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. The 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.
gray tiger salamanderThe 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 legs 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 Tiger Salamander Larvabe 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.
Environmentally 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 .

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Territoriality in cichlid fish and the role of gonadotropin-releasing hormone (GnRH)
  • Changes in social status of males causes a reversible change in the size of an identified group of GnRH neurons in the hypothalamus. When males changes socially from a satellite to dominant status (by acquiring a territory):
    •  Up to an 8 fold increase in size GnRH cells
      • Release of GnRH drives increases gonadal size and hormonal output
        • Increases territorial behavior to other fish.
          • wards off other males
          • attracts females
        • Enhances coloration
    • Also occurs in females but is controlled by reproductive state not social status/interaction
    • Loosing territory reverses this effect

 

spawning h.burtoni

Socio-environmental factors mediate behavior in many cases via hormonal control.

Example: honeybee behavior development.

  • Honeybees are one of many species of social insect.
  • Among  social insects a key feature is division of labor.
    • it is this division of labor that is thought to be the key to the massive success of social insects in general.
  • One of the most impressive features of the division of labor is that the hive is able to modify its workforce based on need: In this sense insect societies are PLASTIC.
Honeybee

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:

  1. juvenile hormone levels are manipulated?
  2. colony conditions are changed?

 

 

  • If young bees are treated with Juvenile hormone they will become "precocious foragers" exhibiting foraging related behaviors prior to normal onset of foraging behavior.
  • If you remove the corpora allata, the juvenile hormone gland bees do not develop into foragers.
    • This effect can be rescued by application of juvenile hormone.
However, changing the social stratification of the hive also influences the rate of development to compensate for the manipulation:
  • If you remove all foragers precocious (~1 week old ) foragers will develop.
    • if you then replace the removed bees with young bees precocious foragers still emerge
    • If you replace removed bees with foragers from another hive precocious foragers do not emerge

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 of the honeybee brain there is a correlated increase in synaptic complexity (cell fibers)
  • Antennal lobes also appear change their responses to odor stimuli once that odor has been learned.
The mushroom bodies described in the text image are shown as the blue shaded area in the 3D histological reconstruction of the honeybee brain