For decades, biologists have known that hermit crabs forced to live in shells that are too small slow their growth. What wasn\u2019t clear was how they did it.<\/p>\n
New research suggests the answer isn\u2019t simply that the crabs eat less. Instead, they appear to regulate growth by changing how efficiently they use the food they consume.<\/p>\n
\u201cHermit crabs depend on empty snail shells for protection, and the right size shell isn\u2019t always available,\u201d says Caitlin Ball, A22, AG23, who led the study as a graduate student in the Tufts Department of Biology. \u201cWhen they\u2019re stuck in shells that are too small, they grow more slowly. The question was: what\u2019s the mechanism?\u201d<\/p>\n
To investigate, researchers compared feeding behavior and waste production in crabs living in well-fitting shells versus shells that were deliberately too small. Surprisingly, crabs in undersized shells did not eat less. Instead, they defecated more frequently, suggesting they were eliminating a greater proportion of nutrients rather than converting them into new tissue.<\/p>\n
\u201cFor years, people observed the growth slowdown but couldn\u2019t identify the mechanism,\u201d says\u00a0Phil Starks<\/a>, associate professor of biology and senior author on the study, which was recently published in Invertebrate Biology<\/a>. \u201cWhat we\u2019re seeing is consistent with something subtle\u2014the crabs appear to regulate growth by adjusting nutrient assimilation.\u201d<\/p>\n The findings point to a broader principle in biology: growth isn\u2019t controlled only by how much an animal eats, but also by how efficiently it turns food into body mass. Under structural constraints\u2014in this case, a shell that limits expansion\u2014animals may alter internal energy processing rather than external consumption.<\/p>\n For humans, how energy is absorbed, partitioned, stored, and expended is also known to vary significantly between individuals, although some people might envy hermit crabs for having so much control over that process.<\/p>\n \u201cWe wouldn\u2019t want to imply that hermit crabs are a model for human metabolism, or that this study directly explains human weight variation, but the broader biological principle does extend beyond crabs,\u201d says Starks. \u201cAcross animals\u2014including humans\u2014body mass isn\u2019t determined solely by how much food is consumed. Growth regulation can occur at the level of nutrient assimilation, not just appetite. Intake and growth aren\u2019t the same thing.\u201d<\/p>\n \u201cIt\u2019s exciting because the study answers a question about hermit crab growth that\u2019s been sitting there for a while,\u201d says Jan Pechenik, professor emeritus of biology, expert in invertebrate biology, and co-author of the paper. \u201cWe knew the pattern. Now we have opened the door to explore evidence for how it might work.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"For decades, biologists have known that hermit crabs forced to live in shells that are too small slow…\n","protected":false},"author":2,"featured_media":504666,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[85,46,141,386],"class_list":["post-504665","post","type-post","status-publish","format-standard","has-post-thumbnail","category-wildlife","tag-il","tag-israel","tag-science","tag-wildlife"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/504665","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/comments?post=504665"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/posts\/504665\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media\/504666"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/media?parent=504665"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/categories?post=504665"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/il\/wp-json\/wp\/v2\/tags?post=504665"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}