(13) Social Influences on reprouction

Question 1

(1)

(I. Social Influences on Reproduction)

1. The biological aim of an individual is to ensure that their genetics are passed on to the next generation. Ideally, you also ensure that this next generation is given every opportunity to succeed both in terms of survival and in mating, so that your genes are passed on for generations to come. The best way to maximize the chance of this happening is to breed with the best available mate: hopefully the characteristics that made them successful will be passed on (you want to include their genetic superiority in your offspring). To this end there is competition for mating opportunities, which involves selection both within the members of a sex and between the sexes. This process is termed what?

Answer 1

1. sexual selection (intrasexual and intersexual respectively)

Question 2

(2)

1. How it is applied depends on the natural history, especially the mating strategy, of the species in question. There are a wide variety of mating systems with varying social interactions employed by animals. Classically they have been divided into systems such as what?

1 male and mult females = ?

1 female and mult males = ?

Others would be the division of polygynous species into whether the male defends a harem or whether males lek (defend a territory - he with the most desirable territory gets the most mating opportunities). A lot of these classical divisions are now realized to not be hard-and-fast; an example is extra-pair matings in allegedly monogamous species (the difference between social and genetic partner). Much of the observational and experimental work in this area has been performed in polygynous species.

Answer 2

1. monogamy and polygamy

polygyny

polyandry

Question 3

(3)

In most species the overall (population) sex ratio is approximately equal (male:female). However, the parental investment of the two sexes is generally unequal:

 Females usually have a far greater physical input into reproduction in terms of raising the next generation. They do the gestation, lactation and most (or all) of the offspring care. Females also produce relatively few gametes (eggs or oocytes) and require relatively few matings to ensure that these are fertilized. While females are engaged in much of their reproductive activity they are unavailable for mating (put another way: mating is a small component of their total reproductive effort).

 Males generally produce lots of gametes (sperm) and have little or no involvement in gestation, lactation and offspring rearing. Thus mating is a large part of their reproductive effort and they are capable of fertilizing more than a single female’s eggs.

As a result, males and females tend to have different priorities:

1. Female repro success limited by what?
2. male?

Answer 3

1. access to resources to develop eggs and raise offspring
2. limited by access to female eggs

Question 4

(4)

(Limiting and Competing Sexes: Choosy and Chosen)

1. While one sex (generally female) is engaged in gestation/lactation/offspring rearing they are not available for mating. The other sex is, so the population sex ratio of 1:1 is effectively altered to give the what?
2. Under these conditions there are relatively fewer of one sex available: the what?
3. his means that members of the other sex (♂) are competing for these limited opportunities to mate: the what?
4. In this situation available females can choose between multiple males (she gets to be the choosy sex) while males must hope to be chosen. The females have a good chance of passing their genes to the next generation, but if a male wants to then he needs to have some characteristic, physical or behavioral, that allows him to out-compete his rivals and convince the females he is worth mating with. Some of these characteristics are tabulated below.

Answer 4

1. operational sex ratio
2. limiting sex
3. competing sex

Question 5

(5)

1. what is the ability to produce young?
2. what is furitfulness, ability to produce many young?

Answer 5

1. fertility
2. fecundity

Question 6

(6)

(Why do females Choose?)

When assessing potential mates in a pool, a female is interested in a number of things:
 Get the best genetics for her offspring o offspring survival
 Disease resistance
 Ability to cope with environment o offspring breeding success
 “Sexy sons” - if a male has characteristics that are particularly attractive he will potentially pass these on to his sons and they will also be attractive and have lots of mating success. So by breeding with an attractive male the female increases the chances that her genes will be passed on.
 Best resources for raising offspring
 Ideally she would like to avoid exposing herself to disease during the mating process.
 Paternal assistance with offspring care

Question 7

(7)

When should the female not be choosy?

1. when?

Answer 7

1. when choosiness decreases fecunidty

For example if population density is extremely low and she needs to expend too much energy comparison shopping for the best mate.
Unless female choice increases the reproductive values of her offspring or directly benefits her, it will be replaced by random mating.

Question 8

(8)

(How are Males Chosen?)

There will obviously be some differences here based on the mating system of the species. However in general terms males advertise for mates.

Advertisements can be long or short-range and most are visual or auditory in nature. They include mostly secondary sex characteristics like ornamentation and song quality in birds. In species that lek, these characteristics are also used to defend the best territory and the resources within it serve to further attract females. So advertising signals are used not only for intersexual mate choice but also in intrasexual competitions between males (intrasexual selection).

Advertisements need to be costly to produce (ornamental feathers) or maintain (harem/territory defense) - this keeps the signal “honest”. If a great advertisement could be produced by low quality males then there would be no point the female using it as a selection criteria because it doesn’t honestly reflect the quality of the male - the best males need to have the best advertisements. Costly advertisements are a direct reflection of the quality (genetic, disease resistance) of the male. To circumvent cheating by males, females will often assess multiple cues (advertisements) in making their decision.

