Section 9 — Population Genetics 



of related characters body size, developmental 

 time, dessication resistance and fertility. 



This reseaich is supported by a grant of the 

 Royal Hellenic Institute of Research. 



may be expected. This finding demands the 

 formulation of a new set of principles for the 

 design of experiments on rice. 



It is not yet possible to assess the exact 

 economic value of this finding but the cumulative 

 results seem indicate a hopeful future possibility. 



9.6. Polymorphism in the Leopard Frog (Rana 

 pipiens). David J. Merrell (Minneapolis, 

 U.S.A.). 



The dominant burnsi mutation is shown to be 

 present in natural populations of the leopard 

 frog in an area of about 100,000 square miles 

 centering on the Anoka Sand Plain of Minnesota. 

 This distribution represents only about 2 per cent 

 of the total range of Rana pipiens. The highest 

 frequencies of the mutant type reach only 5-10 per 

 cent. Evidence will be presented suggesting that 

 the present distribution of this mutation is related 

 both to the glacial history of the area and to the 

 fitness of the mutant in its present environment. 



9.7. Intra-specific Interaction in Rice. Subodh 

 Kumar Roy (Calcutta, India). 



When two varieties of rice are grown together, 

 each may influence the yield of the other. The 

 nature of interaction may differ with the kind of 

 mixture, the genotype mixed, the proportion of 

 the components and the ecological conditions. 

 The effect is as often favourable as unfavourable. 

 However, cooperation occurs, and certain pairs 

 outyield the means of the respective components 

 when grown in monoculture and occasionally 

 the better components. 



The factors involved in such genotype inter- 

 actions seem to be very complex and are not 

 fully understood. However, experimental evi- 

 dences suggest that biologically active chemical 

 substance or substances produced by the roots 

 may be responsible for stimulation or inhibition 

 at least in certain pairs. The two varieties which 

 cooperate may make different demands on the 

 soil or the water and may suffer from comple- 

 mentary metabolic deficiencies. Diverse nature 

 of roots, and of lodging and disease resistance 

 of the components, may have considerable 

 advantage in a mixture over the pure stand. 



The usual breeder's -practice of growing 

 several varieties of rice experimentally side by 

 side without any bond of separation between 

 them may lead to quite false conclusions as to 

 the yields of the varieties in question in pure 

 stand because under such a situation interactions 



9.8. Distribution, Numbers and Natural Selection in 

 a Butterfly Population. M. S. B. Seiger and 

 R. H. T. Mattoni (Lafayette, U.S.A.). 



The Lycaenid butterfly, Philotes sonorensis, 

 tends to form isolated or semi-isolated colonies 

 throughout its distribution range. We selected 

 a relatively isolated population in the San 

 Gabriel Canyon, California, to study population 

 size, ecology, movement and phenotypic vari- 

 ability in the six component colonies of this 

 population. The colonies are no more than 80 m 

 in diameter and are restricted to those areas 

 where the larval food plant, Dudleya lanceolata 

 (Crassulaceae), grows. The two closest and two 

 farthest colonies are 136 and 473 m apart 

 respectively. For three years the population was 

 sampled regularly throughout the flight period 

 by a capture-mark-release-recapture system. The 

 captives were classified according to sex, spot 

 pattern, area and dates of previous captures if 

 the specimen had been recaptured. 



Very few individuals moved from their original 

 capture sites. Most of the interchange of genetic 

 material among the colonies was due to the 

 movement of the males. Thus gene interchange 

 was facilitated while distribution was localized. 

 Small ecological barriers such as rocks and 

 small streams acted as strong deterrents to the 

 movement of Philotes. Evidence indicating iso- 

 lation by minor ecological barriers was derived 

 from differences in sex ratio and spot pattern 

 frequencies among the six colonies. The effects of 

 birth and death rates and rates of incoming and 

 departing individuals on fluctuations in daily 

 colony sizes weie determined for each of the 

 colonies. The effects of natural selection were 

 determined by comparing the population para- 

 meters for the three years. 



9.9. Ecological Genetics of Tribolium and Houseflies. 



Robert R. Sokal (Lawrence, U.S.A.). 



The ecological components of natural selection 

 in Tribolium castaneum populations are examined 

 under two different population systems. (1) The 

 (more natural) overlapping of generations and 



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