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Hybridization in bryophytes involves a fusion of gametes produced by haploid parental gametophytes of different species. The primary hybrid is thus the short-lived diploid sporophyte, which soon undergoes meiosis prior to the formation of large amounts of haploid spores. We compared morphology of gametophytes (branch leaves) and sporophytes (capsule inclination) from sympatric populations and allopatric populations of H. lutescens and H. sericeum. In addition, we used transcriptome data to select 85 nuclear SNP markers that were fixed for alternative alleles in the two species. The SNPs were used to estimate the degree of hybridization in diploid sporophytes. Our study shows that gametophytes from sympatric populations display intermediate morphology in a number of leaf characters, with exception for leaf sizes, which are markedly smaller than those in allopatric populations. None of the 100 sporophytes appeared to be primary hybrids, but 33 displayed admixing—heterozygotic expression of SNP markers or mismatch of occasional markers in homozygous condition—suggesting that extensive introgression takes place in the sympatric populations. Most sporophytes with intermediate capsule inclination, initially classed as putative hybrids, did not display admixture of nuclear SNP markers. Sixty-seven percent of admixed sporophytes have predominantly nuclear SNPs typical for H. lutescens. Our results suggest that interspecific hybridization and bidirectional introgression are relatively common in the studied sympatric populations, giving rise to viable recombinants, but not complete mixing of the parental genomes. Our study is one of the first detailed accounts of hybridization among pleurocarpous mosses, opening for future studies of gene transfer and introgression between bryophyte lineages and its role in local adaptation and long-term evolutionary diversification.

Herbivory on liverworts is rarely reported. We studied the effects of feeding by larvae of the sciarid fly Scatopsciara cunicularius on the growth of the thalloid liverwort Marchantia polymorpha at two different constant temperatures, 12°C and 22°C. Larvae reared at the lower temperature fed slower and over a longer period of time, which resulted in more damage and a greater reduction in the growth of the liverwort than that caused by those reared at the higher temperature. The reduction in growth of the liverwort was positively density-dependent in terms of number of larvae at both temperatures. These results indicate that the larvae of S. cunicularius are likely to be an effective means of controlling M. polymorpha, which is a common weed in plant nurseries and greenhouse cultures.

We studied the behavior, life cycle, and reproductive biology of the sciarid fly Scatopsciara cunicularius (Lengersdorf, 1943) under two constant temperatures . The sciarid was reared at 12.3 ± 0.6°C and 22 ± 1.7°C on its host, the liverwort Marchantia polymorpha L. Our results show that the sciarid fly is able to complete its life cycle with liverwort tissue as its only source of food. The egg-laying potential of the insect ranged from 70–174 eggs per female (mean 110 ± 31 eggs). Reproduction was digenic, meaning that one female can produce both male and female progeny. The overall sex ratio did not depart from 1:1, although the progeny sex ratio was highly variable. The developmental period of S. cunicularius was considerably longer in the colder than the warmer temperature. Mean development time of the egg, larva, and pupal stages, and adult longevity in the warm regime was 4, 20, 4, and 5 d, whereas mean development time of each juvenile stage and adult longevity in the cold regime was 13, 95, 11, and 8 d, respectively. The results suggest that the phenology of S. cunicularius is temperature dependent. Scatopsciara cunicularius could constitute a promising agent for biological control of M. polymorpha .