Biology subjects

Franklin, C. E.

Publications and source records attributed to Franklin, C. E..

9 recordsLinked to original sources

bioRxiv2023

Cold-induced skin darkening does not protect amphibian larvae from UV-associated DNA damage

O_LIMany amphibian declines are correlated with increasing levels of ultraviolet radiation (UVR). While disease is often implicated in declines, environmental factors such as temperature and UVR play an important role in disease epidemiology. C_LIO_LIThe mutagenic effects of UVR exposure on amphibians are worse at low temperatures. Amphibians from cold environments may be more susceptible to increasing UVR. However, larvae of some species demonstrate cold acclimation, reducing UV-induced DNA damage at low temperatures. Understanding of the mechanisms underpinning this response is lacking. C_LIO_LIWe reared Limnodynastes peronii larvae in cool (15{degrees}C) or warm (25{degrees}C) waters before acutely exposing them to 1.5 h of high intensity (80 W cm-2) UVBR. We measured the colour of larvae and mRNA levels of a DNA repair enzyme. We reared larvae at 25{degrees}C in black or white containers to elicit a skin colour response, and then measured DNA damage levels in the skin and remaining carcass following UVBR exposure. C_LIO_LICold acclimated larvae were darker and displayed lower levels of DNA damage than warm-acclimated larvae. There was no difference in CPD-photolyase mRNA levels between cold- and warm-acclimated larvae. Skin darkening in larvae did not reduce larval accumulation of DNA damage following UVR exposure. C_LIO_LIOur results showed that skin darkening alone does not explain cold-induced reductions in UV-associated DNA damage in L. peronii larvae. Beneficial cold-acclimation is more likely underpinned by increased CPD-photolyase abundance and/or increased photolyase activity at low temperatures. C_LI Research HighlightsO_LIL. peroniii larvae darken when exposed to cold temperatures C_LIO_LIDarker larvae were not protected from the effects of UV on DNA damage C_LIO_LICold acclimation of larvae when exposed to UV is likely driven by DNA repair enzymes not melanin C_LI

molecular biology↗

bioRxiv2023

Thermal compensation reduces DNA damage in UV-exposed amphibian larvae: implications for high latitudinal and altitudinal species

1. Increases in ultraviolet radiation (UVR) correlate spatially and temporally with global amphibian population declines and interact with other stressors such as disease and temperature. Declines have largely occurred in high-altitude areas associated with greater UVR and cooler temperatures. 2. UVR is a powerful mutagenic harming organisms largely by damaging DNA. When acutely exposed to UVR at cool temperatures, amphibian larvae have increased levels of DNA damage. Amphibians may be able to compensate for the depressive effects of temperature on DNA damage through thermal acclimatisation, but it is unknown whether they or other ectotherms have this capacity. 3. We reared striped marsh frog larvae (Limnodynastes peronii) in warm (25{degrees}C) and cool (15{degrees}C) temperatures under either a low or moderate daily dose of UVR (10 and 40 {micro}W cm-2 UV-B for 1 h at midday, respectively) for 18-20 days and then measured immediate DNA damage resulting from an acute high UVR dose (80 {micro}W cm-2 UV-B for 1.5 h) at a range of test temperatures (10, 15, 20, 25, and 30{degrees}C). 4. Larvae acclimated to 15{degrees}C and exposed to UVR at 15{degrees}C completely compensated UVR-induced DNA damage compared with 25{degrees}C acclimated larvae exposed to UVR at 25{degrees}C. Additionally, warm-acclimated larvae had higher CPDs than cold-acclimated larvae across test temperatures, which indicated a cost of living in warmer temperatures. In contrast, larvae reared under chronic elevated UVR levels showed no evidence of UVR acclimation resulting in lower DNA damage following an acute high UVR exposure. 5. Our finding that thermal acclimation in L. peronii larvae compensated UVR-induced DNA damage at low temperatures suggested that aquatic ectotherms living in cool temperatures may be more resilient to high UVR than previously realised. 6. We suggested individuals or species with less capacity for thermal acclimation of DNA repair mechanisms may be more at risk if exposed to changing thermal and UVR exposure regimes but cautioned that thermal acclimation of DNA repair mechanisms may not always be beneficial.

zoology↗

bioRxiv2022

Temperature causes species-specific responses to UV-induced DNA damage in amphibian larvae

Anthropogenic ozone depletion has led to a 2-5% increase in ultraviolet B radiation (UVBR) levels reaching the earths surface. Exposure to UVBR causes harmful DNA damage in amphibians, but this is minimized by DNA repair enzymes such as thermally sensitive CPD-photolyase, with cool temperatures slowing repair rates. It is unknown whether amphibian species differ in the repair response to a given dose of UVBR across temperatures. We reared larvae of three species (Limnodynastes peronii, Limnodynastes tasmaniensis, and Platyplectrum ornatum) at 25{degrees}C and acutely exposed them to 80 W cm-2 UVBR for 2 h at either 20{degrees}C or 30{degrees}C. UVBR-mediated DNA damage was measured as larvae repaired damage in photoreactive light at their exposure temperatures. Cool temperatures increased DNA damage in all two species and slowed DNA repair rate in P. ornatum. The magnitude of DNA damage incurred from UVBR was species-specific. P. ornatum had the lowest CPDs and DNA repair rates, and the depressive effects of low temperature on photorepair were greater in L. tasmaniensis. Considering the susceptibility of most aquatic organisms to UVBR, this research highlighted a need to consider the complexity of species-specific physiology when forecasting the influence of changing UVBR and temperature in aquatic ecosystems.

