Cytologia 44: 693-714, 1979

Chromosome Systems in the North American Decticinae' with Reference to Robertsonian Changes (: )

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 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. 40-41, Idiostatus fuscopunctatus: 40, spermatogonial metaphase and 41, first metapnase, polar view. 42-43, Idiostatus hermani: 42, spermatogonial metaphase and 43, polar view of first metaphase. 1979 Chromosome Systems in the North American Decticinae 699 700 Norihiro Ueshima and D. C. Rentz Cytologia 44 decreasing size, while the latter are almost equal in size. The X chromosome is the largest of the rods. There are fourteen bivalents and the unpaired X chromosome at the first spermatocyte metaphase (Figs. 23, 25, 27, 29, 31, 33, 35).

9. Idiostatus elegans Caudell, I. californicus Pictet, I. fuscopunctatus (Scudder), I, hermani (Thomas), I. inermoides Rentz, and I. rehni Caudell The chromosome cytology of these six species is essentially the same. The male diploid chromosome complement consists of one pair of metacentric autosomes, thirteen pairs of rod-shaped autosomes and a metacentric X chromosome (Figs. 36, 38, 40, 42, 44, 46). The thirteen pairs of rods are separable into two groups, six medium and seven small. The X chromosome is a little smaller than the metacentric autosomes. At the first metaphase, fourteen bivalents are present besides the unpaired X chromosome (Figs. 37, 39, 41, 43, 45, 47). The main difference between these six species and the previous seven is the metacentric nature of the X chromosome.

10. Idiostatus nevadensis (Scudder) Cytologically, this species represents a third group in the genus Idiostatus. The spermatogonial metaphase contains 27 chromosomes, instead of 29 in the others. They consist of one pair of metacentric and twelve pairs of rod-shaped autosomes and the large rod-shaped X-chromosome (Fig. 48). Twelve pairs of rods can be classified into three groups, one large, four medium, and seven small. The X chromosome is the largest of the rods. At first metaphase, there are thirteen bivalents and the X-chromosome. The metacentric, and large, medium, and small rods are easily recognizable (Fig. 49).

11. Plagiostira gillettei Caudell The male chromosome complement of this species is 25 (two pairs of metacen tric and ten pairs of rod-shaped autosomes and the metacentric X-chromosome) (Fig. 50). One of the pairs of metacentrics is much larger than the other. Ten pairs of rods can be divided into two groups, four medium and six small. The X-chromosome is close to the large metacentric autosomes in size and is easily distinguished from the autosomes. At first metaphase there are twelve bivalents and the unpaired X-chromosome (Fig. 51). Three groups of bivalents can be easily recognized, two metancetric, four medium rods, and six small rods. As is usual in Orthoptera, the X moves to one pole without dividing at first anaphase. There are, therefore, two types of second spermatocytes: 12A and 12A+X.

12. Steiroxys strepens Fulton, S. sp. (68-19) and S. sp. (69-11) The chromosome cytology of these three species is essentially the same. The spermatogonial metaphase consists of one pair of metacentric autosomes, thirteen pairs of rods-shaped autosomes, and a single rod-shaped X-chromosome (Figs. 52, 54, 56). Thirteen pairs of rods can be classified into two groups, six 1979 Chromosome Systems in the North American Decticinae 701

Figs. 44-63. 44-45, Idiostatus inermoides: 44, spermatogonial metaphase and 45, first metaphase, side view. 46-47, Idiostatus rehni: 46, spermatogonial metaphase and 47, first metaphase, side view. 48-49, Idiostatus nevadensis: 48, spermatogonial metaphase and 49, first metaphase, polar view. 50-51, Plagiostira gillettei: 50, spermatogonial metaphase and 51, first metaphase, side view. 52-53, Steiroxys strepens: 52, spermatogonial metaphase and 53, first metaphase, side view. 54-55, Steiroxys sp. (68-19): 54, spermatogonial metaphase and 55, first metaphase, side view. 56-57, Steiroxys sp. (69-11): 56, spermatogonial metaphase and 57, side view of first metaphase. 58-59, Zacycloptera atripennis: 58, spermatogonial metaphase and 59, first metaphase, side view. 60-61, Neduba (Neduba) diabolica: 60, spermatogonial metaphase and 61, side view of first meta phase. 62-63, Neduba (Neduba) macneilli: 62, spermatogonial metaphase and 63, polar view of first metaphase. 702 Norihiro Ueshima and D. C. Rentz Cytologia 44

