Population structure of depreciated communities: I. the 1977 genetic demographies of colonsay and Jura Islands, the Scottish Inner Hebrides

Abstract

This report compares the 1977 genetic demographies of Colonsay and Jura, adjacent yet isolated islands of the Scottish Inner Hebrides. Completed family analyses demonstrated that the residents of Colonsay have higher fertility, shorter generation length, and longer female reproduction span than those of Jura. Based on oral genealogies of five to six generations, the natives of Jura had a higher inbreeding coefficient (f= 0.0044) than did those of Colonsay (f= 0.0023). Each set of natives mainly derives from small groups of “founding” ancestors. Founder effects in the populations are transitory phenomena dependent upon population decline and the periodic emigration of native families. With their small sizes, the maximum sampling errors due to random genetic drift are ±0.063 for Colonsay and ±0.059 for Jura per generation. An unusual finding was that the effective sizes of Colonsay and Jura exceed their respective breeding sizes. Today Colonsay and Jura are former geographical isolates in dissolution through an increasing marital admixture with immigrants. Human migration dictated in large part by Hebridean economics dominates the mi‐croevolutions of Colonsay and Jura.