Chromosome numbers and karyotypic evolution of Caraboidea

transcript

J. Serrano Museo National de Ciencias Naluraies, CasteDana 80, Madrid 6, Spain

Abstract

The chromosome numbers of 136 species of the Spanish caraboid fauna were studied. The most frequent karyotypes are 2n = 37 (54 species) and 2n = 24 (23 species), and the chromosome number ranges from 2n = 21 to 2n = 69, of which 2n = 69 is the highest diploid number hitherto found among the Coleoptera. It is proposed that 2n = 37 is the ancestral karyotype of the division Caraboidea and the suborder Adephaga as opposed to that of the suborder Polyphaga, 2n = 20, Karyotypic evolution has led to increases and decreases of this number, both tendencies having taken place in four genera. Species of ten genera show a neo-XY bivalent due to an X-autosome fusion. The thirty-three chromosome numbers of Caraboidea reveal that these Coleoptera have a remarkable karyotypical heterogeneity.

Introduction

The number of caraboid beetles cytologically known is 138. Data of chromosome numbers have been compiled by Smith (1953,1960), Bouix (1965), Wahrman (1966) and Wilken (1973). The Cara- boidea show a wide range of chromosome numbers, between 2n = 8 and 2n = 44, and only 6% of the species have a chromosome number lower than 2n = 18 + Xyp, the ancestral karyotype of the order. For this reason Caraboid beetles differ from other major groups of Coleoptera (mainly those belong- ing to the suborder Polyphaga) that are characterised by karyotypes of 20 chromosomes.

Smith (1950) has suggested that the high diploid numbers of Caraboidea have arisen from the ancestral karyotype of 20 chromosomes through repeated dissociations. Wahrman (1966) has com- mented on the possibility of a low-numbered karyotype, and Bouix (1965) has postulated an ancestral karyotype with 37 chromosomes for these Coleop- tera.

In this paper 136 species of the Spanish caraboid fauna are analyzed cytologically, bringing the total number of species studied till now to 257. Using

Genetica 55,51-60 (1981). 016-6707/81/0551-0051/$2.00. @ Dr W. Junk Publishers, The Hague. Printed in The Netherlands,

these data this work discusses the problem of the ancestral caraboid karyotype and the subsequent patterns of karyotypic evolution.

Material and methods

Adult insects were collected in Spain between 1973 and 1977, and identified by the author. The species are listed in Table 1 following the catalogue of the Iberian caraboid fauna of Jeanne (1965, 1966, 1967a, b,c, 1968a, b,c, 1969, 197la, b, 1972a, b, 1973). The systematic criteria used in this work are essentially those of Jeanne1 ( 1941, 1942). Karyological studies have been made on male gonads, the testis being dissected and hypotonized in deionized H*O (5-10 min), fixed in ethanol- acetid acid (3: l), stained with lacto-propionic orcein (lo-20 min) and squashed. A minimum of ten gonial or meiotic metaphases were scored in each individual.

Results

Table 1 shows the chromosome numbers, the localities, and the number of individuals studied.

Tab/e /. Chromosome numbers of Caraboidea,

Species (Reference Nr)

Number of 2n n individuals studied

Localities

Carabidae Carabini - Oreocarabus nentoralis

meridionalis Lap. cl)* (2)

0. errans Gory. Hadrocarabus lusitanicus

brevis Dej. H. cantabricus

Chevr, Chrvsocarabus splendnes 01.

(3) (2) (4)

C. lineatus Dej. a) ssp. basihcus Chevr, b) ssp, lateralis Chevr.

(3) (4)

Ctenocarabus galicianus Gory.

Iniopaehys p.vrenaeus occidentalis Jeann.

Megodontus purpurascens fulgens Charp. (1) (2)

Cicindehdae Cicindelini

Cicindela eampestris L.

(6) C. maroccana

pseudomarocana Roes. Scaritidae

Dyschiriini Dvschirius attenuatus Putz.

Scaritini Scarites planus Bon. S. buparius Forst.

Trechidae Trechini

Trechus obtusus Er. Bembidiidae

Tachyini Tach.vura pat-vu/a Dej.

Bembidiini Asaphidionflavipes L.