medium and seven small in sixe. The latter are quite uniform. The X-chro mosome is the largest of the rods. In the first spermatocyte metaphase, fourteen bivalents besides the unpaired X-chromosome are present. One metacentric, six medium, and seven rod-shaped chromosomes are seen at this stage (Figs. 53, 55, 57).

13. Zacycloptera atripennis Caudell The spermatogonial metaphase of this species contains 23 chromosomes consisting of three pairs of metacentric autosomes, eight pairs of rod-shaped autosomes, and the metacentric X-chromosome (Fig. 58). Eight pairs of rods can be arranged in two groups, two of medium and six of small. The X-chro mosome is close to the largest metacentric pair in size. At first metaphase there are three metacentric bivalents, eight rod-shaped bivalents, and the unpaired metacentric X-chromosome (Fig. 59). As the result of the first division, two types of second spermatocytes are formed, 12A and 12A+X.

14. Neduba (Neduba) diabolica (Scudder), N. (N.) macneilli Rentz, and N. (N.) sp. (67-38) The chromosome cytology of these three species is uniform. The spermato gonial metaphase contains 25 chromosomes consisting of one pair of submetacent ric autosomes, eleven pairs of rod-shaped autosomes, and a single large rod -shaped X-chromosome (Figs. 60, 62, 64). Eleven pairs of rods can be arranged into two groups, six pairs of medium and five pairs of small chromosomes. The X-chromosome is the largest of the rods and is easily distinguished from others. At first metaphase, twelve bivalents besides the unpaired X-chromosome are present (Figs. 61, 63, 65).

15. Neduba (Neduba) sp. (67-86) This species has a neo-XY system of sex determination. The spermato gonial metaphase comprises two pairs of submetacentric autosomes, eight pairs of rod-shaped autosomes, a submetacentric X- and rod- shaped Y-chromosome (Fig. 66). Eight pairs of rods can be arranged in two groups, four medium and four small. The X-chromosome is the largest in the spermatognial chromosome set and the Y is similar to the medium-sized rods. At first metaphase there are ten autosomal bivalents and the X-Y bivalent (Fig. 67). At first anaphase the X and Y segregate to opposite poles, each with the autosomal halves (Fig. 68). As the result of the first division, two types of second spermatocytes, 10A+X and 10A+Y, are formed.

16. Neduba (Aglaothorax) diminutiva Rentz and Birchim This species has a neo-X1X2Y sex determining system. The spermatogonial metaphase consists of ten pairs of rod-shaped autosomes and the X1X2Y sex chromosomes (Fig. 69). The rod-shaped autosomes can be classified into two groups, six pairs medium-sized with decreasing order of size and four pairs small. The X1 is the largest element in the gonial set and is submetacentric, the X2 is 1979 Chromosome Systems in the North American Decticinae 703

rod-shaped and is as small as the medium-sized autosomes , and the Y is submeta centric. At first metaphase, ten autosomal bivalents and the X1X2Ytrivalent are present (Fig. 70). At first anaphase, the X1 and the X2 move to one pole and the Y goes

Figs. 64-75. 64-65, Neduba (Neduba) sp. (67-38): 64, spermatogonial metaphase and 65, first metaphase, side view. 66-68, Neduba (Neduba) sp. (67-86): 66, spermatogonial metaphase, 67, side view of first metaphase, and 68, first anaphase. 69-73, Neduba (Aglaothorax) diminutiva: 69, spermatogonial metaphase, 70, side view of first metaphase, 71, first anaphase, 72, second meta phase with 10A+X1X2 and 73, second metaphase with 10A+Y. 74-75, Neduba (Aglaothorax) ovata armiger: 74, spermatogonial metaphase and 75, first metaphase, side view. to the other pole with the autosomal halves (Fig. 71). As the result of the first division, there are two types of second spermatocytes: one with 10A+X1X2 (Fig. 72), the other with 10A+Y (Fig. 73) 704 Norihiro Ueshima and D. C. Rentz Cytologia 44

