Hatchling Explained

In oviparous biology, a hatchling is a newly hatched fish, amphibian, reptile, or bird.^[1] A group of mammals called monotremes lay eggs, and their young are hatchlings as well.

Fish

Fish hatchlings generally do not receive parental care, similar to reptiles. Like reptiles, fish hatchlings can be affected by xenobiotic compounds. For example, exposure to xenoestrogens can feminize fish.^[2] As well, hatchlings raised in water with high levels of carbon dioxide demonstrate unusual behaviour, such as being attracted to the scent of predators. This change could be reversed by immersion into gabazine water, leading to the hypothesis that acidic waters affect hatchling brain chemistry.^[3]

Amphibians

See main article: Tadpole.

The behavior of an amphibian hatchling, commonly referred to as a tadpole, is controlled by a few thousand neurons.^[4] 99% of a Xenopus hatchling's first day after hatching is spent hanging from a thread of mucus secreted from near its mouth will eventually form; if it becomes detached from this thread, it will swim back and become reattached, usually within ten seconds.^[4] While newt hatchlings are only able to swim for a few seconds, Xenopus tadpoles may be able to swim for minutes as long as they do not bump into anything.^[4] The tadpole live from remaining yolk-mass in the gut for a period, before it swims off to find food.^[5]

Reptiles

The reptile hatchling is quite the opposite of an altricial bird hatchling. Most hatchling reptiles are born with the same instincts as their parents and leave to live on their own immediately after leaving the egg. When first hatched, hatchlings can be several times smaller than their adult forms: Pine Snakes weigh 30 grams when they first hatch, but can grow up to 1,400 grams as adults.^[6] This appears to have been the case even in dinosaurs.^[7] In sea turtles, hatchling sex is determined by incubation temperature.^[8] In species in which eggs are laid then buried in sand, indentations in the sand can be a clue to imminent hatching.^[9] In sea turtles, this usually occurs about 60 days after the laying of eggs, and often at night.^[10] However, exposure to xenobiotic compounds, especially endocrine-disrupting compounds, can affect hatchling sex ratios as well.^[11] Persistent Organic Pollutants (POPs) and other pollutants like octylphenol are also known to increase rate of hatchling mortality and deformity.^{[12] [13]} Upon hatching, animals such as turtles have innate navigational skills, including compass and beacon methods of navigation, to reach safety. For example, turtle hatchlings instinctively swim against waves to ensure they leave the beach and its predators.^[14] They also head towards the brightest part of the horizon in order to reach the water: however, human activity has created sources of light which mislead the turtle hatchlings, causing them to not travel directly to the water, making them vulnerable to dehydration and predation.^[15] Hatchlings of the species Iguana iguana also gain gut flora essential to digestion from adults as part of their development.^[16] In the wild, hatchling survival rates are extremely low due to factors such as predation, for example, by crabs,^[17] as well as due to human-made obstacles.^[18] Human intervention has also benefitted hatchling reptiles at times. For example, late-hatched loggerhead turtles are taken in by such groups as the University of Georgia to be raised.^[19] In species such as crocodiles, hydration levels also play an important role in embryo survival.^[20]

As pets

Reptile hatchlings, especially those of turtles, are often sold as pets. This has been reported to occur even in places where such practices are illegal.^[21]

Birds

Bird hatchlings may be altricial or precocial. Altricial means that the young hatch naked and with their eyes closed, and rely totally on their parents for feeding and warmth. Precocial hatching are feathered when hatched, and can leave the nest immediately.^[22] In birds, such as the bobwhite quail, hatchlings' auditory systems are more developed than their visual system, as visual stimulation is not present in the egg, while auditory stimulation can reach the embryo even before birth.^[23] It has also been shown that auditory development in hatchlings is disrupted by environments high in visual and social stimulation.^[24] Many hatchlings are born with some forms of innate behaviours which allow them to improve their ability to survive: for example, hatchling gulls instinctively peck at long objects with marked colour contrast, which leads them to peck at their parents' bills, eliciting a feeding response.^[25] Endocrine disruption of hatchling birds increases the rate of deformities and lowers the chances of survival.^[26] In bearded vultures, two eggs are laid, but one hatchling will often kill the other.^[27] Bird hatchlings raised by humans have sometimes been noted to act towards their human caregivers as their parents.^[28]

