a single supernumerary element in the LOVA
set
& KUZNETSOVA
(MATCHARASHVILI
KUZNETSOVA
etal.
1990).
&
KUZNETSOVA
1997;
1997).
Rhinocola aceris is a Palearctic species living on Aceris. It is known from all over Europe with the exception o f the Iberian Peninsulas, and from the Asiari part o f the Russian Federation and Turkey (GLOWACKA & HARISANOV
1983; B U R C K H A R D T
B-chromosomes occur in insects relatively frequently and have been described in numerous groups ( W H I T E 1 9 7 3 ; H E W I T T 1 9 7 9 ) . Orthoptera is a group in which the frequency o f Bs may be compared to that in plants ( H E W I T T 1 9 7 9 ; S H A R M A & S H A R M A 1 9 8 3 ) . Examples o f the highest number and peculiar morphology o f B chromosomes have been found in e. g. Myrmeleotettix maculatiis and Eyprepocnemis plorans (Acrididae, Orthoptera)
&
(JOHN
In the present paper a different number and different morphological types o f B-chromosomes in
& HEWITT
1965; H E W I T T & J O H N 1972;
HENRIQUES-GIL6?/O/.
1982, 1984).
The basic karyotype o f this species is composed o f 1 0 autosomes, o f almost equal size, and the X-chromosome, which is the largest element i n the set ( M A R Y A N S K A - N A D A C H O W S K A et al. 1 9 9 2 ) . The B-chromosome was described for the first time in males o f Rhinocola aceris from Georgia ( M A T C H A R A S H V I L I & K U Z LAUTERER
NETSOVA
1989).
1997).
116
A. MARYANSKA-NADACHOWSKA
a population o f Rhinocola aceris originating from southern Poland (Katowice) are described.
Material and Methods Thirty-nine adult males of Rhinocola aceris were collected in Katowice (southern Poland). Males were fixed in glacial acetic acid : 9 6 % ethanol ( 1 : 3 ) . The gonads were dissected from males in a drop of 4 5 % acetic acid and squashed under a coverslip. The coverslips were removed using the dry ice technique ( C O N G E R & F A I R C H I L D 1 9 5 3 ) . Slides were dehydrated in fresh 1:3 mixture and air dried. Slides were stained with a slightly modified C banding method as follows: treatment with B a ( 0 H ) 2 at 5 0 " C for 5 minutes, rinsed in distilled water three times, immersed in 2 x S S C at 6 0 ° C for 1 hour, rinsed, air dried, and stained with 6 % Giemsa i n Sorensen buffer.
and the X . In B s different sized heterochromatin blocks were visible up to early diakinesis. N o other chromosomes showed heterochromatin. A t metaphase I B-chromosomes were maximally spiralized and heteropycnotic. A t this stage heterochromatin blocks in B-chromosomes were not visible. In autosomes and sex chromosomes heterochromatin blocks were absent (Figs 2-7). B i , B 2 , and B3 types which occurred singly were always located at a distance both from the X and autosomes. A t metaphase 1 a B mainly showed a touch-and-go pairing with the X . A t anaphase 1 they separated one from the other and segregated to opposite poles (Figs 2-7). Four males carried two B chromosomes in every nucleus, two of them B 2 and B3, while two others a pair o f B 4 . In the first two males B-chromosomes
Table 1 B-chromosomes in Rhinocola from Katowice
aceris
Results Number Thirty-two o f males studied showed different ; ofB types and different numbers o f B-chromosomes (Table 1). Twenty-two males carried only one B Type of chromosome i n every nucleus, B | , B 2 , and B3, B types. A t prophase the B was always located separately from X and autosomes. B 2 is the most common Male no type o f supernumerary in the population under 1 study. T w o males carried pair B 4 . The size of the B s 2 as well as their pachytene heterochromatic distri3 4 bution pattern were found to be distinctly variable. B-chromosomes could be classified into four distinct types based on the above characters (Figs 1 -7). BI is distinctly larger than the X and bears a comparatively great amount o f heterochromatin. A t pachytene and diffuse stage several prominent heterochromatin blocks are visible (Figs l a , 2c). B 2 is similar in size to the X , and its banding pattern is similar to that o f B i (Figs l b , 3c). B 3 is much smaller than the X and bears a very small amount o f heterochromatin. A t pachytene and diffuse stage, one heterochromatin block is seen in the middle part o f B3 (Figs Ic, 4c). B 4 is similar in size to the X . H a l f o f B 4 is euchromatic. A t pachytene and diffuse stage, one large intercalary and one small terminal block occur, a short euchromatic part being visible between them (Figs Id, 6c). A t post pachytene diffuse stage, B s were seen positively spiralized comparing with autosomes
5 6 7 8 9 10 ' 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26* 27 28* 29 30 31 32 33-39
0
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_
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117
B-chromosome Polymorphism in Rhinocola aceris
V B2
# B4
•3
Fig. 1. Different types of B chromosomes.
v >
• c
Fie. 2 a-d. Meiosis with BI. (a) pachytene, (b) diakinesis, (c) metaphase 1 with X B 1 pseudo-bivalent, (d) metaphase I with X and B| univalents.