17. Neduba (Aglaothorax) ovata armiger (Rehn and Hebard) The spermatogonial metaphase of this species consists of eleven pairs of rod-shaped autosomes and a large rod-shaped X-chromosome (Fig. 74). The autosomes are easily arranged into two groups, four large to medium, seven small. The X-chromosome is the largest element and is easily distinguished from the autosomes. At first metaphase, eleven autosomal bivalents and the unpaired X-chro mosome are present (Fig. 75). As usual, the X moves to one pole without dividing at the first anaphase. There are, therefore, two types of second metaphase; 12A and 12A+X.

Discussion

The chromosome system in the Decticinae is now known for 50 species listed in Table 2. White (1941, 1973) suggested that the modal number of chromosomes in this group was 2n=31 with all acrocentric chromosomes, and that deviation from the mode were due to chromosome rearrangements, mainly centric fusions. Henderson (1961) and Southern (1967) followed White's assumption. John and Hewitt (1968) found 29 chromosomes in Metrioptera saussureana with a pair of metacentric chromosomes and they considered that the 29-chromosome kar yotype was derived by the centric fusion of 2 pairs of rod-shaped autosomes. For North American species, McClung (1902, 1905, 1914) reported 2n=33 in Anabrus sp. with a pair of metacentric chromosomes. We observed 29 chromosomes with a pair of metacentrics (Figs. 1, 2) in Anabrus simplex. The Anabrus sp. reported by McClung (see Fig. 21, 1905) clearly showed a pair of metacentric chromosomes and the multiple formation of sex chromosomes. White et al. (1967) suggested that the Anabrus sp. of McClung (1902, 1905, 1914) might have had 2n=32 or 34, with a neo-XY sex chromosome mechanism. There is a possibility that McClung's material was misidentified and was perhaps

Table 2. Chromosome number and sex determining mechanism in Decticinae 1979 Chromosome systems in the North American Decticinae 705

Table 2. (Contd.)

* Including a pair of B-chromosomes 706 Norihiro Ueshima and D. C. Rentz Cytologia 44

a species of Pediodectes which vaguely resembles Anabrus. McClung never stated where he obtained his material, but both genera occur in Kansas. No chromosome data are available for the latter genus. Thus, we cannot be certain whether the discrepancy between our Anabrus specimens from McClung's is due to intraspecific differences. Davis (1908) found 29 chromosomes in the diploid state, including a pair of metacentrics in Steiroxys trilineata. We observed three other species in the genus, and obtained the same result. White (1941) reported 2n=25, including three pairs of autosomal metacentrics and the X metacentric in Atlanticus pachymerus. Our investigation in A. testaceus (Figs. 5, 6) showed the same chromosome complement. As noted previously, chromosome numbers in North American Decticinae now are known to range from 33 to 23 in diploids (see Table 2).

