Great Basin Naturalist

Volume 35 Number 1 Article 3

3-31-1975

Genetics, environment, and subspecies differences: the case of sabuleti (: Hesperiidae)

Arthur M. Shapiro University of , Davis, California

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Recommended Citation Shapiro, Arthur M. (1975) "Genetics, environment, and subspecies differences: the case of (Lepidoptera: Hesperiidae)," Great Basin Naturalist: Vol. 35 : No. 1 , Article 3. Available at: https://scholarsarchive.byu.edu/gbn/vol35/iss1/3

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GENETICS, ENVIRONMENT, AND SUBSPECIES DIFFERENCES: THE CASE OF POLITES SABULETl (Lepidoptera: Hesperiidae)

Arthur M. Shapiro^

Abstract.— Polites sabuleii is an example of an having a univohine, monophenic high- elevation subspecies and a multivoltine lowland one that produces similar phenotypes only in cold weather. When reared under conditions that induce the warm-weather phenotype in lowland stocks, the montane subspecies P. s. tecumseh continues to produce its usual phenotype, indicating that it has become genetically fixed.

One variant of the persistent "genetics- plants as far back as the 1920s, in the clas- environment" duality in biology concerns sic work of Turesson (1922, 1925, 1929) the nature of subspecies differences. The later brilliantly expanded by Clausen, problem, as it applies to , was Keck, and Hiesey (1940, 1947, 1948, and well simimarized in Klots's (1951) dis- other papers). This work firmly estab- cussion of geographic variation: lished the concept of the ecotype in plant ecology and genetics, a concept more or To what degree much of the recorded geo- less readily generalizable to in graphic variation is a matter of tempera- cases like those discussed Klots ture and humidity differences is something by and which we can only infer. In Papilio glau- Ehrlich et al. Turesson and Clausen et al.

cus . . . spring specimens tend to be small were able, by transplant experiments, to

pale. . . . As go northward find and we we separate phenotypic variation produced that in central Canada, where there is only directly one generation a year, the whole popula- by the physical environment from tion looks similarly small and pale. In Can- that produced indirectly through the se- ada this population has been named as a lection of climaticall}' adapted genotypes. geographic subspecies, ''canadensis,''' i.e. a This paper is the second of a series re- part of the species limited to a certain area and showing distinctive characteristics. The porting on analogous studies of North temptation is strong to attribute the whole American Lepidoptera. thing to lowered temperatures alone. But suppose we brought a batch of eggs of canadensis down to Florida, and reared the The Subspecies of Polites sabuleti butterflies in the conditions under which Situations of sort the very large, richly colored subspecies the described above australis develops there. Would our cana- are not limited to populations separated densis eggs develop as australis ... or would by latitude; many Lepidopterans—like the they develop into the same small pale ]3lants studied by Clausen and his col- specimens that their parents were? leagues—have altitudinal variants, often Twenty-three years later Ehrlich, Holm, described taxonomically at the subspecies and Parnell (1974) could only write that level, and these are especially interesting because of the short ground distances be- many butterflies have spring generations tween the high- and low-elevation popula- that are smaller and darker than their tions possibility of summer generations, the difference pre- and the investigating sumably being due to the seasonal variation the nature of their contacts, if any. in the environment. However, in some Polites sabuleti Boisduval is a small, northern parts of their range, [they] have largely tawny (Hesperiidae), only a single summer generation, which widely distributed in western North is small and dark and resembles the spring generation of southern localities. In the America. Three named subspecies occur northern populations, the individuals are in California: P. s. sabuleti, P. s. tecumseh presumed to have genotypes that produce Grinnell, and P. s. chusca Edwards. The the dwarfing and darkening. Although the last is a very pale desert population and critical transfer experiments have not been done, the greater constancy of the northern has not been examined in this study. P. s. forms in the face of environmental changes sabuleti and P. s. tecumseh are parapatric supports these presumptions [emphasis in northern and central California, occur- added] ring at low and high elevations respec- The same problem was recognized in tively.

'Department of Zoology, University of California, Davis, California 95616.

