| dc.description.abstract | Surprisingly few empirical studies have addressed the evolutionary
ecology of mutualisms. In particular, there are few data available that address the
following crucial questions: 1) what factors align the interests of symbiotic
partners? 2) what is the degree of ecological and genetic variation in symbionts
across multiple populations of a single host species? and, 3) what evolutionary
mechanisms drive variation in host-symbiont compatibility where it exists?
Although there is no general theory of mutualism, conventional wisdom suggests
that mutualisms are best defined as reciprocal exploitations that provide net
benefits to the partners involved. Contemporary theory regarding the evolution of
virulence has identified several factors that help align host and symbiont interests.
However, the extent to which natural systems conform to these theoretical
expectations and what factors are most responsible for maintaining cooperative
symbioses remains unclear. I used Cassiopea xamachana to address what
evolutionary and ecological factors influence endosymbiotic mutualisms.
Cassiopea, like many marine invertebrates, harbors endosymbiotic algae within
its tissues. Algal symbionts are acquired each generation via horizontal
transmission. In chapter 3, I examined variation in host-symbiont compatibility by
performing a series of cross-infection experiments using Cassiopea larvae and
algal symbionts collected from a single medusa at ten sites in the Florida Keys.
Results reveal significant differences among Cassiopea-algal combinations for
both host survival and growth. In chapters 4 and 5, I quantify the observed
variation by increasing the number of polyp lineages used per site. Results
indicate that the observed variation among Cassiopea-algal combinations is
geographically structured. Additionally, significant host-symbiont interaction
effects suggest that the algal symbionts are locally adapted to jellyfish hosts
within a given site. In chapter 5, I re-examine variation in host-symbiont
compatibility by using seawater to infect Cassiopea hosts. The results roughly
mimic the results obtained in chapters 3 and 4. In chapter 6, I investigate the
population genetic structure of the algae inhabiting Cassiopea using RFLP and
ISSR markers. Results indicate that the algal symbionts are members of the same
species, Symbiodinium microadriaticum. Further, there is marked intraspecific
symbiont variation within this species. Overall, host-symbiont compatibility
plays a vital role in the symbiotic outcome. | |
