許多動物的打鬥呈現出一個共同的現象，亦即前次打鬥之勝、負經驗會提升或降低個體在後續打鬥中的攻擊性與獲勝機率，稱之為勝者、敗者效應。由於動物的攻擊性被發現與神經內分泌系統有密切的關係，因而勝者、敗者效應也被認為應受到神經內分泌系統之調控。先前的研究顯示Kryptolebias marmoratus之打鬥行為呈現出明顯的勝敗者效應，而且其打鬥行為與睪固酮(testosterone)和皮質醇(cortisol)分泌量有顯著的關聯；然而，此魚之勝敗者效應卻非經由這些荷爾蒙或雌性激素(estrogen)、睪丸硬甾酮(11-ketotestosterone)等之分泌量所調控形成。由於荷爾蒙除了分泌量的變化外，其受器蛋白的表現量多寡亦會影響個體之攻擊性與打鬥行為，因此我於本研究中探討個體在獲得勝、敗或者控制經驗後，其腦部與生殖腺體之雄性激素受器(androgen receptor)、雌性激素α/β 受器(estrogen α/β receptor)、血清素1A 受器(5-HT1A receptor)與葡萄糖皮質素受器(glucocorticoid receptor)等受器基因表現量是否有所差異。實驗結果顯示，擁有三次落敗經驗的個體，其腦部之雄性激素受器基因與生殖腺之雌性激素α受器基因表現量顯著低於擁有一次控制經驗的個體；而在其他受器基因表現量上，各經驗處理組間並無顯著差異。由於贏的經驗與一次落敗經驗並未顯著的影響任何受器基因表現量，本研究結果顯示這些受器基因表現量應非此魚之勝、敗者效應之主要調控機制。然而本研究之其他分析顯示，接受落敗經驗處理的個體，其基礎睪固酮分泌量與個體在接受第一次落敗經驗訓練時的攻擊性行為(先開鰓蓋展示機率與打鬥持續時間)呈現顯著的正相關；而腦部受器基因表現量(雄性激素受器除外)也與個體在接受第一次經驗訓練時之攻擊性行為(先展示機率、先開鰓蓋展示機率、打鬥持續時間)呈現顯著正相關。這些結果顯示此魚之攻擊性仍與荷爾蒙以及荷爾蒙/血清素受器有密切的關係。因此，整體而言，本研究顯示荷爾蒙以及荷爾蒙/血清素受器雖然與此魚之攻擊性有密切的關係，卻非此魚展現勝、敗者效之主要生理機制。

Recent winning/losing experiences can increase/decrease an individual's aggressiveness and its probability of winning subsequent contests, phenomena referred to as winner/loser effects. Winner and loser effects are probably mediated by the neuroendocrine system because animals’ aggression is closely associated with this system. Kryptolebias marmoratus displays winner and loser effects and its contest behaviors are associated with testosterone and cortisol levels. It appears, however, that neither winner nor loser effects are mediated by changes in the levels of testosterone or cortisol in this fish. Because hormone receptors could also modulate the effect of hormones on behavior, in this study I investigated associations in this fish between androgen receptor, estrogen α/β receptor, 5-HT1A receptor and glucocorticoid receptor gene expression levels and winning and losing experiences. The results showed significantly reduced expression levels of androgen receptor genes in the brains and estrogen α receptor genes in the gonads of individuals with three losing experiences. None of the experience treatments led to differences in brain or gonad estrogen β receptor, 5-HT1A receptor or glucocorticoid receptor gene expression levels. These results did not establish hormone/serotonin receptors to be the primary physical mechanism underlying winner and loser effects. Nonetheless, in those individuals assigned losing experience(s), the baseline hormone (testosterone) levels and the receptor gene expressions levels (except androgen receptor) were positively correlated with aggressive behavior (initiating displays, initiating gill displays and contest duration) in the 1st experience training. These results did demonstrate a relationship between fighting experience and hormones and hormone/serotonin receptor gene expressions. I concluded from these findings that although hormones and hormone/serotonin receptors have important associations with the fish's aggressiveness, they are not the major physiological mechanisms underlying winner or loser effects in this fish.

Abel, T. & Kandel, E. 1998. Positive and negative regulatory mechanisms that mediate long-term memory storage. Brain Research Reviews, 26, 360-378.
