Learning about speciation and phenotypic plasticity this year, made
me come across hybridization several times. Most studies put hybridization into
a negative light, as hybrids of invasive and native species for example often don`t do as
well, and could lead to extinction (Muhlfeld et al. 2014). After our last lecture
with Dan, I was wondering how core gut microbiota could differ in
hybrids of two fish species compared to their parents. Although there has no studies been done on the gut microbiology of hybrid fish, I was surprised to
find, that hybridization has been used as a technique to improve the immune response of farmed animals in aquaculture for a while
now.
Liang et al. (2014) examined the role of hybridization
between two abalone species Haliotis
discus hamnai and Haliotis gigantea,
in improving the immune response and thermal tolerance. The results suggest,
that temperature changes could significantly affect the physiological status
and immunity to pathogens of abalone, however hybrids may be more resistant to
disease and thermal stresses than their parents. The whole study was done following recently frequent
death events of cultured abalone through infections with bacteria (Vibrio harveyi, Vibrio alginolyticus and
Vibrio parahemolyticus).
V. parahemolyticus is found in plankton or often attached to surfaces, zooplankton, fish and shellfish can lead to human illness. I might be missing something out here, but even if the hybrid abalone was more immune against bacteria and therefore not die, I assume the bacteria would still be present in abalone cultures and therefore still able to find their way into the human food? In my opinion there should be more work done on microbial gut communities in farmed animals, especially if techniques like hybridizations are used.
This is a rather short post, hoping to bring across the idea of the problem. If you have any questions concerning the methods used in Liang et al. (2014) please do not hesistate to ask.
Liang S, Luo X, You W, Luo L, Ke C (2014) The role of hybridization in improving the immune response and thermal tolerance of abalone. Fish & Shellfish Immunology 39: 69–77
Muhlfeld CC, Kovach RP, Jones LA, Al-Chokhachy R, Boyer MC, Leary RF, Lowe WH, Luikart G, Allendorf FW (2014) Invasive hybridization in a threatened species is accelerated by climate change. Nature Climate Change 4: 620–624
Hi Tabea,
ReplyDeleteThis is a really interesting study, I was just thinking about your point of the bacteria still being present in immune abalone: would the abalone with immunity not fight off the bacteria, meaning they would no longer be present in the food supply? Perhaps the ones with immunity would have lower numbers of V. parahemolyticus, it would be interesting to see if this immunity in the abalone correlated with human disease.
Thanks,
Freya
Freya - Yes there might be less bacteria present in the more immune hybrids, however who knows? The study only investigates in the death rate when infected with bacteria and the activity of the immune-related enzymes. There is nothing done on whether there are still bacteria present or not at the end of the experiment at all. Yes I think it would be interesting to see if this immunity in abalone correlated with human disease however I don`t think there is enough data present at the moment and I don`t think it should be the aim to just try it out in the future.
DeleteThanks :)
Hi Tabea,
ReplyDeleteAn interesting idea! Are you saying that hybridisation is currently being used in aquaculture as a technique to reduce disease etc? Just wondering where you stand on this, do you think farming hybrid species is a good idea? Surely if there is evidence that using them is beneficial there should be far more work into this?
Cheers
Sam
Hi Sam,
DeleteYes apparently hybridization is an effective method of genetic improvement and has been used in aquaculture for many fish and shellfish species (including abalone, oyster, scallop, carp, catfish, salmonid, sparid, sunfish …). Muhlfeld et al. mention that hybridization can improve traits of the hybrids, such as enhanced growth, survival rate, thermal tolerance, disease resistance and so on. They use the heterosis theory as an explanation: the offspring produced through hybridization either gains better phenotypic traits than both parents or gains intermediate phenotypic traits between parents (yes maybe but how does this actually work out in nature?). In fish especially I assume this will be directly linked to the gut microbiota (that’s why I was a bit surprised today Dan Merrifield hasn`t heard about it). As Dan said today people should rather concentrate on the “real” species we already have and treat them with probiotics for example, but I don`t know which technique I more agree/or disagree with. What do you think? What if a hybrid escapes into nature? It could cause serious evolutionary damage.
Yes, I've seen a couple of papers (I assume of many), which focus on the mentioned hybrids escaping and as a result causing significant negative effects on the wild populations. In regards to what Dan Merrifield suggests about treating the 'real' species rather than using hybrids, I think I am leaning more towards this idea. It is a tough one though, with neither obviously being perfect. As you and Tom were talking about on his post 'Rhabdoviridae to the Rescue?', effective methods of treating these 'real' species are still far from perfect. However I do feel that they will be a more effective tool for aquaculture once they have been improved, than using hybrids. A very interesting topic of discussion though!
