A classic example of an innate releasing mechanism: Gull chicks pecking parent s beak to get food. Red spot

Transcription

1 A classic example of an innate releasing mechanism: Gull chicks pecking parent s beak to get food. Red spot

2 The red spot is a key stimulus for the baby chick to peck at the bill. It releases pecking behavior. Sign or key stimulus CNS evaluates sensory input: does it meet preset criteria? YES NO Release pecking FAP* Do nothing At the same time, the parent having its bill pecked is a releaser for the behavior of regurgitating food. * Command neuron effectively disinhibits the CPG for pecking.

3 The red spot on the yellow bill is a detected by the visual system. A CNS releasing mechanism (AKA neural feature detector) qualifies the signal and releases a pattern generator to start pecking

4 Releaser or releasing stimulus releasing mechanism. The releaser is a key or sign stimulus. The releasing mechanism is a neural process that receives input from recognition circuits and communicates with motor control circuits to activate (release) a behavior.

5 Releasing mechanisms can be very simple, requiring just one or two key stimulus parameters. This means they are easily tricked!.

6 Why do such vulnerable neural mechanisms persist? Processing a few simple key stimuli is faster, relative to CNS processing. They are good enough! Predators and parasites that do code break and deceive animals based on particular stimuli they are looking for will indeed drive an evolutionary response for the receiver to be more selective. If there is no code-breaking, there is no selective pressure to build a more elaborate recognition mechanism.

7 7 Code breaking

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11 Example 1 Testosterone and aggressive and reproductive behavior

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13 Based on placental circulation and random arrangement of embryos, some embryos get a double dose of testosterone produced by neighbors.

14 2F males have 1/2X the amount of T 2M males have 2X the amount of T 14

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16 2M males provide less parental care but are more aggressive about mating. 2M less contact with pups

17 As adults, compared with 2F males, 2M males received 2X the amount of T in utero. mounted females more rapidly. produced more offspring over time. spent more time searching for females. spent more energy searching for females. spent less effort relative to parental care. 17

18 Neurons in Hypothalamus (part of brain (CNS)) pituitary GnRH FSH, LH testes Castration gets rid of testosterone testosterone

19 Reverse experiment re: mice in utero. Now get rid of T increase parental care.

20 and even better, if you can replace the T in a castrate and restore function: Can say that T is both necessary and sufficient for the behavior. 20

21 In this case, Guinea pigs Guinea pig copulatory behavior one can only imagine 21

22 Castrated garter snakes Hormones act on brain neurons as triggers, in other cases as maintenance 22 factors very different time constants

23 Vasopressin and Oxytocin

24 Ancient hormones found in nearly all animalia

25 Oxytocin many different functions. Knockout mice (Oxt - ) behavioral deficit of social amnesia. Every time a male interacts with the same female, the male sniffs as if a novel female.

26 The proximal cause of social amnesia, a behavioral deficit, is really a loss of olfactory memory due to nonproduction of oxytocin. normal mouse 26 With a defective gene, sniffing persists as if a particular is always novel.

27 The vasopressin receptor in the ventral pallium. Prairie voles and Meadow voles differ in the amount of V1R in their brains and also differ in parental care.

28 Prairie voles are monogamous. Meadow voles are polygamous (polygynous = one male, multiple females)

29 1. How monogamy might have evolved? 2. How do you increase V1a receptors?

30 Once upon a time Mutation in a polygamous ancestral Prairie Vole V1aR gene perhaps a allele binds V more strongly. male vole copulates V1aR gene expressed in neurons of the ventral pallium. vasopressin release monogamy New V1aR in pallial neurons = greater response from those neurons when vasopressin binds. Happier male vole, spends more time with female. Greater neural response = increased activation of reward system of brain.

31 So one individual vole has a mutation that leads to... a variation of the V1a receptor that binds hormone more strongly... or a transcription regulator that causes more V1aR to be present in neuron membranes...or a variant of the receptor with lower turn-over... or etc, etc This vole leaves more offspring in the next generation, and so do those offspring, etc., fixing the gene rapidly in the population

32 How to get more V1R in the vole brain The V1aR gene inserted using an adeno-associated viral vector. Vectors contained either: 1. Prairie vole VIaR gene or modified V1aR gene from a genomic library a. Including a neuron-specific enolase promoter 2. Prairie vole VIaR gene and Escherichia coli lacz a. Including a cytomegalovirus promoter The gene is spliced at the neuron-specific enolase promoter to create a NSEpvV1aR viral vector. Properties of Adeno-associated viruses: 1. Contain a single strand of DNA 2. Infect non-dividing cells 3. Non-pathogenic 4. Site specific insertion of genetic material The Adeno-associated viral vectors were syringe-injected into specific sites: The ventral pallium or the caudate putamen. Transduction occurs and the NSE promoter works to restrict expression of the gene to neurons in the brain. Reference: Lim, M.M., Wang, Z., Olazábal, D.E., Ren, X., Terwilliger, E.F., and Young, L. J. Enhanced partner preference in a promiscuous species by manipulating the expression of a single gene. Nature. 429, (2004).

