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Which part of a female mantises's DNA causes her to be a few times larger than a male mantis?

Do other species have that part of DNA?

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Please when you downvote explain why you do it, I see nothing specifically wrong with this question, sex differences in size are well known throughout the animal kingdom. –  nico Sep 1 '12 at 7:51
    
Are they really so much bigger? M. religiosa (75 vs. 60mm), T. sinensis (130 vs. 100mm), S. carolina (47-60 vs. 54mm) from english/german Wikipedia. As the numbers show this is a wrong statement, so I will downvote, too. –  rwst Sep 1 '12 at 8:26
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@rwst: 1) without reporting standard deviations those numbers are useless. Are they statistically different? 2) Sex differences in size/weight are a very well reported and have been studied for decades. I am no expert in insects but definitely for mammals it depends on the fact that the patterns of GH secretion are sexually dimorphic and result in different IGF-1 production by the liver. –  nico Sep 1 '12 at 9:12
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@rwst: by the way, even if we don't care about SD (which is wrong) 75 vs 60 is a 25% increase which I would consider very relevant. –  nico Sep 1 '12 at 9:15
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1 Answer

up vote 7 down vote accepted

Insects and spiders have tremendous sexual dimorphism, with males often being much smaller than females. They are pretty much just sperm carriers and sometimes do not eat. Insects may have two or one sex chromosome, where males my have only one chromosome. As is pointed out in the comments, not all mantis' species display this dimorphism.

Since such dimorphism is probably due to small changes in the genome due to environmental selection pressures and the genetic mechanisms of control are probably not simple.

Its difficult to say which genes are responsible for size per-se. Recent studies of human height indicate that scores of genes may be involved in human size and insects have at least as many genes as humans do; it is pretty hard to look at a human genome sequence and say what height that person is without some other help. I imagine for specific insect species this too would be difficult.

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+1: however, as I was saying in the comments, in mammals the sexual dimorphism of the somatotroph axis is probably the main driver of sexual dimorphism in terms of size/weight. –  nico Sep 2 '12 at 7:17
    
@nico interesting... would love to see a reference - this is new to me :) –  shigeta Sep 2 '12 at 22:26
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Any [neuro]endocrinology book should do. The literature about GH/IGF-1 is immense and obviously many substances are involved, such as steroid hormones (like testosterone). I guess the seminal paper to look at would be: ncbi.nlm.nih.gov/pubmed/2861084 Subsequent papers have investigated the story more in detail, see for instance studies like: ncbi.nlm.nih.gov/pubmed/7768925 and ncbi.nlm.nih.gov/pubmed/9207075 (and references within) –  nico Sep 3 '12 at 6:21
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From the abstract of the Jannson paper: "The results suggest that high, infrequent GH pulses with low plasma GH levels in between (i.e. a masculine plasma GH pattern) promotes growth more effectively than an intermediate, rather constant level of plasma GH (i.e. a feminine plasma GH pattern). Since male sex steroids masculinize the secretory pattern of GH and have only minor growth-promoting effects in hypophysectomized animals it appears that the growth promoting effect of androgens is indirect and is due to an altered secretory pattern of GH." –  nico Sep 3 '12 at 6:22
    
nice reference! I see that there is some possibility that insects have an IGF gene as well. In any event, the same methods could uncover an insect's sexual growth pattern... –  shigeta Sep 4 '12 at 4:50
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