Karyological study of cicindelidia trifasciata (coleoptera, cicindelidae) from cuba: evidence of B chromosomes

Karyological study of Cicindelidia trifasciata (coleoptera, cicindelidae) from Cuba: evidence of B chromosomes

Sónia J.R. Proença, M.J. Collares-Pereira and A.R.M. Serrano

Centro de Biologia Ambiental/Departamento de Zoologia e Antropologia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Edifício C2, 3º Piso, 1700 Lisboa, Portugal. Send correspondence to M.J.C.-P. Fax: [phone]. E-mail address: [e-mail]

ABSTRACT

Metaphases from germinal tissue of eight males and seven females of Cicindelidia trifasciata from Cuba were analyzed. The species karyotype does not fit the pattern described for Nearctic cicindelids (2n = 18 + XXY): it has 11 autosome pairs and a sex chromosome system of the X₁X₂X₃Y/ X₁X₁X₂X₂ X₃X₃ type, thus a diploid value of 2n = 26 in males and 2n = 28 in females. The first two autosome pairs were almost twice as large as the remaining chromosomes, and the sex elements were morphologically well differentiated. This population was found to be polymorphic for supernumerary chromosomes at both the intraindividual and interindividual levels. An extra small B chromosome was observed in all metaphases of one male (2n = 27), and every female showed metaphases with one to three small Bs, with a clearly higher frequency of cytotype 2n = 29.

INTRODUCTION

Very few cicindelid species have been karyotyped, not exceeding 3% of the 2200 described taxa (see Serrano et al., 1986; Yadav et al., 1985, 1987, 1989; Serrano and Collares-Pereira, 1989, 1992; Collares-Pereira and Serrano, 1990; Galián et al., 1990). The majority belong to the Palearctic and Oriental regions, particularly the Iberian Peninsula and India. There are a few karyotypic descriptions of Nearctic species but no reports from cicindelids living in Australian, Neotropical and Afrotropical regions.

Cicindelidia trifasciata is a species with a wide distribution area, extending from North to South America, from the Bahamas to the islands adjacent to the South American coast, west of Trinidad. The aim of the present study is to describe the karyotype of this Nearctic cicindelid based on material collected from a population in Cuba, which exhibits an apparently well-differentiated B chromosome system.

MATERIAL AND METHODS

Adult beetles (nine males and 11 females) were collected at Varadero (El Laguito), from Cuba, on August 14, 1991. Karyological analyses followed the method described by Shaw et al. (1976) and later modified by Rozek (1983). Gonads were dissected from ethyl-acetate-anesthetized beetles, treated with a hypotonic solution of colchicine (0.05% w/v colchicine in 1% sodium citrate) for 20 min at room temperature and fixed with methanol-acetic acid (3:1). These were suspended in a solution of glacial acetic acid:double distilled water:methanol (7:2:1) and the air-dried slides were stained in a 4% Giemsa solution (M/15 Sorensen's buffer, pH = 6.8) for 30-40 min at room temperature.

Well-spread spermatogonial and oogonial metaphases were analyzed and photographed and the best plates selected for statistical analysis, as described in Serrano (1990). The nomenclature proposed by Levan et al. (1964) was followed for the classification of each homologous pair.

RESULTS

Eight males and seven females provided good mitotic metaphases, all with 11 pairs of autosomes. The female set had two more chromosomes (2n = 28) than the male set (2n = 26), therefore the sex chromosome system is of the X₁X₂X₃Y/X₁ X₁X₂X₂X₃ X₃ type (Figure 1A,B).

Figure 1
- A-D, Karyotypes of Cicindelidia trifasciata: (A) male (2n = 26), X5000; (B) female (2n = 28), X5000; (C) male with one B (2n = 27), X5000; (D) female with one B (2n = 29), X5000; (E) oogonial metaphase with two Bs (2n = 30), X4000; (F) oogonial metaphase with three Bs (2n = 31), X5000. Arrows in E and F indicate supernumerary chromosomes; (G) Diakinetic figure, male (2n = 26), X5000. Arrow indicates association bivalent-sex chromosome complex.

Supernumerary chromosomes were found in one male and in all females (Table I). However, the male had a B chromosome in all observed metaphases, giving a 2n = 27 cytotype (Figure 1C), while most females had cells with one to three B chromosomes (Figure 1D,E,F), with a modal number of 2n = 29. The finding of two females where all cells had more than 2n = 28 (1f and 8f) might be explained by the extremely low number of mitoses observed for those individuals (Table I).

Table I
- Distribution (number of metaphases) of diploid chromosome numbers in the specimens of Cicindelidia trifasciata analyzed.

Male No.	2n		Female No.	2n
	26	27		28	29	30	31
1m	11	-	1f	-	2	2	-
2m	7	-	2f	1	7	5	3
3m	13	-	3f	8	11	-	1
4m	7	-	7f	1	-	-	1
5m	1	-	8f	-	1	4	1
6m	5	-	9f	3	2	2	-
7m	2	-	11f	2	3	1	-
8m	-	8
Total	46	8		15	26	14	6

The first two chromosome pairs represent about 40% of the chromosome set of females and 38% of males. The remaining chromosomes, much smaller, gradually decreased in size. The chromosomes were meta- and submetacentrics. However, the last five chromosomes in the female karyotype were very small, making it difficult to determine the exact location of centromeres (Figure 2B,D).

