1.  I wonder if this might  contribute to crows’ vulnerability to West Nile Virus.  I also wonder if it has always been this way. It would be interesting to analyze historic museum specimens to see if the rate of inbreeding has varied over space and time and look at factors that may have contributed to any trends.

2.  I knew that a lot of birds did this. It is probably a form of genetic bet-hedging.

What an interesting tale! I was very surprised to know that crows can lose a foot and survive. I guess that shouldn't be so surprising: I know animals are adaptable and I've known many dogs and cats with amputated limbs. And of course humans can get along without one (or two!) legs. I'd sure think a biped would need to make some major adaptations in balance. Being part of a family group when this happens must be a big advantage. I have heard of animals living in harsher environments, and when they become impaired, they area left behind because of the risk they'll bring on the rest of the group.

I haven't ever noticed crows struggling with this and will pay closer attention now.

I did only once see a dead crow, early in the life of West Nile (or at least when it was first in the news), and I assume that was the cause of death. At that time I called our DNR, but they didn't want to collect it for testing; they said they had plenty of evidence West Nile was at that time wreaking havoc in our area. That had to be 20+ years ago.

I haven't read through ALL the comments, but from what I did look at, and from the lesson, my takeaway is that it's possible (likely?) that the potential genetic problems caused by inbreeding might be balanced by the diversity gained through extra-pair fertilization? Not that the birds would know this, obviously. But it does seem possible that the two strategies zero each other out. Consequently, there wouldn't be a great genetic benefit to the extra-pair fertilization.

I'm just so surprised and pleased to hear about the amazing flexibility in the lives of these birds!

1. I wonder if it would eventually cause deformities or maybe the egg not to hatch at all.

2. I was surprised.  Crows are family oriented so I just assumed they would only have 1 mate. I suppose it could be beneficial by expanding varying genetics.

American Crows--the Hapsburgs of the avian world.

Have any similar genetic studies been carried out on other corvid species?

Has there been any follow-up to Dr. Townsend's research correlating the degree of inbreeding to survival?

1. The inbreeding could cause issues with lack of genetic diversity and potential health risks
2. I’m not really surprised. It benefits the birds by bringing in more genetic diversity.

1.  Inbreeding risks loss of genetic diversity and increased potential for disease susceptibility or congenital defects which may be harmful to long term survival.

2.  Not surprising.  It will increase genetic diversity and may increase the likelihood of a successful breeding season, particularly if both fathers are motivated to provide support to mom and chicks.

1.  Is it possible that the inbreeding is more common in the urban crows you are studying, rather than all crows?

Inbreeding can lead to flaws in the gene pool and genetic defects within the crows and family. Also having disease within the crow family.

 

As I understand it, inbreeding leads to a lack of genetic diversity, which isn't beneficial for a species or the offspring of inbreeding pairs. I have wondered about inbreeding amongst the crows in my area. I wonder if inbreeding can reduce a crow's cognitive abilities.

No, the commonness of extra-pair fertilization among birds is not surprising to me. One of the benefits might include increasing genetic diversity.

1. Inbreeding creates a weaker gene pool, which results in weaker crows less likely to survive disease or other environmental stressors. 2. Extra-pair fertilization is a strategy that ensures successful fertilization in the event the primary male is infertile or otherwise not in optimal breeding form.

1. The young would be more likely to suffer from recessive gene genetic diseases.  They would be less likely to have a gene that helps combat a certain disease, maybe.

2. I am not surprised.  I would guess that it benefits the species, as the more genes are mixed, the less likely it would be that an entire group would be susceptible to some stressor, disease, temperature/climate change.

1. Relating inbreeding back to people or domestic animals, it would  seem to open up the species to more genetic flaws and possibly genetically weaken the species.  For example, in the dog world, dogs breed to the AKC standards often can have more genetic defects than when two different types of dogs, or even "Heinz 57" type dogs.

inbreeding can result in expression of recessive undesirable traits.

out breeding gives more " hybrid vigor " ( not really hybrids but introduction of new genes )

I don't  think that the percentage of inbreeding is high enough to trigger genetic defects that can seriously affect the crow species.  Families too removed from outside breeding opportunities (like being trapped on an island) could find this fatal.  Crows are not Pharaoh's in that they do introduce each enough genetic variability so as not to be a problem.  The advantage of the family cohesive nature might outweigh the downside to inbreeding as the family is more likely to survive intact.  Most genetic mutations are not harmful even if chances increase due to inbreeding.

1.Inbreeding might cause disease, and the crow species might become less diverse due to the tight family(genetically), and could lead to a downfall of the whole species, I wonder if the crows realized this.

2.Extra-pair fertilization might be beneficial, due to the fact that the eggs have a high chance of hatching since their are not in a single nest. The extra-paired males doesn't need to spend that much energy in raising them. The crow population might be more diverse, because traits gets passed around and the young benefits from this.

For individuals, inbreeding could result in genetic defects and greater susceptibility to diseases (overall reduced physical fitness). If the population as a whole has a low level of genetic diversity, the impact of a disease could be more severe, quickly spread throughout the group and lead to the population crashing.

Extra-pair fertilization is a useful strategy for both parties (ie. the breeding female and extra-pair male) to have greater reproductive success, as they aren't putting all of their eggs in one basket, so to speak. The extra-pair male gets to sire extra offspring without spending any energy needing to raise them. The female gets more genetically diverse offspring which should statistically increase their chances of survival - e.g. if the extra offspring have some extra good trait(s) - assuming there is enough food to go around. The only "loser" here is the breeding paired male, who spends time and energy raising young that are not genetically related to him. However, given that crows breed cooperatively, there is still an advantage to this as the extra-pair offspring will help him the future.

I would suppose that inbreeding could be a threat, although the percentage rates of incest and near related are rather high, how many generations has this been happening? If this has been the crow way for eons then maybe there is some sort of genetic advantage. Extra-pair fertilization possibly has some benefit for the health of a flock or family to offset any disadvantage that incest or near related that might occur.

Since American crows spend so much time as a family, inbreeding might lessen the amount of healthy breeding partners long term. It might also exacerbate certain negative traits, predispositions of certain illnesses or other diseases. We see similar concerns show up with dogs that are repeatedly interbred with close relatives to create traits which, while desirable to humans, can be detrimental tot he dogs (see, for example, the snout of the pug being too short.) Could more inbreeding lead to shorter beaks, weaker eyesight, or other negative traits in crows? The species as a whole could be weakened as family groups get tighter and tighter genetically.

1.  When it comes to inbreeding, are these unwilling females?   I'm sure some are unknowing inbreeding too.

2. Extra-pair fertilization is not surprising to me in any species of animal.  It can be beneficial to bring in new strong traits but also go the other way and introduce a weakness.   But I can see that it can also lead to unknowing inbreeding.

I have heard about social vs. sexual monogamy as a common issue. Males with often less investment into raising their offsprings will benefit by more effectively spreading their genes.  For females, I can see the potential advantage of having a genetically more diverse groups of offsprings, which may translate into better chances of survival under changing/challenging conditions.

Inbreeding within the crow families and communities can mess with the crow gene pool. Causing them to potentially die earlier from health problems due to incest. This can also make them less genetically different from each other meaning they can become endangered and potentially not have inherited skills to keep them alive in the wild. This is really interesting considering how smart crows are.

1. The level of threat to crows from inbreding is probably relatively low, but may also serve as a polpulation control mechanism. As states in Ms. Townsend's article, inbreeding did lead to increased vulnerability to mortality from disease. 2. Extra pair fertilization is not suprising to me, as I learned about it in my evolution class. This could be beneficial it helps to diversify the genetic pool of the population.