A Question For The Lone Ranger

[Angakuk]

You are all wrong. It is a Pretzel Snake.

[LadyShea]

Originally Posted by The Lone Ranger

Alabama has indeed been the site of some spectacular fossil finds, including Basilosaurus, an early whale ancestor.

Unfortunately, most of the Cretaceous sites in Alabama are in the central and northwestern parts of the state, and most of them are pretty well-buried. They tend to be exposed during road-building excavations and whatnot. As such, there aren't too many Cretaceous-era sites in Alabama that are readily accessible to the general public.

Yeah I figured not much down here in the delta, but I can take weekenders up North

I'm a little reluctant to recommend museums, since I've never visited any, except in the Tuscaloosa area. (The Alabama Museum of Natural History in Tuscaloosa has some very nice exhibits, including a really nice Basilosaurus display.)

Okay cool, I am glad it is worth a trip. I looked and we can camp and hike at Chickasaw SP, then go on into Tuscaloosa for a day at the museum. It would be a fun short getaway.

The Alabama Paleontological Society, would be a good group to contact, I should think. Not only would they be able to give you information about good museums, they occasionally sponsor fossil-hunting day trips. Most of the accessible fossil sites in the Gulf region are going to be more recent than the Cretaceous, however.

Which would be fine. Kiddo started his fossil collection with a Trilobite he purchased...if he could find any kind of fossil he would be thrilled.

If you think it might be fun to go looking for fossils on your own, the Geological Survey of Alabama has published reports that include information about Alabama fossil sites. They're available through the GSA's Publications Sales Office, which can be contacted at (205) 247-3636.

Awesome, thank you

Along with the Alabama Paleontological Society, the Birmingham Paleontological Society frequently conducts fossil-collecting field trips. I'm sure they welcome enthusiastic amateurs. The Alabama Museum of Natural History occasionally leads fossil-hunting expeditions too.

Very cool again

Thanks so much!

[Listener]

A new question ...

This is a response I put together for a poultry forum. There was a question about whether the sex of a chick could be affected by incubation temperature.

It's true that the sex ratio is affected by incubation temperature in reptiles but in birds there's no effect.

In mammals, a female's sex chromosomes are both the "x" variety and an individual is known as "xx". Males are "xy" which means that I have the same "y" chromosome as my father - and so back with my male ancestors (till you get to a "mutation" or unexpected change).

Birds used to be thought to be the other way round - males "xx" and females "xy" but now it's realised that we are dealing with a different system and males are called "zz" and females "wz".

In mammals, a sperm can be either x or y. If an "x" sperm fertilizes the ovum then the offspring is female, if a "y" sperm then the offspring is male.

In birds, sperm can not be either w or z. All sperm are z. Now the sex of any offspring is dependent on the egg which can be a "w" egg - giving rise to female offspring or a "z" egg giving rise to male offspring.

The incubation temperature makes no difference whatever.

My question is about "primitive" mammals. Are marsupials and monotremes the same in this respect as placental mammals?

If they are the same, what is the modern thinking about their ancestors and sex chromosomes?

[The Lone Ranger]

The amniotes are the reptiles and their descendants (birds and mammals). There's quite a lot of variability in how sex is determined amongst the amniotes. That's actually a subject of considerable interest nowadays, since studies of the genetics of sex determination help reveal evolutionary relationships between the amniotes.


First, it's by no means the case that all reptiles have temperature-dependent sex determination. It's true of many crocodilians, some turtles and some lizards, but in all snake species, apparently, sex is genetically determined.

The genetic evidence suggests that sex was determined by incubation temperature in the earliest amniotes, but that at several different times, genetic mutations occurred which caused a switch to genetic sex determination in several different lineages.


Birds and snakes share the ZZ:ZW sex-determination system, but birds are archosaurs and snakes are lepidosaurs. Birds' closest living relatives (also archosaurs, of course) are the crocodilians. But in crocodilians, sex is generally temperature dependent, not genetically determined. And many lizards (the closest living relatives of snakes) also have temperature-dependent sex determination.

