Loyola University Chicago

Department of Biology

Katie Van Dame

Katie Van Dame

Title: Impacts of Stormwater and Land Cover on the Abundance, Transport, and Composition of Anthropogenic Litter in Urban Watersheds

Date: Tuesday, May 7th, 2024

Time: 11:00 A.M. CST


Time: May 7, 2024 11:00 AM Central Time (US and Canada)
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Meeting ID: 834 8549 9213
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Meeting ID: 834 8549 9213
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Males and females of a species often differ from one another in phenotype—a phenomenon known as sexual dimorphism. Sexual dimorphism is most often attributed to sexual selection. However, sexual dimorphism also derives from natural selection when resource competition generates disruptive selection favoring specialization on different resources, resulting in niche partitioning and the evolution of dimorphism in traits related to competition. Sexual dimorphism may be an important route to increased individual fitness (i.e., more resources, more survival).  An existing dataset was used to quantify the existence of sexual dimorphism in 32 populations of Three-spine Stickleback fish, comprised of 16 paired lake-stream populations. We tested for shared and unique aspects of dimorphism within and across lake-stream pairs and asked whether variation in dimorphism could be explained by variation in the environment. We found mixed evidence that dimorphism varied within and across lake-stream pairs. Ecologically driven divergent selection between sexes may derive from differences in their environments, resulting in the evolution of dimorphism in traits related to habitat use and resource competition.  Such differences between sexes should reduce intersexual competition (Boughman 2011). Based on this, we predict that intersexual competition (males vs. females) should be lower than intrasexual competition (males vs. males, females vs. females) because Three-Spine Stickleback that look more like each other (i.e., within the sexes) should share more similar resources. If true, then survival and growth rates in experimental enclosures that pair same-sex fish should be lower than in enclosures containing opposite-sex pairs. Using Three-spine Stickleback, we ran a 5-week enclosure experiment with 119 cages containing either same-sex or opposite-sex pairs, using body condition and survival to measure dimorphism's effects on competition. We found that male-male pairs ended with better body conditions than female-female and male-female pairs. Individually, males also had slightly better survival rates than females. This suggests that our evidence is mixed and doesn’t strongly support our prediction that ecologically driven selection may play a role in sexual dimorphism.