Diel surface temperature range scales with lake size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at Diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of Diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface Diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer Diel ranges in their near-surface temperatures of between 4 and 7°C. Large Diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored

Summary of OMEGAMAP analyses.

<p>The full output of model parameters including estimates of R, θ, κ and Φ are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063035#pone.0063035.s011" target="_blank">Table S2</a>. Data for an OMEGAMAP analysis of Colorado River <i>O. mykiss</i> are also included.</p

Selection and recombination in the Srahrevagh.

<p>A) Model of the peptide binding region of the reference allele, Satr-<i>UBA</i>*<i>0101</i>. Sites under selection are labelled and colour coded according to their degree of statistical support (see key at bottom right of diagram. Higher <i>p</i> values indicate stronger statistical support). The sites with the highest ω estimates are Tyr113 (ω = 8.57), Ala42 (3.51), Lys156 (3.38), Phe94 (2.08) and Asn96 (2.05). The Lys156 residue appears to occur between the cleft and the so-called “gatekeeper” residue, Gln155. B, C) Plots of site-by-site mean posterior estimates of ω (B) and ρ (C) for <i>Satr-UBA</i> described in this study showing non-correspondence in their pattern of variation. Highest Posterior Density (HPD) 95% confidence intervals are seen in grey about the plot line. In B), the dashed red line indicates ω = 1, values above which indicate selection.</p

Phylogenetics of the α2 domain.

<p>A) <i>Satr-UBA</i> α2 sequences with novel sequences described in this work represented by square nodes. The number of plus signs after a sequence indicates the number of other <i>Satr-UBA</i> alleles which share this sequence in its entirety and, therefore, are sequences which are likely to have been involved in recombination. Known α2 lineages are indicated using roman numerals. Note that a novel α2 lineage, L_IV, unique to <i>S. trutta</i>, which appears to have originated more recently from the α2 L_I lineage, is well supported with the additional data described in this work. The shape of the overall tree is distinct from that of α1 with fewer well-supported lineages and with evidence of extensive radiation within the ‘majority’ α2 L_I lineage.</p

Phylogenetics of the α1 domain.

<p>A) <i>Satr-UBA</i> α1 sequences (blue) together with relevant outgroup sequences from <i>S. salar</i> (green) and <i>O. mykiss</i> (red). Novel Srahrevagh River sequences are represented by square nodes. Accession numbers are included in node labels. The number of plus signs after a sequences indicates the number of other <i>Satr-UBA</i> alleles which share this sequence in its entirety. α1 lineages are indicated using roman numerals. A <i>C. idella UBA</i> is included to highlight the distinct sub-lineages in L_V, not as an outgroup, and these networks are unrooted. B) Possible α1 intradomain recombination event between typical α1 L_III sequences and sequences more similar to <i>Satr-UBA</i>*1301 giving rise to <i>Sasa-UBA</i>*0301. The α1 L_I sequence is included as an outgroup. C) α1 L_V sequences from <i>S. trutta</i>, <i>S. salar</i> and <i>O. mykiss</i>. Loops are observed in the network, affecting L_Vb sequences primarily. Note also in this network the extent of trans-species polymorphism in L_Va sequences.</p

Descriptive statistics for <i>S</i>atr-<i>UBA</i> DNA sequence data from the Colorado River, USA.

<p>Standard errors are presented where relevant. Watterson <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063035#pone.0063035-Watterson1" target="_blank">[67]</a> population mutation rate estimates (θ) are included together with effective population size (N_E) estimates assuming a mutation rate of 1.1×10⁻⁸ per site per sequence <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063035#pone.0063035-Roach1" target="_blank">[68]</a>.</p

Phylogenetics of <i>UBA</i>.

<p>A) SPLITSTREE neighbor-net network of <i>Satr-UBA</i> alleles (blue) with relevant outgroup sequences from <i>S. salar</i> (green) and <i>O. mykiss</i> (red). Square nodes indicate the novel alleles identified from the Srahrevagh River, Co. Mayo. Parallel lines indicate splits in the network. Bootstrap support values (1000 replicates) are presented for the most relevant splits in the network. Large loops imply areas of phylogenetic uncertainty or reticulations. The frequency of these in the network implies that recombination is an important factor in the evolution of <i>Satr</i>-<i>UBA</i>, predominantly between the α1 and α2 domains. Conversely, good bootstrap support for splits involving several closely related <i>Satr-UBA</i> alleles is suggestive of conventional radiation by point mutation. Roman numerals (α1/α2) indicate the lineages to which each <i>Satr-UBA</i> allele's α1 and α2 sequence belongs (see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063035#pone-0063035-g005" target="_blank">Figures 5</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063035#pone-0063035-g006" target="_blank">6</a>). B) Neighbour-joining tree rooted on the midpoint for salmonid UBA amino acid sequences with bootstrap support (1,000 replicates) shown for nodes with 50% support or greater. Nodes in A) and B) highlighted with an orange triangle illustrate how SPLITSTREE is better able to visualise sequences affected by recombination.</p

Selection in the Colorado.

<p>A) Model showing selected sites in the <i>UBA</i> protein for the Colorado River <i>S. trutta</i>. For comparison, this information from the Srahrevagh River <i>S. trutta</i> population is also provided (inset, right, detail in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063035#pone-0063035-g001" target="_blank">Figure 1A</a>). Clear differences in the distribution of selected sites in the peptide binding can be seen. B) Plot of ω for the Colorado River <i>S. trutta</i>. Highest Posterior Density (HPD) 95% confidence intervals are seen in grey about the plot line and are tight about means in all cases, suggesting confidence in the ω estimates.</p

Selected sites in <i>UBA</i>.

<p>Venn diagram showing all sites under significant selection as identified in conjoint CODEML analysis of the three different taxa labelled. Sites in intersections are under selection in two or more species. Significance levels of selection on residues: p<0.001 (bold), p<0.01 (normal) and p<0.05 (italics).</p

Relationship between the diel range in lake surface water temperature and surface area.

<p>Relationship between the observed (light violet circles) and theoretical (red circles) diel surface temperature range with lake area during summer, with the solid line illustrating the fitted generalised additive model with 95% confidence interval shown by the shaded region; lake surface areas where the diel temperature range changes significantly (P < 0.001) are shown with a red line.</p