What Is Courtship Behavior? • Behavior that attracts potential mates and induces mating behavior • Conveys fitness information about the signaler, including species, sex, size/age, territory held, etc.
Who Displays Courtship Behavior? • Almost all vertebrates species • Examples of both male and female courtship behavior exist • Males more often display courtship behavior, due to different energetic costs of gamete creation and offspring care
Useful Species for Courtship Behavior Study • Have dimorphic, robust, easily observed courtship behavior • Frogs, weakly electric fish, birds. • Courtship behavior is also studied in insects (drosophila, bees) but is not as relevant to the study of endocrine function.
Possible Mechanisms for Endocrine Effects • Differential organization of brain circuitry. • Differential activation of (identical or different) brain circuitry by male or female hormones. • Morphological differences caused by differential hormone presence; may or may not have sensitive period.
Aspects of Courtship Behavior • Development of Courtship Behavior • Morphological Structures and Neural Circuits Necessary for Behavior • Expression of Courtship Behavior • Appropriate Response to Stimuli • Female Response to Courtship Behavior • What’s the point of Courtship Behavior?
Clawed Frogs: Organizational Morphological Difference In the African clawed frog, males attract females to a mating site with fast trills. Both males and females produce slower, “clicking” vocalization.
Organizational Morphological Difference • In an isolated male brain/larynx, the motor neurons can be simulated in a pattern that will produce the courtship trill • When a female preparation is stimulated in this way, the muscles cannot move fast enough to create a trill. Fig 1, Marin 1990
Organizational Morphology • Testosterone for 5 weeks at metamorphosis is sufficient to masculinize larynx. • Testosterone in adulthood is much slower to masculinize larynx (not shown). Tobias et al 1991 fig 4
Testosterone Effects Have Sensitive Period • Larynx shows ability to bind androgen at PM 0, and binding ability decreases over time (Sassoon and Kelley, 1986) • Requires more than just androgen- also dependent on prolactin, whose secretion is controlled by thyroxine, an important hormone in metamorphosis.
Organization in the Brain: Birdsong • Some bird species show age-sensitive song learning- song remains the same through the years, i.e. in European Starlings, Zebra Finches • In other bird species, an individual bird’s song can change every year, though it is crystallized in the breeding season, i.e. Canaries
Neural Circuitry of Bird Song Kimpo et al 2003
Size Matters • Male:Female ratios of singing behavior (numbers) correlate with ratio of HVc volume (Y-axis) Kelly and Brenowitz, Behavioral Neuroendocrinology
Hormones in Bird Brains • Hormonal processing in the bird brain in particularly complex. • Brain contains • Aromatase (testosterone into estrogen) • 5-alpha reductase (testosterone into DHT) • 5-beta reductase (testosterone into inactive compound)
Hormones in Bird Brains • Developing female birds contain high levels of circulating androgen, but few androgen receptors in the brain • Adult male brains synthesize enough estrogen to circulate in the plasma
Organization in Birds: Zebra Finches • Estradiol given daily during first week after post-hatching: • partially masculinizes song behavior • increases song nuclei volume compared to female controls • Increases male courtship behavior in adult females treated w. testosterone
Organization in Birds: Zebra Finches Light bars:male Dark bars: female EB: Estradiol Benzoate Number signifies week(s) during which hatchlings received daily treatment Adkins-Regan 1994
Organization in Birds: Zebra Finches • Estradiol given during the first week or first three weeks completely masculinizes dancing behavior. Adkins-Regan 1994
Organization in Birds: Zebra Finches • Estrogen given to developing female finches masculinizes both morphology and function of song system • Testosterone given to developing females sometimes has masculinizing effects; estrogen almost always works better Grisham et al 2001, Grisham and Arnold 1995
Blocking Androgen Blocks Masculinizing Effects of Estrogen Grisham et al 2001
Organization in Birds: Zebra Finches • Developing female finches have high levels of androgen; Low androgen receptors • Estrogen treatment may upregulate androgen receptors Grisham et al 2001
Estrogen in the Brain • Young male and female birds have remarkably high levels of aromatase, throughout their telencephalon. (Schlinger1994) • Both neurons and glia express this protein • In situ shows no difference between males and females for ER alpha, ER beta or aromatase expressed in the brain during late embryonic stages until P1 (Perlman 2003)
Organization: Male Zebra Finches • Too much or too little testosterone action can inhibit brain masculinization and song learning. • In general, estrogen is associated with song plasticity and testosterone is associated with song crystallization. • Not much else is known.
