Geographic variation of Nelima nigricoxa (Opiliones: Sclerosomatidae) showing a hybrid zone in the femoral marking of legs in Tottori Pref., Honshu

Geographic variation of a Japanese harvestman species, Nelima nigricoxa Sato & Suzuki 1939 was studied in Tottori Prefecture and adjacent areas in Honshu, Japan.Populations from the eastern part of the area bear legs with black rings at the base of the femora, whereas those from the western part of the area lacked the black marks.They intergrade one another making a zone of intergradation with ca.20 km wide in the area roughly flanked by the Koch River and the Sendai River.The position of the zone corresponds well to that between the two races of Gagrellula ferruginea, indicating possible Müllerian mimicry between the two species.No difference across the intergradation zone was found in the other morphological characters.Diploid number of chromosomes varied from 16 to 20 from east to west in the other area in western Tottori Pref.A population polymorphic for the number was found on the northern slope of Mt.Daisen where populations with 2n = 20 and populations with 2n = 18 abut.This indicates occurrence of a chromosomal hybrid zone in the Mt.Daisen area.No significant difference was found in the morphology of labrum, penis, and seminal receptacle, among populations differing in the chromosome number.This suggests that the chromosome rearrangements occurred in this area in the species have effects in neither morphology nor reproductive isolation.Both body and legs became smaller or shorter with the increase of altitude in any of the following four different areas: 1) Mt.Hyonosen, 2) central Tottori west of the Sendai River, 3) Mt.Daisen, and 4) Hino-Nichinan areas, though the correlation between the altitude and leg length is not so clear in the Mt.Hyonosen area.