Heredity 56 (1986) 397-408 The Genetical Society of Great Britain Received 20 September 1985 Genetic variation in prairie populations of Melano plus San guinipes, the migratory grasshopper W. Chapco and M. J. Bidochka Department of Biology, University of Regina, Regina, Saskatchewan, Canada S4S 0A2. Genetic variation at two visible loci and 10 electrophoretic loci in populations of the migratory grasshopper, Melanoplus sanguinipes, in the Canadian prairies is described. Tibia colour and femoral stripe loci exhibit considerable geographic variation in frequency. Multiple regression and correlation analyses revealed dma! variation patterns for tibia colour, with minimum annual temperature accounting for about 40 per cent of that variation. The possible direct and indirect effects of this factor are discussed. No spatial patterns were evinced for the femoral stripe locus despite its close linkage to the tibia colour gene. Whatever the nature of selection, coefficients must be large enough to maintain polymorphism and divergence in opposition to the swamping effects of gene flow. This does not appear to be the case for the allozyme loci; frequencies of the most common allele at each locus are high (average heterozygosity =45per cent) and about the same at each location. Tte mean level of polymorphism, 378 per cent, is well within the range of most insects. The migratory grasshopper, Melanoplus to an agricultural ecosystem, which according to sanguinipes (formerly known as M. bilituratus, many (e.g., Roffey, 1970; Turnock, 1977) coincided M. mexicanus and M. atlantis—see Gurney, 1962), with—some say caused—the extinction of the most is widely distributed throughout North America, destructive grasshopper in North America, the occupying (particularly sandy aspects of) a variety Rocky Mountain grasshopper, M. spretus. During of habitats such as grasslands, roadsides, open this century, M. sanguinipes has enjoyed, at areas in forests and even northern tundra (Vickery irregular intervals, massive outbreaks in numbers, and Kevan, 1983). This, in part, is attributable to which today can be predicted largely on the basis the insect's polyphagia (Mulkern et aL, 1969; of climatic conditions (Gage et a!., 1976; Gage and Vickery and Kevan, 1983) and reported capacity Mukerji, 1977). As is typical for most members of to migrate over long distances (Parker et aL, 1955; the Orthopteran order, information on the popula- Johnson, 1969; Vickery and Kevan, 1983). Given tion genetics of M. sanguinipes is patchy (Chapco, these features one might, therefore, expect the 1983b). While there is certainly no shortage of species to be fairly rich genetically depending on reports on phenotypic variability for this species the amount of gene flow. Migratory proclivities (Shotwell, 1930; Gurney and Brooks, 1959), until need not be translated into gene flow effects recently only the polymorphism, in hind tibia (Endler, 1977), but in M. sanguinipes, at least, there colour (red versus blue), has been genetically is good evidence from past records of outbreak researched (King and Slifer, 1955; the locus was periods that migrating females do deposit eggs labelled T by Chapco, 1980a). Brooks' (1958) contributing to the next year's pullulation (Parker classification and Gurney and Brooks' (1959) et a!., 1955). Also based on historical accounts, it monograph on the genus Melanoplus give several is reasonable to assume that the current population qualitative accounts of the geographical distribu- structure was engendered by the development of tion of tibia colour variants. In Canada, the red agriculture on the prairies over a century ago, form is predominant in Quebec, Ontario, British settlement and cultivation providing both suitable Columbia and the prairie parklands (the "more pod laying sites and succulent food (Bird, 1961; humid part"), whereas the blue form is pre- Roffey, 1970; Turnock, 1977). M. sanguinipes was dominant in the prairie grasslands. No distribution probably spottily distributed prior to the transition maps are provided, although Brooks (1958) does 398 W. CHAPCO AND M. J. BIDOCHKA state that the blue form is "usually confined to a tibia allele (TR)decreaseswith about a three-fold narrow strip south of a line from Medicine Hat, drop occurring from the Manitoba-Saskatchewan Alta. to Brandon, Man., but after a series of 'good' border near Ebenezer (51° 22', 102° 27'), located in grasshopper years, or in local dry spots, this form the aspen-parkland to Regina (50° 25', 104° 35'), predominates on the grasslands". Based on rearing located in the grassland area (Chapco, 1983a). studies, Brett (1947) claimed that high humidity Since no material was obtained between these two and high temperature (also the consuming of let- points, it is not known whether the changes are tuce and corn) "produce" a preponderance of abrupt or smooth. Also examined were the distri- individuals with red caudal tibiae. The results are butions of three other traits whose genetics have taken as experimental confirmation of