Genetic resilience of Daphnia populations following experimental removal of introduced fish

Abstract

Dramatic changes in environmental conditions or community composition may impose severe selective pressures on resident populations. These changes in the selective regime can lead to demographic bottlenecks or local extinction. The consequence of demographic contraction is often a reduction of standing genetic variation. Since the level of adaptive genetic variation in populations plays an important role in persistence and adaptive response, understanding genetic resilience and the time course for re-establishment of genetic diversity following demographic perturbations is a critical component of assessing the consequences of changing environments. The introduction of nonnative fish into historically fishless lakes is a particularly dramatic environmental change frequently contributing to demographic bottlenecks and local extinction of native populations. We examine the quantitativeand molecular-genetic recovery of two alpine populations of the zooplankton Daphnia melanica from the Sierra Nevada, California, USA. These populations were extirpated by introduced salmonids and subsequently re-established following the experimental removal of nonnative fish. We obtained data for nuclear and mitochondrial markers and conducted a common-garden experiment to assess the levels of molecular-and quantitative-genetic variation following experimental fish removal. Reestablished D. melanica populations attained levels of nuclear genetic diversity only slightly lower than surrounding fishless populations in the first year following fish removal and substantial mitochondrial and quantitative-genetic diversity within 8 years. This high level of genetic resilience was likely facilitated by multiple sources of genetic variation, including immigration from neighboring populations and hatching from a local reservoir of diapausing eggs. Our results highlight the genetic resilience of taxa with reservoirs of genetic variation in seed or egg banks.

Evaluation of the Egg Bank of Two Small Himalayan Lakes

“…The presence of diapausing eggs in different sections of the two sediment cores confirmed that their production is a fundamental survival strategy in high-altitude lakes. The accumulation in sediments of diapausing eggs of different species, generations and genotypes, represents a potential reserve of biodiversity [12,16], which buffers the consequent extinction risk from anthropogenic impacts and makes the population resilient to the settlement of invasive species [50,51]. Organisms able to survive in extreme environments, such as LCN10 and LCN70, belong to a small number of highly specialized species; nevertheless, the reservoir of diapausing eggs in the sediments was of the same order of size (10 3 -10 5 eggs per m −2 ) of those reported from less remote environments [16].…”

Evolutionary history of alpine and subalpine Daphnia in western North America

“…For some of these additional samples, both ND5 and COI sequences were available; for others, only ND5 sequence data exist (Table 1). Also among the existing sequences were Sierra Nevada samples published previously (Latta et al, 2010). Both gene regions, COI and ND5, were aligned to open reading frames.…”

“…All sequences were deposited in GenBank under accession numbers ‐ (ND5) and ‐ (COI). We also included in our analyses previously existing DNA sequence data from earlier publications (Colbourne et al ., ; Crease, ; Paland & Lynch, ; Mergeay et al ., ; Vergilino, Belzile & Dufresne, ; Latta et al ., ; Vergilino et al ., ). The final alignment of 1089 bp comprised 591 bp of COI and 498 bp of ND5 for 58 samples (Table ).…”

“…We also included in our analyses previously existing DNA sequence data from earlier publications (Colbourne et al, 1998;Crease, 1999;Paland & Lynch, 2006;Mergeay et al, 2008;Vergilino, Belzile & Dufresne, 2009;Latta et al, 2010;Vergilino et al, 2011). The final alignment of 1089 bp comprised 591 bp of COI and 498 bp of ND5 for 58 (Colbourne et al, 1998), Crease99: (Crease, 1999), Latta10: (Latta et al, 2010), Merg08: (Mergeay et al, 2008), Pal06: (Paland & Lynch, 2006), Verg09: (Vergilino et al, 2009), Verg11: (Vergilino et al, 2011), JKC: specimens provided directly by John K. Colbourne. Genbank accessions denoted with 'X' represent sequences that were not available, while 'none' means that the sequences are not archived in Genbank but were obtained directly from the author of the citation (Table 1).…”

Why Should We Preserve Fishless High Mountain Lakes?

“…Also, the egg banks and propagules could subsidise native populations with new individuals and buffer fish predation, but also, in this case, their roles have not been well studied (but see Parker et al 1996 andLatta et al 2010). There are also many overlooked aspects concerning the cascading effects of fish introduction (e.g.…”