|Abstract or Summary
- The results of my research suggest that tadpoles of the Western
toad (Bufo boreas) and the Cascades frog (Rana cascadae) display an
alarm response to chemicals from injured conspecific tadpoles.
Furthermore, results suggest that the Bufo boreas alarm response can
be elicited by a natural predator when it feeds on a conspecific
tadpole and that this response decreases the capture efficiency of
Initially, the alarm responses of B. boreas and R. cascadae were
elicited by extracts containing chemical cues from injured
conspecifics. B. boreas tadpoles increased their activity and avoided
areas into which conspecific extracts were added. The activity and
avoidance responses were not elicited by extracts of non-conspecifics
or by a control solution of water. R. cascadae tadpoles did not
exhibit the avoidance response but did increase activity when a
conspecific extract was added. An extract of non-conspecifics or a
control solution of water did not elicit these reactions.
In the second part of my study, I tested the hypothesis that a
natural predator could injure tadpoles and release the alarm
substance. Results suggest that while capturing and eating a Bufo
tadpole, the giant waterbug ( Lethocerus americanus) caused enough
damage to elicit the alarm reaction in conspecific tadpoles. Test
tadpoles significantly increased their activity over control levels
and avoided the side of the tank where a feeding predator was located
in a visually isolated but interconnected container. When a nonconspecific
tadpole (Pacific treefrog, Hyla regilla) was used as prey,
B. boreas tadpoles did not avoid the side where the predator fed,
although activity did increase. This increase in activity may have
been due to agitation caused by the presence of predators.
I then examined two possible functions of the alarm substance:
direct predator deterrence and warning of conspecifics. I found that
dragonfly naiads (Aeshna umbrosa), another natural predator, neither
moved away from an area into which a Bufo extract was introduced nor
moved away when a control solution was introduced, suggesting that the
alarm substance in extract form may not directly deter predators.
If, however, the alarm substance warns conspecifics, the resulting
alarm response should affect the capturing efficiency of a predator. In fact, Aeshna naiads took significantly longer to catch B. boreas
tadpoles after the introduction of a Bufo alarm substance extract than
after the introduction of a control solution. For aquatic systems,
this is the first evidence that suggests an alarm reaction elicited by
a chemical substance may protect individuals from predation.