Chromosome evolution in North American Decticinae If the modal chromosome number in Decticinae is 2n=31 and decreases in number occurred by fusion, as suggested by White (1973), then an interesting pattern of chromosome evolution is shown by North American Decticinae. Before we discuss chromosome evolution in Decticinae, it is necessary to discuss the organisation of the rod-shaped chromosomes. White (1941) and Ferreira (1969) believe that rod-shaped chromosomes in the Decticinae, as well as in other members of Tettigonidae, are acrocentrics. On the other hand, Southern (1967) and John and Hewitt (1968) claim that rod-shaped chromosomes in Decticinae are telocentrics. From our observations, we prefer to consider them as telocentrics rather than acrocentrics. However, we were not able to detect whether they are really telocentrics or acrocentrics, since we did not employ modern banding patterns in this study. So, the problem is still an open one. The typical karyotype in genera of North American Decticinae is diagrammed in Fig. 76. Neduba is an exception. Decticita has 31 chromosomes all rod -shaped. The chromosome number is reduced to 29 in Anabrus, Ateloplus, Idiostatus, Clinopleura, and Steiroxys. These genera always has a pair of metacent rics. This clearly indicates that centric fusion has taken place between two pairs of rod-shaped autosomes. As described previously, some species in Idiostatus have a metacentic X-chromosome in addition to a pair of metacentric autosomes. This change of the X chromosome might be due to a centromere shift, because of the size relationships of the X. The genus Idionotus shows 27 chromosomes (one pair of metacentrics, twelve pairs of rod-shaped autosomes, and the rod -shaped X-chromosome). The twelve pairs of rod-shaped autosomes can be clas sified into three groups on the basis of size: one large, four medium, and seven small. Comparison of relative sizes of rod-shaped autosomes between Idionotus and genera with 29 chromosomes, enable to suggest that one pair of large rod -shaped autosomes in Idionotus might be derived by tandem fusion of two pairs of medium sized rods in the 29-chromosome genera, thereby reducing the chromo some number to 2n=27. The same pathway of chromosome evolution was also found in Idiostatus nevadensis (Fig. 48). With regard to chromosome evolution, Idiostatus is extremely interesting. 1979 Chromosome Systems in the North American Decticinae 707

Seven species out of 14 so far observed show 2n=29 (one pair of metacentrics, 13 pairs of rod-shaped autosomes, and a large rod-shaped X-chromosome). Although six species (I. elegans, I. californicus, I. fuscopuncatatus, I, hermani, I. inermoides, and I. rehni) show the same chromosome number, but the shape of X-chromosome is different (metacentic instead of rod-shaped). As stated previously, this change of the shape of the X-chromosome is due to centromere

Fig. 76. Typical chromosome complements of various genera in North American Decticinae. shift. It seems to us that the metacentric X-chromosome in those six species is of recent origin, since a great majority of decticines, as well as other tettigoniids, have a rod-shaped X-chromosome. In Idiostatus nevadensisthe chromosome num ber has been reduced to 27 from 29 due to a tandem fusion, also of recent origin. Atlanticus and Plagiostira have 2n=25 (two pairs of metacentrics and 10 708 Norihiro Ueshima and D. C. Rentz Cytologia 44

pairs of rod-shaped autosomes and a metacentric X-chromosome). The chro mosome number in these two genera has been reduced from 31 to 25 in the male. The metacentric X-chromosome might be derived by centromere shift as has occurred in Idiostatus. Thus, two centric fusions are persent. Therefore, a pair of small rods was lost during this chromosome evolution. However, we suspect that some of the genetic materials of that pair of small rods might have been incorporated in other chromosomes in some unknown way. The chromosome number in Capnobotes and Zacycloptera is further reduced to 2n=23 from 2n=31 by three successive centric fusions. Again, a pair of rod-shaped autosomes has been lost in these genera. So far, the evidence noted above supports the idea that Robertsonian change has occurred in the chromosome evolution in the North American Decticinae. However, an exception is found in the genus Neduba. Neduba does not follow the pathway just discussed. Therefore, Neduba might be derived

Fig. 77. Chromosome patterns in the Neduba.

by a different trend from the rest of North American decticines. Ferreira (1969) reported 2n=25 with all rod-shaped chromosomes in the Australian Lanciana albidicornis. This species may share the same evolutionary pathway as in North American Neduba species. In fact, Uvarov (1924) in briefly discussing Lanciana "as appears from this description, the genus Lanciana shows likeness in the external genitalia to Neduba...." Neduba is considered to contain two subgenera: Neduba and Aglaothorax. 1979 Chromosome Systems in the North American Decticinae 709

As far as chromosome evolution is concerned, we find interesting discrepancy in the subgenus Neduba. From our observations, the typical chromosome complement in subgenus Neduba is 2n=25 (one pair of submetacentric and eleven pairs of rod-shaped autosomes and the large rod-shaped X-chromosome) (see Fig. 77). On this basis, we suggest an interesting pathway of chromosome evolution in this subgenus. Three species in the subgenus Neduba, N. (N.) diabolica, N. (N.) macneilli, and N. (N.) sp. (67-38), show 2n=25 chromosomes with a pair of submetacentrics. The chromosome number in N. (N.) sp. (67-86) has been reduced to 2n=22 due to two successive centric fusions, one of them involving the X-chromosome.