Aldegunde, M., Soengas, J. L. & Rozas, G. 2000. Acute effects of L-tryptophan on tryptophan hydroxylation rate in brain regions (hypothalamus and medulla) of rainbow trout (Oncorhynchus mykiss). Journal of Experimental Zoology, 286, 131-135.
Archer, J. 2006. Testosterone and human aggression: an evaluation of the challenge hypothesis. Neuroscience & Biobehavioral Reviews, 30, 319-345.
Austad, S. N. 1983. A game theoretical interpretation of male combat in the bowl and doily spider (Frontinella pyramitela). Animal Behaviour, 31, 59-73.
Baenninger, R. 1970. Visual reinforcement, habituation, and prior social experience of Siamese fighting fish. Journal of Comparative and Physiological Psychology, 71, 1-5.
Bailey, C. H., Kandel, E. R. & Si, K. 2004. The persistence of long-term memory: a molecular approach to self-sustaining changes in learning-induced synaptic growth. Neuron, 44, 49-57.
Bergman, D. A. & Moore, P. A. 2003. Field observations of intraspecific agonistic behavior of two crayfish species, Orconectes rusticus and Orconectes virilis, in different habitats. The Biological Bulletin, 205, 26-35.
Borg, B. 1994. Minireview: Androgens in teleost fishes. Comparative Biochemistry and Physiology, 109, 219-245.
Brick, O. 1999. A test of the sequential assessment game: the effect of increased cost of sampling. Behavioral Ecology, 10, 726-732.
Burmeister, S. S., Kailasanath, V. & Fernald, R. D. 2007. Social dominance regulates androgen and estrogen receptor gene expression. Hormones and Behavior, 51, 164-170.
Caldwell, G. S., Glickman, S. E. & Smith, E. R. 1984. Seasonal aggression independent of seasonal testosterone in wood rats. Proceedings of the National Academy of Sciences of the United States of America, 81, 5255-5257.
Carpenter, R. E. & Summers, C. H. 2009. Learning strategies during fear conditioning. Neurobiology of Learning and Memory, 91, 415-423.
Caramaschi, D., de Boer, S. F. & Koolhaas, J. M. 2007. Differential role of the 5-HT1A receptor in aggressive and non-aggressive mice: An across-strain comparison. Physiology & Behavior, 90, 590-601.
Clotfelter, E. D., O'Hare, E. P., McNitt, M. M., Carpenter, R. E. & Summers, C. H. 2007. Serotonin decreases aggression via 5-HT1A receptors in the fighting fish Betta splendens. Pharmacology Biochemistry and Behavior, 87, 222-231.
Costa, W. J. E. M., Lima, S. M. Q. & Bartolette, R. 2010. Androdioecy in Kryptolebias killifish and the evolution of self-fertilizing hermaphroditism. Biological Journal of the Linnean Society, 99, 344-349.
Dias, B. G. & Crews, D. 2006. Serotonergic modulation of male-like pseudocopulatory behavior in the parthenogenetic whiptail lizard, Cnemidophorus uniparens. Hormones and Behavior, 50, 401-409.
Dickens, M., Romero, L. M., Cyr, N. E., Dunn, I. C. & Meddle, S. L. 2009. Chronic stress alters glucocorticoid receptor and mineralocorticoid receptor mRNA expression in the European starling (Sturnus vulgaris) brain. Journal of Neuroendocrinology, 21, 832-840.
Drummond, H. & Canales, C. 1998. Dominance between booby nestlings involves winner and loser effects. Animal Behaviour, 55, 1669-1676.
Earley, R. L. & Hsu, Y. 2008. Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus. Hormones and Behavior, 53, 442-451.
Edwards, D. H. & Kravitz, E. A. 1997. Serotonin, social status and aggression. Current Opinion in Neurobiology, 7, 812-819.
Ellis, T., James, J. D., Stewart, C. & Scott, A. P. 2004. A non‐invasive stress assay based upon measurement of free cortisol released into the water by rainbow trout. Journal of Fish Biology, 65, 1233-1252.
Emata, A. C., Meier, A. H. & Hsiao, S. M. 1991. Daily variations in plasma-hormone concentrations during the semilunar spawning cycle of the gulf killifish, Fundulus grandis. Journal of Experimental Zoology, 259, 343-354.
