Hermaphroditism in Animals

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Reproduction is a complex, widely varied process, depending on the animals involved. For some animals, it merely involves the duplicating of itself. For others, it is necessary to find a mate. This process can be very difficult or very simple, depending on the species, and different creatures deal with this in different ways. One way that organisms have been designed to deal with the reproduction issue is hermaphroditism, in which individuals have both reproductive organs. This condition is most commonly found in fish, but other animals exhibit it was well.

Hermaphroditism comes in two major forms: sequential and simultaneous. Sequential hermaphroditism refers to organisms that start life as one gender and can potentially transition to the opposite gender as they age. There are two types of sequential hermaphroditism depending on which gender the organism starts life as. If the organism starts life as a male, sequential hermaphroditism is called protandry. If the situation is reversed, it is called protogyny.1

Simultaneous Hermaphroditism

In simultaneous hermaphroditism, animals remain hermaphrodites for their entire lives. This type of hermaphroditism is uncommon in most vertebrates. But it is known among some vertebrates, primarily in fish. When it does occur, it often involves a phenomenon known as “egg trading.” This phenomenon involves a special type of mating where both partners pass eggs to each other and fertilize the ones they receive.2 In other organisms, simultaneous hermaphroditism goes the opposite way with the partners exchanging sperm, involving male gametes instead of female gametes. This condition occurs in fish, snails, crustaceans, and other organisms.3 One or both of these mechanisms is found in fish, mollusks,4 and crustaceans.5

Interestingly, simultaneous hermaphroditism would allow organisms to mate with any member of the same species, but at least some of the simultaneous hermaphrodites are monogamous. For example, the chalk bass, a small schooling reef fish, is a simultaneous hermaphrodite that undergoes egg trading. Yet, despite ample opportunity to mate with any other member of the school, the chalk bass is monogamous.6

Sequential Hermaphroditism

Sequential hermaphroditism is much more common than simultaneous hermaphroditism.

Sequential hermaphroditism is much more common than simultaneous hermaphroditism.7 Unlike the simultaneous type, sequential hermaphrodites only have the reproductive organs for one gender at any given time. Under certain circumstances, they can change gender. Parrotfishes are well known for their ability to change from female to male.8 The females are able to sense the absence of a male in a given territory, and this absence stimulates the development of one of the females in the area to develop into a male. Curiously, unlike other known species of sequential hermaphrodites, it is usually not the largest female that changes into a male.9 Instead, one of the smaller females will develop into a male. A similar pattern occurs in some species of angelfish, though in this instance it is the largest female that changes gender.10

By far, the most common example of this type of protogynous hermaphroditism is found among wrasses, which are a saltwater fish. The blue-headed wrasse is the most well-known and well-studied example. One recent study postulated that the mechanism behind the change in gender from female to male comes from the stress of having the social order interrupted. Essentially, the paper argued that the absence of a male induces a social stress on the females that causes epigenetic modifications (genetic changes outside the genome) which lead to the largest female becoming a male.11 Regardless, the blue-headed wrasse is one of the most well-known examples of protogynous hermaphroditism.

While less common, some fish go from male to female when the need arises. The most well-known of these fish is the popular clownfish. As well as spawning their own movie franchise, these fish are popular with saltwater aquarists too. What is less well known is their ability to change genders. Clownfish live in colonies consisting of a larger female, a smaller male, and up to several juveniles. If the female dies or is removed, the smaller male will grow and internally switch to a female, while one of the juveniles will develop into a male.12

Origins of Hermaphroditism

Evolutionists have struggled to explain hermaphroditism. According to their own phylogenies (studies attempting to determine ancestry), there is no clear line tracing the evolution of the various forms of hermaphroditism in either fish or other organisms.13,14 One paper proposed the idea that hermaphroditism arose from a sort of “proto-hermaphroditic condition.”15 Exactly what that condition was is not well defined, but it supposedly permitted the early fish to exhibit multiple forms of hermaphroditism. This idea is not widespread, however.

There is the unspoken assumption that, somehow, no matter what the answer, hermaphroditism must have evolved because it exists.

The more common view in the evolutionary community is that hermaphroditism is somehow derived from heterosexual organisms.16 Generally, evolutionists think that hermaphroditism arises from the need for mates, to keep up genetic diversity in low mobility organisms, or for the advantage of being larger as a given gender.17 However, none of these models explain how hermaphroditism arose in the first place. One paper said, “Far less certain, however, are answers to the following questions. How exactly does hermaphroditism evolve from gonochorism [distinct genders]? And, does gonochorism ever re-emerge from phylogenetically localized instances of ancestral hermaphroditism?”18 This paper is asking the right questions, even if it fails to answer any of them. There is the unspoken assumption that, somehow, no matter what the answer, hermaphroditism must have evolved because it exists. This is the logical fallacy of begging the question. Just assuming something happened does not make it true. This is another example of the plastic nature of evolutionary explanations where, regardless of the difficulties, evolution has an answer.

Hermaphroditism makes much more sense from a creation perspective. In the pre-fall world, simultaneous hermaphroditism could have permitted organisms with limited interactions to reproduce more easily as they would have been able to mate with any member of their kind. In the post-fall world, sequential hermaphroditism would have also been incredibly useful in maintaining reproduction if the dominant male or female in a group died or was eaten by a predator, particularly for smaller colonial animals like clownfish. Thus, hermaphroditism in animals fits much better with a biblical worldview—knowing that God cares for his creatures and wants them to thrive (Psalm 104:24–28).

