Robustness of newt heads in condition of co-existence: a case of the Carpathian newt and the alpine newt.

Co-existence between potentially competing newt species can lead to niche differentiation (e.g., in terms of diet shifts). This may cause adaptive responses involving changes in head shape. Here, we tested the hypothesis: the head shape of is different in conditions of co-occurrence with than in conditions in which other newt species are absent. We analysed images depicting head shape of specimens of and from a museum collection. All specimens of originated in a habitat where also occurred, whereas specimens of derived from populations that cohabited with and populations in which the presence of another newt species was not recorded. In each image, landmarks and semilandmarks were digitised. Females of from the population where also occurred were characterised by more massive heads and longer mouths in lateral views than females from sites where no other newt species occurred. Significant differences in head shape were also found when analysing ventral views between these species when they occupied the same habitat. We confirmed that the head shape of female differs between conditions of co-occurrence and absence of ; no differences were found for males. A differently shaped head may be an adaptation to diet; females with longer mouths and more robust basal parts of the head can feed on larger invertebrates and compete more effectively with . The co-existence of newt species should be taken into account in future ecomorphological studies.