28 28 28 28

29 28 28

28 28 28

13+xy l3+xY 13+xy

l3+xY I4 + x 13+xy

13+xy 13+xy

l3+xY l3+xY

l3+xY 13+xy

9 + X,X>XJY 9 + X,XZXjY

9 + X,XZX3XdY

19 + x 17 + X,XzY

II +xY

Pto. Lunada (Burgos)

lnvernadeiro (Orense)

Pefialara (Madrid)

Moscoso (Pontevedra)

Isaba (Navarra)

Pto. Lunada (Burgos) Moscoso (Pontevedra), Invernadeiro

(Orense)

Invernadeiro (Orense)

Monte Tobazo (Huesca)

Canfranc (Huesca)

Panticosa (Huesca), Ontfgola (Madrid)

lnvernadeiro (Orense)

Rfo Manzanares (Madrid)

Dofiana (Huelva) Torremolinos (Malaga)

Manzanares el Real, Madrid (Madrid)

R(o Sangrera (Toledo)

Rio Tajutia (Madrid)

Table Z (Cont.)

Number of individuals studied

2n n Localities

Notaphus warms 01, 8 24 ll+xY

N. ephipius Marsh. Emphanes riwdaris Dej. E. tenellum Er. Trepanes assimihs Gyll. T. jmnigatus Duft. T. octomactdatus Goeze.

24 24 24

ll+xY II +xY ll+xY

II +xY ll+xY

Philochtus iricolor Bed. 5 24 ll+xY Bembidion quadripustulatus Sew I 24 II +xY Ocydromus atrocoeruleus Steph. 4 24 II +xY 0. jasciolatus Duft. 5 24 ll+xY 0. tibialis Duft. 3 24 ll+xY 0. decorus Zenk, 7 24 ll+xY

0. ripicola Duft. 5 23 II +x

0. ustulatus L. 0. ,femoratus Sturm. 0. hispanicus Dej. 0. stephensi Crotch. Nepha laterale Dej. Odontium striatum F.

24 24 24

11 +xY II +xY II -+XY 11 +xY ll+xY II +xY

Metallina properans Steph. M. lampros Herbst.

Pogonidae Pogonini

Pogonus chalceus Marsh. Pterostichidae

Abacetini Abacetus salzmanni Germ.

Poecihni Lagarus vernalis Paw. Poecilus lepidus Leske.

(7) P. cupreus L.

23 ll+xY 11 +x

3 22 lo+xY Ontigola (Madrid)

2 41 20 + x Rio Sangrera (Toledo)

46 31 31 43

22-+XY

15 + x 21 +x

@I (7)

(9) P. quadricollis Dej. P. vicinus Levr. I? nitidus Dej. Orthomus expansus Mat. Argutor aterrimus nigerrimus Dej,

A. elongatus Duft,

44 44 43 43 43 41 37 34 37

21 +xY 21 +xY ?I +x 21 +x 21 +x 20 + x 18 + X 16+XY 18+X

Entrepeiias, Rio Ablanquejo (Guadalajara), Rio Manzanares (Madrid), Dofiana (Huelva) Dofiana (Huelva) Dofiana (Huelva) Titulcia (Madrid) Ontigola (Madrid) Titulcia (Madrid) Titulcia (Madrid)

Yesa (Zaragoza), Titulcia (Madrid) Ontigola (Madrid) Rio Trema (Burgos) Rio Trema (Burgos) Lnvernadeiro (Orense) Rio Trema (Burgos), Rio Ablanquejo (Guadalajara) Buendia. Rio Ablanquejo (Guadala-

jara) Rio Trema (Burgos) Anso (Huesca) Rio Manzanares (Madrid) Invernadeiro (Orense) Rio Manzanares (Madrid) Entrepefias (Guadalajara), Rio Manza- nares (Madrid) Bocos (Burgos) Rio Mores (Segovia)

Ontfgola, Titulcia (Madrid) Panticosa (Huesca)

Ontigola, Titulcia, Montejo (Madrid), Bocos (Burgos)

Dofiana (Huelva) Dotiana (Huelva) Dofiana (Huelva) Vellon (Madrid, San Javier (Murcia) Vellon (Madrid), Rio Tietar (Avila), Cornejo (Burgos) Ontigola, Titulcia (Madrid), Aran- zueque (Guadalajara)

Table I (Cont.)

