Anastrepha Grandis and Ceratitis Capitata (Diptera: Tephritidae)
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Proceedings of 6th International Fruit Fly Symposium 6–10 May 2002, Stellenbosch, South Africa pp. 259–263 Variation in symmetrical patterns of development in Anastrepha grandis and Ceratitis capitata (Diptera: Tephritidae) A.O. Pires, D. Selivon* & A.L.P. Perondini Departamento de Biologia, Instituto de Biociências, Universidade de São Paulo, R. do Matão 277, 05508-900 São Paulo, SP, Brazil This paper reports preliminary results on the asymmetrical variation in the number of supra- fronto-orbital and frontal setae in the fruit flies Anastrephagrandis (Macquart) and Ceratitiscapitata (Wiedemann). Brazilian samples of 100 females and 100 males of A. grandis and 50 females and 50 males of C. capitata were analysed. In A. grandis the number of frontal setae varied from two to six on each side,and about 57% of the flies were asymmetrical.The number of orbital setae varied from one to three on each side, and 27% of the individuals were asymmetrical. The scores of asymmetry (R–L) were symmetrically distributed around 0 (zero). For the frontal setae the distribution did not deviate from a normal curve, while for the orbital setae the distribution was leptokurtic. The variation of frontal setae is thus in accordance to the fluctuating asymmetry model, and for the orbital setae it is not clear if the variation does not include a covariation between sides.In C.capitata the number of frontal setae was two and only one male with three setae was found in the sample.The supra-fronto-orbital setae varied between two and three on each side,84% of the males and 92% of the females being symmetrical.The anterior supra-fronto-orbital setae of C.capitata showed sexual dimorphism,being plumose in males.These setae did not present variation.The degree of variation for both types of setae was so low that it does not allow inferences about the mode of asymmetrical deviations. INTRODUCTION at random between the right and left sides of the Development of animals is brought about by the body. FA has been studied in a wide number of action of a multitude of genes that function animal species, and it was found to affect different coordinately to construct the phenotype in a structures of the body (Parsons 1990; Markow precise way. In bilateral animals, perfect symmetry 1995). Although it is clear that FA reflects an insta- for bilateral characters are expected since the bility of developmental processes, and thus is a phenotype of an individual is the product of the measure of the capacity of an individual to respond same genotype (Thoday 1956). However, variation to genetic and environmental perturbations, it is in the morphology of animal body parts is common, not precisely known how and when these stressors ranging from subtle alterations to substantial cause detectable effects (reviews in Parsons 1990; modifications in traits. As the expression of the Møller & Pomiankowski 1993; Markow 1995). As genome is also under the influence of the environ- pointed out by Markow (1995), it is necessary that ment,phenotypic variation may be due to genetics, studies be done across taxa with different environmental disturbances or both (Parsons 1990; biological attributes in order to get a better insight Markow 1995). One form of variability in animals into the phenomenon. with bilateral symmetry is the differences between In the course of an analysis to characterize popu- homologous structures on the left and right sides lations of fruit flies of the genus Anastrepha of the body.Asymmetry of this sort can be of three (Selivon 1996; Selivon & Perondini 1998; Selivon types, directional asymmetry, antisymmetry and et al. 1999; Selivon et al. 2004), the presence of fluctuating asymmetry (Van Valen 1962; Parsons asymmetrical individuals for the frontal head setae 1990; Palmer & Strobeck 1986, 1992). In directional was observed in some species. Some species of asymmetry (DS), the structures on one side of the fruit flies are commonly found over extensive geo- body are almost always more variable than the cor- graphical areas, where they utilize a variety of host responding structures on the other side; fruits and are usually exposed to very different en- antisymmetry (AS) is characterized by the fact that vironmental conditions, even those disturbed by variability is so high that it can not be predicted human activity. Since FA may result from exposure which side will be more variable than the other;and to harmful environmental factors, it seems worth- in fluctuating asymmetry (FA) the differences occur while to analyse species of fruit flies for asymmetri- *To whom correspondence should be addressed. cal variations of morphological traits, and E-mail: [email protected] eventually to correlate these variations to