kiwis on the brain
painting by brookereidt ~ 1888 illustration ~ brooch by debaleigh ~ vinyl wall art by DecorDesigns ~ poster via burlesque of north america
my day started off productive: laundry, dishes, cleaning, emails, organisation, appointments. and then i started writing. i got a few sentences down, made a few edits - just a few easy things to get me started. but then the afternoon hit and i'm stuck again. i just can't seem to make anything out of my discussion for the embryo section of my paper. i know i need to put my results into perspective; how do they fit into the grand scheme of things??
basically my results were very simple - i came up with predicted ages for a collection of unknown aged kiwi embryos by comparing them to known age chicken and ostrich embryos. obviously chickens, ostriches and kiwis all look very different, but as embryos they all have the same basic structures: eyes, bill, limbs, scales, feathers, claws, etc. in order to relate ostrich and chicken embryo age to kiwi age, i have to assume that all of these structures develop in the same pattern and at the same time relative to the incubation length. for example, if scales first appear at day 22 in an ostrich, which has an incubation length of 42 days, i would expect that scales would also appear at approximately 50% of the kiwis incubation of 78-85 days.
so i looked at the external features of my kiwi embryo collection and tried to relate each to chickens and ostriches of the same age. my estimated kiwi ages using the 'ostrich model' and 'chicken model' were relatively similar, but the ostrich model gave the closest estimation for our one known age embryo. this isn't much of a surprise because ostriches and kiwis are in the same ratite family as are expected to grow and develop in very similar ways. the chicken is farther away, in an evolutionary sense, and so the assumption that kiwis and chickens grow similarly is not a strong one. however, there is an inherent pattern of growth that each bird follows that is not necessarily apparent until a chick has hatched.
everyone has seen pictures of a nice fluffy chick of a domestic chicken. it hatches with lots of feathers and can walk pretty soon after it hatches (called precocial). on the other hand, there are the kind of chicks that hatch naked, stay in the nest and let their parents bring them food (called altricial). you can look at the altricial chick as being more immature at hatch in comparison to its adult form, where the precocial chick hatches more mature and more like its adult form. by hatching with a greater level of maturity, however, the precocial chick 'trades off' its ability to grow quickly. the reason has to do with bone strength and development, but i won't go into that.
since the kiwi, ostrich and chicken are all precocial birds, the models i used shouldn't be applied to altricial chicks, who grow quickly after they hatch and thus likely have different patterns of growth before they hatch. basically you can't compare altricial apples and precocial oranges.
so result #1 is that the ostrich and chicken models produced reasonably good estimations of kiwi age, presumably because they follow the same pattern of growth.
i have to say 'reasonably good' in result #1 because result #2 is that sometimes the timing of a particular feature in the kiwi did not exactly match the timing of the same feature in the chicken and ostrich in relation to all other features. it sounds tricky, but really it isn't. for example, the kiwi's bill grows faster in relation to the toes and other body parts than in the ostrich and chicken. this makes sense as the kiwi's bill is much longer and needs to be fully functional by the time it hatches.
observation/result #3 has to do with my actual samples. first, the quality of the embryos was not high since they were preserved rather than fresh samples, so any measurements i took may not be that great and some features that were damaged were hard to use in comparisons. second, i had very few embryos to work with. third, the very few embryos i had to work with consisted mostly of older embryos. there is a lot to be said about the 'problems' with my small skewed sample population.
it could just be random chance that i have a bunch of older embryos, but it is more likely that more old embryos have been collected in the first place because of the program operation nest egg (ONE). this is a program where eggs are collected in the wild and brought into captivity to hatch so that the vulnerable eggs and chicks are protected from predators until they are old enough to defend themselves. very young embryos are fragile and are likely to break down or be eaten or damaged before collection, thus reducing the chance of having young embryos to study. another reason may be that the mortality rate is higher in early embryos, perhaps because they are more vulnerable to disease, temperature changes or genetic defects?
observation/result #4: i may have mentioned i had few embryos in my collection. the main reason for a lack of embryos is that the species is scarce. additionally, kiwis are a taonga, or culturally sacred, species. this means that even if the population was stable and there were enough animals to 'spare', embryos could not be sacrificed at regular age intervals in the same way that other species have been for this kind of study.
a small sample size doesn't necessarily render my observations invalid, if anything this study opens the door for more work as more embryos (preferably ones of known age) become available. the models i used can be tweaked, validated or invalidated, but basically nothing else has been put out there to provide a basis of comparison for future work and that is the knowledge gap that i am aiming to fill.
for the reasons i mentioned before, it isn't likely that a whole lot of new known-aged embryos will become available in the very near future, so this study is the beginning of finding a way to age embryos by non-invasive means.