Elofsson, U. O. E., Mayer, I., Damsgård, B. & Winberg, S. 2000. Intermale competition in sexually mature arctic charr: effects on brain monoamines, endocrine stress responses, sex hormone levels, and behavior. General and Comparative Endocrinology, 118, 450-460.
Francis, R. C., Jacobson, B., Wingfield, J. C. & Fernald, R. D. 1992. Castration lowers aggression but not social dominance in male Haplochromis burtoni (Cichlidae). Ethology, 90, 247-255.
Francis, R. C., Soma, K. & Fernald, R. D. 1993. Social regulation of the brain-pituitary-gonadal axis. Proceedings of the National Academy of Sciences of the United States of America, 90, 7794-7798.
Fuxjager, M. J., Forbes-Lorman, R. M., Coss, D. J., Auger, C. J., Auger, A. P. & Marler, C. A. 2010. Winning territorial disputes selectively enhances androgen sensitivity in neural pathways related to motivation and social aggression. Proceedings of the National Academy of Sciences, 107, 12393-12398.
Genuth, S. M. 1993. The endocrine system. In: Physiology (Berne, R.M. & Levy M.N. ed.), pp. 813-1024. Mosby Year Book, St. Louis.
Giguère, V., Yang, N., Segui, P. & Evans, R. M. 1988. Identification of a new class of steroid hormone receptors. Nature, 331, 91-94.
Goodman, H. M. 2008. Hormonal control of reproduction in the female: the menstrual cycle. In: Basic Medical Endocrinology (Goodman, H. M. ed.), pp. 257-275. Academic Press, San Diego.
Grizzle, J. M. & Thiyagarajah, A. 1987. Skin histology of Rivulus ocellatus marmoratus: apparent adaptation for aerial respiration. Copeia, 1, 237-240.
Harrington, R. W. J. 1963. Twenty-four-hour rhythms of internal self-fertilizaiotn and of oviposition by hermaphrodites of Rivulus marmoratus. Physiological Zoology, 36, 325-341.
Harrington, R. W. J. & Kallman, K. D. 1968. The homozygosity of clones of the self-fertilizing hermaphroditic fish Rivulus marmoratus Poey (Cyprinodontidae, Atheriniformes). The American Naturalist, 102, 337.
Harrington, R. W. J. 1971. How ecological and genetic factors interact to deternime when self-fertilizing hermaphrodites of Rivulus marmoratus change into functional secondary males, with a reapprisal of the modes of intersexuality among fishes. Copeia, 3, 389-432.
Harding, C. F. 1983. Hormonal influences on avian aggressive behavior. In: Hormones and Aggressive Behavior (Svare, B.B. ed.), pp. 435-467. Plenum Press, New York.
Hoefler, C. D. 2002. Is contest experience a trump card? The interaction of residency status, experience, and body size on fighting success in Misumenoides formosipes (Araneae: Thomisidae). Journal of Insect Behavior, 15, 779-790.
Hollis, K. L., Martin, K. A., Cadieux, E. L. & Colbert, M. M. 1984. The biological function of Pavlovian conditioning: Learned inhibition of aggressive behavior in territorial fish. Learning and Motivation, 15, 459-478.
Hollis, K. L. 1999. The role of learning in the aggressive and reproductive behavior of blue gouramis, Trichogaster trichopterus. Environmental Biology of Fishes, 54, 355-369.
Hong, H., Yang, L. & Stallcup, M. R. 1999. Hormone-independent transcriptional activation and coactivator binding by novel orphan nuclear receptor ERR3. Journal of Biological Chemistry, 274, 22618-22626.
Hoyer, D., Hannon, J. P. & Martin, G. R. 2002. Molecular, pharmacological and functional diversity of 5-HT receptors. Pharmacology Biochemistry and Behavior, 71, 533-554.
Hsu, Y. & Wolf, L. L. 1999. The winner and loser effect: integrating multiple experiences. Animal Behaviour, 57, 903-910.
Hsu, Y. & Wolf, L. L. 2001. The winner and loser effect: what fighting behaviours are influenced. Animal Behaviour, 61, 777-786.
Hsu, Y., Earley, R. L. & Wolf, L. L. 2006. Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes. Biological Reviews, 81, 33-74.
Hsu, Y. Y., Lee, I. H. & Lu, C. K. 2009. Prior contest information: mechanisms underlying winner and loser effects. Behavioral Ecology and Sociobiology, 63, 1247-1257.
