Mullin, S. K., Taylor, P. J. & Pillay, N. 2004. Skull size and ... - Durban

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Mullin S. K. et al.
separate Dasymys species was recorded (e.g. Chitau,
Angola; Musser & Carleton 1993; Luluabourg,
Zaire; Crawford-Cabral 1986). Finally, after
consulting vegetation, geology, soil, altitude and
phytogeographic maps, the localities that were
represented by less than three individuals were
pooled into Operational Taxonomic Units (OTUs),
while respecting geographical barriers such as
mountain ranges and rivers, which represented
geographically close localities found in the same
biome type (after Taylor & Meester 1993; Table 1).
If a locality consisted of less than 3 individuals
and it was not possible to combine that locality
into an OTU, the data were treated separately. In
this case, the canonical scores of individuals were
projected onto the scores of the OTUs to produce
a comprehensive plot. Symbols were assigned to
species, subspecies or areas of interest in the diagrams
presented in the results section.
TRADITIONAL MORPHOMETRICS
Multivariate methods were employed on a dataset of
804 individuals. The character suite consisted of the
following 13 cranial characters (see Mullin et al.
2002): GSL-Greatest skull length; UTR-Crown
length of upper (maxillary) toothrow; PWM-Hard
palate width; NAS-Nasal width; ZYN-Zygomatic
arch width; FRO-Greatest internal diameter of zygomatic
arch; IOB-Least breadth of interorbital
constriction; FMW-Foramen magnum width;
UMW-Least width of zygomatic arch; ZPW-
Zygomatic plate width; GML-Greatest mandible
P R O O F
length; MTR-Mandibular tooth row; GHS-Greatest
height of skull. The dataset was normally distributed,
non-kurtotic, non-skewed and homoscedastic.
Only two of the localities examined in this study
(Limalunga, Zambia and Okavango-Omatako,
Namibia) had a large number of unbroken skulls
that could be used to examine non-geographic
variation. A previous study of non-geographic
variation (based on individuals from Limalunga,
Zambia only) revealed that specimens from ageclasses
III, IV, V, VI represent adult D. incomtus
individuals (Mullin et al. 2001) and that sexual
dimorphism is negligible in D. incomtus populations
(Mullin et al. 2001). The same analysis was
completed on individuals from Okavango-Omatako,
4
Namibia and produced the same results. In addition,
Carleton & Martinez showed that neither D. foxi
nor D. rufulus exhibited sexual dimorphism and
therefore the data for adult males and females
were pooled in the analyses presented in this study.
Standardised data were subjected to multivariate
analyses, including a principal component analysis
(PCA), a multi-group canonical variates analysis
(CVA), which tested multivariate differences
among OTUs and an unweighted pair-group
means with averages (UPGMA) cluster analysis (CA)
based on Euclidean distances. A CA was also used
to produce a phenogram of the distinct morphological
groups discerned in this study. The PCA and
CVA plots and CA phenograms for each subgroup
were all used to obviate bias possibly resulting from
the use of only one approach. Since the different
approaches provided similar results, we subjectively
chose scatterplots and phenograms for the results
section for ease of presentation. Although CA is
considered an exploratory method, we included
the phenograms since strong patterns were seen.
An Analysis of Variance (ANOVA) was completed
on morphologically distinct groups (see results
section) to determine significant differences in both
cranial and external measurements. A Student
Newman-Keuls (SNK) multiple range test was
used to examine inter-group variation. These tests
included the following additional characters to the
ones mentioned above: BBC-braincase breadth,
HB-head-body length (mm), TL-tail length (mm),
HF-hind foot length (mm), E-ear length (mm),
TOT-total body length (mm), M-Mass (g) and
HB/TL-head-body/tail ratio (mm). These characters
were not included in multivariate methods as
one (BBC) was highly correlated with other characters
used and others (HB, TL, HF, E, TOT, M and
HB/TL) had a large number of missing values.
All of the statistical analyses were undertaken
using the program NTSYS-pc (Rohlf 1996), except
for the ANOVA and Student Newman-Keuls
multiple range test which were done using Statistica
(StatSoft 2001).
GEOMETRIC MORPHOMETRICS
A 5mm Leica DC100 camera attached directly to
a PC was used to capture images of the dorsal and
MAMMALIA • 2004 • 68 (2)