33 If you provide more receptors to the brain of a nonmonogamous meadow vole, it will start behaving somewhat like the monogamous prairie vole. Meadow voles with tweaked brains.

34 Bees have pretty small brains and you might think all their behaviors are innate, programmed, and each bee is a behavioral duplicate of the next. In fact, different bees in a hive have different behaviors, and this is under hormonal control.

35 Bee brains (which control bee behavior!) vary in terms of gene expression. So even though the genotype is the same across individuals, gene expression is not.

36 Juvenile hormone and octopamine are involved in transitioning young hive cleaner bees into forager bees.

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38 Surgically remove corpora allata no JH made delayed transition to forager bees. Methoprene (JH analog) injection to allatectomized (!) bees restored timing (normal transition)

39 Octopamine levels in bee brain higher when bees become foragers. Inject octopomine more foraging flight behavior.

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41 How bee behavior changes over time sterile worker bees initially less binding to transcription regulator nurse bees: low level of juvenile hormone later forager bees high level of juvenile hormone So an old hive: build up higher % forager bees more binding to transcription regulator

42 Another chemical regulator, ethyl oleate, modulates the overall rate at which bees transition to foragers.

43 How bee behavior changes over time sterile worker bees initially nurse bees Feed to nurse bees later forager bees Synthesize ethyl oleate Ethyl oleate slows transition of nurse bees to worker bees. Old hive: Higher % forager (old) bees. Old bees die off, less EO, increase transition to foragers.

44 Old hive: Higher % forager (old) bees. Old bees die off less EO faster transition to foragers. sterile worker bees initially nurse bees Feed to nurse bees later forager bees Synthesize ethyl oleate

45 Experimental addition of old (forager) bees slows transition to make new foragers old bees die off too few foragers Add young bees amount of EO per bee goes down fast transition to make lots of foragers. Bottom line: Nurture (development) can affect non-learned/ genetically programmed behaviors.

46 Two different physiological and behavioral male morphs in the midshipman fish (Porichthys notatus). Type I males Delayed maturity: incr growth, larger vocal apparatus Type II males Put more developmental energy into gonads. Smaller as adults, don t advertisement call. good dads sneaker deadbeats

47 Note error in text pg 95 type II males, have a very high gonad-to-body size Should be type II males have a small gonad-to-body size as per this table. Court females Do not court females

48 Sonic muscles larger in type I males. Command neurons pacemaker neurons (CPG) sonic motor nucleus sonic muscles Preoptic area (POA) Command neurons

49 Arginine vasotocin (AVT) inhibits command neurons in Type II males. 6x more AVT-ir (immunoreactive) neurons per gram body weight in type II males! Preoptic area (POA) pacemaker neurons (CPG) Command neurons

50 Natural populations of midshipmen more dense and less dense. Lab raise fish in low density or high density. Low Density juveniles High Density juveniles Fewer AVT-ir neurons & type I morph More AVT-ir neurons & type II morph

51 Hormones and long term oscillators

52 White Crowned Sparrow experiment Birds have seasonal sensitivity to light level. When daytime coincides with a period of light sensitivity, reproductive development is triggered. An oscillator is reset every day at dawn. Light sensitivity occurs hours later. Will it be light out hours after dawn?