molecular biology↗

bioRxiv2022

The role of environmental calcium in the extreme acid tolerance of northern banjo frog (Limnodynastes terraereginae) larvae

Many aquatically respiring animals inhabiting low pH waters can suffer acute inhibition of ion uptake and loss of branchial (gill) epithelial integrity, culminating in a fatal, rapid loss of body Na+. Environmental calcium levels ([Ca2+]e) are pivotal in maintaining branchial junction integrity, with supplemental Ca2+ reversing the negative effects of low pH in some animals. Tolerance of some naturally acidic environments by aquatic animals is further complicated by low [Ca2+]e, yet many of these environments are surprisingly biodiverse. How these animals overcome the combined damaging actions of low pH and low environmental Ca2+ remains unknown. Here, we examined the effects of [Ca2+]e on the response to low pH in larvae of the highly acid tolerant frog Limnodynastes terraereginae. Acute exposure to low pH water in the presence of low [Ca2+]e increased net Na+ efflux. Provision of additional [Ca2+]e reduced net Na+ efflux, but the effect was saturable. Acclimation to both low and high [Ca2+]e improved the resistance of larvae to Na+ efflux at low pH. Inhibition of apical Ca2+ uptake by ruthenium red resulted in an abrupt loss of tolerance to low pH in larvae acclimated to low pH water. Acclimation to acidic water increased branchial gene expression of the intracellular Ca2+ transport protein calbindin, consistent with a role for increased transcellular Ca2+ trafficking in the tolerance of acidic water. This study confirmed the physiological challenge of low [Ca2+]e on branchial integrity in acidic waters and highlighted a potential role for maintenance of transcellular Ca2+ uptake in the acid tolerance of L. terraereginae. Summary statementTolerance of naturally acidic, dilute, and soft waters by larvae of the frog Limnodynastes terraereginae involves adaptations to the branchial calcium transport pathway which protects intercellular junctions against damage.

physiology↗

bioRxiv2021

Early exposure to UV radiation causes telomere shortening and poorer condition later in life

Determining the contribution of elevated ultraviolet-B radiation (UVBR; 280 - 315 nm) to amphibian population declines is being hindered by a lack of knowledge about how different acute UVBR exposure regimes during early life history stages might affect post-metamorphic stages via long-term carryover effects. We acutely exposed tadpoles of the Australian green tree frog (Litoria caerulea) to a combination of different UVBR irradiances and doses in a multi-factorial experiment, and then reared them to metamorphosis in the absence of UVBR to assess carryover effects in subsequent juvenile frogs. Dose and irradiance of acute UVBR exposure influenced carryover effects into metamorphosis in somewhat opposing manners. Higher doses of UVBR exposure in larvae yielded improved rates of metamorphosis. However, exposure at a high irradiance resulted in frogs metamorphosing smaller in size and in poorer condition than frogs exposed to low and medium irradiance UVBR as larvae. We also demonstrate some of the first empirical evidence of UVBR-induced telomere shortening in vivo, which is one possible mechanism for life-history trade-offs impacting condition post-metamorphosis. These findings contribute to our understanding of how acute UVBR exposure regimes in early life affect later life-history stages, which has implications for how this stressor may shape population dynamics. SUMMARY STATEMENTWe demonstrate physiological carryover effects in amphibians that link larval UV exposure to detrimental impacts on juvenile frogs, including telomere shortening, which has implications for how UV shapes amphibian populations.

physiology↗

bioRxiv2020

Low light levels increase avoidance behaviour of diurnal fish species: Implications for road culverts

Inadequately designed culverts are known to pose hydraulic barriers to fish passage, but they may also be behavioural barriers if they adversely affect light levels within them. To test this, we performed a choice experiment and quantified the amount of time individuals of four Australian fish species spent in darkened and illuminated areas of an experimental swimming fume. Behavioural responses were reflective of the species diel activity patterns; diurnal species preferred illuminated regions, while nocturnal species preferred the darkened region. We then determined a threshold light level of only ~100-200 lux (c.f. midday sunlight ~100,000 lux) was required to overcome the behavioural barrier in ~ 70% of the diurnal fish tested. Placing these threshold values into field context, 100% of culverts sampled recorded inadequate light levels. Attention is required to better understand the impacts of low light levels in culverts on fish passage and to prioritise restoration.

zoology↗

bioRxiv2019

Physiological and morphological correlates of extreme acid tolerance in larvae of the acidophilic amphibian Litoria cooloolensis (Anura: Pelodryadidae)

