Patterns of asymmetry in wing traits of three island and one continental population of Merodon albifrons (Diptera, Syrphidae) from Greece

Abstract

Background: Individuals of populations experiencing environmental and/or genetic disturbance during their development experience a reduction in buffering capacity of the developmental system. Such a reduction influences the level of developmental stability, which is often reflected in morphological traits such as asymmetry. Three kinds of asymmetry have been described: directional asymmetry (DA; i.e. left and right body side consistently differ from each other), fluctuating asymmetry (FA; i.e. subtle non-directional differences between left and right sides in bilaterally symmetrical traits), and antisymmetry (i.e. deviation from symmetry towards either the right or left sides). Fluctuating asymmetry is often used as an indicator of developmental stress. The variation of FA level is considered to be taxon, trait and stress specific. Accordingly, being exposed to various forms of environmental and/or genetic stress, the levels of FA may differ among demes. Moreover, different genetic constraints of two wing traits (lower heritability of wing size vs. higher heritability of wing shape) may influence the difference between island and mainland populations in the level of size FA would be more prominent than in the level of shape FA. Hypothesis: Island populations, which are often isolated and small, operate different evolutionary processes affecting developmental processes from those present in mainland populations. Hence, island populations experience significantly different FA compared with continental populations. Organism: The hoverfly, Merodon albifrons (Diptera, Syrphidae) Times and places: We collected a total of 60 female and 141 male specimens in spring 2009, 2010, and 2011 from the Greek islands of Lesbos (25 females and 38 males; May 2009), Chios (11 females and 60 males; May 2009), and Naxos (12 females and 13 males; May 2010). We also collected from the Greek mainland locality of Volos (12 females and 30 males; May 2009 and May 2011). Analytical methods: We used landmark-based geometric morphometrics to analyse level and patterns of asymmetry (FA, DA, and antisymmetry) in two wing traits (size and shape) within/among populations. We completed morphometric and statistical analyses using the MorphoJ package (version 1.04a) (Klingenberg, 2011), R software 2.15.1 (R Development Core Team, 2008), and Statistica 10 (StatSoft, 2012). Since male and female wing shape asymmetries were not significantly different, we pooled the sexes in all analyses. Results: We found highly significant FA, DA, and differences among individuals in wing size and shape in all studied samples. Antisymmetry was absent from the data. We found no significant difference in FA level in wing size (Levene's test: F2,156 = 2.11, P = 0.12) and shape (Levene's test: F2,156 = 2.40, P = 0.09) among three island populations, or in wing shape (Levene's test: F1,199 = 0.55, P = 0.46) between island and mainland populations. In contrast, the level of FA in wing size was significantly different (Levene's test: F1,199 = 14.01, P < 0.001) between island and mainland populations. The pattern of FA shape variation measured by matrix correlation and visualized using principal component analysis suggested similarities among the populations analysed. In all populations, landmarks located in the proximal part of the wing (wing base) contributed substantially to overall shape variability, which reflected a response of the same developmental processes to disturbance during the development of individuals. Conclusion: Populations from the island and mainland localities are connected, resulting in a common pattern of wing shape development. © 2012 Jasmina Ludoski.