Variation in body size and degree of melanism within a lizards clade: is it driven by latitudinal and climatic gradients?

MORENO AZOCAR DL; PEROTTI MG; BONINO MF; SCHULTE JA; ABDALA CS; CRUZ FB

JOURNAL OF ZOOLOGY (1987)

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015 vol. 295 p. 243 - 253

0952-8369

Body size (BS) varies in response to several selective pressures. In ectotherms,thermal inertia may affect thermoregulation, since larger BSs increase heat conservationas Bergmann originally stipulated for endotherms. However,Bergmann?s rule is controversial in ectotherms. The heat balance hypothesis statesthat ectotherms? thermoregulatory capability is relevant for trends in BS. In coldclimates, larger BSs would be advantageous for small thermoregulatingectotherms, by increasing heat conservation. However, BS implies a delayingeffect on heating too; therefore, ectotherms may need another trait to compensatethe later effect. Thermal melanism hypothesis posits that melanism increases heatgain, and may be adaptive for animals inhabiting cold climates. We propose thatthe higher solar radiation absorption from increased melanism may be such acompensatory trait. We expect BS and melanism to increase with latitude inresponse to seasonal temperatures and solar radiation. To test this, we studied themonophyletic Liolaemus goetschi group of lizard species across its 2200 km (32?48° S latitude) range. We used phylogenetically informed analyses to study geographicvariation of BS and melanism (dorsal, ventral and total) in relation totemperatures, thermal amplitude, cloudiness and net solar radiation. Our resultsshow that lizards? BS increases latitudinally in relation to thermal amplitude andtemperature. Only ventral melanism varied latitudinally, but all melanism variablesvaried in response to cloudiness and net radiation. The relationship betweenBS and melanism was significant and positive in all cases. We suggest thermalinertia may be a fair candidate mechanism explaining geographic variation in BS(heat balance hypothesis), while melanism may influence heat gain according tothe thermal melanism hypothesis. However, it remains unclear why latitudinalvariation is related to ventral instead of dorsal melanism, and further investigationis needed to clarify the relationship between BS and melanism in light of coldclimates.