'
f
I
•
/ Fig. 3 a-c. Meiosis with B , . (a) pachytene, (b) diakinesis, (c) metaphase I.
were visible separately from each other at prophase (Fig. 5a). A t metaphase I, one o f them formed a pseudo-bivalent with the X chromosome, whereas the other remained as a univalent (Fig. 5b,c). Thus, pseudo-bivalents X B T or X B 3 appeared randomly and briefly. The pseudobivalent X and B segregated at anaphase 1 to the opposite poles be-
fore autosomes. The univalent B segregated randomly. Sometimes B 2 formed a pseudo-bivalent with B3 whereas the X chromosome occurred as a univalent (Fig. 5d). Sporadically, B 2 , B3, and the X chromosomes formed a trivalent (Fig. 5e). A s a result of the above described segregation patterns the following types o f metaphase II were formed:
118
A. MARYANSKA-NADACHOWSKA
Fig. 4 a-d. Meiosis with B,. (a) pachytene, (b) diaiBi pseudo-bivalent and X univalent, (e) metaphase I with XB2B3 pscudo-trivalcnt, (f-k) metaphases II. (0 5+X, (g) 5+B:, (h) 5+B3, (i) 5+X+B2, Q) 5+X+B3, (k) 5+B2+B3.
5+X, 5+B2 5+B3, 5+X+B., 5+X+B3, 5+B2+B3 (Fig. 5f-k).
In two males displaying a pair o f B4 supernumeraries in prophase B s always formed a chiasmatic bivalent, with one chiasma placed at one o f two euchromatic parts (Fig. 6a-c). A t metaphase I chiasma was terminalized, while at anaphase I B-chromosomes segregated to the opposite poles at the same tempo as autosomes (Fig. 6e, f).
In four males three B-chromosomes, two B4 and one B 2 , were found. A t prophase, bivalent B4B4 with one chiasma and univalent B 2 were visible (Fig. 7a). A t metaphase I B 2 and the X formed a pseudo-bivalent (Fig. 7b) and at anaphase I segregated to opposite poles. Thus, each o f the sister metaphases II contained seven elements: 5+X+B4 and 5+B4+B2 ( F i g . 7c).
Two males were mosaic in respect to the B chromosomes. In one male some cysts bore two supernumeraries ( B 2 and B3), while other cysts
B-chromosome Polymorphism in Rhinocola aceris
119
n
m
d
•
' • .* e
Fig. 6 a-e. Meiosis with B4B4. (a) pachytene, (b) different locations of chiasma, (c) diakinesis. (d) metaphase I with B4B4 bivalent and X univalent, (e) anapnasc 1.
Fig. 7 a-c. Meiosis with B4B4 and B^. (a) pachytene, (b) metaphase 1 with B4B4 bivalent and X B i pseudo-bivalent, (c) anaphase I.
bore three supernumeraries, chiasmatic bivalent B4B4 and univalent B i . In the second male some cysts were found to have only B 2 while other cysts showed a chiasmatic B4B4 bivalent.
Discussion In Homoptera B-chromosomes have been described in Aphidoidea, Coccoidea, Cicadoidea and Psylloidea. Although the relatively many species have been karyotyped to date in these groups, descriptions o f B are few in number ( B L A C K M A N 1976; N U R & BRETT 1988; K l R I L L O V A & K U Z NETSOVA
1990;
MATCHARASHVILI
NETSOVA 1997; KUZNETSOVA
&
KUZ-
Polymorphism o f B-chromosomes in respect to their number, size, heterochromatin pattern and meiotic behaviour is described in Psylloidea for the first time in the present study. Quite recently a similar B-chromosome polymorphism has been described in the grasshopper Eyprepocnemis plorans from different populations of the Iberian Peninsula ( H E N R I Q U E S - G I L et al. 1 9 8 2 ; 1 9 8 4 ) . Polymorphism was shown to be more frequent in populations which inhabit environments most favourable for a particular species. Results obtained in R.aceris seem to agree with these observations. Geographically Southern Poland is placed centrally with respect to the distribution o f this species in Europe.
1997). Among
over 1 5 0 described species o f Psylloidea B chromosomes were reported only in six species. In all cases supernumerary chromosomes occurred as one per nucleus and were both sinaller and/or similar in size to the X . ( M A T C H A R A S H V I L I & K U Z N E T S O V A 1 9 9 7 ; K U Z N E T S O V A e/c//. 1 9 9 7 ) .
