Abstract
AbstractAimStudying clearly delineated populations in marine lakes, islands of sea, we investigated the interplay of habitat size, dispersal potential, and priority effects in shaping marine population genetic structure.LocationMarine lakes and coastal locations in Indonesia, Palau, Papua New Guinea and Australia.TaxonMussels (Mytilidae, Brachidontes spp.)MethodsPopulations were sampled from four coastal locations and 22 marine lakes of similar age (~8,000 years), yet differing in size (0.04–4.7 km2) and degree of connection to the adjacent sea. While some lakes are highly connected, allowing potential influx of larvae from the sea, others have very limited water exchange. We assessed the phylogeographical structure and demographic history using mitochondrial and nuclear DNA sequence data, and combined this with geometric morphometrics. The effects of lake characteristics on population genetic diversity and structure were tested using linear regression and Mantel tests.ResultsEach lake contained one of six distinct genetic lineages, which were characterized by deep phylogenetic splits and significant morphometric differences. These lineages likely represent separate species. The lineages showed similar demographic patterns, with lakes containing founder populations that rapidly expanded and diverged. Genetic diversity within lake populations was significantly correlated with lake area, but not with physical connection to the adjacent sea. Within lineages that occurred in multiple lakes there was strong population structure (average ΦST 0.65), which did not conform to an isolation‐by‐distance pattern or to the degree of dispersal potential.Main ConclusionsMarine lakes across a gradient of physical isolation show strong population structure and evidence for in situ divergence. We hypothesize that the observed genetic structure is the result of priority effects. In addition, reduction of habitat size appears to reduce genetic diversity, even at very small spatial scales. Our findings are relevant in the context of ongoing alterations to coastal hydrodynamics, which lead to habitat reduction and influence migration among populations at fine spatial scales.
Highlights
The Coral Triangle houses the global maximum of marine biodiversity (Hoeksema, 2007; Roberts et al, 2002), yet the origins of this high diversity remain unresolved
By analysing population genetics and geometric morphometrics, we aimed to (a) identify the distribution of lineages of Brachidontes mussels in the Indo-Pacific, (b) test whether marine genetic diversity conforms to the prediction of accumulation of diversity with area and (c) assess which levels of dispersal potential can lead to local divergence and structure among populations at small spatial and temporal scales
That likely represent at least six distinct species, were detected based on the genetic and morphological characteristics of mussels found in 22 marine lakes and four coastal locations in the Indo-Pacific
Summary
The Coral Triangle (located between the Philippines, Indonesia and Papua New Guinea) houses the global maximum of marine biodiversity (Hoeksema, 2007; Roberts et al, 2002), yet the origins of this high diversity remain unresolved. Selection of marine lakes with different sizes, degrees of connection to the adjacent sea and at different spatial scales offers an opportunity to assess the influence of area, geographical distance and porosity of landscape barriers in shaping marine population genetic structure. With respect to the population genetic structure of Brachidontes sp., Maas et al (2018) examined one lineage that inhabited seven marine lakes in Indonesia, which were similar in age and size but varied in environmental regimes and degrees of connection to the sea. By analysing population genetics and geometric morphometrics, we aimed to (a) identify the distribution of lineages of Brachidontes mussels in the Indo-Pacific, (b) test whether marine genetic diversity conforms to the prediction of accumulation of diversity with area and (c) assess which levels of dispersal potential can lead to local divergence and structure among populations at small spatial and temporal scales
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