33 1

34 GREAT BASIN NATURALIST Vol. 35, No. 1

P. s. sabuleti is very widespread on the lowest Yosemite-area record of P. s. sandy soils, in saline and alkaline marsh- tecumseh is Gin Flat (7,036 ft.) and there lands, and in urban vacant lots. It is are no records of P. s. sabuleti at all (al- usually closely associated with its normal though it is abundant on the floor of the larval host, alkali grass {DisticJilis spicata San Joaquin Valley). The nature of the [L.] Greene, Gramineae), but may breed east-slope contacts has not been studied, occasionally on Bermuda grass (Cynodon but few habitats suitable for either sub- dactylon [L.] Pers.), an introduced lawn species occur on the abrupt Sierran es- grass and weed. P. s. sabuleti is strongly carpment. multivoltine at sea level, with possibly as Polites sabuleti tecumseh differs from five many as generations a year. The summer P. s. sabuleti in being smaller, flight season is Aery long, ranging from hairier, and more heavily marked, especi- late March-April to mid- or late Novem- ally on the hindwing ventrally. The dark ber at Sacramento and Suisun City, Cali- markings on this wing are often described fornia. as being a "colder," grayer color than in P. s. in tecumseh occurs subalpine mea- P. s. sabuleti. Although a series of 23 dows that become dry in summer, and in tecumseh from the vicinity of Donner alpine fell-fields in the high Sierra Neva- Pass shows considerable variation, no sea- da. Its plant is host not known, but many sonal pattern is apparent. In P. s. sabuleti collectors have noted an association with from Sacramento and Suisun City (over species of sedges {Carex^ Cyperaceae). 450 specimens examined) there is marked Tilden (1959) reports P. s. tecumseh fly- seasonal variation: March-May and Sep- ing from Jul}' to September in Yosemite tember-November specimens are, on the National Park, which he interprets as in- average, smaller, darker, and hairier than dicating two broods. The more complete summer ones, and some are superficially data given in Tilden Garth and (1963) exceedingly similar to P. s. tecumseh, al- do not support .this interpretation, as there though there are minor ( but fairl}^ con- is no wide spread of dates within a given sistent) differences in certain details of year at a single locality. Farther north, the pattern. The phenotypes of wild at Donner Pass (7,000 feet) there is no specimens of both taxa are illustrated in indication of more than one brood. Em- Figures 1-3. mel and Emmel (1962) found it there from 19 June to 19 August, 1960; Sha- Experimental Methods and Results piro found it at the same localities from 1 July to 24 August, 1973, and 18 July to Would stock of P. s. tecumseh reared 12 August, 1974. The condition of Don- under conditions that produce summer ner Pass specimens does not suggest even phenotypes of P. s. sabuleti produce the a partial second brood. Like many mon- normal tecumseh phenotype, or would it tane butterflies, P. s. tecumseh emerges be modified in the direction of the low- later at higher elevations; thus, at 10,000 land, summer one? Ova were obtained feet it flies mainly in August and into from a female tecu?nseh collected at Don- ver}'^ early September. ner Pass (7,000 ft), 24 July 1974, and As with the altitudinal subspecies of from two female sabuleti collected in a Phyciodes campestris Behr (N^mphali- salt marsh at Suisun City, Solano County dae) previously studied (Shapiro, 1975a), (10 ft.), 6 August 1974. The resulting those of Polites sabuleti are separated by progeny were reared side by side in a zone in which neither seems to occur. plastic Petri dishes (51/2" diameter X %") At the latitude of Sacramento, P. s. sabu- at comparable densities (5-8 larvae/dish) leti is unknown as a breeding resident under continuous illumination from a 60w above 1,500 feet and P. s. tecumseh is un- bulb at 25C (77F). All larvae were fed recorded below 5,000 feet. Tilden (1959) fresh cuttings of Bermuda grass (Cynodon confuses the matter by indicating that P. dactylon), and mortality in both stocks s. sabuleti extends much higher at Yo- was negligible. Thirty adult P. s. sabuleti semite, but his data (given in Garth and (16 14 ? ) and thirteen P. s. tecumseh Tilden, 1963) make it plain that this re- cf fers to the arid east slope only: the rec- (8 cf 5 ? ) were obtained. Continuous ords are from Bridgeport (6,743 ft.) and light was selected as a regime ecologically Mono Lake (6,419 ft.). On the west slope nonsignificant to both stocks but known March 1975 SHAPIRO: POLITES SABULETI 35