DeleteInteresting post, and interesting comments from both Freya and Sam. In response to Freya's comment, traces of any diseases can be still in the organism and still be considered an immunity, perhaps an over simplification; but the consider the flu jab. It contains inactivated strains of the flu virus, and as a result, stated that it cannot cause flu (open for debate). However, my point is, their immunity from a physiological viewpoint may not be as telling. They could still contain the disease but have a higher threshold due parental gene transfer. Also, due to being for human consumption, I doubt they are around long enough to find out. Environmental factors need to be considered also, perhaps the combination is not right to set a reaction?
ReplyDeleteIt is surprising to me also that hybridisation is implemented within aquaculture as you would normal consider hybrids with lower fitness, thus higher susceptibility to disease perhaps?
Hmmmm, lots to ponder over!! :)
Thanks,
Dean
Hi Dean,
DeleteAn interesting addition, cheers. I was just wondering your stance on this topic? If indeed it is true that hybrids can show a higher immunity to disease etc, do you think this would be a useful tool for aquaculture to take into account? I can't make my mind up!
Cheers,
Sam
Thanks Dean for the input! In the experiment they used different temperatures (20° as control and 28°) as the were looking at the thermal tolerance of hybrids as well, therefore tested immune response when in stressed conditions. However, there are still other environmental factors that should be tested!
DeleteSam... Yes I agree with you. Have a read what I replied to your previous comment!
Hi Sam, to be honest I am not read up around the subject to make that judgement, and before Tom's comment, I personally thought most (if not all) hybrids had a lower fitness.
DeleteTabea, between the 20° and 28°; was there any real difference shown in temperature thresholds?
Hi Dean, I think you are getting mixed up by 'fitness' and beneficial characteristics such as disease resistance in aquaculture. Fitness is really dependent on the ability to produce offspring that are going to survive, individual survival is also important but it really boils down to can an organism produce viable offspring. A hybrid could have loads of beneficial characters but be completely unable to back-cross into either species or reproduce its self due to a quirk of its genetics so therefore has a fitness of zero (e.g. Mules). But in an aquaculture sense it would be worth producing as you could just recross each time between the two pure species. These kind of aquaculture studies are looking at beneficial characteristics in a way that is quite different than what you might assess in ecology. However, note I have a feeling that the hybrids considered in this study might be fertile, for more information read the review I have referenced in another comment.
DeleteTom - thanks for the input!
DeleteDean- They tested a few things to see how they managed temperature stressed environments. Overall they found that both at 20° and the stressed temperature (12 or 28°) hybrids either exhibited higher levels of some immune system components or showed less fluctuation in some components. F.e. testing THC (hemocytes which are closely connected with mollusk`s immune function) they found that the THC density in hybrids was higher and more stable than in the parents throughout temperature changes. When looking at the HSP70 they found that the hybrids either expressed higher levels of HSP70 at long-time exposure to stressed temperatures, or less fluctuation in HSP70 expression. Hybrids ar therefore more capable of dealing with temperature stress!. Hope that helps!
I definately think what this study is missing, is looking at the microbiota of the hybrids and parents itself!!
Interesting stuff.
ReplyDeleteJust a few notes, this kind of hybridisation is possible in the wild, from reading Lafarga de la Cruz and Gallardo-Escarate 2011 it looks like the above species do show hybrids in the wild (its probably where they got the idea from). Its probably quite common if species of Haliotis exist together as they are broad cast spawners (hybrid zones exist in nature). Given this I think that the evolutionary impacts of releasing hybrids into the wild, given that they exist in nature is not going to be particularly profound. However, you might get a dilution of both species natural genepool with hybrids given they are broadcast spawners, which may not be too good (depends if those hybrids are fertile). In terms of hybrid vigour, this is well documented as a tool in agriculture/aquaculture although your right Dean you do get the opposite, outbreeding depression. From having a glance at a few reviews on plants it looks like it’s mostly considered genetic. Although that’s a really nice novel idea that it might have a microbial basis Tabea!
(if people want the papers mentioned give me a shout)
Hi Tom,
DeleteThanks for clearing a couple of things up. I was just wondering if you found anything on the similarity between the natural hybrids and the farmed hybrids? Are they near enough identical or are there differences between them? As if they are indeed very similar genetically then the use of hybrid species in farms begins to make a bit more sense to me!
Cheers
Sam
No I haven't found anything on a direct comparison. To be honest I doubt they are going to be different, it appears as if the method used to produce them the same as what happens in the wild. The only obvious difference I think is there abundance, they are relatively low abundance in the wild but obviously of high abundance in an aquaculture environment. I think with regards to environmental impact their probably the least of our concern. What about use of antibiotic in aquaculture, transfer of disease, concentration of parasites, habitat destruction etc. etc. Just to bring things back to the microbes it appears as if the Chinese have adopted hybrids in order to combat massive disease outbreaks.
DeleteIf your interested in all thinks abalone hybrids (there's loads) read Lafarga de la Cruz and Gallardo-Escarate 2011. Intraspecies and interspecies hybrids in Haliotis: natural and experimental evidence and its impact on abalone aquaculture. Reviews in Aquaculture 3, 74-99.