User:Shippley.3/sandbox

The origins of echidnas

Ben Shippley

Recitation: Tues. 10:20 am-11:15 am

Research question: How did an organism like the Echidna come to be? From where did an egg-laying and lactating mammal originate?

Annotated biliography:

Phillips, M. J., T. H. Bennett, and M. S. Y. Lee. "Molecules, Morphology, and Ecology Indicate a Recent, Amphibious Ancestry for Echidnas." Proceedings of the National Academy of Sciences 106.40 (2009): 17089-7094. Web. 14 Sept. 2014.

This suggests a relationship between echidnas and amphibious species that were around more recently than the assumed time of divergence of monotremes before. It also goes into great detail about the exact timeline of said divergence, even finding the subsitution rates in the lineage to be relative to those of reptiles, birds, and therian mammals.

Weisbecker, V., and A. Goswami. "Brain Size, Life History, and Metabolism at the Marsupial/placental Dichotomy." Proceedings of the National Academy of Sciences 107.37 (2010): 16216-6221. Web. 14 Sept. 2014.

This study was meant to examine several biological differences between marsupials and placental mammals. It is however relevant to monotremes as well as it makes several comparisons of them as well to these classes of organisms. Even pointing out that echidnas more resemble marsupials in their maternal investment however their brain size is relatively large compared to marsupials.

Retief, Jaques D., Robert J. Winkfein, and Gordon H. Dixon. "European Journal of BiochemistryVolume 218, Issue 2, Article First Published Online: 3 MAR 2005." Evolution of the Monotremes. Department of Medical Biochemistry, 3 Mar. 2005. Web. 14 Sept. 2014.

This paper set out to show the genetic similarities between monotremes, like the echidna and platypus, and birds (such as the echidna's odd ability to lay eggs). Specifically, the study of the P1 protamine genes allowed the relationships between marsupials, eutherian mammals, and birds to be better understood.

Musser, A.m. "Review of the Monotreme Fossil Record and Comparison of Palaeontological and Molecular Data." Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 136.4 (2003): 927-42. Web. 14 Sept. 2014.

Fossil records were studied in order to challenge the traditional view that monotremes descended from a few particular Mesozoic era mammals. Through the practice of jaws from some then newly discovered Cretaceous monotremes, parallels could be drawn from those organisms to the one we see today. It also presents some insight into what the ancestors of the monotremes may have been like.

Oftedal, Olav T et al. "Can an Ancestral Condition for Milk Oligosaccharides Be Determined? Evidence from the Tasmanian Echidna (Tachyglossus Aculeatus Setosus)." Glycobiology 24.9 (2014): 826-39. Web. 14 Sept. 2104.

The genetic bases for milks in mammals were studied through the examination of the milk in Tasmanian echidna. The reasoning for this being that the reproductive basis for all mammals at one time was very likely egg-laying. This study provides a very in depth analysis of the workings of the birth process and lactation of echidnas.

October 1 assignment

Page: https://en.wikipedia.org/wiki/Echidna

Sentence and citation

Under section "Tachyglossus": Despite the similar dietary habits and methods of consumption to those of an anteater, there is no evidence supporting the idea that echidna-like monotremes have been myrmecophagic (ant/termite-eating) since the Cretaceous. The fossil evidence of invertebrate-feeding bandicoots and rat-kangaroos, from around the time of the platypus–echidna divergence and pre-dating Tachyglossus, show evidence that echidnas, despite competition from marsupials at the time, expanded into new ecospace.[20]

Full reference: Phillips, Matthew; Bennett, T.; Lee, Michael (January 26, 2010). "Reply to Camens: How recently did modern monotremes diversify?". Proceedings of the National Academy of Sciences of the United States of America 107 (4). doi:10.1073/pnas.0913152107. Retrieved 10/1/2014.

Talk Page suggestions

• Under section "spiny anteater": Maybe it should also be made clear that echidnas are not actually anteaters, despite this seemingly increasingly more common nickname. It mentions that they are not closely related but there is no real evidence to show that echidnas have descended from anteaters at all, even those that do eat termites and ants. It's more likely that they diverted from ancient marsupials instead. I'm not sure if that level of technical information really belongs in the intro but it should be made apparent somewhere that there is no direct relationship between echidnas and anteaters at all. — Preceding unsigned comment added by Shippley.3 (talk • contribs) 21:55, 1 October 2014 (UTC)
• Under section "Expansion of Evolution section": The section mentions the divergence of platypus-echidna and that this might imply that echidnas came from water-foraging ancestors. However, I feel that this could use a little more explanation of the evidence, such as their anatomical and physiological traits such as: as aquadynamic streamlining, dorsally projecting hind limbs acting as rudders, and locomotion founded on hypertrophied humeral long-axis rotation, which provides a very efficient swimming stroke. — Preceding unsigned comment added by Shippley.3 (talk • contribs) 22:05, 1 October 2014 (UTC)
• Under section "Expansion of Evolution section": At the end of the section it mentions how olviparous reproduction may have given monotremes an advantage over marsupials however it can be expanded. This advantage can in part lead to the observed associated adaptive radiation of echidnas and expansion of the niche space, which together contradict the fairly common assumption of halted morphological and molecular evolution that continues to be associated with monotremes. — Preceding unsigned comment added by Shippley.3 (talk • contribs) 22:22, 1 October 2014 (UTC)

