Reproductive Behaviour - Part1

Overview of Reproductive Behavior

Reproductive behavior is a complex series of acts and interactions rather than a single event

• Territorial and Social Dominance Behavior: Many species engage in territorial displays to secure and defend their mating areas, which can involve aggressive encounters or the establishment of visual markers to deter rivals. Social hierarchies often dictate access to resources and mating opportunities based on dominance.

• Courtship Rituals: These intricate behaviors are designed to attract mates and facilitate successful mating. Courtship can include visual displays, vocalizations, or even complex dances that signify the health and genetic fitness of the individual.

• Copulation and Sexual Reproduction: This is the actual mating process, which may involve various techniques and rituals that vary significantly across species.

• Post-Copulatory Behaviors: After copulation, behaviors such as mate guarding or soliciting further copulation can occur, which may increase reproductive success.

• Parental Care and Feeding: Many species invest considerable effort into nurturing their offspring, which can influence the survival rates and future reproductive potential of the young.

Example - Bowerbirds

• Male satin bowerbird builds a courtship structure known as a bower. A bower is a vertical nest that is made out of twigs and flowers, and the male will decorate it with ornaments found in forested habitat (flowers and berries). They tend to have a preference for the color blue, so they seek for blue items in order to decorate their bower, and then try to seduce the females to mating with him.

  • It is not unusual for a female to reject a bower. The main evaluation of the males are the bowers.

  • The male has no contribution to the family life, his role is to build a bower and donate sperm. The entire courtship is based exclusively on the quality of the bower, as well as a few little elements of evaluating the male himself

  • The bowers are an indicator of the quality of the male because they are hard to build

    • Every time males go to the forest to find resources, other male bowers come back and break the bower or steal items. Having a good quality bower implies that the male is good quality.

    • It confers information about their intellectual abilities, because the relative brain size of bower building birds is significantly higher than the average for the birds of their group. Non bower building birds have significantly smaller brains

    • If able to maintain the bower, it implies the male is physiologically superior

    • There is a correlation with those who have higher cognitive ability are mating more if they have attractive bowers

  • The mate choices are highly asymmetrical. Most female birds will mate with only one male once they’ve chosen him. Almost none will mate with 3 or more.

    • Very important for the female to make the right choice because that’s the only male she’s going to mate with

    • Therefore only his genetics will be going towards her offspring

  • The attractive males end up having lots of mates

  • This mate choice scenario is highly specific and highly selective, meaning it is based on the criteria of being able to do a very complicated task, and females are looking for only genes

  • Females uses indices of the genes that can give her an honest refection of the quality of the genes of the males

  • When there is high competition between the sexes for access to each other, there sexual strategies that evolve to allow the sorting and the courtship process to aim for ultimate fitness benefits and the highest reproductive success payoff

Intersexual Selection

These two forms of sexual selection illustrate different strategies for reproductive success:

Intersexual Selection involves females being choosy, selecting males based on traits that signal their fitness, while males are more promiscuous.

• For this reason, males compete with one another for access to choosy females, and this leads to the evolution of ornaments and armaments that are hugely to produce

• Therefore can be seen as honest signals for the quality of the individuals are producing them (long feathers, elaborate plumage, sound generating mechanisms, pigmentation, and armature). All of these things are considered very costly ornaments because they are costly in terms of nutrients and development for production, that they have immunosuppression effects due to their relationship with testosterone

• They will have consequences on survivorship because it is very costly to carry these things around

• Honest reflection of the quality of the individuals because they are very hard to produce and hard to maintain

• Intersexual selection means that the selection is occurring between the sexes

Parental investments

• Other instances where the males will provide important material resources (food or protection, parental investment) can be an important consideration that contribute to the attractiveness

• When ones investment into reproduction increases, the animals choosiness increases because when investment increases the costs of losing that investment increase as well

• Example:

  • Male frog with tadpoles on his back protecting them from predators and keeping them oxygenated.

  • Wasps bringing in cicada back to a nest to feed their off spring.

