Ong Karen, Norris D Ryan
Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada.
PLoS One. 2025 Apr 4;20(4):e0319043. doi: 10.1371/journal.pone.0319043. eCollection 2025.
For the small number of temperate and boreal species that cache perishable food, previous research suggests that increasing freeze-thaw events can have a negative impact on fitness by degrading the quality of cached food. However, there is no experimental evidence that directly links freeze-thaw events to cache quality. To examine how the timing, frequency, duration, and intensity of freeze-thaw events influenced cached food mass loss, a proxy for caloric content, we conducted a series of month-long laboratory experiments by placing simulated caches (raw chicken placed between two pieces of black spruce Picea mariana bark) in programmable freezers. Freeze-thaw treatments were modelled after weather data from Algonquin Provincial Park, Ontario, where a population of Canada jays (Perisoreus canadensis), a species that caches perishable food for overwinter survival and to support late-winter breeding, has declined by > 70% since the 1980s. First, we found no evidence that an increased frequency of freeze-thaw events influenced mass loss, suggesting that microstructural damage caused by crystal reformation does not significantly influence cache quality. Instead, our experimental results demonstrated that mass loss was positively influenced by longer individual thaws, which likely reflects increased microbial growth, oxidation, and progressive drip loss. We also found that caches lost more weight when subjected to early freeze-thaw events compared to late freeze-thaw events. Finally, we show that milder freezes led to less mass loss and, unexpectedly, warmer than average thaws post-freeze also led to less mass loss. Our results suggest that longer thaw periods post-freezing and milder freezes cause or lead to significantly increased spoilage of perishable cached food. All of these temperature-related conditions are closely associated with long-term changes in climate and, thus, the effects on cache degradation reported in these experiments should be applicable to species caching perishable food in the wild.
对于少数储存易腐食物的温带和寒带物种，先前的研究表明，冻融事件增加会因降低储存食物的质量而对其健康产生负面影响。然而，尚无实验证据直接将冻融事件与储存质量联系起来。为了研究冻融事件的时间、频率、持续时间和强度如何影响储存食物的质量损失（热量含量的一个指标），我们进行了一系列为期一个月的实验室实验，将模拟储存物（生鸡肉夹在两片黑云杉树皮之间）置于可编程冰箱中。冻融处理是根据安大略省阿冈昆省立公园的气象数据模拟的，自20世纪80年代以来，当地的灰噪鸦（一种为越冬生存和支持冬末繁殖而储存易腐食物的物种）数量减少了70%以上。首先，我们没有发现证据表明冻融事件频率增加会影响质量损失，这表明晶体重新形成引起的微观结构损伤不会显著影响储存质量。相反，我们的实验结果表明，质量损失受到个体解冻时间延长的正向影响，这可能反映了微生物生长、氧化和渐进性滴漏损失的增加。我们还发现，与后期冻融事件相比，早期冻融事件会使储存物减重更多。最后，我们表明较温和的冷冻导致的质量损失较少，而且出乎意料的是，冷冻后的解冻温度高于平均水平也会导致较少的质量损失。我们的结果表明，冷冻后较长的解冻期和较温和的冷冻会导致或显著增加易腐储存食物的变质。所有这些与温度相关的条件都与气候的长期变化密切相关，因此，这些实验中报告的对储存变质的影响应该适用于在野外储存易腐食物的物种。
