Reproductive suppression
[2] It includes delayed sexual maturation (puberty) or inhibition of sexual receptivity, facultatively increased interbirth interval through delayed or inhibited ovulation or spontaneous or induced abortion, abandonment of immature and dependent offspring, mate guarding, selective destruction and worker policing of eggs in some eusocial insects or cooperatively breeding birds, and infanticide of the offspring of subordinate females either by directly killing by dominant females or males in mammals or indirectly through the withholding of assistance with infant care in marmosets and some carnivores.
Therefore, neuroendocrine cues for assessing reproductive success should evolve to be reliable at early stages in the ovulatory cycle.
[4] Reproductive suppression occurs in its most extreme form in eusocial insects such as termites, paper wasps and honeybees, and in a mammal, the naked mole rat, which depend on a complex division of labor within the group for survival and in which specific genes, epigenetics and other factors determine whether individuals will permanently be unable to breed or able to reach reproductive maturity under particular social conditions.
[9][10][11][12] In eusocial and cooperatively breeding animals, most non-reproducing helpers engage in kin selection, enhancing their own inclusive fitness by ensuring the survival of offspring they are closely related to.
Female mammals experience delays in the onset of puberty or increase their interbirth intervals in response to environmental conditions that are associated with low abundance and poor quality of foods.
Female attackers are often in advanced stages of pregnancy and have the most to lose if the number of infants in the group reaches an unsustainable level.
A similar study of Chacma baboons (Papio ursinus) noted high levels of female-female aggression around the mating season when the number of ovulating females was high (indicated by sexual swellings) and that aggression directed toward suppressing the mating opportunities of ovulating females.
[11][18][19][20] In response to stress the HPA axis (hypothalamic-pituitary-adrenocortical axis) is activated, producing high concentrations of circulating adrenal glucocorticoids which, when chronically present, negatively influence an animal's health and can lead to reproductive suppression in male marmots (Marmota marmota), and blocks of ovulatory cycles of female talapoin monkeys (Miopithecus talapoin), meerkats (Suricata suricatta) and marmots.
[11] Evicted subordinates suffer repeated attacks during the later stages of the breeding female's pregnancy and showed glucocorticoid levels twice normal.
[11] However, reproductive suppression through stress does not apply to many species including orangutans for which subordinate males have lower GC levels than dominant ones,[21] marmosets for which nonbreeding subordinate females were not found to have higher GC levels than dominant breeding females,[22] social carnivores and other animals.
[9] Yellow, banded and dwarf mongooses live in families similar to wolf packs with scent marking done almost exclusively by the dominant pair.
When the subordinate females leave the parental pack they will become fully reproductively active in new groups they help establish.
[29] Game theory suggests that subordinates suppress their own reproduction to avoid the social cost imposed on them if they reproduce, including expulsion from the group and infanticide against their progeny by dominant breeding individuals.
[24] Forced dispersal from the group may be extremely dangerous, involving high levels of predation and difficulty finding food and sleeping sites.
When group members are closely related, independent breeding opportunities are poor, and detection of mating and pregnancy is high, subordinates choose to suppress their own reproduction.
When they are introduced into a new group, female marmosets are immediately subordinate, experience a drop in chrorionic gonadotrophin (CG) and within the first four days and stops ovulating.
However, continued exposure to the dominant female may represent a social, rather than biological, cue that causes the subordinates to shut down their ovulation.
[5] In the Cape honeybee social parasites that are of the worker caste enter the colony and kill the resident queen, activate their own ovaries and parthenogenetically produce diploid female offspring (thelytoky) – behaviors linked to a single locus on chromosome 13.
The parasites produced queen-like pheromones falsely signally the presence of a queen suppressing the reproduction of worker's native to the colony and policing or destroying these eggs.
[5] Alternative slicing of a gene homologous to the gemini transcription factor of Drosophila controls worker sterility.
[5] As for many eusocial insects, termite workers are totipotent and rarely produce offspring although they are capable of reproduction when the breeding pair dies.
[8] In Cape honey bees (Apis mellifera capensis), the multiple mating of the queen and existence of half-siblings creates sub-families within the colony.
[34][35] Social stress and resource limitation can lead to high rates of spontaneous abortion as a mechanism of reproductive suppression.