Localities

Pterostichini Platvsma nigrita F.

P. nigrita F. (7)

Plafysma gracile Dej. Platvsma nigrum Schall. (8)

Srero~us madrdus F. S. ghiliani Putz. S. globosus ebenus Quens. Petrophilus brevipennis Chew. Pterosnchus crisiatus camabricus Schauf

(7) Anchomenini

Europhilus thoreyi melanocephalus Dej, (7)

Agonum marginalum L. A. lugens Duft. A. ruficornis Goeze.

Sphodrini Anchomenidius astur Sharp. Platyderus lusitanieus Dej. P. varians Schauf Calathus ambiguus chevrolari Gaut. C. errams Shalb.

(8) C. asluriensis Vuill. C. granafensis Vuill. C. circumseprus Germ. C. mollis Marsh C. melanocephalus L.

(81 C. rotundatus Duv. C. jiiscipes iruermedius Gaut.

W C. dejeani hispanicus Gaut.

C. vuiliefro.vi Gaut.

C. minums F. Eucrvpiotrichus pineiicola Graells.

Zabridae Amarini

Amara aenea de Geer. A. familiaris Duft.

40 46 37 37 37 37

37 37 37 37

35 35 37 34 37

37 37 37 39 31 43 39 37 37 39 37

39 37 37

19+xy 22+xy 18 +X 18 + X I8 + X 18 + X I8 + X

18+X 18 + X I8 + X

17+x 17+x 18 + X l6+XY 18 + X

18+X 18+X 18+X 18+X

18+X 18+X

19 + x 18+X 18+X

18 + X

18 + X I8 + X

17 + x 16+X 16+XY

VeIlon, S. Agustin de Guadalix (Madrid) Vellon (Madrid), lnvernadeiro (Orense)

Titulcia (Madrid) Montejo (Madrid)

Canfranc (Huesca) Pto. Cotos (Segovia) Vellon (Madrid), Cornejo (Burgos) lnvernadeiro (Orense) lnvernadeiro (Orense)

Titulcia (Madrid)

Yesa (Zaragoza) Titulcia (Madrid) Veilon (Madrid). Caurel (Lugo)

Invernadeiro (Orense) lnvernadeiro (Orense) Pto. Cotos (Segovia) Vellon, Madrid (Madrid) Canfranc, Villanua (Huesca)

lnvernadeiro (Orense) Colmenar Viejo (Madrid) Cabrera (Baleares) Vellon (Madrid) lsaba (Navarra), Cuenca (Cuenca)

lnvernadeiro (Orense) Villalba, Montejo (Madrid), Tafavera (Toledo), La Adrada (Avila), ViLLantia, Jaca (Huesca), Cornejo (Burgos) Talavera (Toledo)

La Barranca (Madrid), Pto. Cotos (Segovia) Pefialara (Madrid), Pto. Cotos (Sego- via) Moscoso (Pontevedra) Las Cerradillas (Madrid)

Montejo (Madrid), Jaca (Huesca) Buendia (Guadalajara)

Table I (Cont.)

Localities

C.wtonotw aulicus Panz. Zabrini

Zabrus seidhtzi Schaum. Harpalidae

Anisodactylini Anisodactylus hispanus Puel. A. kens Dej.

Ditomini Carterus rotundicollis Ramb. C. fulvipes Latr. Ditomus capito obscuroides Paul. D. c(vpeatus Rossi.

D. sphaerocephalus 01. Harpalini

Ophonus cordatus Duft.

0. parallelus Dej. 0. brevicollis Serv. 0. azureus F. 0. similis Dej. 0. subquadratus Dej. 0. ardosiacus Lutsh. 0. rufipes de Geer. Harpalus afJnis Schrank.