(i-,-.:^ fei*:^ 'Ls^mJ'

\K,M£AJ 36 GREAT BASIN NATURALIST Vol. 35, No. 1 to inhibit diapause in P. sahuleti and re- stock. Normally, high-elevation or -lati- lated species. tude stocks of Lepidoptera develop more The two stocks differed in several re- rapidly than conspecific ones from more spects in the laboratory. First- and second- temperate climates when reared under instar larvae oi P. s. sabuleti were yellow- uniform laboratory conditions; the rever- ish green; in the third instar they turned sal of this situation in Polites sabuleti is purplish brown; and thereafter they re- to my knowledge unique in Lepido])teran mained that color. P. s. tecumseh larvae stocks in which diapause is not manifested were purplish brown throughout their de- in culture. velopment. At corresponding points in The developmental differences noted the life cycle the early stages of P. s. sabu- above were not mirrored in larval be- leti were always larger than their high- havior or morphology. The adults, how- altitude counterparts. The developmental ever, were obviously different and "true" rates of the two stocks differed very sig- to their normal phenotypes (Figs. 4, 5): nificantly, with little overlap: from egg to nondiapaused tecumseh reared at high adult P. s. sabuleti took 39-76 days temjieratures retained all of their distin- (weighted mean, 58.5 days) and P. s. guishing characters, including size. It thus tecumseh, 70-111 days (weighted mean, appears that the complex of characters 86.0). No diapause was observed in either present as a developmental option in low-

n

Fig. 4. Dorsal and ventral surfaces of representative bred Polites sabuleti sabiileti; continuous light, 25C.

Fig. 5. Dorsal and ventral surfaces of representative bred P. s. tecumseh; same conditions as in Figure 4. ;

