Reproductive success

Last updated April 08, 2024

Reproductive success is an individual's production of offspring per breeding event or lifetime.^[1] This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves.

Reproductive success is different from fitness in that individual success is not necessarily a determinant for adaptive strength of a genotype since the effects of chance and the environment have no influence on those specific genes.^[1] Reproductive success turns into a part of fitness when the offspring are actually recruited into the breeding population. If offspring quantity is not correlated with quality this holds up, but if not then reproductive success must be adjusted by traits that predict juvenile survival in order to be measured effectively.^[1]

Quality and quantity is about finding the right balance between reproduction and maintenance. The disposable soma theory of aging tells us that a longer lifespan will come at the cost of reproduction and thus longevity is not always correlated with high fecundity.^[2]^[3]

Parental investment is a key factor in reproductive success since taking better care to offspring is what often will give them a fitness advantage later in life.^[4] This includes mate choice and sexual selection as an important factor in reproductive success, which is another reason why reproductive success is different from fitness as individual choices and outcomes are more important than genetic differences.^[5] As reproductive success is measured over generations, longitudinal studies are the preferred study type as they follow a population or an individual over a longer period of time in order to monitor the progression of the individual(s). These long term studies are preferable since they negate the effects of the variation in a single year or breeding season.

Nutritional contribution

Nutrition is one of the factors that influences reproductive success. For example, different amounts of consumption and more specifically carbohydrate to protein ratios. In some cases, the amounts or ratios of intake are more influential during certain stages of the lifespan. For example, in the Mexican fruit fly, male protein intake is critical only at eclosion. Intake at this time provides longer lasting reproductive ability. After this developmental stage, protein intake will have no effect and is not necessary for reproductive success.^[6] In addition, Ceratitis capitata males were experimented on to see how protein influence during the larval stage affects mating success. Males were fed either a high protein diet, which consisted of 6.5g/100mL, or a no protein diet during the larval stage. Males that were fed protein had more copulations than those that were not fed protein, which ultimately correlates with a higher mating success.^[7] Protein-deprived black blow fly males have been seen to exhibit lower numbers of oriented mounts and inseminate fewer females than more lively fed males.^[8] In still other instances, prey deprivation or an inadequate diet has been shown to lead to a partial or complete halt in male mating activity.^[9] Copulation time lasted longer for sugar-fed males than protein-fed flies, showing that carbohydrates were more necessary for a longer copulation duration.^[10]

In mammals, amounts of protein, carbohydrates, and fats are seen to influence reproductive success. This was evaluated among 28 female black bears evaluated by measuring the number of cubs born. Using different foods during the fall including corn, herbaceous, red oak, beech, and cherry, nutritional facts of protein, carbohydrate, and fat were noted, as each varied in percent compositions. Seventy-percent of the bears who had high fat and high carbohydrate diets produced cubs. Conversely, all 10 females who had low carbohydrate diets did not reproduce cubs, deeming carbohydrates a critical factor for reproductive success where fat was not a hindrance.^[11]

Adequate nutrition at pre-mating time periods showed to have the most effect on various reproductive processes in mammals. Increased nutrition, in general, during this time was most beneficial for oocyte and embryo development. As a result, offspring number and viability was also improved. Thus, proper nutrition timing during the pre-mating time is key for development and long-term benefit of the offspring.^[12] Two different diets were fed to Florida scrub-jays and breeding performance was noted to have different effects. One diet consisted of high protein and high fat, and the other consisting of just high fat. The significant result was that the birds with the high protein and high fat diet laid heavier eggs than the birds with the rich-in-fat diet. There was a difference in the amount of water inside the eggs, which accounted for the different weights. It is hypothesized that the added water resulting from the adequate protein-rich and fat-rich diet may contribute to development and survival of the chick, therefore aiding reproductive success.^[13]

