Shrews shrink in winter and regrow in spring
The tiny mammals reduce the size of their organs in the winter and can even decrease and rebuild bones
During winter, the skull of common shrews shrinks by up to 15 per cent, only to grow back during spring by up to nine per cent. The animals lose almost a fifth of their body weight in the cold months, and nearly double their body mass again during warmer periods. Scientists from the Max Planck Institute for Ornithology in Radolfzell and Seewiesen found that not only bones, but also organs and even the brain itself take part in this depletion. In their study, the scientists assume that this reversible shrinkage ensures the survival of these highly energetic animals during the penurious winter months.
Shrews live their lives on the fast track. These constantly active insect eaters with a weight of only ten grams are closely related to moles and hedgehogs. Their apparent close relationship to mice is only because of their body shape. The energy requirement of a shrew is so high that it will starve if it does not find any food for two to three hours. Neither the day time nor the seasons keep them from feeding during their short, no more than thirteen-months long life. In summer, shrews feed mainly on worms and larvae in the soil. In winter, under unequally tougher life conditions, shrews live primarily from insects and spiders.
In the 1950s the Polish zoologist August Dehnel noticed that shrews caught in winter are not only lighter, but actually smaller. His surveys show that the skulls are flatter and the spine is shorter. But also many organs and particularly the brain of his animals showed a smaller volume than during the summer, with seasonal fluctuations in a size range of not insignificant 20 per cent.
Adaptation to the winter's living conditions?
In order to investigate whether single individuals actually altered their body size in that way, or whether this was only a selection process in the population studied by Dehnel, the PhD student Javier Lazaro from the Max Planck Institute for Ornithology in Radolfzell caught around 100 common shrews around the campus close to the Lake Constance. He equipped the animals with rice grain-sized electronic ID chips, as they are also used - somewhat bigger - for pets. All of the animals’ skulls were X-rayed before releasing them back into the wild. Through regular recapture initiatives, approximately one-third of the animals could be recaptured at least once, and again got X-rayed.
All the investigated individuals had shrunk in the winter and had regrown in spring. “In winter, the skull height decreased by an incredible 15 percent and even up to a maximum of 20 percent, to then increase again in spring by up to nine percent”, says Javier Lazaro. Dina Dechmann, co-author of the study, interprets this phenomenon as a previously unknown strategy of this highly metabolic animal, to survive the lack of food and the low temperatures during winter. “Normally, animals in colder zones are larger and have a good volume-to-surface ratio to compensate for heat losses. The shrew, on the other hand, has a low volume-to-surface ratio and could possibly save vital energy through shrinking”, says Dechmann. Recently her working group succeeded in demonstrating similar changes in the skull of the weasel. These small predators, members of a completely different mammalian group, also have an extremely high energy requirement and do not have the option of avoiding winter or or entering hibernation.
“The measured changes found on the bone and organ levels provide some starting points for further exciting research. Currently, in collaboration with colleagues of a university hospital, we are looking at changes in the bone substance and observe reversible processes that are reminiscent of lesions in osteoporotic bones. The alterations of the brain and heart also underline medically interesting similarities”, says Moritz Hertel from the sub-institute in Seewiesen, senior-author of the study. This study connecting shrew fieldwork to medical research is a good example of how basic research of the Max Planck Society can lead to unexpected discoveries.
SSp/HR
연구팀은 약 100마리의 야생 뾰족뒤쥐를 포획했다. 이들에게 쌀알만 한 크기의 전자칩을 몸에 넣고 두개골을 X선으로 촬영했다. 그런 뒤 다시 야생에 방사하고, 정기적으로 다시 잡아서 X선 촬영을 했다. 한 번에 최소 3분의 1은 다시 포획할 수 있었다.
분석 결과 모든 개체들이 겨울에는 작아지고 봄에는 커졌다. 라자로 연구원은 “겨울에는 두개골의 길이가 최대 20%까지 줄어들고 봄에는 9%까지 커졌다”고 말했다. 연구에 참여한 디나 데크만 연구원은 이런 현상이 겨울의 낮은 기온과 먹이가 부족한 상황에서 생존하기 위한 전략일 것이라고 추정했다. 그는 또 “일반적으로 추운 지역에 사는 동물들은 열손실을 줄이기 위해 몸집이 큰 편인데 뾰족뒤쥐는 몸집을 줄여서 생존에 필요한 에너지를 줄이는 것 같다”고 말했다. 데크만 연구원은 최근 뾰족뒤쥐와 전혀 다른 종류의 포유동물인 족제비의 뇌가 뾰족뒤쥐와 비슷하게 작아지는 것을 발견했다.
연구팀은 이 연구 결과가 골다공증 같은 사람의 질병을 연구하는 데에도 시사점을 제공한다고 설명했다. 현재 병원 연구진과 함께 뼈 구성 물질의 변화 등을 관찰하고 있다. 연구팀은 이번 연구 결과를 국제학술지 ‘커런트 바이올로지’ 10월 24일자에 발표했다.
https://www.mpg.de/11667328/shrews-shrink-in-winter-and-regrow-in-spring?filter_order=L&research_topic=
뾰족뒤쥐는 일본에 주로 사는 설치류 포유동물로 주로 곤충과 벌레들을 잡아먹고 몸무게는 약 10g에 불과하다. 몸집은 작지만 매우 활발히 움직이기 때문에 에너지를 보충하기 위해 쉴 새 없이 먹이를 먹는다. 두세 시간만 먹이를 먹지 못해도 굶어 죽을 정도다.