Footnotes

  1. Robert R. Warner, “The Adaptive Significance of Sequential Hermaphroditism in Animals,” The American Naturalist 109, no.965 (1975): 61–82, https://courses.pbsci.ucsc.edu/eeb/bioe161/wp-content/uploads/2012/12/Warner-Robert.-The-Adaptive-significance-of-sequential-hermaphroditism-in-animals.pdf.
  2. Eric A. Fischer, “Egg trading in the Chalk Bass, Serranus tortugarum, a simultaneous hermaphrodite,” Ethology 66, no. 2 (1984): 143–151, https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0310.1984.tb01361.x.
  3. Warton Monteiro, Jose Maria G. Almeida Jr., and Braulio S. Dias, “Sperm sharing in Biomphalaria snails: a new behavioural strategy in simultaneous hermaphroditism,” Nature 308 (1984): 727–729, https://www.nature.com/articles/308727a0.
  4. John A. Downing, J.-P. Amyot, M. Perusse, and Y. Rochon, “Visceral sex, hermaphroditism, and protandry in a population of the freshwater bivalve Elliptio complanate,” Journal of the North American Benthology Society 8, no. 1 (1989): 92–99, https://www.researchgate.net/profile/John_Downing4/publication/238104298_of_the_freshwater_bivalve_Elliptio_complanata/links/54132a6f0cf2fa878ad3d5b1/of-the-freshwater-bivalve-Elliptio-complanata.pdf.
  5. Helio Laubenheimer and Andrew L. Rhyne, “Experimental confirmation of protandric simultaneous hermaphroditism in a Caridean shrimp outside of the genus Lysmata, Journal of the Marine Biological Association of the United Kingdom 88 no.2 (2008): 301–305, https://docs.rwu.edu/cgi/viewcontent.cgi?article=1162&context=fcas_fp.
  6. Eric A. Fischer, “Simultaneous Hermaphroditism, Tit-for-Tat, and the Evolutionary Stability of Social Systems,” Ethology and Sociobiology 9 (1988): 119–136, http://courses.washington.edu/ccab/Fischer%20on%20hamlets%20&%20tit%20for%20tat%20-%20ESB%201988.pdf.
  7. Robert R. Warner, “Mating Behavior and Hermaphroditism in Coral Reef Fishes,” American Scientist 72 (1984): 128–136, https://pdfs.semanticscholar.org/4213/9446eeaca4c3686666f87f92c60b8f506d06.pdf.
  8. J.H. Choat and D.R. Robertson, “Protogynous Hermaphroditism in Fishes of the Family Scaridae,” in Intersexuality in the Animal Kingdom, ed. Rudolf Reinboth (Berlin: Springer-Verlag, 1975), https://www.researchgate.net/profile/D_R_Robertson/publication/280557474_Protogynous_Hermaphroditism_in_Fishes_of_the_Family_Scaridae/links/55b9004b08aec0e5f43c0c75.pdf.
  9. Roldan C. Muñoz and Robert R. Wagner, “Alternative contexts of sex change with social control in the bucktooth parrotfish, Sparisoma radian,” Environmental Biology of Fishes 68, no. 3 (2003): 307–319, https://www.researchgate.net/profile/Robert_Warner2/publication/227128011_Alternative_Contexts_of_Sex_Change_with_Social_Control_in_the_Bucktooth_Parrotfish_Sparisoma_radians/links/0912f50883b8a0e34f000000.pdf.
  10. Jack T. Moyer and Akinobu Nakazono, “Population Structure, Reproductive Behavior and Protogynous Hermaphroditism in the Angelfish Centropyge interruptus at Miyake-jima, Japan,” Japanese Journal of Ichthyology 25, no. 1 (1978): 25–39, https://www.jstage.jst.go.jp/article/jji1950/25/1/25_1_25/_pdf.
  11. Erica V. Todd et al., “Stress, novel sex genes, and epigenetic reprogramming orchestrate socially controlled sex change,” Science Advances 5, no. 7 (2019), https://advances.sciencemag.org/content/5/7/eaaw7006/tab-pdf.
  12. Associated Press “How some fish undergo sex changes spontaneously,” CBC, July 11, 2019, https://www.cbc.ca/news/technology/fish-sex-change-1.5207852.
  13. Jack T. Moyer and Akinobu Nakazono, “Protandrous Hermaphroditism in Six Species of the Anemonefish Genus Amphiprion in Japan,” Japanese Journal of Ichthyology 25, no. 2 (1978): 101–106, https://www.jstage.jst.go.jp/article/jji1950/25/2/25_2_101/_pdf.
  14. J.C. Avise and J.E. Mank, “Evolutionary Perspectives on Hermaphroditism in Fishes,” Sexual Development 3, no. 2–3 (2009): 152-163, https://faculty.sites.uci.edu/johncavise/files/2011/03/299-SexDev-herms.pdf.
  15. Gavin C. Woodruff, “Insights Into Species Divergence and the Evolution of Hermaphroditism From Fertile Interspecies Hybrids of Caenorhabditis Nematodes,” Genetics 186, no. 3 (2010): 997–1012, https://www.genetics.org/content/genetics/186/3/997.full.pdf.
  16. Yvonne Sadovy de Mitcheson and Min Liu, “Functional hermaphroditism in teleosts,” Fish and Fisheries 9 (2008): 1–43, https://www.researchgate.net/profile/Min_Liu5/publication/229778735_Functional_hermaphroditism_in_teleosts/links/5c45ace6a6fdccd6b5bd0f97/Functional-hermaphroditism-in-teleosts.pdf.
  17. Avise and Mank, 2009.
  18. Wagner, 1975.
  19. Avise and Mank, 2009.

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