Polyphenism and Population Biology of Eurema Elathea (Pieridae) in a Disturbed Environment in Tropical Brazil
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Journal of the Lepidopterists' Suciety 53( 4), 1999, 159- 168 POLYPHENISM AND POPULATION BIOLOGY OF EUREMA ELATHEA (PIERIDAE) IN A DISTURBED ENVIRONMENT IN TROPICAL BRAZIL FABIO VANINI, VINfcIUS BONATO AND ANDRE VICTOR LUCCI FREITAS] Museu de Hist6ria Natural, Instituto de Biologia, Universidade Estadual de Carnpinas, CP 6109, 1308,3-970, Campinas, Sao Paulo, Brazil ABSTRACT. A population of E. elathea was studied for 13 months, from \Aay 1996 to May 1997 in a disturbed environment in suburban Campinas, southeastern Brazil. The population showed fluctuations in numbers throughout the study period, with well-marked peaks of abun dance in June-July, November- December and February. Sex ratio was male biased in four months and the time of residence was higher in the dry season. Both sexes were polypheni c; p aler phenotypes occurred in the dry season and darker phenotypes in the wet season, Paler pheno types were more frequently recaptured and had higher residence values than darker ones. Differences in behavior were attrihuted to adapta tion to seasonally different environments. Additional key words: Coliadinae, mark-recapture, urban butterflies. The recent surge of interest in the conservation of 1992). The polyphenism in this species was reported tropical environments has led to an increase in studies by Brown (1992), who noted that dry season forms of th e natural history and ecology of organisms resid were dorsally paler than wet season forms, The species ing in the tropiCS (Noss 1996). These have included is common on the Campus of the Universidade Estad some long-term studies on population biology of ual de Campinas (Unicamp), where it can be observed neotropical butterflies, focused mainly on aposematic flying on the lawns and visiting several species of wild groups such as Heliconiini, Ithomiinae and Troidini flowers (Oliveira 1996), (Turner 1971, Ehrlich & Gilbert 1973, Brown & Ben This paper provides a detailed account of the popu son 1974, Drummond 1976, Young & Moffett 1979, lation parameters of Eurema elathea, and our objec Brown et a1. 1981, Saalfeld & Araujo 1981, Vasconcel tives are to: (1 ) examine the age-structure, size and sex los-Neto 1980, 1986, 1991, Freitas 1993, 1996, Haber ratio and size of the population; (2) describe the varia 1978, Rogner & Freitas 1999). Population studies with tion in proportions of the different polyphenic types the Pi eridae, however, have focused on non-tropical throughout the year; and (3) provide subsidies to the species, especially agricultural pests (Watt et a1. 1977, management of this species in urban habitats, 1979, Tabashnik 1980) common in this family (Chew 1995). MATERlALS AND METHODS Seasonal polyphenism (Shapiro 1976, 1984) is an in A mark-release-recapture (MRR) study was carried teresting feature of some pierid butterflies (the out on the Campus of the U niversidade Estadual de "whites" and "small yellows"). Numerous insect groups, Campinas (Unicamp), Sao Paulo state, southeastern especially butterflies, are polyphenic in response to sea Brazil, as part of a project of study of urban ecology on sonal abiotic factors (Shapiro 1976). Degree of the Campus of the University, Annual rainfall is about melanization, number of wing spots (especially eye 1360 mm and mean temperature 20.6°C (data from like markings on the wings in Satyrinae), and color the Instituto Agronomico de Campinas). The regional variations have been attributed to adaptation to sea climate is markedly seasonal, with a warm wet season sonally different environments and thermoregulation from September to April and a cold dry season from (Shapiro 1976, Brakefield & Larsen 1984, Kingsolver May to August. During the research, the mean tem & Wiernasz 1987, Braby 1994, Van Dyck et a1. 1997, perature of the coldest month was 17.6°C and of the Windig et aI. 1994). In general, seasonal morphs are warmest month was 24.8°C, with climate typical of the related to dry VS. wet season in the tropics, and spring region (Fig. 1), except for May 1997, which was a rainy VS . summer or fall in temperate regions (Nylin 1989), month and thus was included in the wet season. Many different environmental factors induce poly The vegetation on the campus where the study was phenism (sec Shapiro 1984 and Jones 1992). Different conducted consists oflarge lawns with sparse trees and behaviors linkcd to different color patterns also have scattered small flowering shrubs, The lawn was mowed been reported (Shreeve 1987, Nakasuji & Nakano five times during the period of study, as part of normal 1990, Van Dyck et aI. 1997). procedures of maintenance of the campus. The study The pi erid Eurema elathea (Cramer, 1777) is a small area was divided into nine plots corresponding to Neotropical butterfly common in lawns, pastures, and lawns separated by walking trails connecting the build other disturbed environments (DeVries 1987, Brown ings on the Campus (Fig, 2), Butterflies were marked and recaptured between 28 I address correspondence to this author May 1996 and 27 May 1997 (1- 3 times per week) , in 160 JOURNAL OF THE LEPIDOPTERISTS' SOCIETY 400 300 0 ~ 200 ...J 100 ...J ....