Re: [asa] historical versus experimental sciences

From: David Campbell <>
Date: Mon Aug 17 2009 - 15:30:25 EDT

> I have no objection to the basic logic of such an approach.  The
> difficulties I was posing were further along the line.  If you don't know
> very much about a species to start with (and we were talking about just such
> a case), how are you going to determine its close evolutionary relatives?
> You can't determine that X and Y are close evolutionary relatives unless you
> know at least something about both X and Y.  Now in the case of the fruit
> fly invader, you've already suggested that we would have no direct knowledge
> of its biochemistry and won't have sequenced its genome yet.  So the
> evolutionary classification you are talking about can't be based on either
> of those things.  On what is it based, then?

Not necessarily "no direct knowledge of its biochemistry", just not
knowing the specific issue of interest (e.g., a pheromone). The
evolutionary classification could be based on morphological
features-not merely "these two flies look similar" from you or me, but
in the judgement of an actual entolomogist who has studied the group
and has determined what features give a consistent pattern within the
group of interest. It could also be based on genes unrelated to the
character of interest, such as mitochondrial genes.

Perhaps a real-life example that I am familiar with would be less
confusing, involving fewer hypotheticals. Freshwater mollusks have
the highest rate of imperilment (extinction, endangerment, etc.) of
any major group of organisms, with land snails close behind. In order
to effectively protect them, we need to know about their life history.
 This is especially an issue for freshwater mussels, which have a
juvenile stage parasitic on certain fish and so need the host fish
protected and available, too. Many species are too rare to make
experimenting on them a practical option. How do we know what more
common species would be the best model to use? Molecular and
morphological studies help us identify the closest relatives, which
then can be checked for relevant patterns such as sensitivity to
pollutants, ecological requirements, host needs, etc. For example,
the purple pigtoe was placed in Fusconaia, the sculptured pigtoe in
Quincuncina, and the purple wartyback in Cyclonaias, all often
assigned to the tribe Pleurobemini. In fact, all three belong in
Rotundaria (based on genetic data, as well as some previously
neglected morphological and anatomical features), tribe Quadrulini, a
group with very different characteristic strategies for getting larvae
and host together. Conversely, enough genetic variation exists
within the sculptured pigtoe, corresponding to geographic separation,
to suggest that not all populations will be identical in their
biology. These data can help us narrow down what to anticipate
regarding the rarer species for currently unknown features (such as
host fish for the two pigtoes).

Evolutionary theory gives us the reason to extrapolate from one
similarity to another when we know about some similarities but not
about some other feature of interest.

Likewise, based on observed patterns of relationships, I can predict
patterns in other organisms. For example, many ordinary pond snails
belong to the family Lymnaeidae. A few oddballs belong there, too.
Lantzia and Erinna are unusual ones, somewhat similar in shell form,
from Mauritius and Hawaii, respectively. Every lymnaeid from close to
the Indian Ocean that's been sequenced groups as relatives of Radix
(chromosome number and anatomical features also support the grouping,
whereas shell shape is quite variable). The minimal available data on
the Hawaiian ones relates them to primarily North American forms. I
predict (and once a colleague finishes the anatomical work, will be
submitting a paper for publication mentioning this) that detailed
anatomy, chromosome number, sequencing, etc. will associate Lanztia
with Radix and its relatives, whereas the Hawaiian ones will show
additional similarities to the primarily North American group.

> More arguments with detailed examples aren't necessary here.  Just give me
> *a list of the criteria* by which a biologist could deduce that two fruit
> flies are close evolutionary relatives if the biologist had *zero* knowledge
> of the first fruit fly's genome, biochemistry, and physiology.  A list of
> words or phrases will do, e.g.:  "We could ascertain beyond a reasonable
> doubt that the two fruit flies were close evolutionary relatives if they had
> similar flight patterns, similar mating habits, a similar response to
> high-pitched noises, or a similar diet."

Things like that would be possible, but I expect that the features are
more likely to be along the lines of pattern of hairs on a particular
body part, shape of the eyes, particular color patterns, exact wing
vein configuration, etc.

Searching reveals that Bactrocera albistrigata is the newly found
invasive fruit fly. It's not that closely related to the lab favorite
Drosophilia. has some specific
features of relevance for the larvae. has some
morphological features.
"The genus Bactrocera is comprised of over 500 fruit fly species, of
which many are considered serious
pests that threaten the agricultural crops of countries in which they
are found. The majority of these species
are native to the South Pacific, Australia, India, and Southeast Asia
(, although many have
moved into Africa, Europe, and South America. It appears that some
have been so recently discovered or
separated from like species (B. dorsalis group, Clarke et al., 2005)
that very little information is available
on their life cycles and host preferences. "

In other words, there are several fruit flies in this group that are
currently rather poorly known, providing uncertainty about whether
they are a threat and how to control them.

Phylogenetic relationships among Bactrocera species (Diptera:
Tephritidae) inferred from mitochondrial DNA sequences
Paul T. Smith, Srini Kambhampati and Karen A. Armstrong
Molecular Phylogenetics and Evolution
Volume 26, Issue 1, January 2003, Pages 8-17
Several members of the dipteran family Tephritdae are serious pests
because females lay eggs in ripening fruit. The genus Bactrocera is
one of the largest within the family with over 500 described species
arranged in 28 subgenera. The phylogenetic relationships among the
various species and subgenera, and the monophyly of specific groups
have not been examined using a rigorous phylogenetic analysis.
Therefore, phylogenetic relationships among 24 Bactrocera species
belonging to 9 subgenera were inferred from DNA sequence of portions
of the mitochondrial 16S rRNA, cytochrome oxidase II, tRNALys, and
tRNAAsp genes. Two morphological characters that traditionally have
been used to define the four groups within the subgenus Bactrocera
were evaluated in a phylogenetic context by mapping the character
states onto the parsimony tree. In addition, the evolutionary trend in
male-lure response was evaluated in a phylogenetic context. Maximum
parsimony analyses suggested the following relationships: (1) the
genus Bactrocera is monophyletic, (2) the subgenus B. (Zeugodacus) is
paraphyletic, (3) the subgenus B. (Daculus) is a sister group to
subgenus B. (Bactrocera), and (4) the subgenus B. (Bactrocera) is
monophyletic. The mapping analyses suggested that the morphological
characters exhibit a simple evolutionary transition from one character
state to another. Male-lure response was identified as being a labile
behavior that has been lost on multiple occasions. Cue-lure response
was plesiomorphic to methyl-eugenol response, and the latter has
evolved independently within the Bactrocera and Zeugodacus groups of
subgenera. The implications of our results for devising a coherent,
consolidated classification for Bactrocera is discussed.

In other words, they ran an evolutionary analysis of one feature
(mitochondrial DNA) and examined the correlation with a feature of
interest (response to particular trap types), so that analysis of
mtDNA for another species will help us to predict what traps are
likely to be most effective, even though evolution provides the only
link between the trap vulnerability and the mtDNA pattern.

Genome is not known for the species, but a handful of genes have been

Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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Received on Mon Aug 17 15:31:22 2009

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