One possible explanation for this is that the ZZ:ZW sex-determination system evolved quite some time ago, and that subsequent back-mutations led to some lepidosaurs and many crocodilians reverting to temperature-dependent sex determination. This doesn't seem likely, however. The most recent genetic analyses strongly suggest that the ZZ:ZW sex-determination system evolved independently in archosaurs and lepidosaurs. (The sex-determining genes are on different chromosomes in birds and snakes, and so this must surely be a case of independent evolution of similar traits.)


The sex-determining genes in birds apparently evolved after the split between the avian and crocodilian lineages of the archosaurs. That raises an interesting question: since it's almost certainly the case that birds are the direct descendants of theropod dinosaurs, did some or perhaps even all of the dinosaurs use the ZZ:ZW sex-determination system, just as do modern birds? Unfortunately, there's no real way to say.




All mammals use some variation of the XY sex-determination system, but there are some considerable differences. This means that there has been considerable evolution of the sex-determining genes even after the split between the three main mammal lineages.

In monotremes (or at least in the platypus, in which this has been studied), there are 5 different sex chromosomes. In fact, sex determination in monotremes is, in some ways, more similar to sex determination in birds than it is in other mammals. This is apparently completely coincidental, however.

The sex-determining chromosomes in a monotreme are -- somehow -- linked, and so a male monotreme inherits 5 "X" chromosomes and 5 "Y" chromosomes. A female monotreme, of course, inherits 10 "X" chromosomes (5 from each parent).


In marsupials, there is only a single XY chromosome pair, just as in eutherian (placental) mammals. The "Y" chromosome of a marsupial is even smaller and less-functional than is the "Y" chromosome of a eutherian mammal, however. (That is, even more of its function has been transferred to the "X" chromosome.) So while sex determination in marsupials is essentially the same as in eutherian mammals, the "X" chromosome plays a much larger role in the formation of male sexual organs than it does in eutherian mammals.


All of this indicates that genetic sex-determination evolved independently in several different amniote lineages. And what's more, even after a particular sex-determination system evolved, the chromosomes responsible have continued to evolve to a surprising degree.



Cheers,

Michael

[Listener]

Thanks TLR - very interesting and informative. I thought you would know more than I could find out.

I can still edit my poultry post so I'll pop a "some" in front of the word reptiles (and fix my spelling).

[Ensign Steve]

One of my facebook friends is hatching 32 baby chickens in her incubator today.

Yesterday she said they [the eggs] were wiggling and peeping.

Today they are hatching all at once, one right after the next.

What makes them all hatch at the same time? Do they always incubate for exactly the same period of time, down to the hour? Or can they hear their fellows peeping outside of their shells and get motivated to join them? Or what?

[JoeP]

I'll wager the eggs were not all laid at the same time, so there must be a mechanism for the pre-hatchlings to synchronise hatching. Hatching is probably a hazardous time in terms of predation and it would pay off for the mother hen to have them all hatch at once ... also, so that she doesn't have to sit on the unhatched eggs while feeding some of the chicks.

I'll further wager that TLR will post a longer, more accurate and more interesting reply.

[Ensign Steve]

Originally Posted by JoeP

I'll wager the eggs were not all laid at the same time

Good point!

[Adam]

Originally Posted by Corona688

whenever I try it's just incredibly awkward.

[The Lone Ranger]

Many reptiles and birds will take from several hours to several days to lay a full clutch of eggs. What happens next depends.

In several species (like many owl species, for instance), the parents begin incubating as soon as each egg is laid. Naturally then, the eggs don't hatch all at once. Accordingly, it's not unusual for there to be a great disparity in size between chicks within an owl's nest, since the oldest may have hatched more than a week before the youngest.

In many other species, the parents wait until the last egg is laid before they begin to incubate. Since the embryo doesn't begin to grow and develop until it's warm enough, this ensures that all of the eggs hatch at about the same time. What's more, in many bird (and crocodilian) species, the youngsters will peep (or grunt, in the case of crocodilians) inside their eggs when they're about ready to hatch. This appears to be a mechanism that allows them to communicate with each other and thus to synchronize their hatching.

