Peaches: A Juicy Overview of Artifical Selection

I came across this interview of Dr. Desmond R. Layne, Clemson Peach Specialist, on Peach domestication in the States and I found it summed up all the main aspects of artificial selection in a brief, quirky manner.

Everything is covered, from the origin of peaches, to it's cultivation history and how we have selected for such a wide variation in traits based on consumer demand: colour, size, shape, texture, flavour and fruiting season. It is an eye-opener that cultivated peaches are heavily dependent upon us for survival as we are on them for food cultivation and economy and that left untended they will die. 

FUN FACT: Did you know that a nectarine is a 'fuzz-less' peach? They are genetically the same, expect for the loss of that one genetic 'fuzz' trait.  

ALSO: Have you ever heard of a Donut Peach? Watch this video to find out more...

Differences in Guinea Pig Behaviour: Wild vs Domestic

Domestic guinea pig (Cavia porcellus)

Guinea pigs (Cavia aperea f. porcellus) originated in the highlands of South America where they were domesticated from wild cavies (Cavia aperea) approx. 3000-6000 years ago for food. During domestication there was a tremendous increase in population densities. While cavies live in large home ranges (200m² – 1000m²) guinea pigs can be kept in groups of up to 20 individuals in 6m² enclosures without any problems.  

Domestication removes some pressures of natural selection and replaces them with new selection pressures created from an artificial environment. This, along with direct artificial selection by humans can result in marked alterations in the biobehavioural profile of a species. These profiles are also influenced by heritage and an ontogeny phase: adolescence; which is the gradual transition from infancy through stages resulting in sexually mature adults. During adolescence there is an extensive alteration in anatomy, endocrine systems, neural circuits and behaviour. This is especially important in the development of guinea pigs as development is heavily influenced by the social circumstances the individual is exposed to during adolescence.  

Zipser et al (2014) analysed differences in emotional and social behaviours and cortisol reactivity across adolescent male guinea pigs and cavies. Major differences in behavioural and endocrinological parameters were found. Young individuals show that adaptations that reflect the differences between the natural habitat of cavies and manmade housing conditions guinea pigs emerge early in ontogeny well before attainment of sexual maturity.

Differences in emotional behaviour found cavies to be more explorative, risk-taking and socially less active. From an evolutionary standpoint, extensive exploration is crucial for wild animals in order to obtain access to vital recourses such as water, food, shelter and mates. Cavies also consistently showed higher cortisol reactivity. In highly demanding circumstances energy is expensive, therefore appropriate physiological adaptations to provide the necessary energy quickly is required. High cortisol reactivity can be interpreted as the energy provisioning mechanism that meets these demands.

In contrast, the biobehavioural profile of guinea pigs is characterised by higher levels of social activity and lower levels of risk-taking, exploration and cortisol reactivity. They are more social interactive with lower cortisol reactivity levels than cavies as they are adapted to a less challenging environment with much higher population densities. Higher degrees of agreeableness, sexual behaviour and lower levels of aggression are common in domestication as dangerous and challenging environmental factors (hence selection pressures) are removed, such as in manmade housing systems which provide all relative resources for guinea pigs to thrive. 

image accessed 25/04/2014: http://www.vetwest.com.au/pet-library/guinea-pig-care
 

Does Domestication Affect Mutual Partners?

Figure 1: Diagram of Mycorrhizal Fungi. (accessed 10/04/2014)

Multiple studies of the domestication process have been conducted on grain crops where above-ground traits (increasing yield quantity/size and prolonging fruiting season) are typically favoured over below-ground traits. Less is known about domestication in crops which require a mutualistic relationship with below-ground mycorrhizal fungi. Fruit crops (which constitute to a large part of the human diet) are enhanced by these root symbionts by allowing the plant to access nutrients as well as increasing disease resistance and adding protection from pathogens. Mycorrhizal fungi are beneficial and can potentially influence plant fitness, community structure, biodiversity, ecosystem productivity and variability (Fig 1). 

