• Behavioural and physiological adaptations to low-temperature environments in the common frog, Rana temporaria

      Muir, Anna P.; Biek, Roman; Mable, Barbara K.; University of Chester; University of Glasgow (BioMed Central, 2014-05-23)
      Background: Extreme environments can impose strong ecological and evolutionary pressures at a local level. Ectotherms are particularly sensitive to low-temperature environments, which can result in a reduced activity period, slowed physiological processes and increased exposure to sub-zero temperatures. The aim of this study was to assess the behavioural and physiological responses that facilitate survival in low-temperature environments. In particular, we asked: 1) do high-altitude common frog (Rana temporaria) adults extend the time available for larval growth by breeding at lower temperatures than low-altitude individuals?; and 2) do tadpoles sampled from high-altitude sites differ physiologically from those from low-altitude sites, in terms of routine metabolic rate (RMR) and freeze tolerance? Breeding date was assessed as the first day of spawn observation and local temperature recorded for five, paired high- and low-altitude R. temporaria breeding sites in Scotland. Spawn was collected and tadpoles raised in a common laboratory environment, where RMR was measured as oxygen consumed using a closed respiratory tube system. Freeze tolerance was measured as survival following slow cooling to the point when all container water had frozen. Results: We found that breeding did not occur below 5°C at any site and there was no significant relationship between breeding temperature and altitude, leading to a delay in spawning of five days for every 100 m increase in altitude. The relationship between altitude and RMR varied by mountain but was lower for individuals sampled from high- than low-altitude sites within the three mountains with the highest high-altitude sites (≥900 m). In contrast, individuals sampled from low-altitudes survived freezing significantly better than those from high-altitudes, across all mountains. Conclusions: Our results suggest that adults at high-altitude do not show behavioural adaptations in terms of breeding at lower temperatures. However, tadpoles appear to have the potential to adapt physiologically to surviving at high-altitude via reduced RMR but without an increase in freeze tolerance. Therefore, survival at high-altitude may be facilitated by physiological mechanisms that permit faster growth rates, allowing completion of larval development within a shorter time period, alleviating the need for adaptations that extend the time available for larval growth.
    • Local adaptation with high gene flow: temperature parameters drive adaptation to altitude in the common frog (Rana temporaria)

      Muir, Anna P.; Biek, Roman; Thomas, R.; Mable, Barbara K.; University of Chester; University of Glasgow; Royal Zoological Society of Scotland (Wiley, 2014-01-20)
      Both environmental and genetic influences can result in phenotypic variation. Quantifying the relative contributions of local adaptation and phenotypic plasticity to phenotypes is key to understanding the effect of environmental variation on populations. Identifying the selective pressures that drive divergence is an important, but often lacking, next step. High gene flow between high- and low-altitude common frog (Rana temporaria) breeding sites has previously been demonstrated in Scotland. The aim of this study was to assess whether local adaptation occurs in the face of high gene flow and to identify potential environmental selection pressures that drive adaptation. Phenotypic variation in larval traits was quantified in R. temporaria from paired high- and low-altitude sites using three common temperature treatments. Local adaptation was assessed using QST -FST analyses, and quantitative phenotypic divergence was related to environmental parameters using Mantel tests. Although evidence of local adaptation was found for all traits measured, only variation in larval period and growth rate was consistent with adaptation to altitude. Moreover, this was only evident in the three mountains with the highest high-altitude sites. This variation was correlated with mean summer and winter temperatures, suggesting that temperature parameters are potentially strong selective pressures maintaining local adaptation, despite high gene flow.
    • Spatial variation in species composition of Saprolegnia, a parasitic oomycete of amphibian eggs, in Scotland

      Muir, Anna P.; Kilbride, Elizabeth; Mable, Barbara K.; University of Chester; University of Glasgow (The British Herpetological Society, 2015-10-01)
      Parasitic water moulds in the genus Saprolegnia cause mortality of amphibian embryos and reduced size at metamorphosis, leading to increased adult mortality. Most studies of virulence have focused on only a single Saprolegnia species, but the Saprolegnia species associated with amphibian eggs and their distributions are not well known. This study aimed to investigate the distribution of amphibian-associated water moulds in Scotland. In particular, we asked the questions: i) Does Saprolegnia species composition vary between sites?; and ii) Is presence of Saprolegnia related to environmental parameters? Common frog (Rana temporaria) eggs with evidence of Saprolegnia infection were sampled from ten sites, cultured, and the 28S region of the rDNA array sequenced. Thirteen samples isolated from four sites were identified as members of the Saprolegniaceae and the ITS region of these samples were subsequently sequenced to further resolve species identification. Four species of Saprolegnia were found in total, with one or two species of Saprolegnia present in each of four sites. S. diclina was the most common species identified and was found at three of the four sites. Acidity was significantly lower and altitude significantly higher at sites where Saprolegniaceae were present. Therefore, R. temporaria eggs in different pools are subject to infection by different, and in some instances more than one, species of Saprolegnia. Overall, our findings suggest that future studies of virulence need to consider the effect of multiple Saprolegnia species within a site as well as the population of origin of the amphibian host