title: The effect of leaf shape on the thermoregulation and frost tolerance of an annual vine, Ipomoea hederacea (Convolvulaceae).
abstract: OBJECTIVE
  Leaf shape is predicted to have important ecophysiological consequences; for example, theory predicts that lobed leaves should track air temperature more closely than their entire-margined counterparts. Hence, leaf-lobing may be advantageous during cold nights (∼0°C) when there is the risk of damage by radiation frost (a phenomenon whereby leaves fall below air temperature because of an imbalance between radiational heat loss and convective heat gain).
  
  
  METHODS
  Here, we test whether radiation frost can lead to differential damage between leaf shapes by examining a leaf-shape polymorphism in Ipomoea hederacea, where leaves are either lobed or heart-shaped depending on a single Mendelian locus. We logged leaf temperature during midautumn, and measured chlorophyll fluorescence and survival as proxies of performance. Furthermore, we tested if the leaf-shape locus confers freezing tolerance using freezing assays on leaf tissue from different leaf shapes.
  
  
  RESULTS
  We found that lobed leaves consistently remain warmer than heart-shaped leaves during the night, but that no pattern emerged during the day, and that temperature differences between leaf shapes were typically small. Furthermore, we found that leaf types did not differ in frost tolerance, but that a 1°C decrease leads to a transition from moderate to complete damage.
  
  
  CONCLUSIONS
  Our results demonstrate that Ipomoea hederacea leaf shapes do experience different nighttime temperatures, and that only minor temperature differences can lead to disparate levels of freezing damage, suggesting that the differential thermoregulation could result in different levels of frost damage.
authors.affiliation: Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S3B2, Canada.
authors.forename: Brandon E
authors.initials: BE
authors.lastname: Campitelli
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Gorton
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Ostevik
authors.forename: John R
authors.initials: JR
authors.lastname: Stinchcombe
mesh_terms: D001833:Body Temperature Regulation; D003080:Cold Temperature; D005615:Freezing; D027741:Ipomoea / Q000033:anatomy & histology* / Q000502:physiology*; D009657:North Carolina; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology
keywords: Ipomoea hederacea; boundary layer; cline; energy budgets; freezing tolerance; leaf shape; radiational cooling; thermoregulation