Echidna Wiki Page Edits

Article: https://en.wikipedia.org/wiki/Echidna

Under "Evolution" section

• The first divergence between oviparous (egg-laying) and viviparous (offspring develop internally) mammals is believed to have occurred during the Triassic period. [19] However, there is still some disagreement on this estimated time of divergence. Though most findings from genetics studies (especially those concerning nuclear genes) are in agreement with the paleontological findings, some results from other techniques and sources, like mitochondrial DNA, are in slight disagreement with findings from fossils.[20]

• Further evidence of possible water-foraging ancestors can be found in some of the echidna's phenotypic traits as welll. Traits such as: as aqua dynamic streamlining, dorsally projecting hind limbs acting as rudders, and locomotion founded on hypertrophied humeral long-axis rotation, which provides a very efficient swimming stroke.[19]

• This advantage could as well be in part responsible for the observed associated adaptive radiation of echidnas and expansion of the niche space, which together contradict the fairly common assumption of halted morphological and molecular evolution that continues to be associated with monotremes. Furthermore, studies of mitochondrial DNA in platypuses have also found that monotremes and marsupials are most likely sister taxa. It also implies that any shared derived morphological traits between marsupials and placental mammals either occurred independently from one another or were lost in the lineage to monotremes.[22]

• From before even this water-foraging ancestor, some evidence shows that echidnas originated from birds and even reptiles as well. A genetic study that sequenced the DNA of echidnas and platypuses and compared their protein sequences to those of many other mammals and birds was performed. It was hypothesized that the original mammals, or prototheria, may have emerged from a line originating from birds and reptiles. Before even the divergence of ancient mammals into monotreme and therian mammals, the protein sequencing of monotremes indicates that they have a close relatedness to birds and reptiles before them. Their many computer-generated phylogenetic trees all seemed to be in agreement of this as well as the time of the platypus-echidna divergence.[20] Another study found that some of the sex chromosomes of monotremes even have homology with the Z sex chromosomes of birds. Gene mapping showed that they even have bird autosome regions in their genetic makeup.[21] Given the close relationship between birds and reptiles as well, it's safe to assume there's a connection between echidnas (and all monotremes) and reptiles as well.

Final Draft of Paper

The echidnas of Australia and New Guinea are a particularly interesting species all their own. Though they are wholly mammals since they have all the prerequisites needed: hair, lactating mammary glands, three middle ear bones, and the neocortex; they are however in another class of animals together. Together with only the platypus, the echidna makes up the class of mammals known as the “monotremes” due to their one defining trait that sets them apart from any other mammals: the fact that they lay eggs. Every other known mammal is considered to be viviparous, or growing their young inside themselves and giving birth to live offspring (also known as “therian” mammals). All other mammals, including both marsupials and placental mammals, besides the five species of monotremes, from both only the echidnas and platypuses, are therians. Though similar to any other mammal in every other way, this one significant difference in the monotreme reproduction system can potentially open up many other avenues of possible origins for the monotremes. This paper is written in the hopes of expounding upon some of the alternative ancestry that might be responsible for the echidnas being apart from so many other similar organisms. Hopefully, some light may be shed on what paths the echidnas’ ancestors may have come from and since taken to set apart this truly unique creature from the numerous other mammalian species that are nearly identical, save this one glaring difference.

