Things that produce milk and aren't mammals

[jasonpatterson]

There was also an inverse relationship between the concentration of sodium and potassium ions in the milk and the concentration of lactose. Perhaps for osmotic reasons the aquatic mammals' milks must be higher in salt concentration. (Just guessing that whale blood is saltier than primate blood, on average, and milk and blood are always isosmotic for any given species.)

 

[shadron]

Fascinating. Wikipedia says that some Lepidoptera larvae eat Forsythia. Does that mean those species can (or prefer to?) digest lactose. I had been under the impression that mammals and certain bacteria were the only critters that were able to.

All it takes is the right enzyme (lactase). It's workable in mammals, then anything else can do it too, if they get the right mutations. Te probability may be low, but it can not be ruled out.

All humans (well, all normal humans have lactase production within their graps; it is active at birth, and is used to digest human milk, ampng other milks. The production machinery used to shut down during late childhood, and lactose intolerance sets in: without lactase, gut flora will metabolize it causing lots of gas production, the typical symptom of lactose intolerance. However, about 30,000 years ago when man started domesticating animals, this rather rich, alien source of fats and protein suddenly became available to all ages, and mutations that disabled the lactase turnoff became useful. As it stands now, roughly 30% of all humans can produce lactase throughout life, and these are concentrated in the herding populations of the world.

Lactose is a disaccharide, each molecule is a molecule of glucose bound to a molecule of galactose (just as sucrose (table sugar) is a similar disaccharide of glucose and fructose). Both are digestible by humans once they are separated, but only the glucose is available for fueling. Given that the possible number of sugars that the body can break down into glucose is considerable, I imagine the reason lactose works for mammals is that it was hit upon randomly very close to the point where reptiles and mammals parted ways and the mammary glands were being expressed, and has remained in that role since. There might be some other advantages, such as better shelf (!?!) life.

 

[jasonpatterson]

I wonder why this adaptation isn't more common. I believe some human males lactate, so it seems like the basic equipment for producing milk is close to existing in male mammals and yet almost no males of any mammal species routinely produce milk.

Even in this case, the article suggests that it might be hormones in the diets of the bats that make it possible.

Did lactation start out as female only?

Some animals would seem particularly well placed to benefit from male lactation. In the case of bats swapping infant feeding duties so that one parent could remain behind while the other one hunts might be a really good strategy. Especially fruit bats where hunting can be spread out throughout the night as opposed to insectivores where particular hunting times are much better than others.

It's hormone levels that control lactation, and in women, prolactin and oxytocin are produced during pregnancy and when the nipples are stimulated. There are some drugs (and brain tumors) that can cause males to release large amounts of prolactin, which causes milk production, when their nipples are stimulated regularly. Oxytocin, which causes milk to be released from the breast, is also released in gigantic amounts during labor. It's what causes labor to get going in the first place and also creates the instant bond between a mom and baby at birth following a natural delivery. It's also produced when the nipples are stimulated.

 

[Miss_Kitt]

...
Also, as someone else mentioned that among the mammals are the marsupials and the platypus, but I'd like to throw in the other, more often forgotten monotreme (egg laying mammal,) the echidna (spiny anteater.) Poor little critters, most people (outside of Australia/New Zealand) don't even know they exist... As I recall, these don't even have teats, their milk just sort of leaks out of a special patch on their skin. (Could be wrong about the last bit, I don't have time to research echidna lactation at the moment...)

I love echidnas! It is one of my personal life goals to see one, ideally waddling about in Oz and not in a zoo, but I haven't even found one in a zoo yet. They're so cool-looking! Whatta schnoz!!! I even have a fairly accurate stuffed animal echidna, thus proving that Miss_Kitt is very, very strange.

ETA -- Having read further through the thread, I would also like to add that the "let-down hormone" that causes a nursing mom's milk to actually flow is probably the best anti-depressant / good times chemical ever invented. Part of the bonding between mother and child, I am convinced, is that you're functionally stoned and staring at this little creature who is so tiny, so helpless, so cute and so uniquely yours. It would not surprise me if studies showed that the degree of bonding between breast-feeding moms and their offspring, at least early on, is higher than it is for those who use bottles. The baby is just as cute in either case, but you're not on the Let Down Train having a good ol' time watching the world's most beautiful child feed. This is only my unsupported opinion at this time, maybe I'll get a chance to look into it at a later date.

 

[shadron]

Evolutionarily, marsupials form a sort of intermediary between where we started akin to reptiles and where we wound up as full-blown mammals (and even perhaps where we're headed to, in the long run). Had it not been for the disappearing land bridge from Asia to Australia we would know of these forms only as fossils as the were out-competed by the newer mammals. We occasionally hear about marsupial forms which filled niches which are filled today by other mammals (such as predators, like Dasyuromorphia^WP, which includes the extinct Tasmanian Tiger, the Thylacine^WP). It is neat to witness evolution in action in this manner; here are the evolutionary predictions come true.

