BREEDING STRATEGIES & GENETIC MANIPULATION IN GUPPIES
© Alan S. Bias
Permission granted for nonprofit reproduction or duplication of photos and text with proper credit for learning purposes only.
January 1, 2012
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| 5 month old Grey Asian Blau Vienna Emerald Lower with Blue Peduncle |
PREFACE
Too successfully breed a strain of guppies’ long-term one must first set attainable goals. After aesthetic value, manipulating a small snapshot of genetics, consisting of fixed strains, has always been my primary interest in breeding guppies. It is often accomplished by an intense quest into understanding Population Genetics in conjunction with a study of Color. This article will attempt to expand on my last and focus on potential routes to achieve fishroom goals through two linebreeding techniques.
It must be remembered that linebreeding is a normal strategy for the establishment and refinement of a strain. It will increase uniformity, followed by predictability in a genetically related population of fish. Predictability is a major attribute breeders find of use. To create a healthy breeding program one must choose initial breeding stock with care. A primary responsibility as a guppy breeder should be to maintain and enhance strain quality in selected areas.
A very limited school of thought has been offered to guppy breeders in the past that stresses hybrid vigor to counteract issues often perceived as reduced fitness brought on by inbreeding. Much of this has been accomplished through maternal linebreeding (linecrossing) outcross sires from different stocks. This is a good way to identify various traits within a strain. It may not be the best way to concentrate selected traits after they have been identified. Nor, does it reflect the only avenue of improving guppies by breeders over the last century.
DEFINITIONS
1. Inbreeding: The mating of highly related individuals such as father to daughter or brother to sister. An inbred individual or population often shows increased homozygosity. Progeny may exhibit a reduction in desired traits or loss of fitness.
2. Linebreeding: Planned mating to maintain a high degree of relation to a common ancestor or ancestral group of high regard. The intent is to avoid a reduction in desired traits or loss of fitness. A linebred individual has at least one common ancestor on the sire and dam side within 3-5 generations.
3. Homozygous: When a gene inherited from a sire is the same as the one inherited from the dam.
4. Heterozygous: If two alleles for a specific trait are different.
5. Inbreeding Depression: The expression of undesired recessive genes in homozygous combination leading to genetic faults or weaknesses.
6. Hybrid Vigor: Results from a masking of unfavorable recessive alleles in heterozygous combination. Benefit may also derive from overdominance in which one heterozygous allele confers superior environmental benefit over either in homozygous form.
7. Outcrossing: The mating of unrelated or distantly related individuals. Resulting in increased heterozygosity.
8. Population Genetics: A study of allele and genotype frequency & distribution and changes effected by evolutionary processes in the wild and additionally breeder selection in domestics.
9. Heritable Traits: Genetic characteristics which are capable of being transmitted to successive generations.
10. Developmental Noise: Produces phenotypic differences in identical genotype during later embryonic development. This results from variation in cytoplasm, gene interaction and regulation in combination with epigenetic variation (In example the stripes on tigers, zebras, or snakeskin guppies.)
ESTABLISHING STRAIN GOALS
Prior to purchasing foundation stock you should familiarize yourself with guppy standards if you intend to show results from your program. Do you wish to raise seed stock or keep a few guppies? If the prior, foundation animals should meet or exceed standards in the areas of interest. Visit with several breeders before making your selections. Online purchases are only as reliable as the breeder’s reputation. Great variation can be found in guppy strains.
In many fish rooms the most important component is often overlooked, the female. A top end production female should only be discarded if she has been duplicated, replaced by at least one improved daughter, or you cease working with a strain. These breeding age females should be retained unless you have reached your population goals or limits. From these females, you can (re)build a strain and target the specific traits you desire. Seek out breeding females that produce offspring who produce as well or better in subsequent generations, and don't pass on negative recessive genes.
Desired traits in females worth retention include:
*Females that drop regularly each month;
*Females that never get sick;
*Females that never show excessive aggression towards a tank mate;
*Easy keepers who thrive & rebound after delivery on regular rations;
*Females that produce consistent litters that increase in number with maturity;
*Well balanced moderate sized females with good visible maternal depth;
*Females that exhibit fitness and fertility into advanced age.
As a firm believer in a balanced breeding program, the selection and retention of females who thrive under limited conditions is a must. If you are pumping your fish full of super high protein foods and retaining offspring from those who thrive, you are reversing centuries of selection for minimal feed rations. This can be a risky approach long-term. Guppies evolved on foraging to meet their needs, and developed the ability to efficiently convert and thrive on this input alone.
