Nocturnal anti-predator adaptations in eared and earless

Nocturnal flight exposes insects to selection pressures that include reduced light and the hunting behavior of insectivorous bats. Using a phylogenetically based selection of wild moths collected from a Nearctic site, we report that earless species fly less throughout the night than eared species. This supports the hypothesis that this behavior has evolved as a passive defense against the transient attacks of aerially foraging bats in insects that do not possess long-range auditory detection abilities. We measured the eyesize of a selection of moths whose 24-h flight activities are known and confirm that nocturnal lifestyle results in larger eyes. With the exception of hawkmoths, there is no eyesize difference between eared and earless moths, suggesting that earless moths do not preferentially use vision to detect the approach of bats. Key words: auditory state, bats, defense, eyesize, flight, moths. [Behav Ecol] Animals are active at various times of the 24-h day (dielperiodicity) and experience different selection pressures arising from the predators they encounter during those times. Insects, with their diversity of lifestyles and short generation times, can be used to study the effects of diel selection pressures on the evolution of defenses ( Joron and Mallet, 1998; Roeder, 1952). The Lepidoptera (moths and butter-flies) is a speciose taxon exhibiting a wide variety of lifestyles and diel periodicities (Dreisig, 1986) and is well suited for these studies. Diurnal predators of Lepidoptera have selected for many well-studied, visually governed primary and second-ary defenses (i.e., those that function before and after the predator has discovered them [Edmunds, 1974; Endler, 1991]), such as crypsis (Majerus et al., 2000; Sargent, 1969