Effect of light quality and larval diet on morph induction in the polymorphic caterpillar Nemoria arizonaria (Lepidoptera: Geometridae)

Abstract

The emerald moth Nemoria arizonaria (Geometridae) is bivoltine, with distinct broods of caterpillars hatching in the spring and summer. Caterpillars of the spring brood develop into mimics of oak catkins, while caterpillars of the summer brood develop into mimics of oak twigs. Previous rearing experiments showed that all caterpillars reared on oak catkins developed into catkin morphs, while all caterpillars reared on oak leaves developed into twig morphs, regardless of temperature or photoperiod. However, those previous rearing experiments did not control the colour of light perceived by the caterpillars independently of their dict. Since wavelengths of light perceived by some species of polymorphic caterpillars can influence their colour, it is possible that morph induction in Nemoria arizonaria is due to the characteristics of light reflected from yellow catkins or green leaves, rather than larval diet itself. The experiments reported here independently varied larval diet and light characteristics to determine if light quality is involved in morph induction. Only larval diet influenced morph induction, since all caterpillars reared on catkins developed into the catkin morph, and all caterpillars reared on oak leaves developed into the twig morph, regardless of whether they perceived yellow light, green light, or were raised in the dark.

The Evolution of Color Polymorphism: Crypticity, Searching Images, and Apostatic Selection

“…Many mantids (Edmunds 1976) and katydids (Owen 1980) are polymorphic, as are water boatmen (Popham 1941), walking sticks (Sando-val 1994), and spittlebugs (Halkka & Halkka 1990). Perhaps the best-researched examples of color polymorphism are found among moths, in which both the larvae and the adults are usually cryptically colored and frequently polymorphic (Greene 1996, Janzen 1984, Kettlewell 1973, Poulton 1890, Sargent 1976. In some moth taxa, polymorphism is pervasive: Roughly 40% of the species in Barnes & McDunnough's (1918) survey of the underwing moths of North America occur in multiple distinctive forms.…”

“…Because diversity is limited by the number of substrate types, specialist polymorphisms generally involve fewer, more distinctive forms, often only green and brown (Dearn 1990, Edmunds 1976, Owen 1980, Poulton 1890, Wente & Phillips 2003 or dark and light (Kettlewell 1973). In many cases, the dimorphism is genetically determined; in others, it is a polyphenism, a developmental difference in color pattern cued by physical or chemical signals (Edmunds 1976, Greene 1996, Rowell 1971. Because each morph specializes on a particular substrate type, these species may be highly selective in choosing a resting location, actively avoiding nonmatching backgrounds (Edmunds 1976, Owen 1980, Sargent 1981.…”

The evolution of alternative morphs: density-dependent determination of larval colour dimorphism in a butterfly

“…Direct experimental tests of the correlation between larval morph and immune function are required to resolve this issue. Selection for crypsis is obviously one of the main adaptive explanations for variation in colour patterns and for larval polymorphisms/polyphenisms (Kettlewell, 1973;Greene, 1989;Greene, 1996;Majerus, 1998). In P. xiphia, the two morphs have reflectance spectra that are distinguishable by the human eye and by potential bird predators, which are generally better able to discriminate between colours than are humans .…”

“…Colour polymorphisms within the Lepidoptera not only include some classic cases of Mendelian inheritance (Ford, 1975), but also fascinating examples of where morph determination is strongly dependent on the environment during development (Wiklund, 1975;Shapiro, 1976;Hazel, 1977;Hazel & West, 1979;Greene, 1989;Greene, 1996). For example, butterfly larvae and adults may develop darker morphs in response to late or early seasonal cues, such as shorter photoperiods and colder temperatures, which allows more efficient thermoregulation under both cold and warm periods of the season (Shapiro, 1976;Fields & McNeil, 1988;Goulson, 1994;Kingsolver, 1995;Hazel, 2002;Nice & Fordyce, 2006).…”

Color Change, Phenotypic Plasticity, and Camouflage

“…In some prawns and caterpillars there is evidence from early and recent work that diet may have an important role, alone or in combination with vision, in influencing appearance changes (Keeble and Gamble, 1899;Gamble and Keeble, 1900;Greene, 1996;Noor et al, 2008).…”