Figure 2
- Idiograms of Cicindelidia trifasciata: (A) male, 2n = 26; (B) female, 2n = 28; (C) male with one B, 2n = 27; (D) female with one B, 2n = 29. RL - Relative length; chromosomes 18 to 22 were represented in females by vertical bars due to the difficulty in determining the exact position of centromeres.

The Y chromosome was the largest sex chromosome, being morphologically well-differentiated from the others, and almost twice the size of chromosomes X₂ and X₃. Male figures of meiosis I were made up of 11 bivalents either rod- or ring-shaped, and of a sex chromosome complex with four elements (Figure 1G). In all the figures one of the bivalents was apparently associated with the sex chromosome complex. A few spermatogonial metaphases with 52 and 54 chromosomes (the latter only in the male with 2n = 27) were also found due to technical artifacts.

The supernumerary chromosomes were the smallest chromosomes in the genome and it was not possible to determine the exact position of the centromere, and therefore their shape. Significant differences between individuals with and without supernumerary chromosomes in terms of the size and shape of the standard chromosomes were not apparent (Figure. 2C,D). The only exception concerns the morphology of the X₃ chromosome, which in the male with the B chromosome was metacentric (arm ratio, AR = 1.39), while in the other males with 2n = 26 it was submetacentric (AR = 1.90). This could be due either to misidentification or to measurement errors, but could be due to interindividual polymorphism. However, some differences in the morphology of this chromosome, as well as for chromosome 15, between male and female normal metaphases were also observed (Figure 2A,B).

DISCUSSION

The karyotype of C. trifasciata is asymmetric and has some interesting features, such as: 1) large size of the first two autosome pairs in comparison to the remaining chromosomes; 2) an apparent association of one pair of autosomes with the sex chromosome complex in diakinesis, and 3) supernumerary chromosomes both in males and females.

Although common in some other groups (see revision of Beukeboom, 1994), in cicindelids B chromosomes were until now only reported by Serrano et al. (1986). They were also found in germinal tissue of Cylindera (Cylindera) paludosa in six out of the 10 males analyzed. No intraindividual polymorphism was found. Specimens possessing B chromosomes are apparently phenotypically indistinguishable from those without. Their origin is still unknown, although some hypotheses have been suggested. They may have arisen from trisomic autosome variants, with evolution acting on the univalent unpaired A chromosome via mechanisms similar to those operating on sex chromosomes. This is substantiated to a certain extent by the finding that some B chromosomes share homology with certain regular A chromosomes (Beukeboom, 1994), but the same may happen with the X chromosomes, as has been suggested for Orthoptera (Jones, 1985). The existence of metaphases in the same individual with different numbers of Bs suggests somatic non-disjuction. Thus, non-disjunction at mitosis can be the commonest method of B accumulation, and is assumed to be the cause of the numerical variation among different follicles of the gonads. In the majority of cases, the B chromosomes segregate at random with autosomes and sex chromosomes. If males with 2n = 27 are fertile and the B chromosome assortment follows the X chromosomes, females with 2n = 29 might be produced in this population, which would explain the apparently high frequency of this cytotype.

In the genus Cicindelidia (according to the systematic criteria of Rivalier, 1954 and Wiesner, 1992), the only species karyotyped until now was Cicindelidia punctulata (n = 10 + Xx) (Goldsmith, 1919). However, the sex chromosome system then suggested was later considered incorrect by Smith and Edgar (1954), and it was not revised. Therefore, no comparison of the karyotypes of the two taxa (Cicindelidia punctulata and Cicindelidia trifasciata) can be performed.

Considering the correlation between biogeographic region and karyotype suggested by J. Serrano (1986) (Oriental region - 2n = 20 + XXY, Palearctic region - 2n = 18 + XXXY and Nearctic region - 2n = 18 + XXY), this species seems to be an exception to the Nearctic type, because it has more autosome pairs and a distinct sex chromosome system. Other cases of deviations from this correlation were already reported for the Palearctic fauna (Serrano and Collares-Pereira, 1989). In the Nearctic region, karyotype descriptions only exist for 10 species and four of them need to be revised, according to Galián et al. (1990).

ACKNOWLEDGMENTS

Thanks are due to Centro de Biologia Ambiental for providing equipment and facilities. This work was also supported by Sociedade Portuguesa de Entomologia and by a grant of 3/Prodep/96.

RESUMO

Metáfases provenientes de tecido germinal de oito machos e de sete fêmeas de Cicindelidia trifasciata provenientes de Cuba foram analisadas. O cariótipo da espécie não segue o padrão descrito para os cicindelídeos da região Neártica: possui 11 pares de autossomas e um sistema cromossómico sexual múltiplo do tipo X₁X₂X₃Y/X₁ X₁X₂X₂X₃ X₃, sendo por isso o valor diplóide de 2n = 26 nos machos e 2n = 28 nas fêmeas. O tamanho dos dois primeiros pares de autossomas era quase o dobro dos restantes cromossomas e os elementos sexuais eram morfologicamente bem diferenciados. A população estudada é polimórfica no que respeita à existência de cromossomas supranumerários quer a nível intraindividual quer interindividual. Um cromossoma B extra foi observado em todas as metafáses de um macho (2n = 27) e todas as fêmeas possuíam metáfases com um a três pequenos cromossomas Bs, apresentando uma clara dominância do citotipo 2n = 29.

REFERENCES

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(Received February 26, 1998)

Publication Dates

• Publication in this collection
  02 June 1999
• Date of issue
  Mar 1999

History

• Received
  26 Feb 1998