Download Herbivory, phenotypic variation, and reproductive barriers in fucoids

Herbivory, phenotypic variation, and
reproductive barriers in fucoids
Helena Forslund
Academic dissertation for the Degree of Doctor of Philosophy in Plant
Ecology at Stockholm University to be publicly defended on Thursday 11
October 2012 at 10:00 in föreläsningssalen, Botaniska institutionen, Lilla
Frescativägen 5.
Abstract
Along the shores of the Northern hemisphere Fucus (Phaeophyceae) species are a prominent
presence, providing substrate, shelter, and food for many species. Fucus evanescens, a nonindigenous species (NIS) in Sweden, and F. radicans, a recently described species that so far has
only been found inside the species poor Baltic Sea, are the focus of this thesis.
Interactions with enemies (e.g. predators, herbivores, parasites) have been shown to play a role in
the success of NIS. The low consumption of Fucus evanescens by the generalist gastropod Littorina
littorea in Sweden was found to depend on high levels of chemical defense in the introduced
population, not the failure of the herbivore to recognize F. evanescens as suitable food.
A survey of the relative abundance of F. radicans and F. vesiculosus and the most common
associated fauna along the Swedish Bothnian Sea coast showed that F. radicans and F. vesiculosus
are equally abundant throughout the range of F. radicans. The most common associated fauna
were found to be more abundant on F. radicans compared to F. vesiculosus. In Sweden, where F.
radicans had lower levels of defense chemicals than F. vesiculosus, F. radicans was grazed more
than F. vesiculosus in bioassays. This could, together with other factors, influence the range of F.
radicans.
Fucus radicans and F. vesiculosus are closely related, recently separated, and growing
sympatrically, therefore, possible reproductive barriers between F. radicans and F. vesiculosus were
studied. In Estonia F. radicans and F. vesiculosus reproduces at different times of the year. No such
clear reproductive barrier was found between the two species in Sweden where they reproduce at
the same time and fertilization success and germling survival were the same for hybrids as for F.
vesiculosus.
Since the high clonality of F. radicans means that the gentic diversity in F. radicans populations
is low I investigated how genetic diversity translates to phenotypic diversity in nine traits.
Phlorotannin levels, recovery after desiccation, and recovery after freezing showed inherited
variation, while the other six traits showed no variation related to genetic diversity. Phenotypic
variation in populations of F. radicans will be higher in populations with higher genetic diversity
and this might be beneficial to the community.
Keywords: Non-indigenous species, Enemy Release Hypothesis, Asexual reproduction,
Phlorotannins, Distribution.
Stockholm 2012
http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-79481
ISBN 978-91-7447-538-8
Department of Botany
Stockholm University, 106 91 Stockholm