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Wood frog adaptations to overwintering in Alaska: new limits to freezing tolerance | Journal of Experimental Biology | The Company of Biologists (opens in a new tab)

journals.biologists.com · 2014-06-15

Short answerEvidenceSource

Short answer

Mixed

Mixed.

One claim goes further than the study. One other point was not covered by the paper.

  • 3 supported
  • 1 overstated
  • 1 not covered

Checked against the study summary. The full text wasn't available, so some details couldn't be settled either way.

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1

The story

Wood frog adaptations to overwintering in Alaska: new limits to freezing tolerance | Journal of Experimental Biology | The Company of Biologists

journals.biologists.com · 2014-06-15

The story’s checkable claims.

Read the original story (opens in a new tab)
2

NewsLink checks it

Mixed

One claim overstates the study. Three of five check out. One claim the study doesn't address.

  • 3 supported
  • 1 overstated
  • 1 not covered
Open claim evidence
3
Source paper

Source layer

The 27 papers the story cites

Source study separated from background citations.

The research anchor for the report.

Then inspect each claim

Evidence layer

Claim by claim

Each claim gets a verdict. Expand it to see the evidence directly below.

5 claims in this story

Showing all 5 claimsChoose a verdict to focus the list.

Claim 1 of 5OverstatedAll 18 free-living wood frogs in natural hibernacula survived winter, remaining frozen for an average of 193±11 consecutive days, with average temperatures of −6.3°C and average minimum temperatures of −14.6±2.8°C; the coldest minimum experienced by surviving frogs was −18.1°C.View evidenceHide evidence

As stated193±11 days; −6.3°C average; −14.6±2.8°C average minimum; −18.1°C minimum

Why this verdict

The numerical details are supported by the abstract: frogs remained frozen for 193 ± 11 consecutive days, experienced average October–May temperatures of −6.3°C, average minimum temperatures of −14.6 ± 2.8°C with range down to −18.1°C, and had 100% survival with N=18. However, the presented claim is marked as causal; at abstract depth, the paper evidence is an observational field report of exposure and survival, not causal proof that the specific conditions caused survival. Descriptively, the result is supported; causal-strength framing is overstated.

1

Study evidence

Free-living wood frogs tracked into natural hibernacula remained frozen for extended periods through winter and experienced very low temperatures yet survived until spring.193 ± 11 days frozen; average October–May temperature −6.3°C; average minimum −14.6 ± 2.8°C (range −8.9 to −18.1°C).

“We investigated the ecological physiology and behavior of free-living wood frogs [Lithobates (Rana) sylvaticus] overwintering in Interior Alaska by tracking animals into natural hibernacula, recording microclimate, and determining frog survival in spring.”
Claim 2 of 5Not coveredThe researchers reported thermal hysteresis activity consistent with an antifreeze glycolipid in muscle and internal organs, but not skin, and concluded that the activity was not due to a protein antifreeze.View evidenceHide evidence

Why this verdict

The abstract supports detection of antifreeze glycolipid in muscle and internal organs but not skin. However, the profile at abstract depth does not provide the claimed details about thermal hysteresis activity or the conclusion that the activity was not due to a protein antifreeze. Those specifics may be in the full paper, but they are not verifiable from the supplied abstract-level profile.

1

Study evidence

Mean glucose concentrations were higher in naturally freezing frogs than in laboratory-frozen frogs (muscle: 13-fold higher; heart: 10-fold higher; liver: 3.3-fold higher).muscle 13-fold; heart 10-fold; liver 3.3-fold

“We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs.”
Claim 3 of 5SupportedFree-living wood frogs overwintering in Interior Alaska were tracked into natural hibernacula, and the study followed their microclimate, freezing duration, survival, and physiological responses.View evidenceHide evidence

Why this verdict

The abstract supports the story’s description that free-living Interior Alaska wood frogs were tracked into natural hibernacula, with microclimate, duration frozen, spring survival, and physiological/biochemical responses assessed. The profile also supports comparison with laboratory-frozen captive frogs for glucose measurements.

1

Study evidence

Free-living wood frogs tracked into natural hibernacula remained frozen for extended periods through winter and experienced very low temperatures yet survived until spring.193 ± 11 days frozen; average October–May temperature −6.3°C; average minimum −14.6 ± 2.8°C (range −8.9 to −18.1°C).

“We investigated the ecological physiology and behavior of free-living wood frogs [Lithobates (Rana) sylvaticus] overwintering in Interior Alaska by tracking animals into natural hibernacula, recording microclimate, and determining frog survival in spring.”
2

Study evidence

Mean glucose concentrations were higher in naturally freezing frogs than in laboratory-frozen frogs (muscle: 13-fold higher; heart: 10-fold higher; liver: 3.3-fold higher).muscle 13-fold; heart 10-fold; liver 3.3-fold

“We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs.”
Claim 4 of 5SupportedNaturally frozen frogs had much higher tissue glucose than laboratory-frozen frogs, including about 13-fold higher glucose in muscle, 10-fold higher in heart, and 3.3-fold higher in liver.View evidenceHide evidence

As stated13-fold muscle; 10-fold heart; 3.3-fold liver

Why this verdict

The abstract directly reports the same fold differences: naturally freezing frogs had mean glucose concentrations 13-fold higher in muscle, 10-fold higher in heart, and 3.3-fold higher in liver than laboratory-frozen frogs.

