Population‐specific gender‐biased hybridization betweenDryopteris intermediaandD. carthusiana: evidence from chloroplast DNA

Abstract

As has been shown for many kinds of organisms, barriers to interspecific hybridization may differ in strength between reciprocal crosses, resulting in a bias in the probability that one or the other species may be the maternal or paternal parent of hybrids. The fern Dryopteris Xtriploidea, the "backcross" hybrid between the diploid D. intermedia and the tetraploid D. carthusiana, occurs in large numbers in nature, providing an opportunity to investigate whether such a bias exists. Differences in the chloroplast genome distinguishing the two parental species were discovered in the sequence of the trnL region following amplification by polymerase chain reaction (PCR), including a Mse I restriction site. This allowed rapid identification of the donor of the chloroplast genome, and therefore the maternal parent of each hybrid, assuming chloroplast DNA to be maternally inherited in Dryopteris. Analysis was carried out on 127 hybrids, shown to be of independent origin using allozymes, occurring at three localities in Virginia and West Virginia. When samples from all localities were pooled, 91 possessed the D. carthusiana trnL genotype and 36 possessed the D. intermedia genotype, a ratio that is significantly different (P < 0.001) from the null hypothesis of no gender bias. The strength of the bias differed significantly among the three sites, however, with bias at the West Virginia site much stronger (5.6:1 carthusiana:intermedia; P < 0.001) than at either Virginia site (1.55:1 and 1.43:1 carthusiana:intermedia, respectively; P > 0.05 in both cases). The cause of the strong bias in the West Virginia sample is unknown, as is the cause of the population differences. Causes of bias could include differences between the parental species related to their ploidy difference, including sizes of gametes and/or gametangia, sperm motility, breeding system (D. intermedia is outcrossing while D. carthusiana is selfing), or the nature and strength of interspecific isolating mechanisms.

Independent origins of tetraploid cryptic species in the fern Ceratopteris thalictroides

“…This result was in agreement with other reports on cpDNA transmission in ferns (Gastony and Yatskievych 1992;Stein and Barrington 1990;Vogel et al 1998;Xiang et al 2000). On the basis of this evidence, we can use chloroplast DNA to assess the maternal lineage of Ceratopteris cryptic species.…”

Species boundaries and frequency of hybridization in the Dryopteris carthusiana (Dryopteridaceae) complex: A taxonomic puzzle resolved using genome size data

“…polyploids are predominantly selfi ng Soltis, 1987 , 1990 ;Soltis et al, 1988 ;Masayuma and Watano, 1990 ;Xiang et al, 2000 ;Flinn, 2006 ). Therefore, the probably selfi ng breeding system in tetraploid D. carthusiana and D. dilatata ( Xiang et al, 2000 ;Flinn, 2006 ) likely reduces opportunities for interspecifi c hybridization, which is consistent with the lower number of crosses ( D. × deweveri ) discovered in the current study.…”

“…Based on evidence of genome homology between D. expansa and D. dilatata ( D. expansa is hypothesized as one of the progenitors of the allotetraploid D. dilatata ; Gibby and Walker, 1977 ;Viane 1986 ;Krause 1998 ;see also ( Tryon and Britton, 1966 ;Xiang et al, 2000 ). Dryopteris carthusiana and D. dilatata also share the D. intermedia genome ( Table 1 ), which may facilitate their interspecifi c hybridization.…”

Molecular evidence for natural intergeneric hybridization between Liquidambar and Altingia

“…The difference in the results from the two studies may be due to different sampling locations or insufficient samples in both studies. Population-specific unidirectional hybridization has been reported in previous studies (Xiang et al 2000;Wu and Campbell 2005), but we cannot test this hypothesis because we were unable to find a diagnostic chloroplast marker from matK and three other chloroplast intergenic spacers to distinguish A. chinensis from L. formosana in the Heishiding and Nanling samples.…”