Oliveira, Rui FilipeCarvalho, NatachaMiranda, JasonGonçalves, Emanuel João2012-04-052012-04-052002Ethology, 208, 223-2350179±1613http://hdl.handle.net/10400.12/1308In the Azorean rock-pool blenny, sexually active males may adopt alternative reproductive tactics. In the present paper the relationship between the presence of satellite males and the reproductive success of nest-holders was investigated by comparing nests with and without an associated satellite male. Males with an associated satellite male suffered more conspeci®c intrusions but they did not display a higher frequency of attacks towards conspeci®cs. Nest-holder males were more aggressive towards other conspeci®cs than towards satellites and the tolerance of nest-holders towards satellites was inversely correlated with the time spent by the satellites in the breeding territory, which suggests control by the nest- holder male of the satellite investment in shared territorial defence. Nest-holders with an associated satellite male had higher condition factors and received more female visits and more spawnings. These results bear two possible interpretations. (1) Nest-holders bene®t from the presence of a satellite male by increased attractiveness of their nests to females; satellite males are mutualists helping to defend the nest-owner's territory and to attract females, which is why they are tolerated. (2) Satellite males associate preferentially with more successful nest- holder males which have higher condition factors, and by doing so have more opportunities to achieve parasitic fertilizations. Only experiments will allow these two hypotheses to be distinguished.engjournal article