Network of large pedigrees reveals social practices of Avar communities.

From AD 567-568, at the onset of the Avar period, populations from the Eurasian Steppe settled in the Carpathian Basin for approximately 250 years1. Extensive sampling for archaeogenomics (424 individuals) and isotopes, combined with archaeological, anthropological and historical contextualization of four Avar-period cemeteries, allowed for a detailed description of the genomic structure of these communities and their kinship and social practices. We present a set of large pedigrees, reconstructed using ancient DNA, spanning nine generations and comprising around 300 individuals. We uncover a strict patrilineal kinship system, in which patrilocality and female exogamy were the norm and multiple reproductive partnering and levirate unions were common. The absence of consanguinity indicates that this society maintained a detailed memory of ancestry over generations. These kinship practices correspond with previous evidence from historical sources and anthropological research on Eurasian Steppe societies2. Network analyses of identity-by-descent DNA connections suggest that social cohesion between communities was maintained via female exogamy. Finally, despite the absence of major ancestry shifts, the level of resolution of our analyses allowed us to detect genetic discontinuity caused by the replacement of a community at one of the sites. This was paralleled with changes in the archaeological record and was probably a result of local political realignment.

When two evils are not equal: Differential biofouling of unionid bivalves by two invasive dreissenid species.

Byssate bivalves are ecosystem engineers with world-wide impact on aquatic communities through habitat forming and biofouling of hard-shelled organisms. In fresh waters, they are represented by invasive Ponto-Caspian dreissenid mussels spreading throughout Europe and North America. They negatively affect globally threatened unionid mussels by fouling, which deteriorates their condition and survival. The appearance of quagga mussels (D. rostriformis bugensis, QM) in areas occupied by zebra mussels (Dreissena polymorpha, ZM) usually has led to the replacement of ZM by QM. We combined long-term field survey (Lake Balaton, Hungary) and experimental data to check differences in fouling of unionid mussels (Unio tumidus and Sinanodonta woodiana) by the two dreissenids, determine their mechanisms and predict environmental consequences of the species replacement. ZM fouled unionids evenly throughout the year, whereas QM exhibited high fluctuations, being common on unionid shells during their recruitment peak (summer), decreasing towards autumn and almost completely absent in spring. Such fluctuations did not occur on stony substrata. This pattern suggests that interspecific differences in fouling did not result from recruitment preferences, but from greater detachment of QM from unionid substratum, whereas ZM more often remained attached to their initial recruitment sites. This was supported by the results of the laboratory experiments, in which dreissenid mussels did not show any consistent preference or avoidance of unionid mussels. Whereas, QM attached less often than ZM to hard objects and showed a higher detachment rate. Furthermore, dreissenids increased detachment after substratum immersion into soft sediments, indicating their capability of coping with suffocation after the burrowing of the living substratum or its siltation. The observed pattern indicates that the replacement of ZM by QM in the dreissenid assemblage may reduce fouling pressure on unionids. On the other hand, unionids may become a refuge for ZM in habitats invaded by competitively superior QM.