Modification of the activation of the hypothalamic-pituitary-gonadal axis in males of the house mouse (Mus musculus wagneri) exposed to the odor of receptive con- and heterospecific females: influence of early experience and maternal environment

Developmental plasticity is one of the main factors driving the formation of individual, sexual, and species identity. We demonstrated a modification of the activation of the hypothalamic-pituitary-gonadal axis in male house mice as a result of early postnatal experience and the maternal environment upon exposure to the odor of receptive females of their own and closely related species. To determine the effect of rearing in families of closely related species on the activation of the hypothalamic-pituitary-gonadal axis in males, in particular, to compare the hormonal response (serum levels of free testosterone, hereafter FTL) in M. m. wagneri males reared by M. spicilegus , in response to the odor of receptive conspecific females and females of the foster species. Adult male offspring of two taxa of Mus musculus s. l. species group was reared either by their biological mothers ( M. m. wagneri – 18 males, M. spicilegus – 19 males), unrelated conspecific females ( M. m. wagneri – 11 males, M. spicilegus – 4 males), or by heterospecific foster mothers ( M. m. wagneri – 13 males). We used the previously described method with modifications (Kotenkova E, Romachenko A, Ambaryan A, Maltsev A (2019) Effect of early experience on neuronal and behavioral responses to con- and heterospecific odors in closely related Mus taxa: Epigenetic contribution in formation of precopulatory isolation. BMC Evol Biol 19(l): 51. 10.1186/s12862-019-1373-8). Each male was exposed to urine twice: once from females of his own and the second time from a closely related species with an interval of 8 or 16 days. In a separate series of experiments (control), the males were exposed to saline. After a 30-minute exposure, blood samples (≤150 µl) were obtained from the retro-orbital sinus with heparinized capillaries following the standard technique (Parasuraman et al. 2010). The serum was separated by centrifugation at 3000 g for 10 minutes and stored at -20ºC until free testosterone analysis. Serum-free testosterone concentrations were measured using a commercially available ELISA kit. The level of free testosterone in the blood serum of males reared by a conspecific female was significantly lower when exposed to the urine odor of a heterospecific female in comparison with exposure to the odor of a conspecific female. When male M. m. wagneri was fostered by females of a closely related species, the testosterone response of the males to the female's chemosignals (both hetero- and conspecific)