Stickleback fathers glue weed nests with kidney cement
Gasterosteidae sticklebacks swim Holarctic fresh, brackish, and marine waters—closer to eelpouts and sculpins than to seahorses, modern trees say. FishBase lists about sixteen species in five genera, many with subspecies still needing taxonomic cleanup, and bold or shy personalities that decide who leads a shoal.
Stickleback courtship is a fixed routine. In spring freshwater males turn red, build a nest of weeds glued with spiggin, a secretion from their kidneys, and wait. A female ready to spawn leaves the shoal, holds her head up and shows a belly swollen with eggs. The male then zig-zags toward her and prods her abdomen with his dorsal spines. Niko Tinbergen's studies of this sequence made the fish a textbook case of a fixed action pattern in the early days of ethology.
Because the male guards the eggs, both sexes are choosy. Females prefer males with the reddest throats and give them larger eggs; since only parasite-free males can produce that colour, the preference fits the Hamilton–Zuk hypothesis. Yet the signal can mislead, because the most colourful males may divert protective carotenoids away from their sperm, leaving more DNA damage. Females in poor condition are less picky, males favour bigger females, and females given a choice avoid mating with a familiar brother, since inbred eggs fertilise and hatch less often.
The family Gasterosteidae has about 16 species in five genera across the northern hemisphere. They lack scales, though some carry bony plates, and bear sharp, separate dorsal spines. The three-spined stickleback rarely exceeds 3 inches, while the fifteen-spined species reaches 22 centimetres. Populations trapped in fresh water after the last Ice Age evolved new forms: deep-bodied bottom feeders in shallow lakes and plankton eaters in deep ones, a pattern that makes them a favourite model for evolutionary genetics since a reference genome appeared in 2012.
Individual fish even show bold or shy personalities, and a statue in Kronstadt honours the sticklebacks that fed residents during the Siege of Leningrad.
Source: Stickleback
