common names/systematics

[dphowson]

Following this line of reasoning, does anyone know what is the isolating 
barrier that prevents Small White(pieris rapae) and Green-veined 
White(pieris napi) mating together? They are such closely similar species, 
are common in Europe, and fly together.

dave

-----Original Message-----
From:	Pierre Zagatti [SMTP:zagatti at versailles.inra.fr]
Sent:	11 June 1999 09:56
To:	leps-l at lists.yale.edu
Subject:	Re: common names/systematics

Maybe a lot of science after that discussion about common names
that seems a little bit wordy for non-english speaking entomologists....

In theory (!) there is a good system to recognize species or subspecies
among contiguous populations. Look at the single mate recognition systems
(smrs of Patterson) in both populations. They may be secondary sexual 
characters,

behaviors or androconia and Bernardi (among others) has shown that
in really contiguous or overlapping populations, these systems evolved in a 
way
to produce strong isolating barriers, whereas these barriers may not exist 
in
geographically
isolated populations. If these barriers exist, the two populations should 
belong
to
different species.
Frequently, species A won't mate with species B in contiguous populations
although
forced matings (artificial pairing with hand in the case of leps) will 
produce
quasi-fertile
offspring. On the other hand, species A will mate with (geographically 
isolated)
species
C without 'help', resulting in sterile mating.

Now practically, the main problem is to identify these smrs. In moths, the 
sex
pheromone
is a good approach, but immediate conclusions may be hazardous: if we 
consider 2
groups
of day-flying moths, the burnet (genus Zygaena - Zygaenidae) and clearwing 
moths
(Sesiidae),
they have developed totally different smrs.
The absolute isolation in Zygaena is induced by sex pheromone. Once the 
male has
been
stimulated by his female pheromone, he will try to copulate with everything
showing a
strong red contrast (including your red pencil cap or a female of a 
different
species
you viciously placed here).
In Sesiidae the isolation is essentially visual. A few molecules of sex 
pheromone
may
attract many different species but mating will occur only by visual
identification of the
partner.
Such difference between two families with similar biology is probably 
related to
different
strategies to avoid predation: Mullerian mimicry in burnets (i.e. species 
mimic
each other)
and wasp mimicry in Sesiids.

--
Pierre ZAGATTI
INRA Unite de Phytopharmacie et Mediateurs Chimiques
78026 Versailles Cedex
FRANCE
Tel: (33) 1 30 83 31 18
e-mail zagatti at versailles.inra.fr
http://www.jouy.inra.fr/papillon/