Bathing is somewhat about preventing parasites, its solvant be it water, dust or mud. Some species like using soap. I was thinking about plants, didn’t you? Yep, certain plants use soapy mucilages and are keen on bathing…
Evolution is often the road into solving basic issues of life. And life is organically complicated by the fact that, being not alone, species will evolve because of other species. Well, you might think it is yet again the “Nature, red in tooth and claw” picture (and indeed it still is, even if “green in wormy parasites” would capture it more acurately). Anyway, take the time to consider the fabulous adaptation of water calyces.
Calyx is a fairly general term of floral morphology describing sepals which are fused. A protective role is often acknowledge for this structure. Indeed, flowers are essential to the plant’s reproduction, and protecting them is directly increasing one’s fitness. Sepals may thus be ‘hairy’ (or producing trichomes in a botanically correct language, which is a good protection against aphids for example), develop into thick scales (the shield strategy), or…
… turn into a bath and retain water (alone or along with other chemicals), and let the flower immerged until it blooms. This latter situation is rare, but occurs occasionnally. A perfectly panglossian explanation for this curious characteristic would of course be that, since flowers strive for beauty, the water calyx is aimed at perfecting the final dressing.
Well, as naive as it is, such a panglossian explanation may not be completely devoid of interest as seems at first sight: a regular dressing is of importance to a flower, and whenever petals may go bad, attractiveness to pollinators decreases (and thus the odds of being fertilised). But the actual reason for the existence of water calyces is not about protecting beauty, but probably about protecting sexually organs directly. Indeed, a recent study* on Chrysothemis friedrichsthaliana (a member of the Gesneriaceae family), a species producing water calyces, demonstrated that the forced bath of developing flowers is a protection against its main floral herbivore, a moth laying its eggs in the corolla. Experimentally draining the calyx lead to a more than doubled infestation by the moth caterpillars, resulting in a complete absence of sexual structures (stigma and stamen) upon flowering. On the other hand, flower abortion did not differ between filled and drained calyces, indicating that water calyce is not an adaptation against dessication (the main competing hypothesis).
Developping flowers can be seen in bottom buds, deeply protected in their water calyx.
But I think it is now time I get a bath… :-)
* J. E. Carlson, and K. E. Harms (2007). The benefits of bathing buds: water calyces protect flowers from a microlepidopteran herbivore. Biology Letters 3: 405–407