To begin, echidnas fall under the family “Tachyglossidae” and, once again, are classified under the order of “monotremes”, the only mammals that lay eggs. The four extant species of echidnas, along with the one species of platypus, are the only five species that exist in the order. Not only that, but the four echidna species are only found in New Guinea and Australia. The monotreme order is without a doubt a very small, possibly one of the smallest, category of the whole of Earth’s biodiversity. Echidnas themselves are rather small in size and tend to have long snouts and are covered in spines. Superficially they tend to resemble a kind of cross between a small anteater and a porcupine. In fact, this resemblance to anteaters, as well as the aforementioned spines, has given rise to the echidnas’ colloquial nickname of “spiny anteaters”. However, there is absolutely no evidence to show that any of the echidna species at any point descended from a common line with anteaters. Even the Tachyglossus aculeatus species of echidna shows no such evidence despite the fact that they too are myrmecophagic (ant/termite-eating), like anteaters. Despite the similar dietary habits and methods of consumption to those of an anteater, there is no evidence supporting the idea that echidna-like monotremes have been myrmecophagic (ant/termite-eating) since the Cretaceous period. Fossil evidence of invertebrate-feeding bandicoots and rat-kangaroos, from around the time of the platypus–echidna divergence and pre-dating Tachyglossus, help to show this. It points infers that echidnas, despite competition from marsupial taxa at the time, expanded into new ecospace in Australia as early as the Cretaceous (Camens, 2010). This divergence between the platypus and echidna most likely occurred somewhere over 112.5 million years ago (Phillips et al. 2009). The olviparous (egg-laying) nature of their reproduction could have much to do with giving the monotremes an evolutionary advantage over the contemporary marsupials as well to more easily compete with the marsupials and allow them to fill said new ecospaces. In fact, this advantage can in part lead to the observed associated adaptive radiation of echidnas and expansion of the niche space. These observations together contradict the fairly common assumption of halted morphological and molecular evolution that continues to be associated with monotremes.

As to when exactly monotremes as a whole may have come about, things are still a bit hazy around that question. Unfortunately, monotremes have left a fairly poor fossil record. However the study of ancient monotreme fossils have already helped to identify, at the very least, when they may have come about. The first divergence between olviparous and viviparous mammals is believed to have occurred during the Triassic period (Rowe et al, 2008). However, there is still some disagreement on this estimated time of divergence. Though most findings from genetics studies (especially those concerning nuclear genes) are in agreement with the paleontological findings, some results from other techniques and sources, like mitochondrial DNA, are in slight disagreement with findings from fossils (Musser, 2003). Studies of mitochondrial DNA in platypuses have also found that monotremes and marsupials are most likely sister taxa. It also implies that any shared derived morphological traits between marsupials and placental mammals either occurred independently from one another or were lost in the lineage to monotremes (Janke, 1996).

There’s also evidence to show the possibility that echidnas may have a somewhat recent amphibious and/or water-foraging ancestor as well. Although the platypus is an actual semi aquatic mammal, the echidna too has many such water-suited anatomical and physiological traits such as: as aqua dynamic streamlining, dorsally projecting hind limbs acting as rudders, and locomotion founded on hypertrophied humeral long-axis rotation, which provides a very efficient swimming stroke. The echidna has these traits that give it an almost unnecessary advantage in the water and they must have been derived from some aquatic ancestor. This ancestor is most likely one that the echidna and platypus shared before the species’ divergence into the later monotremes. Many studies have been done of the fossils of the oldest known monotreme, Teinolophos trusleri, an ancient species of platypus. From the findings, it has been hypothesized that it is in fact the basal, crown species of modern monotremes. It is very likely the same species that would eventually diverge into modern platypuses and echidnas. The semi-aquatic traits and shared aquatic ancestor with platypuses helps to support the idea of an even older, possibly fully aquatic or amphibious ancestor.

A common hypothesis of the possible origins of monotremes is the possibility that they came from birds in some way. A genetic study by Retief et al. that sequenced the DNA of echidnas and platypuses and compared their protein sequences to those of many other mammals and birds was performed. It was hypothesized that the original mammals, or prototheria, may have emerged from a line originating from birds and reptiles. Before even the divergence of ancient mammals into monotreme and therian mammals, the protein sequencing of monotremes indicates that they have a close relatedness to birds and reptiles before them. Their many computer-generated phylogenetic trees all seemed to be in agreement of this as well as the time of the platypus-echidna divergence (1993). Another study found that some of the sex chromosomes of monotremes even have homology with the Z sex chromosomes of birds. Gene mapping showed that they even have bird autosome regions in their genetic makeup (Willem, 2007). This extensive genetic research into the origins of monotremes helps to further prove that they more than likely came from birds. This is given by their similar protein sequencing and homology between their many sex chromosomes, and to even reptiles and possibly amphibians by extension.

