Factors affecting population variation in eastern Adriatic isolates (Croatia).

Inhabitants of the Croatian islands of Brac, Hvar, Korcula, and the Peljesac Peninsula have been the subject of extensive previous studies of local population differentiation. Most of these studies used biological and ecological variables, but some also considered historical and sociological factors. In this study we use genetic, morphological, kinship, and language distance data, collected for individuals from 26 rural communities on the islands of Brac, Hvar, Korcula, and the Peljesac Peninsula in the Adriatic, to further explore the interaction of historical, sociological, and biological factors in small populations and to test the significance of some of these proposed causes. First, we use matrix correlation methods to evaluate the relationships among different types of distance measures. The specific measures of genetic distance used here do not correlate well with other measures of population distance, and it appears that for the studied genetic systems the populations are not strongly differentiated. As expected, kinship and language distances have a high degree of association. Morphological differences among populations seem to be more closely tied to kinship distances than to genetic distances. This may result from modification of some morphological features by environmental rather than genetic factors, or it may be attributed to extensive, selective, nonrandom emigration of the population during the first decade of the twentieth century. In the second part of our analysis we use matrix correlation methods to evaluate and possibly identify the external factors that have contributed to the population differences. Specifically, we use design matrices to test hypotheses that population differences can be explained by one of the following factors: geographic isolation on the islands and peninsula, distance from the mainland, geographic barriers within the islands and peninsula, and the historical factors that differentially affected the three islands and the peninsula. Most of these design matrices reflect geographic distances; although correlations between morphological variables and simple geographic distance between localities were not significant, correlations between these localities and a design matrix incorporating geographic distance along with geographic barriers, such as bodies of water and mountain ranges, are particularly important for explaining distances among kin. Design matrices provide an important tool for quantifying the relationship between historical and geographic factors, and measures of population distance.