Dietary intake also improves egg production, which can also be considered to help create viable offspring. Post-mating changes are seen in organisms in response to necessary conditions for development. This is depicted in the two-spotted cricket where feeding was tested for in females. It was found that mated females exhibited more overall consumption than unmated. Observations of female crickets showed that after laying their eggs, their protein intake increased towards the end of the second day. The female crickets therefore require a larger consumption of protein to nourish the development of subsequent eggs and even mating. More specifically, using geometrical framework analysis, mated females fed off of a more protein rich diet after mating. Unmated and mated female crickets were found to prefer a 2:1 and 3.5:1 protein to carbohydrate, respectively.^[14] In the Japanese quail, the influence of diet quality on egg production was studied. The diet quality differed in the percent composition of protein, with the high-protein diet having 20%, and the low-protein diet having 12%. It was found that both the number of eggs produced and the size of the eggs were greater in the high-protein diet than the low. What was found unaffected, however, was the maternal antibody transmission. Thus, immune response was not affected since there was still a source of protein, although low. This means that the bird is able to compensate for the lack of protein in the diet by protein reserves, for example.^[15]

Higher concentrations of protein in diet have also positively correlated with gamete production across various animals. The formation of oothecae in brown-banded cockroaches based on protein intake was tested. A protein intake of 5% deemed too low as it delayed mating and an extreme of 65% protein directly killed the cockroach. Oothecae production for the female as was more optimal at a 25% protein diet.^[16]

Although there is a trend of protein and carbohydrates being essential for various reproductive functions including copulation success, egg development, and egg production, the ratio and amounts of each are not fixed. These values vary across a span of animals, from insects to mammals. For example, many insects may need a diet consisting of both protein and carbohydrates with a slightly higher protein ratio for reproductive success. On the other hand, a mammal like a black bear would need a higher amount of carbohydrates and fats, but not necessarily protein. Different types of animals have different necessities based on their make-up. One cannot generalize as the results may vary across different types of animals, and even more across different species.

Cooperative breeding

Evolutionarily, humans are socially well adapted to their environment and coexist with one another in a way that benefits the entire species. Cooperative breeding, the ability for humans to invest in and help raise others' offspring, is an example of some of their unique characteristics that sets them apart from other non-human primates even though some practice this system at a low frequency.^[17] One of the reasons why humans require significantly more non-parental investment in comparison to other species is because they are still dependent on adults to take care of them throughout most of their juvenile period.^[17] Cooperative breeding can be expressed through economic support that requires humans to financially invest in someone else's offspring or through social support, which may require active energy investment and time.^[17] This parenting system eventually aids people in increasing their survival rate and reproductive success as a whole.^[17] Hamilton's rule and kin selection are used to explain why this altruistic behavior has been naturally selected and what non-parents gain by investing in offspring that is not their own.^[17] Hamilton's rule states that rb > c where r= relatedness, b= benefit to recipient, c= cost of the helper.^[17] This formula describes the relationship that has to occur among the three variables for kin selection take place. If the relative genetic relatedness of the helper with the offspring is closer and their benefit is greater than the cost of the helper, then kin selection will be most likely be favored.^[17] Even though kin selection does not benefit individuals who invest in relatives' offspring, it still highly increases the reproduction success of a population by ensuring genes are being passed down to the next generation.^[17]

Humans

Some research has suggested that historically, women have had a far higher reproductive success rate than men. Dr. Baumeister has suggested that the modern human has twice as many female ancestors as male ancestors. ^[18]^[19]^[20]^[21]

Males and females should be considered separately in reproduction success for their different limitations in producing the maximum amount of offspring. Females have limitations such as gestation time (typically 9 months), then followed by lactation which suppresses ovulation and her chances of becoming pregnant again quickly.^[22] In addition, a female's ultimate reproductive success is limited due to ability to distribute her time and energy towards reproducing. Peter T. Ellison states, "The metabolic task of converting energy from the environment into viable offspring falls to the female, and the rate at which she can produce offspring is limited by the rate at which she can direct metabolic energy to the task"^[22] The reasoning for the transfer of energy from one category to another takes away from each individual category overall. For example, if a female has not reached menarche yet, she will only need to be focusing her energy into growth and maintenance because she cannot yet place energy towards reproducing. However, once a female is ready to begin putting forth energy into reproduction she will then have less energy to put towards overall growth and maintenance.

