Cytologia 44: 693-714, 1979 Chromosome Systems in the North American Decticinae' with Reference to Robertsonian Changes (Orthoptera: Tettigoniidae) Norihiro Ueshima1 and D. C. Rentz2 Received January 17, 1978 Differences of chromosome numbers and forms in closely related groups are of great interest as far as chromosome evolution is concerned. However, karyotypes in related groups are sometimes relatively constant, as in grasshopers of the family Acrididae. In the shield-backed katydids (Tettigoniidae) of the subfamily Decticinae, five Old World genera (Decticus, Gampsocleis,Metrioptera, Pholidoptera, and Platycleis) have been recorded as having 2n=30+X in the male (John and Hewitt 1968, White 1973). However, an interesting exception is Lanciana from Australia, described as having 2n=24+X (Ferreira 1969). All above have rod-shaped chromosomes, except for one species, Metrioptera saus sureana (John and Hewitt 1968). The North American Decticinae differ from the Old World genera in having one or more pairs of metacentric chromosomes. McClung (1902, 1905 and 1914) reported 2n=33 in Anabrus sp., with a pair of metacentric autosomes and a sex chromosome of multiple configuration, but White et al. (1967) suggested that its chromosome number was 2n=32 or 34, rather than 33, with a neo-XY sex determining mechanism. Davis (1908) reported 29 chromosomes in Steiroxys trilineata, with a pair of metacentric autosomes. White (1941) investigated Atlanticus pachymerus and showed 2n=24+X, with two pairs of metacentric autosomes and a metacentric X-chromosome. The metacentric autosomes in those species are considered to have arisen by centric fusion (White 1973, John and Hewitt 1968). In the Old World Metrioptera saussureana, John and Hewitt (1968) reported 2n=28+X with a pair of metacentric autosomes, which believed had arisen by centric fusion. We have investigated chromosome systems of North American Decticinae extensively and found an interesting pattern in chromosome evolution. Robert sonian change has played an important role and neo-XY and X1X2Ysex mechanisms have arisen in the genus Neduba. Materials and methods The materials used in this study are listed in Table 1 with collecting data. Testes were fixed in Carnoy and stained with aceto-carmine. Observations were made on squash preparations. Drawings were made with the aid of a camera lucida and are reproduced with 10ƒÊm scale alongside. 1 Matsusaka College, Kubo-cho, Matsusaka, Mie, 515 Japan. 2 CSIRO , Dept. of Entomology, Box 1700, Canberra, Australia. 694 Norihiro Ueshima and D. C. Rentz Cytologia 44 Table 1. Materials studied 1979 Chromosome Systems in the North American Decticinae 695 Table 1. (Contd) Observations Anabrus simplex (Haldeman) The chromosome complement of this species is 29 in the male, consisting of one pair of metacentric autosomes, thirteen pairs of rod-shaped autosomes, and a large rod-shaped X chromosome (Fig. 1). The rod-shaped chromosomes are considered to be telocentric. The thirteen pairs of rod-shaped autosomes can easily be arranged in two principal groups, six pairs of medium and seven pairs of small chromosomes. The former group are of decreasing size, but the latter group are uniform in size. The X chromosome is extensively large and can easily be distinguished from the rod-shaped autosomes. At first metaphase there are fourteen pairs of autosomal bivalents, one of which is metacentric, and the X chromosome (Fig. 2). At first anaphase, the 696 Norihiro Ueshima and D. C. Rentz Cytologia 44 Figs. 1-19. 1-2, Anabrus simplex. 1, spermatogonial metaphase and 2, first metaphase, polar view. 3-4, Ateloplys hesperus: 3, spermatogonial metaphase and 4, first metaphase, side view. 5-6, Atlanticus testaceus: 5, spermatogonial metaphase and 6, first metaphase, side view. 7-8, Capnobotes attenuatus: 7, spermatogonial metaphase and 8, first metaphase, side view. 9, sper matogonial metaphase of Capnobotes arizonensis. 10-11, Capnobotes occidentalis: 10, spermatogo nial metaphase and 11, first metaphase, side view. 12-13, Clinopleura infuscata: 12, spermatogonial metaphase and 13, first metaphase, side view. 14-15, Clinopleura minuta: 14, spermatogonial metaphase and 15, first metaphase, side view. 16-17, Decticita brevicauda: 16, spermatogonial metaphase and 17, first metaphase, side view. 18-19, Idionotus brunneus: 18, spermatogonial metaphase and 19, first metaphase, side view. 1979 Chromosome Systems in the North American Decticinae 697 X moves to one pole without dividing, as is usual in Orthoptera . There are therefore two types of second metaphases , 14A and 14A+X, respectively. 2. Ateloplus hesperus Hebard Spermatogonial metaphases of this species show 29 chromosomes, one pair of metacentric autosomes, thirteen pairs of rod-shaped autosomes, and a large rod-shaped X chromosome (Fig. 3). The thirteen pairs of rods are easily clas sified into two groups, six pairs of medium-sized and seven pairs of small chro mosomes. At first metaphase, fourteen bivalents are formed, besides the unpaired X. The metacentric bivalent, with a high number of chiasmata, and the X are recognizable (Fig. 4). 