Chromosoma. "S", Springer- Verla.g, Heidelberg Mskr. 279 Martin 1-14 Seiten 1-8 H. Sturtz AG, Wiirzburg ZG 6-8 Provisorische Seifenzahl Ii~ '" 1. Korl'. 25.11. 73 Provisional page numbers q. - 'Ii Chromosoma (Berl.) II, II-II (197. © by Springer. Verlag 1973 A Review of the Genus Chironomus (Diptera, Chironomidae) IX. The Cytol~ie of Chironomus tepperi Skuse Jon Martin Department of Genetics, University of Melbourne Abstract. Analysis of the banding pattern of the salivary gland chromosomes of Okironornus tepperi indicates that, despite a somewhat modified male hypopygium, the relationships of this species are close to the other Australian species of the genus, particularly to Ok. oppositus. No inversion polymorphism has been found in Ok. tepperi and this, together with the relatively high chiasma frequency as measured at metaphase I, would appear to be an adaptation to provide genetic variability necessary for its colonizing ability. Introduction The Australian species Ohironomus tepperi is of interest to biologists for a number of reasons . The species is widespread in Australia where it is largely found colonizing rain-filled pools or areas which have been recently inundated (Edward,1964; Martin, unpublished data), such as feshly filled rice paddies where it reaches such high numbers that it is a commercial pest of rice crops (Jones, 1968). Oh. tepperi has apparently dispensed with the necessity to swarm prior to mating, possibly to facIlitate dispersion, and a pair of flies will mate on contact. Consequently the species can be readily bred in the laboratory (Scharf, 1969) and is therefore suitable for genetical or other studies. The species has already been utilized in studies of its haemoglobins (Plagens et al., 1972) and other investigations are under way (Hagele, personal communication). In his revision of Australian Chironomidae, Freeman (1961) noted that the enlarged male hypopygium of Oh. tepperi suggested relationship to Oamptochironomus, although he felt the species was best left in the genus Ohironomus sensu stricto. An analysis of the banding pattern of the salivary gland chromosomes, besides providing essential background information for a laboratory species, might also be expected to indicate whether the relationships of this species are to other Australian species such as Oh. oppositus (Martin, 1969) or to the Oamptochironomus species of Europe and North America (Beermann, 1955; Acton, 1959). 1A Material and Methods Material for cytological p%poses has been collected from many parts of Australia, although details of the localities will not be given. J. Martin 2 Cytological techniques and the details of band identification are as used for Ch. oppositus (Martin, 1969). In making up the photographic plates of the chromosome arms (Figs. 1-8) the convention of Keyl (1962) of having the centromere on the right has been followed . The chromosomes of Ch. tepperi are often of poor quality and show extreme stretching, particularly near the centromere. It ha,s therefore not always been possible to find a single specimen of each arm which showed all regions with clear bands and a similar degree of stretching. Instead it has been necessary in some instances to use a montage of sections from different cells in order to show the bands more clearly. Results Description 01 Salivary Gland Chromosomes Like Ch. oppositus, this species has the chromosome arm combination AE, BF, CD, G-i.e. the pseudothummi-complex, rather than the combination AB, CF, DE, G, of the Camptochironomus-complex possessed by the known Camptochironomus species (Keyl, 1962). No inversion polymorphism has been found in Ch. tepperi. Chromosome I, with arms BF, is very similar in gross morphology . to its counterpart in Ch . oppositus . The sequence in arm B appears to be identical to the Avoca sequence of Ch. oppositus, i.e. with the region from lC3 to 3A7 inverted (Fig. 1). lA IB lC I ID 1-2 '7-1 lA IB lC 3A 2A 2B 2C 2D 3A 3B I 3C 3D ~ 13-3 I 8-11 3A 2D 2C 2B 2A ID lC oppositus Standard 3B 3C 3D oppositus Avoca tepperi Arm F shows the same banding sequence as Ch. oppositus, although some