Females have a constraint on the amount of energy they will need to put forth into reproduction. Since females go through gestation they have a set obligation for energy output into reproduction. Males, however, do no have this constraint and therefore could potentially put forth more offspring as their commitment of energy into reproduction is less than a females. All things considered, men and women are constrained for different reasons and the number of offspring they can produce. Males contrastingly are not constrained by the time and energy of gestation or lactation. Females are reliant on the genetic quality of their mate as well. This refers to sperm quality of the male and the compatibility of the sperms antigens with the females immune system.^[22] If the Humans in general, consider phenotypic traits that present their health and body symmetry. The pattern of constraints on female reproduction is consistent with human life-history and across all populations.

A difficulty in studying human reproductive success is its high variability.^[23] Every person, male or female, is different, especially when it comes to reproductive success and also fertility. Reproductive success is determined not only by behavior (choices), but also physiological variables that cannot be controlled.^[23]

In human males of advanced age (≥40 years), infertility is associated with a high prevalence of sperm DNA damage as measured by DNA fragmentation.^[24] DNA fragmentation was also found to be inversely correlated with sperm motility.^[24] These factors likely contribute to reduced reproductive success by males of advanced age.

The Blurnton-Jones 'backload model' "tested a hypothesis that the length of the birth intervals of !Kung hunter-gatherers allowed women to balance optimally the energetic demands of child bearing and foraging in a society where women had to carry small children and foraged substantial distances".^[23] Behind this hypothesis is the fact that spacing birth intervals allowed for a better chance of child survival and that ultimately promoted evolutionary fitness.^[23] This hypothesis goes along with the evolutionary trend of having three areas to divide up one's individual energy: growth, maintenance, and reproduction. This hypothesis is good for gaining an understanding of "individual-level variation in fertility in small-scale, high fertility, societies( sometimes referred to by demographers as 'natural-fertility' populations".^[23] Reproduction success is hard to study as there are many different variables, and a lot of the concept is subject to each condition and environment.

Natural selection and evolution

To supplement a complete understanding of reproductive success or biological fitness it is necessary to understand the theory of natural selection. Darwin's theory of natural selection explains how the change of genetic variation over time within a species allows some individuals to be better suited to their environmental pressures, finding suitable mates, and/or finding food sources than others. Over time those same individuals pass on their genetic makeup onto their offspring and therefore the frequency of this advantageous trait or gene increases within that population.

The same may be true for the opposite as well. If an individual is born with a genetic makeup that makes them less suited for their environment, they may have less of a chance of surviving and passing on their genes and therefore may see these disadvantageous traits decrease in frequency.^[25] This is one example of how reproductive success as well as biological fitness is a main component of the theory of Natural Selection and Evolution.

Evolutionary trade-offs

Throughout evolutionary history, often an advantageous trait or gene will continue to increase in frequency within a population only due to a loss or decrease in functionality of another trait. This is known as an evolutionary trade-off, and is related to the concept of pleiotropy, where changes to a single gene have multiple effects. From Oxford Academic, "The resulting 'evolutionary tradeoffs' reflect necessary compromises among the functions of multiple traits".^[26] Due to a variety of limitations like energy availability, resource allocation during biological development or growth, or limitations of the genetic makeup itself means that there is a balance between traits. The increase in effectiveness in one trait may lead to a decrease in effectiveness of other traits as result.

This is important to understand because if certain individuals within a population have a certain trait that raises their reproductive fitness, this trait may have developed at the expense of others. Changes in genetic makeup through natural selection is not necessarily changes that are either just beneficial or deleterious but are changes that may be both. For example, an evolutionary change over time that results in higher reproductive success at younger ages might ultimately result in a decrease in life expectancy for those with that particular trait.^[27]

Related Research Articles

<span class="mw-page-title-main">Sexual selection</span> Mode of natural selection involving the choosing of and competition for mates

Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. These two forms of selection mean that some individuals have greater reproductive success than others within a population, for example because they are more attractive or prefer more attractive partners to produce offspring. Successful males benefit from frequent mating and monopolizing access to one or more fertile females. Females can maximise the return on the energy they invest in reproduction by selecting and mating with the best males.

