There is a really cool paper in Current Biology about the how even an animal's sensory apparatus adapt to their particular evolutionary niche.
Greiner et al. looked at four closely-related species of ants from the genus Myrmecia. (As you can see from the picture, these ants are also huge.) These four species are all relatively similar lifestyles, going out to forage on daily intervals. The four species differ, however, on when they go out to look for food. Some of them go out in mid-day; some go out only at night.
The authors compared the time when the animals would forage with the size. The data is shown in the following figure (Figure 1 in the paper, click to enlarge):
The left column shows a picture of the ant species in question. The middle column shows a histogram of the ant species' activity at different times of the day. The right column shows an section of the ants eye for the comparison of size. You can see that the ant species with the smaller eyes are spend most of their time foraging during the day whereas the ant species with the larger eyes are either nocturnal or forage at dawn/dusk.
The authors went on to calculate the optical sensitivity of the ants eyes to show that it follows a similar trend. This trend was not accounted for by difference in the relative size of the ants i.e. the ants with the largest eyes were not necessarily the largest overall.
The authors conclude that this suggests that the eye sizes and sensitivities have adapted for each ant species relative foraging times. They present these four species as a model organism of adaptation to a visual niche -- meaning I think that the visual stimuli associated with that animals food and world. To whit:
In conclusion, the large differences in photoreceptor and lens dimensions in these ants do not scale with body size but are clearly related to periods of foraging activity that occur in different ambient light conditions. Both superposition and apposition compound eyes have been modified in relation to ambient light conditions in a number of insect groups [10], [11] and [12]. Myrmecia ants, however, represent an ideal model system to investigate the evolution of visual niche specialisation, including the metabolic and space constraints on eye design, as they exhibit such a tight correlation between the timing of foraging bouts and the structural adaptations of their apposition compound eyes. Moreover, in contrast to many flying insects, the walking, central place foraging ants may allow us to identify the range of visual tasks they are confronted with during their regular excursions.
The full citation for this paper is:
Greiner B, Narendra A, Reid SF, Dacke M, Ribi WA, Zeil J. "Eye structure correlates with distinct foraging-bout timing in primitive ants." Curr Biol 2007 Oct 23 17(20):R879-80
Hat-tip: Faculty of 1000
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