Hatchling
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In
oviparous Oviparous animals are female animals that lay their egg Diagram of a chicken egg in its 9th day. Membranes: allantois, chorion, amnion, and vitellus/ yolk. An egg is the organic vessel containing the zygote in which an embryo develops un ...
biology, a hatchling is a newly hatched
fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class , with over 95 ...

fish
,
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
,
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
, or
bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwide and range in size from the to the . There ar ...

bird
. A group of mammals called
monotreme Monotremes are prototherian mammals of the order Monotremata. They are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). Monotremes are typified by structural differences in their brain ...
s 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. 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.


Amphibians

The behavior of an amphibian hatchling, commonly referred to as a
tadpole A tadpole is the larval stage A larva (plural larvae ) is a distinct juvenile form many animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...
, is controlled by a few thousand neurons. 99% of a ''
Xenopus ''Xenopus'' () (Gk., ξενος, ''xenos''=strange, πους, ''pous''=foot, commonly known as the clawed frog) is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extan ...

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. While
newt A newt is a salamander Salamanders are a group of amphibians typically characterized by a lizard Lizards are a widespread group of Squamata, squamate reptiles, with over 6,000 species, ranging across all continents except Antarctica, ...

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. The tadpole live from remaining
yolk Among animals which produce egg An egg is the organic vessel containing the in which an develops until it can survive on its own, at which point the animal hatches. An egg results from of an . Most s, (excluding s), and lay eggs, al ...

yolk
-mass in the gut for a period, before it swims off to find food.


Reptiles

The
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

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. This appears to have been the case even in dinosaurs. In sea turtles, hatchling sex is determined by incubation temperature. In species in which eggs are laid then buried in sand, indentations in the sand can be a clue to imminent hatching. In sea turtles, this usually occurs about 60 days after the laying of eggs, and often at night. However, exposure to xenobiotic compounds, especially endocrine-disrupting compounds, can affect hatchling sex ratios as well. Persistent Organic Pollutants (POPs) and other pollutants like octylphenol are also known to increase rate of hatchling mortality and deformity. 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. 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. Hatchlings of the species ''Iguana iguana'' also gain gut flora essential to digestion from adults as part of their development. In the wild, hatchling survival rates are extremely low due to factors such as predation, for example, by crabs, as well as due to human-made obstacles. 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. In species such as crocodiles, hydration levels also play an important role in embryo survival.


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.


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. 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. It has also been shown that auditory development in hatchlings is disrupted by environments high in visual and social stimulation. 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. Endocrine disruption of hatchling birds increases the rate of deformities and lowers the chances of survival. In bearded vultures, two eggs are laid, but one hatchling will often kill the other. Bird hatchlings raised by humans have sometimes been noted to act towards their human caregivers as their parents.


References

{{Authority control Ornithology Bird breeding