THE VALUE OF CYTOLOGY IN TAXONOMY WITH PAltTICULAR REFERENCE TO THE PODISMINI (ACRIDOIDEA: ACRIDIDAE: MELANOPLINAE) V. R. VICKERY Lyman Entomological Museum apd Researcb Laboratory Macdonald College, MCGill University`., St¿. Amne de Bellóvue, Qué. HOA ICO M.].D. White, working in the United States in the 1940's and early 1950's and subsequently in Australia from 1954 to the present, has been thp main driving force in promotio:n. of use of cytology in :;ystematics, particularly of Orthoptera, Use of cytology in systematics of the group is not new; Mcclung (1908, 1914) and others stu_dÉed chromosomes of Orthoptera and Robertson (1916) deve]oped a rather good trea,tise on many species of Orthoptera® More recently, White has carried out a very comprehensive survey ot the Morabine grasshoppers of Australia (Orthoptera: Eumastacidae) which enabled-Key (1976) to complete the work on generic and suprageneric classification of the group. Forty genera are now recognized in the Morabinae (36 of which were new) and 33 new species were described® One of the more interesting aspects of this work is that karyotypic characters were used in a numeT'ical a,nalysis, together with dimensional and meristic characters and those of the phallic complex. White (1970) stated that the Eumastacoidea showed a greater diversity of karyoty- pes than the Acridoidea, each subfarnily of the former usually showing a different typical karyotype. Karyotypes are ueful ri tlHmselves and it is becoming rather common to see ka,ryotypes or even more often the number of male diploid chromosome complement listed in species descriptions. In fact, karyotype can be used in precisely the same way as shape of the genitalia as ¿t `taxonomic character. However, since "evolution is a cytogenetic process" (White 1970) one usuálly will delve deeper into the study of chromosome structure and behaviour. The basic number, "modal number" or"nombre fondamental" of chromosomes in Acrididae is said to be 2n ó =23, meaning that there are 11 pairs of autosomes and a single X or sex-determining chromosome. In ma,ny genera, this is the case. However, we know that in the Acrididae there occur 13 different chromosome numbers, ranging from 23 to 8. The numbers less than 23 are the result of chromosome fusions or chromosome deletions which have occurred during species evolution. Species which have even-numbered complements in the males (¢..e., 27¢ ó = 22 or 27¢ ó = 8 are ones in which the X-chromosome has undergone fusion with autosome resulting in neo-XY sex chromosome makeup rather than the original XO (White, 1970; Hewitt and John, 1972). While karyotypes are useful, they cannot be used to distinguish betwcen many known geriera íz..G., very many have a complement of 2n ó= 23). Careful examination of the chromosomes making up these karyotypes often will provide valuable information. Careful measurements may show differences between species in lerigths of comparable chromosomes. Spectrophotometric analysis to measure amount of DNA preserit may reveal differences (]ohn and Hewitt 1966). One useful character, one that has bcen foünd to vary greatly even in closely related species, is the length of the small séccmd arh§ of acrocentric chromosomes® Since we are concerned with variation, the study of polymorphic chrdmosomal rearrangements is useful, though sometimes confusing in that populations máy contain individuals with slighdy differing karyotypes. REV. SOC. ENT. ARGENTINA, Tomo 36 (1-4): 89-95. 90 Revista de la sociedad Entomológica Argentina 36,1977 P.G. Fontana, a former student of White, and more recently a student under my direction, worked on cytology of North American orthopteroids, and in particular on three genera of eastern North American grasshoppers, Boo#¢c77.s, Dc7?droíe£}Í.# and APP¢/¢cbí.c} (Acrididae; Melan'oplinae; Podismini). Thirteen populat.ions of 2 species of Boo7?¢crz.s, one with 3 subspecies, were studied and compared with representatives of the other two genera. In` general the eastern populations of Boo7?¢cr¢.s, which included 8. t;czrz.cg¢£¢ (Scudder),B. glacialis glaciali§ (Scudder), 8. glacialis canadensis (E.Mo Wa+ker) a.nd 8. g/¢c¢.¢/!.s ¢772P/z.ccrc¢ (Caudell and Allard), showed a high degree of karyotypic stability. The standard karyotype of thesc eastern Boo7¢¢cw.s species is 20 telocentric autosoñes; the sex-determining mechanism is the XO/XX type. The autosomes occur as 2 long, 6 medium and 2 short pairs; the X-chromosome is the third largest member of the complement. The ,amount of intra -and inter-population variation is quite similar to that observed between taxa. The length of each member of the chromosome complement is extremely stable and could not be used to differentiate between species of subspecies. A single B-chromosome wa.s found in a small proportion of individuals of each sex of a population of Boo7%c77.s tJ#g.cgcz£¢ (Scudder) from Mt. Mitchell, North Carolina. No supernumerary c.hromosome was found in any of the other populations of Boo#¢crí.s. TABLE 