analogous structures

Paul Zambino paulz at PUCCINI.CRL.UMN.EDU
Wed Nov 20 12:30:52 EST 1996

>I think you folks are off base in seeing products of meiosis as
>"analogous" to products of mitosis - the strucutres may have
>superficial gross similarities but are intrinsically different.

If you refer to the generation of recombinants, then of course the spores
produced by mitosis cannot be analogous to those from meiosis.  However,
the structures enclosing the spores may be either analogous in function, or
might even be homologous in the sense of having similar derivation and
regulation.  Structures might be formed that are intrinsically designed for
sexual function, yet in the absence of mating take on a different function.

In some monosporic cultures of Ophiostoma nigrum and other Ophiostomas that
I was maintaining for making crosses at one time, sterile perithecia formed
that had ostiolar conidiospores.  Conidia were produced and held in wet
droplets that did not have the extremely sticky matrix material found with
ascospores, and examination confirmed the lack of ascospores or asci within
the perithecia.  THe  positioning of the droplets at the top of the
perithecial neck could serve the same insect dispersal function as for
ascospores, and the origin of the perithecial is undoubtedly designed for
sexual function.  In fact, transfer of spores between perithecia will
effect crossing.

If some strains lost the ability to undergo sexual recombination or produce
ascospores yet continued to produce perithecia as a form of conidial
dispersing structure, the asexual "perithecia" would be homologous
structures evolved from functional perithecia.  Synnemata, on the other
hand, are also produced by some Opiostomas and provide for dispersal of
conidia by bark beetles, etc. similar todispersal of ascospores from
perithecia with elongated necks, but I would not expect the regulation of
perithecial and synnematal development to be similar, and any morphological
similarities would be by analogy only.

At any rate, I do not discount out of hand that papulospores could have
been derived at some point from cleistothecia.  Paul

Paul Zambino, Ph.D.
USDA Forest Service
Forestry Sciences Lab
5985 Highway K
Rhinelander, WI 54501
FAX: (715)362-1166
EMAIL: paulz at

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