Biology Reference
In-Depth Information
larval periods (
Wilbur, 1980
). Multiyear larval periods are simply not pos-
sible within the context of anuran life history strategies that depend upon
seasonally limiting resources. In contrast, salamander larvae present greater
developmental flexibility to utilize more permanent aquatic habitats by
extending the length of the larval period, indefinitely in the case of some
paedomorphic species.
2. PAEDOMORPHOSIS AND SALAMANDER LIFE HISTORY
VARIATION
Salamander life histories can be broadly classified into three categories:
biphasic, paedomorphic, and facultative (
Table 8.1
). These are simply cat-
egories of convenience and do not adequately treat the continuum of life
histories represented by each class, and the possibility of different genetic,
developmental, and physiological bases within classes. Species with biphasic
life histories almost invariably undergo a metamorphosis. This life history
strategy is viewed as an adaptation to exploit transient opportunities for larval
Table 8.1 General characteristics of metamorphic, paedomorphic, and facultative
salamander life histories
Metamorphic
Paedomorphic
Facultative
Associated with ephemeral
aquatic habitats
a
Associated with stable
aquatic habitats
b
Associated with landscapes
with ephemeral and stable
aquatic habitats
c
Individuals almost
invariably metamorphose
in nature
a
Individuals rarely/never
metamorphose in nature
b
Populations often vary in
the proportion of
individuals that
metamorphose or exhibit
paedomorphosis
c
Generally reach sexual
maturity after
metamorphosis
c,d
Reach sexual maturity
while remaining in larval
aquatic habitat
d,e
Timing of sexual maturity
may vary between
metamorphic and
paedomorphic individuals
of the same population
(but not always)
f-h
Thyroid hormones cause
morphological changes
(e.g., gill reduction, larval
to adult skin changes, tail
fin reduction, etc.)
i
Individuals may or may
not respond to thyroid
hormone with
morphological signs of
metamorphosis
i
Thyroid hormones cause
morphological changes
j,k
