Proffitt Melissa R, Smith G Troy
Department of Biology, Indiana University, Bloomington, Indiana, USA.
Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, Indiana, USA.
J Exp Zool A Ecol Integr Physiol. 2025 Jul 14. doi: 10.1002/jez.70011.
The development and maintenance of sexually dimorphic behavior often depends on gonadal steroids. Interspecific variation in the magnitude of behavioral sex differences may be mediated by differences in steroid action on neural circuits controlling behavior. The electric communication signals of South American knifefishes are an excellent model to study the evolution and neuroendocrinology of sexually dimorphic behavior because species vary in the sexual dimorphism of these signals and because simple and well-characterized neural circuits regulate the production of electrocommunication signals. Specifically, electric organ discharge frequency (EODf) is controlled by the hindbrain pacemaker nucleus (Pn) and differs between sexes in some species but not in others. Species differences in EODf sexual dimorphism are linked to variation in Pn expression of genes for steroid receptors, steroidogenic enzymes, and receptor cofactors (Proffitt and Smith, 2024). In this study, we asked whether differences in sexual dimorphism of EODf across populations of black ghost knifefish (Apterontus albifrons) are also associated with variation in expression of these genes. Compared to an A. albifrons population with sexually dimorphic EODf, sexually monomorphic A. albifrons populations had reduced Pn expression of genes for androgen receptors and enzymes that increase potency of androgens and had greater expression of genes for a steroid receptor corepressor and for enzymes that reduce gonadal steroid potency. These findings suggest that changes in hormone-related gene expression in brain regions controlling behavior constitute control points for the evolution of variation in sexually dimorphic behavior across populations as well as across species.
两性异形行为的发展和维持通常依赖于性腺类固醇。行为性别差异程度的种间变化可能由类固醇对控制行为的神经回路的作用差异所介导。南美刀鱼的电通讯信号是研究两性异形行为的进化和神经内分泌学的绝佳模型，因为这些信号的两性异形在不同物种间存在差异，而且简单且特征明确的神经回路调节着电通讯信号的产生。具体而言，电鳔放电频率（EODf）由后脑起搏器核（Pn）控制，在某些物种中存在性别差异，而在其他物种中则不存在。EODf两性异形的物种差异与Pn中类固醇受体、类固醇生成酶和受体辅因子基因的表达变化有关（Proffitt和Smith，2024）。在本研究中，我们探究了黑鬼刀鱼（Apterontus albifrons）不同种群间EODf两性异形的差异是否也与这些基因的表达变化有关。与具有两性异形EODf的黑鬼刀鱼种群相比，两性单形的黑鬼刀鱼种群中，雄激素受体基因以及增强雄激素效力的酶的Pn表达降低，而类固醇受体共抑制因子基因以及降低性腺类固醇效力的酶的表达则增加。这些发现表明，控制行为的脑区中激素相关基因表达的变化构成了种群间以及物种间两性异形行为变化进化的控制点。
