Color, activity period, and eye structure in four lineages of ants: Pale, nocturnal species have evolved larger eyes and larger facets than their dark, diurnal congeners

Evolution of compound eye morphology underlies differences in vision between closely related Drosophila species

BACKGROUND

Insects have evolved complex visual systems and display an astonishing range of adaptations for diverse ecological niches. Species of Drosophila melanogaster subgroup exhibit extensive intra- and interspecific differences in compound eye size. These differences provide an excellent opportunity to better understand variation in insect eye structure and the impact on vision. Here we further explored the difference in eye size between D. mauritiana and its sibling species D. simulans.

RESULTS

We confirmed that D. mauritiana have rapidly evolved larger eyes as a result of more and wider ommatidia than D. simulans since they recently diverged approximately 240,000 years ago. The functional impact of eye size, and specifically ommatidia size, is often only estimated based on the rigid surface morphology of the compound eye. Therefore, we used 3D synchrotron radiation tomography to measure optical parameters in 3D, predict optical capacity, and compare the modelled vision to in vivo optomotor responses. Our optical models predicted higher contrast sensitivity for D. mauritiana, which we verified by presenting sinusoidal gratings to tethered flies in a flight arena. Similarly, we confirmed the higher spatial acuity predicted for Drosophila simulans with smaller ommatidia and found evidence for higher temporal resolution.

CONCLUSIONS

Our study demonstrates that even subtle differences in ommatidia size between closely related Drosophila species can impact the vision of these insects. Therefore, further comparative studies of intra- and interspecific variation in eye morphology and the consequences for vision among other Drosophila species, other dipterans and other insects are needed to better understand compound eye structure-function and how the diversification of eye size, shape, and function has helped insects to adapt to the vast range of ecological niches.

Rediscovery of the Canary Islands endemic Aphaenogaster hesperia Santschi, 1911 (Hymenoptera, Formicidae, Myrmicinae)

The Canary Islands endemic species Aphaenogaster hesperia Santschi, 1911 was described based solely on two workers captured in a north-western coastal area of Tenerife (Canary Islands) in 1902 and 1903. The species has not been recorded in the last 100 years and only information on its type locality is known. This species, belonging to the crocea group, has been recently rediscovered in a new site within a pine forest at 950 m a.s.l. The new area is a very different habitat, revealing a lack of ecological knowledge of the species, which may have caused the species to have remained unnoticed for more than 100 years. Novel distributional and morphological data are provided.