Huhman, K. L., Moore, T. O., Ferris, C. F., Mougey, E. H. & Meyerhoff, J. L. 1991. Acute and repeated exposure to social conflict in male golden hamsters: increases in plasma POMC-peptides and cortisol and decreases in plasma testosterone. Hormones and Behavior, 25, 206-216.
Kallman, K. D. & Harrington, R. W., JR. 1964. Evidence for the existence of homozygous clones in the self-fertilizing hermaphroditic teleost Rivulus marmoratus (Poey). The Biological Bulletin, 126, 101-114.
Kanamori, A., Yamamura, A., Koshiba, S., Lee, J. S., Orlando, E. F. & Hori, H. 2006. Methyltestosterone efficiently induces male development in the self-fertilizing hermaphrodite fish, Kryptolebias marmoratus. Genesis, 44, 495-503.
Koutoku, T., Zhang, R., Tachibana, T., Oshima, Y. & Furuse, M. 2003. Effect of acute L-tryptophan exposure on the brain serotonergic system and behavior in the male medaka. Zoological Science, 20, 121-124.
Laidre, M. E. & Elwood, R. W. 2008. Motivation matters: cheliped extension displays in the hermit crab, Pagurus bernhardus, are honest signals of hunger. Animal Behaviour, 75, 2041-2047.
Lan, Y.-T. 2010. Does contest experience from more than a month previously in Kryptolebias marmoratus influence winner/loser effect arising from recent contests? Master's thesis. Taipei, Taiwan: National Taiwan Normal University.
Larson, E. T. & Summers, C. H. 2001. Serotonin reverses dominant social status. Behavioural Brain Research, 121, 95-102.
Lee, I. H. 2009. The hormonal mechanisms of the loser effect in Kryptolebias marmoratus. Master's thesis. Taipei, Taiwan: National Taiwan Normal University.
Leshner, A. I. 1983. The hormonal responses to competition and their behavioral significance. In: Hormones and Aggressive Behavior (Svare, B.B. ed.), pp. 393-404. Plenum Press, New York.
Lu, C. K. 2010. Winner effect and its relationship with testosterone and cortisol in Kryptolebias marmoratus. Master's thesis. Taipei, Taiwan: National Taiwan Normal University.
Mackiewicz, M., Tatarenkov, A., Perry, A., Martin, J. R., Elder, J. F., Jr., Bechler, D. L. & Avise, J. C. 2006a. Microsatellite documentation of male-mediated outcrossing between inbred laboratory strains of the self-fertilizing mangrove killifish (Kryptolebias marmoratus). Journal of Heredity, 97, 508-513.
Mackiewicz, M., Tatarenkov, A., Taylor, D. S., Turner, B. J. & Avise, J. C. 2006b. Extensive outcrossing and androdioecy in a vertebrate species that otherwise reproduces as a self-fertilizing hermaphrodite. Proceedings of the National Academy of Sciences of the United States of America, 103, 9924-9928.
Malenka, R. C. & Nicoll, R. A. 1999. Long-term potentiation—a decade of progress? Science, 285, 1870-1874.
Marini, F., Pozzato, C., Andreetta, V., Jansson, B., Arban, R., Domenici, E. & Carboni, L. 2006. Single exposure to social defeat increases corticotropin-releasing factor and glucocorticoid receptor mRNA expression in rat hippocampus. Brain Research, 1067, 25-35.
Maxson, S. C. 2000. Genetic influences on aggressive behavior. In: Genetic Influences on Neural and Behavioral Functions (Pfaff, D.W. et al. ed.), pp. 405-416, CRC Press
McEwen, B. S. 2000. The neobiology of stress: from serendipity to clinical relevanceur. Brain Research, 886, 172-189.
Miczek, K., Fish, E., de Bold, J. & de Almeida, R. 2002. Social and neural determinants of aggressive behavior: pharmacotherapeutic targets at serotonin, dopamine and γ-aminobutyric acid systems. Psychopharmacology, 163, 434-458.
Mohanan, V. v., Kaimal, S. B. & Paulose, C. S. 2005. Decreased 5-HT1A receptor gene expression and 5-HT1A receptor protein in the cerebral cortex and brain stem during pancreatic regeneration in rats. Neurochemical Research, 30, 25-32.
