Three-spined Stickleback - Reproduction

Reproduction

From late April until July, males and females move from deeper waters to shallow areas. There, each male defends a territory where he builds a nest on the bottom. He starts by digging a small pit. He then fills it with plant material (often filamentous algae), sand, and various debris which he glues together with spiggin, a proteinaceous substance secreted from the kidneys (the word spiggin comes from spigg, the Swedish name for the three-spined stickleback). He then creates a tunnel through the more or less spherical nest by swimming vigorously through it. Nest building typically takes 5–6 hours though it may also be spread out over several days. After this, the male courts gravid females that pass by with a zigzag dance. He approaches a female by swimming very short distances left and right, and then he swims back to the nest in the same way. If the female follows, the male often pokes his head inside the nest, and may swim through the tunnel. The female then swims through the tunnel as well, where she deposits 40-300 eggs. The male follows to fertilize the eggs. The female is then chased away by the male. For the duration of the eggs' development, the male will chase away other males and non-gravid females. He may, however, court other gravid females (more than one batch of eggs can be deposited in the same nest).

The sequence of territorial, courtship and mating behaviours was described in detail by Niko Tinbergen in a landmark early study in ethology. Tinbergen showed that the red colour on the throat of the territorial male acts as a simple sign stimulus, releasing aggression in other males and attracting females. The red colouration may also be used by females as a way to assess male quality. Red colouration is produced from carotenoids found in the diet of the fish. As carotenoids cannot be synthesised de novo, the degree of colouration gives an indication of male quality (ability to find food), with higher quality males showing more intense colouration. Also, males that bear fewer parasites tend to exhibit brighter red colours. Many studies have shown that females prefer males with brighter red colouration. However, it is noteworthy that the response to red is not universal across the entire species, with black throated populations often found in peat-stained waters.

The male takes care of the developing eggs by fanning them. He lines himself up with the entrance of the nest tunnel and swims on the spot. The movement of his pectoral fins creates a current of water through the nest, bringing fresh (well oxygenated) water to the eggs. He does this not only during the day, but throughout the night as well. Fanning levels tend to increase until the eggs are about to hatch, which takes 7–8 days at 18-20 °C. Fanning levels also increase when the water is poorly oxygenated. Towards the end of the egg development phase, the male often makes holes in the roof and near the rim of the nest, presumably to improve ventilation of the nest during fanning at a time when the eggs are more metabolically active. Once the young hatch, the male attempts to keep them together for a few days, sucking up any wanderers into his mouth and spitting them back into the nest. Afterwards, the young disperse and the nest is either abandoned by the male, or repaired in preparation for another breeding cycle.

In Nova Scotia, Canada, a form of three-spined stickleback departs from the usual pattern of parental care. Unlike other sticklebacks who nest on the substrate, Nova Scotian male sticklebacks build nests in mats of filamentous algae. Surprisingly, almost immediately after fertilization the males disperse the eggs from the nest and resume soliciting females for eggs. Hence, there appears to have been a loss of parental care in this population. Because these males have reduced dorsal pigmentation, resulting a pearlescent white appearance, they have been dubbed "white stickleback". It is currently unknown whether they are a distinct species, or simply a morph of the common Atlantic stickleback.