Month: October 2024

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

Shape-Shifting in the Face of Climate Change: The Long and the Short of How Australian Birds Are Adapting

/ gtattersall

As global temperatures rise, animals are facing mounting pressure to adapt, and Australian birds are no exception. Our recent research (from Sara Ryding’s PhD research) has examined over 5,000 museum specimens, representing 78 bird species across Australia, revealing clear changes in their body and appendage sizes. These changes are aligned with two well-known ecological principles: Bergmann’s rule, which predicts smaller body sizes in warmer climates in endotherms, and Allen’s rule, which argues that animals (namely endotherms) will develop larger appendages to regulate body heat. Consistent with these theories, our study found that birds are experiencing a long-term decrease in body size, particularly in absolute wing length, while their appendages, such as bills and tarsi (leg bones), are getting larger relative to their bodies. This phenomenon, often referred to as “shape-shifting,” is a widespread response to the increasing temperatures driven by climate change.

Interestingly, our research also highlights a more complex picture when it comes to short-term responses. While long-term trends show a clear increase in appendage size to aid thermoregulation, birds displayed smaller appendages in the years following hotter temperatures. This suggests that while birds are gradually adapting to rising temperatures over time, short-term weather events may create different selection pressures that affect growth and development. Factors like food availability and reproductive challenges could contribute to these opposing trends. This study underscores the intricate balance between long-term evolutionary changes and the immediate pressures exerted by fluctuating environmental conditions, offering critical insights into how birds—and potentially other animals—might continue to respond to our rapidly changing world.

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

Citation

Ryding, McQueen, A, Klaassen, M, Tattersall, GJ, and Symonds, MRE. 2024. Long- and short-term responses to climate change in body and appendage size of diverse Australian birds. Global Change Biology, 30:e17517. https://doi.org/10.1111/gcb.17517

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.

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