In the case of crocodilians, the grunting also allows the mother to know that her eggs are about to hatch. One does not normally think of reptiles as being good parents, but female crocodilians are quite attentive parents, and will guard their eggs from all would-be attackers. They will guard the youngsters for some time after they're hatched, too. (First, Mama Crocodile/Alligator carefully takes her babies into her mouth and carries them down to the water. She then watches over them for a few weeks or so as they're learning to hunt.) The reason the mother must know when her eggs are about to hatch is that (since she's not an endotherm), she cannot incubate the eggs herself. So she buries her eggs in warm sand and/or a nest made of rotting vegetation. (The heat generated by decomposition warms the eggs.) She must know when her eggs are ready to hatch, so that she can dig them up. So she listens for the youngsters' grunting, and digs them up when she hears it.

Actually, there are a handful of bird species that bury their eggs and allow the heat given off by rotting vegetation to incubate them. That's pretty rare though. The Maleo bird (Macrocephalon maleo) of Indonesia has an even better trick: females lay their eggs in sandy volcanic soils and let the geothermal energy incubate their eggs.


Cheers,

Michael

[LadyShea]

Sea turtles tend to hatch in unison as well, and they are left alone. Do they alert each other through noises, or is it due to them being laid all at once?

[The Lone Ranger]

In most sea turtle species, since the eggs in a given nest are all laid at once, they tend to hatch at pretty-much the same time. But the youngsters do coordinate their emergence. It usually takes them 3 - 7 days to dig to the surface, and then they'll wait until nightfall and all emerge at once. (Presumably, this decreases their chances of being seen and captured by predators.)


Cheers,

Michael

[JoeP]

Originally Posted by The Lone Ranger

It usually takes them 3 - 7 days to dig to the surface

Days? How deep are they buried? Even allowing for smallness and weakness, that sounds like a long time.

[The Lone Ranger]

In most species, they seem to take their time in digging to the surface. This may help them to coordinate their emergence. (They're got enough yolk in their bellies that they won't need to eat for several days after they hatch.)

But it's not unusual for mother sea turtles to dig down as much as 3 feet (or more), and then to pack the sand down over the eggs. So it does take some time for the hatchlings to make their way to the surface through 2 - 3 feet of densely-packed sand. Even so, it seems that they don't rush the process.


Cheers,

Michael

[Listener]

I just try to make them all hatch on a Sunday afternoon for convenience

[wei yau]

Immortal Jellyfish

Just a quick question, TLR.

Just how screwed are we?

[Ensign Steve]

[The Lone Ranger]

It's worse than you think. They have no heads, so the standard decapitation trick for dealing with immortals won't work.


There can be only 1,000,000,000,000,000!

[JoeP]

Originally Posted by the article wei linked

How are we supposed to get rid of millions of an animal that doesn’t taste good?

I reject their plan, despite its evident logic:

Our only hope — I mean our only hope — is to genetically engineer a super race of hyperintelligent sharks who enjoy the taste of jellyfish. They should also have arms with opposable thumbs, in order to grip weapons for hunting the jellyfish. This plan could not possibly go wrong.

How else could we get rid of millions of an animal that doesn't taste good?

wei, you need to get a message out ...

[BrotherMan]

Originally Posted by JoeP

[Naru]

I have a question for TLR. In the lab I work in, we frequently use lipofection to transform kidney cells with plasmids. Once a plasmid is actually inside of a eukaryotic cell, how does it get into the nucleus? It seems like plasmids, though tiny relative to a chromosome, would be way too big to just pass through the nuclear envelope.

[The Lone Ranger]

The nuclear envelope that surrounds a eukaryote's nucleus has quite a few relatively large nuclear pores in it that are easily large-enough to allow even molecules the size of nucleic acids to move into and out of the nucleus.

In addition, specialized transport proteins (transportins) can bind to nucleic acids (normally mRNA) and help to move them out of (or into) the nucleus. Off the top of my head, I'd guess that the plasmids are bound by transportins and brought into the nucleus that way, through the nuclear pores.


Cheers,

Michael

[Dingfod]

What is this that supposedly washed up on a Florida beach?

[Naru]

Glaucus atlanticus - Wikipedia, the free encyclopedia

And they are awesome.

[erimir]

The wiki article says they can be more venomous than man-o'-wars (due to consuming them and storing the venom), so...

Holding one seems like it could be a bad idea. Unless it was raised in captivity without access to such venomous foods.