Changes in reproductive physiology and behaviour over the nesting cycle in male three-spined sticklebacks

Plasma 11-Ketotestosterone (11 KT) and testosterone (T) levels and spiggin-mRNA levels, as well as the kidney-somatic index (I-K) were measured in sexual males and in paternal males at the middle (5 days paternal) and at the end (8 days paternal with hatched eggs) of the nesting cycle in three-spined sticklebacks Gasterosteus aculeatus from two populations. Glueing (using threads of 11 KT induced kidney-protein spiggin) and fanning behaviour was measured daily. Fanning increased in paternal fish and remained low in sexual males. Plasma 11 KT and T levels, on the other hand, declined significantly in parental compared to sexual males as did spiggin expression, I-K and glueing behaviour. Thus, the drastic decrease in circulating 11 KT levels during the later parental phase may have resulted in an energy-saving decrease in spiggin-production and glueing, when this was no longer needed for nest maintenance. In addition, the mRNA levels of the beta-subunits of both gonadotropins, luteinising hormone (LH) and follicle stimulating hormone (FSH) were measured. The expression of both gonadotropins declined in the parental phase (not significant for beta-FSH in one of the populations) which was consistent with a decline in androgen levels possibly controlled via decreased gonadotropin secretion. (c) 2005 The Fisheries Society of the British Isles.