 

[a_unique_person]

Wow.

But how do you milk them?

I have heard it is good for your skin if you bathe in it.

 

[a_unique_person]

I love echidnas! It is one of my personal life goals to see one, ideally waddling about in Oz and not in a zoo, but I haven't even found one in a zoo yet. They're so cool-looking! Whatta schnoz!!! I even have a fairly accurate stuffed animal echidna, thus proving that Miss_Kitt is very, very strange.

I was amazed to see one wondering along a freeway a few weeks ago. They aren't very common around the suburbs.

 

[Delvo]

Evolutionarily, marsupials form a sort of intermediary between where we started akin to reptiles and where we wound up as full-blown mammals

In what way? Both groups originated at roughly the same time, coexisted for a long time before one went extinct in one place and the other went extinct in other places, and have all of the basic mammalian traits I can name offhand (live birth, hair, various kinds of teeth in the same mouth, upright stance, higher metabolism than ectotherms, milk, mammalian retinal pigment set, mammalian inner ears with those little bones in them, XX/XY sex determination, mammalian skin glands). The only thing I can think of that's even close to intermediate is their metabolism and body heat regulation being somewhat lower than ours. In at least some ways, they're even more developed/derived than we are, such as not only having an open pouch, but also burying their mammary glands inside it.

Might your impressions of marsupials and monotremes have gotten mixed? With monotremes, I can definitely name intermediate or even seemingly reptilian traits: eggs, a more splayed-out stance in at least the platypus, mammary glands that are more similar to sweat glands than ours are, an even lower metabolism than marsupials' (although still higher than reptiles', and possibly having been higher in the past), sex determination not by the XX/XY system... they're even the only mammals to produce venom, possess an electrical sense like sharks, and lack REM sleep.

 

[ImaginalDisc]

There was also an inverse relationship between the concentration of sodium and potassium ions in the milk and the concentration of lactose. Perhaps for osmotic reasons the aquatic mammals' milks must be higher in salt concentration. (Just guessing that whale blood is saltier than primate blood, on average, and milk and blood are always isosmotic for any given species.)

The only marine mammal with saltier blood than you or I would be a very sick or dead one.

Osmoregulation in marine mammals is pretty crazy. For one thing, they mostly rely on water created as a product of their metabolisms, and don't drink.

 

[jasonpatterson]

In what way? Both groups originated at roughly the same time, coexisted for a long time before one went extinct in one place and the other went extinct in other places, and have all of the basic mammalian traits I can name offhand (live birth, hair, various kinds of teeth in the same mouth, upright stance, higher metabolism than ectotherms, milk, mammalian retinal pigment set, mammalian inner ears with those little bones in them, XX/XY sex determination, mammalian skin glands). The only thing I can think of that's even close to intermediate is their metabolism and body heat regulation being somewhat lower than ours. In at least some ways, they're even more developed/derived than we are, such as not only having an open pouch, but also burying their mammary glands inside it.

Might your impressions of marsupials and monotremes have gotten mixed? With monotremes, I can definitely name intermediate or even seemingly reptilian traits: eggs, a more splayed-out stance in at least the platypus, mammary glands that are more similar to sweat glands than ours are, an even lower metabolism than marsupials' (although still higher than reptiles', and possibly having been higher in the past), sex determination not by the XX/XY system... they're even the only mammals to produce venom, possess an electrical sense like sharks, and lack REM sleep.

There seems to be a general misunderstanding about the order of the three groups of surviving mammals. A great many people are under the impression that marsupials evolved from monotremes and that placentals evolved from the marsupials. It's also important to realize that the monotremes didn't just stop evolving once the marsupials and placentals arrived. The two that remain are highly specialized creatures that are well adapted to their environment.

As regards the similarities you mentioned, I agree with their intermediate status as regards eggs, sex determination (which is by a related 5 chromosome system, at least in the platypus) and their milk production method, and I'll defer via ignorance on the metabolism, but much of the rest of the things you list aren't quite right.

The stance: We only have two examples of monotremes, one is extremely thoroughly adapted for life in the water, the other appears to walk just like a porcupine or hedgehog to me. Though you did make it clear that you were only referring to the platypus, a generalization about their gait from a total of two examples seems a bit much to me. I will admit that I didn't research their anatomy to find whether there were significant differences in how their hips and or shoulders were articulated.

Electrical sense: The platypus electrolocation ability has nothing to do with shark's ability to sense the electrical fields of prey. It's convergent evolution.

REM sleep: Both monotremes, and many reptiles, exhibit REM sleep.

Venom: Some shrews, the slow lorises, and the Cuban solenodon (a primitive placental) also have venom.

 

[arthwollipot]

I was amazed to see one wondering along a freeway a few weeks ago. They aren't very common around the suburbs.

