DIVERSITY IN HORMONE-BEHAVIOR RELATIONS
Different species have evolved very different modes of reproduction. Nevertheless, there are also some general principles across species that are true. Furthermore, by learning about both the general principles and the exceptions, we can begin to understand how some of the systems evolved.
PATTERNS OF REPRODUCTION AMONG SEASONAL BREEDERS (why is this distinction only important for seasonal breeders?)
Associated vs Dissociated Reproductive Patterns
Associated: animal produces and releases sperm or eggs during the mating season
Dissociated: Eggs or sperm are produced at some time other than during the mating season
I showed 4 graphs (which are a simplification of figure 6.1).
1) Associated pattern of reproduction in a seasonal breeder
2) Associated pattern of reproduction in a non-seasonal breeder
3) Dissociated pattern of reproduction : gonadal growth and gamete production occur at a time different from the time when sexual behavior occurs.
4) Mixed reproductive strategy - this is probably the most confusing because one sex has an associated pattern and the other sex is dissociated. If the female is associated then the male will store sperm in reproductive tract over to be released when the female ovulates. If the male is associated, then the female mates with the male and stores the sperm in her reproductive tract until eggs are produced at some later time.
These types of strategies develop because there are constraints on reproduction. These constraints include:
Environmental Constraints:
Ultimate factors - times of adequate food, availability of nesting material, predators, etc
Proximate factors: seasonal fluctuations in daylength, temperature, moisture, etc
-> these constraints are of greater importance in harsh climates
Developmental and Physiological Constraints:
length of time to produce sperm or eggs
temperature dependence of gonadal activity (sperm must be produced when temperatures are warm, but can be stored in many species
embryonic diapause - storage of fertilized embryo prior to implantation (1 wk - years occurs in bears, kangaroos, skunk) in order to get around some constraints
Evolutionary Constraints:
What has come before determines to a great extent what will come after. Related species are likely to exhibit similar reproductive patterns.
Other Constraints: Mate Compatibility
-> stimulus from male may be necessary to initiate the estrous cycle in the female
-> voles
-> ring doves
-> green anole lizard
Example: Kittiwake Gull
Year 1 -> off spring ? -> year 2
female #1
+ +++++ female 1 & male 1 still together
male #1
female #2
+ 0 (divorce) - female #2 with different male
male #2
female #3
+ ++++ (male #3 dies) female #3 with different male
male #3
-> If female has young she stays with a male the next year. If she does not have young she changes partners - only other reason for changing partners is if the original male dies.
Canvasback Ducks
female + self-selected male -> eggs are produced
female + experimenter chosen male -> no eggs - the female lacks the specific hormone changes required to produce eggs.
Constraints Affecting Reproductive Strategies and reproductive Success include those that have evolved due to Natural Selection and Sexual Selection
Natural Selection: results in traits that are adaptational responses to changes in the environment -> animals that survive are those with traits that are adaptive to their environment.
Sexual Selection: results from interactions among individuals that compete for mating opportunities -> male-male competition and mate choice
Natural selection and sexual selection may act in opposite ways on male traits. Example: plumage, antlers, horns, tusks
THE RED-SIDED GARTER SNAKE
a novel neuroendocrine mechanism mediating courtship behavior.
Home: northern USA & Manitoba, Canada where there are severe winters and animals spend up to 9 months hibernating in subterranean limestone caverns
Mating occurs in spring - stimulated by the rising temperatures.
1) males emerge all at once but remain in crevice region near entrance to the hibernaculum - they do not disperse
2) Females emerge about 1 week later - 1 at a time
3) Males approach the female
there is a pheromone on female's back that elicits "chin-rubbing behavior" by male on female's back
male attempts to align body along the female's and attempts to intromit a hemipenis
over 100 males may be attracted and a mating ball results
4) After the female has mated (usually with only 1 male) she immediately leaves the den area
5) About 3 weeks later all of the females will have emerged from the hibernaculum. The intensity of the male courtship waned and the males disperse. They do not return until fall.
Dissociation of gonadal growth and sexual behavior
The sperm the male uses in mating were produced during testicular growth the previous summer and stored in the epididymus over the winter. Spermatogenesis begins about 6 weeks after emergence and continues for 10-12 weeks. This is associated with an increase in serum androgens. Testicular regression occurs when the male returns to the hibernaculum
The females are induced ovulators and induced ovarian development. Females emerge with regressed ovaries and low serum estrogen. Mating causes females to be unattractive and receptive to males because mating triggers a neuroendocrine reflex that induces prostaglandin release and this results in ovulation six weeks later.
