title: Gross mismatch between thermal tolerances and environmental temperatures in a tropical freshwater snail: climate warming and evolutionary implications.
abstract: The relationship between acute thermal tolerance and habitat temperature in ectotherm animals informs about their thermal adaptation and is used to assess thermal safety margins and sensitivity to climate warming. We studied this relationship in an equatorial freshwater snail (Clea nigricans), belonging to a predominantly marine gastropod lineage (Neogastropoda, Buccinidae). We found that tolerance of heating and cooling exceeded average daily maximum and minimum temperatures, by roughly 20°C in each case. Because habitat temperature is generally assumed to be the main selective factor acting on the fundamental thermal niche, the discordance between thermal tolerance and environmental temperature implies trait conservation following 'in situ' environmental change, or following novel colonisation of a thermally less-variable habitat. Whereas heat tolerance could relate to an historical association with the thermally variable and extreme marine intertidal fringe zone, cold tolerance could associate with either an ancestral life at higher latitudes, or represent adaptation to cooler, higher-altitudinal, tropical lotic systems. The broad upper thermal safety margin (difference between heat tolerance and maximum environmental temperature) observed in this snail is grossly incompatible with the very narrow safety margins typically found in most terrestrial tropical ectotherms (insects and lizards), and hence with the emerging prediction that tropical ectotherms, are especially vulnerable to environmental warming. A more comprehensive understanding of climatic vulnerability of animal ectotherms thus requires greater consideration of taxonomic diversity, ecological transition and evolutionary history.
authors.affiliation: Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Brunei Darussalam. Electronic address: gianluca.polgar@gmail.com.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Polgar
authors.affiliation: Institute of Mathematical Sciences, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address: tfkhang@um.edu.my.
authors.forename: Tsung Fei
authors.initials: TF
authors.lastname: Khang
authors.affiliation: Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Brunei Darussalam. Electronic address: teddy.chua@ubd.edu.bn.
authors.forename: Teddy
authors.initials: T
authors.lastname: Chua
authors.affiliation: Environmental and Life Sciences Programme, Faculty of Science, Universiti Brunei Darussalam, Brunei Darussalam. Electronic address: davidmarshall11@gmail.com.
authors.forename: David J
authors.initials: DJ
authors.lastname: Marshall
mesh_terms: D000064:Acclimatization; D000818:Animals; D005075:Biological Evolution; D005618:Fresh Water; D057232:Global Warming; D006339:Heart Rate; D012908:Snails / Q000502:physiology*; D013696:Temperature; D014329:Tropical Climate
keywords: Animal ectotherms; Buccinidae; Clea nigricans; Cold tolerance; Heat tolerance; Thermal safety margins