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| Iridescent |
Observe your fish during pregnancy, or even better just prior to dropping for structural faults or flaws. Robustness and deep flanks in combination is a sign of high maternal traits. Females lacking this trait often show reduced fertility. An ideal breeder female will not be super long in the body. Nor will she be too tightly coupled, appearing overly short and stocky in stature. She should be well balanced from front to back with neither end over powering the other, and of moderate size. Look for females with a good depth to body length ratio. Excessive length will cause issue in male offspring, especially when caudal weight is of concern. Weak top lines and dips in the forehead will pass to both sexes. These positive traits will help produce fry that develop with good physical characteristics in your strain.
In my opinion, one of the worst mistakes a breeder can make is purchasing stock based solely on wins accrued on the show circuit. Especially, when done without viewing related individuals within the strain. Show males are often F1 hybrids resulting from outcross of two divergent strains and will not breed true. Award Ribbons are the result of one individual’s opinion on a particular day. They are disproportionately based on visual phenotype and not genetic potential. Yes, it is true a good judge can contribute to recognition of fish that exhibit proper confirmation and meet strain standards. They cannot evaluate strengths in offspring if they are not available. One way to avoid the pitfalls of F1 hybrid males produced specifically to win is through fish room visits.
What are some of the characteristics I seek in breeding males? At any age after sexual maturity is evident, masculinity is the primary objective in selection.. In addition to strain standards, masculinity should be visible in the head, body, and peduncle. Top line should be straight and is best viewed from front and sides and should create a level plane. If a male is not active in his youth he will not be so with advancing age. Any physical deformities should be grounds for culling, no matter how insignificant they may seem. Avoid males that are unable to digest and metabolize their rations, i.e. they get chesty. Some autosomal selected traits have been linked to a disproportionate number of XX males.
LINEBREEDING
There are two constants among all serious guppy breeders: a quest for knowledge, and a continual search for improved genetics via replacements. A serious breeder cannot underestimate the contributions or weaknesses of sires. As many color and pattern traits in guppies are located on the Y chromosome it is common practice for breeders to produce males on a regular basis for use within their strains. Most normally retain females from offspring produced and additionally outsource for new sires This common form of linebreeding is referred to as maternal, and utilized by many today. A second less common version is paternal linebreeding. One of the best tools available for obtaining potential sires is paternal linebreeding.
The single most important factor is selection of the foundation sire(s). It is an absolute must you start with a superior individual(s) in the traits you are seeking to concentrate. Potential weaknesses can accumulate just as easy as strengths if not avoided. Selected traits are not limited to color and pattern. They also encompass confirmation, longevity, disposition, disease resistance, and fertility; feed conversion ability to name but a few. If you keep good records and track your female lines it becomes readily visible that a small percentage of foundation females routinely produce the retained superior offspring used to establish breeding lines.
I. Maternal Linebreeding
What are the differences and benefits in these two linebreeding techniques? For a start maternal linebreeding is usually associated with a closed &/or related nucleus of breeding females complemented by males obtained from outside sources. In a loose sense this is a form of linecrossing akin to outcrossing within the strain. Many breeders have adopted maternal linebreeding as standard practice for guppies. Not only do they assume expressed color and pattern traits are predominantly sex-linked, but also seek hybrid vigor gained through heterosis resulting from the use of outside sires.
Maternal linebreeders tend to use a male(s) on a group of females over a set period. Often involving sib breedings or limited back cross. Followed by line crosses every few generations. Then secure new sires from outside in an attempt minimize the concentration of genes from a single source within the strain. This technique forces a breeder to constantly be on the lookout for males outside their program with improvements in desired traits.
Many maternal breeders are less concerned about positive or negative combinations of genes in male offspring within the strain. Heterosis through maternal sires can avoid problems associated with potential combinations of negative genes. These combinations of genes are normally recessive. Most initial benefit of heterosis in males is short lived and will also quickly diminish in successive generations of retained females. A drawback to this practice may show in the ever changing phenotypical structure of your fish.
Predictability in the male you produce is also limited, if not eliminated, as many of his traits will be in heterozygous form. The bulk of hybrid vigor gained from maternal outcrossing remains concentrated within your female family groups. Limited benefit is passed to breeders purchasing your males, unless sold in breeding groups. Many times maternal sires tend to lack masculinity, and overall "rugged appearance" traditionally associated with a male. In mammals these sires have been shown to lack proper testicular development, shape and testosterone production. Use of sires with lower production & quality of semen can result in extended breeding time.
