98
The Biology of Sea Turtles, Vol. II
taste. The same group of researchers also tested for olfaction by temporarily inducing
anosmia (loss of the sense of smell) in their subject animals (Manton et al., 1972b).
By exposing the internal nares to ZnSO4, while ensuring that the oral cavity did not
come into contact with the chemical, they were able to temporarily render the
olfactory sense inoperative. After treatment with ZnSO4, the turtles were unable to
distinguish the chemical from the control, indicating that these animals were using
olfaction and not taste for chemoreception. Chemosensory acuity was also estimated
from the data. These turtles were found to be able to detect chemicals at a relatively
low level; the threshold occurred at concentrations of approximately 5 ¥ 10–6 to 5
¥ 10–5 M (Manton et al., 1972b).
3.4.3 CHEMICAL IMPRINTING HYPOTHESIS
Chemoreception has long been proffered as the basis for orientation and longdistance migration by sea turtles (Koch et al., 1969; Manton, 1979; Owens et al.,
1982). Though there appears to be very little evidence that sea turtles use chemoreception to navigate long distances, some research has been performed on the role
that chemical cues play in the identification of a natal beach by adult nesting female
sea turtles. Grassman et al. (1984) explored the theory that these animals can retain
olfactory information gathered from the nesting beach and surrounding waters as
hatchlings (that is, they become imprinted) and store this information for many years
until they return as nesting females. They used Kemp’s ridley (Lepidochelys kempii)
hatchlings collected from Rancho Nuevo, Mexico, during oviposition and moved
the eggs to Padre Island National Seashore in Texas. The eggs were incubated in
Padre Island sand until hatching; hatchlings were allowed to perform their natural
crawl across the sand and enter the surf zone. These animals were recaptured, and
raised in tanks. At 4 months old, these same turtles were tested in a multipartitioned
arena. When placed in this arena, the turtles could choose among a section containing
a solution of Padre Island sand and water; a section containing a solution of
Galveston, TX, sand and water; and two sections containing untreated solutions.
Turtles spent significantly more time in the Padre Island compartment than either
the Galveston or untreated sections. Although the turtles entered the Galveston
compartment frequently, they did not stay in the compartment any longer than when
the turtles had entered the untreated sections. The authors interpreted this behavior
as a preference for the Padre Island treatment (Grassman et al., 1984).
A second experiment investigated the behavioral responses of sea turtles exposed
to two chemicals, morpholine and 2-phenylethanol (Grassman and Owen, 1987).
These chemicals were chosen because they are not naturally occurring, yet from the
previous operant conditioning studies (Manton et al., 1972b), the researchers knew
that green turtles could detect low concentrations of similar organic chemicals. Eggs
were collected; the artificial nest environment was moistened with either one of the
two chemicals or with untreated water. When the sea turtles hatched, they were
placed in holding tanks that were also treated with the same chemical as the nest
for 3 months. The turtles were segregated into four treatments: (1) both the nest and
the water were treated with a chemical, (2) only the nest was treated, (3) only the
water was treated, and (4) both the nest and water were untreated. After 2 additional
1123 book.book Page 98 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
taste. The same group of researchers also tested for olfaction by temporarily inducing
anosmia (loss of the sense of smell) in their subject animals (Manton et al., 1972b).
By exposing the internal nares to ZnSO4, while ensuring that the oral cavity did not
come into contact with the chemical, they were able to temporarily render the
olfactory sense inoperative. After treatment with ZnSO4, the turtles were unable to
distinguish the chemical from the control, indicating that these animals were using
olfaction and not taste for chemoreception. Chemosensory acuity was also estimated
from the data. These turtles were found to be able to detect chemicals at a relatively
low level; the threshold occurred at concentrations of approximately 5 ¥ 10–6 to 5
¥ 10–5 M (Manton et al., 1972b).
3.4.3 CHEMICAL IMPRINTING HYPOTHESIS
Chemoreception has long been proffered as the basis for orientation and longdistance migration by sea turtles (Koch et al., 1969; Manton, 1979; Owens et al.,
1982). Though there appears to be very little evidence that sea turtles use chemoreception to navigate long distances, some research has been performed on the role
that chemical cues play in the identification of a natal beach by adult nesting female
sea turtles. Grassman et al. (1984) explored the theory that these animals can retain
olfactory information gathered from the nesting beach and surrounding waters as
hatchlings (that is, they become imprinted) and store this information for many years
until they return as nesting females. They used Kemp’s ridley (Lepidochelys kempii)
hatchlings collected from Rancho Nuevo, Mexico, during oviposition and moved
the eggs to Padre Island National Seashore in Texas. The eggs were incubated in
Padre Island sand until hatching; hatchlings were allowed to perform their natural
crawl across the sand and enter the surf zone. These animals were recaptured, and
raised in tanks. At 4 months old, these same turtles were tested in a multipartitioned
arena. When placed in this arena, the turtles could choose among a section containing
a solution of Padre Island sand and water; a section containing a solution of
Galveston, TX, sand and water; and two sections containing untreated solutions.
Turtles spent significantly more time in the Padre Island compartment than either
the Galveston or untreated sections. Although the turtles entered the Galveston
compartment frequently, they did not stay in the compartment any longer than when
the turtles had entered the untreated sections. The authors interpreted this behavior
as a preference for the Padre Island treatment (Grassman et al., 1984).
A second experiment investigated the behavioral responses of sea turtles exposed
to two chemicals, morpholine and 2-phenylethanol (Grassman and Owen, 1987).
These chemicals were chosen because they are not naturally occurring, yet from the
previous operant conditioning studies (Manton et al., 1972b), the researchers knew
that green turtles could detect low concentrations of similar organic chemicals. Eggs
were collected; the artificial nest environment was moistened with either one of the
two chemicals or with untreated water. When the sea turtles hatched, they were
placed in holding tanks that were also treated with the same chemical as the nest
for 3 months. The turtles were segregated into four treatments: (1) both the nest and
the water were treated with a chemical, (2) only the nest was treated, (3) only the
water was treated, and (4) both the nest and water were untreated. After 2 additional
1123 book.book Page 98 Monday, November 11, 2002 11:11 AM