Morphological variation in a hybrid zone between two chromosomal races (2n=16 and 2n=22) of the Japanese harvestman Gagrellopsis nodulifera

Abstract

We analyzed morphological variation in a hybrid zone between 2n = 16 and 2n = 22 chromosomal races of a Japanese harvestman, Gagrellopsis nodulifera (Arachnida: Opiliones; Sclerosomatidae). We found negative correlations between the sizes of four metric traits and altitude in all populations analyzed. Morphological variation was positively correlated with chromosomal heterozygosity. A karyotypically conspicuous population with an intermediate karyotype 2n = 20, was also morphologically unique in that individuals from this population were much smaller than those from other populations. Besides, in this population the profile of the correlation for the four metric traits analyzed was different from those in the other populations. In one of the hybrid populations, the body size of the chromosomal heterozygotes was significantly smaller than that of homozygotes. Hybrid populations and parental races did not differ in level of fluctuating asymmetry. Possible mechanisms of the karyotype-phenotype associations in the chromosomal hybrid zone are discussed.