Contributions to Zoology, 74 (3/4) (2005)J. Alexandrino; N. Ferrand; J.W. Arntzen: Morphological variation in two genetically distinct groups of the golden-striped salamander, Chioglossa lusitanica (Amphibia: Urodela)

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Results

Morphometrics

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The first and the second PCA axes explained, respectively, c. 47% and c. 20% of the variance, for both males and females (Table 1). The first axis had high factor loadings for limb and digit variables (0.76 to 0.89). The second axis had high loadings for head length and head width (0.54 to 0.84). Hence, the variation observed for head shape and the size of the extremities was largely independent. Mean population factor scores for the first axis increased from south to north, reflecting an increase in relative size of limbs and digits (Figs. 3 and 6). Mean factor scores for the second axis did not show any readily interpretable geographic pattern (Fig. 3).

Colour pattern

Colour pattern type 2 was the most common one in all examined populations, except for populations 10 and 11 in which type 3 was most frequent (Fig. 1).

FIG2

Fig. 3. First two axes from PCA of six size adjusted morphometric variables in 18 populations of Chioglossa lusitanica. Population centroids and minimum convex polygons enclosing individual factor scores for group 1 and group 2 populations. Open dots and dashed polygon lines represent southern ‘group 1’ populations; solid dots and uninterrupted polygon lines represent northern ‘group 2’ populations.

Type 3 was present in all populations south of the Douro River. Other pattern types were present in some populations and not in others. Types other than type 2 were absent north of the Douro, with the exception of type 4 that was present, albeit at low frequency, in populations 12, 13 and 20.

Testing causal hypotheses

Scores on the first PCA axis were significantly associated with geographic distance, group membership (Table 2) and latitudinal distance (Fig. 5). Scores on the second axis were not associated with either of the independent variables (Table 2).

FIG2

Fig. 4. Means and standard deviations for the a posteriori probability (P) of classification of individuals in each population to northern group 2, from Discriminant Analysis of six size adjusted morphometric variables in 18 populations of Chioglossa lusitanica.

FIG2

Fig. 5. Regression of mean factor scores of the fi rst Principal Component axis of 18 populations of female Chioglossa lusitanica against distance along a south-north axis.

Classification of individuals (both females and males) in group 2, following DA, increased gradually from south to north (Fig. 4). In females, head length and head width were associated with geographic distance and group membership, respectively. Size of the extremities was associated with geographic distance, with the exception of FLL# in males. Digit length and HLL# in males were also associated with group membership. Colour pattern was associated to neither geographic distance or group membership. Morphometric variability was not associated with any of the formulated independent variables (Table 3). Colour pattern variability was associated with hybridity and not with geographic distance or heterozygosity. Additionally, a trend was observed for colour pattern variability to decrease from south to north in group 2 populations (Fig.1).

 

Table 2: Partial Mantel test results for association between morphological differentiation across 18 populations of Chioglossa lusitanica versus geographic distance and group membership (see text for details). Dependent variables are A) top panel, the first and second PCA-axis and B) lower panel, individual size adjusted (#) morphometric variables and colour pattern.

Casual hypothesis

(independent variables)

Morphological distance

Geographic

Group

(dependent variable)

distance

Membership

A)

PCA 1 (females)

***

**

PCA 1 (males)

*

***

PCA 2 (females)

ns

ns

PCA 2 (males)

ns

ns

B)

HL# (females)

*

ns

HL# (males)

ns

ns

HW# (females)

ns

**

HW# (males)

ns

ns

FLL#(females)

***

ns

FLL (males)

ns

ns

HLL# (females)

***

ns

HLL# (males)

*

*

TFL (both sexes)

*

***

FTL (both sexes)

**

***

Colour pattern (both sexes)

ns

ns

ns – not significant, * - p<0.05,** - p<0.01, *** - p<0.001.

 

Table 3: Partial Mantel test results for association between morphological variability across 18 populations of Chioglossa lusitanica versus geographic distance, heterozygosity and hybrid versus non-hybrid population status.

Causal hypothesis

Morphological

(independent variables)

variability distance

Geographic

Heterozygosity

Hybridity

(dependent variable)

distance

PCA1 (females)

ns

ns

ns

PCA1 (males)

ns

ns

ns

PCA2 (females)

ns

ns

ns

PCA2 (males)

ns

ns

ns

Colour pattern

(both sexes)

ns

ns

**

ns - not signifi cant, ** - p<0.01