Considering decoupled phenotypic diversification between ontogenetic phases in macroevolution: An example using Triggerfishes (Balistidae)

Across the Tree of Life, most studies of phenotypic disparity and
diversification have been restricted to adult organisms. However, many
lineages have distinct ontogenetic phases that differ from their adult
forms in morphology and ecology. Focusing disproportionately on the
evolution of adult forms unnecessarily hinders our understanding of the
pressures shaping evolution over time. Non-adult disparity patterns are
particularly important to consider for coastal ray-finned fishes, which
often have juvenile phases with distinct phenotypes. These juvenile forms
are often associated with sheltered nursery environments, with phenotypic
shifts between adults and juvenile stages that are readily apparent in
locomotor morphology. Whether this ontogenetic variation in locomotor
morphology reflects a decoupling of diversification dynamics between life
stages remains unknown. Here we investigate the evolutionary dynamics of
locomotor morphology between adult and juvenile triggerfishes. We
integrate a time-calibrated phylogenetic framework with geometric
morphometric approaches and measurement data of fin aspect ratio and
incidence and reveal a mismatch between morphospace occupancy, the
evolution of morphological disparity, and the tempo of trait evolution
between life stages. Collectively, our results illuminate how the
heterogeneity of morpho-functional adaptations can decouple the mode and
tempo of morphological diversification between ontogenetic stages.