The animal kingdom is extremely diverse consisting of a wide-range of anatomies and behaviours. In this article, we will explore the scientific reasons for some of the mind-blowing strategies developed by some species to court, reproduce and produce offspring. Some will leave you speechless!
By Ricardo Ribas
1. Males that get pregnant!!
Seahorses, pipefishes and seadragons have a very peculiar and different reproductive strategy, as they are the only fishes to undergo male pregnancy. Depending on the specie, the males have a pouch located in the abdomen or in the tail where the females deposit the eggs during mating. It is in the male’s pouch that the sperm fertilise the eggs and it is the male’s responsibility to carry and develop the fertilised eggs for a period between 9 and 45 days. The male pouch functions similarly to the mammal’s and human’s placenta, providing protection, the nutrients and the oxygen necessary for the fish development as well as the structure necessary to get rid of the waste products. By the end of the pregnancy, the males can deliver between 5 and 2000 young fish.
2. Sexual Cannibalism
Some animals use reproductive strategies resembling horror movies. Take as an example the family of black and venous spiders, commonly named as black widows as a result of the females’ gruesome behaviour of killing and eating the males after mating. Scientists believe this form of sexual cannibalism appear to provide the females with an extra source of proteins increasing their chance for reproductive success and offspring survival. Studies have also shown that females who practice this type of cannibalism produce larger eggs and healthier offspring with a better chance of survival, than the females that don’t eat the males. Understandably, some males prefer to court females that have already eaten, even if they are less fertile and fruitful. Scientists believe the males are able to tell how hungry the females are by the presence of pheromone smells in the silk of their cob webs.
There are other examples of sexual cannibalism in nature, such as is the case of the mantises, where females also kill and eat the males during mating. Whilst the purpose for their behaviour is still unknown, studies shown that females with poor diets are more likely to eat their partners, and that, similarly to spiders, it appears to provide them with extra nutrients necessary to improve the chances of reproductive success.
3. Transsexual animals
Other species have the astonishing capacity to change sex throughout lifetime. All clownfish are born male but they carry both male and female reproductive systems. Their school is composed by one female, often the larger animal in the group; a dominant breeding male, usually the second biggest in the group; and several immature males. When the female dies or disappears, the dominant males starts a process of sex change taking about 45 days to be complete, during which the male hormones are inhibited and the female hormones are activated. At the same, one of the immature males becomes the dominant male. Scientists believe this sex-change capacity allows the clownfish to remain in their habitat, circumventing the need to travel and risk their life to find females to mate. Wrasses use the same sex-change strategy as clownfish but in the opposite way. In this case, is the larger female of the group that changes sex and transforms into a male, taking the role of the previous dominant male of the harem upon his death or disappearance.
4. Inflated balloons to attract females’ attention
Male dromedary camels have a very strange and peculiar way to attract females. They hold an organ located in their throat that once inflated turns into a giant pink balloon (often confused with the tongue) that hangs and dangles from one of the sides of the male’s mouth to show their dominance and to attract females. This organ is called dulaa, what means “soft-palate” in Arabic. Male seals have a similar organ also used for sexual attraction and territorial fights, however, in their case, this large pinkish inflated balloon-like sac appears from the animal’s nostrils.
5. Animals with multiple genitals
Some animals own more than one genital. Female marsupials, such as kangaroos, koalas and Tasmanian devils own three vaginas and two uteri, whilst the males have two pronged penises. The two-sided vaginas are used to transport the sperm to their two uteruses, whilst the middle vagina is used for birth. This process allows the females to be constantly pregnant by carrying a baby in their pouch, a foetus developing in one utero and a fertilised egg waiting to be released in the second utero. Marsupials also have the capacity to store sperm for long periods and even delay birth until the pouch becomes free, a great strategy particularly during harsh times of drought and starvation. Due to these reproductive tactics, the population of kangaroos can increase rapidly!!!
Snakes and the lizards are other examples of species carrying multiple genitals. Males own two penises (hemipenes) each one connected to a single testicle and the females have two clitorises (hemiclitoris). Scientists are still unsure why females require two clitorises, but they believe the reason for the two penises is to allow the males to be more flexible and able to mate with the female from either side, particularly during mating aggregations, where as many as 100 males can compete for the same female. Remarkably, female snakes can mate with several males and store their sperm for up to five years and have the capacity to choose which sperm to use to fertilise the eggs.
6. And some without genitals at all
Conversely, there are examples in nature of animals without genitals, such as the squids which lack vaginas. To reproduce, the males store their sperm in enclosed sacs called spermatophores and during mating, they use a special arm to transfer and implant the sacs into the female’s body, generally around her head or near her mouth, where the eggs are waiting to be fertilised. Once fertilised, the female releases the eggs from her mouth or funnel hiding them in the rocks or in holes until they are ready to hatch.
