Department of Biology, Indiana University, 1001 E. 3(rd) St., Bloomington, IN 47405, USA; Center for the Integrative Study of Animal Behavior, Indiana University, 409 N. Park Ave., Bloomington, IN 47505, USA.
Department of Biology, Indiana University, 1001 E. 3(rd) St., Bloomington, IN 47405, USA; Center for the Integrative Study of Animal Behavior, Indiana University, 409 N. Park Ave., Bloomington, IN 47505, USA.
Horm Behav. 2024 Aug;164:105576. doi: 10.1016/j.yhbeh.2024.105576. Epub 2024 Jun 8.
Sexually dimorphic behaviors are often regulated by gonadal steroid hormones. Species diversity in behavioral sex differences may arise as expression of genes mediating steroid action in brain regions controlling these behaviors evolves. The electric communication signals of apteronotid knifefishes are an excellent model for comparatively studying neuroendocrine regulation of sexually dimorphic behavior. These fish produce and detect weak electric organ discharges (EODs) for electrolocation and communication. EOD frequency (EODf), controlled by the medullary pacemaker nucleus (Pn), is sexually dimorphic and regulated by androgens and estrogens in some species, but is sexually monomorphic and unaffected by hormones in other species. We quantified expression of genes for steroid receptors, metabolizing enzymes, and cofactors in the Pn of two species with sexually dimorphic EODf (Apteronotus albifrons and Apteronotus leptorhynchus) and two species with sexually monomorphic EODf ("Apteronotus" bonapartii and Parapteronotus hasemani). The "A." bonapartii Pn expressed lower levels of androgen receptor (AR) genes than the Pn of species with sexually dimorphic EODf. In contrast, the P. hasemani Pn robustly expressed AR genes, but expressed lower levels of genes for 5α-reductases, which convert androgens to more potent metabolites, and higher levels of genes for 17β-hydroxysteroid dehydrogenases that oxidize androgens and estrogens to less potent forms. These findings suggest that sexual monomorphism of EODf arose convergently via two different mechanisms. In "A." bonapartii, reduced Pn expression of ARs likely results in insensitivity of EODf to androgens, whereas in P. hasemani, gonadal steroids may be metabolically inactivated in the Pn, reducing their potential to influence EODf.
性二态行为通常受性腺类固醇激素调节。行为性别差异的物种多样性可能是由于介导类固醇作用的基因在控制这些行为的大脑区域中的表达而产生的。无鳍刀鱼的电通讯信号是研究神经内分泌调节性二态行为的理想模型。这些鱼产生和检测微弱的电器官放电（EOD）以进行电定位和通讯。EOD 频率（EODf）受髓质起搏器核（Pn）控制，在某些物种中具有性二态性，并受雄激素和雌激素调节，但在其他物种中则具有性单态性且不受激素影响。我们量化了两种 EODf 具有性二态性的物种（Apteronotus albifrons 和 Apteronotus leptorhynchus）和两种 EODf 具有性单态性的物种（“Apteronotus”bonapartii 和 Parapteronotus hasemani）的 Pn 中类固醇受体、代谢酶和辅助因子的基因表达。“A.”bonapartii Pn 表达的雄激素受体（AR）基因水平低于 EODf 具有性二态性的物种的 Pn。相比之下，P. hasemani Pn 强烈表达 AR 基因，但表达 5α-还原酶基因的水平较低，该酶将雄激素转化为更有效的代谢物，而表达 17β-羟甾脱氢酶基因的水平较高，该酶将雄激素和雌激素氧化为效力较低的形式。这些发现表明，EODf 的性单态性通过两种不同的机制趋同产生。在“ A.”bonapartii 中，Pn 中 ARs 的表达减少可能导致 EODf 对雄激素不敏感，而在 P. hasemani 中，性腺类固醇可能在 Pn 中代谢失活，从而降低其影响 EODf 的潜力。
