Evolutionary constraints shape the diversity of microinsects' wing morphology

Miniaturisation profoundly alters animal morphology, particularly
locomotory structures like insect wings. Larger insects possess membranous
wings optimised for flight dominated by inertial forces, while
microinsects have highly derived bristled wings with a reduced membrane,
adapted to viscous interactions. Distantly related microinsects share
striking similarities in some aspects of wing architecture, such as
elongated bristles or narrowed wing blades, while features such as
venation or proportion of bristled wing area vary widely. The basis of
these differences remains unknown. Although insect wing morphology is
largely shaped by evolutionary history, the role of evolutionary
constraints in macro-to-micro wing transition has not been examined. For
the first time, we combined morphological analyses with evolutionary
modelling to explore how selection for wing optimisation during
miniaturisation is constrained by evolutionary inertia in key wing
features. Analysing 39 bark beetle species, ranging greatly in size, we
found that some modifications, like bristle elongation or wing narrowing,
exhibit very low evolutionary constraints, enabling rapid adaptation to
miniaturisation. In contrast, traits like venation development or bristled
area proportion were highly constrained, requiring longer evolutionary
timescales to adapt. Our findings provide novel insights into the origins
of wing‑architecture diversity in microinsects, emphasising the role of
evolutionary constraints in modulating the transition from macro‑ to
micro‑wings.