Download Aspidoscelis tesselata

Example of Herpetological Research in
Colorado
BL/ENVS 476: Colorado Flora and Fauna
September 19, 2011
A Fundamental Problem
• Sexual reproduction is predominant in vertebrates
• The common perception is that long-term evolutionary
success is based on phenotypic variability generated by
genetic recombination.
• But there are many parthenogenetic lizards that exhibit
ecological success; e.g., Aspidoscelis tesselata.
• Alternatives to sexual reproduction in vertebrates:
• Hybridogenesis and gynogenesis: in a few fish species
Parthenogenesis: in a few lizard species
• The purpose of this research was to test the idea that genetic
recombination is critical for phenotypic variation, using
parthenogenetic and sexual species of the lizard genus
Aspidoscelis.
A. Aspidoscelis marmorata
B. And C. A. gularis septemvittata
D. A. tesselata E (2n)
F. A. tesselata C
E. A. tesselata D
G. A. sexlineata
H. A. neotesselata (3n)
How do you reproduce without males?
• 1. Premeiotic doubling of chromosome number
– DNA synthesis
– A. tesselata: 46 single-stranded chromosomes (46 DNA molecules)
– Endoreplication  46 double stranded chromosomes
– Centromeres separate: 92 single-stranded chromosomes
• 2. Provide each chromosome with a genetically identical synaptic partner.
– DNA synthesis
– 92 single-stranded chromosomes  92 double-stranded
chromosomes.
• 3. Undergo the two meiotic divisions as found in sexual species.
– Synapsis and crossing over with “sister” (identical) chromosomes
• 1st division: 92 double-stranded chromosomes /cell  46 doublestranded chromosomes/cell
• 2nd division: 46 double stranded chromosomes/cell  46 single
stranded chromosomes/cell
• One becomes an ovum. genetically identical with mother
Patterns of Morphological Variability
• 1. Among “uniclonal” and “multiclonal” groups of two color pattern
classes of A. tesselata
– Multiclonal = more than one allele for a particular gene locus
– Glucose-6-phosphate isomerase (GPI)
– Multiclonal: GPI ab and GPI ac
– Uniclonal: GPI ac
• 2. Between each of four geographically disjunct groups of A. tesselata and
a sympatric sexual species
– Controlling for environmental effects on phenotypic variation
• 3. Among the four species
– Can the variability of the parthenogenetic species exceed the
variability of a sexually reproducing species?
• The phenotypic characters used are quantitative: GAB, FP, COS, LSG, SDL
• Meristic characters: counts
The pattern of variability has to be simplified
Done with multivariate statistics
Principal components analysis
Uses variance/covariance relationships among characters
Establishes coefficients to multiple times the values of the original characters
New variables are produced called principal components
Linear compounds of the original meristic character scores and coefficients
Concentrate as much of the variation of the original variables in a reduced number
of new variables: principal components.
Each specimen has score for principal component 1 and principal component 2.
Scores are plotted to show patterns of variation.
Variances of the principal component scores can be compared for relative
variability.
Do “multiclonal” groups A. tesselata express greater variability than “uniclonal” groups?
Multiclonal: more than
one GPI allele
Uniclonal: one GPI allele
Example of verification
Are differences in phenotypic
variability related to reproductive mode?
Are differences in phenotypic
variability related to reproductive mode?
How does A. tesselata rank on a scale of relative variability
with sexual A. sexlineata, A. marmorata, and A. gularis septemvittata?
Conclusions
• Aspidoscelis tesselata is organized as a collection of
independent mother-daughter arrays.
• Cohesiveness achieved by ecological constraints.
• This would mean that the relative phenotypic variability of a
particular parthenogenetic groups should not be predictable
by reproductive mode, color pattern class, or geographic
location.
• This was confirmed by the present study.
• Presumably, phenotypic variation increases as development is
variously modified in clones produced by random mutation.