David A. West

Arsenic Tolerance in a Population of the Grass Andropogon scoparius Michx

Samples of Andropogon scoparius Michx. collected on an arsenic mine exhibited a wide range of tolerance to arsenic in solution, whereas plants of the same species growing in uncontaminated soil showed no tolerance. Arsenic tolerance must be an evolved character under genetic control. Furthermore, the degree of tolerance is related to the amount of arsenic in which the plant was growing.

Environmental control of pupal colour in swallowtail butterflies (Lepidoptera: Papilioninae): Battus philenor (L.) and Papilio polyxenes Fabr.

Abstract. 1. Some swallowtail butterflies produce both green and brown pupae. The phenotypes result from the joint action of genotype and environment and usually make the pupae cryptic in their habitats.

Pupal colour dimorphism in swallowtail butterflies as a threshold trait: Selection in Eurytides marcellus (Cramer)

SummaryThe pupal colour dimorphism of Eurytides marcellus is nearly lost when the species is forced to pupate on a clear plastic substrate. Selection for extreme brown and green pupal colour under these circumstances was successful in a single generation in 3 out of 5 and 7 out of 10 lines respectively, but selection for an intermediate colour gave no response in 3 out of 3 lines. The results support a threshold model of pupal colour dimorphism in this species, with “sensitivity” to substrate characteristics being the underlying continuous variable. The consequently strong environmental component of variation in pupal colour in natural populations thus serves to maintain the genetic variation, since natural selection will be only weakly stabilizing.

Natural pupation sites of swallowtail butterflies (Lepidoptera: Papilioninae): Papilio polyxenes Fabr., P.glaucus L. and Battus philenor (L.)

Abstract. 1. Natural pupation sites have been found in Papilio polyxenes and P.glaucus by releasing prepupal larvae marked with UV‐fluorescent paint and locating them at night with a UV lamp, and in Battus philenor by searching a forest habitat where the larval foodplant is abundant.

The effect of larval photoperiod on pupal colour and diapause in swallowtail butterflies

ABSTRACT. 1 There are significant differences in the effects of larval photo‐period on diapause and pupal colour among the species Papilio polyxenes Fabr., P.troilus L., Battus philenor (L.) and Eurytides marcellus (Cramer). 2 Diapause and pupal colour in P.polyxenes and P.troilus are strongly influenced by larval photoperiod, short photophase eliciting brown diapausing pupae. Photoperiods of 15L:9D permit the expression of the green and brown pupal colour alternatives. 3 Pupal colour in B.philenor and E.marcellus is not affected by larval photoperiod, but short photophase induces diapause in these species. 4 All species except B.philenor show an association between brown pupal colour and diapause: Emarcellus when reared on long (midsummer) photophase, P.polyxenes and P.troilus when reared on short (autumnal) photophase. 5 In P.polyxenes, short photophase can affect pupal colour responses directly, whether the individual enters diapause or not. 6 Differences among the species are related to differences in the ecology of their natural pupation sites.

AN EXPERIMENTAL TEST OF NATURAL SELECTION FOR PUPATION SITE IN SWALLOWTAIL BUTTERFLIES

The pupae of some swallowtail butterflies are dimorphic-usually green or brown-while those of others are monomorphic. We have suggested (West and Hazel, 1979) that one important factor determining whether a species evolves dimorphism or monomorphism is the type of pupation site that the species uses. The use of a narrow range of cryptic sites in the leaf litter, for example, would favor monomorphic brown pupae, while the use of a variety of sites on exposed stalks, tree trunks, etc. would favor the ability to develop green or brown pupae in response to such substrate characteristics as color or texture (Hazel and West, 1979). This suggestion immediately raised the question why different species prefer different kinds of pupation sites to begin with. Clarke and Sheppard (1972) successfully selected for changes in pupation site preference in Papilio polytes, thereby revealing genetic variation in the trait, and we have shown (West and Hazel, 1979 and unpubl.) that there are some striking differences in natural pupation sites among six eastern North American swallowtails. Among these there are two species which, despite the similar forest habitats of their immature stages, prefer very different pupation sites: Papilio glaucus in the leaf litter and Battus philenor well off the ground on exposed surfaces like tree trunks and cliffs (West and Hazel, 1979). These species differ in two other important respects. Papilio glaucus lays eggs singly and widely spaced on trees (includ-

Pupal colour dimorphism in swallowtail butterflies: timing of the sensitive period and environmental control

ABSTRACT. Two North American swallowtail butterflies with pupal colour dimorphism, Eurytides marcellus (Cramer) and Papilio troilus L., use chiefly the colour of the pupation substrate to determine pupal colour, and are affected hardly (P.troilus) or not at all (E.marcellus) by substrate texture. The use of colour cues in these species is in contrast to the greater importance of texture in two other sympatric swallowtails (Hazel & West, 1979). E.marcellus larvae evacuate the gut and start prepupal wandering around mid‐day. If they have not reached the sensitive period for pupal colour determination by nightfall they will delay the sensitive period until the next day. Among other North American swallowtails with pupal colour dimorphism there is no tendency for those species that use textural cues for pupal colour determination to evacuate the gut later in the day than those using pupation site colour.