Genotypic confirmation of a biased phenotypic sex ratio in a dryland moss using restriction fragment length polymorphisms

Abstract

Premise In dioicous mosses, sex is determined by a single U (female, ♀) or V (male, ♂) chromosome. Although a 1 : 1 sex ratio is expected following meiosis, phenotypic sex ratios based on the production of gametangia are often female‐biased. The dryland moss Syntrichia caninervis (Pottiaceae) is notable for its low frequency of sex expression and strong phenotypic female bias. Here we present a technique to determine genotypic sex in a single shoot of S. caninervis , and report results of a case study examining genotypic and phenotypic sex ratios. Methods We reanalyzed 271 non‐expressing gametophyte shoots from a previous study on S. caninervis sex expression across microhabitats using a restriction fragment length polymorphism (RFLP) method. Results We recovered a genotypic sex ratio in non‐expressing shoots of 18.4♀ : 1♂, which exceeds the female bias of the phenotypic ratio (5.3♀ : 1♂; P = 0.013). We also found that the distribution of male and female genotypes across microsites with different levels of sun exposure was not predicted by patterns of sex expression in these microsites. Discussion These findings contribute to our understanding of how the environment may modulate sex ratios in S. caninervis , either through its direct influence on sex expression or through selection on genotypes with particular sex expression phenotypes.

Life-history characteristics and historical factors are important to explain regional variation in reproductive traits and genetic diversity in perennial mosses

“…Recently, sex ratios in adult non-reproductive populations were reported for a few species, commonly exhibiting a female bias. Some studies indicated overall sex-independent expression rates ( Hedenäs et al , 2010 ; Bisang and Hedenäs, 2013 ; Bisang et al , 2015 , 2020 ), but in others, expression levels varied between sexes and regions (present study; Baughman et al , 2017 ; Ekwealor et al , 2022 ).…”

“…He hypothesized that males should have a higher mortality in severe conditions because they allocate more resources prezygotically in sexual reproduction than females, which could result in genetic deprivation. However, newer evidence showed that non-reproductive males occurred in similar frequencies to females in exposed microsites ( Ekwealor et al , 2022 ), and male rarity was probably attributable to lower male sex expression. Finally, restricted sexual recruitment in unfavourable environmental conditions might facilitate the evolution of ‘genetic sterility’ through selection against traits involved in sex.…”

“… Chopra and Bathla, 1983 ; Rydgren and Økland, 2002 ), and geographical variation in sex phenotypes and sex expression have been demonstrated repeatedly in different plant groups ( Benassi et al , 2011 ; Yakimowski and Barrett, 2014 ; Blackstock, 2015 ; Pereira et al , 2016 ). Sex expression rates differed between different microenvironments in the desert moss Syntrichia caninervis ( Baughman et al , 2017 ; Ekwealor et al , 2022 ) and varied across Europe along macroscale environmental gradients in the perennial pleurocarpous moss Pseudoscleropodium purum ( Boquete et al , 2023 ). However, little is known about environmental effects on genotypic sexes in bryophytes (Bisang et al , 2015 , 2020 ).…”

Methodologies in gametophyte biology

“…Focusing on the species Syntrichia caninervis Mitt. as a study system, Ekwealor et al ( 2022 ) provide a method for the sex classification of sterile shoots. Using a restriction fragment length polymorphism (RFLP) approach, the authors identified a locus on the sex chromosomes which they then used to develop targeted PCR primers to screen non‐expressing shoots.…”