Abstract
Intraspecific genetic variation can have similar effects as species diversity on ecosystem function; understanding such variation is important, particularly for ecological key species. The brown trout plays central roles in many northern freshwater ecosystems, and several cases of sympatric brown trout populations have been detected in freshwater lakes based on apparent morphological differences. In some rare cases, sympatric, genetically distinct populations lacking visible phenotypic differences have been detected based on genetic data alone. Detecting such “cryptic” sympatric populations without prior grouping of individuals based on phenotypic characteristics is more difficult statistically, though. The aim of the present study is to delineate the spatial connectivity of two cryptic, sympatric genetic clusters of brown trout discovered in two interconnected, tiny subarctic Swedish lakes. The structures were detected using allozyme markers, and have been monitored over time. Here, we confirm their existence for almost three decades and report that these cryptic, sympatric populations exhibit very different connectivity patterns to brown trout of nearby lakes. One of the clusters is relatively isolated while the other one shows high genetic similarity to downstream populations. There are indications of different spawning sites as reflected in genetic structuring among parr from different creeks. We used >3000 SNPs on a subsample and find that the SNPs largely confirm the allozyme pattern but give considerably lower FST values, and potentially indicate further structuring within populations. This type of complex genetic substructuring over microgeographical scales might be more common than anticipated and needs to be considered in conservation management.
Highlights
Identifying and understanding patterns of population genetic structure is an important task in evolutionary and conservation biology, because such intraspecific, genetic biodiversity represents results of evolutionary processes that provide the basic units for future adaptation processes (Allendorf et al 2013)
We address the following questions: (a) can the sympatric populations detected using allozyme markers be identified with SNPs? (b) What is the spatial distribution and genetic relationships of the two populations with respect to brown trout in neighbouring lakes? (c) Are there indications of differences with respect to spawning site?
The SNP data largely provide consistency with allozyme patterns (FIS = 0.022, P ≪ 0.001); the structure analysis combined with the Evanno method identified K = 2 as the highest hierarchical structure (Online Resource 1, Table S4) when using the 3093 SNP markers
Summary
Identifying and understanding patterns of population genetic structure is an important task in evolutionary and conservation biology, because such intraspecific, genetic biodiversity represents results of evolutionary processes that provide the basic units for future adaptation processes (Allendorf et al 2013). Research over the past decade has reported that genetic biodiversity can affect species productivity, diversity and viability (Reusch et al 2005; Lindley et al 2009), resilience to environmental stressors (Frankham 2005; Hajjar et al 2008; Hellmair and Kinziger 2014) and adaptation to changing environmental features including climate change (McGinnity et al 2009; Barshis et al 2013) This knowledge is of key importance for sustainable management and is recognised in the Convention on Biological Diversity (CBD; http://www.cbd.int), and in the Strategic Plan for 2011–2020 where increasing efforts to protect genetic diversity is called for Indications of genetically divergent populations contributing to different ecosystem roles include the portfolio effect documented in sockeye salmon (Schindler et al 2010), where intraspecific life history variation stabilises ecosystem services, as well as in lake whitefish, in which different ecotypes take on different ecological roles as they occupy separate trophic niches (Rogers and Bernatchez 2007)
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