Re: mole rats (was Re: Sociality, eusociality, ...)

Gerold Firl (geroldf@sdd.hp.com)
30 Mar 1995 13:23:58 -0800

In article <dyanega-2303951959430001@catalpa.inhs.uiuc.edu> dyanega@denr1.igis.uiuc.edu (Doug Yanega) writes:

>I disagree. Consider very carefully the distinction in an evolutionary
>sense between an organism which, over its lifetime, can express two
>different phenotypes (and experience selection, therefore, on both) and an
>organism which expresses only ONE phenotype, even though other members of
>the population express yet another.

You refer to the species which change sex during their lifetime, right?

>Dramatically different evolutionary
>scenarios. Allow me to give the best and closest parallel for you to
>ponder:
>(1) Do you classify organisms by their sex ratio, OR do you categorize
>them first by whether they are asexual, true sexuals, hermaphrodites,
>sequential hermaphrodites, etc.???

These are not exclusive criteria; while I normally use an evolutionary
classification, which categorizes by evolutionary relationships, the others
you mention also have their uses. The lizards which reproduce
parthanogenetically, and the fish which change sex (are those sequential
hermaphrodites?) have unusual characteristics, but they are still
vertebrates.

Eusociality is not an evolutionary categorization, but a description of the
extent to which the individual is subordinated to the group - how would you
describe the colonial organisms like jellyfish and slime molds, which have
not acheived a truely cellular organisation? Again, nature appears to be a
continuum.

>(2) Next, do you expect sexual
>selection (and the evolution of sexual roles and such) to be the *same* in
>an organism which has true sexes versus an organism which is facultatively
>hermaphroditic?? If you cannot answer with a resounding YES to both
>questions, then I suggest you have been applying the wrong logic to the
>issue of sociality.

Hmm ... but *nothing* is the same, yet everything is similar. Gibbons and
elephant seals are both sexual organisms, yet their different social
organisation has led to some very different characteristics.

I'm a little out of my depth here; what does facultatively hermaphroditic
mean?

>There is no logical, conceptual problem with drawing a
>DIRECT parallel between eusocial organisms/sexuals (permanent, discrete
>behavioral/gametic classes) versus non-eusocial organisms/hermaphrodites
>(facultative switching from one class to another).

I'm not sure what you mean by this; in species using haplo-diploidy to
create a worker caste, we have permanent distinctions between workers and
breeders. OK. (Note: what about bees? Are they considered truely eusocial?
If the queen is killed, isn't another queen created by feeding a larva
"royal jelly"? - thus abrogating the requirement of permanent castes?)

Are you drawing a parallel between switching sex during adulthood, and
changing reproductive strategy during the lifetime of non-eusocial
individuals? Organisms always have a juvenile phase, during which they are
unable to reproduce; some have a "grandmother" phase, during which they are
also unable to reproduce. I'm not sure how significant that is.

>> Any mammal society where the alpha pair alone are breeders seems to have
>> significant components of eusociality.

>Depends on whether you consider eusociality to have any components other
>than permanent castes. I define it by that ONE criterion alone.

Many human societies have used eunuchs for certain social roles. Does that
make them eusocial? How permanent does a caste have to be?

>>Mole rats use a less-flexible system
>> for maintaining the social order than wolves, relying on neurochemical
>> mediators and processes at a more fundamental level than the more
>> behavioral-type mediators availible to more intelligent animals, but the
>> benefits of the social division of labor is the same regardless, from
>> insects to mammals.

>I disagree completely; if the division of labor is *permanent*, it makes a
>tremendous evolutionary difference, and is not at all "the same
>regardless".

The *benefits* of the division of labor are the same, although the
implementation and biological consequences are certainly different. A
social species has certain advantages (and perhaps certain disadvantages as
well, but that's another story) regardless of the method by which that
sociality is maintained. There are advantages and disadvantages to using
the kind of discrete classification you suggest; the criterion of permanent
castes does simplify matters somewhat (though I'm still wondering about the
bees). Maybe I just have a bias in favor of analytic systems which use
continuous/fuzzy variables rather than discrete classes; in general, it
seems like discrete systems are plagued by the problem of
exception-handling. 

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