OPTICAL SCALING IN CONSPECIFIC CATAGLYPHIS ANTS

This study examines the effects of body size variation on the optical properties of the compound eyes of visually guided desert ants belongi ng to the genus Cataglyphis, Although linear head size may vary by a f actor of 2 within conspecific workers and most optical parameters chan ge accordingly, the extent of the visual field remains constant, Compa rative measurements carried out on workers of three species (C, albica ns, C, bicolor and C, fortis) and on reproductive females and males of one species (C, bicolor) show that the form (size and shape) of the v isual field is highly characteristic for each caste/species, A constan t visual field is realised by reciprocal scaling rules for the number of ommatidia and the angular spacing of ommatidia, While larger ants h ave more ommatidia per compound eye, interommatidial angles are reduce d accordingly, thus giving rise to a constant visual field, Among cons pecific ant workers, the relationship between spatial visual acuity an d eye size is similar to that found in interspecific comparisons and r eflects optical constraints imposed on the design of the compound eye. Mapping of spatial visual directions onto the compound eye surface re veals a characteristic, inhomogeneous distribution of interommatidial spacing, particularly a foveal band with increased visual acuity in th e vertical direction, This 'visual stretch' viewing the horizon is sim ilar to that found in a variety of flying insects, Although, among con specific workers, both the number of ommatidia and the interommatidial angles vary with varying head size, the overall pattern of interommat idial spacing is maintained so that corresponding positions on the com pound eye of small and large individuals look in equivalent directions in space, These findings are in accordance with the observation that the shape of the compound eye surface, as expressed by the radius of c urvature along cross sections, is similar in small and large ants.