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Migration is a common life history strategy across the animal tree of life. This behavior is energetically demanding and may trigger strong selection for the evolution of an optimal ecomorphology to lessen energetic costs, yet the ecomorphology of migratory aquatic species remains poorly understood. Previous studies have demonstrated that migratory fishes exhibit predictable phenotypic patterns in body size evolution in response to evolving migration: migratory fishes are larger than non-migratory fishes. Migratory fishes may also have functional traits (e.g. fin shape) associated with locomotion that have experienced similar selective forces and exhibit predictable evolutionary patterns, resulting in migratory lineages sharing a single adaptive peak. Fishes display an extreme migratory behavior called diadromy, which is the migration between fresh and saltwater environments. Diadromy has independently evolved more than 10 times within Clupeiformes, an order of ray finned fishes that includes anchovies, herring, sardines, and their allies. In this study, I investigated the phenotypic differences of locomotive traits among diadromous and non-diadromous Clupeiformes. I hypothesized that (1) diadromous and non-diadromous species will differ in locomotive traits and body shape and (2) diadromous and non-diadromous species will display no differences in morphological traits that are not associated with locomotion. I tested these hypotheses by employing linear morphometrics and phylogenetic comparative methods to analyze phenotypic traits across 15 diadromous and 77 non-diadromous clupeiformes. My results provided evidence that diadromous and non-diadromous species significantly differ in caudal aspect fin ratio (P = 0.02) and body width (P = 0.047), however there was a great deal of variation among all Clupeiformes in this study. Overall, my results demonstrated that diadromous species do not occupy a single adaptive peak. Instead they are found in several regions of morphospace, suggesting that a many-to-one mapping scenario may better describe migratory ecomorphology. Morphological trade-offs can play a critical role in the form-performance impact on populations, and it can inhibit or put constraints on the optimization of a species and its ecological success.
DeHaan, Lindsey, "The Macroevolution of Diadromous and Non-Diadromous Clupeiformes." (2019). Honors Theses. 3211.
Honors Thesis-Open Access