Undesirable side effects of selection for high production efficiency in farm animals: a review

Milk yield per cow has more than doubled in the previous 40 years and many cows now produce more than 20,000 kg of milk per lactation. The increase in production should be viewed with concern because: i) the increase in milk yield has been accompanied by declining fertility, increasing leg and metabolic problems and declining longevity; ii) there are unfavourable genetic correlations between milk yield and fertility, mastitis and other production diseases, indicating that deterioration in fertility and health is largely a consequence of selection for increased milk yield; and iii) high disease incidence, reduced fertility, decreased longevity and modification of normal behaviour are indicative of substantial decline in cow welfare. Improving welfare is important as good welfare is regarded by the public as indicative of sustainable systems and good product quality and may also be economically beneficial. Expansion of the Profitable Lifetime Index used in the UK to include mastitis resistance and fertility could increase economic response to selection by up to 80%, compared with selection for milk production alone. In the last 10 years, several breeding organisations in Europe and North America followed the example of Nordic Countries and have included improving fertility and reducing incidence of mastitis in their breeding objectives, but these efforts are still timid. A multi-trait selection programme in which improving health, fertility and other welfare traits are included in the breeding objective, and appropriately weighted relative to production traits, should be adopted by all breeding organisations motivated in their goal of improving welfare.

The impact of genetic selection for increased milk yield on the welfare of dairy cows.

Fish aquaculture for commodity production, fisheries enhancement and conservation is expanding rapidly, with many cultured species undergoing inadvertent or controlled domestication. Cultured fish are frequently released, accidentally and deliberately, into natural environments where they may survive well and impact on wild fish populations through ecological, genetic, and technical interactions. Impacts of fish released accidentally or for fisheries enhancement tend to be negative for the wild populations involved, particularly where wild populations are small, and/or highly adapted to local conditions, and/or declining. Captive breeding and supplementation can play a positive role in restoring threatened populations, but the biology of threatened populations and the potential of culture approaches for conserving them remain poorly understood. Approaches to the management of domestication and cultured-wild fish interactions are often ad hoc, fragmented and poorly informed by current science. We develop an integrative biological framework for understanding and managing domestication and cultured-wild fish interactions. The framework sets out how management practices in culture and for cultured fish in natural environments affect domestication processes, interactions between cultured and wild fish, and outcomes in terms of commodity production, fisheries yield, and conservation. We also develop a typology of management systems (specific combinations of management practices in culture and in natural environments) that are likely to provide positive outcomes for particular management objectives and situations. We close by setting out avenues for further research that will simultaneously improve fish domestication and management of cultured-wild fish interactions and provide key insights into fundamental biology.

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Cultured fish: integrative biology and management of domestication and interactions with wild fish

This text synthesizes existing knowledge of the process of domestication and how domestication has affected the behaviour of captive wild and domesticated animals, including both farm, zoo and companion animals. Three broad themes are addressed: genetic contributions to the process of domestication; experimental contributions to the process of domestication; the process of feraliztion (i.e. the adaptation of domesticated animals when returned to their natural habitat.

Animal Domestication and Behavior

The immune system is a life history trait that can be expected to trade off against other life history traits. Whether or not a trait is considered to be a life history trait has consequences for the expectation on how it responds to natural selection and evolution; in addition, it may have consequences for the outcome of artificial selection when it is included in the breeding objective. The immune system involved in pathogen resistance comprises multiple mechanisms that define a host's defensive capacity. Immune resistance involves employing mechanisms that either prevent pathogens from invading or eliminate the pathogens when they do invade. On the other hand, tolerance involves limiting the damage that is caused by the infection. Both tolerance and resistance traits require (re)allocation of resources and carry physiological costs. Examples of trade-offs between immune function and growth, reproduction and stress response are provided in this review, in addition to consequences of selection for increased production on immune function and vice versa. Reaction norms are used to deal with questions of immune resistance vs. tolerance to pathogens that relate host health to infection intensity. In essence, selection for immune tolerance in livestock is a particular case of selection for animal robustness. Since breeding goals that include robustness traits are required in the implementation of more sustainable agricultural production systems, it is of interest to investigate whether immune tolerance is a robustness trait that is positively correlated with overall animal robustness. Considerably more research is needed to estimate the shapes of the cost functions of different immune strategies, and investigate trade-offs and cross-over benefits of selection for disease resistance and/or disease tolerance in livestock production.