(~0) H. aescuians Pant. H. distinguendus Duft,

H. contemptus Dej. 2 H. oblitus patruehs Dej. I H. dimidiatus Rossi. 1

H. attenuatus Steph. H. rubripes Duft. H. tenebrosus Dej.

H. stratus Latr. H. sulphuripes Germ. H. honestus Duft. H. wagnerii Schaub. H. decipiens Dej.

H. neglectus Serv.

H. anxius subcylindricus Dej. H. serripes Quens.

Acinopini Acinopus picipes 01.

31 31 31 31 37

31 31 35

31 31 31

31 30 37

37 31 39

28 + X Las Cerradillas. La Barranca (Madrid)

18+X Becerril, Colmenar Viejo (Madrid) 18 + X Ontigola (Madrid)

28 + X 34 + x 22 + x

27 + x

Valdemoro (Madrid) Cobefias, Valdemoro (Madrid) Rio Sangrera (Toledo) Ibiza (Baleares), Huertahernando (Gua- dalajara) Vellon, Montejo, Patones (Madrid)

18 + X

18+X 18+X 18 + X 18-I-X I8 + X 18+X I8 + X 18+X 18+x

La Barranca (Madrid), Huertahernando (Guadalajara) Huertahernando (Guadalajara) Ontigola (Madrid) Huertahernando (Guadalajara) Buendia (Guadalajara) S. Agustm de Guadalix (Madrid) Jaca (Huesca) Jaca (Huesca) Cornejo (Burgos)

Masegoso (Guadalajara) Armufia (Guadalajara), Madrid (Madrid)

18+X 18+X 17 + x

La Barranca (Madrid) Bocos (Burgos)

18+X 18 + X 18 + X

18+X 18+X 18+X l4+xY 18+X

i8 + x

Armutia, Aranzueque, Huertahernando (Guadalajara), Jaca (Huesca), Navas de Riofrio (Segovia), Cornejo (Burgos) Los Molinos (Madrid) Canfranc, Jaca (Huesca) Jaca (Huesca), Valdemoro (Madrid), S. Javier (Murcia) Canfranc (Huesca) Villantia (Huesca) Panticosa, Canfranc (Huesca) Los Molinos, Colmenar Viejo (Madrid) Pto. Cotos (Segovia), Las Cerradillas (Madrid) Rfo Sangrera (Toledo), El Pardo (Madrid)

18 + X S. Agustin de Guadalix (Madrid) 18 + X Isaba (Navarra) 19 + x Jaca (Huesca)

Canfranc (Huesca)

Jaca (Huesca), La Adrada (Avila), Buendia (Guadalajara)

Table I (Cont.)

Localities

Selenophorini hmphonus hirsufulus Dej.

Stenolophini Slenolophus teutonus Schrank. S. proximus Dej. S. mixlus Dej.

Chlaemdae Chlaenini

Chlaenius velulinus auricollis Gene.

C. spoliatus Rossi. Chlaeniellus vestirus Payk.

Dinodes fulgidicollis Duf. Licinidae

Licinini Licinus punclatulus F.

a) ssp. punctufulus b) ssp. grurzulatus Dej.

Badistrini Baudia anomala Perris.

Lebiidae Cymindini

Cymindis bedeli Tschits. C. lineolu Duft.

Syntomini Syntomus foveatus Fourcr.

Lyonichini Lyoniehus albonolalus Dej.

Dryptidae Dryptini

Dr.yp~u denrulu Rossi. Brachynidae

Brachynini Brach.vnus crepitans L. B. plagiatus Reiche. B. sclopela F. B. variivenfris Schauf.

B.fulvivenrris Motsch. B. exhalans Rossi.

2 20 + x Vellon (Madrid)

2 ll+xY VeIlon (Madrid) I 24 Dofiana (H uelva) I 36 17+xy Titulcia (Madrid)

II 37 I8 + X

4 37 18+X 8 37+ 18+X

VeIlon (Madrid), Aranzueque (Gua- dalajara) Vellon (Madrid), Doriana (Huelva) Vellon (Madrid)

IB I 37

2 26 4 26

2 2 37

2 16+X S. Agustin de Guadalix (Madrid)

I 39 I 32

IO 32 3 32

8 25 4 21

15+xy Becerril (Madrid)