Notes and References

1. Encyclopedia: 2000 . Hatchling . The American Heritage Dictionary of the English Language . Houghton Mifflin Company . 4th .
2. Brouwer. Marius. Kuhl. Adam J.. Antiestrogens Inhibit Xenoestrogen-Induced Brain Aromatase Activity but Do Not Prevent Xenoestrogen-Induced Feminization in Japanese Medaka (Oryzias Latipes). Environmental Health Perspectives. April 2006. 114. 4. 10.1289/ehp.8211. 16581536. 1440771. 500–506.
3. Raloff. Janet. Acidification Alters Fish Behavior: Higher Carbon Dioxide in Oceans May Affect Brain Chemistry. Science News. February 25, 2012. 181. 4. subscription. 10.1002/scin.5591810412. 14.
4. Roberts. Alan . Wen-Chang Li . Steve R. Soffe. How neurons generate behavior in a hatchling amphibian tadpole: an outline. Front. Behav. Neurosci.. 24 July 2010. 4. 16. 16 . 10.3389/fnbeh.2010.00016. 2903309. 20631854. free .
5. Book: Duellman. W. E.. Trueb. L. . illustrated by L. Trueb . Biology of amphibians. 1994. Johns Hopkins University Press. 0-8018-4780-X.
6. Book: Burger, Joanna. Whispers in the Pines: A Naturalist in the Northeast. 228. Rutgers University Press. 2006. subscription .
7. Book: Paul, Gregory S.. 43. The Princeton Field Guide to Dinosaurs. Princeton University Press. 2010. subscription .
8. Book: Richard P. . Reading . Brian . Miller. Endangered Animals: A Reference Guide to Conflicting Issues. 172. Greewood Press. 2000. subscription .
9. Hartman. Hailey B.. Share the Beach: Teamwork for Turtles. Endangered Species Update. March–April 2003. 20. 2. subscription .
10. Zattau. Dawn. Habitat Conservation Plan for Sea Turtles. Endangered Species Bulletin. January 1998. 23. 1. subscription .
11. Crews. David. Rhen. Turk. Sakata. Jon T.. Willingham. Emily. Embryonic Treatment with Xenobiotics Disrupts Steroid Hormone Profiles in Hatchling Red-Eared Slider Turtles (Trachemys Scripta Elegans). Environmental Health Perspectives. 108. 4. April 2000. 10.1289/ehp.00108329 . 10753091. 1638010. 329–332.
12. Hodge. Mary. Chemical Contamination of Green Turtle (Chelonia Mydas) Eggs in Peninsular Malaysia: Implications for Conservation and Public Health. Environmental Health Perspectives. September 2009. 117. 9. 10.1289/ehp.0900813 . 1397–1401. etal. 19750104. 2737016.
13. Chiu, Suzanne. Octylphenol (OP) Alters the Expression of Members of the Amyloid Protein Family in the Hypothalamus of the Snapping Turtle, Chelydra Serpentina Serpentina. (Articles). Environmental Health Perspectives. March 2002. 110. 3. 10.1289/ehp.02110269 . 11882478. subscription. 269–275. etal. 1240767.
14. Book: Gould. Carol Grant. Gould. James L.. 128. Nature's Compass: The Mystery of Animal Navigation. Princeton University Press. 2012. subscription .
15. Haworth. Holly. And Incredible Bright: ... and Blotted out the Night Sky. Earth Island Journal. 28. 1. Spring 2013. subscription .
16. Book: Leigh Jr., Egbert Giles. 33. Tropical Forest Ecology: A View from Barro Colorado Island. Oxford University Press. 1999. subscription .
17. Stap. Don. The Crocodile's Power Play - until Everglades Habitat Is Restored, Some Unexpected Nesting Sites Are Helping the American Crocodile Come Back in South Florida. National Wildlife. February–March 2002. 40. 2. subscription .
18. News: Festival to Show off Georgia's Wild Side; Turtle Hatchling to Be on Display. Stepzinski. Teresa. subscription . The Florida Times Union. Brunswick, Georgia. October 2, 2003.
19. News: Landers. Mary. Large Living Just Got a Little Larger for This Sea Turtle; Raised in Aquariums, a Loggerhead Finally Heads to the Atlantic. The Florida Times Union. September 12, 2008. subscription .
20. Book: Kelly, Lynne. 196. Crocodile: Evolution's Greatest Survivor. Allen & Unwin. 2006. subscription .
21. Lee. David S.. Sellers. L. George. Can We Teach Proactive Turtle Conservation in Our Classrooms?. The American Biology Teacher. 74. 7. September 2012. subscription. 10.1525/abt.2012.74.7.6. 459–463. 83814558.
22. Book: Burton, Robert . Bird behaviour . 1985 . 186 - 187 . London . Granada . 0-246-12440-7 .
23. Book: Devenney, Darlynne A.. Gerald Turkewitz. Developmental Time and Timing. 109. Lawrence Erlbaum Associates. 1993. subscription .
24. Book: Lickliter, Robert. David J. Lewkowicz. 73. The Development of Intersensory Perception: Comparative Perspectives. Lawrence Erlbaum Associates. 1994. subscription .
25. Book: Gould, Stephen Jay. Eight Little Piggies: Reflections in Natural History. 258. W. W. Norton & Company. 1993. subscription .
26. Melo. Ana Clara. Ramsdell. John S.. Sexual Dimorphism of Brain Aromatase Activity in Medaka: Induction of a Female Phenotype by Estradiol. Environmental Health Perspectives. March 2001. 109. 3. 10.1289/ehp.01109257 . 11333187. 257–264. 1240244.
27. Letters to the Editor. International Wildlife. May–June 2000. subscription .
28. News: Jackson. Gordon. Owl Hatchlings Taken to Sapelo Island Sanctuary; the Rehabilitated Birds Were Then Released to Fend for Themselves. The Florida Times Union. May 7, 2010. subscription .