From: bivalve (bivalve@mail.davidson.alumlink.com)
Date: Sat Jul 19 2003 - 13:31:44 EDT
> The claim isn't that there aren't any nocturnal animals, just fewer of them than the day-jobbers. I would be interested in any contrary data to Parker's claim.<
Birds are the only major group that I know are principally diurnal. The majority of mammals are nocturnal. I don't know relative numbers for all insects, but certainly the primarily nocturnal moths far outnumber the primarily diurnal butterflies. The insect diversity around the porch light at night seems to exceed the diversity at flowers during the day. I believe most marine invertebrates that show a preference are more active at night. This is much of the appeal of night diving and night shell collecting. Likewise, there is the abundant plankton that forms the scattering layers, hanging out in deep water with little light during the day and coming shallow at night. I think the nocturnal species probably outnumber the diurnal ones, though a lot would depend on whether beetles show an inordinate fondness for one or the other. Being diurnal ourselves, we detect and observe the diurnal ones much more easily.
Ironically, this may acually support his main thesis, in that an advantage of being nocturnal is to hide from visual predators or visually wary prey. On land, it may also help avoid dessication or overheating.
>>This depends very strongly on the choice of taxon and the
>>sampling. Deep sea diversity appears to be quite high for many groups.
>Which ones? I would prefer specifics than generalities. If Parker's suggestion is wrong, I would like data to put it in the grave, not generalities.<
Polychaetes, holothurians, various mollusk groups (aplacophorans, protobranchs, septibranchs, turrids, etc.), and various crustaceans are among the most diverse in the deep sea. In fact, petroleum exploration has a major role in motivating much of the detailed surveys of deep-sea faunas and the resulting suggestions that they are extremely diverse. The Minerals Management Service has some publications; I have had no success getting to their website to download the information but was able to get some of their stuff mailed. Blake and Grassle are a couple of the authors to keep an eye out for. I can look up some exact reference titles if this does not give enough of a direction. If BP had funded multiple postdoc positions instead of just two, I might have been specifically studying this and could have given a more detailed answer offhand. As is, I can tell you all about freshwater mussels of the US instead.
>But are they recent imigrants to that area?
There seems to be a fairly continuous exchange between deep and shallow water in the fossil record. Some currently deep-sea species are actually opportunists, survivors but poor competitors, who occasionally turn up shallower in the fossil record. We do not have as good information about the deep-sea fossil record as for shallow water, so there is a strong sampling bias. There are some claims of a pattern of evolutionary innovation often proceeding from onshore to offshore, but I don't know how strong the evidence is.
At least some of the deepwater mollusk groups appear to be recent arrivals, whereas others appear to have diversified there for a long time (Mesozoic or Paleozoic origins).
Another complicating factor is that the modern deep sea is not entirely dark. There is some light due to bioluminescence and some organisms are able to detect infrared radiation from hydrothermal vents.
In aquatic habitats, touch-like senses can detect motion at a distance as well (e.g., a fish lateral line), so the lack of vision is not necessarily equal to dectection by bumping.
In summary, the development of good eyes around the beginning of the Cambrian probably played some role in promoting the metazoan radiation, but I doubt it was the only factor and I am doubtful about some of the proposed supporting details.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487-0345 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
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