[Learn Something New...] Small Males

[Aeries]

So I was studying for my endocrinology exam, and came across something pretty interesting.
Full Article: http://people.oregonstate.edu/~mason...5smallmale.pdf

Small male body size in garter snake depends on testes
D. Crews, M. A. Diamond, J. Whittier and R. Mason

In the red-sided garter snake (Thamnophis sirtalis parietalis) adult females are larger than adult males; this difference is apparent within 3 wk of birth, a time coinciding with high circulating levels of androgens. To study the ontogeny and regulation of this sexual dimorphism, male neonates were either castrated, castrated and given Silastic capsules containing testosterone or estradiol, or given a sham operation at 8, 9, or 10 wk of age. Female neonates were either given a Silastic capsule containing testosterone or dihydrotestosterone or given a sham operation at 8, 9, 10, or 14 wk of age. The sex difference in body size and growth rate in neonates was abolished by castration; the pattern of growth of castrated males was similar to sham-operated females. Androgens in the amounts administered failed to reverse the effects of castration, because castrated male and female neonates receiving exogenous androgens grew at the same rate as did sham-operated females. Males castrated as adults grow larger than adult males given a sham operation, indicating the inhibitory role of the testes on body size exists after sexual maturity. Treatment of adult males with testosterone, however, prevented the increase in body size after castration, suggesting that the mechanism regulating weight gain in the garter snake depends on gonadal androgen.

Personally I think this is uber cool. It makes total sense that body size is regulated by hormones, but the really neat part is that androgens appear to be supressing the male's body size throughout its whole life, its not just an organization effect as a neonate.
I'm interested in seeing how relevent this is in other species of snakes were the females are larger in size. Garter snakes are oddballs when it comes to hormone function, so I'm not sure whether this finding would be generalizable.

[rabernet]

That is very interesting! Thanks for sharing!

[Vypyrz]

If I am reading this correctly, it is saying that castrated males got larger due to lack of testosterone. This makes sense if you look at other species. Neutered cats and dogs generally will show more weight gain as well as human eunuchs. This may be caused by an increase in body weight and body fat caused by a lack of aggressiveness and increased dormancy due to lack of testosterone. The same effect can also be seen in middle aged males when the testosterone production slows...

[Aeries]

True enough, but in those species males are typically larger to begin with, where in garters females average three times heavier than their male counterparts. For the males to catch up to their weight in 8 weeks is pretty impressive.

-It would have been neat to see a measure of activity...did they gain so much weight because they became less active after castration?
-A measure of fat levels...is the added weight of the males a similar ratio to females, or are these obese?
-Additionally it would have been interesting to see a measure of energy effcientcy. Its theorized the females grow larger in size to be able to more suitable to carry greater quantity of offspring, but males can stay small because they don't need to be big, so why waste the energy?

[4theSNAKElady]

Very interesting! Thanks for posting!