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Abstract
Genetic subdivision within populations can ultimately lead to the evolution of new
species, and in populations of broadcast-spawners a potential facilitator of genetic
subdivision is asynchronous reproduction. However, the factors that shape genetic
variation in marine systems are complex and ambiguous, and ecological genetic structure
may be influenced by the overriding signature of past demographic events. Here, the
relative roles of the timing of reproduction and historical geography on the partitioning
of genetic variation were examined in seven populations of the broadcast-spawning
coral Acropora tenuis over 12° of latitude. The analysis of multiple loci (mitochondrial
control region, two nuclear introns and six microsatellites) revealed significant
genetic division between the most northern reef and all other reefs, suggesting that
WA reefs were re-colonized from two different sources after the Pleistocene glaciation.
Accompanying this pattern was significant genetic differentiation associated with
different breeding seasons (spring and autumn), which was greatest in PaxC, in which
there were two divergent lineages (ΦST=0.98). This is the second study to find divergent
clades of PaxC associated with spring and autumn spawners, strengthening the suggestion
of some selective connection to timing of reproduction in corals. This study reiterates
the need to incorporate reproductive timing into population genetic studies of corals
because it facilitates genetic differentiation; however, careful analysis of population
genetic data is required to separate ecological and evolutionary processes.