bands differ in staining intensity (Fig. 2). Chromosome II, with arms CD, shows a certain gross similarity to the same chromosome in Ch. oppositus, although the sequences present are different from any known in that species. Arm D (Fig. 3) appears to be derived from a previously undescribed sequence of Ch. oppositus, D4, which differs from the Standard by an inversion from about 8A9 to 9A13 (Cragg, unpublished) . The sequence in Ch. tepperi can then be derived from this sequence by a further two included inversions which share one common breakpoint. The first inversion would have breaks at about 7C3 and 8A17 and gives an intermediate sequence which is hypothetical since it is not presently known to exist. The second inversion is from about 7C3 to 8C1. 7 A 7B 7C 7A 7B 7C I 1-2 7 A 7B 7C 1-2 7 A 7B 7C 7D 8A 8B I 1-8 8A 8C 8D 9A I 9B 20-91 8A 9B 9C 8A 7D 8A 9A 8D 8D 8C 8B 8B 8D 9A 17-20 8A 8B 7D 8A 7D 9A 117 - 20 8A 9D OPPOSilllS Standard \ I 9C I 9D oppositus D4 16-9 8-1 1-8 9 B 9 C 9 D hypothetical 16-9 8C 8A 9B 9C 9D tepperi 4 Figs. 1---4. Chromosomes I and II of Ch. tepperi. Fig. 1 Arm B. Fig. 2 Arm F . Fig. 3 Arm D. Fig. 4 Arm C. Centromeres are on the right in each figure (Figs. 1-8) J. Martin 4 Arm C is considerably changed from any sequence known in Ch. oppositus. Some regions such as lOA-10C9 and 11A4-11C are quite readily recognisable, but other regions cannot be identified with any certainty. The sequence shown in Fig. 4 appears to be the best allocation of bands. However it requires that certain band groups, such as 11D-l1E, must have changed considerably in appearance. This sequence could be derived from the Standard sequence of Ch. oppositus by a simple inversion and two three- break inversions, requiring two hypothetical intermediate steps. Other ways of deriving this sequence can be imagined but they would require more intermediate steps. oppositus lOA lOB lOC lOD 10E 11A 11B 11C 11D 11E I I Standard 1-9 '12-1 lOA lOB lOC 11E 11D 11C 11B 11A 10E 10D 1 12-10 13-15 10C I 11E hypothetical 1 1 , , 1-12 10-12 1-9 3-10 lOA lOB 10C 10E 11A 11B 11C 11D 11 E 110C IOD I I I 1-2 tOE :) 1-9 3-10 1-3 '12-1 lOA lOB 10C 10E llA liE liD 11C liB 11-4 7-1 11A lOD I 13-15 11E 1 12-10 8-11 lOC lOD hypothetical 2 1-2 13-15 lOE liE tepperi An identical sequence occurs in one of the other species currently included in the Ch. alternans group (Martin, 1969). This species is presently undescribed but has been allocated the manuscript name Ch. pseudoppositus . Chromosome III, with arms EA, is once again very similar to its homologue in Ch. oppositus . Arm E carries the Standard sequence (Fig. 5) and arm A the Franklin sequence of Ch. oppositus (Fig. 6), thus also being identical to chromosome III of Ch. australis (Martin, 1971). Chrol1wsome I V , or arm G, appears to differ from that of Ch. oppositus by an inversion of regions 17A to 17C although differences in the appearance of bands make it difficult to be certain. Therefore the breakpoints are difficult to determine but they seem to be about 17A1 and 17C9. 16A 16B 16C 16D 17A 16A 16B 16C 16D 17C : 17B 17C 18A 18B 18C 18D oppositus 17B 17 A 18A 18B 18C 18D tepperi : Cytology of Ckironom1tS tepperi 5 5 16 Figs.5-S. Chromosomes III and IV of Ck. tepperi. Fig. 5 Arm E. Fig. 6 Arm A. Fig. 7 Arm G showing development of puffs in regions 16B and 1SB. Fig. S Arm G with no development of puffs in regions 16B and 1SB (j J. Martin The arm shows a number of different phenotypes due to the development of puffs in 16B and 18B in some specimens but not in others (Figs . 