1

Study evidence

Mean glucose concentrations were higher in naturally freezing frogs than in laboratory-frozen frogs (muscle: 13-fold higher; heart: 10-fold higher; liver: 3.3-fold higher).muscle 13-fold; heart 10-fold; liver 3.3-fold

“We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs.”
2

Study evidence

Tissue glucose (cryoprotectant) concentrations measured in captive frogs frozen in the laboratory to -2.5°C were markedly lower than in naturally freezing frogs: muscle ~13-fold lower, heart ~10-fold lower, liver ~3.3-fold lower (natural vs laboratory).muscle: ~13-fold lower; heart: ~10-fold lower; liver: ~3.3-fold lower (laboratory vs natural)

“...tissue glucose concentrations in captive wood frogs frozen in the laboratory to -2.5°C.”
Claim 5 of 5SupportedThe authors hypothesize that enhanced freeze tolerance in Alaskan wood frogs may result from higher cryoprotectant levels produced by repeated freezing and thawing cycles under natural autumn conditions.View evidenceHide evidence

Why this verdict

The abstract-level profile supports this as a hypothesis: the authors propose that enhanced freeze tolerance is associated with higher cryoprotectant glucose levels produced by repeated freezing and thawing during natural early-autumn conditions. The story appropriately presents this mechanism as hypothesized rather than proven.

1

Study evidence

Free-living wood frogs tracked into natural hibernacula remained frozen for extended periods through winter and experienced very low temperatures yet survived until spring.193 ± 11 days frozen; average October–May temperature −6.3°C; average minimum −14.6 ± 2.8°C (range −8.9 to −18.1°C).

“We investigated the ecological physiology and behavior of free-living wood frogs [Lithobates (Rana) sylvaticus] overwintering in Interior Alaska by tracking animals into natural hibernacula, recording microclimate, and determining frog survival in spring.”
2

Study evidence

Mean glucose concentrations were higher in naturally freezing frogs than in laboratory-frozen frogs (muscle: 13-fold higher; heart: 10-fold higher; liver: 3.3-fold higher).muscle 13-fold; heart 10-fold; liver 3.3-fold

“We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs.”
Then look for missing context

Context layer

What the story left out

Important study details the story did not include.

  • Behavioral observations of wood frogs preparing to freeze in artificial hibernacula.

    The abstract-level paper profile includes this as a supporting component, but the presented story summary and claims do not mention the artificial-hibernacula behavioral observations.

    From behavioral observation in artificial hibernacula

  • Generalizability is limited: findings are specific to the tracked Interior Alaska frogs and the reported October–May overwintering period; broader representativeness is not documented at abstract depth.

    The story identifies the setting as Interior Alaska and gives N=18, but it does not explicitly caveat that the results may not generalize to other populations, regions, or winters. This limitation is material for interpreting the scope of the finding.

    From field observational study

7 things the story did carry across
  • Field tracking of free-living Interior Alaska wood frogs into natural hibernacula, with in-situ microclimate monitoring and spring survival assessment.
  • Quantitative field outcome: 193 ± 11 consecutive days frozen, average temperature −6.3°C, average minimum −14.6 ± 2.8°C, range down to −18.1°C, and 100% survival among N=18 tracked frogs.
  • Tissue glucose comparison between naturally freezing wild frogs and laboratory-frozen captive frogs, showing much higher glucose in natural frogs.
  • Detection of antifreeze glycolipid in muscle and internal organs but not skin.
  • Authors’ hypothesis that enhanced freeze tolerance may arise from higher cryoprotectant levels produced by repeated natural freeze–thaw cycles.
  • Biochemical assays were conducted on subsamples, and abstract-level evidence lacks sample sizes, variability, statistical tests, and detailed assay methods for those biochemical findings.
  • Laboratory-frozen captive frogs served as a comparator but the abstract lacks detailed protocol information and the lab conditions may not reproduce natural freeze–thaw exposure.
Then read the study layer

Study layer

Study at a glance

Scan the study first. Expand only the parts you want to inspect.

Pieces of work

4

Evidence read

study summary

Lead result

in vivo animal

1Lead resultin vivo animalCharacterize overwintering ecology/physiology of free-living Alaskan wood frogs in natural hibernacula (microclimate exposure, duration frozen, and spring survival), establishing new limits to freezing tolerance.field observational studyExpand

In plain English

Field study tracking free-living wood frogs (Lithobates sylvaticus) into natural hibernacula in Interior Alaska, recording overwinter microclimate across October–May and assessing spring survival; frogs remained frozen for extended durations at subzero temperatures and showed complete survival (N=18).