Activation: More Than Just Machinery • In the presence of adequate machinery, what induces courtship behavior? • Appropriate response to stimuli to express courtship behavior often depends on hormonal activity.
Frog Song Depends on Testes • Male frogs castrated as adults do not loose their masculine vocal cords, but they do not sing. Wetzel and Kelley 1983
Avian Seasonal Changes in Testosterone • Testosterone can be seen to vary seasonally • Does testosterone cause singing? Smith et al 1997
Size Matters • HVc, RA, and area X can increase by as much as 300% during the breeding season in temperate-zone birds. Smith 1997
Effects of Long Days and Testosterone on Bird Song nuclei size. Tramontin 2000
Testosterone Binding in Song Circuit • Both testosterone and estrogen show binding in song circuit Brenowitz and Lent 2001
Activation: Response to Stimuli • Many species display seasonal courtship behavior- what is the seasonal stimuli? • How is this stimuli linked to testosterone?
Photoperiod and Testosterone • Both photoperiod and T treatment can have some effect on nuclei size alone- effects of T treatment are much stronger (Smith 1997) • Long photoperiod induces GnRH release at the beginning of spring (Dawson et al 2001) • Melatonin can also decrease testosterone secretion (Bentley et al 1999)
Female as Stimuli In male starlings, song activity is dependent on both season and presence of a female. Riters et al, 2000
Female as Stimuli Mechanism inducing courtship song behavior only in presence of female is unknown.
Canary Song Depends on Testosterone • In canaries, both male and female have neural circuitry to sing. When adult ovx females are given testosterone, they begin to sing • HVc reaches 90% and RA reaches 53% of male volumes. (Nottebohm 1980) • Growth by increased dendrites and increased survival of constantly born neurons
Adult “organization”- Blurring the Lines • “A vast surplus of new neurons is constantly produced in the ventricular zone of the adult canary brain, but only a fraction of these cells survive . Many of these new neurons are incorporated into the HVC, a large, anatomically discrete forebrain nucleus that is part of the songbird song system” Rasika et al 1999
Adult Canary Organization • Testosterone treatment increased female HVc size and neuron number • BDNF inhibitor can block testosterone effect Rasika et al 1999
Adult Canary Organization • Testosterone treatment increases BDNF in female HVC Rasika et al 1999
Adult Canary Organization Testosterone can induce female canary singing behavior as well as masculinization of neural circuit in the adult through BDNF action in HVc, increasing survival of new neurons.
Adult Canary Organization: A Paradox • Ovariectomy decreases RA dendritic arbors • DHT and estrogen treatment restores RA volume to control female size • Testosterone increases RA volume to control male size Sclinger 1997
Female Response to Courtship Behavior • Female Cowbirds respond to male cowbird song with “copulatory postures” (lordosis-like posture). Wings lowered and spread apart, neck and body arched, feathers around cloacal region separated. King and West, 1977
Neurons in Female HVc nucleus respond differently to sexual vs. nonsexual song • Tested during breeding season • Phase A: courtship song • Phase B: non-courtship song Del Negro et al 2000
Circuits of Response • Still largely unknown • Seems to involve HVc • May be difficult to elucidate, as not all species display robust, immediate response as does the cowbird.
Female Choice • More Complex Songs • Longer Songs • “Faster” Songs Are these accurate measures of “Fitness”?
Can the Song Lie? • Birds were randomly assigned to control, food-restricted, or cortisone-treated groups. • Controlled for genetics and parenting Spencer 2003
Cellular Response • Immediate early gene ZENK is expressed in the HVc and caudal-medial neostriatum (NCM) in response to song, esp. con-specific song (Gentner et al 2001) • In ventral portions of NCM, ZENK was activated more by long song bouts (which are strongly preferred by females).
Circuits of Choice • Discrimination is somewhat associated w. HVc volume in females (Riters et al 2003, Leitner et al 2002)
Circuits of Choice Choice Circuits are probably more complex than simple postural response circuits They may involve HVc and NCM
Summary • Hormones can act to masculinize song nuclei and behavior both in development and adulthood. • Both estrogen and androgen are involved in masculinization. • Testosterone seems to be involved in seasonal activation of courtship song