Mealworms are the larval form of the yellow mealworm beetle, Tenebrio molitor, a species of darkling beetle. Like all holometabolic insects, they go through four life stages: egg, larva, pupa, and adult. Larvae typically measure about 2.5 centimetres (0.98 in) or more, whereas adults are generally 1.25 to 1.8 centimetres in length.

Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.

Parental investment, in evolutionary biology and evolutionary psychology, is any parental expenditure that benefits offspring. Parental investment may be performed by both males and females, females alone or males alone. Care can be provided at any stage of the offspring's life, from pre-natal to post-natal.

Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives from the Greek roots philo, "liking, loving" and patra, "fatherland", although in recent years the term has been applied to more than just the animal's birthplace. Recent usage refers to animals returning to the same area to breed despite not being born there, and migratory species that demonstrate site fidelity: reusing stopovers, staging points, and wintering grounds.

Life history theory (LHT) is an analytical framework designed to study the diversity of life history strategies used by different organisms throughout the world, as well as the causes and results of the variation in their life cycles. It is a theory of biological evolution that seeks to explain aspects of organisms' anatomy and behavior by reference to the way that their life histories—including their reproductive development and behaviors, post-reproductive behaviors, and lifespan —have been shaped by natural selection. A life history strategy is the "age- and stage-specific patterns" and timing of events that make up an organism's life, such as birth, weaning, maturation, death, etc. These events, notably juvenile development, age of sexual maturity, first reproduction, number of offspring and level of parental investment, senescence and death, depend on the physical and ecological environment of the organism.

Monogamous pairing in animals refers to the natural history of mating systems in which species pair bond to raise offspring. This is associated, usually implicitly, with sexual monogamy.

Cooperative breeding is a social system characterized by alloparental care: offspring receive care not only from their parents, but also from additional group members, often called helpers. Cooperative breeding encompasses a wide variety of group structures, from a breeding pair with helpers that are offspring from a previous season, to groups with multiple breeding males and females (polygynandry) and helpers that are the adult offspring of some but not all of the breeders in the group, to groups in which helpers sometimes achieve co-breeding status by producing their own offspring as part of the group's brood. Cooperative breeding occurs across taxonomic groups including birds, mammals, fish, and insects.

<span class="mw-page-title-main">Sexual conflict</span> Term in evolutionary biology

Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females, due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.

<span class="mw-page-title-main">Mate choice</span> One of the primary mechanisms under which evolution can occur

Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior. In other words, before an animal engages with a potential mate, they first evaluate various aspects of that mate which are indicative of quality—such as the resources or phenotypes they have—and evaluate whether or not those particular trait(s) are somehow beneficial to them. The evaluation will then incur a response of some sort.

The sexy son hypothesis in evolutionary biology and sexual selection, proposed by Patrick J. Weatherhead and Raleigh J. Robertson of Queen's University in Kingston, Ontario in 1979, states that a female's ideal mate choice among potential mates is one whose genes will produce males with the best chance of reproductive success. This implies that other benefits the father can offer the mother or offspring are less relevant than they may appear, including his capacity as a parental caregiver, territory and any nuptial gifts. Fisher's principle means that the sex ratio is always near 1:1 between males and females, yet what matters most are her "sexy sons'" future breeding successes, more likely if they have a promiscuous father, in creating large numbers of offspring carrying copies of her genes. This sexual selection hypothesis has been researched in species such as the European pied flycatcher.

