Chapter 4: The Effect of Environment Behavior Development
Environmental factors can strongly influence behavior and physiological developmental.
Example: Conditional neoteny and cannibalism in Tiger Salamanders
|In the Barred Tiger Salamander (Ambystoma tigrinum mavortium) the dark spots are larger than in the last two and tend to form the background color, while there are yellow bars or stripes that extend from the belly to the middle of the back, though these are irregular in form. In the south of this subspecies range it is a winter breeder, in the north an early spring breeder, migrating to ponds after heavy rains.||
Home range by sub species
|The Eastern Tiger Salamander (Ambystoma tigrinum tigrinum). They are characterized by a dark background with light yellow-gold markings extending down their sides.It is found in the eastern half of North America. In the south it is also a winter breeder, in the north an early spring breeder, migrating to ponds after heavy rains.|
|In the Blotched Tiger Salamander (Ambystoma tigrinum melanostictum) the background color is dull yellow and is lighter than in the Gray Tiger Salamander. The dark markings are also larger but usually take up less area than the background color. These irregular markings often form a network-like pattern. The Blotched Tiger Salamnader is also an early spring breeder.||
Arizona Tiger Salamander (Ambystoma tigrinum nebulosum; above)
also has a dark black or gray background with light yellow markings in the
form of mottled spots or bars that are smaller and/or fewer than in the
Tiger Salamander. Some specimens in small populations may have their color
pattern in the reverse, making them look similar to the Gray Tiger
Salamander, with the black spots or bars on lighter background. Breeding
occurs in conjunction with rains in the more arid parts of its range.
|The Gray Tiger Salamander (Ambystoma tigrinum diaboli) are easily recognized with their dark green to gray background speckled with tiny black dots. It breeds in the early spring, migrating to ponds as soon as the ice on them begins to melt.||
Tiger Salamander Larvae - external gills distinguish salamander
larvae from frog tadpoles (which have internal gills). The
of the younger (and smaller) larva above left have not yet emerged. In
contrast to anurans, the front legs emerge first, then the back. The larva
above was found in May, the one below in August.
|Environmentally Induced Neoteny. Some populations of Tiger Salamanders, particularly in western North America and especially at high altitudes tend to be neotenic. This means that although the salamanders become sexually mature and can reproduce they do not metamorphose, remaining as larvae and breathing with gills. Neotenic Tiger Salamanders can become larger than individuals that metamorphose, reaching total lengths of 15 inches.|
induced cannibalism. Under normal circumstances salamander larvae
metamorphose from a tadpole-like larvae into the terrestrial dwelling
adults; these are called typical type larvae. These larvae
typically eat aquatic insects. However, under a specific set of
environmental circumstances, some larvae will eat other salamander larvae
cannibal type. Cannibal type have specially adapted mouths and are
physically larger than the typical type. Furthermore once converted,
cannibal type larvae develop faster than typical type. it is important to
note for our purposes that the cannibal type only appear in the population
when the pond is densely populated and the population is primarily not
directly related to the individual .
Territoriality in cichlid fish and the role of
gonadotropin-releasing hormone (GnRH)
Socio-environmental factors mediate behavior in many cases via hormonal
Example: honeybee behavior development.
Three basic morphs in the hive:
Associated with this progression through these behavioral
roles is a shift in the relative levels of juvenile hormone.
Gene Robinson and his colleagues asked what happens to behavior when:
However, changing the social stratification of the hive also
influences the rate of development to compensate for the manipulation:
This means that socio-hormonal interaction of older bees influences the hormonal expression and behavior of younger bees. this is a mechanism by which the hive maintains a homeostatic balance of each worker cast.
However, not all changes in bee behavior are necessarily
mediated by hormonal control imposed by the dynamics of the hive. Honeybees,
particularly foragers are adept learners. At least 2 associated part of
the brain changes in relation to pollen and nectar foraging behaviors.
|The mushroom bodies described in the text image are shown as the blue shaded area in the 3D histological reconstruction of the honeybee brain|