Fig. 78. Diagrammatical scheme of the origin of neo-XY and -X1X2Y in the Neduba.

Therefore, N. (N.) sp. (67-86) established the neo-XY sex chromosome system and carried two pairs of submetacentric autosomes instead of one pair of submeta centrics as seen in N. (N.) diabolica and other species (Fig. 77). No change in number of chromosome arms has taken place in N. (N.) sp. (67-86) in reducing numbers from 25 to 22. There is no doubt that the XY sex chromosome mecha nism is of more recent origin, since that Y chromosome was not heterochromatic. Rentz and Birchim (1968) reported that the subgenus Aglaothorax might contain two groups morphologically (Neduba -Aglaothorax relationships we will discuss later). This is also true cytologically. N. (A.) diminutive has 2n=23 chromosomes including a neo-X1X2Y sex chromosome system. Reduction of 710 Norihiro Ueshima and D. C. Rentz Cytologia 44 the chromosome number to 23 in this species from the typical 25 in the genus Neduba was probably due to a tandem fusion. Consequently, the 25 chromosome species have three pairs of large, three medium, and five small rod-shaped autoso mes, while N. (A.) diminutiva has four pairs of large, two medium, and four small rods. From these size relationships, we can easily assume that a pair of small chromosome has been incorporated into a pair of medium sized chromosomes; thus N. (A.) diminutiva has four pairs of large ones instead of three in the 25 chromosome species. The multiple sex chromosome system in N. (A.) diminutiva has definitely been derived from the chromosome rearrangement between original X-chromosome and a pair of submetacentrics in 25 chromosome species. Thus, N. (A.) diminu tiva has established the neo-X1X2Y system. The probable interpretation for the establishment of neo-X1X2Y system in N. (A.) diminutiva is schematically shown in Fig. 78. The neo-XY and neo-X1X2Y sex chromosome mechanisms and their evolu tionary significance have been reviewed and discussed by White (1973), particularly for Orthoptera. In Tettigoniide, clear evidence for the occurrence of neo-XY and X1X2Y mechanisms was first recorded by Dave (1965). Subsequently, White et al. (1967) and Ferreira (1969, 1976) reported additional neo-XY systems in several species of tettigoniids. These discoveries are in Phaneropterinae, Tet tigoniinae, and Listroscelinae. In the Decticinae, this is the first recorded presence of neo XY and X1X2Y sex chromosome mechanisms. For Neduba (Aglaothorax) ovata, the pathway of chromosome evolution cannot be suggested at this time. However, we assume that the separation of N. (A.) ovata from Neduba (Neduba) and Neduba (A.) diminutiva is probably very old.

Phylogenetic relationships of North American Decticinae The proposed phylogenetic scheme (Fig. 79) based on the known chromosome systems of decticine genera compares well with the present knowledge of relation ships based on morphology. No one has proposed a formal phylogenetic model in this group. Current knowledge of relationships is based on inference from the sequence of genera used by Caudell (1907) in his monograph. The discovery or recognition of many new genera in recent years (since 1968, four new genera have been described) indicates that a phylogenetic scheme would be too speculative at this time. However, the grouping of genera reflected by the present cytological data is very similar to that indicated by Caudell with the exceptions noted below. Idionotus and Idiostatus have been considered rather close relatives. But this does not seem to be the case as reflected by our studies on the chromosomes. Rentz and Birchim (1968) suggested that Idionotus was probably related to the European Anataxius and Rhacocleis. Unfortunately, the chromosome complem ents of those European genera are unknown. The grouping of Capnobotes and Zacycloptera is interesting. Zacycloptera has long been considered a relative of Plagiostira by Caudell (1907) pointed out that the coal-black wings and relatively slender hind femora which are possessed by both genera were superficial characters when other more primary characters 1979 Chromosome Systems in the North American Decticinae 711 such as the non-carinate pronotum and armed prosternum were considered. The relationships of Capnobotes have not been discussed recently but species were at one time thought to be in the European genus Drymadusa Stein. Of particular interst is Decticita which has twice been noted to be related