An important staple food crop across the Tropics and Oceania is breadfruit (Artocarpus altils). Over 2000-3000 years domestication has changed breadfruit significantly from its ancestor, breadnut (A. camansi) by extending fruiting season, creating fleshier fruit with fewer seeds and increasing fruiting loads (Fig 2). To be considered domesticated, it must be wholly dependent upon human intervention for dispersal, growth and reproduction, which can be seen in all cultivated seedless breadfruit species.

Figure 2: Change in Breadfruit morphology from wild breadnut (left) to modern seedless varieties (right). (accessed 10/04/2014)

 A study by Xing et al., (2012) followed the domestication process of breadfruit species (Artocarpus sp.) across a strong geographical gradient from west to east across the Melanesian and Polynesian islands with a focus on its mutualistic partner - arbuscular mycorrhizas (AM fungi). It was found that modern breadfruit species are less able to support AM fungi than wild ancestors. This is supported by a decrease in quantity and colonization rate across the domestication gradient from wild ancestors to modern species.

 

It is possible that a trade-off in resource allocation has occurred. Fruits are considered a strong sink for photosynthate, where sugar and other chemicals created from photosynthesis are primarily allocated for fruit production. As selection for high fruit yield in breadfruit has occurred, the amount of photosynthate may have been limited with fewer resources available for below ground root colonization and the maintenance of the mutualistic AM fungi relationship. 

The consequences of reduced AM fungi colonisation could result in higher disease vulnerability/reduced resistance to pathogens as well as less efficiency in accessing nutrients and water under stressful conditions. Breadfruit has the potential to be propagated at an industrial crop scale internationally in new environments using a single cultivated genotype. However there is much uncertainty in its success - especially in places that have nutrient limitations or drought stress. This study suggests that human-driven selection, as seen in cultivated breadfruit, can have unintended effects on below-ground mutualists, with potential impacts on the stress tolerance of crops and overall long-term food security.

Fishing for Goldfish

Carp domestication is thought to date back as early as the Neolithic but culturing for food is predominantly thought to have started with the Romans. This domestication was then expanded upon by monks who kept them in ponds at monasteries followed by the prolific culture of nishikigoi (Koi) in Japan where ‘fancy coloured carp’ are kept for pleasure. Wild carp lived up to 15 years old, weighed up to 5kg and were over half a meter long however a wild form may no longer exist (are very rare) due to the rampant introduction of domesticated species as well as the elimination of their natural habitat - floodplains (Balon, 1995).

Original wild carp from Danube (Left). Domesticated Koi with size and colour variation (Right).

A study done on two species of common carp by Klefoth (2013) found that domesticated fish are more vulnerable to angling. Some theories suggest that domesticated fish (especially for human consumption) have reduced cognitive abilities due to selection for rapid growth, which corresponds with reduced energy allocation into the construction of the neural network. Or that artificial conditions in which fish are held are responsible for the inability to learn complex tasks, which lead to a constantly higher catchability of domestic fish compared to wild species.

 However, vulnerability was tested across two environments (pond and fish tanks) where both species’ indicated learning a hook avoidance by exhibiting decreased catchability over time. Fish are regulated by hereditary anti-predator behaviour as a result of established predator-prey relationships. Although anti-predator behaviour is genetic in carp, learning from experience over time can influence the development of the behaviour. In ornamental tank fish where there are no predators, this genetic behaviour becomes lost or diminished throughout generations, but can be ‘re-learned’. 

Under farming conditions, domesticated fish have become adapted to carbohydrate rich artificial food which alters their food preference and digestive ability from that of wild counterparts. Along with food preferences, consumption rate and food-intake speed also differ. It is believed boldness of behaviour (especially when foraging) is a developed trait in domesticated species that plays an important role in rendering these species vulnerable to angling. Overall, domesticated carp are found to be vulnerable to angling mostly due to genetics and bold behaviour that have been selected for in the process of domestication (Klefoth et al., 2013). 

Carp image: http://img46.imageshack.us/img46/5288/sazan88cm92kg1ss1.jpg
Koi image: http://amazepicsvids.blogspot.com.au/2010/05/koi-fish-or-japanese-carp-colourful.html
Websites accessed: 03/04/2014