Animal Behavior/Hormones in Behavior
- 1 Hormones
- 1.1 The Glandular Systems
- 1.2 Sex Determination
- 1.3 Homeostasis
- 1.4 Behavioral Endocrinology
- 1.5 Example: Arthropod Molting
The Glandular Systems
The body has two types of glandular systems, the endocrine, which generally secrete hormones through the bloodstream, and the exocrene which secrete fluids to the outer surfaces of the body, such as sweating.
The Endocrine System combines neural and glandular mechanisms which control physiological functions/behavior via the secretion of hormones. Hormones are chemical signaling molecules which play an integral role during development (organizational effects) and day-to-day functioning (activational effects) of target tissues at critical times. Secretory cells of a particular type are often clumped together into a well defined gland (e.g. pituitary, thyroid, adrenal, testes, ovaries). Secreted at that site they distribute throughout the body via the blood stream, and cause physiological changes at any other sites.
- Steroids: derived from cholesterol
- Amines: derived from amino acids
- Peptides: short chains of amino acids via protein synthesis
Sex hormones, largely steroids, are secreted from gonads and adrenal cortex. Androgens (e.g., testosterone) are usually higher in male mammals while levels of estrogens (e.g., estradiol) in female mammals exceed those in males. Circulating levels of sex hormones then provide the basic organization for gender phenotypes.
Neurohormone refers to a compound that is released into the bloodstream at specialized neurohemal release sites. It binds to receptors anywhere in the body and thereby coordinates disparate biochemical responses.They are released from glands, transported via the circulatory system and influence the activity of target organs.
Functionally hormones are categorized as Effector hormones (e.g. Vasopressin, Oxytocin) or Tropic hormones, releasing factors (e.g. Gonadotropin Releasing Hormone - GnRH, Growth Hormone Releasing Hormone - GHRH). Target Organs receive hormones via blood stream, respond directly or release their own hormones in response (steroid hormones), and these hormones circulate back to turn off hormonal secretion: endocrine feed back loops. Compensatory hypertrophy results from feedback loops control levels of activity where systems are upregulated until they achieve sufficient functional effects (e.g. thyroxine and goiter). Activational Effects and Organizational Effects
Hormonal influences during critical periods produce fairly permanent changes in nervous and endocrine systems. Sex-determination may be chromosomal or environmental:
- Mammals: hormonal cascade of events takes an individual down one of two paths (default is female). testes determining factor (tdf) in mammals or Sexchromosomal Abnormalities: Turner syndrome (XO monosomy), Klinefelter syndrome (XXY trisomy), XYY syndrome ("supermale"), Multi-X syndrome ("superfemale"), XX Male syndrome (SRY gene transference) XY Female syndrome (SRY gene missing)
- Birds: Males are homogametic (ZZ), females are heterogametic (ZW)
- Turtles: temperature
- Fish: social stimuli
internal sex organs: Precursors for both internal sex organs are present in the embryo: the Mullerian system for the female sex; the Wolffian system for males. Controlled by the levels of circulating hormones, only one set of organs develops while the other shrinks. Secreted by the testes, Müllerian inhibiting hormone (i.e., a peptide hormone) has defeminizing effects while androgens (i.e., steroid hormones) exert a masculinizing effect. Gonads: testes or ovaries, first to develop. External genitalia: Androgens are essential for the development of primary sexual characteristics.
Androgen insensitivity syndrome: A genetic male lacking functional androgen receptors develops testes, secretes Müllerian inhibiting substance and androgens. Internal sex organs progress onto the intended male path, but female external genitalia result from the inability to respond to androgens correctly. Turner’s syndrome, with genotype XO (i.e., a single X chromosome and no Y), lacks testes and ovaries.
Maternal effects explain influenced by effects of the mother that are not due to direct genetic inheritance. Positional effects in the mammalian uterus
Hormonal secretion or its inhibition may bring about some rapid physiological changes in a variety of target tissues. Vasopressin.
Hormones influence sensory perception (human visual, rat odor, preference in castrated vs. intact). Hypothalamus neurons monitor the internal state (thirst, hunger) and send neurosecretory cell axons to the posterior pituitary.
In females, Oxytocin, released from the posterior pituitary, triggers milk let-down in mammary glands or contraction in the uterus during child-birth. It is also associated with powerful emotional effects (affective states) in parental behavior and maternal competence. Moreover, the hypothalamus secretes releasing factors to stimulate or inhibit manufacture and secretion of hormones in anterior pituitary portal system: Prolactin, Follicle stimulating hormone (FSH), Luteinizing hormone (LH); receives, stores and releases neurohormones from hypothalamus. Sex behaviors: gonadotropin releasing hormone (GnRH) -> gonadotropin -> gonad maturation and gonadal steroid production -> feed back to brain. Sex steroids initiate the basic female and male anatomies (i.e., organizing effects in sexual differentiation cascade) but also allow animals to later respond to activational effects. Expression of sex differences in behavior also requires that steroids activate many aspects of the phenotype during maturation. Reproductive Neuroendocrinology of Ring Doves (Streptopelia risoria): monogamous, sexually monomorphic, parental care from both male and female (incubate eggs, crop "milk"); Lordosis in female hamsters: female soliciting behavior triggered by a touch on the side of the haunches.
synchronisation of menstrual cycles in female mammals housed together
estrous cycles slow and stop in female mice housed together in the absence of any males in the surrounding environment
individuals start cycling again in synchrony if exposed to male odor
acceleration of onset of puberty in female rat when exposed to odor of male
failure of pregnancy if female rat is housed with a male who is not the father
Example: Arthropod Molting
Hormonal Control of Arthropod Molting: Brain: releases ecdysiotropin which stimulates release of molting hormone (MH) from Prothoracic Gland; Corpora allata: Juvenile Hormone (JH) suppresses metamorphosis; Prothoracic Gland; Corpora allata: Juvenile Hormone (JH) suppresses metamorphosis