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. 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 double-stranded 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 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.