Abstract

Biodiversity is shaped by the interplay of ecological, evolutionary, and historical processes. Understanding these patterns, particularly the drivers of speciation and diversification, is a key challenge in evolutionary biology. Using flatfishes (Order: Pleuronectiformes) as a model system, and combining phylogenetic comparative methods, global datasets of fish traits and phylogenies, and geospatial analyses of marine regions, this thesis examines broad-scale evolutionary patterns across fishes. Chapter 1 provides strong statistical support for three longstanding ecogeographical rules across all teleost fishes. It also presents the first large-scale, phylogenetically informed test of Jordan’s Rule and pleomerism using comparative methods. Variation across orders suggests these patterns may reflect lineage-specific constraints rather than universal principles. We evaluated two leading hypotheses proposed to explain the latitudinal diversity gradient: clade age and speciation rate. Despite a clear latitudinal gradient in flatfish species richness, neither factor predicts increased diversity across latitudes or marine ecozones. However, older clades tend to be more species-rich, supporting a time-for-speciation effect at the clade level. We then focus on flatfishes as a group that exhibits both elevated diversification rates and the inverse latitude-diversification gradient observed in teleost fishes. To investigate the drivers of this pattern, species-level ecological and behavioral traits were analyzed. While body size, depth range, and trophic level show no significant associations, migratory behavior emerges as a consistent predictor of increased diversification across all flatfishes and within Pleuronectidae. These findings suggest that migration-driven ecological opportunity plays a central role in facilitating speciation in benthic marine fishes.

Together, these results provide an integrated perspective on how morphology, environment, lineage history, and behavior interact to shape biodiversity in marine systems. This work contributes to ongoing debates in evolutionary biology and offers insight into how marine biodiversity may respond to environmental change