ta-daa! let's see if that gets the creative juices flowing...
speaking of creativity, i am getting my friend jillian, aka hellojilli, to make me a kiwi pendant necklace with the 1888 kiwi illustration at the top. something along the lines of this one - so excited!
basically my results were very simple - i came up with predicted ages for a collection of unknown aged kiwi embryos by comparing them to known age chicken and ostrich embryos. obviously chickens, ostriches and kiwis all look very different, but as embryos they all have the same basic structures: eyes, bill, limbs, scales, feathers, claws, etc. in order to relate ostrich and chicken embryo age to kiwi age, i have to assume that all of these structures develop in the same pattern and at the same time relative to the incubation length. for example, if scales first appear at day 22 in an ostrich, which has an incubation length of 42 days, i would expect that scales would also appear at approximately 50% of the kiwis incubation of 78-85 days.
so i looked at the external features of my kiwi embryo collection and tried to relate each to chickens and ostriches of the same age. my estimated kiwi ages using the 'ostrich model' and 'chicken model' were relatively similar, but the ostrich model gave the closest estimation for our one known age embryo. this isn't much of a surprise because ostriches and kiwis are in the same ratite family as are expected to grow and develop in very similar ways. the chicken is farther away, in an evolutionary sense, and so the assumption that kiwis and chickens grow similarly is not a strong one. however, there is an inherent pattern of growth that each bird follows that is not necessarily apparent until a chick has hatched.
everyone has seen pictures of a nice fluffy chick of a domestic chicken. it hatches with lots of feathers and can walk pretty soon after it hatches (called precocial). on the other hand, there are the kind of chicks that hatch naked, stay in the nest and let their parents bring them food (called altricial). you can look at the altricial chick as being more immature at hatch in comparison to its adult form, where the precocial chick hatches more mature and more like its adult form. by hatching with a greater level of maturity, however, the precocial chick 'trades off' its ability to grow quickly. the reason has to do with bone strength and development, but i won't go into that.
since the kiwi, ostrich and chicken are all precocial birds, the models i used shouldn't be applied to altricial chicks, who grow quickly after they hatch and thus likely have different patterns of growth before they hatch. basically you can't compare altricial apples and precocial oranges.
so result #1 is that the ostrich and chicken models produced reasonably good estimations of kiwi age, presumably because they follow the same pattern of growth.
i have to say 'reasonably good' in result #1 because result #2 is that sometimes the timing of a particular feature in the kiwi did not exactly match the timing of the same feature in the chicken and ostrich in relation to all other features. it sounds tricky, but really it isn't. for example, the kiwi's bill grows faster in relation to the toes and other body parts than in the ostrich and chicken. this makes sense as the kiwi's bill is much longer and needs to be fully functional by the time it hatches.
observation/result #3 has to do with my actual samples. first, the quality of the embryos was not high since they were preserved rather than fresh samples, so any measurements i took may not be that great and some features that were damaged were hard to use in comparisons. second, i had very few embryos to work with. third, the very few embryos i had to work with consisted mostly of older embryos. there is a lot to be said about the 'problems' with my small skewed sample population.
it could just be random chance that i have a bunch of older embryos, but it is more likely that more old embryos have been collected in the first place because of the program operation nest egg (ONE). this is a program where eggs are collected in the wild and brought into captivity to hatch so that the vulnerable eggs and chicks are protected from predators until they are old enough to defend themselves. very young embryos are fragile and are likely to break down or be eaten or damaged before collection, thus reducing the chance of having young embryos to study. another reason may be that the mortality rate is higher in early embryos, perhaps because they are more vulnerable to disease, temperature changes or genetic defects?
observation/result #4: i may have mentioned i had few embryos in my collection. the main reason for a lack of embryos is that the species is scarce. additionally, kiwis are a taonga, or culturally sacred, species. this means that even if the population was stable and there were enough animals to 'spare', embryos could not be sacrificed at regular age intervals in the same way that other species have been for this kind of study.
a small sample size doesn't necessarily render my observations invalid, if anything this study opens the door for more work as more embryos (preferably ones of known age) become available. the models i used can be tweaked, validated or invalidated, but basically nothing else has been put out there to provide a basis of comparison for future work and that is the knowledge gap that i am aiming to fill.
for the reasons i mentioned before, it isn't likely that a whole lot of new known-aged embryos will become available in the very near future, so this study is the beginning of finding a way to age embryos by non-invasive means.
ta-daa! let's see if that gets the creative juices flowing...
speaking of creativity, i am getting my friend jillian, aka hellojilli, to make me a kiwi pendant necklace with the 1888 kiwi illustration at the top. something along the lines of this one - so excited!
Comments