It has been shown in some delphacid species (Auchenorrhyncha) that B s occur in various number showing an association with the X chromosome at metaphase 1. In contrast to R. aceris, in delphacid species segregation was irregular, especially in males with more than one B , but meiotic pertur-
120 bances
A. MARYANSKA-NADACHOWSKA
did not occur ( K l R I L L O V A & K U Z N E T -
SOVA 1990).
In Psylloidea the behaviour of Bs during meiosis varies in different species. In all species with XO a single B-chromosome tends to form a pseudobivalent with the X-chromosome. However, in some species the B was found to associate with the X in the majority of metaphases I ( K U Z N E T S O V A et al. 1 9 9 7 ) , while in others {Cacopsylla crataegi and Rhinocola aceris) only in part o f metaphases I ( M A T C H A R A S H V I L I & K U Z N E T S O V A 1 9 9 7 ) . Seg-
regation o f B s was regular in all the above cases. On the contrary, in Bactericera ciirvatinervis with X Y a single B univalent always segregated randomly ( K U Z N E T S O V A et al. 1 9 9 7 ) . In specimens o f R. aceris with a different number of Bs there occurred a distinct tendency to maintain the correct course o f meiosis. In males with two B4 they formed a chiasmatic pair at prophase. In males with single supernumeraries, that is B i , B 2 , or B3 types do not form a pseudo-pair with the X at prophase and only for a short time at metaphase 1. This behaviour resulted in the correct segregation at anaphase I. Abnormalities in the segregation process were observed only in one male with two supernumeraries B 2 and B3. In this case the B , which did not form a pseudo-bivalent with the X , segregated randomly. The maintenance o f a correct course o f meiosis provides the possibility o f accumulating and fixing B-chromosomes in the set. This is also promoted by the holokinetic nature o f psyllid chromosomes, in which no fragment is lost during division being involved in meiosis together with other chromosomes. In insect groups with monocentric chromosomes, supernumerary elements o f karyotype being acentric fragments o f chromosomes, show a very high tendency to eliminate at meiotic anaphase and even during cleavage divisions. O n l y fragments o f chromosomes with centromeres are preserved as Bs in the karyotype ( L O P E Z - L E O N et al. 1 9 9 3 ) . In the organisms with holokinetic chromosomes fusions and fissions are important in the karyotype evolution ( B L A C K M A N 1 9 8 0 ; K U Z N E T S O V A 1 9 9 2 ) .
That is why one may expect that many Bs might occur in their karyotypes. However, in these organisms the Bs do not occur more frequently than in species with centric chromosomes, thus some regulation mechanisms are involved.
It is generally accepted that selective forces act against individuals with a high number o f Bs being, however, counteracted by cytological accumulation mechanisms ( S H A W & H E W I T T 1 9 9 0 ) . On the other hand,it is suggested that some genes suppressing the meiotic drive o f Bs exist ( S H A W et al.
1 9 8 5 ; N U R & B R E T T 1 9 8 8 ; R O M E R A et
al.
1991).
The various number o f Bs at M I indicates that the pre-miotic mechanisms are involved in their accumulation. One o f the common mechanism is nondisjunction o f B-chromosomes during mitosis in germ lines (JONES & R E E S 1 9 8 2 ) . Specific accumulation o f Bs, which mechanisms is supposedly a fragmentation o f already existing supernumeraries, is also registered in groups with holokinetic chromosomes ( K l R I L L O V A & K U Z N E T S O V A 1 9 9 0 ) .
In spite o f the relatively common occurrence o f Bs their origin is not clear. For instance, in Orthoptera ( H E W I T T 1 9 7 9 ) and in Delphacidae ( K l R I L L O V A & K U Z N E T S O V A 1 9 9 0 ) at least some of theBs were suggested as originating from the X chromosome. In the acridid Eyprepocnemis plorans polymorphism o f Bs could be a result o f changes in the most common variant o f B-chromosome ( H E N R l Q U E S - G I L et al. 1 9 8 4 ) . Some B chromosome vari-
ants which are rare in natural populations of E. plorans were recurrently formed in each generation ( L O P E Z - L E O N etal. 1 9 9 3 ) . In R. aceris the various morphological types o f B-chromosomes occur in males collected in the same place and at the same time. Meiotic behaviour o f Bs, their morphology and heterochromatin distribution suggest that the origin o f B | , B 2 , B3 with comparison to B4 is independent. It seems that chromosomes o f B i and B3 types could appear by different transformations, fusions and/or fissions, o f the most frequently occurring B 2 . The homological pair o f supernumeraries B4B4 is suggested as originating by nondisjunction o f sister chromatids o f any initial B4. On the basis o f results obtained in this work, it may be concluded that Rhinocola aceris from K a towice has a very high tolerance for different numbers o f Bs. Only studies o f some other geographically distant populations would answer whether this phenomenon is characteristic o f R. aceris as a whole and what kind o f consequences it bears for the evolution o f the species.
B-chromosome
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ism in Rhinocola aceris
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