Too sum it up politely, maternal linebreeding and production of resulting males allows a breeder to mask any genetic flaws in the progeny produced. They do not go away, but rather are unknowingly passed on as recessives. It has been stated that maternal outcrossing is the simplest form of pedigree stock breeding. In practice maternal linebreeding is a good way to boost overall numbers with the greatest genetic diversity and the least amount of predictability.
II. Paternal Linebreeding
This is a practice of old in the livestock world that fell out of favor after 1950 with reliance on marketing fads, current scientific knowledge, and less on the results of a "proven breeders eye." It has never quite taken hold in the world of guppy breeding. A partial reason may be found in the need to maintain 4 or more lines of females as opposed to the minimum of two in maternal line breeding. Continued selection and retention of homebred males with masculine phenotype will result in offspring of similar traits
In order to pass on predictability males should be of paternal decent and not maternal. Too create a paternal sire takes much more knowledge of your strain genetics. One must learn the genetic makeup of your fish and how to mix and match breedings based on genotype vs. phenotype (or pedigree). In a good paternal based program it is not uncommon for a sire to be used on females until his demise or he produces a superior son. This son can be used on 1/2 siblings to produce predictable results geared towards your criteria.
The possibility of regression from inbreeding depression in future generations can be avoided by creating future sires from selected outside females. New genes cannot be created in any breeding program. New genetics should be introduced by carefully selecting outside females meeting your criteria. Breed new females to your paternal males with concentrated genetics reflecting your strain goals. In essence you will be adding another female line with minimal dilution by use of your existing males.
Introduction of outside maternal bred males can weaken your existing concentrated strain genetics. Careful selection of a desired outside female(s) will satisfy most needs for new blood. She should be bred to your own paternal sires for an infusion into the strain without an overall weakening of established phenotype. In return her genetic base will be incorporated into the strain over several generations by sons & daughters. Autosomal traits can also be introduced from females. The exception to this rule would be when you wish to introduce Y-linked traits not already found within your strain.
When a pedigree breeder identifies a superior male that reproduces with above average results you need to concentrate the effect upon your females. Otherwise, resulting F1 offspring are only 50% of the sire. F2's are down to 25%. Yet, two females are involved in producing your offspring, dam of the sire and mother of the fry. Numerous breeders comment that, "much of the genetic improvement resulting from new sires is lost by F3-4 offspring". It has not been lost, just not managed into the successive generations. Another comment I have mixed feelings on states, "mating individuals of two distinct phenotypes types will result in F1 offspring somewhere in the middle, that segregates out in subsequent generations." Without concentrating the genetics of either parent in your strain you cannot regularly reproduce the phenotype of either. You can only create stable phenotype & resulting predictability in a strain by concentrating the genetics of your superior sire(s).
Retained F3 & F4 females can be breed to their uncles, cousins sired by their father, half brothers or grandsires. Cull any potential problems with vigilance, &/or backtrack when possible. This is one of the primary reasons I maintain distinct age groups within my tanks. When possible you should maintain a minimum of four or more female paternal family lines. These lines having been established by a superior foundation sire and bred back to sires from another line. For example, you maintain lines A, B, C, D. Sires from A are only bred to B, C, D. Sires from B are only bred to A, C, D. If you are unable to maintain the needed lines cooperate with another breeder having similar goals and breeding program.
Breeding a sire to his own daughters is the best way to test the strengths, weaknesses, and progress of your paternal breeding program. Paternal linebred females should possess the concentrated genetic makeup needed to compliment your sires, i.e. they contain a related X chromosome. Resulting in the strain characteristics you desire, while performing in your environment. When you obtain fish from an environment radically different than yours, it is not uncommon for them to never fully adjust. Resulting offspring may also go through the same extended process.
GENETIC CONSEQUENCES
An outcross will not eliminate undesired recessive genes. It only masks such genes, allowing them to persist in a strain or population and reappear at a later time. Linebreeding does not create these recessive genes, it only makes them visible. Knowing which recessive genes are present in your strain can be of benefit to a breeder. It should also be noted that neither hybrid vigor, nor inbreeding depression are heritable traits. Heritable traits are qualities which can be passed by individuals or related groups of individuals to offspring (descendants). The closer the relation, the more shared traits will be found in a strain. In a very loose sense most variation among strains is genetic and that among the lines comprising a strain are environmental. Paternal line breeding can develop a strain of guppies which breed true for selected traits. This includes highly prepotent sires that produce predictable offspring for traits sex-linked, autosomal or in combination.
