Intraspecific Life History Variability in the Florideophycidae (Rhodophyta)

Authors: Maggs, C.A.

Journal: Botanica Marina

Volume: 31

Issue: 6

Pages: 465-490

eISSN: 1437-4323

ISSN: 0006-8055

DOI: 10.1515/botm.1988.31.6.465

Abstract:

Intraspecific life history variations in the Florideophycidae have been reviewed by classification into five categories: (1) formation of monosporangia, bisporangia (binucleate or quadrinucleate), meiotic polysporangia, mitotic parasporangia, or vegetative propagules by a species that also forms meiotic tetrasporangia; (2) simultaneous occurrence of gametangia and tetrasporangia (mixed phase reproduction) on either haploid or diploid plants, involving mitotic tetrasporangia or diploid gametangia; (3) occurrence of bisexual thalli or branches in a ‘normally’ unisexual species; (4) direct development of tetrasporophytes from tetraspores (exclusively or mixed with gametophytes), and (5) direct development of gametophytes from carpospores (exclusively or mixed with sporophytes). New experimental data on same aspects of these phenomena is presented here. Three species, Atractophora hypnoides (Bonnemaisoniales) and Schmitzia hiscockiana (Gigartinales) from Ireland and Gloiosiphonia capillaris (Cryptonemiales) from Ireland, Scotland and Nova Scotia (Canada), show direct development of a proportion of tetraspores into tetrasporophytes. In A. hypnoides, gametophytes are haploid (n = c. 23) and sporophytes diploid. Mixed progeny develop in single tetrads and spore developmental plasticity is indicated by the interactive effects of genetic and environmental factors on gametophyte frequency, which was 0 – 85% in 36 isolates. Each species shows a preponderance of crustose sporophytes over ephemeral erect gametophytes, and tetrasporophyte recycling is likely to be important in maintaining populations in high-disturbance habitats. Complex life history patterns in the genera Gymnogongrus (Phyllophoraceae) and Mastocarpus (Petrocelidaceae) (both Gigartinales) have been investigated karyologically. Gymnogongrus devoniensis from Ireland and N France and G. ?devoniensis from Nova Scotia follow a direct, carpospore to female gametophyte, life history that is diploid (2n = c. 46) and apomictic. Gymnogongrus devoniensis and G. ?devoniensis may be genetically related to undescribed mitotic bisporangial and tetrasporangial crusts that occur with them. Nova Scotia isolates of M. stellatus are likewise diploid (2n = c. 58) and apomictic but carpospores form mixed crustose and gametophytic progeny. In the direct-type apomictic life history in both species female gametophytes are diploid, carposporophyte development occurs without fertilization, and all carpospores develop into females. This life history is here interpreted as a consequence of a double female genetic complement, rather than a male and a female genome as in diploid tetrasporophytes. Genetic information associated with maledetennining genes is lacking and carpospores therefore develop into diploid females rather than tetrasporophytes. Supporting evidence for this hypothesis is the derivation of a direct-type life history from sexual Mastocarpus isolates by self-fertilization with genetically-female spermatia, and the rare occurrence of apomictic plants among sexual plants grown from tetraspores, presumably due to failure of meiosis resulting in diploid spores. Apomictic reproduction may be important in some species near distributional margins, since single spores can develop into founder individuals, and spores are produced year-round, not seasonally as in sexual populations. Copyright © 1988 Walter de Gruyler.

Source: Scopus