  • Females receiving highly nutritious spermatophore from male, now competing to get access to the limited male resources

• Reproduction is more costly for females, that’s why they are more choosy. For males, sperm is cheap, and could export it to any potential fertile vessel to make more offspring

Sex Role Reversals

• In some cases, males contribute significantly to the reproductive process, and become more reserved (sex role reversals)

  • Example: Mormon Cricket (not a cricket). Female has been recently mated. Spermatophore is a package if sperm and nutrients that are donated from the male to the female that will benefit both of them by contributing important resources to the offspring and increasing reproductive success. In the male’s perspective, that is a very costly “gift” because that spermatophore can be up to 25% of his body weight (not a lot to go around), so he will be careful about which females he will give that spermatophore to. Females can become competitive looking to get these spermatophores. Spermatophores are important nutritional resources for her while the inside portion is engaging in the fertilizing her eggs

    • Guarantees his sperm will fertilize her eggs, until that plug is removed, she is not capable of mating with another male

Intrasexual Selection

Intrasexual Selection: within one sex where the selection occurs where there is a sorting process leading to a social hierarchy, which is established through fighting and through social interactions (typically by males, but can have sex role reversals)

Dominance and Mating Success

• Example: Deer’s locking antlers together to determine the alpha (subordinate trickle downs their reproductive rights). This is a form of natural selection sorting the best genes. This is a competition

• This dominance hierarchy leads to mating success

• Example: Savannah baboons have males fight aggressively amongst one another to establish who is the alpha and beta. Also leads to reproductive rights. Studies show individuals that are average level of dominance rank have better reproductive success, because they have better access to females, passing on their genes. Savannah baboons can only reproduce if they fight their way to the top of the alpha chain

• Evolution favors strategies that can get genes passed on into the next generation

Alternative mating strategies

• Example: Marine iguanas from the Galapagos islands where the dominant males will protect their territory in a harem of females, and will prevent any subordinates from being able to mate with his females. The controlling factor is that the copulation process. Marine iguanas involves at least a couple of minutes of engaged sexual activity before the males can ejaculate and therefore fertilize any eggs. This means that if a subordinate male tries to mount one of the females in alpha’s male harem, before he can ejaculate in the females, the alpha males comes along, removes him, and asserts that only he can reproduce. The subordinate individual evolved an alternate strategy, which is to pre ejaculate into his cloaca (includes urogenital chamber), so when he mounts onto the female, he can instantly transfer that sperm allowing successful reproduction, so even if dismounted, sperm was still transferred. Therefore these subordinate males have alternate strategies to pass on genes

Conditional Satellite Males

• Quality is not constant throughout one’s life. In some cases, the quality can start out high, then become low as one ages.

• Strategies can vary based on this relative quality, with high-quality males opting for "Plan A" (dominant strategy) and lower-quality males switching to "Plan B" (alternative strategy).

• This dynamic is seen in species with external fertilization, such as frogs in ponds or horseshoe crabs in intertidal zones.

• For horseshoe crabs, females often choose a primary male ("attached male") as the main sire for their offspring, but other males ("satellite males") may stay nearby during fertilization.

• Satellite males, unable or unwilling to compete as attached males due to lower quality or effort required, adopt a conditional alternative strategy to gain partial reproductive success.

• The decision to be an attached male (higher payoff) or a satellite male (lower payoff) depends on an individual male's condition and assessment of his chances.

• These two strategies result in varying payoffs based on male condition, with attached males being the primary fertilizing source and satellite males fertilizing some eggs opportunistically.

• Reproductive success is highest for the attached male, but only if he is in good condition.

• Males in poor condition are unlikely to become attached, leading to reduced reproductive success.

• For males in optimal condition, it is advantageous to compete for the attached male role, as it provides the highest payoff.

• When a male's condition drops below average, the benefit shifts to adopting the satellite male strategy.

• Satellite males avoid competing for the prime position and gain some reproductive success, which is better than none.

• This strategy is conditional, as a male's choice depends on his physical condition.

• A male in good condition benefits from striving for the prime role, while a male in poor condition finds it more feasible to adopt the satellite strategy.

• Although the satellite strategy yields less success than the prime role, it is a practical alternative when the prime position is unattainable.