Abstract
Directional selection in a population yields reduced genetic variance due to the Bulmer effect. While this effect has been thoroughly investigated in mammals, it is poorly studied in social insects with biological peculiarities such as haplo-diploidy or the collective expression of traits. In addition to the natural adaptation to climate change, parasites, and pesticides, honeybees increasingly experience artificial selection pressure through modern breeding programs. Besides selection, many honeybee breeding schemes introduce controlled mating. We investigated which individual effects selection and controlled mating have on genetic variance. We derived formulas to describe short-term changes of genetic variance in honeybee populations and conducted computer simulations to confirm them. Thereby, we found that the changes in genetic variance depend on whether the variance is measured between queens (inheritance criterion), worker groups (selection criterion), or both (performance criterion). All three criteria showed reduced genetic variance under selection. In the selection and performance criteria, our formulas and simulations showed an increased genetic variance through controlled mating. This newly described effect counterbalanced and occasionally outweighed the Bulmer effect. It could not be observed in the inheritance criterion. A good understanding of the different notions of genetic variance in honeybees, therefore, appears crucial to interpreting population parameters correctly.
Highlights
Many populations of social insects are currently exposed to intense levels of natural selection due to climate change, pesticides, habitat fragmentation, or parasites (Chapman and Bourke 2001; Le Conte and Navajas 2008; Mikheyev et al 2015)
Two years after the introduction of the breeding scheme, a second drop in genetic variance occurred with a reduction
The different criteria for assessing the genetic variance within a honeybee population (IC, performance criterion (PC), and selection criterion (SC)) showed different behavior upon the introduction of breeding schemes, which entails the question of which criterion is the most relevant for honeybee breeding
Summary
Many populations of social insects are currently exposed to intense levels of natural selection due to climate change, pesticides, habitat fragmentation, or parasites (Chapman and Bourke 2001; Le Conte and Navajas 2008; Mikheyev et al 2015). (See Table 1 for an overview of the used variables.) Most breeding traits in honeybees possess maternal and direct effects, which generally have different additive genetic variances σ2A;m and σ2A;d, respectively, as well as a covariance σA,md, which usually takes on negative values The reason is that, while sire drones and drone producing queens are no longer random samples of the population, they still are unselected descendants of the dams of the drone producing queens which in turn are randomly chosen among the population When it comes to the variance structure of worker groups, differences appear in the term covðuDiðwÞ; uDjðwÞÞ, as the drones which are involved in a controlled mating are generally related, whence there are positive covariances between their breeding values. We will denote this covariance term by
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