7 and 8). The puff in 18B, which apparently corresponds to the similar puff in Ok. oppositus, is only rarely developed . The puff in 16B, which again could correspond to the puff in this position of Ok. opp08itU8 although it is not as large, exists as a polymorphism in the species, with heterozygotes as well as the two homozygotes occurring, similar to the case reported in a Chinese species by Hsu and Liu (1948). A preliminary study (Martin, 1966) suggests that the alternative forms occur in Hardy-Weinberg proportions but a more careful analysis using similarly aged larvae is necessary to ensure that there is no difference in the occurrence of the puff with larval age which might bias the results. Meiosis Male meIOSIS in Ok. tepperi was studied in seven specimens and found to be essentially similar to that of other species which have been investigated (Wolf, 1941; Martin, 1967; Martin and Sublette, 1972) and no irregular features were noted. Few cells in diakinesis were observed and of these only three were clear enough for the chiasmata to be counted: two had seven chiasmata, the third had six chiasmata. At metaphase I there were regularly two chiasmata in one of the large metacentric chromosomes. The three metacentrics could not be distinguished so it could not be determined if it was the same chromosome in all cases. A second chiasmata was also commonly present in a second metacentric and rarely in all three. The acrocentric chromosome showed only a single chiasmata. In the seven individuals the chiasma frequency at metaphase I ranged from 4.56 to 5.43 chiasmata per cell with an average of 5.11 ± 0.08 chiasmata per cell. This is somewhat higher than the chiasmata/cell values found at metaphase I in Ok. yoskimatsui (Martin and Sublette 1972), Ok. oppositus (4.09), Ok. australis (4.45), Ok. pseudoppositU8 (4 .38), Ok. cloacalis (4 .32),Ok. duplex (3.05) with only three pairs of chromosomes, Ok. zealandicU8 (4.48) or North American Ok. tentans (4.04), but slightly lower than the frequency in Ok. lebruariU8 (5.46). Discussion The banding pattern of its salivary gland chromosomes indicates that OkironomU8 tepperi is nearly related to Ok. oppositU8. Arms B, F, E and A appear identical to sequences present in Ok. oppositU8, arm G differs by a simple inversion, while arms D and C show the greatest deviations, requiring several inversion steps for their derivation. Although somewhat altered compared to Ok. OPPOSitU8, D and C show close relationship to the species with the manuscript name of Ok. pseudop- Cytology of Chironornus tepperi 7 positus, in which arm D is related to that of Ck. tepperi by a further simple inversion (Martin, unpublished) and arm C is identical. There is no cytological evidence to support the suggestion that Ck. tepperi should be placed in another genus or subgenus because it has a somewhat modified male terminalia. The relationships of Ck. tepperi are to the Australian species of the genus Ckironornus with the chromosome arm combination characteristic of the pseudotkummicomplex and not to the Camptockironomus species. The results therefore support Freeman's decision to leave the species in the genus Ckironomu8 (Freeman, 1961). Despite its obvious cytological relationship to Ck. oppositus, Ck. tepperi is apparently on a different line of descent to the australis group (Martin, 1971) although they have some sequences in common e .g . chromosome III of Ck. australis and Ck. tepperi are identical. In other arms the sequence in Ck. tepperi is related to a different sequence in Ck. oppositus to that from which the australis group are derived. Thus arm B of Ck. australis is very similar to the Standard sequence of Ck. oppositus, while arm B of Ck. tepperi is identical to the Avoca sequence. In arm D, Ck. australis has the Warburton sequence of Ck. oppositus, while Ck. tepperi is related to the D4 sequence of Ck. oppositus. This indicates that either Ck. tepperi and Ck. australis have derived from a common ancestor at times when different sequences were present, or that the common ancestor was polymorphic for a number of sequences which still occur as polymorphisms only in Ck. oppositus. Although colonizing species adopt a variety of genetic strategies, it IS common to find that they have reduced chromosomal polymorphism compared to related speCIes (Mayr, 1965). The variability made available by recombination is also considered to be important in the adaptation of colonizing species to new or variable environments (Ellis, Lee and Calder, 1973). Many of the rain-filled pools inhabited by Ck. tepperi are probably colonized by only one or two females. Under these conditions a wide range of phenotypes amongst the