Pattern evolution

[skinheaddave]

Okay, so I'm sick and ended up taking the day off work. Under the influence of a low-grade fever, I found myself pondering the patterns on tarantulas -- particularily those that repeat frequently across species that are only distantly related. In particular, two came to mind. The first is striping down the legs, as in A.seemanni and the second is thick banding as in the various "red knees" and A.geniculata etc.

So my question is why do you think the patterns have evolved? My first thought was that it was the same as with snakes, where banding and striping confuses predators as to the direction and speed of movement. Are there any other thoughts, though? Anyone know of any published speculations?

Cheers,
Dave

 

[Static_69]

The only thing I could think of is that the stripes and patterns on T's evolved to just better suit their life. We learned some stuff about Darwin's theories and stuff like that. Well if you think of his theory of natural selection, then tarantulas probably evolved to fit the "better adapted survive" category. The tarantulas probably evolved their different patterns for either better hunting abilities, better camoflauge, or maybe to just intimidate predators.
Then again there is the chance that the only reason they have their patterns is for mating.






Risto

 

[JacenBeers]

I have often pondered the same thing. I mainly wondered why a species like Cyclosternum fasciatum has such neat striping on their abdomen.

 

[skinheaddave]

Well, the bright ventral marking on soemthing like a Poecilatharia are likely evolved for something like scaring predators, as they work in well with the standard threat display.

As for their being adapted for mating, I am highly skeptical. Given that tarantulas aren't particularily visual creatures, it would not make sense for them to develop particular patternings for mate identificaiton or the likes. Things like the drumming and chemical cues are going to be vastly more important. On the other hand, some Ts show notable sexual dimorphism in their patterning which tends to be an indication that there is some adaptive significance for mating. Still, it may be that the adaptive advantage is not in mate recognition but in the more nomadic existance of a mature male.

Chamoflage/predator confusion still seems to me the best explanation. Of course knowing some other things would help, such as the patternings on prehistoric tarantulas. Is the OW/NW banding an example of parallel evolution or is it ancestral?

Cheers,
Dave

 

[JacenBeers]

I agree with you dave that tarantulas probably did not evolve their patterns for mating or for any other reason that involves idenification among other spiders. It has to be something to do with how other animals other than tarantulas would visualize the spiders because a tarantula cant really see the patterns on other spiders. I think camouflage and the confusion of predators are the two most likely answers.

 

[skinheaddave]

Originally posted by JacenBeers
I have often pondered the same thing. I mainly wondered why a species like Cyclosternum fasciatum has such neat striping on their abdomen.

That is another good one. Repeated in many, many species. Lost with age in some, retained in others. Once again, the intuitive explanation would be that it breaks up the outline and is used in chamoflage. That being said, intuition on such matters often proves itself wrong (such as the giraffe's long neck, which is now proving a good example of our overall ignorance as to the evolutionary significance of structures or behaviours).

Cheers,
Dave

 

[JacenBeers]

It is also strange how some tarantulas do not have any markings at all. Or just slight markings. Rosehairs for example. THey do not have very defined markings but they are often found in areas where the other species of tarantulas have very well defined markings. I wonder what environmental factors or other external factors would cause this difference.

 

[Mendi]

I've always thought that the C.fasciatum was using it's bright markings as a warning code to anything trying to eat them. Seems many species copy and use the warning colors of truly dangerously venomous creatures very successfully. As for Pokeys and Hetmacs, most of their markings have to do with camo, though they do have the warning colors on the underside of their legs. Their markings really do hide them on the bark of trees very well and the way they have the marking breaks up their body outline very well...

 

[caligulathegod]

Maybe they just be stylin'

 

[Vayu Son]

><

nice edit man

-V

 

[nemesis6sic6]

lol

Maybe they just be stylin'

lol s/he's pimp. is he pimpin' them girls/guys yet?
funny stuff. any ways have a nice day
geo

 

[spider]

Yeah funny pic. I bet that T is thinkin BLING BLING!
















later Spider,

 

[xBurntBytheSunx]

i don't put any stock in evolution...natural selection makes perfect sense though....

 

[Sean]

Originally posted by caligulathegod
Maybe they just be stylin'

LMFAO@the gold tooth i cracked up when i seen that

 

[Henry Kane]

Originally posted by Mendi
I've always thought that the C.fasciatum was using it's bright markings as a warning code to anything trying to eat them. Seems many species copy and use the warning colors of truly dangerously venomous creatures very successfully. As for Pokeys and Hetmacs, most of their markings have to do with camo, though they do have the warning colors on the underside of their legs. Their markings really do hide them on the bark of trees very well and the way they have the marking breaks up their body outline very well...

Yeah, the coloring/pattern of Poecilotheria makes pretty obvious sense. Camo on top, warning colors, where they will only be seen when it matters most.
Then you start to think about Chromatopelma cyanopubescens for instance, a bright orange, blue and green T that lives in the Venezuelan scrublands. In the bases of cacti no less.
Why is camo influential enough in the evolution of some species and seemingly not much of an importance in other species?

Atrax

 

[deifiler]

Evolution has probably also selected colours that work best in camoflauging the spiders in regards to the predators, and how they would possibly locate the spider.

Predators of each will have different eyes, see in different spectrums, different light sources etc... Not every eye works like the humans does. Perhaps the predators of a Cyaneo' have eyes that interpret the woniderous colours as a dull colour, or of little contrast to their surroundings

I'm not naming any examples of different predators and of their specific eyesight, as I don't know too much about it. We all know how say a bee's vision differs from that of a human or a cat's though.

Also colours benefit in other ways, with darker colours absorbing greater amounts of light etc, which is beneficial for cold blooded animals I guess. I doubt that's why the colouration sticks, but you get what I mean.

The hair and hair placement 'blurs' the outline of the spider though. Perhaps that's why certain species have different hair patterns, such as the hair on Lasiodora femurs and how it isn't present within the similar Genus Lasiodorides.

The standard weather and environmental conditions will play a part in the colouration too I should assume

Just some thoughts of mine:}

 

[Code Monkey]

Originally posted by Atrax
Why is camo influential enough in the evolution of some species and seemingly not much of an importance in other species?

Probably has to do with both pathways working but being mutually exclusive. You can adapt towards staying hidden and we get the numerous shades of brown to black that make up so many of the Ts out there, with things like the Pokies and H. maculata being some of the absolute best examples. OTOH, you can try the "I look dangerous" approach and get things like bright Brachypelma and some of the Avics and Psalmopoeus.

In other words, if your marking pattern *happens* to make some individuals less likely to be seen and eaten, over time better and better camouflaged variations of that initial pattern will be selected for. If your marking pattern happens to intimidate would-be predators such that some indivuals are more likely to just be passed up, over time more and more "frightening" variants will be selected for.

I can't think of any T species that is both conspicuous in its normal environment and lacking in typical warning colors.

 

[Henry Kane]

So it's not a matter of evolving to be invisible. More like evolving to not be preyed upon. That makes pretty good sense to me. Camo works for obvious reasons but I can see how the opposite would be effective as well.

ATrax