Reliability of cranial base measurements on lateral skull radiographs.

OBJECTIVE: To explore the reliability of identification of anatomic landmarks on lateral skull radiographs of young unaffected individuals that has conventionally been used to diagnose pathologic relationships in the craniovertebral junction. MATERIAL AND METHODS: From the Helsinki longitudinal growth study, 20 randomly selected lateral radiographs were analyzed and re-analyzed by two examiners. Both located seven cephalometric landmarks based on which five measurements were calculated. The differences of results were compared. With similar method three radiographs were analysed by 11 examiners and results were compared. RESULTS: Some anatomic landmarks were easier to locate than others on lateral skull radiographs leading to differences in measurements based on them. We found the magnitude of the difference to be dependent on the landmark serving as reference. Inter- and intra-examiner errors were of similar magnitude, although intra-examiner error declined in the repeated landmark identification. Variation in a single landmark location had in general little effect on the measurement value. CONCLUSION: Variations in landmark location lead to differences in numeric evaluation of the anatomic relationships in the skull base area. These differences were, however, shown to have little clinical significance. Hence, the documented methods are applicable for screening of basilar pathology.

Sire coloration influences offspring survival under predation risk in the moorfrog.

When breeding, male moor frogs Rana arvalis develop a bright blue dorsal coloration which varies in intensity between males. We tested whether this colour acts as a potential signal of a male's genetic quality to female moor frogs by artificially crossing pairs of males differing in the extent of the blue coloration to the same female. Maternal half-sibships provide a powerful means to detect paternal genetic effects on offspring as they control for other potentially confounding variables. We assayed the ability of offspring to survive an ecologically realistic test of fitness by exposing them to predation by the larvae of the predatory water beetle Dytiscus marginalis. Although sire's coloration did not influence tadpole body size, it did affect their ability to survive the predation trial. Offspring of bright blue males had higher survival than those of dull males when exposed to large predators, which were more voracious predators than smaller ones. Our results indicate that paternal secondary sexual traits provide information about genetic effects on offspring fitness in this species, but suggest that these effects may be context-dependent. Variable selection caused by contextual dependence may have important consequences for the evolution of female choice rules, and for the maintenance of genetic variation for both male trait and female preference.