Animals subject to environmental stress often exhibit developmental instability, measured as Fluctuating Asymmetry (FA) - small, random deviations from perfect left-right symmetry in bilateral traits. Recent studies have demonstrated increased FA in forest-dwelling animal populations in areas where vegetation is removed by logging. In April 1999, a Class 5 tornado struck near Cincinnati, causing major damage to the University of Cincinnati Benedict/Hazelwood Botanical Preserve. Approximately half of the 65 acre forest was destroyed, and the area is currently the site of studies on ecosystem stress and recovery. We used FA measurement as a means of determining the impact of this ecosystem disturbance on populations of Schizocosa ocreata (Hentz), a common forest-dwelling wolf spider. As FA in sexually selected male traits has been shown to be a sensitive indicator of environmental stress, we measured FA of foreleg tufts in male S. ocreata. Spiders from the first post-disturbance generation were collected in the Spring of 2000 from both disturbed and undisturbed sites within the preserve, and preserved specimens were photographed and measured using digital imaging. Signed (R-L) FA of male tuft area was normally distributed with a mean of zero, indicating 'ideal' or 'true' FA, a reflection of Developmental Instability (DI). Tuft area FA in male S.ocreata was significantly higher in the disturbed site, suggesting that ecosystem-level stress may produce higher levels of developmental instability in arthropod populations. To our knowledge, this is the first study of FA in invertebrates associated with environmental stress from a major natural catastrophe.
Species 1: Araneae Lycosidae Schizocosa ocreata (Brush-legged wolf spider)
Keywords: fluctuating asymmetry
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