Investigations into non-destructive biomarkers for endocrine disruption in wild Rana temporaria (common frogs) in Scotland

When last assessed in 2022, 40.7% of amphibian species were reported to be threatened withextinction (an increase of 2.8% since 2004), which is greater than for any other vertebrate group.Chemical pollution (such as from agriculture, pharmaceuticals, or industry) is the second mostimportant threat impacting amphibians after habitat loss. Although chemical pollutant profiles insmall freshwater bodies, where amphibians typically live and breed, are not well known, they arelikely to contain high concentrations of chemicals, many of which are known or suspectedendocrine disrupting chemicals (EDCs). Endocrine disrupting chemicals (EDCs) are chemicalsubstances that can alter the function of the endocrine system by interfering with hormonereceptors, hormone synthesis, or the metabolism of hormones, and can cause adverse healtheffects. There is a need for biomonitoring tools for contaminant exposure, including EDCs, ofwild amphibians that are preferably non-lethal in nature.This thesis aimed to investigate non-lethal methods for identifying contaminant exposure effectsin wild common frogs, Rana temporaria, that relate to reproductive health, growth anddevelopment. Firstly, the land use and water quality around the areas where R. temporaria adultsand tadpoles were collected in central Scotland were used to determine if there was a relationshipbetween frog/tadpole morphometry and water quality/land uses. Adult and tadpole mass, tadpolelength, and adult male nuptial pad length were all influenced by changes in land use aroundponds, as well as changes in some water quality parameters. Development of a cell basedluminescence assay was attempted which would have allowed analysis of water from the sameponds to determine whether chemicals present were causing androgenic/anti-androgenic activity.However, this was unsuccessful. Expression of genes involved in sex differentiation anddetermination in the gonads of tadpoles collected from these ponds weas examined usingdestructive techniques. No relationship was found between gonad morphology and expression ofany of the genes investigated (amh, cyp17, foxL2, cyp19), although a small significant differencein amh expression was identified between two study sites. Finally, the non-destructive monitoringof R. temporaria tadpoles over time was carried out at six pond sites, focusing on the effects of arange of metal elements and water quality parameters on tadpole morphometrics. Differentdevelopmental stages of tadpoles were shown to be affected by different elements and waterquality.The most effective biomonitoring tool identified throughout this thesis was the use of tadpolemeasurements, with the mass and length of tadpoles showing particular promise asmorphometrics affected by land use, water quality, and element concentrations. More work isnow needed to refine the findings of this thesis to confirm the use of tadpole morphometrics as afield-based biomarker of endocrine disruption.