Hormonal Influences on Behavior and Infanticide in Mice and Birds

Key Concepts of Hormones and Behavior

  • Bidirectional Causal Relationship

    • Interplay between hormones and animal behavior.

    • Behavior may change an animal's endocrine state, affecting hormone levels.

    • Hormones increase the probability of specific behaviors occurring rather than directly causing them.

Infanticidal Behavior in Male House Mice

  • Light-Dark Cycle Influence

    • Infanticidal behavior in male house mice varies with light exposure (L:D cycles).

    • Males under fast-day conditions cease infanticide by day 20 post-mating.

    • Males in slow-day conditions take about 25 days to show a similar decline.

Hormonal Mediators of Aggression

  • Chemical/Physiological Links to Aggression

    • Key questions remain on the mediators connecting daylight changes to increases in male aggression.

Activational Effects of Hormones

  • Effects on Infanticide

    • Castration reduces infanticide in male mice.

    • Testosterone implants can revive this behavior within days (Perrigo and vom Saal, 1989).

    • Steroid hormones like testosterone have varied action times, with some acting within seconds.

Organizational vs. Activational Effects

  • Definitions

    • Activational Effects: Rapid, temporary hormone effects.

    • Organizational Effects: Permanent hormonal influence on nervous system development, affecting long-term physiology and behavior.

  • Case Study with Male Rats

    • Castration at 20 days with adult hormonal injection does not yield female mating behaviors.

    • Castration at 1 day leads to female postures when later mounted, signifying early organizational effects (Gorski, 1993).

Infanticidal Behavior and Aggression in Mice

  • Behavioral Trends

    • C57BL/6 males show high aggression and infanticide tendencies.

    • PRKO mice exhibit no such aggressive behaviors and have comparable progesterone levels to intact mice.

Hormonal Influences on Behavior

  • Progesterone's Role

    • Certain progesterone concentrations prime males for infanticide under specific conditions.

    • Hormonal changes after mating influence paternal behavior positively over time, decreasing aggressive tendencies towards one’s own progeny.

Influences of Receptor and Hormonal Interactions

  • Hormone and Receptor Dynamics

    • Hormones do not work in isolation.

    • Surface receptors bind peptide hormones (AVP, E2) and influence rapid effects.

    • Nuclear receptors handle slower steroid hormones like testosterone.

    • Factors like receptor density and transport proteins modulate behavioral changes influenced by hormones (Fuxjager and Shuppe 2018, Lipshutz et al. 2019).

Steroid Signaling Systems

  • Regulatory Mechanisms

    • Multiple steroid signaling pathways can manage gene expression over extended periods.

    • Non-genomic effects can occur rapidly within 20 minutes, affecting neuronal activity.

Sexual Behavior Changes in Japanese Quail

  • Behavioral Observations

    • Post-mating, Japanese quail males show significant behavioral changes towards females.

    • Castrated males require testosterone implants to regain sexual behaviors.

    • Testosterone can convert to estradiol in the brain, influencing sexual motivation and behaviors, such as song production.

Impact of Aromatase Inhibitors

  • Behavioral Effects of Inhibitors

    • Castrated males with testosterone implants exhibit sexual motivation; removal of aromatase reduces this behavior by preventing conversion to E2 (essential for motivation).

Gender Development in Birds

  • Males as Default Sex

    • In absence of gonadal hormones, development follows male-typical pathways.

    • Female-like traits require specific hormonal activity post-development.

  • Case Study of Aromatase Inhibition

    • Female birds, when treated with inhibitors during egg development, display male-mimicking copulatory behavior (Balthazart and Ball 1995).

Sexual Differentiation and Gene Influence in Birds

  • Gynandromorphic Zebra Finch

    • The existence of gynandromorphic individuals shows gene influence in sexual differentiation beyond hormonal control.

    • Identical hormonal conditions result in differing genetic influences across body halves, illustrating complex interactions in sexual development.