Origin of the sterile taxa in Lycoris
Species Evolution by Hybridization in the genus Lycoris, Amaryllidaceae
Siro Kurita, Emeritus Professor
Department of Biology, Faculty of Science, Chiba University, Japan
| The royal road to species evolution is gene mutation and isolation, but thehybridization also bears very important role of the speciation.
The possibility of new species formation by hybridization was already noticed in the mid-eighteenth century as reported by Linnaeus and Rudberg in Linaria, Scrophulariaceae (Linnaeus, 1760).
Most research workers at that time, however, made little account of the evolutionary role of hybridization until the early twentieth century because of the sterility of the interspecific hybrids. They considered that the hybrid is the blind alley of evolution.
The situation dramatically changed by verification of Winge’s hypothesis (Winge, 1917). He proposed the fruitful hypothesis of chromosome number doubling in interspecific hybrids. Winge’s hypothesis was soon confirmed experimentally by artificial interspecific hybridizations in Nicotiana, Raphanus-Brassica, and Galeopsis (Clausen and Goodspeed, 1925; Karpechenko, 1927; Muntzing, 1932).
Recent researchers have recognized the significance of hybrid speciation for evolution and the essential part of the mechanism of hybrid speciation is the stabilization of breeding behavior of the hybrids. At present various methods of stabilization in hybrid reproduction are known. The methods are:
(1) vegetative propagation; (2) agamospermy; (3) amphiploidy; (4) permanent odd polyploidy; (5) permanent translocation heterozygosity; (6) recombinational speciation; and (7) the segregation of a new genotype isolated by external barriers (cf. Grant, 1981).
present, two methods, (1) and (7) are recognized among the hybrids of the genus Lycoris.
an endemic genus to Sino-Japanese flora. It
consists of about 13 fertile taxa (2n=12, 14,
16, 22: NF=22) and 14 or more sterile taxa
(2n=13, 15, 17, 18, 19, 23, 27, 29, 30, 31: NF=22, 23, 32, 33), excepting for several
artificial hybrids produced by horticulturists. These taxa are distributed in
warm temperate to subtropical zone of East Asia from southwestern China
and southern Korea、 with a few extending to northern Indochina and Nepal.
OBSERVATION AND DISCUSSION
| In the karyological point of view, the fertile taxa can be divided into
The first group has the
genomes consisting of large metacentric
chromosomes and telocentric chromosomes. The [M+T] is the brief account of this genome.
The second group has the genomes consisting of 11 acrocentric chromosomes. L. sanguinea, L. sprengeri, L. rosea, L. haywardii, and L. radiata var. pumila are included in this group (2n=22=22A). The [A] is an abridgement of this acrocentric genome.
On the other hand, excepting a few autopolyploids such as L. radiata, almost all of the sterile taxa have both [M+T] and [A] type genomes, which supposed to be originated in hybridization between the species having [M+T] and that having [A].
of the genus Lycoris
are easily hybridized; diverse morphological features occur frequently among
them in nature and in cultivation.
1) L. flavescens ：
２) L. chejuensis :
China, especially the drainage basin area of the Yangtze-Kiang, is the center of speciation of the genus, in where six fertile stem species are known. They are L. radiata var. pumila, L. sprengeri, L. aurea, L. longituba, L. chinensis, and L. anhuiensis.
1) L. radiata
X L. chinensis
In Mt. Mogan, two more interesting sterile taxa were collected.
interesting taxon is triploid. The karyotype is 2n=30=3M+5T+22A.
The same karyotype was reported in L. houdyshelii (Bose, 1957; Kurita, 1987).
2) L. chinensis
X L. sprengeri
3) Other sterile species originated in Chinese flora.
a) L. straminea 2n=19=3M+5T+11A
b) L. incarnata 2n=30=3M+5T+1M’+20A+1m
c) L. houdyshelii 2n=30=3M+5T+22A
d) L. cardwellii 2n=27=6M+10T+11A
e) L. squamigera 2n=27=6M+10T+11A
f) L. aurea sensu stricto 2n=15=7M+8T
4) Semisterile taxa
b) L. haywardii 2n=22=22A
c) L. longituba x L. chinensis ? 2n=16=6M+10T
Speciation Patterns in Lycoris
1. Successive speciation:
The species evolution of sexually reproducing fertile taxa such as L. sprengeri (2n=22=22A) and L. chinensis (2n=16=6M+10T) should be successive. The formation of two or more reproductively isolated species from a common ancestral breeding population by accumulation of mutations and geographical isolation is a time-consuming process. The existence of variable fertile species in Lycoris at present may be the result of successive speciation.
2. Extemporaneous speciation:
In this genus, new species are frequently formed extemporaneously by fusion of heterogeneous gametes. These new species propagate exclusively by fission of their bulbs. Three types are recognized.
Bose, S. 1957. Cytological investigations in Lycoris 2. Cytological similarity
L. aurea and L. traubii. Plant Life 14:33-37