Though the exact origins of echidnas are still a bit unclear, and different studies yield slightly different time periods of their possible basal, evolutionary divergences, a few things seem to be clear. Long before the prototherian divergence into monotremes and therian mammals, monotremes seemed to more or less follow a very similar evolutionary path as that of the therians. They more than likely came from reptiles and birds however at some point before the monotreme-therian divergence. An amphibious or possibly waterfowl ancestor of some kind definitely had to be present though. From even the earliest known monotreme species, every monotreme species since, both platypus and echidna, have displayed an innate affinity for the water. Though the platypus in particular is more commonly found in the water, it is undeniable that echidnas too have the same phynotipic traits that adapt them for the water as well. Fossil records have shown these traits to always be present in monotremes as far back as we could study them. Genetic data has also shown that the monotremes are more closely related to birds, and by extension reptiles, than the therian mammals. Their similar protein sequencing and homology between their different sex chromosomes add up to show a strong connection between them. It’s this strong connection to birds and reptiles, stronger than that of any other mammal clade, which could very possibly be responsible for the monotremes’ egg-laying properties. As for the echidna’s shared traits with some therian mammals, like the spines of a porcupine and the long, anteater-like snout in some species of echidnas, there’s one explanation for those. All of the evidence points to monotremes almost undeniably diverging from mammals before those species, or at least their contemporary versions, even existed. Again, the only explanation coming to mind for echidnas having those traits then is that they evolved them to fill niches in their ecosystems. Both the anteater-like snout and the shared myrmecophagic diet were most likely developed out of necessity rather than any divergence from an anteater species. Like the porcupine’s spines, most likely born out of a need on the echidna’s part for some kind of defense since that is how it has been observed to use them. The study of these animals is very difficult, not only because of their poor fossil records but because of the fact that they are only found in the relatively small and isolated ecosystems of Australia and New Guinea. Not to mention how old the species is. The low migration rate, amount of time that the species has existed for, and relatively large population sizes in their singular ecosystems have done nothing but to potentially increase the possible genetic diversities in each separate population. The founder effect is not very relevant due to the almost nonexistent migration of echidnas. They’ve also had millions of years more than many mammals, with little phenotypic change, to develop many mutations among themselves and their large population sizes ensure drift isn’t very significant either. All of these factors combine for pretty significant genetic diversity among echidnas. So not only are they hard to study from a paleontological side because of a lack of sufficient fossils but also from a genetic side because of their genetic diversity. In a sense, the echidna’s description of being a living fossil of sorts is somewhat accurate. One thing is without a doubt certain though and that is that their name is very fitting. The Echidna in Greek mythology was a half-woman, half-snake monster known as the mother of all monsters whom gave birth to many other infamous monsters. Though the echidna today is not so much a common ancestor for so many other species as the name might imply, it too certainly looks to be an amalgamation of many of the Earth’s creatures. Phenotypically resembling some mix of hedgehog, anteater, porcupine, otter, and platypus and genotypically being very closely related to birds and even reptiles, it’s easy to see how at first glance it might be perceived as some kind of mother, or at least the progeny of, so many varied organisms.

References

Camens, A. B. 2010. Were Early Tertiary Monotremes Really All Aquatic? Inferring Paleobiology and Phylogeny from a Depauperate Fossil Record. Proc. of the Nat. Acad. of Sci. 107.4: E12.

Janke, A., Gemmell, N.J., Feldmaier-Fuchs, G., Haeseler, A., and Pääbo. S., 1996. The Mitochondrial Genome of a Monotreme—the Platypus (Ornithrohynchus Anatinus). Journ. of Molec. Evo. 42.2: 153-159.

Janke, A., Xiufeng, X., and Arnason. U., 1997. The Complete Mitochondrial Genome of the Wallaroo (Macropus Robustus) and the Phylogenetic Relationship among Monotremata, Marsupialia, and Eutheria. Proc. of the Nat. Acad. of Sci. 94.4: 1276-1281.

Musser, A.M., 2003. Review of the Monotreme Fossil Record and Comparison of Palaeontological and Molecular Data. Comp. Biochem. and Phys. Part A: Molec. & Integ. Phys. 136.4: 927-942.

Phillips, M. J., Bennett, T.H., and Lee, M.S.Y., 2009. Molecules, Morphology, and Ecology Indicate a Recent, Amphibious Ancestry for Echidnas. Proc. of the Nat. Acad. of Sci. 106.40: 17089-17094.

Retief, J.D., Winkfein, R.J, and Dixon, G.H., 1993. Evolution of the Monotremes. European J. of Biochem. 218: 457-461.

Rowe, T.,Rich, T.H., Vickers-Rich, P., Springer, M., and Woodburne, M.O., 2008. The Oldest Platypus and Its Bearing on Divergence Timing of the Platypus and Echidna Clades. Proc. of the Nat. Acad. of Sci.. 105.4: 1238-1242.

Willem, R., O'brien, P.C.M., Grutzner, F., Clarke, O., Graphodatskaya, D., Tsend-Ayush, E., Trifonov, V.A., Skelton, H., Wallis, M.C, Johnston, S., et. al. 2007. The Multiple Sex Chromosomes of Platypus and Echidna Are Not Completely Identical and Several Share Homology with the Avian Z. Gen. Bio. 8.11: R243-R243.21.