Question 9

(9)

Examples of Sensory Cues in Reproduction

(Visual)

Intersexual Selection (Mate selection)
Secondary sex characteristics, usually present in males, are designed to attract mates. In some they are taken to extreme degrees and represent quite a tax on the individual developing them. They advertise the general fitness of the male, his quality and freedom from disease, and the females can use them to comparison shop.

Intrasexual selection (Male competition)
Visual signals between males in establishing a dominance hierarchy for mating purposes
can avoid battles and potential injury. For example, red deer stags will trot parallel to each other, turn and trot back again and again while sizing each other up. In most cases one will give way after this display.

Question 10

(10)

Examples of Sensory Cues in Reproduction

(olfactory cues)

Pheromones
These are substances secreted by one individual that give specific physiologic reactions in other
individuals of the same species.

It used to be thought that all these signals were detected by the vomeronasal organ and processed
through this “accessory olfactory system” (AOS).

1. now known that many pheromonal signals are interpreted by what?

Sending a “notice”
Pheromones are used to unite males and females of species that may be separated for most of the year. In this regard they are secreted by the female to attract males.

Note that when females are using long-distance pheromones to signal heat, this is often termed a notice rather than an advertisement, because it is not considered costly for the female to produce. In fact it is a lot cheaper than having to move to find the male. Moving is expensive energetically, and especially if you have to leave familiar territory it carries increased risks of predation. By posting the pheromonal notice she allows the male to assume the costs associated with responding to it.

Answer 10

1. main olfactory system (MOS) and that the systems cooperate to influence behavior and physiology

The MOS is particularly useful at interpreting distant signals because the vomeronasal organ has to actually contact the pheromone source (e.g. urine).

Question 11

(11)

Examples of Sensory Cues in Reproduction

(olfactory cues - cont)

Intersexual Selection
Similar to visual cues, olfactory cues influence mate selection.

1. Both sexes may use pheromones in mate choice as a mechanism for avoidance of inbreeding. The scent of an individual is specific and represents the genetic constitution of the what?
2. It has been shown that within a species individuals will choose a mate with a different chemical signal in preference to one who is similar. This confers several potential advantages: what are they?

Olfactory cues can also be used to determine the health of potential mates. In several species females have shown the ability to differentiate diseased and healthy males based on scent alone, and they chose the healthy one.

Answer 11

1. the MHC (major histocompatibilty complex)
2. 1. Inbreeding avoidance and the associated loss of fitness that accompanies it.
3. MHC heterozygosity. If your mate is different in the MHC then by combining yours with theirs you give genetic variation to your offspring - they are likely to have resistance to a greater range of parasites and pathogens

Question 12

(12)

(Auditory Cues)

 Sending a “notice”
Auditory cues are used to reinforce olfactory cues when females are sending out a notice of their willingness to mate. Lionesses will vocalize to attract a distant male. Similar behavior can be seen in house cats.

 Intersexual Selection
Female songbirds use the quality of a male’s song to make mate selections. Subsequently, songs are used in pair bonding.

 Intrasexual Selection
The red deer stags mentioned in visual cues also use auditory cues to establish dominance by engaging in roaring contests.
Similarly, the songbirds engage in aggressive sing-offs to get the most desirable home range.

Question 13

(13)

“Named” Social Effects in Reproduction

The Whitten Effect

1. involves what?
2. In sheep and goat breeding this phenomenon is known as the what effect?

used to do what?

3. Introduction of a novel ram to ewes on the verge of cycling often results in the majority of ewes starting synchronized cycles immediately. Pheromones present where are responsible?

produced under the influence of what?

4. Females use both the MOS and AOS to detect the signals which are relayed through the amygdala to KNDy neurons in the arcuate nucleus. This increases firing rate of these neurons and thus the frequency of GnRH release.

Females (ewes and does) with well-developed follicles will experience an LH surge in 24 hours and ovulate by day 3 after male introduction (1st ovulation). Some of them might go on to have regular cycles after this but in many you get the following sequence:
The corpus luteum of this first cycle undergoes early luteolysis and she has a second ovulation 6-9 days after the males were introduced. On this second cycle the CL functions for a normal length of time and she has regular cycles hereafter.

Answer 13

1. introduction of novel male into a group of females

Females housed in groups often have suppressed cycles. The introduction of the male overcomes this suppression and the induced cycles are synchronized in a majority of the females.

2. ram or buck effect

hasten the entry of late anestrus ewes and does into the breeding season

3. in the neck fleece and secretions of the orbital (head) glands of the ram and buck

dihyrdotestosterone (DHT)

Question 14

(14)

“Named” Social Effects in Reproduction

The Whitten Effect

(what’s the physiology?)

