amphibians

When Salamanders Surface: Understanding the Secrets Behind Spotted Salamander Overwintering Emergence

/ gtattersall

Amphibians have long fascinated researchers due to their unique life cycles and environmental sensitivities, but many aspects about the biology of fossorial (i.e., burrowing) species remain shrouded in mystery. Fossorial amphibians like the Spotted Salamander (Ambystoma maculatum) spend most of their lives underground, emerging to the surface only briefly to breed or forage. In our latest paper, we address some of the intrinsic and extrinsic factors that may trigger emergence from overwintering by evaluating the interplay between temperature, gravity, and innate migratory cues over salamander behaviour.

Our study focussed on the role of soil temperature inversion—a seasonal shift where surface soils warm faster than deeper layers—in signalling salamanders to leave their winter refuges and begin their overland journey to breeding ponds. Using a vertical thermal gradient in the lab, we examined how salamanders responded to temperature cues at different depths and whether their activity levels changed with temperature shifts that mimicked soil temperature inversion. Our findings suggested that salamanders are not only tolerant of a wide thermal range but are also displaying a circannual phenomenon known as “migration restlessness”. Migration restlessness is characterised by a surge in movement often seen in animals preparing to migrate. Coupled with negative geotaxis, a tendency to move upward against gravity, this restless behaviour may explain why salamanders begin their spring migration at just the right moment, maximising their chances of reproductive success while avoiding the dangers of emerging too early and potentially freezing.

Representation of soil temperature inversion in the forest surrounding Bat Lake, Algonquin Provincial Park, ON, Canada, from where the spotted salamanders were collected.

A. Schematic of the vertical thermal gradient used to assess the effects of thermal inversion and gravity on salamander behaviour. Thermal image of the active (B) and overwintering (C) thermal gradients used in the study. The thermal gradient was always kept at a 45º angle relative to the horizontal axis, imitating underground burrows. 

Sped-up time-lapse of a male Ambystoma maculatum tested within the active thermal gradient. Frames were taken every 30 s, for a total of 18 h of experiment (20 frames/sec).

For a link to an interview with the first author ECR, Danilo Giacometti, please see the following link.

For a link to the paper, please see the citation below.

Citation

Giacometti D., Moldowan P. D., Tattersall G. J.; Ups and downs of fossorial life: migration restlessness and geotaxis may explain overwintering emergence in the Spotted Salamander. J Exp Biol 2024; jeb.249319. doi: https://doi.org/10.1242/jeb.249319

Blog Author: Danilo Giacometti

Twists of fate and the hidden story of salamander abnormalities

/ gtattersall

A new paper has been accepted in the Canadian Journal of Zoology, resulting from Gloria Gao’s (Njal Rollinson’s lab at University of Toronto) hard work and based (in part) on the long-term study of the spotted salamanders at Bat Lake, Algonquin Park along with other field sites in Algonquin Park.

This study investigates the prevalence and fitness consequences of morphological abnormalities in Spotted Salamanders (Ambystoma maculatum) within an uncontaminated ecosystem in Algonquin Provincial Park, Canada. Over a 12-year period, the study found that abnormality rates ranged from 4.3% to 5.8% annually, aligning with baseline frequencies observed in other minimally impacted amphibian populations. Interestingly, despite expectations that abnormalities might reduce fitness, salamanders with abnormalities in this study displayed slightly higher body condition and significantly earlier arrival times at breeding sites—traits typically associated with high fitness. These results suggest a potential survivorship bias, where only individuals with favourable genetic or environmental factors survive to be observed, masking the true impact of abnormalities.

The study also highlights the importance of understanding abnormality rates in uncontaminated environments, as these can provide valuable baselines for comparison with more impacted habitats. It appears that Caudata (salamanders and newts) generally have a higher prevalence of abnormalities compared to Anura (frogs and toads), although the reasons for this remain speculative. The findings from this study underscore the complex relationship between abnormalities and fitness and emphasize the need for further research to explore how environmental factors influence these dynamics in amphibian populations.

Examples of abnormalities observed among Spotted Salamanders at Bat Lake, Algonquin Provincial Park: A. polydactyly (additional phalanges) resulting from partial duplication of the hand on the right forelimb; B. partial syndactyly (fused digits) and abnormal arrangement of the right forelimb phalanges; C. polymelia (limb duplication) of the right forelimb; D. micromelia (proportionately small or short limb) of the left hindlimb demonstrating early stage regeneration following probable amputation; E. tail bifurcation.

Citation

Gao, GHY, Moldowan, PD, LeGros, DL, Sahar, M, Tattersall, GJ, and Rollinson, N. 2024. Frequency of adult amphibian abnormalities and consequences for traits related to fitness in an uncontaminated environment. Canadian Journal of Zoology, doi.org/10.1139/cjz-2024-0063.

Proofs are not yet available, but will update when they are.