Islands of Sea: The evolution, ecology and conservation of marine lake invertebrates
it is maintained. Biodiversity is multifaceted, and genetic diversity within populations is one
of its components besides species and ecosystem diversity (Vellend and Geber, 2005).
Thesis on evolution, ecology, and conservation of marine lake invertebrates.
Studies of microevolution focus on intra-specific variation within populations which
eventually might lead to the macroevolutionary process of speciation (Hendry et al., 2009).
Genetic diversity within populations is usually measured via allele frequencies, or the
number of times a variant of a gene occurs in a population. Allele frequencies can change
due to mutation, selection, gene flow (migration between populations) and genetic drift
(stochastic loss or gain of alleles). The fields of population genetics and genomics aim to
improve our understanding of population differentiation (Charlesworth, 2010; Luikart et al.,
2018), by questioning how spatial and environmental factors influence microevolutionary
processes. Microevolutionary studies in marine systems are lagging behind terrestrial
counterparts for several reasons (Selkoe et al., 2008, 2016), first and foremost being the
difficulty to access many marine areas. Furthermore, there is a long-standing assumption
that marine populations show low rates of genetic differentiation due to the lack of clear
physical barriers, assumed high dispersal potential, and associated large effective
population sizes (Palumbi, 1994; Ward, 1994; Bowen et al., 2013). While this assumption
has both been confirmed and rejected for different organisms (Bierne et al., 2016), in any
case the open nature of the marine realm makes defining marine populations a priori
challenging. Still, recent studies are showing more population structure in marine
ecosystems and at finer spatial scales (1-100kms) than expected by predicted larval
dispersal distances (Hauser and Carvalho, 2008; Marshall et al., 2010; Van Wyngaarden et
al., 2016; Bernatchez et al., 2018). Further elucidating marine population genetic patterns
on small scales and shedding light on what drives marine population connectivity and
adaptation is particularly pressing in a changing world. This thesis aims to disentangle
relative importance of neutral (geographic and dispersal barriers) and selective (local
adaptation) processes on marine population genomic variation using the unique opportunity
presented by marine lakes which offer replicated, independent natural laboratories of
evolution and ecology.