Alien Hybrids: friend or foe?

When Invasive Alien Species enter a new environment they  impact others in many different ways, one of them being Hybridisation!

What is Hybridisation?

Hybridisation as defined by Todesco et al, is when two populations that have distinguishably different genes mate together to produce a "hybrid" offspring. This offspring will then have combined genes of both of the adults and will likely show a mix of morphological features too. 

How frequently does it occur?

Interestingly, in 1992 Abbott states how out of 2834 plant species listed in the New Flora of the British Isles, 1264 of these are Invasive Alien Species (IAS). Out of these 1264 species, 70 are recognised as being hybrids due to native-IAS interactions, 21 are due to IAS-IAS and 4 are even due to hybrid-native species interactions.  

It isn't even just retrained to plants, Mooney and Cleland explored other examples of species known for undergoing hybridisation as shown below.

A hybrid of the invasive Mallard Duck when it was introduced to the native New Zealand Grey Duck.

 A Japanese Sitka Deer stag running with a UK Red Deer group which commonly produces hybrid offspring despite  major differences in body size.

Are there any negative impacts?

The hybridisation between two or more species has sadly been known to cause extinctions. It can do this in a number of ways as explained by Todesco et al;

Being better than their parents: the hybrid that is produced can become very successful due to the creation of a mosaic of morphological features that allow them to occupy new environments and exploit extra resources. But why is this negative? Well, this can then lead to the decrease of either one or both of the parent species due to the hybrid out competing them. If one of them is already under threat or has low population numbers, then this can be detrimental.
Being worse than their parents: commonly, the hybrid offspring that are produced are infertile due to an imbalance in the number of genes. Also each parent may has physical adaptations to their local environment and when these are combined it may make the hybrid offspring no longer able to survive in the area they are born. As a result, these can both reduce the reproductive success of the parent species and the offspring and could eventually lead to extinction.

Meilink et al also explored the idea of "Genetic Pollution" where by the genes of the invasive species "pollute" the native gene pool during the hybridisation. This can lead to a reduction in genetic diversity and the eventual disappearance of all the native genes. 

It's not all doom and gloom though!

As conservation becomes an increasingly important area for exploration, more people are discovering that good things can come from this blend. Richards and Hobbs explored this and concluded that hybridisation can lead to an increased amount of genetic diversity as new genes come into a habitat from a elsewhere which some believe in turn makes an ecosystem function more efficiently. Also, as mentioned previously, the mosaic of physical features that hybrids can obtain can actually lead to that organism being able to occupy a new habitat and with this isolation leads to an entire new species being created. This is particularly important due to the overall global decline in species numbers seen today.  

Interestingly, Chris D Thomas believes that the hybridisation of plants in the UK has led new species being produced (due to hybridisation) similar to that of the extinction rate of mammals in the past 100 years. From this he seems to justify that the extinction of mammals is okay, because of the new development of plant species but this is something I do not think is comparable, what do you think?

To find out about a cool hybrid between wolves, dogs and coyotes, click the link below!
  https://www.youtube.com/watch?v=D3MgXRJ_fys