DIVERGENCE OF PHOTOPERIODIC RESPONSE AND HYBRID DEVELOPMENT IN TELEOGRYLLUS (Orthoptera : Gryllidae)

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Three Japanese forms of Teleogryllus are closely related to the tropical species, T. mitratus. They have, however, different means of seasonal regulation. The two northern species, T. emma and T. yezoemma, have obligatory diapause in the egg stage and belong to short-day insects in that their nymphal development is accelerated by a short photoperiod and delayed by a long one. On the other hand, the subtropical form, T. taiwanemma, is a long-day species, which enters a nymphal diapause in short-day conditons but not in long-day conditions. The tropical form, T. mitratus, is devoid of any conspicuous response to photoperiod in regard to its developmental rate. All the Japanese forms produced hybrid offspring when mated with T. mitratus, and the hybrid eggs hatched in the periods almost comparable to the non-diapause egg stage. When the hybrid nymphs developed normally, the photoperiodic response of the parental forms was manifested in their deveopmental rate. The amount of this response was variable according to the combination of parental stocks. When the development of hybrids was not normal, the photoperiodic response was obscure. The developmental disturbance was mainly observed in the male hybrids and grouped as follows : (1) the males developed at an unusually rapid rate and the females normally ; (2) the males were retarded but completed development, and the females developed normally ; (3) a few males were accelerated but the majority were retarded to develop and failed to mature, while the females developed normally ; (4) the males were retarded to develop and died before maturity, and the females developed normally ; and (5) the males failed to mature, and the females grew at an abnormally slow rate though they completed development. The degree of developmental disturbance was not necessarily correlated with the overall genetic similarity or dissimilarity between the parental forms. Fertile hybrids were obtained only by the reciprocal matings between T. mitratus and T. taiwanemma even though the hybrid males (taiwanemma ♀×mitratus ♂) were not viable. There was evidence of segregation in regard to the developmental disturbance in the F_2, F_3 or backcross generations. Based on speculations about the divergence of diapause behaviour and photoperiodic response of these field crickets, it is surmised that each of the three Japanese species has independently descended from the non-diapause ancestor, T. mitratus itself or its predecessor, and a hypothetical picture on the speciation of the Japanese forms is presented. In this picture, T. yezoemma appears as a first offshoot from the tropical ancestor, T. emma comes next in the scene, and lastly T. taiwanemma is differentiated and reaches the island chain. It is pointed out that this repeated speciation and the subsequent multiple invasions can be accounted for by multiple glaciations.
日本昆虫学会の論文
1967-06-20

DIVERGENCE OF PHOTOPERIODIC RESPONSE AND HYBRID DEVELOPMENT IN TELEOGRYLLUS (Orthoptera : Gryllidae)

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