Fig. 79. Phylogenetic relationships in the North American Decticinae, based on chromosome systems.

to European genera such as Metrioptera and Platycleis, first by Hebard (1939) and later by Rentz and Birchim (1968). Species of Decticita have 2n=31, a complement not yet discovered in any other North American decticine but present in thier European relatives. Taxonomic considerations Neduba-Aglaothorax relationships: Neduba was described by Walker 712 Norihiro Ueshima and D. C. Rentz Cytologia 44

(1869) on a single species, N. carinata, from "California." Subequently authors brought the known species number to six (sensu stricto). All species are from the pacific slope of North America and inhabit forest thicket environments.

Aglaothorax was proposed in 1907 by Caudell and included 3 species.

The type species as designated by Caudell was Tropizaspis ovata Scudder.

Subsequently authors have reassigned his species to Neduba because he either misinterperted characters or lacked specimens of both sexes in making his generic assignments. Rentz and Birchim (1968) described several species in both genera and on the basis of overlapping characters discovered mainly in the genitalia, synonymized the two genera and suggested that each be maintained as subgenus. They showed that certain species such as N. morsei and N. diminutiva had the external characters of color and structure of the genus Neduba but possessed genitalia of the type found in Aglaothorax species. Conversely, Aglaothorax castanea has the external appearance of an Aglaothorax but genitalia of Neduba. On this evidence, the two genera were synonymized. Furthermore, Rentz and Birchim

(1968) classified N. diminutiva in the subgenus Aglaothorax, on the structure of genitalia.

However, our cytological investigations indicate that N. diminutiva is closer to the subgenus Neduba than to subgenus Aglaothorax, although we have observed only one species, ovata of Aglaothorax. Neduba (Aglaothorax) ovata is quite different from either Neduba (Neduba) species or Neduba (Aglaothorax) diminutiva, as far as chromosome cytology is concerned. Unfortunately, we have no opportu nity to observe chromosome cytology in N. (A.) morsei, N. (N.) castanea, and other species in Aglaothorax. Therefore, in order to clarify the taxonomic situation of Neduba and Aglaothorax, further information in chromosome cytology as well as taxonomic study is desirable. Idiostatus nevadensis (Scudder): Rentz (1973) considered I. nevadensis as synonymous with I. aequalis citing geographical separation and "minor" charac ters as the only reason for formerly considering I. nevadensis a distinct species.

Our cytological studies of the specimens from near the type locality (Ruby valley,

Eiko Co., Nevada) of I. nevadensis show that it should be reinstated as distinct species, since it has 2n=27 (•‰), while all other species in Idiostatus so far studied cytologically have 29 chromosomes. Morphologically, I. nevadensis (Scudder) can be distinguished from I. aequalis

(Scudder) by its overall greyish rather than brownish coloration, proportionately shorter legs; shorter porjections of the tenth tergite of the male. All Nevada locality recorded by Rentz (1973) pertain to I. nevadensis. I. nevadensis has not been discovered in California.

Acknowledgements

We are greatly indebted to Dr. M. J. D. White (Australian National Univer sity) for his critical reading of the manuscript. This work was sponsored in part by NSF grant GB-31044 and DEB76-10581, 1974 Chromosome Systems in the North American Decticinae 713

to DCR and the Academy of Natural Sciences of Philadelphia, and the California Academy of Sciences. Travel grant to NU was supported by Matsusaka College.

Summary

Chromosome systems of 12 genera and 36 species of the North American Decticinae have been studied. The chromosome number of these species ranges from 2n=22 to 2n=31 in the male (see Table 2). Robertsonian changes has played an important role in chromosome evolution in these decticines. Neduba sp. has a neo-XY sex determining mechanism and Neduba diminutiva an X1X2Y one. The probable pathways of chromosome evolution and the origin of the neo - XY and -X1X2Y sex determining mechanisms are discussed, as well as the phylogeny and present taxonomic status of the North American Decticinae based on chromosome systems.

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