THE EVOLUTIONARY SIGNIFICANCE OF 
REDUNDANCY AND VARIABILITY IN 
PHENOTYPIC-INDUCTION MECHANISMS OF 
PIERID BUTTERFLIES (LEPIDOPTERA)* 
By Arthur M. Shapiro 
Department of Zoology 
University of California 
Davis, California 95616, U.S.A. 
One of the major discoveries in the study of seasonal polyphenism 
in butterflies was the role of larval photoperiodic exposure (Dani- 
levskii, 1948). Following this discovery, experiments on two Pierid 
species — Colias eury theme Bdv. (Watt, 1969; Hoffman, 1974) and 
Pieris protodice Bdv. & LeC. (Shapiro, 1968) — appeared to 
establish that temperature played no role in the seasonal polyphen- 
isms of that family. This was clearly not the case in at least one 
Nymphalid, Araschnia levana (L.): Siiffert (1924) had shown a 
temperature effect, and later work by Danilevskii (1948), Muller 
(1955, 1956, 1960), Reinhardt (1969, 1971), and Muller and Rein- 
hardt (1969) showed that photoperiod and temperature interact in a 
characteristic way. Long-day larvae or young pupae, normally 
destined to produce the summer form prorsa, if experimentally 
cooled will produce either the winter form levana or an intermediate 
form {porima). Short-day larvae give rise to diapause pupae which 
always give levana, regardless of temperature. Thus photoperiod, 
acting on 4th- and 5th-instar larvae, can irreversibly determine the 
vernal phenotype, but not the estival one, which can be overridden 
by temperature acting on the young pupa. 
Shapiro (1977) established that pupal diapause and adult pheno- 
type, normally tightly coupled in the Pieris napi (L.) group of 
Pieridae, could be decoupled in P. n. venosa Scudder. In napi 
generally, diapausing pupae give rise to vernal phenotypes and non- 
diapausing ones to estival phenotypes. Populations consist of a 
mixture of obligate diapausers, apparently determined genetically, 
and facultative ones responsive to daylength. In some but not all 
populations, inducing photoperiods can be overridden by high 
* Manuscript received by the editor December 30, 1978. 
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