We've got a couple that live on our property. We see them only occasinally. They're pretty shy.

 

[plumjam]

About half the people on our street are convinced our milkman isn't a mammal.

 

[neutrino_cannon]

There seems to be a general misunderstanding about the order of the three groups of surviving mammals. A great many people are under the impression that marsupials evolved from monotremes and that placentals evolved from the marsupials. It's also important to realize that the monotremes didn't just stop evolving once the marsupials and placentals arrived. The two that remain are highly specialized creatures that are well adapted to their environment.

Preach it brother! All living animals share a common ancestor, and are therefore equally evolved. "Living fossil" is a stupid term and should be summarily abolished.

[qupte]As regards the similarities you mentioned, I agree with their intermediate status as regards eggs, sex determination (which is by a related 5 chromosome system, at least in the platypus) and their milk production method, and I'll defer via ignorance on the metabolism, but much of the rest of the things you list aren't quite right.[/quote]

IIRC monotremes and marsupials both have slower metabolisms than eutherians.

The stance: We only have two examples of monotremes, one is extremely thoroughly adapted for life in the water, the other appears to walk just like a porcupine or hedgehog to me. Though you did make it clear that you were only referring to the platypus, a generalization about their gait from a total of two examples seems a bit much to me. I will admit that I didn't research their anatomy to find whether there were significant differences in how their hips and or shoulders were articulated.

Multituberculate mammals also had a sprawling stance. I think it's actually basal for mammals.

Electrical sense: The platypus electrolocation ability has nothing to do with shark's ability to sense the electrical fields of prey. It's convergent evolution.

A novelty for sure.

Venom: Some shrews, the slow lorises, and the Cuban solenodon (a primitive placental) also have venom.

Monotremes have venom glands in their feet though (though the ones in echidnas are non-functional and vestigal). That's something rather different, no? A couple of fossil mammals or non-crown mammaliformes (can't remember) have venom spurs, so they may be basal for mammals proper.

 

[Professor Yaffle]

I think monotremes also have a different sex determination system to the rest of mammals.

ETA:

In therian mammals (placentals and marsupials), sex is determined by an XX female: XY male system, in which a gene (SRY) on the Y affects male determination. There is no equivalent in other amniotes, although some taxa (notably birds and snakes) have differentiated sex chromosomes. Birds have a ZW female: ZZ male system with no homology with mammal sex chromosomes, in which dosage of a Z-borne gene (possibly DMRT1) affects male determination. As the most basal mammal group, the egg-laying monotremes are ideal for determining how the therian XY system evolved. The platypus has an extraordinary sex chromosome complex, in which five X and five Y chromosomes pair in a translocation chain of alternating X and Y chromosomes. We used physical mapping to identify genes on the pairing regions between adjacent X and Y chromosomes. Most significantly, comparative mapping shows that, contrary to earlier reports, there is no homology between the platypus and therian X chromosomes. Orthologs of genes in the conserved region of the human X (including SOX3, the gene from which SRY evolved) all map to platypus chromosome 6, which therefore represents the ancestral autosome from which the therian X and Y pair derived. Rather, the platypus X chromosomes have substantial homology with the bird Z chromosome (including DMRT1) and to segments syntenic with this region in the human genome. Thus, platypus sex chromosomes have strong homology with bird, but not to therian sex chromosomes, implying that the therian X and Y chromosomes (and the SRY gene) evolved from an autosomal pair after the divergence of monotremes only 166 million years ago. Therefore, the therian X and Y are more than 145 million years younger than previously thought.​

http://genome.cshlp.org/content/18/6/965.full.pdf
​

Everyone knows that the duck-billed platypus is pretty strange. But it seems this mammal's eccentricities extend beyond its famous bill, and habit of laying eggs, to the way its genes determine sex.
Not content with one pair of sex chromosomes, the platypus (Ornithorhynchus anatinus) has five. This is the largest number found in mammals so far, and also hints that the sex determination systems of birds and mammals may be linked.

http://www.bioedonline.org/news/news.cfm?art=1318

 

[jasonpatterson]

I was unaware of the existence of fossil foot spurs, thanks for the info. To be fair though, that wasn't his statement, Delvo just said that they were the only mammals with poison. (There are also several fossilized mammalian teeth with what appear to be poison grooves as well.)

 

[neutrino_cannon]

I was unaware of the existence of fossil foot spurs, thanks for the info. To be fair though, that wasn't his statement, Delvo just said that they were the only mammals with poison. (There are also several fossilized mammalian teeth with what appear to be poison grooves as well.)

MM, I tend to respond in a rather haphazard manner. And I was likewise unaware that slow lorises are poisonous. I had not heard about the grooved teeth in poisonous fossil mammals, but I'm not that surprised. Venom seems to be fairly widespread in insectivores.

And of course, who can forget when it was thought that there were no poisonous birds?