Chromosomes are DNA structures containing multiple genes. Alleles are variations in the form of a gene. When both genes in a pair are the same (Ex. "AA"), they are referred to as homozygous. If two genes in a pair are different (Ex. "Aa"), the pair is called heterozygous. When an ancestor appears on both sides of a pedigree the inbreeding coefficient is increased. All non-variable gene pairs in a breed are homozygous, and allow species to breed true, if “developmental noise” is limited. Variable gene pairs in guppies produce the majority of visible distinctions in individuals. Paternal linebreeding increases the chance for single gene pairs to be homozygous.
Advantages and disadvantages can be found in both linebreeding and outcrossing of domestic strains. Each technique complements the other when used with forethought, helping breeders attain genetic goals. Several methods exist to measure the genetic diversity of a strain. One is to measure the average inbreeding coefficient. The inbreeding coefficient is a measurement of the genetic relatedness of a sire and dam. Linebreeding can be measured, allowing for planned matings that avoid potential depression.
Many guppy breeders are overly concerned with diversity on a strain level and suggest matings to those least related. No type of breeding alters the frequency of single genes, only how they are paired in resulting offspring. Population bottlenecks may occur from overuse of a sire, resulting in loss of diversity. Genetic diversity within guppies is maintained by breeder diversity and not linecrossing with each others excess males.
Select what is best for your program to maintain strain quality. Using an inferior sire because he is unrelated is of little benefit. Retention of a sound paternal sire will accomplish much more. If we all continue to use maternal linecross sires, few if any true unrelated lines would result in very short order. Yet many insist on this fallacy to preserve diversity in strains. Remember guppy strains are the result of linebreeding. Their diversity requires breeders utilizing different linebreeding programs of carefully selected bloodlines without an over abundant use from a single source.
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| 5 month old Blond Vienna Emerald Lower with Tigrinis |
SUMMARY
There is an ongoing difference of opinion among guppy breeders. It revolves around the question of further importation of genes into your strain to maintain diversity and improve quality. This is not the case unless there is a difference in standards or desired traits not found in current populations. Importation of new blood is not a necessity, but may speed up desired results with usage of predictable sires. Your selection of genetics should be based on characteristics, or needs within your individual breeding program.
There are many positive consequences seen with increased homozygosity. Prepotent sires who are highly homozygous breed true, and pass on many dominant genes. Selective linebreeding is a sound method to create and fix hereditable traits. Natural selection is enforced by Mother Nature. It eliminates undesired dominant genes in the wild, such as found in healthy island populations left to their own devices. It also eliminates undesired recessive genes when they are in homozygous condition. Hence, the reason unfavorable genes are normally recessive. It is also evidenced by healthy captive populations bred by man. A prime example is the Flett Flock of Sheep. This breeding program remained closed for the better part of 50 years. All animals descending from an initial importation of 1 male and 3 females. They were maintained with good records, sound retention and planned breedings.
Linebreeding takes time, research, commitment, and a willingness to cull ruthlessly. No breeding strategy fits all situations. Each can be selected for certain goals and production systems. As a dedicated guppy breeder you should pick a technique to fit your own beliefs and goals. Paternal linebreeding will result in uniform offspring when combined with a commitment to adopt it as a long-term strategy to create healthy, consistent, predictable bloodlines. Careful selection of foundation stock geared towards your goals will determine the quality of results. Concentrating the degree of relationship among your males and females will influence the degree of uniformity in the offspring.
Domestic guppies as strains can benefit from a variety of breeding strategies. It can be good for strains to have farms practicing paternal linebreeding with very limited and selective goals. While those with less defined goals adhere to maternal linebreeding (linecrossing). In the end genetic diversity across strains will be maintained in various fishrooms around the world. A single philosophy claiming "diversity" will not fit all situations. Instead, we as breeders need to encourage some diversity of technique to preserve and improve the quality of guppies as a whole.
REFERENCES
Sponenberg, D. P., Virginia - Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, (2000). “Breeding Strategies”. The Goat Farmer, May/June 2000. Pg. 12-13. email: dpsponen@vt.edu
Center for Biological Informatics of the U.S. Geological Survey website, The National Biological Information Infrastructure (NBII) (2007). “Introduction to Population Genetics” & “Introduction to Genetic Diversity “.
(Last viewed: 1.5.12) email: nbii@nbii.gov
Fry, Gearld (????). “Creating Predictable Herd Genetics for Good Eating Grassfed Beef”,
“Cows That Should Not Be Sold - Seed Stock & Commercial”, “A Well Balanced Bull and the Benefits of Masculinity”, “Creating Predictable Paternal Bull Gene Pools for Grassfed Meat Production”,
“Constitution of a Superior Bull”, “Concentration and combinations of desirable genes and genetics”.
http://www.bovineengineering.com (Last viewed: 1.5.12)
