Morphological shifts linked to urbanization compromise pollination services by orchid bees

Urbanization impacts biodiversity in multiple ways by creating novel environmental conditions that challenge individual survival. The expansion of building areas, along with habitat loss and rising temperatures in urban areas, not only affect species diversity and composition, but often drive morphological, physiological, and functional changes either as adaptative responses or as outcomes of environmental stress. Such individual-level shifts in key traits can compromise critical ecosystem services like pollination. In this sense, orchid bees (Apidae: Euglossini) are essential pollinators in Neotropical ecosystems and could serve as excellent model organisms for studying whether potential effects of urbanization on morphology compromise specialized pollination services. In this study, we sampled orchid bee communities across 14 sites representing an urbanization gradient in a Neotropical city surrounded by cloud forest in Mexico. We estimated urbanization using satellite imagery, assessed a set of morphometric measurements in the five most abundant orchid bee species, and quantified pollination of Gongora galeata (Orchidaceae), a specialized orchid that is exclusively pollinated by Euglossa obrima. At the assemblage level, urbanization was associated with smaller body sizes (i.e. head width) and higher wing asymmetry, revealing developmental stress. In the case of E. obrima, wing asymmetry was associated with lower pollination probability of G. galeata. These findings suggest that urbanization promotes morphological changes in orchid bees, and such changes at the individual level are compromising pollination, a fundamental ecosystem service provided by these specialized Neotropical bees.