IO + x

Ontigola (Madrid) Ontfgola (Madrid) Valdemoro (Madrid) VeIlon, S. Agustin de Guadahx (Madrid) Valdemoro (Madrid) Dofiana (Huelva)

12+xy Cabrera (Baleares) 12+xy S. Javier (Murcia)

22 + x Titulcia (Madrid)

21 +x Valdemoro (Madrid) S. Agustin de Guadalix (Madrid)

20 + x Valdemoro (Madrid)

Canfranc (H uesca)

*References: (I) Bouix, 1962; (2) Weber, 1966; (3) Puissegur & Bouix, 1963; (4) Mossakowski & Weber, 1976; (5) Bouix, 1965; (6) Guenin, 1952; (7) Nettmann, 1976; (8) Wilken, 1973; (9) Kowalczyk, 1976; (IO) Smith, 1960.

The chromosome numbers vary between 2n = 21 bini by 2n = 28, the tribe Bembidiini by 2n = 24, (Brachynus exhalans) and 2n = 69 (Ditomus and the tribes Pterostichini, Sphodrini, Harpahni, capita), 2n = 37 (54 species) being the most and Chlaenini by 2n = 37. The tribes Ditomini and common karyotype, followed by 2n = 24 (23 Zabrini show unusually high chromosome numbers species). Some of the most widely studied tribes are among caraboid beetles, between 2n = 45 and 2n = characterized by a basic karyotype: the tribe Cara- 69.

No. of species

8 24 28 37 46 57 69 2n

Fig. /. Frequency distribution of male diploid chromosome numbers of 257 species of Caraboidea.

One B-chromosome was found in Chlaenius vesrjlus. This is the first time that these chromosomes have been reported in Caraboid beetles.

In the histogram it can be observed that: (a) there are three modes corresponding to the diploid numbers of 24 (27 species), 28 (41 species), and 37 (87 species); (b) the numbers are more definitely grouped around the most frequent mode, 2n = 37; (c) there are thirty-three different chromosome numbers ranging from 2n = 8 to 2n = 69. The latter is the highest number hitherto found among the Coleoptera, so that the diploid range of Caraboidea is also that of the order.

Five species seem to be numerically polymorphic: Poecilus cupreus, 2n = 43, 44, Platysma nigrita, 2rr = 41, 43 (2n = 40, 46 according to Nettmann, 1976), Calathus fuscipes, 2n = 37, 39, Amara familiaris, 2n = 33 (2n = 34, according to Smith (1960), Harpalus serripes, 2n = 37, 39.

Discussion

.The ancestral karyotype of Caraboidea

The male diploid number of Caraboidea is The three modes observed in the histogram are represented in the histogram of Figure 1. Presum- not equally representative. The first one, corre- ably erroneous results of Karppinen (1956) and sponding to 2n = 24, is mainly due to the tribe Puissegur & Bouix (1963) which figured in the Bembidiini (24 species), and the mode of 28 chro- histogram of Wahrman (1966) have been replaced mosomes is characteristic of the tribe Carabini (36 by those of Weber (1966, 1968). The results of species); by contrast the most frequent mode 2n = Bouix (1965) have been added together with those 37, is found in eleven tribes. Based on the represen-

published after Wahrman by Weber (1966, 1968, and in Wilken, 1973), Lahiri and Manna (1969), Kudoh et al. (1970), Kiauta & Brandmayr (1971) Sanyal(l971), Mossakowski& Weber( 1972,1976), Manna & Lahiri (1972), Dasgupta & Chakravarti ( 1973), Wilken ( 1973), Brandmayr & Kiauta (1973) Nettmann (1976) Kowalczyk (1976), Petitpierre, Takenouchi & Virkki (in Smith & Virkki, 1978) including those of the present paper as well. We have also added the chromosome numbers of the family Cicindelidae (included in the division Cara- boidea by Jeannel, 1941) determined by Guenin (1952), Smith & Edgar (1954), Joneja (1960) Dasgupta (1967) and Giers (1977). Earlier reports of Stevens (1906,1909), and Goldsmith (1919) have not been taken into account in view of the results of Smith & Edgar (1954).

