Skull variability of Martino\u27 vole Dinaromys bogdanovi (Rodentia: Cricetidae): sexual dimorphism, allometry and phylogeny

Dinarska voluharica, Dinaromys bogdanovi, je paleoendemični glodavec Balkana in filogenetski relikt. Kljub majhnemu arealu se deli na tri evolucijske linije, ki so geografsko ločene z rekami in v alopatriji ţe pribliţno 1,3 oz. 0,3 milijona let. Naš namen je bil analizirati morfološko variabilnost ventralne strani lobanje med spoloma, ontogenetskim razvojem in filogenetskimi skupinami. Zanimalo nas je ali je vzorec morfološke variabilnosti enak filogenetskemu ter ali imajo filogenetske skupine enaka ali različna vzorca spolnega dimorfizma in ontogenetske alometrije. Uporabili smo metode geometrijske morfometrije, s katerimi smo lahko velikost in obliko lobanje obravnavali ločeno. V raziskavo smo vključili 184 lobanj s celotnega območja poselitve, ki smo jih a priori razvrstili v tri filogenetske in pet starostnih skupin. Z analizo morfološke variabilnosti med spoloma nismo zaznali sekundarnega spolnega dimorfizma v velikosti ali obliki lobanje pri nobeni starosti ali filogenetski skupini. Iz tega sklepamo, da med osebki istega spola ni izrazite kompeticije za parjenje z nasprotnim spolom in da sta spola pod vplivom podobnih okoljskih selekcijskih pritiskov. Z raziskavo ontogenetske alometrije smo ugotovili tesno povezanost oblike in velikosti lobanje. Odnos oblike in velikosti je bil pri vseh starostih linearen. Oblika lobanje se med ontogenetskim razvojem pri vseh treh filogenetskih linijah spreminja enako hitro. Alometrija torej nima pomembnega vpliva na nastanek razlik v obliki lobanje med filogenetskimi skupinami, saj le-te nastanejo ţe v prenatalnem obdobju. Vzorec morfološke variabilnosti se je skladal s filogenetskim. Najbolj se je od ostalih dveh skupin razlikovala severozahodna skupina, ki je v alopatriji z ostalima skupinama ţe pribliţno 1,3 milijona let. Osebki iz te skupine so imeli najširši gobčni del lobanje in moţganski del lobanje, najdaljšo in na stran pomaknjeno nebno odprtino, navzven ukrivljen niz meljakov in največjo zatilnično odprtino. Ugotovili smo, da ima ventralna stran lobanje dinarske voluharice determinacijsko vrednost, saj omogoča zanesljivo klasifikacijo v filogenetske skupine. Ker med filogenetskimi skupinami v velikosti lobanje ni bilo razlik in ker je bila morfološka variabilnost lobanje kljub alopatriji majhna, sklepamo, da je lobanja dinarske voluharice pod vplivom stabilizirajoče selekcije, razlike v obliki pa so nastale kot posledica procesov nevtralne evolucije.Martino\u27s vole, Dinaromys bogdanovi, is a Balkan paleoendemic rodent and a phylogenetic relict. Despite its small area of occupancy it is divided into three evolutionary lineages that are geographically separated by rivers and in allopatry for approximately 1.3 or 0.3 million years. The aim of this study was to analyze morphological variability of the ventral side of the skull between the sexes, during the ontogenetic development and among phylogenetic groups. We were interested in whether the pattern of morphological variability is the same as the phylogenetic. As well as, whether different phylogenetic groups have the same or a different pattern of sexual dimorphism and ontogenetic allometry. We employed the geometric morphometric methods, which allowed us to analyze the size and shape of the skull separately. The study included 184 skulls from the entire range of the species classified a priori into three phylogenetic groups and five age groups. The analysis of morphological variability between the sexes did not detect the secondary sexual dimorphism in size or shape of the skull at any age or phylogenetic group. We could therefore conclude that the competition between the individuals of the same sex for mating with the opposite sex is not pronounced and that the sexes are under similar ecological selection pressures. The study of ontogenetic allometry showed a close relation between the skull shape and size. The relationship was linear at all ages. During the ontogenetic development, the shape of the skull changed at the same rate in all three phylogenetic lineages. Allometry therefore does not have a significant influence on the development of the skull shape differences among the phylogenetic groupsskull shape differences are probably produced prenatally. A pattern of the morphological variability was the same as the phylogenetic. The Northwestern group, which has been in allopatry for approximately 1.3 million years, was the most different from the other two groups. Specimens of the Northwestern group had the widest rostrum and neurocranium, the longest and laterally moved incisive foramen, laterally bent row of molars, and the largest foramen magnum. We found out that the identified morphological characteristics have a determinating value and allow reliable classification into phylogenetic groups. Because there were no differences in skull size among the phylogenetic groups and the morphological variability was despite the allopatry small, we believe that the skull of the Martino\u27s vole was subjected to a stabilizing selection and shape differences are the result of a neutral evolution