A newly metamorphosed two-day-old juvenile of the Australian sea-urchin Heliocidaris erythrogramma. In freespawning species such as this, the order in which males mate affects the quality of the offspring that they sire. See Marshall et al. Proc. R. Soc. B. 271, 1585–1589 (photograph, R. Emlet). Top: cereal aphids (Sitobion avenae, black siphunculi; Metopolophium dirodum, white siphunculi) on wheat (Triticum aestivum) (centre right, an aphid 'mother' parasitized by the wasp Hymenoptera parasitica; bottom centre, white egg of an aphid predator, the hoverfly (Syrphidae)) (photograph, I. Roschewitz). Middle: A stained cross section of a cypress twig preserved for 45 Myr in Baltic amber (photograph, B. Koller). Bottom: a pair of sockeye salmon (Orcorhynchus nerka) spawning in Iliamna Lake, Alaska; allometry for sexual size dimorphism is related to life history in Pacific salmon and trout (photgraph, Andrew P. Hendry).