Lordosis behavior

Lordosis behavior, also known as mammalian lordosis (Greek lordōsis, from lordos "bent backward"[1]) or presenting, is the naturally occurring body posture for sexual receptivity to copulation present in most mammals including rodents, elephants, and cats. The primary characteristics of the behavior are a lowering of the forelimbs but with the rear limbs extended and hips raised, ventral arching of the spine and a raising, or sideward displacement, of the tail. During lordosis, the spine curves dorsoventrally so that its apex points towards the abdomen.

This article is about the animal sexual posture. For the human spinal shape and disorders thereof, see Lordosis.

Lordosis behavior by a female cat during copulation

Lordosis in hamsters

Description

Lordosis is a reflex action that causes many non-primate female mammals to adopt a body position that is often crucial to reproductive behavior. The posture moves the pelvic tilt in an anterior direction, with the posterior pelvis rising up, the bottom angling backward and the front angling downward. Lordosis aids in copulation as it elevates the hips, thereby facilitating penetration by the penis. It is commonly seen in female mammals during estrus (being "in heat"). Lordosis occurs during copulation itself and in some species, like the cat, during pre-copulatory behavior.

Neurobiology

Lordosis is particularly marked among felines.

Lordosis in lions

The lordosis reflex arc is hardwired in the spinal cord, at the level of the lumbar and sacral vertebrae (L1, L2, L5, L6 and S1).[2] In the brain, several regions modulate the lordosis reflex. The vestibular nuclei and the cerebellum, via the vestibular tract, send information which makes it possible to coordinate the lordosis reflex with postural balance. More importantly, the ventromedial hypothalamus sends projections that inhibit the reflex at the spinal level, so it is not activated at all times.[3] Sex hormones control reproduction and coordinate sexual activity with the physiological state. Schematically, at the breeding season, and when an ovum is available, hormones (especially estrogen) simultaneously induce ovulation and estrus (heat). Under the action of estrogen in the hypothalamus, the lordosis reflex is uninhibited.[4] The female is ready for copulation and fertilization.

When a male mammal mounts the female, tactile stimuli on the flanks, the perineum and the rump of the female are transmitted via the sensory nerves in the spinal cord. In the spinal cord and lower brainstem, they are integrated with the information coming from the brain, and then, in general, a nerve impulse is transmitted to the muscles via the motor nerves. The contraction of the longissimus and transverso-spinalis muscles causes the ventral arching of the vertebral column.[2]

Hormonal and cerebral regulation of lordosis

Sexual behaviour is optimized for reproduction, and the hypothalamus is the key brain area which regulates and coordinates the physiological and behavioural aspects of reproduction.[5] Most of the time, the ventromedial nucleus of the hypothalamus (VMN) inhibits lordosis. But when environmental conditions are favorable and the female is in estrus, the estrogen hormone, estradiol, induces sexual receptivity by the neurons in the ventromedial nucleus,[6] the periaqueductal gray, and other areas of the brain. The ventromedial hypothalamus sends impulses down axons synapsing with neurons in the periaqueductal gray. These convey an impulse to neurons in the medullary reticular formation which project down the reticulospinal tract and synapse with the neurobiological circuits of the lordosis reflex in the spinal cord (L1–L6). These neurobiological processes induced by estradiol enable the tactile stimuli to trigger lordosis.

The mechanisms of regulation of this estrogen-dependent lordosis reflex have been identified through different types of experiments. When the VMN is lesioned lordosis is abolished; this suggests the importance of this cerebral structure in the regulation of lordosis. Concerning hormones, displays of lordosis can be affected by avariectomy, injections of estradiol benzoate and progesterone,[7] or exposure to stress during puberty.[8][9] Specifically, stress can suppress the hypothalamic-pituitary-gonadal (HPG) axis and therefore decrease concentrations of gonadal hormones. Consequently, these reductions in exposure to gonadal hormones around puberty can result in decreases in sexual behavior in adulthood, including displays of lordosis.[8]

In humans

Lordosis behavior is non-functional in humans, although lordosis-like positions can be observed in women being mounted from behind.[10]