1. The follicles present in late anestrus at the time of male introduction are of what quality?
2. After the male is introduced they respond to increased gonadotropins by secreting what?
3. Reduced function of the large luteal cells (from gluteal cells) means that what?
4. The wave of follicle growth occurring at this time increases what?
5. Reduced progesterone and increased estrogen increases the E:P ratio which results in premature onset of the what?

In ewes the first ovulation and often the second one is silent (no signs of estrus), whereas in does about 60% show estrous on the first male-induced ovulation and all show by the second. Why? Ewes need progesterone priming (prior exposure) to show the full signs of estrus, does do not. For ewes the short-lived lower-level exposure to progesterone from the first CL is also often not enough to prime them for the second cycle, so they have 2 silent heats (one at about day2-3 and the next at day 6-9) following ram introduction.

Answer 14

1. lower quality, (particularly in regard to their granulosa cell function)
2. enough estrogen to induce the LH surge and ovulate (but they result in a lower quality CL)
3. rogesterone secretion from these CLs is lower by day 4 post-ovulation than that of normal CLs
4. systematic estrogen levels
5. luteolytic mechanism (by day 5-6) and the CL is destroyed.

Question 15

(15)

The bruce effect

Seen in several rodent species and best described in the mouse, occurrence in other species less certain.

1. what is this?

(Explanation 1 - usual/traditional explanation)

2. what is it?

(Explanation 2 )

Testes of male mice secrete estrogens and these are higher in male mice exposed to females they don’t know and when agitated by the fact that these females won’t allow mating (because they are early pregnant). Estrogen is secreted in the male urine and absorbed into females via the vomeronasal organ. “Just right” levels of estrogen are vital for embryo implantation but too much estrogen makes the uterus non-receptive. The extra estrogen absorbed from the male urine makes levels too high and the pregnancy fails.

true? still don’t know

Answer 15

1. when expose an early pregnant female (prior to implantation, before day 4 in mouse) to a differentl male, her pregnancy will fail and she will return to estrus

The significance for the new male is that he gets to put his genes into the population more quickly

2. Basis is a pheromone in male urine, detected by the female which causes an increase in dopamine release from the hypothalamus resulting in suppression of prolactin secretion from the anterior pituitary. Since prolactin is a required luteotropin at this stage in mice the CL regresses and pregnancy fails.

Question 16

(16)

Lee-Boot Effect

Another one from mice.

1. Females housed in crowded groups have what?
2. how does it work?

Answer 16

1. extended estrous cycles by entering a period of pseudopregnancy/extended diestrus
2. An estrogen dependent pheromone in the urine (likely of dominant females) is received by the vomeronasal organ of other females where it increases prolactin levels, which are luteotrophic in mice – extending the cycle.

Question 17

(17)

Coolidge Effect

Noted first in male rodents where it is thought to be pheromonally mediated.

1. what is it?

Answer 17

1. Males mated to exhaustion or refusal with one female will recover libido when exposed to another female.

(Also seen in other species where it may not be entirely pheromonal (e.g. visual) and is also described in females on exposure to new males.)

Question 18

(18)

Illegitimate Receivers: The perils of signaling

Many of the signals used by animals as part of intrasexual competitions and intersexual selection are used by their predators and parasites as a means of locating prey and hosts. It doesn’t help that the victims tend to be more interested in sex than avoiding being eaten.

This is true for both visual signals - bird feather adornments, fish coloration and auditory signals - grass snakes and bats keying on calling frogs.

So sexual selection for these ornaments/songs/etc that increase the individual’s chance of mating is acting against natural selection which says you should only develop those characteristics which help the species survive. The characteristics maintain some kind of compromise between these two selection pressures.

Question 19

(19)

(What’s a wimpy male to do? - Interceptors, Impersonators and Sneaky Rutters)

Alternate mating strategies are employed by some males to avoid the dangers of intrasexual competition with rivals, or to circumvent their lack of success in regular competition.

Especially in lekking species, by having your territory near that of the dominant male (who has the best territory) you can intercept females that have been attracted to his resources as they pass through yours.

This is also a way of avoiding parasites and predators that are attracted by displays. Silent “satellite male” crickets wait around the territory of singing males. Parasitic flies are attracted to the singing males as are female crickets. The silent males avoid parasitism and intercept females on their way to the singing male.

Subordinate males in the social group of a very dominant male may have a chance to breed attracted females. This may be especially true of females attracted from neighboring groups who are seeking extra-pair matings. In some cases these attracted females seem to believe they are breeding with the dominant male, instead it’s an impersonator.

Immature or weaker males of some species can wait at the edge of a harem or lek in “no mans land” for the dominant male to be occupied (generally in defense of his realm against another rival) and then run in to breed and run away again.