Bergmann’s rule and the terrestrial caecilian Schistometopum thomense (Amphibia: Gymnophiona: Caeciliidae)

Question: Do caecilians follow Bergmann’s rule? Hypothesis: Bergmann’s rule explains the wide variation in body sizes found among populations of the terrestrial caecilian Schistometopum thomense. Field site: This is a range-wide study incorporating most terrestrial habitats throughout the island of São Tomé in the Gulf of Guinea. Methods: We performed morphological measurements on 95 museum specimens and 187 field-collected individuals and compared them with site data from 13 separate localities on the island. Conclusions: This is the first example of a caecilian amphibian that follows Bergmann’s rule. Total body mass doubles and length increases by nearly 50% up to 1050 m of altitude. This result is surprising as it occurs virtually on the equator, over a very small spatial scale (<16 km horizontal), and within a relatively small temperature range (<10 C).