53 White Crowned Sparrow circannual synchronization

54 What the oscillator controls... environmental synchronization (light level & duration) oscillator 54 Change in behavior: Territoriality Aggression Mating Parental care Change in hormone levels

55 Counting mechanisms Artificial day length manipulation can change when a mouse loses its tendency for infanticide. Is the control (1) the number of light/dark cycles post copulation, or (1) the real amount of time that has passed? 55

56 Day length manipulations: make 22, 24, or 27 hour days. Infanticide stops on day 22 for slow days and day 22 for fast days counting Infanticide stops here for long days 56

57 Interpretation of previous slide: Probably a stable chemical is produced, one burst per day/night cycle. The rate of accumulation corresponds to the # d/ n cycles, not on the absolute amount of time that has passed (next slide). 57

58 The behavior match is with number of light/dark cycles since mating, not the real days since mating. Match with hours: NOT Match with #cycles: YES 58

59 REPRODUCTIVE BEHAVIOR AND HORMONES IN RED-SIDED GARTER SNAKE At the beginning of the mating season, Red-Sided Garter Snakes have a low level of hormones as well as the smallest size of gonads. The cue for the beginning of the mating season is the increase in temperature when they come out of their dens. Also, female garter snakes have small ovaries at the beginning of the mating season. The gametogenesis in garter snakes begins at the end of the mating season. In males the testicles grow during six weeks after mating season when they reach their largest size. The sperm is stored in the vas deferens for mating during the following spring. When they enter their dens in the fall their testicles have regressed. Their testicles do not grow until the end of the next mating season. If the male garter snake does not use the stored sperm for the next mating season then the stored sperm will disintegrate. In the female garter snake mating induces the follicles to grow and to fill with yolk. Females store sperm in the oviduct while the follicles mature during a six to eight week period. At the beginning of the next mating season the female garter snake will expulse the stored sperm in her oviduct that is not used. Other studies have described the relationship of hormones and hibernation in the Red-Sided Garter Snakes. Still other studies have tried to explain the relationship of the gonads, adrenal gland, pituitary gland, and other hormones that may be involved with mating behavior when the snakes emerge from their dens in the spring. Postmating gametogenesis is an advantage for Red-Sided garter snakes. Also, in Mexico garter snakes do not hibernate and they have several mating seasons, unlike Canada garter snakes.

60 P M M V M P P There is genetic control over monogamy a complex behavioral trait! Yellow circle: mostly monogamous, (except 2 Microtus species recently polygynous). P M Likely ancient split: Monogamy behavior arises

61 Is the new monogamy behavior adaptive? Would it win? We can imagine a scenario in which the new behavior becomes established. (next slide)

62 Evolutionary or adaptive reason keeping genes in population Guarding females = guarding pups from other males*. Males fight back [new gene arises??!!] by guarding females, so parentage is certain. Females become promiscuous so males can never be sure which pups carry their genes. Kill pups you believe are not your own; potentially allows mating with female who enters estrous sooner. *You have less chance to mate with many females, but higher chance that all of your offspring survive. Fitness must be higher for parental care than promiscuity!

63 So the gene we are looking for causes males to hang with females more, compared with the ancestral type behavior

64 Insertion of the V1aR Gene in the Prairie Vole The V1aR gene is inserted using an adeno-associated viral vector. A modified V1aR gene is used from a genomic library. The gene is spliced at the neuron-specific enolase promoter to create a NSE-pvV1aR viral vector. The viral vector is inserted into the ventral pallidum of anesthetized prairie voles. Transduction occurs and the NSE promoter works to restrict expression of the gene to neurons in the brain.

65 Adeno-associated viral vectors contained either: 1. Prairie vole VIaR gene a. Including a neuron-specific enolase promoter 2. Prairie vole VIaR gene and Escherichia coli lacz a. Including a cytomegalovirus promoter Properties of Adeno-associated viruses: 1. Contain a single strand of DNA 2. Infect non-dividing cells 3. Non-pathogenic 4. Site specific insertion of genetic material The Adeno-associated viral vectors were injected into specific sites; the ventral pallium or the caudate putamen, of the Prairie vole s brains using a syringe. Reference: Lim, M.M., Wang, Z., Olazábal, D.E., Ren, X., Terwilliger, E.F., and Young, L. J. Enhanced partner preference in a promiscuous species by manipulating the expression of a single gene. Nature. 429, (2004).

66 A cross-section of a vole brain cross and sagittal sections

67 Mechanistic reasons for behavior can be tested Experimental manipulation: add hormone receptors to the vole brain. How do you do that? Use adeno-associated viral vector with prairie vole V1aR gene. Use micro-syringe to inject solution of the single-strand DNA vectors into a particular region of the brain (pallium or caudate putamen). Genes insert in host neuron DNA, and so that neuron overexpresses the gene product: the hormone receptor. Presence of hormone in vole causes more than normal activity from the neuron, which over-activates other neural circuits.

68 The ventral pallium in particular is concerned not just with reward, but reward in the context of a familiar partner. Why is not known. Result with monogamous vole Induction of more hormone receptors leads to more cuddling with a familiar vole.