Nam, R. H., Kim, W., & Lee, C. J. 2004. NMDA receptor-dependent long-term potentiation in the telencephalon of the zebrafish. Neuroscience Letters, 370, 248-251.
Neat, F. C., Taylor, A. C. & Huntingford, F. A. 1998. Proximate costs of fighting in male cichlid fish: the role of injuries and energy metabolism. Animal Behaviour, 55, 875-882.
Nelson, R. J. & Chiavegatto, S. 2001. Molecular basis of aggression. Trends in Neurosciences, 24, 713-719.
Ogawa, S., Lubahn, D. B., Korach, K. S. & Pfaff, D. W. 1997. Behavioral effects of estrogen receptor gene disruption in male mice. Proceedings of the National Academy of Sciences of the United States of America, 94, 1476-1481.
Ogawa, S., Eng, V., Taylor, J., Lubahn, D. B., Korach, K. S. & Pfaff, D. W. 1998. Roles of estrogen receptor-alpha gene expression in reproduction-related behaviors in female mice. Endocrinology, 139, 5070-5081.
Ogawa, S., Chan, J., Chester, A. E., Gustafsson, J. A., Korach, K. S. & Pfaff, D. W. 1999. Survival of reproductive behaviors in estrogen receptor beta gene-deficient (beta ERKO) male and female mice. Proceedings of the National Academy of Sciences of the United States of America, 96, 12887-12892.
Ogawa, S., Chester, A. E., Hewitt, S. C., Walker, V. R., Gustafsson, J. A., Smithies, O., Korach, K. S. & Pfaff, D. W. 2000. Abolition of male sexual behaviors in mice lacking estrogen receptors α and β (α/βERKO). Proceedings of the National Academy of Sciences of the United States of America, 97, 14737-14741.
Olsen, K., 1983. Genetic determinants of sexual differentiation. In: Hormones and Behaviour of Higher Vertebrates (Balthazart, J. et al. ed), p. 138, Springer-Verlag
Otronen, M. 1990. Mating behavior and sperm competition in the fly, Dryomyza anilis. Behavioral Ecology and Sociobiology, 26, 349-356.
Øverli, Ø., Kotzian, S. & Winberg, S. 2002. Effects of cortisol on aggression and locomotor activity in rainbow trout. Hormones and Behavior, 42, 53-61.
Øverli, Ø., Korzan, W. J., Hoglund, E., Winberg, S., Bollig, H., Watt, M., Forster, G. L., Barton, B. A., E, O. V., Renner, K. J. & Summers, C. H. 2004. Stress coping style predicts aggression and social dominance in rainbow trout. Hormones and Behavior, 45, 235-241.
Oyegbile, T. O. & Marler, C. A. 2005. Winning fights elevates testosterone levels in California mice and enhances future ability to win fights. Hormones and Behavior, 48, 259-267.
Oyegbile, T. O. & Marler, C. A. 2006. Weak winner effect in a less aggressive mammal: Correlations with corticosterone but not testosterone. Physiology & Behavior, 89, 171-179.
Rosa, M. L. N. M., Guimarães, F. S., Pearson, R. C. A. & Del Bel, E. A. 2002. Effects of single or repeated restraint stress on GluR1 and GluR2 flip and flop mRNA expression in the hippocampal formation. Brain Research Bulletin, 59, 117-124.
Ruiz-de-la-torre, J. L. & Manteca, X. 1999. Effects of testosterone on aggressive behaviour after social mixing in male lambs. Physiology & Behavior, 68, 109-113.
Sakakura, Y., Tagawa, M. & Tsukamoto, K. 1998. Whole-body cortisol concentrations and ontogeny of aggressive behavior in yellowtail (Seriola quinqueradiata Temminck & Schlegel; Carangidae). General and Comparative Endocrinology, 109, 286-292.
Schmittgen, T. D. & Livak, K. J. 2008. Analyzing real-time PCR data by the comparative CT method. Nature Protocols, 3, 1101-1108.
Schuett, G. W. 1997. Body size and agonistic experience affect dominance and mating success in male copperheads. Animal Behaviour, 54, 213-224.
Schuett, G. W. & Grober, M. S. 2000. Post-fight levels of plasma lactate and corticosterone in male copperheads, Agkistrodon contortrix (Serpentes, Viperidae): differences between winners and losers. Physiology & Behavior, 71, 335-341.