pertur- 260 Proceedings of the 6th International Fruit Fly Symposium Fig. 1. Heads of a male Anastrepha grandis (A) and of a male Ceratitis capitata (B) in frontal view. Note that this specimen of A. grandis is asymmetrical for the frontal setae (arrow). In C. capitata, the plumose form of the anterior orbital setae is seen (arrow). bations, either genetic or environmental. We RESULTS present here results on the type of variability of the frontal and orbital setae of Anastrepha grandis Anastrepha grandis (Macquart) and Ceratitis capitata (Wiedemann). The heads of adult Anastrepha species display a series of conspicuous seta. The orbital setae are MATERIALS AND METHODS located in front of the ocelli, and in the frons there A. grandis was collected from pumpkins (Cucur- are two rows of frontal setae,one on each side par- bita pepo) from an inland plateau in the state of São allel to the eyes in a dorsal/ventral orientation Paulo (22°35’S,46°50’W), while C. capitata was re- (White & Elson-Harris 1992),as shown in Fig. 1A for covered from infested fruits of Terminalia catappa A. grandis. (tropical almond) collected in the coastal area of Substantial variation in the number of both types the state of São Paulo (23°40’S,45°20’W). Adults of of setae per side was observed in A.grandis.For the both species were recovered in the laboratory and frontal setae, sides with 2–6 setae were found transferred to 70% ethanol for storage. (Fig. 2A).When sides were analysed independently, Samples of 100 adults of each sex of A. grandis it was found by a Kolmogorov test that there were and 50 of C. capitata were used. The heads were no significant differences in the distributions of the examined under a stereo-microscope and the number of setae between the left and right sides of number of orbital and frontal setae on each side male or female individuals (males, d = 0.03 < d5% = was recorded. Males and females were scored 0.192, n.s.; females, d = 0.08 < d5% = 0.192, n.s.), nor separately.The number of setae could be unambig- differences between males and females (pooled uously determined, even in cases where they were sides),as shown in Fig. 2 (d = 0.09 < d5% = 0.136,n.s.). lost or broken during collection or processing The mean number (±S.D.) of setae per side was of the specimens, owing to the presence of the 3.82 ± 0.67 in males and 3.85 ± 0.73 in females. For socket of setae implantation. From a sample of the orbital setae, sides bearing 1–3 setae were specimens, images of the head were taken by found,and those with two setae were the most fre- a Leica DC100 CCD camera coupled to the stereo- quent,as shown in Fig. 2B.There were no significant microscope. differences among males and females, the mean The frequency distributions of the number of number of orbital setae per side being 1.60 ± 0.49 setae per side, and between males and females, and 1.65 ± 0.47, respectively. were compared by a Kolmogorov-Smirnov test Symmetrical and asymmetrical specimens were (Sokal & Rohlf 1981). Asymmetry was evaluated by found, as illustrated in Fig. 1A. Since for both types the right minus left (R–L) scores (Van Valen 1962, of setae no significant differences between sexes Palmer & Strobeck 1986),and the parameters of the were observed, the data were pooled for the next distributions, means, standard deviations, skew- analysis. The scores of asymmetry (R–L) for both ness, kurtosis for signed (R–L) values of each trait, types of setae were distributed around 0 (zero), as and confidence intervals. Significant differences shown in Fig. 3. Parameters of these curves are were calculated according to Zar (1974). shown in Table 1. For the frontal setae (Fig. 3A) the Pires et al.: Variation in symmetrical patterns of development in Anastrepha grandis and Ceratitis capitata 261 Fig. 2. Frequency distributions of specimens of Anastrepha grandis according to the number of frontal (A)or orbital (B) setae per side. Fig. 3. The distribution of asymmetry scores (R–L) of frontal (A) and orbital (B) setae of Anastrepha grandis, and of orbital setae (C)ofCeratitis capitata. The expected normal distribution curve for each seta is superimposed on the graphs. distribution did not deviate from a normal curve, may show symmetrical distribution of R–L scores since skewness was non-significant (t = 0.1547; (Palmer et al. 1993). In the present case, however, 0.50 < P < 0.60), and the curve was mesokurtic, scatterplots were not very informative since the although at a marginal level (t = –1.705,0.025 < P < data are discrete variables (1, 2,..., 6 setae). Instead, 0.05). For the orbital setae (Fig. 3B), the curve was we scored the frequencies of the individual pheno- symmetrical (non-significant skewness, t = 0.326, types to get information on the association of sides 0.60 < P < 0.70) but it departed from normality bearing different number of setae.