Inter-individual variability in developmental traits in tadpoles of the Baja California chorus frog (Pseudacris hypochondriaca) in response to temperature
Authors: St. Onge Cameron , Mueller Casey 
Published: May 2024

Phenotypic plasticity is the intraspecific expression of different phenotypes in response to environmental conditions. Inter-individual variability refers to the range of phenotypes produced between conspecifics within a population, and such variability is ubiquitously observed among animals. Investigating inter-individual variability can help develop a more comprehensive understanding of how phenotypes respond to environmental change. The Baja California chorus frog ( Pseudacris hypochondriaca) is found in a variety of ecosystems that differ in temperature and elevation throughout its latitudinal range (∼1400 km) from Santa Barbara County, California to Baja California, Mexico. The chorus frog experiences a variable thermal environment across its life history and males initiate mating calls at a wide range of water temperatures, between 4 and 20°C. Embryos develop successfully between 8 and 29°C, and tadpoles between 0 and 33°C. We have previously observed inter-individual variability in developmental traits, such as development rate and metabolic rate, and therefore aimed to investigate this variability within and between temperatures more closely. Chorus frog eggs were collected from a wetland on the CSUSM campus the day after being laid, and incubated at 15°C or 22°C. Once tadpoles reached the target stage (Gosner Stage 33; hind limb toe differentiation), oxygen consumption rate (Vȯ2) was measured using intermittent respirometry, and body length, wet mass and dry gut-free masses were measured. We also investigated the effect of temperature on swimming speed and time to exhaustion. Average time to stage, wet mass, dry gut-free mass and body length all decreased at 22°C, while mass-specific Vȯ2 increased. We observed decreased variability at 22°C compared to 15°C in time to reach stage (days from first to last tadpole to reach stage: 30.2 ± 2.7 days at 15°C, 15.4 ± 1.1 at 22°C), wet mass (wet mass range: 148.8 ± 14.2 mg at 15°C, 105.1 ± 11.3 mg at 22°C), and dry gut-free mass (dry gut-free mass range: 14.2 ± 1.2 mg at 15°C, 7.3 ± 0.7 mg at 22°C). Variability in body length did not differ between temperatures (total length range: 7.7 ± 0.4 mm at 15°C, 6.4 ± 0.5 mm at 22°C). In contrast to other traits, variability in mass-specific Vȯ2 increased at 22°C compared to 15°C (mass-specific Vȯ2 range: 0.61 ± 0.07 μl h−1 mg−1 at 15°C, 1.63 ± 0.21 μl h−1 mg−1 at 22°C). Overall, there is a correlation between the average effect of temperature and the inter-individual variability of phenotypic traits, with higher temperature resulting in less inter-individual variability in development rate and morphological characteristics, which are faster and smaller at higher temperature, while variability in mass-specific Vȯ2 increased with temperature, reflecting the increase in average Vȯ2 that occurs at higher temperature. CS supported by a Beckman Scholarship. CAM supported by a CSUSM Research, Scholarship and Creative Activities Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.