The number of species included in the histogram is 257, but the total of chromosome numbers is 267, because of the polymorphic species. Besides those already mentioned there are three more: Bradybae- nus festivus, 2n = 37 (Joneja, 1960) 2n = 36 (Dasgupta & Chakravarti, 1973), Pheropsophus catoirej, 2n = 35 (Joneja, 1960; Agarwal, 1962), 2n = 27 (Dasgupta & Chakravarti, 1973) and Chlae- nius xanthospilus, 2n = 34 (Lahiri & Mandrira, 1969), 2n = 36 (Sanyal, 1971).

tativeness of this karyotype, Bouix ( 1965) suggested that it might be the ancestral karyotype of Cara- boidea. The existence of dytiscid beetles, included in the suborder Adephaga like the Caraboidea, with a diploid complement of 37 chromosomes (Smith, 1960; Suortti, 197 1) favours the hypothesis that 2n = 36 -I- X is the primitive karyotype of the suborder Adephaga, in contrast to that of the suborder Polyphaga with 2n = 18 -t X+ chromosomes. Thus morphological and anatomical differences between both suborders seem to be corroborated by karyotypical ones.

It is generally admitted that 2n = 18 + Xy is the ancestral karyotype of the order Coleoptera, !o that the karyotype with 37 chromosomes must be con- sidered as a derived one. Smith (1950) has postulated that the high chromosome numbers of Caraboidea are due to dissociations of metacentric chromosomes. This hypothesis does not seem ade- quate at present because the supposed ancestral karyotype has not yet been found in Caraboidea and the expected karyotypes resulting from dissociations are rather infrequent amongcarabid beetles which are chiefly characterised by meta- or sub- metacentric chromosomes. Smith & Virkki (1978) have suggested that in the case of both ancestral and derived karyotypes with metacentricchromosomes, Robertsonian changes may have been masked by pericentric inversions or by neo-formation of second arms by accretion of heterochrotnatin. However, Weber (1968) found only one pair of ‘diphasic’ chromosomes in species of the genus Carubus s. 1. Our results in this and other genera agree with those of Weber.

The ideas of Wahrman (1960) about the origin of high chromosome numbers in the Caraboidea through repeated polyploidisation of a low-numbered karyotype have been criticised by Smith &I Virkki (1978). With the addition of new chromosome numbers of Caraboidea it is becoming clear that the karyotype of Graphipterus serrator (2n = 8), is an extreme case of a numerical reduction that has also occurred on a lower scale in other genera, as we shall see later.

Karyotypic evolution of Caraboidea

The karyotype with 37 chromosomes must have undergone major changes in ancient times because among the first genera well dated paleontologically

(about middle Tertiary, Handlirsch, l906), there are several that now show stable basic karyotypes clearly different from that with 37 chromosomes, such as Carabus s. l., 2n = 26 + XY, Cicindela, 2n = 18 + XnY, Bernbidion s. l., 2n= 22 -t XY. In ten genera (Harpalus, Chlaenius, and Agonum among others) a tendency to numerical decrease from the karyotype of 37 chromosomes has been observed accompanied by changes in the sex-chromosome systems. The same can also be found in genera with other basic karyotypes such us Carabus s. l., and Ocydromus. The changes in the sex-chromosome systems are probably due to X-autosome fusions and in fact the sexual bivalent of a number of species has the shape, heterochromatin distribution, and chiasma localization typical of neo-XY systems.

The existence of a number of species with a small Y-chromosome suggests that this chromosome may have undergone ‘erosion’ processes, of the kind postulated by John & Shaw (1967). In this way the neo-XY system may have developed into a new X0 one, after the loss of the Y-chromosome. This hypothesis would explain the existence of two sex- chromosome systems (XY and X0) in Poecilus cupreus and Amara familiaris.

In a great number of genera, reiteration of X- autosome fusions and ‘erosion’ of the Y-chromosome may have led to a numerical decrease associated with successive changes in the direction X0-neoXY-X0 . . ., as is the case of the genus Brachynus (Tab. 2).

In other genera the numerical changes have followed the opposite tendency, thus increasing the number of chromosomes of the hypothetical ancestral karyotype. Most species of the genera Pla- tysma, Calathus, and Harpalus, for example, have

Tab/e 2. Chromosome numbers in the genus kuchynu% The progressive numerical decrease is associated with the alternation of XO;XY sex-chromosome systems.

