December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
Intraspecific Cytotype Variation and Conservation:
An Example from Phlox (Polemoniaceae)
Shannon D. Fehlberg
Desert Botanical Garden, Phoenix, AZ
and Carolyn J. Ferguson,
Herbarium and Division of Biology, Kansas State University, Manhattan, KS
Abstract. Information on genetic structure in rare plants, such as patterns of genetic diversity, differentiation and
gene flow, is useful when planning management strategies for conservation. However, few studies of genetic structure
in rare plants include an investigation of intraspecific cytotype variation. A number of reviews have suggested
that cytotype variation, or variation in chromosome structure or number, may be more widespread in natural populations
than previously thought. A recent review of federally listed plant species found that 75% of species belonged to
genera exhibiting both interspecific and intraspecific cytotype variation. Cytotype variation among populations of
rare plants raises intriguing questions about the origin(s), extent, evolutionary relationships, and ecological differentiation
of various cytotypes. While traditional cytological methods may not be feasible for population level sampling,
advances in the accuracy and cost of flow cytometry now make examination of intraspecific cytotype variation possible.
We initiated an investigation of cytotype variation in the genus Phlox (Polemoniaceae) using flow cytometry.
Phlox comprises ca. 65 species in North America and includes many poorly studied endemic taxa in the western
United States. Our results indicate noteworthy variation in chromosome numbers (ploidy level) across a subset of
western taxa. A detailed study of two endemic species of conservation concern, P. amabilis and P. woodhousei, revealed
that these species are made up of diploid, tetraploid and hexaploid populations. Ongoing analyses suggest that
these populations are spatially, ecologically, and genetically differentiated. These results caution against the common
assumption of homoploidy of species based on limited data and indicate the value of incorporating an understanding
of cytotype variation into conservation biology studies.
The interdisciplinary field of conservation biology
aims to provide the knowledge and tools necessary for
the long-term preservation of biodiversity. Studies of
population genetics are one important source of information
for conservation biology. These studies can provide
basic information about populations of rare plants
such as levels of genetic variation, the distribution of
genetic variation within and among populations, the degree
of population fragmentation and isolation, the patterns
of historical and contemporary gene flow, the levels
of inbreeding, the effective population size, the presence
of taxonomic distinctiveness, and the occurrence of
hybridization (Booy et al. 2000; Ellis and Burke 2007;
Murray and Young 2001). Ultimately, this basic information
can be combined with other sources of data to
form more effective conservation strategies.
One component of genetic variation that is often
overlooked in studies of rare plants is intraspecific cytotype
variation (De Lange et al. 2008; Severns and Liston
2008). Intraspecific cytotype variation ranges from
chromosomal inversions and translocations to variation
in the number of whole genomes present (polyploidy).
Recent reviews have suggested that intraspecific cytotype
variation may be more widespread in natural plant
populations than previously thought (Soltis et al. 2007;
Suda et al. 2007). It may also be widespread in populations
of rare, threatened and endangered plants. A survey
of cytotype variation in 416 US federally listed
plant taxa found that cytotype data were available for
only 182 of these taxa (44%). Of these 182 taxa, 158
belonged to genera with interspecific cytotype variation
(87%; New World congeners with aneuploidy or polyploidy),
and 121 belonged to genera with at least one
taxon showing intraspecific cytotype variation (66%;
Severns and Liston 2008). Intraspecific cytotype variation
can be important when planning conservation
strategies because it has the potential to affect patterns
of genetic diversity and gene flow. Knowledge of such
variation may also be important for clarifying taxonomy,
identifying unique evolutionary lineages (perhaps
accompanied by ecological differentiation), and determining
appropriate populations for reintroduction or
augmentation (De Lange et al. 2008; Murray and Young
2001; Severns and Liston 2008).
Recent advances in the application of flow cytometry
to evolutionary and population biology studies now
make the assessment of cytotype variation across large
taxonomic and spatial scales possible (Kron et al. 2007).
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