Correlated and direct responses to selection for high and low pollen yield in a small, open population of Apis mellifera carnica

Abstract

SummarySelection for high-pollen (HP) and low-pollen (LP) yield was performed in Apis mellifera carnica for four generations using pollen traps. HP and LP yields were compared with an unselected control (C) line. Our procedure provided a constant inflow of new genes from the C line to the HP and LP lines that is useful in small apiaries. A significant (p < 0.01), asymmetrical (greater in HP), direct response to selection was observed. Correlated responses were also detected in: the pollen forager ratio (proportion of the pollen forager number to the total forager number) and pollen forager number in the HP line; and single-pollen load weight, honey yield, stored pollen area, and brood area in the LP line. No response was found in the total forager number. Correlated selection pressures were detected in the pollen forager ratio (in HP and LP), the stored pollen area (mostly in LP), and the brood area (slight in LP). Taken together, these observations indicate that pollen yield is determined by a small number of major genes. The selection results and the correlated response patterns suggest that pollen yield, pollen forager ratio, and the stored pollen area were mostly genetically correlated, but correlations between the pollen yield and the other traits examined resulted from the environmental background or from worker interrelations within the colony that function as a network of mutually dependent processes. The correlated response was also asymmetrical; it was greater and involved more of the monitored traits in LP. Consequently, the high pollen-hoarding genetic potential decrease results in the reduction of colony fitness and other traits, but its increase does not impact on the other traits or fitness values, as within-colony inter-trait relationships are involved.