How have the environmental and physiological constraints been overcome in the red-sided garter snake?
- hormone manipulation after emergence from hibernation does not affect behavior
- dormancy period necessary (at low temperatures) to see male sexual behavior
Chin-rubbing behavior in the male red-sided garter snake is elicited by tongue-flick delivery of a pheromone that the female produces
The anterior hypothalamus-preoptic area (AHPOA) is involved in this behavior because lesions of the AHPOA abolish chin-rubbing
The female pheromone attracts the males as indicated by their flocking to a pheromone-treated side of a paper towel
1. Androgens prime the neural mechanisms mediating chin-rubbing behavior
2. Environmental cues (warming after the cold temperature) triggers the behavior (hormones are necessary but not sufficient to activate the behavior)
The red-sided garter snake is also an example of an animal with alternative life history strategy -> diandrous males
2 types of males:
"He-Males" normal males, never courted by other males
testosterone: estrogen in serum is 94:1
"She-Males" produces female attractiveness pheromone
in 16% of the mating balls the she males are the object of courtship
testosterone:estrogen 250:1
competitive advantage in mating ball
enzyme in she-male's skin converts testosterone to estrogen - estrogen induces the release of pheromone - very powerful
Mating induces a neuroendocrine reflex in the female - if the input is not received by the brain (via the spinal cord) then ovulation does not occur) Figure 6.10
CONCLUSIONS:
Even with the diversity of reproductive modes and patterns there is conservation of the neural circuits underlying reproductive behavior
There can be behavioral facilitation of reproduction: male -> female , where the male's behavior ensures that the female is in the appropriate reproductive state (induced estrus) to facilitate implantation, etc
female -> female synchronous reproduction may reduce predator risk and maternal cost of producing off spring
what is the function of sexual behavior?
or - What are males needed for? sperm for fertilization of egg
behavior to insure normal gonadotropin secretion on females
induce neuroendocrine reflex to promote successful embryo development
Behavioral facilitation of reproduction can occur in many species including bacteria and algae
EXAMPLE: Parthenogenic Whiptail Lizard (Cnemidophorous uniparens)
In the Crews lab there is continuous video monitoring of behavior by remote control, and the temperature and humidity are carefully controlled.
Descended from c. inornatus (maternal ancestor) and c. burti (paternal ancestor)
in these gonochoristic lizards:
1) Male approaches female
2. Receptive female stands still
3. Male grasps with his jaws the female's neck or foreleg and begins to move his tail beneath the female's
4. With intromission the male shifts his jaw from the neck to the pelvic region forming the doughnut position which is maintained for 5-10 min.
A similar sequence of events is observed in parthenogenic (unisexual) whiptail lizards.
The reproductive cycle of the whiptail lizard:
3-4 discrete ovarian cycles, 3-4 weeks long
estradiol increases as the follicles grow peaking around ovulation
progesterone increases during later stages of follicular maturation (maximum after ovulation)
-> when estrogen is elevated female-like receptive behavior is exhibited (ovariectomy abolishes receptive behavior)
-> display of male-like behavior occurs only during the post-ovulatory phase when estrogen is low and progesterone is elevated - ovariectomy abolishes pseudocopulatory behavior in unisexual lizards
-> Figure 6-13
Hormone-replacement in unisexual lizards after ovariectomy
-> pseudocopulatory behavior only occurs when animals are in pairs:
1) treated with estradiol exhibits female-like behavior
2) treated with progesterone exhibits male-like behavior
What is the underlying neural basis for these effects of gonadal hormones on behavior?
In c. inornatus: POA is larger in males than in females while VMH is bigger in females than in males
POA - mounting behavior
VMH - female sexual behavior
Where does progesterone act in the unisexual lizard?
1. In gonochoristic lizard - progesterone can restore male sexual behavior in 1/3 of castrated males
all progesterone-sensitive males are sensitive to both progesterone and androgens
R5020 stimulates sexual behavior (progesterone agonist cannot be converted to androgen)
RU486 prevents sexual behavior induced by progesterone
EXAPTION -TRAIT CO-OPTED FOR USE IN PARTHENOGENIC LIZARDS
-> different from mammals where progesterone suppressed androgen-dependent behaviors
-> male sexual behavior in this species may be linked to progesterone!