<l: 80 ~ Z w C{ 0: 0: ::> d I- <I 0: w 20 ::."- w I- AMJJASONDJFMAM 1996 (MONTHS) 1997 FIG. 1. Climagram for the Campinas region during the research FIG. 3. Color types for malcs (top and middle rows ) and females (based on Santos 1965 and Walter 1985). Hatched = humid periods, (bottom row) of Eurerna elathea (background pale yellow, solid = black = superhumid periods, and dotted = dry periods. bla<:k, dotted = orange). sessions with 2-3 persons lasting 2-3 hours near mid color types. The amount of black on the dorsal day, totaling 84 field days. The sessions ended when forewing inner margin was recorded for males and fe more than 80% of individuals captured represented re males (details in next section). captures of marks already given or recorded on that day. The mark-release-recapture (MRR) data were ana Butterflies were net-captured, numbered on the un lyzed by the Jolly-Seber (Southwood 1971) method for derside of the foreWings (felt-tipped pen), and re estimating population parameters (CMLR software leased. Wing wcar (seven "age" classes), point of cap developed by Dr. R. B. Francini, Unisantos) for the ture, sex, forewing length and food sources were obtainment of estimated population numbers and recorded (all follOwing Freitas 1993, 1996, and Rogner standard errors. Daily results were tabulated as "num & Freitas 1999). Forewing length was measured with ber of individuals captured per day" (NICD), and a ruler, to the nearest mm. The age of individual but "number of individuals present per day" (NIPD). To terflies was estimated in seven categories based on estimate the NIPD, recaptured individuals were con wing wear (Ehrlich & Davidson 1960, Brussard & sidered to be present in the population on all previous Ehrlich 1970, Ehrlich & Gilbert 1973), posteriorly days since the day of first capture (=marked animals at grouped into three: new, intermediate and old (as in risk) (following Rogner & Freitas 1999). The data were Freitas 1993, 1996 and Rogner & Freitas 1999). Values grouped for analysis into "dry season" (May-August from one to seven, attributed to each wing wear class 1996) and "wet season" (September 1996-May 1997), (where 1 = teneral and 7 = tattered) were used to com in accord with the rainfall (climagram in Fig. 1) . pare the mean "age" of first captures in the different Phenotype. Males were classified in six color types (I to VI) based on the amount of black on the dorsal forewing inner margin (Fig. 3), following a classifica tion used previously by Ruszcsyk and collaborators (unpublished data) for E. elathea in central Brazil. The extremes were "marginal black bar absent" (type I) 50% MJJASONDJFMAM 1996 (MONTH S ) 1997 FIG. 2. Study area on the Campus of the Universidade Estadual de Campinas, showing the eight grassy areas (closed figures) sepa FIG. 4. Monthly percent of different male color types of E. rated hy open trails. The small circular area, covered hy dense elathea from May 1996 to May 1997. From top to bottom in first col shrubs (Calliandra sp., Fabaceae) was not sampled. umn, types I to VI. VOLUME 53, NUMBER 4 161 50% J JASONDJFMAM 1996 (MONTHS) 1997 Frc.6. Number of individuals present per day (NIPD) of males N 0 J F M A (below) and females (above) of E. elathea from May 1996 to May 1997. Arrows indicate mechanized grasscuttings. 1996 I i997 F1C . .5. Monthly percent of different female color types of E. the study, with .320 of these recaptured at least once. elathea from May 1996 to May 1997. White = type I (pale), black = type II (dark). Because the type II was absent from May to October In the dry season (25 days), the number of individuals 1996, the first six months were combined in a single bar.. captured per day varied from 0 to 53 individuals (mean = 21.3; SD = 14.3) for males and 0 to 32 (mean = 13.6; SD = 8.2) for females. In the wet season (59 days) , the and "broad and complete marginal black bar" (type number of individuals captured per day varied from 0 VI). In females only two color types were defined: to 32 individuals (mean = 9.8; SD = 8.4) for males and "marginal black bar absent" (type I) and "short mar o to 27 (mean = 7.9; SD = 7.8) for females. The num ginal black bar" (type 11). Intermediates, as defined by ber of individuals present per day in the dry season the length and width of the black stripe, were not ob varied from 0 to 64 individuals (mean = 27.9; SD = served in females. The variation appeared to be con 17.2) for males and 0 to 39 (mean = 17.6; SD = 11.0) tinuous in males, causing some problems in defining for females.