In a 2017 study, using 3D models and eye-tracking technology it is shown that the slight thrusting out of a woman's hips influences how attractive others perceive her to be and captures the gaze of both men and women.[11] The authors argue "while reflexive lordosis posture is not exhibited by human females and receptivity is not passive or obligatory for them, a manifestation of lumbar curvature might serve as a vestigial remnant of proceptivity-/receptivity-communicative signal between men and women".[12] Previously, anthropologist Helen Fisher also speculated that when a human female wears high-heeled footwear the buttocks thrusts out and the back arches into a pose that simulates lordosis behavior, which is why high heels are considered "sexy".[13]

See also

• Ethogram
• Pelvic thrust

References

1. "lordosis". The American Heritage Dictionary. Archived from the original on January 4, 2017. Retrieved January 3, 2017.
2. Pfaff D. W. , Schwartz-Giblin S., Maccarthy M. M., Kow L-M (1994). "Cellular and molecular mechanisms of female reproductive behaviors", in Knobil E., Neill J. D. The physiology of reproduction, Raven Press, 2nd edition.
3. Kow L.M., Florea C., Schwanzel-Fukuda M., Devidze N., Kami K.H., Lee A., Zhou J., Maclaughlin D., Donahoe P., Pfaff D. (2007). "Development of a sexually differentiated behavior [lordosis] and its underlying CNS arousal functions". Curr. Top. Dev. Biol. Current Topics in Developmental Biology. 79: 37–59. doi:10.1016/S0070-2153(06)79002-0. ISBN 9780123739131. PMID 17498546.CS1 maint: multiple names: authors list (link)
4. Flanagan-Cato L.M. (2011). "Sex differences in the neural circuit that mediates female sexual receptivity". Frontiers in Neuroendocrinology. 32 (2): 124–136. doi:10.1016/j.yfrne.2011.02.008. PMC 3085563. PMID 21338620.
5. Plant T., Zeleznik A. (Eds). Knobil and Neill's Physiology of Reproduction. Academic Press, 4th edition, 2015
6. Kow LM, Pfaff DW (May 1998). "Mapping of neural and signal transduction pathways for lordosis in the search for estrogen actions on the central nervous system". Behav. Brain Res. 92 (2): 169–180. doi:10.1016/S0166-4328(97)00189-7. PMID 9638959.
7. Olster, D.H.; Blaustein, J.D. (1989). "Development of steroid-induced lordosis in female guinea pigs: effects of different estradiol and progesterone treatments, clonidine, and early weaning". Hormones and Behavior. 23 (1): 118–129. doi:10.1016/0018-506x(89)90079-2. PMID 2538389.
8. Jasmina Kercmar; Stuart Tobet; Gregor Majdic (2014). "Social Isolation during Puberty Affects Female Sexual Behavior in Mice". Frontiers in Behavioral Neuroscience. 8: 337. doi:10.3389/fnbeh.2014.00337. PMC 4179611. PMID 25324747.
9. D. Daniels; LM. Flanagan-Cato (2000). "Social Isolation during Puberty Affects Female Sexual Behavior in Mice". Journal of Neurobiology. 45 (1): 1–13. doi:10.1002/1097-4695(200010)45:1<1::AID-NEU1>3.0.CO;2-W. PMID 10992252.
10. Pfaus, J. G.; Flanagan-Cato, L. M.; Blaustein, J. D. "Female sexual behavior". in Plant T., Zeleznik A. (Eds). Knobil and Neill's Physiology of Reproduction. Academic Press, 4th edition, 2015
11. Elizabeth Hawkins (October 25, 2017). "Why arched backs are attractive". springer.com.
12. Pazhoohi, F.; Doyle, J.F.; Macedo, A.F.; Arantes, J. (2017). "Arching the Back (Lumbar Curvature) as a Female Sexual Proceptivity Signal: an Eye-Tracking Study". Evolutionary Psychological Science. 4 (2): 1–8. doi:10.1007/s40806-017-0123-7.
13. Laura T. Coffey (Sep 23, 2009). "Do high heels empower or oppress women?". TODAY msnbc.com. Archived from the original on September 26, 2009.