Female sperm storage is a biological process and often a type of sexual selection in which sperm cells transferred to a female during mating are temporarily retained within a specific part of the reproductive tract before the oocyte, or egg, is fertilized. This process takes place in some species of animals, but not in humans. The site of storage is variable among different animal taxa and ranges from structures that appear to function solely for sperm retention, such as insect spermatheca and bird sperm storage tubules, to more general regions of the reproductive tract enriched with receptors to which sperm associate before fertilization, such as the caudal portion of the cow oviduct containing sperm-associating annexins. Female sperm storage is an integral stage in the reproductive process for many animals with internal fertilization. It has several documented biological functions including:

Eusociality evolved repeatedly in different orders of animals, notably termites and the Hymenoptera. This 'true sociality' in animals, in which sterile individuals work to further the reproductive success of others, is found in termites, ambrosia beetles, gall-dwelling aphids, thrips, marine sponge-dwelling shrimp, naked mole-rats, and many genera in the insect order Hymenoptera. The fact that eusociality has evolved so often in the Hymenoptera, but remains rare throughout the rest of the animal kingdom, has made its evolution a topic of debate among evolutionary biologists. Eusocial organisms at first appear to behave in stark contrast with simple interpretations of Darwinian evolution: passing on one's genes to the next generation, or fitness, is a central idea in evolutionary biology.

A biological ornament is a characteristic of an animal that appears to serve a decorative function rather than a utilitarian function. Many are secondary sexual characteristics, and others appear on young birds during the period when they are dependent on being fed by their parents. Ornaments are used in displays to attract mates, which may lead to the evolutionary process known as sexual selection. An animal may shake, lengthen, or spread out its ornament in order to get the attention of the opposite sex, which will in turn choose the most attractive one with which to mate. Ornaments are most often observed in males, and choosing an extravagantly ornamented male benefits females as the genes that produce the ornament will be passed on to her offspring, increasing their own reproductive fitness. As Ronald Fisher noted, the male offspring will inherit the ornament while the female offspring will inherit the preference for said ornament, which can lead to a positive feedback loop known as a Fisherian runaway. These structures serve as cues to animal sexual behaviour, that is, they are sensory signals that affect mating responses. Therefore, ornamental traits are often selected by mate choice.

Interlocus sexual conflict is a type of sexual conflict that occurs through the interaction of a set of antagonistic alleles at two or more different loci, or the location of a gene on a chromosome, in males and females, resulting in the deviation of either or both sexes from the fitness optima for the traits. A co-evolutionary arms race is established between the sexes in which either sex evolves a set of antagonistic adaptations that is detrimental to the fitness of the other sex. The potential for reproductive success in one organism is strengthened while the fitness of the opposite sex is weakened. Interlocus sexual conflict can arise due to aspects of male–female interactions such as mating frequency, fertilization, relative parental effort, female remating behavior, and female reproductive rate.

The theoretical foundations of evolutionary psychology are the general and specific scientific theories that explain the ultimate origins of psychological traits in terms of evolution. These theories originated with Charles Darwin's work, including his speculations about the evolutionary origins of social instincts in humans. Modern evolutionary psychology, however, is possible only because of advances in evolutionary theory in the 20th century.

Filial cannibalism occurs when an adult individual of a species consumes all or part of the young of its own species or immediate offspring. Filial cannibalism occurs in many species ranging from mammals to insects, and is especially prevalent in various types of fish species with males that engage in egg guardianship. The exact evolutionary purpose of the practice in those species is unclear and debated among zoologists, though there is consensus that it may have, or may have had at some point in species' evolutionary history, certain evolutionary and ecological implications.

Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.

Human reproductive ecology is a subfield in evolutionary biology that is concerned with human reproductive processes and responses to ecological variables. It is based in the natural and social sciences, and is based on theory and models deriving from human and animal biology, evolutionary theory, and ecology. It is associated with fields such as evolutionary anthropology and seeks to explain human reproductive variation and adaptations. The theoretical orientation of reproductive ecology applies the theory of natural selection to reproductive behaviors, and has also been referred to as the evolutionary ecology of human reproduction.

Gnatocerus cornutus, the broadhorned flour beetle, is a common species of beetle in the Tenebrionidae family. It is distributed worldwide and is commonly found in warm, tropical regions. The total development time is about 47 days. G. cornutus is predominately found in mills as a storage pest and has a wide distribution.

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