 |
| |
Postdoctoral Research: Sex Ratio Variation
in Tigriopus californicus.
Advisor: Dr.
Brad Anholt, Director
BMSC, University of Victoria
The harpacticoid copepod, Tigriopus californicus,
lives in the splash zone above high tide. Field work on Tigriopus has shown that the sex ratio (proportion of males and females) in natural
populations often deviates from 50:50. Fifty years ago, Ar-Rushdi (1958) selected T. californicus for male-biased and female-biased sex ratios and
succeeded in establishing populations that were >90% male and <20% male,
respectively leading Belser (1959) to claim that T. californicus was the first organism known to science with polygenic sex determination.
|
| Check out our BMSC Lab webpage |
| Polygenic sex determination is when sex is determined as a threshold trait
by the cumulative action of many loci that are located on more than one chromosome
(Bulmer & Bull 1982). Dr. Maarten Voordouw, a PhD student and Postdoctoral
Fellow of Dr. Brad Anholt, showed that sex ratio is heritable, primarily through
the paternal line, and that there is an environmental component; typically
more males are present at higher temperatures. Currently, we are trying to
get at the mechanism of inheritance. |
Phylogeography and phenotypic/genotypic associations
Understanding the relative roles of contemporary selection
versus historical processes in determining the mechanisms
driving population differentiation and ultimately speciation
may be best achieved by examining well-studied model
systems. For my PhD dissertation I examined patterns
of morphological and molecular divergence among Poecilia
reticulata (the guppy) populations across the entire
range of this species,a model system for the study of
evolution, testing whether patterns of neutral genetic
differentiation (mtDNA and a nuclear locus - Xsrc)
are associated with vicariant events, and whether patterns
of morphological divergence are correlated to neutral
genetic divergence, or have arisen as a consequence
of selection. In particular, I examined whether parallel
evolution observed among Trinidad populations are persistent
across the natural range. PDF
|
|
|
Sexual selection and speciation
Theory predicts that sexual selection can promote the evolution
of reproductive isolation and speciation. We examined a highly
divergent group of P. reticulata populations occurring
in Cumaná, Venezuela. Our study suggest that the Cumaná
guppy has most likely differentiated from other guppy populations
due to divergent sexual selection, and may be the first documented
case of incipient speciation in the guppy. PDF |
Differentiation
in male secondary sexual characters maintained in
the Cumaná guppy despite mtDNA and nuclear
introgression.
In the phylogeographic study of Poecilia reticulata Peter (the guppy) across the entire natural range,
two highly divergent mtDNA lineages were inferred
for the morphologically divergent Cumaná guppy. In
this study microsatellite loci were used to test whether
these divergent mtDNA lineages would also be observed
in data from nuclear loci (nDNA). Shared haplotypes
and microsatellite alleles between upstream guppy-morph
and downstream Cumaná morph males suggest partial
introgression from upstream into downstream populations.
Despite introgression via downstream migration, the
distinctive Cumaná male morphotype is maintained,
suggesting sexual selection by female choice has imposed
differential rates of introgression among genes that
do or do not code for characters related to biological
divergence. ABSTRACT |
|
MSc research: Protogynous sex
change in the intertidal isopod Gnorimosphaeroma luteum and G. oregonense.
Advisor: Dr. R. Davies, University of Calgary,
BMSC |
|
In Crustacea, the dominant pattern of sequential hermaphroditism
is protandry (sex change from male to female). In the
study I provide the first evidence from external morphology
and population structure that G. oregonense and G. luteum, abundant, sexually dimorphic
intertidal isopods, undergo protogynous (female to male)
sex change. In the field, females had rudimentary penes,
suggesting sex change, and laboratory growth experiments
confirmed that females produced one brood of juveniles,
then passed through a variable number of molts as immature
males before becoming sexually mature males. Contrary
to reports for other protogynous Crustacea, this study
suggests that sex change is not socially mediated, although
it may be facultative, because a large percentage of
laboratory-reared juvenile isopods developed directly
into males. PDF
«To the top |
|
©
Heather J. Alexander 2009
|