offspring would give the greatest chance of survival. The absence of inversion polymorphism in Ck. tepperi and the relatively high chiasma frequency are probably both related to this colonizing habit. A high rate of recombination, as implied by the high chiasma frequency at metaphase I, and the minimum of genome tied up in inversion polymorphisms which would prevent effective recombination, should allow the species a large degree of genetic plasticity, and provide the genetic variability necessary for its colonizing ability. Acknowledgements. This work was supported by Grant D71J17815 from the Australian Research Grants Committee. I am greatly indebted to Miss Elspeth Cragg for providing the details of the D4 sequence in Ch. oppositus, and also to the numerous people who have provided material of Ch. tepperi. Technical assistance 8 J. Martin has been provided by Miss Roslyn Winter and the photographs were prepared by Mr David Jenkins. I also thank Dr. B. T. O. Lee for critically reading the manuscript. References .. , ON ) Acton, A. B.: A study of the differences between widely separated populations of Chirorwrnus (= Tendipes) tentans (Diptera). Proc. roy. Soc. B 1Sl,277-296 (1959) :.. Beerman, W.: Cytologische Analyse eines Camptochirorwrnu.s-Artbastards. 1. Kreuzungsergebnisse und die Evolution des Karyotypus. Chromosoma (Berl.) 7, 198-259 (1955) Edward, D. H. D . : The biology and taxonomy of the Chironomidae of Southwestern Australia. Ph. D. Thesis, University of Western Australia 1964 Ellis, W.M., Lee, B.T.O., Calder, D.M.: Chromosome pairing in Poa annua L. Canad. J. Genet. CytoI. (in press, 1971) :b~reman, P. : The Chironomidae (Diptera) of Australia. Aust. J. Zool. 9, 611-737 (1961) \ Hsu, T.C., Liu, T.T.: Microgeographic analyis of chromosomal polymorphism in a Chinese species of Chironomu.s. Evolution (Lawrence, Pa.) 2, 49-57 (1948) Jones, E.L. : Chironomu.s tepperi Skuse (Diptera: Chironomidae) as a pest of rice in New South Wales . .Aust. J. Sci. 31, §1. (1968) Keyl, H.-G.: Chromosomenevolution bei Chiro'lUJ'fYtu.s. II. Chromosomenumbauten und phylogenetische Beziehungen der Arten. Chromosoma (Berl.) 13, 464-514 (1962) Martin, J.: Population genetics of chironomids: cytogenetics and cytotaxonomy in the genus Chiro'lUJ'fYtus. Ph. D. Thesis, Univ. of Melbourne (1966) Martin, J.: Meiosis in inversion heterozygotes in Chironomidae. Canad. J. Genet. Cytol. 9, 255-268 (1967) Martin, J.: The salivary gland chromosomes of Chironomus oppositu.s Walker (Diptera: Nematocera). Aust. J. Zool. 17, 473-486 (1969) Martin, J.: A review of the genus Chironomus (Diptera, Chironomidae) IV. The karyosystematics of the au.stralis group in Australia. Chromosoma (Berl.) 3S, 418-430 (1971) Martin, J., Sublette, J.E.: A review of the genus Chironomus (Diptera, Chironomidae) III. Chironomus yoshimatsui new species from Japan. East. New Mexico Univ. Stud. Nat. Sci. 1, (3), 1-59 (1972) Mayr, E.: Summary. In: The genetics of colonizing species (H. G. Baker and G.L. Stebbins, eds.) 553-562. New York: Academic Press Inc. 1965 Plagens, U., Fittkau, E.J., Jonasson, P.M., Braunitzer, G.: Vergleichende Untersuchungen der Hamoglobine verschiedener Chironomiden. Abhandl. Dtsch. Akad. Wissensch. Berlin, 183-190 (1972) Scharf, B.: Eine weitere, im Labor leicht ziichtbare ChirO'lUJ'fYtu.s-Art. Chironomus (1111) 1, 50 (1969) Wo~Die Chromosomen in der Spermatogenese einiger Nematoceren. Chromosoma (Berl.) 2, 192-246 (1941) Received September 28, 1973/ Accepted by H. Bauer Ready for press October 2, 1973 Dr. Jon Martin Department of Genetics University of Melbourne Parkville Victoria 3052 Australia Minerva Access is the Institutional Repository of The University of Melbourne Author/s: MARTIN, J Title: A review of the genus Chironomus (Diptera, Chironomidae) IX. The cytology of Chironomus tepperi Skuse Date: 1974-03 Citation: MARTIN, J. (1974). A review of the genus Chironomus (Diptera, Chironomidae) IX. The cytology of Chironomus tepperi Skuse. Chromosoma, 45 (1), pp.91-98. https://doi.org/10.1007/BF00283832. Persistent Link: http://hdl.handle.net/11343/124209 File Description: Accepted version