Posted 06 Dec 10
Is Line Breeding Still Relevant Today?
Professor Dr Kaspar Bienefeld, Länderinstitut für Bienenkunde, Hohen Neuendorf.
E -Mail – Kaspar Bienefeld
Translated from Deutsches Bienen Journal 2/2010, pp16– 17.
by A.E. McArthur MIL
When purchasing queen bees many beekeepers prefer Line bred Queens.
There is reason to believe however, that Line Breeding does not offer better colonies or higher honey yields
Some 70% of breeders define their queens with a Line name. Many buyers are guided by these names. The beekeepers give essentially 3 reasons for their loyalty to the Line:
This article will investigate if the Lines fulfil these expectations.
What constitutes a Line Relative to the Honey Bee?
In animal breeding in general the term line breeding is understood as the selection within a particular small sub-group of a specific race in order to retain the genes of a special ancestor. In the honeybee line breeding normally does not depend on individual colonies, but rather on the stock of known breeders (Sklenar, Peschetz) or on mating station (Troiseck, Lattbusch). According to Friedrich Ruttner: Lines are defined as being derived from the female parentage. All colonies which possess at least 50% of the genes of the particular Line are considered as Line members. Germany according to the “Breeding Value Appraisal Databank” possesses 120 Lines. Most of these Lines consist of very few colonies, which the founder of the Line identifies by his family name. Most Lines only last for a few years, so it is really not possible to talk of a further development and consolidation of a particular Line. Relative to the evaluation process, only Lines which have a supra-regional influence were considered.
How Uniform are the Lines?
The table lists the average number of colonies as well as the average, minimal and the maximum level of inbreeding in the Line per year. All of the lines are alarmingly small.
If really persistent mating were to occur within the Lines, inbreeding values at least 10 times higher than the values listed would arise. Inbreeding occurs when the progeny resulting from the pairing of related individuals receive identical genes from the mother and father. The Inbreeding Coefficient gives the probability for such an event. It is dependent on how closely the parents are related. The smaller a Line, the greater the risk of inbreeding. In bee breeding added to this, by virtue of the limited number of mating stations, every year only a limited number of ‘fathers’ can be employed. A look at the data makes it clear that it is not possible to speak of a persistent selected Line. The Hoffmann –Line is the only Line in which a nominal inbreeding rate can be confirmed. In the Sklenar sub-Line, the values in relation to the size of the sub-Lines are extremely small. This accounts for the frequent crossing between the individual Sklenar sub-Lines, and also for the out-crossing with unrelated Lines (or queens, which do not have a pedigree). Out –crossing with unrelated Lines is not practiced merely by Sklenar alone. There are of course differences, out-crossing, however is carried out in all Lines, the percentage of out-crossing varies between 20 – 60%.
Do the Lines Differ from Each Other?
In fig 2 the average Breeding Values for honey yield and gentleness are listed for the 4 largest Lines in Germany as well as for colonies which have no Line data. At the start of the Breeding Value Assessment only the Hoffmann Line indicates clear differences relative to gentleness and (swarm impulse). This comes as no surprise, since the Hoffmann Line can be designated as the earliest Line to achieve stability. There are 2 reasons for the closeness of the other Lines to the Hoffman Line with reference to the behavioural characteristics: The Hoffmann Line was crossed directly with the other Lines due to its superior behavioural Breeding Value. Still more important however was, that the behavioural characteristics have been considered more deeply in the selection process since the start of the Breeding Value Assessment and more accurate information about the genetic value of colonies has been available. Behavioural characteristics have a higher hereditability than honey yield, thus the selection was a success. It is very clear, that all the Lines improved, but they were also similar. There are no noticeable distinctly different selection targets present.
Are Honey Yields Improved by Line Out Crossing?
