The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion–reaction model of O₂ distributions in egg masses, using egg masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from –1.5° to +1.5°C, embryos of T. challengeriana showed large increases in O₂ consumption (Q₁₀ values of 9.6–30.0). Oxygen electrode measurements in intact masses showed, however, that O₂ levels were high throughout and virtually unaffected by temperature. The model suggested that both effects stemmed from very low metabolic densities in egg masses. Detailed morphological measurements of egg masses of T. challengeriana and a temperate congener, T. diomedea, revealed large differences in structure that may be related to O₂ availability. Egg masses of T. challengeriana were approximately twice as thick. However, the most dramatic effects were observed in embryos: embryos of T. challengeriana were >32 times larger (by volume) than embryos of T. diomedea. Antarctic embryos also were contained singly in large egg capsules (∼500 μm diameter). Consequently, Antarctic embryos occurred at much lower densities, with very low metabolic densities.

A pheromone is implicated in the trail marking behavior of caterpillars of the nymphalid silverspot butterfly, Dione juno huascuma (Reakirt) (Lepidoptera: Heliconiinae) that feed gregariously on Passiflora (Malpighiales: Passifloraceae) vines in Mexico. Although they mark pathways leading from one feeding site to another with silk, this study shows that the silk was neither adequate nor necessary to elicit trail following behavior. Caterpillars marked trails with a long-lived pheromone that was deposited when they brushed the ventral surfaces of the tips of their abdomens along branch pathways. The caterpillars distinguished between pathways deposited by different numbers of siblings and between trails of different ages. Caterpillars also preferentially followed the trails of conspecifics over those of another nymphalid, Nymphalis antiopa L., the mourning cloak butterfly.