A novel approach to estimating the cost of male fertility restoration in gynodioecious plants

Abstract

Summary• In many gynodioecious plants, sex is determined by cytoplasmic male sterility genes (CMS) and nuclear male fertility restorers (Rf). Models predict that the costs of restoration are important determinants of population sex ratios. However, current approaches to the estimation of these costs require prior identification of CMS genotypes, information that is available for few species.• We tested a novel approach to estimating the cost of restoration in natural populations without determining CMS or Rf genotypes. We used estimates of pollen viability and offspring sex ratios from open-and hand-pollinated families of Lobelia siphilitica to test whether the cost of restoration, expressed as low pollen viability, is higher in populations with more females.• Among populations with CMS, we found that variation in pollen viability was higher in small populations with more females, as expected if the proportion of females within populations increases with the maximum cost of restoration. In controlled crosses, families with low pollen viability also produced fewer females, suggesting that variation in viability is primarily determined by the number and frequency of Rf alleles carried.• This approach to estimating the cost of restoration can be applied to other cytonuclear gynodioecious species, offering new opportunities for testing gynodioecy models in the wild.

Frequency-dependent fitness in gynodioeciousLobelia siphilitica

“…There were four levels of the sex ratio treatment: 20%, 40%, 60%, and 80% females. These treatment levels were chosen both to provide a conservative test of frequency‐dependent fitness and to reflect the range of female frequencies observed in nature (Caruso and Case , ; Case and Caruso ; C. M. Caruso and A. L. Case, unpubl. data).…”

Breakdown of Dioecy: Models Where Males Acquire Cosexual Functions

“…Most gynodioecious species with male‐like forms also clearly present are assumed to be intermediates in the evolution of dioecy, and taken to suggest that separate sexes evolved recently (see Introduction), rather than taxa that may have ancient dioecy that has reverted to cosexuality. Gynodioecious populations with high female frequencies are assumed to involve cytonuclear male‐sterility, because high female frequencies can arise when cytoplasmic male sterility factors are present in the absence of nuclear restorers, or when high fitness costs of restoring cytoplasmic male fertility keep restorers at low frequencies (Ashman ; Case and Caruso ; Delph and Bailey ). Our results show that breakdown of dioecy is generally more difficult than suggested by the modeling of Ehlers and Bataillon () (though it is incorrect that ancient dioecy cannot break down when the cosexes cannot self‐fertilize), particularly when dioecy evolved recently, and Y chromosome homozygotes are viable (Fig.…”

Effects of crossing distance on performance of the native wildflower Lobelia siphilitica: Implications for ecological restoration1

“…GERMINATION AND GROWTH. As part of a larger project to test models of sex ratio evolution in gynodioecious plants Caruso 2010, Caruso andCase 2013), we germinated seeds from 26 L. siphilitica populations in Illinois, Indiana, Iowa, Ohio, and Ontario (Table 1). Seeds were germinated in two separate experiments because of space limitations, and the methods used to break dormancy differed between these experiments.…”