3. Atlanticus testaceus (Scudder) The spermatogonial metaphase of this species comprises two pairs of metacent ric autosomes, ten pairs of rod-shaped autosomes, and the metacentric X (Fig. 5). One of the two pairs of metacentrics is much larger than the other. Ten pairs of rod-shaped autosomes are easily divided into two groups, four pairs of medium size and six small chromosomes. The X chromosome is close to the larger metacentric in size. The first metaphase shows twelve bivalents and an unpaired metacentric X (Fig. 6). The bivalents consist of two metacentrics, four medium-sized and six small rods. 4. Capnobotes attenuatus Rentz and Birchim, C. arizonensis (Rehn), and C. oc cidentalis (Thomas) The chromosome cytology of these species is essentially the same. The spermatogonial metaphases have 23 chromosomes, consisting of three pairs of metacentric autosomes, eight pairs of rod-shaped autosomes, and a metacentric X (Figs. 7, 9, 10). Each of three pairs of metacentrics is recognized by size. One of the eight pairs of rods is larger than the others, which are almost uniform in size. The arms of the X chromosome in C. attenuatus are unequal, while in C. arizonensis and C. occidentalis they are nearly the same size. At first metaphase, eleven bivalents, in addition to the unpaired X chromosome, are formed (Figs. 8, 11). There are three metacentrics and one medium-sized and seven small sized telocentrics. As the result of the first division, there are two types of second metaphases: 11A and 11A+X, respectively. 5. Clinopleura infuscata Caudell and C. minuta Caudell The male chromosome complements of these two species consist of one pair of metacentric autosomes, thirteen pairs of rod-shaped autosomes, and a large rod-shaped X chromosome (Fig. 12, 14). Thirteen pairs of rods can be arranged in two groups, six medium size and seven small, almost equal in size. The X chromosome is easily noticeable among the rods because of its larger size. The first spermatocyte metaphase comprises fourteen bivalents, one of which 698 Norihiro Ueshima and D. C. Rentz Cytologia 44 is metacentric, and the X chromosome (Figs. 13, 15). The X moves precociously to one pole without dividing at first anaphase. Two types, therefore, of second metaphases, with 14 autosomes and with 14 autosomes and the X-chromosome, are formed. 6. Decticita brevicauda (Caudell) The spermatogonial metaphase of this species consists of 31 chromosomes which are all rod-shaped (Fig. 16). The unpaired X chromosome is the largest member of the set. Fifteen pairs of autosomes can be classified into three groups, one large, seven medium sized with decreasing order of size, and seven uniform small sized. At first metaphase, fifteen bivalents, besides the unpaired X are present; one large, seven medium, and seven small bivalents are easily recognizable (Fig. 17). 7. Idionotus brunneus Scudder and I. tehachapi Hebard The chromosome cytology of these two species is essentially the same. The spermatogonial metaphase of these species has 27 chromosomes, consitsing of one pair of metacentric autosomes, twelve pairs of rod-shaped autosomes, and a single rod-shaped X chromosome which is the largest chromosome (Figs. 18, 20). Twelve pairs of rods can be arranged into three groups by their size, one large, four medium and seven small. The last are quite uniform in size. The first spermatocyte metaphase comprises thirteen bivalents and the unpaired X (Figs. 19, 21). Among the bivalents, one metacentric and one large rod-shaped one are easily separable from the remainder. 8. Idiostatus aequalis (Scudder), I. apollo Rentz, I. bechteli Rentz, I. gurneyi Rentz, I. inermis (Scudder), I. kathleenae Rentz, and I. magnificus Hebard These seven species are uniform in their chromosome cytology. The sperma togonial metaphases of these species contain 29 chromosomes consisting of one pair of metacentric and thirteen pairs of rod-shaped autosomes and the large X chromosome (Figs. 22, 24, 26, 28, 30, 32, 34). The thirteen pairs of rods are divided into two groups, six medium and seven small. The former are of gradually Figs. 20-43. 20-21, Idionotus tehachapi: 20, spermatogonial metaphase and 21, first metaphase, side view. 22-23, Idiostatus aequalis: 22, spermatogonial metaphase and 23, side view of first metaphase. 24-25, Idiostatus apollo: 24, spermatogonial metaphase and 25, first metaphase, side view. 26-27, Idiostatus bechteli: 26, spermatogonial metaphase and 27, first metaphase, polar view. 28-29, Idiostatus gurneyi: 28, spermatogonial metaphase and 29, first metaphase, side view. 30-31, Idiostatus inermis: 30, spermatogonial metaphase and 31, side view of first metaphase. 32-33, Idiostatus kathleenae: 32, spermatogonial metaphase and 33, first meta phase, polar view. 34-35, Idiostatus magnificus: 34, spermatogonial metaphase and 35, ploar view of first metaphase. 36-37, Idiostatus elegans: 36, spermatogonial metaphase and 37, first meta phasse, side view. 38-39, Idiostatus californicus: 38, spermatogoinal metaphase and 39, first metaphase, side view.