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Abstract

The ecological and developmental selective pressures associated with evolution have shaped most animal traits, such as behavior,
morphology and neurobiology. As such, the examination of phylogenetic characteristics of the nervous system can be utilized as a
means to assess these traits, and thus, to evaluate the underlying selective pressures that produce evolutionary variation between
species. Recent studies across a multitude of Drosophila have hypothesized the existence of a fundamental tradeoff between two
primary sensory organs, the eye and the antenna. However, the identification of any potential ecological mechanisms for this observed
tradeoff have not been firmly established. Our current study examines two monophyletic species within the obscura group,
and asserts that despite their close relatedness and overlapping ecology, they deviate strongly in both visual and olfactory investment.
Here we contend that both courtship and microhabitat preferences mirror and support the observed inverse variation in these
sensory traits. Moreover, that this variation in visual and olfactory investment between closely-related species seems to provide
relaxed competition, a process by which similar species can use a shared environment differently and in ways that help them both
coexist. The nervous system has a unique role in evolution as it provides the functional connection between morphology, physiology,
and behavior. As such, characterizing any tradeoffs between costs and benefits for the nervous system may be essential to our
understanding of animal diversity, as well as vital to our understanding of the selective forces that have shaped the natural world.