7. Strange Penises
Apart from the kangaroos, snakes and lizards, there are other examples of animals with strange penises. Both ducks and pigs have penis in a shape of a corkscrew or spiral-shaped, which are compatible with a corkscrew-shaped vagina. Boar’s half a meter penis rotates rhythmically during mating and can ejaculate more than half a litter of semen over a period of 15 minutes, whilst duck penises are equally not small, measuring in average about 20cm in length or even half a meter long in the case of the Argentine lake duck. Lucky Donald Duck and Daisy!!
Sea slug’s also use a strange reproductive strategy. They hold three penises and have the capacity to dispose and regenerate one of these penises every time it mates. And scientists seem to know the reason for this perplexing strategy. It appears the sea slugs use their first penis to remove any sperm left inside the female by other males. They then dispose this penis, before using the second penis to inject its own sperm, ensuring that it’s his genes that are passing to the next generation. Miraculously, a few hours later, the male is able to regenerate its first penis and to mate again. Similarly, orb-weaver spiders and other sea creatures also use very similar strategies as the sea slugs.
8. Orphan species
Finally, some animals are orphans from the time they are born. Octopus only go through one single reproductive period and die before their offspring hatch. The males usually die after mating, sometimes killed by the females in an act of cannibalism, whilst the females tend to survive until the eggs are hatched. After fertilization, the female lay the eggs and stand close to them to protect them from intruders, but very soon they stop eating and wastes away starting a process known as programmed death. At later stages some females even go further and start self-mutilation, often slamming against surfaces, tearing off pieces of skin and eating the tips of their own tentacles. By the time the eggs hatch the mother is dead. Scientists are still uncertain why these intelligent animals undergo this process, but it appears it may be an effective strategy to ensure the female does not consume their youngster, particularly since these are remarkable cannibals. Other researchers believe that, since octopus can grow pretty much indefinitely, this may be a strategy to eliminate very big, old and hungry adults that could potential compromise hatchling and to maintain the ecosystem free of massive animals.
Squid use similar strategies during reproduction. Male squid die very soon after mating in order to provide food for the predators that otherwise would feed on the eggs, whilst the female die after releasing the eggs. Similarly, male salmons also die just after spawning but the females survive to guard the eggs, after which they die by exhaustion and the lack of capacity to travel thousands of miles back home to reinitiate their reproductive cycle.
Animals undergo astonish strategies and even ultimate sacrifices, to ensure propagation of their species and generation of viable and healthy offspring. Many more examples exist in nature and these will be part of a future article. Meanwhile, let’s keep observing the world around us and understand the reason behind their complex’s behaviours.
By Ricardo Ribas, Veterinary Doctor, doctorate in veterinary sciences and researcher in the London.
1. Foster, S.J.; Vincent, C.J. (2004). “Life history and ecology of seahorses: implications for conservation and management”. Journal of Fish Biology. 65: 1-61. doi:10.1111/j.0022-1112.2004.00429.x
2. Kawaguchi M, Okubo R, Harada A, Miyasaka K, Takada K, Hiroi J, Yasumasu S. Morphology of brood pouch formation in the pot-bellied seahorse Hippocampus abdominalis. Zoological Lett. 2017 Oct 17;3:19. doi: 10.1186/s40851-017-0080-9. eCollection 2017.
3. The biology of seahorses: Reproduction. The Seahorse Project.”The biology of seahorses: Reproduction” Retrieved July 2020
5. Johnson, J. Chadwick; Trubl, Patricia; Blackmore, Valerie; Miles, Lindsay (August 2011). “Male black widows court well-fed females more than starved females: silken cues indicate sexual cannibalism risk”. Animal Behaviour. 82 (2): 383–390. doi:10.1016/j.anbehav.2011.05.018
6. Baruffaldi, Luciana; Andrade, Maydianne C.B. (April 2015). “Contact pheromones mediate male preference in black-widow spiders: avoidance of hungry sexual cannibals?”. Animal Behaviour. 102: 25–32. doi:10.1016/j.anbehav.2015.01.007
7. Iwata E, Mikami K, Manbo J, Moriya-Ito K, Sasaki H. Social interaction influences blood cortisol values and brain aromatase genes in the protandrous false clown anemonefish, Amphiprion ocellaris. Zoolog Sci. 2012;29(12):849-855. doi:10.2108/zsj.29.849. DOI: 10.2108/zsj.29.849
8. Godwin, J.; Thomas, P. (1993). Sex change and steroid profiles in the protandrous anemonefish Amphiprion melanopus (Pomacentridae, Teleostei). Gen Comp Endocrinol 91: 144-157.
9. Liu H, Todd EV, Lokman PM, Lamm MS, Godwin JR, Gemmell NJ. Sexual plasticity: A fishy tale. Mol Reprod Dev. 2017;84(2):171-194. doi:10.1002/mrd.22691
Camels and Seals
10. Arnautović I. · Abdel Magid A.M. (1974). Anatomy and mechanism of distension of the dulaa of the one-humped camel. Acta Anat. 115-124
11. Hooded Seal (Cystophora cristata), a weird animal. Drawfluffy.com. https://web.archive.org/web/20101229183024/http://www.drawfluffy.com/hooded-seal.html. Retrieved in July 2020.