Hebard's previously been worked out: red back (Prolocus), (1925) assertion that in South Dakota, the red femoral stripe (Ostlocus)and lactate dehy- forms are more frequent in the "more humid sec- drogenase (Ldh locus) (Chapco, 1980a; 1980b; tions of the state; elsewhere in more arid areas, 1984). Ost exhibits considerable geographical vari- hind tibiae are mostly glaucous". Brett's experi- ation; Pro is uniformly rare everywhere; and the ments, unfortunately, are difficult to evaluate since most common Ldh allele is uniformly frequent in information on source of material, and in some all sampled areas. cases, sample sizes, and proper controls are The present study concentrates on the southern lacking. Saskatchewan area in order to (a) establish the In a preliminary survey of several North nature of the TR dine, (b) test statistically the American populations, it was shown that from hypothesis, suggested by the literature, that the Quebec to Saskatchewan, the frequency of the red distribution of T' is connected to moisture and Table 1 Red tibia colour and femoral stripe allelic frequencies at 32 prairie locations Latitude Longitude Locality ('North) ('West) N %TR %Ost 1.Carnduff 4917 10183 254 14 53 2.Oxbow 4923 10218 115 13 56 3.Mankota" 4942 10707 74 11 28 4.Pangman 4965 10463 111 13 62 5.Kayville 4973 10517 42 20 65 6.Assiniboja* 4963 10598 125 12 38 7. Ormiston* 4975 10537 185 12 69 8.Bateman 5002 10675 71 12 71 9.Gull Lake 5013 10845 78 12 58 10. Rowatt 5033 10462 184 11 38 11.Whitewood 5033 10425 106 25 60 12. Jameson* 5042 10228 104 19 33 13.Grenfell 5042 10293 100 31 65 14.Indian Head* 5053 10367 148 16 33 15.Stockholm 5067 10225 51 20 72 16.Keeler 5070 10585 55 16 44 17.Bethune 5072 10513 186 12 44 18.Russell 5077 10128 48 25 62 19.Tugaske 5088 10627 173 13 59 20.Melville* 5092 10280 55 44 34 21.Craik 5105 10582 80 8 45 22.Roblin 5120 10145 46 58 100 23.Yorkton* 5122 10247 56 31 31 24.Springside 5135 10275 15 42 42 25.Ebenezer 5137 10245 345 41 31 26.Outlook 5150 10705 72 17 49 27.Good Spirit Lake Park 5157 10265 20 50 68 28.Canora* 5162 10243 51 46 30 29.Harris 5173 10745 34 18 21 30.Preeceville* 5197 10267 77 53 29 31. Biggar 52'07 10800 135 23 48 32.Hague 5250 10642 110 21 41 *Sites also sampled for variation. GENETIC VARIATION IN GRASSHOPPER POPULATIONS 399 temperature, and (c) by including several other trophorsis. A portion of the eviscerated tissue was loci, mostly electrophoretic, lay the foundation for stored at —70°C for later analysis. Two gel buffer discovering the genetic structure of what appears systems were used: (1) 0375 M tris HC1, pH 89 to be a continuously distributed species. The results (for LDH, MDH, G-6PD, ODH, SDH, ODH and should provide an interesting antithesis to the few SOD) and (2) O1 M tris borate with 2mM EDTA allozyme studies that have tended to concentrate (pH 89) for aGPDH-1, aGPDH-2, XDH, GLDH on acridids of low mobility (Tepper, 1979; Daly and ME. A 05 M tris glycine (pH 8.9) running et a!., 1981; Gill, 1981a; 1981b; 1981c). buffer was used throughout. The stains for XDH, G-6PD and SDH were essentially the same as those described by Shaw and Prasad (1970); SOD, ME, MATERIALS AND METHODS aGPDH-2 and ODH were stained (with some slight modifications) according to Ayala et al. (1972);LDH and MDH were stained according Collection to Chapco (1984), 50mg malic acid substituting Adult M. sanguinipes, scored for visible poly- for lactic acid in the latter case. Gels were run at morphisms, were collected between the months of 7 per cent acrylamide and electrophoresis per- July and August, 1978 to 1984, from 30 different formed for 2 hours at 250 volts. localities in southern Saskatchewan; two localities were in Manitoba (table 1). For electrophoretic analysis, grasshoppers from nine of the sites Analysis (marked with an asterisk in the table), situated Allelicfrequencies were estimated by gene count- along a climatic gradient (Richards and Fung, ing in the case of the enzyme loci (all alleles proved 1969) that extends from the generally hot and dry to be codominant) and in the case of the two colour (summer) short grass prairie in the south-west to traits, Hardy-Weinberg equilibrium was assumed the relatively cooler and moister aspen parkiand and the frequencies of the dominant alleles esti- in the north-east, were sampled in 1982; three mated by taking the square-root of the correspond- places were resampled in 1983. Collections were ing recessive phenotypic frequencies and subtract- made using a sweep net, usually along roadsides ing the values from 1. and/or adjacent fields. Locations were compared by applying log- likelihood ratio tests or G-tests (Everitt, 1977) to 2 (phenotypes) x 32 (locations) contingency tables Traits in the case of the colour traits and to 2 (common Animalswere scored for two colour traits: hind allele versus "other" alleles pooled) x 9 (locations) tibia colour (red allele, T' dominant to blue allele, contingency tables in the case of the elec- TB)andhind femoral stripe (orange stripe allele, trophoretic traits.