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Immune response from a resource allocation perspective

ummary
We have provided a bridge between geneticists, who tend to concentrate on genes and their frequencies, and other biologists, who are much more aware of how severely the environment constrains and limits life. This bridge is the recognition that

a. fitness is a product of important component traits,
b. these and most other traits consume environmental resources and these resources are additively related and can sum to no more than the total resources an animal can obtain from the environment,
c. allele frequencies can alter only to the degree that the phenotypes that carry the alleles reproduce themselves successfully, i. e. are fit,
d. fitness must rise, because it is never free from natural selection upwards, to the point where it can rise no further, because all environmental resources available to an animal are being used most efficiently,
e. in this state of adaptation, fitness is completely limited by the environment and all other traits important to the animal are constrained to a greater or lesser degree at intermediate, “optimal” values, and
f. traits or molecules unimportant to animals, so that they are completely neutral with respect to fitness, are free to drift genetically and hence gene substitutions can occur at rates related to their mutation rates.


This bridge between genetics and other parts of biology shows that the various theories apparently causing concern for the modern synthetic theory of evolution are entirely compatible with it. Bursts of rapid evolutionary change between long periods of evolutionary stasis are the necessary consequences of strong natural selection acting on fitness, in ecosystems that are stable until external forces cause them to change. Neutral (random) evolution describes the fate of genetic material that is unimportant for organisms, i. e. material that is truly neutral with respect to fitness.

Zusammenfassung
Quantitative Genetik und Evolution. Genugt unser genetisches Verstandnis um Evolution zu erklaren?

Wir bauten eine Brucke zwischen Genetikern, die mit Genen und ihren Frequenzen arbeiten, und anderen Biologen, die wissen wie stark die Umwelt Lebewesen hemmend beeinflust. Diese Brucke besteht aus den folgenden Erkenntnissen:

a. Fitness ist ein Produkt der wichtigsten Komponenten.
b. Diese und die meisten anderen Merkmale verbrauchen Nahrung. Die Nahrung, die ein Lebewesen nur aus der Umwelt erhalten kann, enthalt die maximale Summe der metabolischen Ressourcen, die das Wesen dann in additiver Weise in einzelne Merkmale investiert.
c. Allelfrequenzen konnen sich nur erhohen, wenn der Phanotyp, der die Allele tragt, sich erfolgreich fortpflanzt.
d. Weil Fitness immer unter naturlicher Selektion nach oben steht, mus der Fitnesswert steigen bis alle Umweltressourcen so effizient wie moglich genutzt werden.
e. In solchem Stadium der volligen Anpassung an die Umwelt, ist Fitness ganz durch die Umwelt limitiert und alle anderen wichtigen Merkmale in groserem oder kleinerem Mase in Optimalwerte gezwangt.
f. Unwichtige Merkmale oder genetische Molekule, die keine Wirkung im Lebewesen haben, so das sie wirklich neutral sind gegenuber Fitness, durfen ungehemmt driften und zeigen deshalb Substitutionsraten, die ihren Mutationsraten entsprechen.


Diese Brucke zwischen Genetik und der ubrigen Biologie zeigt, das die Evolutionstheorien, die angeblich die moderne Evolutionssynthese storen, vollkommen mit ihr im Einklang sind. Sprungartige Evolution zwischen langen, stabilen Zeitraumen sind die Zwangsfolgen starker naturlicher Selektion auf Fitness in Okosystemen, die sich nicht andern bis ein Druck auserhalb des Systems das bewirkt. Neutrale Evolution beschreibt, was mit dem Material passiert, das unwichtig fur Lebewesen ist.

J. L. Wilkinson

Papers

Quantitative genetics and evolution: Is our understanding of genetics sufficient to explain evolution?