Key findings

  • Free-living wood frogs tracked into natural hibernacula remained frozen for extended periods through winter and experienced very low temperatures yet survived until spring.193 ± 11 days frozen; average October–May temperature −6.3°C; average minimum −14.6 ± 2.8°C (range −8.9 to −18.1°C).
  • Reported spring survival of tracked frogs was 100%.100% survival (N = 18).
“We investigated the ecological physiology and behavior of free-living wood frogs [Lithobates (Rana) sylvaticus] overwintering in Interior Alaska by tracking animals into natural hibernacula, recording microclimate, and determining frog survival in spring.”
What this piece can’t prove
  • Survival result is based on the reported sample (N = 18); the abstract does not indicate broader sample representativeness or potential attrition.

2 further details could not be confirmed from the summary.

2in vivo animalIdentify physiological/biochemical correlates of natural freezing in Alaskan frogs (tissue cryoprotectant glucose levels and presence of antifreeze glycolipids) and contrast them with laboratory-frozen captive frogs.tissue biochemical assaysExpand

In plain English

Tissue biochemical assays on subsamples of naturally freezing Alaskan wood frogs measured cryoprotectant (glucose) concentrations and tested for antifreeze glycolipids. Compared with captive frogs frozen in the laboratory to -2.5°C, naturally freezing frogs showed markedly higher tissue glucose (muscle 13-fold, heart 10-fold, liver 3.3-fold). Antifreeze glycolipid was detected in extracts from muscle and internal organs but not in skin.

Key findings

  • Mean glucose concentrations were higher in naturally freezing frogs than in laboratory-frozen frogs (muscle: 13-fold higher; heart: 10-fold higher; liver: 3.3-fold higher).muscle 13-fold; heart 10-fold; liver 3.3-fold
  • Antifreeze glycolipid was detected in extracts from muscle and internal organs of frozen frogs but not in skin.
“We measured cryoprotectant (glucose) concentrations and identified the presence of antifreeze glycolipids in tissues from subsamples of naturally freezing frogs.”
What this piece can’t prove
  • Abstract does not report sample sizes for the biochemical assays or number of individuals used for glycolipid detection.
  • No statistical details (tests, p-values, confidence intervals) or measures of variability are provided for the reported fold-changes.

2 further details could not be confirmed from the summary.

3in vivo animalIdentify physiological/biochemical correlates of natural freezing in Alaskan frogs (tissue cryoprotectant glucose levels and presence of antifreeze glycolipids) and contrast them with laboratory-frozen captive frogs.laboratory freezing of captive frogs to -2.5°CExpand

In plain English

Captive wood frogs were frozen in the laboratory to -2.5°C and tissue glucose (cryoprotectant) was quantified as a comparator to naturally freezing Alaskan frogs; laboratory-frozen frogs had substantially lower tissue glucose than naturally freezing frogs (muscle ~13-fold lower, heart ~10-fold lower, liver ~3.3-fold lower).

Key findings

  • Tissue glucose (cryoprotectant) concentrations measured in captive frogs frozen in the laboratory to -2.5°C were markedly lower than in naturally freezing frogs: muscle ~13-fold lower, heart ~10-fold lower, liver ~3.3-fold lower (natural vs laboratory).muscle: ~13-fold lower; heart: ~10-fold lower; liver: ~3.3-fold lower (laboratory vs natural)
“...tissue glucose concentrations in captive wood frogs frozen in the laboratory to -2.5°C.”
What this piece can’t prove
  • Abstract lacks explicit sample size and detailed protocol information for the laboratory freezing experiment (e.g., duration at target temperature, cooling rate, number of freeze–thaw cycles).
  • Antifreeze glycolipids were identified in naturally freezing frogs per the abstract; the abstract does not indicate whether the laboratory-frozen frogs were assayed for or contained these glycolipids.
4in vivo animalDescribe behavioral preparation to freeze in artificial hibernacula as contextual support for natural overwintering mechanisms.behavioral observation in artificial hibernaculaExpand

In plain English

The authors report that they recorded the behavior of free-living wood frogs preparing to freeze in controlled/semicontrolled artificial hibernacula; this behavioral observation component is presented as contextual support for the study's investigation of natural overwintering mechanisms but the abstract provides no behavioral detail or quantitative metrics.

Key findings

  • Behavior of wood frogs preparing to freeze was recorded in artificial hibernacula (reported in the abstract), but no specific behavioral descriptions or quantitative results are provided in the abstract.
“We also recorded the behavior of wood frogs preparing to freeze in artificial hibernacula...”
What this piece can’t prove

3 further details could not be confirmed from the summary.

Finally, the search trail

Method layer

NewsLink found the paper. Tessa takes you deeper.

NewsLink checks the story. Tessa is where you inspect the paper, authors, evidence, and research context.

Papers considered

The selected paper, plus nearby candidates.

PubMed, Crossref, Europe PMC · 36 candidate papers

Candidate

Overwintering in Yellowjacket Queens (Vespula vulgaris) and Green Stinkbugs (Elasmostethus interstinctus) in Subarctic Alaska

Physiological Zoology · 1996 · Crossref

Source (opens in a new tab)

And 30 more candidates considered.