In the coastal sandy lowlands of east Australia, several anuran species including the Cooloola Sedgefrog Litoria cooloolensis, show remarkable tolerance to dilute highly acidic waters as low as pH 3.5. To investigate the physiological and morphological underpinnings of acid tolerance in L. cooloolensis larvae, we compared Na+ balance, uptake and efflux rates, and gill and skin morphology in larvae reared in circum-neutral (pH 6.5) and pH 3.5 water. We hypothesised that acute exposure to pH 3.5 water would cause an initial loss of ionic homeostasis in larvae, but with chronic exposure larvae would restore Na+ balance. Net Na+ flux rates were not significantly different from zero in larvae reared at pH 3.5 and in acid-na&iumlve animals maintained in pH 6.5 water. Animals reared at pH 6.5 and acutely exposed to pH 3.5 exhibited a net loss of Na+, due to a significant inhibition of Na+ uptake. In contrast, L. cooloolensis larvae reared at pH 3.5 maintained Na+ balance at pH 3.5 and did not exhibit inhibition of Na+ uptake at this pH. Investigation of Na+ transport kinetics and the morphology of the gills and integument suggests tolerance of L. cooloolensis larvae to low pH may be attributed to a high capacity for branchial Na+ uptake, increased tight junction length and elevated mucus production in the gills and integument. These factors confer resistance to acid damage and disruption of ionic homeostasis which would otherwise result in the death of larvae exposed to waters of pH 4.0 and less.

zoology↗

bioRxiv2019

Swimming performance traits of twenty-one Australian fish species: a fish passage management tool for use in modified freshwater systems

Freshwater ecosystems have been severely fragmented by artificial in-stream structures designed to manage water for human use. Significant efforts have been made to reconnect freshwater systems for fish movement, through the design and installation of dedicated fish passage structures (fishways) and by incorporating fish-sensitive design features into conventional infrastructure (e.g. culverts). Key to the success of these structures is making sure that the water velocities within them do not exceed the swimming capacities of the local fish species. Swimming performance data is scarce for Australian fish, which have a reduced swimming capacity when compared to many North American and European species. To help close this knowledge gap and assist fisheries management and civil engineering, we report the swimming performance capacities of twenty-one small-bodied fish and juveniles (< 10 cm) of large bodied species native to Australia as measured by critical swimming speed (Ucrit) and burst swimming speed (Usprint) in a recirculating flume. This data is complemented by endurance swim trials in a 12-meter hydraulic flume channel, and by measures of flume traverse success. Building on the utility of this dataset, we used a panel of morphological, behavioural and ecological traits to first assess their relative contributions to the observed swimming performance data, and second, to determine if they could be used to predict swimming performance capacity - a useful tool to assist in the management of species of conservation concern where access to swimming performance data may be limited. We found that body length combined with depth station (benthic, pelagic or surface) explained most of the interspecific variation in observed swimming performance data, followed by body shape and tail shape. These three traits were the most effective at predicting swimming performance in a model/unknown fish. This data will assist civil engineers and fisheries managers in Australia to mitigate the impact of in-stream structures on local fish populations.

zoology↗

bioRxiv2018

Utilising the boundary layer to help restore the connectivity of fish habitats and populations

SignificanceHabitat fragmentation is a significant contributor to the worldwide decline of freshwater ecosystem health, the most pervasive cause of which is culverts. Culverts act as a barrier to fish movement, impacting feeding, predator avoidance, spawning, and community structures. Here we show that a common remediation strategy that involves baffles, is detrimental to the successful passage of small bodied and juvenile fish at high velocities. To remedy this widespread problem, we present a novel remediation design that benefits a range of small-bodied species and juvenile fish at the same high velocities, regardless of morphology or ecological niche. The application of this remediation design may be expanded to any smooth surfaced anthropogenic structure, to improve fish passage and restore ecosystem functionality.\n\nAbstractCulverts are a major cause of habitat fragmentation in freshwater ecosystems, are a barrier to fish movement, and are regarded as a significant contributor in the decline of freshwater fish populations globally. To try to address this, various culvert remediation designs have been implemented, including the installation of vertical baffles and the provision of naturalistic (rock) substrates. While remediation strategies generally aim to reduce the velocity of water flowing through the structure, there is often resistance to their use because the resultant reduction in culvert discharge can negatively impact upstream flooding while also resulting in debris clogging and increased culvert maintenance costs. In addition, baffles markedly increase water turbulence that may be detrimental to passage by some fish species or size classes. Here we present some novel remediation designs that exploit the reduced water velocity in boundary layers along the culvert wall to enhance fish passage without significantly compromising discharge capacity. These longitudinal designs produce an expanded reduced velocity zone along the culvert margins that generate minimal turbulence. We show that these novel designs are significantly advantageous to the swimming endurance and traversability for six small-bodied Australian fish species. We also provide data on how and why some culvert baffle designs may impede small-bodied fish passage. This data scales with increasing water velocity, encompassing inter-specific differences in swimming capacity. These results have broad implications for fish community structure and the requirement of juvenile cohort of large-bodied commercially important species where baffles have been implemented to facilitate fish passage.

animal behavior and cognition↗