Cold hardiness and development rate as elements of adaptive strategies of phalangiid harvestmen (Opiliones,Phalangiidae) in northeastern Asia

Three species of phalangiid harvestmen (Mitopus morio, Homolophus arcticus, and Oligolophus tienmushanensis) were studied. These species overwinter at the egg stage and have embryonic diapause, suppressing hatching in autumn and preventing death from low temperatures. The eggs do not survive freezing, but can be supercool. The comparison of the growth rate under natural conditions and in containers with controlled temperature indicates that in the seasons with unfavorable climatic conditions, not all individuals have time to lay eggs before cold weather sets in; however, in favorable seasons, oviposition occurs approximately 30–45 days before the death of the adults. The high cold hardiness of M. morio and H. arcticus eggs suggests that the northward distribution of these species cannot be limited by low winter temperatures. The cold hardiness of O. tienmushanensis also does not appear to prevent their colonization of most biotopes of the region, except for those having a thin snow cover or no cover at all. However, this colonization does not happen. The northward distribution of O. tienmushanensis appears to be restricted by some other factors.