Nirel Marofsky
Animal Behaviour
Coursera / U of Melbourne
7 July 2014
I see you, I smell you, I love you: zebrafish kin recognition
An evolutionary trait seen in many animal species, cooperative behavior requires some
degree of restriction in order to be an evolutionarily stable strategy. When it comes to
cooperation between an individual and its kin, the ability to distinguish its kin from
nonkin is an important one. This ensures that the individual is not wasting resources on
conspecifics (members of the same species) that don’t share its genes.
Phenotype matching is a social-recognition mechanism by which animals learn early in
life which phenotypes are exhibited by their kin. They create an olfactory, visual or
acoustic template that helps them later in life discriminate between kin and nonkin.
Think of it as a blueprint: Individuals may recognize familiar traits in kin because the kin
hold similar traits as those in their mental blueprint -- indicating that they are, by some
degree, related. Conversely, they may find certain traits unfamiliar and categorize
conspecifics with that trait as unrelated.
Very little is known about how animals create a phenotype-matching template to begin
with, but new research is beginning to investigate this process. Studies using zebrafish
have found that larvae can recognize kin by olfactory cues (using a phenotype-matching
process) and later in life prefer to associate with kin, based on those cues.
One 2013 study published in Animal Behavior examined whether additional visual cues
(as well as olfactory cues) are involved in the imprinting, or blueprint-forming, stage in
zebrafish.
At days 5-7 post fertilization of zebrafish eggs, researchers introduced olfactory cues to
the eggs by replacing some tank water with water from either their kin group or nonkin
group. Then, they introduced visual cues to about half the fish that had received water
from the kin group tank. They did this by placing beakers containing the fish in glass
bowls in which other conspecific larvae were present. Another variable researchers were
interested in testing was whether visual imprinting occurs in the same time window as
olfactory imprinting. In order to test this, the fish were exposed to visual cues over the
course of a few days (some earlier, some later).
Next came the test: Would the fish that had been exposed to kin olfactory cues
recognize and prefer kin to nonkin? Would those that had been exposed to nonkin cues
prefer nonkin, or would some underlying genetic preference cause them to still prefer
kin?
Results showed that larvae (now at 8-12 weeks post fertilization) able to choose between
water from unfamiliar kin and water from unfamiliar nonkin preferred the water from kin.
However, the larvae only recognized kin when they had, earlier in life, experienced a
combination of olfactory and visual cues of the kin. Mere exposure to one or the other
was found to be insufficient.
Researchers also wondered if there is a critical period for visual imprinting – a period of
time during which larvae must be exposed to visual cues in order for visual imprinting to
occur. As it turns out, one does exist. Only larvae that had been visually exposed to kin
on day 5 post fertilization showed a significant preference for kin odor.
Finally, it turns out that even when exposed to olfactory and visual cues during the
critical period, larvae still do not imprint on nonkin. This suggests that some genetic
predisposition to recognize kin may come into play.
Two questions arise as a follow-up to this study:
1. Why are visual cues required for imprinting when later in life kin can be recognized by
olfaction alone?
This need for the combination of both visual and olfactory cues probably keeps larvae
from imprinting on the wrong cues.
2. If a predisposition to attend to visual and olfactory cues from kin already exists, why is
imprinting necessary?
The genetic component to kin recognition likely prevents larvae from imprinting on
conspecific nonkin, while larvae may learn phenotypes associated with kin during visual
imprinting that are necessary to identifying kin during later olfactory imprinting.
…So what? Why are the findings of this study important in the greater context of
understanding animal behavior? In short, we now know that zebrafish have evolved
sophisticated strategies to distinguish even unfamiliar kin from non-kin. This changes the
way individuals cooperate with one-another, making cooperation with kin a worthwhile
one because it ensures that doing so will eventually lead to the propagation of their
genes. The study demonstrates another fascinating example of the way animals learn and
interact.