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Patterns of geographic variation in Florida snakes / by Steven P. Christman.

About: The article was published on 1975-01-01 and is currently open access. It has received 8 citations till now.

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Summary

  • Changing sea levels, "Ocala Islands," Suwannee Straits and the like have all been cited as influencing the patterns of distribution and variation in Florida plants and animals.
  • Maps 26, 27, and 28 show the geographic variation as interpreted in the present study.
  • Maps 98, 99, and 100 show the geographic variation of this character in Florida E. guttata- Ventral check shape .
  • Maps 234 through 245 show the results of the variables examined.
  • Most of the geographic variation observed in Florida snakes is distributed along a north-south axis.
  • Darker shading represents generally lower values for supralabial pigmentation and higher values for keeling of the second scale row.
  • The disjunct nature of this pattern suggests a retention of ancestral character states in these regions while adaptation in geographically intermediate regions has led to partial differentiation.
  • The shape of the ventral spot was recorded, and assigned values from zero (slightly higher than wide) to five (as wide as the whole ventral scale).

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PATTERNS
OF
GEOGRAPHIC
VARIATION
IN
FLORIDA
SNAKES
By
STEVEN
P.
CHRISTIAN
A
DISSERTATION
PRESENTED TO THE
GRADUATE
COUNCIL
OF
THE
UNIVERSITY
OF
FLORIDA
IN PARTIAL
FULFILLMENT OF THE
REQUIREMENTS
FOR THE
DEGREE OF DOCTOR
OF
PHILOSOPHY
UNIVERSITY
OF
FLORIDA
1975

ACKNOWLEDGMENTS
During
the course
of
my
graduate
training at
the University
of
Florida
I have
received
financial support
from the
Society of
Sigma
Xi,
and I
held
a National Defense
Education Act
Fellowship for one
year.
Funds
for computer
analysis
were made
available
by the
North-
east
Regional Data Center. I
thank all those
people who
loaned me
specimens
or
data for
analysis
in
this study. I
especially
thank
my
wife, Sheila,
for financial,
moral and
physical help
in all
phases of
my
academic work.
n

TABLE
OF
CONTENTS
Page
ACKNOWLEDGMENTS ii
ABSTRACT
iv
INTRODUCTION
1
MATERIALS
AND METHODS
6
The
Problem of Samples and
Populations
8
The
Mapping Procedure 9
Multivariate Analysis 10
Comparison of Mapped Data 10
Geography
11
RESULTS
14
The
Species 15
The
Patterns 54
The
Correlations
59
DISCUSSION
331
Pattern
of
Variation 331
Phylogenetic Considerations 343
SUMMARY
371
APPENDIX
A
CHARACTERS
EXAMINED 373
B
ENVIRONMENTAL
VARIABLES EXAMINED
388
LITERATURE
CITED
389
BIOGRAPHICAL SKETCH
394
m

Abstract
of
Dissertation
Presented
to the
Graduate
Council
of
the
University
of Florida in
Partial
Fulfillment
of the
Requirements
for
the
Degree of
Doctor
of
Philosophy
PATTERNS
OF
GEOGRAPHIC
VARIATION IN
FLORIDA
SNAKES
By
Steven
P.
Christman
December,
1975
Chairman:
Archie
Carr
Major Department:
Zoology
I
analyzed
geographic
variation
in fifteen
species
of
Florida
snakes.
Machine-produced
contour maps
were
created for each
of
over
200
morphologic
variables
and 17
climatic
variables.
One
hundred
of
the maps
were
factor
analyzed,
and seven
major
patterns
of
geographic
variation
extracted.
These seven patterns
were
found to
account
for
over
60%
of the
information
contained in the
original
contour maps.
Each
of
the patterns of
geographic
variation can
be
explained
in terms
of natural
selection by
past or
present
environments.
Disjunct popu-
lations
showing phenetic
similarities
are the
result
of
an
earlier
widespread
phenotype
followed by
differentiation
in
geographically
intermediate
regions.
Recourse to
land
bridge
hypotheses
and retro-
gressive
evolution are
not necessary
to
explain
polytopic
phenotypes.
Correlations
between the
patterns of
variation
and
environment are
discussed,
but
experimental
verification of
cause and
effect
relation-
ships are
not
provided.
The
geographic
localities
of
primitive character
states
and/or primitive species
are not the
centers
of origin
for the
groups,
but are
considered
to
be areas
in
which evolution
has
proceeded
relatively
more slowly.
iv

INTRODUCTION
Darwin's
theory of
natural
selection
has as
its
keystone one
important
requirement:
variation.
Implicit in
any
interpretation
of
natural
selection as the
guiding
force
behind
organic evolution
is
the
assumption
that
organisms are
not all
alike.
The
members of a
population
of sexually-reproducing
plants
or
animals are
in fact
(except
for identical
twins) all
different,
both genetically
and
phenotypically.
Mutations and
recombinations
of existing
genes
insure
the
continuance
of this
variability.
1
Selection
acts on
the
differences
between
organisms by
eliminating
unfit phenotypes
(and
hence their
associated
genotypes) from
the reproductive
effort
of a
population.
However,
phenotypes which
are unfit in
one part
of a
species'
geographic
distribution
may be quite
fit in
another
region.
Thus
geographic
variation
in
selective pressures,
brought
about by
geographic
variation
in
environment,
predisposes
organisms to
vary geographically
in morpho-
logical,
physiological and behavioral
traits,
even within a
single
biological
species.
The
process of
speciation
begins when
differential selective
pressures act on populations of a
species
in remote parts
of
its
geo-
graphic range. Natural selection
creates
different phenotypes
in
response
to
these
different selective
regimes.
When the
degree of
But
see
Murray
(1972)
for a
discussion of
genetic diversity
maintained by natural selection.
1

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Journal ArticleDOI
TL;DR: It is now possible to identify phylogeographical lineages, delimit species using molecular and morphological data, and estimate their relationships in a single coherent set of analyses, allowing for more rapid and objective assessments of cryptic diversity at the species level.