Ontogeny:

Ontogeny is the developmental history of an organism. When looking at the ontogeny of an organism or species, it is important to look at the relationship between aspects of behaviors that are learned and aspects that are genetic.

 

The development of migrating behavior has two important components.

1. The "CHOICE" between becoming a migrating salmon rather than a sneaky salmon. is a conditional, based on genetic levels....

2. The LEARNING required for the salmon to return to its natal site.

 

The "choice" explained...

Salmon migration is a conditional strategy.This means that salmon populations are genetically monomorphic (showing little or no variation) and that different strategies, or decision rules, are conditional upon each fish's status (how big, strong and health you are-we normally look at overall size for this, larger means healthier.) [19] If a fish's status is above a threshold their strategy will cause them to develop into one morph, if they are bellow they will develop into another morph. Tactics are the phenotypes that result from the chosen strategy.

1a. High status salmon develop into parasitic (or sneaker) adults if they are above the particular threshold for a given population (if they are bigger), fish below that threshold develop into territorial adults (if they are smaller) [6]. Sneakers adopt the residency tactic(Look to image 1) meaning that they remain in fresh water during their entire lives. Territorial adults adopt the anadromy tactic(Look to image 2) meaning that they undertake a feeding migration to sea before returning to freshwater to spawn–these salmon end up being much larger than the sneakers. [20]

Genetic basis- There is also a genetic coorelation between size and life history tactic. Theriault, V. et al. found a heritability for body size, which is a good index for the fish's status, this shows that genetic factors can also effect the tactic choice. [20]

Variations in threshold by genetics-

It also seems logical that the threshold itself will be different between genetically isolated Salmon populations. This difference can likely be attributable to the environmental factors of the natal site and the distance from this site to the ocean, which will vary greatly between different populations.

Variations in threshold by environment-

The threshold for the migration tactic varies across habitats and can be affected by environmental fluctuations like season as well as a possible parental effect[7]. A decrease in food availibility leads to an increased number of migratory salmon, this speaks to the adaptive value and status determinant nature of salmon migration [8].

Why do the two tactics have those names?

During spawning, Territorial males try to dominate the area beside female's nests so that they can be the first the fertilize the eggs, however, Sneaker males are so small that they can actually get closer to females without territorial males noticing! [14]

 

 

salmonarrowontogeny

Image 1: high status fish stay in river

Image 2: low status fish go to sea

 

 


The learning explained...

2a. -It has been demonstrated that salmon primarily use olfactory cues for orientation once they have reached the proximity of their natal river. In order to do this, salmon have to imprint on the odors from the local geology and flora of their natal pond and use these olfactory memories years later when they return to spawn [4]. The process of this olfactory imprinting is intimately linked with hormone levels at different life stages. The parr stage starts when samon are about one year old when they begin actively feeding in fresh water; the change from the parr to smolt stage occurs when salmon are getting ready to go out to sea (either 2nd 3rd or 4th years). The transition from the parr stage to the smolt stage (migration phase) is accompanied by physiological changes, including increased levels of thyroid hormones that have been associated with imprinting. [5]

 

 

 

Take home message:

It is important to remember that these are pacific salmon so, if you are an animal behavior student living on the west coast, there have even been sightings of coho salmon in the reed lake. Pacific salmon even swim through the Willamette River! Their habitat ecompasses all our western coast and environment around us.

Critical Pacific Northwest salmon habitat extends as far inland as Idaho. Source: NOAA Special Projects.