In some species, such as Halocynthia roretzi and Ciona intestinalis, a self-incompatibility mechanism is in place to avoid self-fertilization
(autologous fertilization) (Morgan, 1944; Rosati and de Santis, 1978; Fuke and Numakunai, 1982).
For example, all autopolyploids maintain heterozygosity via cross fertilization and exhibit low fertility in response to self-fertilization
. However, most allopolyploids are self-compatible with several being highly self-pollinated (Mackey, 1970).
generates identity disequilibrium, the association of homozygous genotypes between loci (Haldane 1949).
For each genotype, one ramet was left unfertilized (to assess the level of sperm contamination or self-fertilization
), one ramet was fertilized about 22 ([+ or -]2) h after the beginning of siphon opening (when results from the previous experiment indicated that all siphons should be open), and remaining ramets (2-3) were fertilized at various times up to 85 h after initial siphon opening.
Inbreeding depression, neutral polymorphism and copulatory behavior in freshwater snails: a self-fertilization
and maternal enzymes in the planulae of the coral Goniastrea favulus.
Since Silen (1966) first described the release of sperm by bryozoan zooids two questions have remained unanswered: (1) can spawned sperm enter maternal zooids and (2) are there aspects of sperm and egg spawning that influence whether zygotes are produced by self-fertilization
This estimation model is based on the assumption that progeny genotypes are a product of either self-fertilization
or random outcrossing, that mating system is uniform among maternal parents, and that alleles exhibit tetrasomic inheritance without double reduction.
While there is strong selection against the products of self-fertilization
within the capsule (Griffin et al.
Examination of 1,000 unfertilized eggs from each trial confirmed that the spawning procedures were effective in preventing self-fertilization
. No self-fertilized eggs were observed.
Mechanisms that allow sperm to discern self eggs from non-self eggs may allow for flexibility in mating systems, promoting outcrossing when non-self eggs are available but permitting self-fertilization
to occur when no other options are available.
Prof Bentzen from Dalhousie University said: "Although this study focused on MHC genes in vertebrates, the evolutionary dynamics described in it likely apply to other gene families, for example resistance genes and those which prevent self-fertilization
in plants (self-incompatibility loci) that are caught up in their own evolutionary races."