Steroid hormones and paternal care in the plainfin midshipman fish (Porichthys notatus)

The present study investigated the relationship between plasma steroid horm one levels and the expression of paternal behavior in the plainfin midshipm an fish (Porichthys notatus), where males may simultaneously care for multi ple clutches in different stages of development. Blood samples were collect ed from free-living parental males during that part of the breeding season when males may be found in various stages of parental care. Plasma 11-ketot estosterone levels were significantly higher in males with empty nests and nests containing only eggs than in males with nests containing embryos. All males with nests containing embryos had undetectable testosterone levels, whereas testosterone levels were detectable in many males with empty nests or nests containing only eggs. Estradiol levels were detectable in only a f ew males from nests with no eggs or nests containing only eggs. Cortisol le vels were not correlated with stage of paternal care or with handling time. These results follow the frequently reported vertebrate pattern of declini ng androgen levels over the course of the breeding season or during the per iod of parental care. However, many male midshipman guarding nests containi ng only eggs had androgen levels similar to those of males whose nests cont ained no offspring. Thus the pattern of androgen levels exhibited by reprod uctively active parental male midshipman may reflect a compromise between i nvestment in paternal care versus courtship and/or territoriality. (C) 1999 Academic Press.