March 1975 SHAPIRO: POLITES SABULETI 37

land, multivoltine populations is geneti- them seems to rim the length of the Sier- call}' fixed in P. s. tecumsch, confirming ra Nevada. Ehrlich et al.'s prediction. These experiments have been duplicated with a latitudinal subspecies pair—Cali- Discussion fornia Pieris occidentalis and its subspe- cies P. o. nelsoni Edwards from Fairbanks, Three sets of "altitudinal subspecies" Alaska (Shapiro, 1975b). Their pheno- have now been investigated in butterflies, typic differences are clearly heritable, and representing three different and quite un- the res]:)onse of both phenot}'pe and dia- related families. They are Picris occident- pause to photoperiod has been observed in alis Reakirt and its alpine representative, Fi and F:. hybrids. familiarly (but incorrectly) known as P. Studies of the Pieris occidentalis and P. o. "calyce^' Edwards (Pieridae); PJiycio- napi L. species complexes (Shapiro, 1975 des campcstris Behr and its montane sub- c) strongly imply that univoltinism is species montana Behr (Nymphalidae) evolutionarily derivative from multivoltin- and Politcs sahidcti. The first two are dis- ism, accompanying the successful invasion cussed at length in Shapiro (1975a). Each of increasingly rigorous climates. High- species presents a jiicture different from altitude and -latitude populations of wide- the others. spread species are probably derived from Pieris occidentalis shows xery little, if lowland sources, as has been well docu- any, genetic differentiation of the univol- mented for the Sierran alj^ine flora (Cha- tine, monophenic and bivoltine, diphenic bot and Billings, 1972). The overall pic- populations of high and moderate eleva- ture emerging from these studies supports tions, respectively. The alpine stock re- the suggestion that seasonal ])henotypes tains the ability to produce an estival of multivoltine populations may become phenot}'pe and to develop without dia- fixed through selection of modifiers in- pause, and its own phenotype is indis- fluencing thresholds tinguishable from the vernal one produced of develo]:)mental ex- pression ("genetic assimilation," Wad- downslope. Their mating behavior in- dington, 1953). somewhat unusual volves male aggregations on mountain- The circumstances in Phyciodes campestris tops, a behavior pattern conducive to gene montana will be explored in another pa- flow, and in laboratory experiments no per. reproductive barriers have been found be- tween uni- and bivoltine populations. Acknowledgments Phyciodes campestris shows a superfi- Collection of livestock for this study was cially similar picture, in that the high al- funded by Grant D-804 from the Com- titude subspecies montana, when reared mittee on Research of the Academic Sen- under outdoor conditions at sea level, pro- ate, U. C. Davis. Steven R. Sims, John duces the foothill phenotype rather than H. Lane, and Adriejine R. Shapiro assisted its own. However, the cold-season pheno- in field work. Aspects of this research type of lowland populations is quite dif- benefited from conversations from Mich- ferent from montana, and the ability to ael Rosenzweig, William E. produce the montana phenotype appears Bradshaw, and E. Jameson, Jr. to be restricted to high-elevation popula- W. tions. In this case, then, phenotypic plas- ticity is not reciprocal, and the high- LiTER' Ci elevation population is genetically dif- Chabot, B. F., and W. D. Billings. 1972. Ori- ferentiated. gins and ecology of the Sierran alpine flora Polites sabuleti shows the highest de- and vegetation. Ecol. Monographs 42:163- gree of differentiation yet encountered. 199. Clausen, J., D. D. The possibility that it has achieved repro- Keck, and W. Hiesey. 1940. Experimental studies on the nature of spe- ductive isolation (i.e., speciation) between cies. I. Effects of varied environments on high- and low-elevation populations can- western North American plants. Carnegie not be discounted. Because of the differ- Inst. Wash., publ. 520. ence in developmental time, no crosses . 1947. Heredity of geographically and between the stocks could be made. They ecologically isolated races. Amer. Nat. 81: 114-133. are not known to intergrade anywhere, . 1948. Experimental studies on the na- since the altitudinal discontinuity i)etween ture of species. III. Environmental responses 38 GREAT BASIN NATURALIST Vol. 35, No. 1

of climatic races of Achillea. Carnegie Inst. . 1975b. Photoperiodic control of devel- Wash., publ. 581. opment and phenotype in a subarctic popula- Ehrlich, p. R., R. W. Holm, and D. R. Parnell. tion of Pieris occidcntalis (Lepidoptera: Pi- 1974. The process of evolution, 2d ed. Mc- eridae). Canad. Entomol., in press.

Graw-Hill, New York. 378 pp. . 1975c. Developmental and phenotypic Emmel, T. C, and J. F. Emmel. 1962. Eco- responses to photoperiod in uni- and bivoltine logical studies of Rhopalocera in a high Sier- Pieris napi (Lepidoptera: Pieridae) in Cali- ran community—Donner Pass, California. I. fornia. Trans. Roy. Ent. Soc. London, in press. Butterfly associations and distributional fac- Tilden, J. W. 1959. The butterfly associations tors. J. Lepid. Soc. 16:23-44. of Tioga Pass. Wasmann J. Biol. 17:249- 271. Garth, J. S. and J. W. Tilden. 1963. Yosem- TuRESsoN, G. 1922. The species and the variety ite Butterflies. J. Res. Lepid. 2:1-96. as ecological units. Hcreditas 3:100-113. Klots, a. B. 1951. A field guide to the but- . 1925. The plant species in relation to terflies of North America, east of the Great habitat and climate. Hereditas 6:147-236. Plains. Houghton Mifflin, Boston. 349 pp. . 1929. Zur Natur und Begrenzung der Shapiro, A. M. 1975a. Ecotypic variation in Artenlieiten. Hereditas 12:323-334. montane butterflies. Wasmann J. Biol., in Waddington, C. H. 1953. Epigenetics and evo- press. lution. Symp. Soc. Exptl. Biology 7:186-199.