Posted by OneGlove(Part2) [OneGlove] on November 26, 1999 at 09:09:30 {2lTH7z2znE4DjahjRee6VOGhhkwG5g}:
In Reply to: **WOW! posted by OneGlove on November 26, 1999 at 09:04:31:
(Part 2 of 2)
5.6 Flour Beetles (Tribolium castaneum) Halliburton and Gall (1981) established a population of
flour beetles collected in Davis, California. In each generation they selected the 8 lightest and the 8
heaviest pupae of each sex. When these 32 beetles had emerged, they were placed together and
allowed to mate for 24 hours. Eggs were collected for 48 hours. The pupae that developed from
these eggs were weighed at 19 days. This was repeated for 15 generations. The results of mate
choice tests between heavy and light beetles was compared to tests among control lines derived
from randomly chosen pupae. Positive assortative mating on the basis of size was found in 2 out of 4
experimental lines.
5.7 Speciation in a Lab Rat Worm, Nereis acuminata In 1964 five or six individuals of the
polychaete worm, Nereis acuminata, were collected in Long Beach Harbor, California. These were
allowed to grow into a population of thousands of individuals. Four pairs from this population were
transferred to the Woods Hole Oceanographic Institute. For over 20 years these worms were used
as test organisms in environmental toxicology. From 1986 to 1991 the Long Beach area was
searched for populations of the worm. Two populations, P1 and P2, were found. Weinberg, et al.
(1992) performed tests on these two populations and the Woods Hole population (WH) for both
postmating and premating isolation. To test for postmating isolation, they looked at whether broods
from crosses were successfully reared. The results below give the percentage of successful rearings
for each group of crosses.
WH X WH - 75%
P1 X P1 - 95%
P2 X P2 - 80%
P1 X P2 - 77%
WH X P1 - 0%
WH X P2 - 0%
They also found statistically significant premating isolation between the WH population and the field
populations. Finally, the Woods Hole population showed slightly different karyotypes from the field
populations.
5.8 Speciation Through Cytoplasmic Incompatability Resulting from the Presence of a
Parasite or Symbiont In some species the presence of intracellular bacterial parasites (or
symbionts) is associated with postmating isolation. This results from a cytoplasmic incompatability
between gametes from strains that have the parasite (or symbiont) and stains that don't. An example
of this is seen in the mosquito Culex pipiens (Yen and Barr 1971). Compared to within strain
matings, matings between strains from different geographic regions may may have any of three
results: These matings may produce a normal number of offspring, they may produce a reduced
number of offspring or they may produce no offspring. Reciprocal crosses may give the same or
different results. In an incompatible cross, the egg and sperm nuclei fail to unite during fertilization.
The egg dies during embryogenesis. In some of these strains, Yen and Barr (1971) found substantial
numbers of Rickettsia-like microbes in adults, eggs and embryos. Compatibility of mosquito strains
seems to be correlated with the strain of the microbe present. Mosquitoes that carry different strains
of the microbe exhibit cytoplasmic incompatibility; those that carry the same strain of microbe are
interfertile.
Similar phenomena have been seen in a number of other insects. Microoganisms are seen in the eggs
of both Nasonia vitripennis and N. giraulti. These two species do not normally hybridize. Following
treatment with antibiotics, hybrids occur between them (Breeuwer and Werren 1990). In this case,
the symbiont is associated with improper condensation of host chromosomes.
For more examples and a critical review of this topic, see Thompson 1987.
5.9 A Couple of Ambiguous Cases So far the BSC has applied to all of the experiments
discussed. The following are a couple of major morphological changes produced in asexual species.
Do these represent speciation events? The answer depends on how species is defined.
5.9.1 Coloniality in Chlorella vulgaris Boraas (1983) reported the induction of multicellularity in a strain
of Chlorella pyrenoidosa (since reclassified as C. vulgaris) by predation. He was growing the
unicellular green alga in the first stage of a two stage continuous culture system as for food for a
flagellate predator, Ochromonas sp., that was growing in the second stage. Due to the failure of a
pump, flagellates washed back into the first stage. Within five days a colonial form of the Chlorella
appeared. It rapidly came to dominate the culture. The colony size ranged from 4 cells to 32 cells.
Eventually it stabilized at 8 cells. This colonial form has persisted in culture for about a decade. The
new form has been keyed out using a number of algal taxonomic keys. They key out now as being in
the genus Coelosphaerium, which is in a different family from Chlorella.
5.9.2 Morphological Changes in Bacteria Shikano, et al. (1990) reported that an unidentified bacterium
underwent a major morphological change when grown in the presence of a ciliate predator. This
bacterium's normal morphology is a short (1.5 um) rod. After 8 - 10 weeks of growing with the
predator it assumed the form of long (20 um) cells. These cells have no cross walls. Filaments of this
type have also been produced under circumstances similar to Boraas' induction of multicellularity in
Chlorella. Microscopic examination of these filaments is described in Gillott et al. (1993).
Multicellularity has also been produced in unicellular bacterial by predation (Nakajima and Kurihara
1994). In this study, growth in the presence of protozoal grazers resulted in the production of chains
of bacterial cells.
Therefore, DaJahveu, the people who told you such evidence didn't exist were lying to you.
--OneGlove