Results
Breeding and Egg development. The proportion breeding was
significantly affected by pairing (Fisher’s Exact Test, p <
0.001). Pairings with A. texanum females bred 100% of the time
and pairings with A. barbouri mothers bred 33% of the time
(Figure 3). Egg laying locations or oviposition locations were also
significantly affected by maternal species (Fisher’s exact test,
p=0.0004). The paternal species did not have a significant effect on
oviposition location (Fisher’s exact test, p=0.1906). Only A.
barbouri laid their eggs underneath rocks, meanwhile only A.
texanum scattered their eggs loosely throughout the aquarium (Figure
4.). Both readily laid eggs attached to vegetation. Oviposition began
within 24 hours of pairing and all pairs that oviposited completed
oviposition within 72 hours. Time of embryonic period was significantly
affected by genotype (one-way ANOVA, F = 25.09, p < 0.001),
however, only A. barbouri significantly differed from the other
genotypes in post-hoc t-tests (Supp. Table 1.). A. barbouri had a
much slower rate of egg development, nearly doubling the time of the
other three genotypes (Figure 3.). The number of larvae per clutch was
affected by genotype (one-way ANOVA, F = 5.453, p = 0.009, Table 1.),
however, genotypes with the same maternal species did not significantly
differ. Pairings with A. texanum mothers had nearly double the
number of eggs than those genotypes with A. barbouri mothers
(Figure 3.). Differences in initial larval size between genotype pairs
were significant (one-way ANOVA, F = 13.08, p = 0.001, Table 1.), withA. barbouri♀ x A. barbouri♂ and A. barbouri♀ x A. texanum
♂ larvae being significantly larger than A. texanum♀ x A.
texanum♂ and A. texanum♀ x A. barbouri♂ larvae. No differences
in initial larval size were seen between hybrid and non-hybrid genotypes
with the same maternal species (Figure 3.). Pigmentation was
significantly affected by genotype (one-way ANOVA, F = 49.82, p
< 0.001, Table 1.), however, the effect of clutch was
significant, indicating significant differentiation between clutches (F
= 7.01, p < 0.001, Table 1.). Only A. barbouri♀ x A.
barbouri♂ larvae significantly differed between the genotypes, being
much darker than the other genotypes. The hybrids were intermediate in
pigmentation between A. barbouri♀ x A. barbouri♂ and A.
texanum♀ x A. texanum♂ but were slightly more similar to their maternal
parents.
Laboratory and Mesocosm Fitness Experiments. Size at
metamorphosis in the laboratory was significantly affected by genotype
(one-way ANOVA, F = 12.593, p < 0.001, Table 2.), and results
were not influenced by the effect of clutch (p-value 0.203, Table 2.).
The largest genotype at metamorphosis was A. texanum♀ x A.
texanum♂ , followed by A. barbouri♀ x A. texanum ♂ , and the
smallest genotype was A. barbouri♀ x A. barbouri♂ (Figure 3.).
The effect of genotype on time to metamorphosis of laboratory raised
larvae was significant (one-way ANOVA, F = 29.841, p < 0.001,
Table 2.). On average A. texanum♀ x A. texanum♂ metamorphosed
40-60 days later than the other genotypes, which all metamorphosed at
similar times (Figure 5.). Laboratory survival to metamorphosis was not
significantly affected by genotype (one-way ANOVA, F = 0.853, p = 0.477,
Table 2.), and results again were not influenced by the effect of clutch
(F = 1.758, p = 0.165, Table 2.). The lowest survival was in A.
texanum♀ x A. texanum♂ , which significantly differed from the other
genotypes, all which had similar survival (Figure 5.). Time to
metamorphosis, size at metamorphosis and survivorship to metamorphosis
were all correlated, with increasing time leading to increased size and
lower survivorship.
In the mesocosm experiment, size at metamorphosis was significantly
affected by genotype (one-way ANOVA, F = 5.514, p = 0.008, Table 2.),
and clutch effect did not influence these results (p = 0.132, Table 2.).
The largest genotype was A. texanum♀ x A. texanum♂ followed byA. barbouri♀ x A. texanum ♂ , with the smallest genotype beingA. barbouri♀ x A. barbouri♂ (Figure 5.). Time to metamorphosis of
mesocosm raised larvae was significant (one-way ANOVA, F = 23.116, p
< 0.001, Table 2.). The A. texanum♀ x A. texanum♂ andA. texanum♀ x A. barbouri♂ genotypes took a much longer time to
metamorphose than A. barbouri♀ x A. barbouri♂ and A.
barbouri♀ x A. texanum ♂ (Figure 5.). Clutch effect on time to
metamorphosis was also statistically significant (one-way ANOVA, F =
5.042, p = 0.007, Table 2.), indicating variation between clutches
within genotypes, albeit the effect of clutch was much weaker than that
of genotype. Additionally, survival to metamorphosis was significantly
affected by genotype (one-way ANOVA, F = 8.154, p < 0.001,
Table 2.), with no statistically significant effect from clutch
variation influencing this result (F = 1.25, p = 0.312, Table 2.).Ambystoma texanum♀ x A. texanum♂ and A. texanum♀ x A.
barbouri♂ both had significantly fewer individuals surviving to
metamorphosis then the A. barbouri maternal parent genotypes. The
survival differences were extreme, with the A. barbouri maternal
genotypes having survivorship more than twice the amount of A.
texanum maternal genotypes (Figure 5.).