Results
Shape and size
The first two principal component (PC) axes of humerus shape explained
34.5% (PC1) and 13.7% (PC2) of the observed shape variation (Fig.2).Echinotriton andersoni occupied a slightly different morphospace
than Tylototriton , although there was some overlap especially
with T. uyenoi and T. kweichowensis . Generally shape
changes on the first PC corresponded to humerus thickness, representing
thick humeri for negative PC1-scores and thin humeri for positive
PC1-scores. The second PC corresponded to the thickness of the middle
part of the humerus and the orientation of the Crista dorsalis humeri.
According to that, Echinotriton exhibits more robust humerus
shape compared to Tylototriton , T. taliangensis exhibiting
the most gracile humerus. PC1 explained 20.1% and PC2 11.6% of the
observed shape variation (Fig.3) of the PCA of cranial shape.
Echinotriton was well separated from all other species of the genusTylototriton , but T. asperrimus showed the highest
similarity to Echinotriton . Among Tylototritonspp., T. kweichowensis occupied the most distinct
morphospace (Fig.3). Echinotriton -skull shape (positive PC1
scores) showed a robust skull with a strong maxillary connection to the
quadrate and pterygoid. The snout was more pointed and with lower and
anteriorly ranging nasals than in all Tylototriton . The second PC
axis corresponds to the height of the fronto-squamosal arch in relation
to the skull roof, the posterior extent of the squamosal and the occiput
width.
Procrustes ANOVA revealed a strong allometric effect both in humerus and
cranial shape (Tab.1). The allometric trajectories differed
interspecifically (Fig.4) but not intersexually (Fig.5), indicated by a
significant interaction of size and species but not size and sex
(Tab.1). In allometric trajectories of the humerus, T. uyenoi andT. shanorum exhibited a different direction (Fig.4a) while in
cranial shape, especially T. asperrimus showed a different
pattern (Fig.4b). Accounting for sexual allometry only, generally large
specimens exhibited a thinner humerus (Fig.5a) whereas in the cranium
the dorso-lateral ridge became more elaborate and the connection of the
maxillary with the pterygoid and quadrate turned more pronounced and the
quadrate shifted more posteriorly (Fig.5b).
Sexual dimorphism
The Procrustes ANOVA revealed different interspecific patterns of sexual
dimorphism, indicated by the significant interaction of species and sex
(Tab.1). In order to test our hypothesis that the mating mode might
explain different shapes, we carried out additional Procrustes ANOVAs on
shape including mating mode as explanatory variable. The mating mode
explained a significant amount of variation, with and without log(CS) as
covariate, in the humerus and cranium (Tab.2). In general the species
applying a circle dance had more robust and thicker humeri including an
elaborated crista dorsalis and a higher crista ventralis compared to
species employing a ventral amplexus (Fig.6). The cranium of circle
dancers was wider at its occiput, exhibited a shorter frontal arch, less
connection between the maxillary bone and the quadrate and pterygoid, a
higher snout tip, longer vomerine tooth rows and more distal internal
nares. The interaction term of mating mode with sex was significant in
cranial shape when accounting for size as covariate (Tab.2 b),
indicating different SShD-trajectories between the two different mating
modes among identical size classes (Tab.2 b, d). We found no indication
for different SShD-trajectories between mating modes in humerus shape.
As the analysis indicated different SD-trajectories, we performed a
trajectory analysis with sex as grouping factor to figure out and
illustrate shape changes in different trajectories across male and
females between species (Fig.7, 8). Echinotriton andersoni did
not differ markedly from Tylototriton spp. In the latter, cranial
SD-trajectories showed contrary directions between some species (Fig.8).
Pairwise species-comparison revealed only one pair of species (T.
asperrimus : T. taliangensis ) with an alpha-level below 5% and
six species pairs below 10% for humerus SShD patterns and two species
pairs below 5% and 10% (T.himalayanus : T. kweichowensisand T. shanjing : T. verrucosus ), respectively in SShD
patterns of cranium shape (Appendix Tab. A2). To illustrate the
different male to female SD-trajectories we plotted TPS-grids for
amplecting T. himalayanus and circle dancing T.
kweichowensis , both species deviating strongly in SD-trajectories
(Fig.7, 8). In T. himalayanus, the humerus turned thinner in the
middle part while the distal end was more twisted in females. Further,
the crista ventralis was slightly more pronounced in females. InT. kweichowensis especially the crista dorsalis appeared more
elaborate in females (Fig.7). Male to female shape changes in cranium
morphology of T. himalayanus included an elaborated squamosal
bony ridge, a posterior shift of the quadrate, a stronger connection of
the maxillary with quadrate and pterygoid, lower nostrils and a shorter
frontal arch. In T. kweichowensis cranial shape changes between
sexes were much less pronounced and comprised a posterior shift of the
quadrate and a slightly posteriorly shift of the palatal fissure between
the vomers. Shape changes from the mean shape to male and female shape,
respectively, were similar in the humerus, but differed between males
and females in their extent, whereas cranial shape changes to the mean
deviated between sexes of T. himalayanus but not in T.
kweichowensis (Fig.9).
Procrustes ANOVA on humerus and cranium log(CS) of species and sex
revealed interspecific but also intersexual differences in size (Tab.3
a, b). Further, SSD differed between species indicated by a significant
interaction of species and sex (Tab.3 a, b) . Analysis of the effect of
mating mode on size yielded no general size differences in the humerus
between dancing and amplecting species but the interaction of sex and
mating mode was close to significance level (Tab.3 c) which would
indicate differences of SSD patterns between mating modes. Cranial size
and SSD-patterns do differ between mating modes (Tab.3 d). Pairwise
comparisons showed that male and females of amplecting species differ
(Z=2.04, p=0.019) in cranial size while this is not the case for circle
dancers (Z=-1.76, p=0.96). For the humerus, the same pattern applies but
the effect size between amplecting males and females is only close to
significance (Z=1.53, p=0.066).