The more diverse the parentage, the greater the improvement in performance from cross breeding may be expected. A cross breeding effect (heterosis) occurs when the resulting progeny are an improvement on the average parental qualities. Practical, meaningful heterosis occurs, when the performance of the progeny surpasses the best individual parental performance. This situation is reported in cross breeding between different races – thus a carnica and mellifera cross should result in improved honey yields, but also lead to increased aggression. In Line breeding the inbreeding effect has to be considered. Line breeding as a rule leads to higher levels of inbreeding and inbreeding leads to noticeably reduced honey yields. Surpassing the performance of a parent line which is already affected by inbreeding is therefore no great challenge. A more accurate measure would be results from an average population, which is not affected by inbreeding. Colonies without line breeding input produced on average 38.9 kg of honey and thus exceeded by 0.7kg, the performance of line bred colonies , which gathered on average 38.2 kg. Also in quite special line combinations the results are disenchanting. By way of comparison the highest yields are found when breeding lines are combined with stock from the average population. The Peschetz and Sklenar Lines – as already described, not distinctly marked by fixed characteristics, indicate clearly better results due to this influence than the Celler Line, but better especially than the Hoffmann Line. A special problem of bee breeding is seen here: If two inbred lines are crossed, the worker bees are crosses – but not the queen. The queen remains a representative of the ancestral Line and because of this affected by inbreeding. Inbred queens negatively affect the performance and behaviour of the crossed colony: hence the reason for the poorer results, when the maternal Line comes from the comparatively heavily inbred Hoffmann Line. If the Hoffmann Line is the paternal source and the queens derive from Lines exhibiting little inbreeding, the honey yields are considerable better.
Does Line Breeding Result in Variety?
The genetic variety of many canine races is certainly much higher than that within the wolf races, from which the dog was originally bred. The example demonstrates that breeding need not necessarily lead to genetic paucity. It could also be argued that the genetic variety among selectively bred races of bees, at best remains intact if the total population is divided into many Lines. That is the theory, in practice especially with the honey bee this does not happen. During the peak period of line breeding in the 60s to 80s, colonies with low Inbreeding Coefficients provided almost twice as much breeding stock as colonies with extremely high Inbreeding Coefficients. The reason for the preference was their some 15% higher honey yield. The breeders had observed the negative results of inbreeding, which due to their selection decisions had worked against a standardisation of the Lines.
These decisions from the views current at the time were correct, because there were no Breeding Coefficients available to the breeders at that time. They were unable to differentiate between reduced yields due to inbreeding pressure and poor genetic quality. The consequence was that the principle of line breeding, in which inbreeding was the basic concept, in the case of the honey bee, led to the elimination of extreme (mostly very good) colonies and which accelerated the genetic impoverishment.
Positive Statements on Quality
Results from the breeding practices tends to indicate a more negative picture of line breeding. But possibly this is not due to the principle but more to inadequate methodology. As previously described breeding is carried out using a preponderance of very small Lines with a comparatively small total of breeding stock. Line specific breeding targets are not discernible, as a rule no distinct Line discipline exists. There is only minimal evidence within the Lines of any long term planning. Besides which there is a lack of cooperation and specific goals in Line breeding.
Not one single element of the points raised offers support for line breeding of the honey bee. The honest answer to the question posed in the title of this article must therefore be: No, line breeding is no longer suited to modern beekeeping. Despite this the particular Line will continue to play a role in the choice of bee and purchase decisions, because it is trusted by many beekeepers and at least with many established lines within certain limits allows a prediction of the quality of the queen. Today however according to the results from the Breeding Value Assessment there are significant improvements possible for breeder and beekeeper.
|Average Number of Colonies per Year and Average Inbreeding Coefficient over the years.|
|Average Breeding Values for honey yield and gentleness of the Lines with supra- regional significance. The Sklenar sub-Lines have been consolidated into a single Line. By the parentage definition “without details“ is meant, those which have no Line Coding.|
|The highest honey yields are shown to be returned by colonies, which were paired with Lines which have no Line Coding.|