Are Weeds Wild Or Domesticated?

There is often discrepancy when considering where weeds belong in the evolution of domesticated species from wild ancestor species. It is known that classes of wild plants and animals have merged into the domestic class by continuous stages in the degree of their intimacy with man. Wild is thought of as plants that do not require human cultivation, flourish in the natural, undisturbed environment and cannot invade permanently man-disturbed habitats whereas domesticates cannot survive in the ‘wild’ due to intense selection and they require cultivation and continuous help to propagate within a human control environment. Weeds also flourish in man-made environments, however they don’t require cultivation. Where do weeds come from? De Wet & Harlan (1975) define weed evolution

under three methods:

• as successful colonizers selected for continuous habitat disturbance in a man-made habitat 
• as derivatives of hybridisation between wild and cultivated species 
• and through selection towards re-establishing seed dispersal mechanisms in abandoned domesticates

Weeds and domesticates differ in the degree of dependence on man for success in permanently disturbed man-made habitats. Some seed crops have hybridised with their ancestral races to produce weedy derivatives wherever wild and cultivated species are sympatric. This leads to weed sunflowers, weed carrots, weed maize and weed watermelons.

Domesticates can be weedy (when no longer cultivated) and weeds are sometimes grown as crops. However weeds never require artificial propagation. They are capable of establishing new populations within the disturbed habitat without further help by man.  Most of our common weeds are Eurasian in origin such as dandelion (below) and crabgrass and occupy an array of niches such as some are strictly associated with agriculture.

Common Australian Weed: Dandelion TARAXACUM SP

‘Weediness’ is not only confined to plants as numerous animal species have weedy races. For example:  worldwide houseflies, rabbits in Australia, the Brahman cow in India, and most shocking humans are the ultimate weed being obligated and confined to the habitat he is creating.

 Image accessed 27/05/14:  http://aggregata.blogspot.com.au/2013/03/dandelions-weed-medicinal-herb-and.html

Domestication As A Form Of Conservation??

An interesting piece for the enjoyment of Tasmin :) 

Australia has such unique fauna with great diversity as shown by native mammals such as whale that patrol the coastline to microbats weighing no more than a few grams. However many people are unfamiliar with their native fauna, such as quolls, quokkas and antechinuses. This unfamiliarity and anonymity of species can be due to our urbanisation where cities are harsh in terms of food sources, shelter and predation/competition from domestic cats and dogs. Many of our Australian mammals aren’t spectacular and go un-noticed in that they are particularly small, in some cases less than 100 grams, some even being nocturnal.

An article by Paul Hopwood (1996) puts forth the idea of allowing the keeping of Australian natives as pets. Currently government policy across all states prevents the keeping of endangered species, with some states enforcing a blanket ban irrespective of species status. Hopwood’s perspective is that there is great conservation value in maintaining colonies of endangered mammal species – provided that they make good pets. Now, two obvious sides emerge: potential detrimental outcomes for species survival in a conservation sense, morally wrong to restrict a wild animal; or positives in that native species are less environmentally damaging and the set-up of commercially viable pet industry with regards to breeding colonies can buffer the endangered species from extinction.

Focusing on practicality, certain characteristics such as easy to handle, readily available, affordable food supply, housing requirements and robustness are required for an Australian native mammal to be suitable. Another major issue is zoonotic diseases carried by native mammals; however in most situations preventative medical services are available.

Mitchells Hopping Mouse (Notomys mitchelli)

One animal species that would be suitable is Notomys. They will not kill your local birds and lizards, they eat little, have non-smelly poo, can be kept in a mouse tank and have a temperament suitable for handling. Best of all, if you were to keep Notomys mitchelli you would be doing conservation in New South Wales a service as this hopping mouse has been extinct from this State for over 50 years.

This point of view raises many questions, especially on intent behind the domestication of a species. Is it possible that future conservation plans may incorporate domestication as a last resort for survival of a species? It is a definite possibility for many endangered native Australian rodents whose numbers are dwindling.

Image accessed 12/05/2014:  http://www.lochmantransparencies.com/products/australian-wildlife/mitchells-hopping-mouse-notomys-mitchelli-ly-516/

Cats: Are They Commensal Or Domestic?

I came across this article by Bar-Oz et al (2014) in an Archaeology journal which attempts to explain why cats are at times so un-willing to be our pets. Research into early Chinese Neolithic agriculture (6,000–5,000 B.P.) at the site of Quanhucun, Shaanxi Province has created uncertainty regarding cat –human interactions.

The cat remains in question have tentatively been identified as a Felis species, similar to the four small-bodied cat genera and species in the Shaanxi Province region. One explanation put forward is that the cat represents a local wild species, placing the current trajectory of cat domestication in China in question. It is known that felids are obligate carnivores and require a diet of meat; therefore we would expect the carbon isotopic fingerprint of cats to be relative to the carbon source of their diet. However, the isotopic data suggests that the Quanhucun cat’s levels are a result of feeding on foods enriched with carbon from C4 domesticated plants. The Quanhucun cat’s isotope could be indicative of having eaten rodents that fed upon domesticated crops such as millet as found on related newsblog:  

http://www.theguardian.com/science/2013/dec/17/ancient-cat-bone-research-china-domestic-pet (accessed 11/05/14)

An explanation could be a result of in situ commensalism with humans. Commensal animals benefit from changes in their environment engendered by humans and form a fairly stable, direct or indirect, bond with their human hosts. Commensalism is widespread and represents one of several pathways to domestication. It is true though that the majority of animals in such human-animal interactions are never domesticated, which can be traced through microevolutionary changes and detailed taxonomic identification. 

This observation of aberrant findings in the absence of more detailed taxonomic identification (morphometric or genetic) requires further evaluation through analysis of stable isotopes in large samples of both domestic and wild cats with variable diets in China is needed before these findings can be substantiated. 

At times it feels like cat commensalism (benefiting off our resources at their will) rather than cat domestication (humans having tamed/melded them to our will) is a more accurate representation.

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.