Simon, N. G. & Gandelman, R. 1978. The estrogenic arousal of aggressive behavior in female mice. Hormones and Behavior, 10, 118-127.
Smith, J. M. & Price, G. R. 1973. The logic of animal conflict. Nature, 246, 15-18.
Smith, J. M. & Parker, G. A. 1976. The logic of asymmetric contests. Animal Behaviour, 24, 159-175.
Sloman, K. A., Metcalfe, N. B., Taylor, A. C. & Gilmour, K. M. 2001. Plasma cortisol concentrations before and after social stress in rainbow trout and brown trout. Physiological and Biochemical Zoology, 74, 383-389.
Summers, C. H., Larson, E. T., Summers, T. R., Renner, K. J. & Greenberg, N. 1998. Regional and temporal separation of serotonergic activity mediating social stress. Neuroscience, 87, 489-496.
Summers, C. H., Watt, M. J., Ling, T. L., Forster, G. L., Carpenter, R. E., Korzan, W. J., Lukkes, J. L. & Overli, O. 2005. Glucocorticoid interaction with aggression in non-mammalian vertebrates: reciprocal action. European Journal of Pharmacology, 526, 21-35.
Taylor, D. S. 1990. Adaptive specializations of the Cyprinodont fish Rivulus marmoratus. Florida Scientist, 53, 239-248.
Taylor, D. S., Fisher, M. T. & Turner, B. J. 2001. Homozygosity and heterozygosity in three populations of Rivulus marmoratus. Environmental Biology of Fishes, 61, 455-459.
Tilbrook, A. J., Turner, A. I. & Clarke, I. J. 2000. Effects of stress on reproduction in non-rodent mammals: the role of glucocorticoids and sex differences. Reviews of Reproduction, 5, 105-113.
Trainor, B. C., Bird, I. M. & Marler, C. A. 2004. Opposing hormonal mechanisms of aggression revealed through short-lived testosterone manipulations and multiple winning experiences. Hormones and Behavior, 45, 115-121.
Trainor, B. C., Rowland, M. R. & Nelson, R. J. 2007. Photoperiod affects estrogen receptor α, estrogen receptor β and aggressive behavior. European Journal of Neuroscience, 26, 207-218.
Vermeulen G. J., Lambert J. G., van der Looy M. J. & Goos H. J. 1994. Gas chromatographic-mass spectrometric (GC-MS) analysis of gonadal steroids in plasma of the male African catfish, Clarias gariepinus: effects of castration or treatment with gonadotropin releasing hormone analogue. General and Comparative Endocrinology, 96, 288-297.
Weiger, W. A. 1997. Serotonergic modulation of behaviour: a phylogenetic overview. Biological Reviews, 72, 61-95.
Wells, M. S. 1988. Effects of body size and resource value on fighting behaviour in a jumping spider. Animal Behaviour, 36, 321-326.
Wendelaar Bonga S. E., Balm P. H. M. & Lamers A. E. 1995. The involvement of ACTH and MSH in the stress response in teleost fish. Netherlands Journal of Zoology, 45, 103-106.
Whitehouse, M. E. A. 1997. Experience influences male-male contests in the spider Argyrodes antipodiana (Theridiidae: Araneae). Animal Behaviour, 53, 913-923.
Wingfield, J. C. & Hahn, T. P. 1994. Testosterone and territorial behaviour in sedentary and migratory sparrows. Animal Behaviour, 47, 77-89.
Winberg, S., Nilsson, G. E., & Olsen, K. H. 1992. Changes in brain serotonergic activity during hierarchic behavior in Arctic charr (Salvelinus alpinus L.) are socially induced. Journal of Comparative Physiology A, 170, 93-99.
Winberg, S. & Nilsson, G. E. 1993. Roles of brain monoamine neurotransmitters in agonistic behaviour and stress reactions, with particular reference to fish. Comparative Biochemistry and Physiology C, 106, 597-614.
Winberg, S. & Lepage, O. 1998. Elevation of brain 5-HT activity, POMC expression, and plasma cortisol in socially subordinate rainbow trout. American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 274, R645-654.
Zielinski,W. J., & Vandenbergh, J. G. 1993. Testosterone and competitive ability in male house mice, Mus musculus: laboratory and field studies. Animal Behaviour, 45, 873-891.