Kangaroos multiple genitals
12. Ed Yong. Kangaroos have three vaginas. National Geograhic. https://www.nationalgeographic.com/science/phenomena/2012/04/17/ kangaroos-have-three-vaginas/. April 17, 2012.
13. Marsupial, Wikipedia. Wikipedia foundation. Updated August 2020. Accessed August 2020. https://en.m.wikipedia.org/wiki/epipubic_bone.
14. Matt Hayes. 10 unexpected examples of animal genitalia. Listverse. https://www.google.co.uk/amp/s/listverse.com/2012/11/29/10-bizarre-animal-genitalia/amp/. 2012
Snakes and Lizards
15. Tina Deines. Why Do Snakes Have Two Penises and Why Are Alligators Always Erect? https://www.nationalgeographic.com/news/2018/02/snakes-alligators-reptiles-genitalia-animals/ National Geographic. February, 2018
16. Friesen CR, Uhrig EJ, Squire MK, Mason RT, Brennan PL. Sexual conflict over mating in red-sided garter snakes (Thamnophis sirtalis) as indicated by experimental manipulation of genitalia. Proc Biol Sci. 2013;281(1774):20132694. Published 2013 Nov 13. doi:10.1098/rspb.2013.2694
17. King, RB.; Jadin, R.C.; Grue, M.; Walley, H.D. Behavioural correlates with hemipenis morphology in New World natricine snakes, Biological Journal of the Linnean Society, Volume 98, Issue 1, September 2009, Pages 110–120, https://doi.org/10.1111/j.1095-8312.2009.01270.x
18. Morse P, Huffard CL. Tactical Tentacles: New Insights on the Processes of Sexual Selection Among the Cephalopoda. Front Physiol. 2019;10:1035. Published 2019 Aug 21. doi:10.3389/fphys.2019.01035
19. Pharyngula Friday Cephalopod: Undead Squid Penis. Science Blogs. https://scienceblogs.com/pharyngula/2017/08/25/friday-cephalopod-undead-squid-penis. August 2017
20. Stephanie Watson. How Squid Work. How stuff works. https://animals.howstuffworks.com/marine-life/squid2.htm.
21. Squid. Wikipedia. Wikipedia Foundation. Last updated 16 August 2020. Accessed September 2020. https://en.wikipedia.org/wiki/Squid#cite_note-Ruppert-7
22. McCracken KG, Wilson RE, McCracken PJ, Johnson KP. Sexual selection. Are ducks impressed by drakes’ display?. Nature. 2001;413(6852):128. doi:10.1038/35093160
23. Knox, RV. (2003). The Anatomy & Physiology of Sperm Production in Boars. Published in the internet. http://www.ansci.wisc.edu/jjp1/pig_case/html/library/boara&p.pdf. Department of Animal Sciences. University of Illinois.
24. Rebecca Morelle. Sea slug’s ‘disposable penis’ surprises. BBC news. BBC. https://www.bbc.co.uk/news/science-environment-21431678. February 2013
25. Ed Yong. Sea Slug Amputates Its Disposable Penis, But Has Two Spares. National Geographic.https://www.nationalgeographic.com/science/phenomena/2013/02/12/sea-slug-amputates-its-disposable-penis-but-has-two-spares/. February 2013
26. Sekizawa Ayami, Seki Satoko, Tokuzato Masakazu, Shiga Sakiko and Nakashima Yasuhiro. 2013. Disposable penis and its replenishment in a simultaneous hermaphrodite Biol. Lett.9. 2012.1150. http://doi.org/10.1098/rsbl.2012.1150
Animals who die after giving birth
27. Christina Root. Animals who die giving birth, Petsonmom.com. https://animals.mom.com/animals-die-giving-birth-9247.html. Accessed September 2020
28. Z. Yan Wang, Clifton W. Ragsdale. Multiple optic gland signaling pathways implicated in octopus maternal behaviors and death. The Journal of Experimental Biology, 2018; jeb.185751 DOI: 10.1242/jeb.185751
29. Matt Wood. The grim, final days of a mother octopus. University of Chicago Medical Center. https://www.uchicagomedicine.org/forefront/biological-sciences-articles/the-grim-final-days-of-a-mother-octopus. September 2018.
30. Rocha F, Guerra A, González AF. A review of reproductive strategies in cephalopods. Biol Rev Camb Philos Soc. 2001;76(3):291-304. doi:10.1017/s1464793101005681
31. Anderson RC, Wood JB, Byrne RA. Octopus senescence: the beginning of the end. J Appl Anim Welf Sci. 2002;5(4):275-283. doi:10.1207/S15327604JAWS0504_02
The material discussed on this article are for informational purposes only. For more information consult a vet or a professional in the area. Whilst every effort is made to make sure the article is accurate at the time of publication, I take no liability for any new developments on the subject as well as any errors or omissions.