Ros, Albert F. H.Ferreira, CatarinaSantos, Ricardo SerrãoOliveira, Rui Filipe2012-03-222012-03-222006Journal of Experimental Zoology, 305A, 986-9941932-5231http://hdl.handle.net/10400.12/1290In Parablennius parvicornis, small reproductive males with relatively low expression of secondary sexual characters (M morphotype) parasite on the parental investment of the larger nest-holder males which have fully developed secondary sexual characters (M1 morphotype). In comparison with M1 males, M males have relatively low levels of androgens while having high blood cell percentages of lymphocytes and antigen responsiveness. Here we test the hypothesis that androgens are a causal factor for these differences in immunocompetence between morphotypes. After drawing an initial blood sample, males received a silastic implant containing either oil only (C), or oil with testosterone (T) or 11-ketotestosterone (KT). Males were re-caught 2 weeks later for drawing of the final blood sample. KT but not T induced the development of secondary sexual characters in M males. M males treated with KT showed lower swimming activity than the males treated with T or C implants, suggesting that KT also mediates behavioral changes in M males. As expected, blood cell percentages of lymphocytes, but not of granulocytes, were higher in M males than in M1 males. Overall, lymphocyte percentages increased in the C group which might have been a response to the surgery/treatment. In concordance with the hypothesis, lymphocyte percentages were suppressed in males treated with T in comparison with controls. However, no significant change was found in KT-treated males. This suggests that androgens modulate central, morphological and immunological traits by partly independent androgen mechanisms in P. parvicornis.engjournal article