[Pollinator] [beemonitoring] Hummingbird "sweet genes"

[Peter Bernhardt]

Dear Lisa:

That's very interesting.  There's also a question of digestion.  I do
remember some publications about 20 years ago about the ability of birds to
digest sucrose.  Apparently, many passerines like the enzyme sucrase. Their
systems can't split the molecule and they either derive no energy or it's a
dangerous feed for them.  That's why you are not supposed to give a pet
canary a sugar lump.  This is also supposed to explain why so many small
berries are hexose rich and low in sucrose.  More important for us, nectar
analyses of flowers pollinated by orioles, honeyeaters, sunbirds etc. were
hexose rich or dominant.  In contrast, most hummingbird nectars are sucrose
rich/dominant.  I wish I could remember the authors of these articles but
someone in our group should know.

Peter


On Sun, Aug 24, 2014 at 11:45 AM, Lisa Horth <lisahorth at gmail.com> wrote:

> Peter,
>
> I think your point is an interesting one.
>
> The NewScientist blurb says T1R2 was lost from birds (but retained in
> lizards).
>
> Now, hummers were just found to use T1R1 for tasting sweet (instead of
>  tasting 'savory' with it, like other vertebrates).
>
> Liberies is quoted as saying "The re-evolution of sugar receptors may have
> happened multiple times". So, I'd expect that the authors of the Science
> paper would agree with you and will very likely search other (sugar eating)
> bird species for a functional T1Rs (especially T1R1s since part of their
> cool find is that it has been co-opted for a new function: sweet detection
> not savory detection).
>
> The loss and regain (or shift in use) of sensory receptor function is cool
> and occurs in vomeronasal and visual receptors, too. For example, deep sea
> coelacanths have functional 'visual receptors' (opsins) that have evolved
> to only a tiny range of light that is visible in deep sea water. They have
> lost some receptors entirely, like the T1R2 was lost from birds.
> Shallow-water, sexually selecting guppies however, have a large number of
> visual color receptors, explaining how the females see all those dramatic
> tail colors.
>
> Similarly, butterflies have more opsins than bees do, but that might not
> be news to this list........
>
> Lisa
>
>
>
>
>
> On Fri, Aug 22, 2014 at 11:43 AM, Peter Bernhardt bernhap2 at slu.edu
> [beemonitoring] <beemonitoring-noreply at yahoogroups.com> wrote:
>
>>
>>
>> The following link will take you to a popular article on the evolution
>> and genetics of taste buds on a hummingbird's tongue.  The article insists
>> that most birds have lost the ability to taste the sweetness in foods.  I'm
>> not so sure I agree.  What about all those fruit eating species in so many
>> families as well as nectar drinking birds in the Meliphagidae,
>> Nectarinidae, Zosteropidae etc.?
>>
>>
>> http://www.newscientist.com/article/dn26089-hummingbirds-turned-savoury-into-sweet-to-taste-nectar.html#.U_diqFb5gTs
>>
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>
>
>
> --
> Lisa Horth, PhD
> Haupt Fellow
> Smithsonian Gardens
> Washington DC
> (202) 633-5849
>          &
> Associate Professor
> Dept of Biological Science
> Old Dominion University
> Norfolk, VA 23529
> lhorth at odu.edu
>
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