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Striped Dolphins
Striped dolphins have three types of bodies we say look like girl bodies, like boy bodies, and bodies that look like both!
The same is true of Bowhead Whales and Fin Whales.
Updated from: “All Genders Are Perfectly Natural” (K-5) poster by Reflection Press, from the Gender Now Coloring Book © 2011.
Spotted Red Hyena
The boys and the girls look AND act so much alike, it can be difficult to tell them apart, even if you look closely. One girl hyena usually is the strongest hyena in the family, and she leads the pack.
Updated from: “All Genders Are Perfectly Natural” (K-5) poster by Reflection Press, from the Gender Now Coloring Book © 2011.
Beluga whales
Beluga whales have three body types: boy bodies, girl bodies, and boy-and-girl bodies. Oh whale!
All females have ovotestes (ovotestes are gonads containing both ovarian & testicular tissue) XX have ovotestes & make eggs and testosterone only, XY have testes only and make sperm only.
Image caption: A Spanish blind mole emerges from underneath a rock. Photo credit (C) Tiago Magalhães.
Most gender-gene committees, with or without the presence of SRY, pass a resolution creating only a testis in males and only an ovary in females. In some species, though, even this most elemental aspect of bodily gender has been given a different configuration.
Among Talpa occidentalis—another burrowing mammal, an old world mole from the Iberian peninsula—all females have ovotestes, gonads containing both ovarian and testicular tissue. The ovotestes occur at the site in the body where simple ovaries are found in other species.
Talpa XX individuals have ovotestes and make eggs in the ovarian part of their ovotests. They don’t make sperm, but they do have both sperm-related and egg-related ducts. The testicular part of these ovotestes secretes testosterone. XY individuals have testes only and make sperm.
R. Jiménez, M. Burgos, A. Sánchez, A. Sinclair, F. Alarcón, J. Marin, E. Ortega, and R.D. de la Guardia, 1993, Fertile females of the mole Talpa occidentalis are phynotypic intersexes with ovotestes, Development 118:1303-11.
Roughgarden p. 202
How do changing temperatures affect a sea turtle egg’s development?
How will average global temperature changes affect a sea turtle egg’s development?
M. Ewert, D. Jackson, and C. Nelson, 1994, Patterns of temperature-dependent sex determination in turtles, J. Exp. Zool. 270:3-15.
Roughgarden p. 203.
How do changing temperatures affect a crocodile egg’s development?
How will average global temperature changes affect a crocodile egg’s development?
Predict an increase, decrease, or stable population change if average temperatures increase or decrease.
Book excerpt: Among reptiles, specifically turtles, crocodiles, and some lizards, gonadal identity is determined by the temperature at which eggs develop, not by chromosomes. The eggs are usually laid in the ground and covered with sand or moist dirt from which they absorb water, swelling in size as they age. Reptile embryos start developing within their egg, and after a while primordial germ cells form. When reptile primordial germ cells move to the genital ridges of their parents, both the germ cells and the parental embryo presumably experience the same environmental temperature. Both germ cells and parent therefore receive the same message about which sex to develop as, and their agendas automatically agree.
Scientists reported the first case of intersexuality in an African dwarf crocodile (Osteolaemus tetrapspis), a 10 year-old male-presenting crocodile with gonads that were ovotestes.
We used to think crocodiles couldn’t be intersex, because we had never found any before. Our understand was that crocodiles needed two separate types of cells that never occur together.
This discovery shows we have so many more questions to ask about sex determination!
Image caption: A dwarf crocodile. (C) Jim Frazee
Because the model we use to explain sex determination in crocodiles cannot help explain this evidence, we must keep asking questions and build better models for looking at our evidence.
Langer: Half of the 22 extant species of crocodilians have been examined for occurrence of temperature dependent sex determination (TSD). In TSD reptiles, masculinizing temperatures yield 100% or a majority of males, whereas feminizing temperatures yield 100% or a majority of females. In the transition range of temperature (TRT), a mix of males, females and sometimes intersexes are obtained. However, the molecular mechanisms behind TSD and an explanation for the occurrence of intersexuality remain elusive.
References
C. Johnston, M. Barnett, and P. Sharpe, 1995, The molecular biology of temperature-dependent sex determination, Phil. Trans. R. Soc. Lond., ser. B, 350: 297-304.
J.W. Lang and H. Andrews, 1994, Temperature-dependent sex determination in crocodilians, J. Exp. Zool. 270-28-44.
S. Langer, K. Ternes, D. Widmer, & Frank Mutschmann. The first case of intersexuality in an African dwarf crocodile (Osteolaemus tetraspis). Zoo Biol. 33:459–462, 2014. DOI:10.1002/zoo.21149
C. Smith and J. Joss, 1993, Gonadal sex differentiation in Alligator mississippiensis, a species with temperature-dependent sex determination, Cell Tissue Res. 273:149-62.
Wibbles, Bull, and Crews, 1994, Temperature-dependent sex determination. Journal of Experimental Zoology 270(1):71 - 78. DOI: 10.1002/jez.1402700108