Species 2n sex-chromosomes Authors

crepitans plagiatus variiventris sclopeta

fulviventris exhalans

janthinipennis cordicoUis

39 x0 32 XY 32 XY 32 XY 25 x0 21 x0 18 XY 18 XY

present paper present paper present paper present paper present paper present paper Smith (1960) Smith (1960)

a diploid number of 37 except for a few with 39,40, 41, 43, and 46 chromosomes. The nature of the rearrangements which originated the increase is still obscure, because the orcein technique has ‘not provided conclusive cytological results. The chromosome banding techniques may probably help to solve this question.

Numerical increases reach unusually high values in species of the tribes Ditomini (2n = 45 to.69) and Zabrini (2n = 57). A discussion about the changes that have originated these karyotypes is at present speculative. They might be the result of progressive dissociations or alternatively of polyploid changes followed by numerical decreases.

The multiple X-chromosomes of cicindelid beetles constitute a particular case of numerical increase. Species have been reported with one X- chromosome (Giers, 1977), two X-s (Smith & Edgar, 1954; Joneja, 1960; Dasgupta, 1967), three X-s (Guenin, 1952; Giers, 1977; this paper), and four X-s (this paper).

By comparing the chromosome formula of European and North-American species it can be seen that the increase of heterosomes from the hypothetical ancestral karydtype of the family 2n = 18 -I XY, has taken place without changes in the number of autosomes. Therefore, it does not seem probable that the new.heterosomes have arisen by incorporation of autosomes into the sex-chromosome system, contrarily to the suggestions of White (1973) and Smith & Virkki (1978) about the tene- brionid genus Blaps.

The fact that numerical changes can produce increases as well as decreases in the number of chromosomes explains the shape of the chromosome number histogram. The mode corresponding to the hypothetical ancestral karyotype of 37 chromosomes has nearly symmetrical tails between 2n = 30 and 2n = 46, due to numerical changes in both directions. In fact, both tendencies have occurred in four genera, Harpalus, Poecilus, Caiaihus, and Scarites. The second mode of 28 chromosomes is mainly (95%) due to the tribe Carabini that has been widely studied and shows a remarkable karyotype stability. Deviant karyotypes are found in two species with 27 chromosomes and one with 26; in this family only a tendency to decrease numerically has been manifested (species with 29 chromosomes reported by Puissegur 8~ Bouix, 1963 and Bouix, 1965 must be confirmed, in view of the results of

Weber, 1966, 1968, and in Wilken, 1973). The third mode of 24 chromosomes is due mainly to the great number of Bembidiini species studied (26), which also show numerical stability with the exception of two species having 23 chromosomes. The chromosome numbers of Cicindelidae are also grouped: four species have 21 chromosomes, five have 22 chromosomes, four have 23 chromosomes, and one species has 18 chromosomes. These variations are due mainly to different numbers of heterosomes.

The low-numbered karyotypes on the left repre- sent different stages of numerical reduction. Besides the case of the genus Brachynus mentioned before, we can find another example in Scarites in&s that has 15 chromosomes (Dasgupta & Chakravarti, 1973) while S. subterraneus (Smith, 1960) and S. buparius (this paper) retain the karyotype of 37 chromosomes, and S. planus has 39 chromosomes (this paper). These karyotypes and the unusual one of Graphiplerus serrator 2n = 8 (Wahrman, 1966) may well be the result of complex but not improbable changes that began in the hypothetical ancestral karyotype of 37 chromosomes. Such a numerical reduction has been demonstrated in the acridid Dichroplus silveira- guidoi (Saez and Perez-Mosquera, 1977).

Acknowledgement

I am grateful to Professor Eugenio Ortiz for his guidance in the development of this work and his valuable comments regarding the manuscript. I also wish to thank Dr. Novoa for identifying some specimens. This work has been supported by a grant of Formation de Personal Investigador (C.S.I.C.).

References

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Received 24.9.1979 Accepted 15.2.1980.

Chromosome numbers and karyotypic evolution of Caraboidea

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