1. Assignment of geriera in tribál groupings by Rehn and Randell (1963, pp.10-11) Compare With Table 2 Supertribe Melanoplini Tribe Podismini 1. Group Podismae 2. Group Miramellae Micropodisma Podjsma lndopo dsma Parapo disma Zubovskya Bobemanella Orop od¿sma Sinop odisma Boonacris Odontopodisma* Copbopodisma Pseudoprumna* Dendrotettix Pseudopodisma* Epipodisma APpalacbia Yunnanacris* Miramella Eirenepbilus Niitakacris* Cbortopodisma Ognevia 3. Group Bradynotae 4. Group Primnoae Hypsal Qnia K¿ngdonella Primn oa He bardacris Asem oplus Prumn acris Aistacris Bradyn otes Pacbyp odisma Buckellac ris * Atypic al V. 8~ VLCKEKy , Tbe value of cytologN in taxonomy 91 TABLE 2. Propo§w:d assignment of gcnera of d`c Podismini to subtribd group.ings (Bascd upon known cytogenctic data of the spccics) Subfamily Melanoplinae Tribe Podismini 1. Subtribe Podismina (2n d= 22+ XO) 2. Subtribe Miramellina (2n ó = 20+ XO) Podisma Miramella pedestris pedestris alpina pedestris melisi Boonacris pedestris caprai ' g|acia|is dacia|is Pedestris decbambreil - glacidis canadensis emiliae glacialis amplicerca Copbopod¿sma variegata costai Parapodisma Dendrotettix mikado da¿risamá quercus APpalacbia Sinopod¿sma /' arc.ana2 sbirakii2 splendida2 (Parapodisma? .) kodamae2 sapporensis Niitakakris nosaceanum (Podisma? ) motodamariensis 1 Some populations have mále complement 20 + neo XY, due to X-L3 fusion. 2 Some chromosomes acrocentricc All others in all species are telocentric. medium and 3 short pairso Two males were found to have B-chromosomes; one had a si`ngle 8, while the other had 2 Bs. In both cases the Bs were small but highly stable, but beh.aved differently than those found ih .Boo7g¢c#.s cJ¢rz.cg¢£¢, being isopycnotic with the aut®somes at lst metaphase rather than negatively heteropycnotic as in 8. tJ¢".eg¢f¢. Th€ chromosome complement of the unique endemic species from Michigan, APP4rí¢icbí.¢ #rc¢7z¢ Hubbell and Cantrall, ís rather similar to that of Dc7gdro£e£#.* gz/ercz/s, 92 Revista de la sociedad Entomológica Argentina 36,19i7 •TAB`LE 3. Karyotypes of some gencra of Nemobfinae. 2nd Karyotype EUROPE: Nemobius N. sylvestris Bosc.* 17 NORTH AMERICA Neonemobius N. P¢/z/sfrz.s (Blatchley) N. variegatus (B"ner) Pictonemobius P. ¢77¢b£.£z.osz/s (Scudder)* 19 Allonemobius A fasciatus (De Geer)* 15 A. ¢//¢rdí. (Alex. & Thomas) 15 A. 77z#cz//#£a£s (Blatchley) 15 A. g. grz.scz# (E.M. Walker) 15 A. £¢.7¢7zz//z/s (Fulton) 15 Eunemobius E. carolinus carolinus (Scudder)* E. melodius (Alex. & Thoma.s) E. co7¢/z/sz£s (Blatchley) *Type species of the genus. male-23, femalcr24 chromosomes; 2 large, 6 medium and 3 short autosomes; single X ranking third in size. However, the similarity is superficial as three major differences between them were found. In A. #rc¢7¢¢, the short arms are considerably.longer than in any other of the taxa which were studied (in fa,ct, the S10 is unusual in being a genuine acrocéntric (twcrarmed pair) and overall lengt was greater; S10 is heterochromatic and precociously heteropycnotic at prophase 1; mean cell chiasma frequency is much greater. It is clear that the ¿ifferences in chromosome complements separates the taxa studied into two groups: (1) Boo7¢¢c77.s with 2nó=21 and (2) De.7gdro£f?££# and _ApP¢/¢cb¢.¢ with 2n ó = 23. It appears obvious, on morphological and other grounds, that V . FL VLC;KERy , Tbe value of cytology in taxonomy 93 the genera are related and are derived from common basic stock from which the contemporary genus Podz.s77% has differentiated only slightly. This brings the problem of different complements into focus: finding an explanation for the difference made necessary a study of the entire podismoid complex, or at least those members for which cytological information was available in literature. It soon became apparent that the "podismoid complex" is composed of two groups, one with male 2n ó = 21 and the other with mále 2n ó = 23 chromosome t rcomplements. , The group with male diploid compiement ot Zi cnromosomes is obviously derived from the 23 chromosome group. The difference, probably caused by chromosome deletion, certainly took place early in the evolution of podismoid stock, probably prior to the expansionary phase of the ancestral Asiatic stock. It is highly improbable that the species with 21 chromosomes have oristnated independendy by means of separate chromosomal rearrangements involving different autosomes. In fact, the available data show that in the 21-chromosome species it is always the smallest autosome pair (S11) which is missing. There is convincing evidence that elimination of small, unstable heterochromatic autosome pairs and :s:bÉp:q:urn::p:h:1:::=oi:eoonrfeía:%::;es:::::¥:St:n:d:;:1::::7ile:snt:fn:c:tia:Lc2t:h_a:Tg;oniies;s:a:£glfa:tiáp:l:: greater than the lengths of the equivdent autosome pairs of the 23-chromosome group. This indicates that the pair of autosomes which is missing in the 21-chromosome group is not, in fact, lost, but that their chromatin material has been added to other autosomes.