Mating system, sex ratio, and persistence of females in the gynodioecious shrub Daphne laureola L. (Thymelaeaceae)

Abstract

Although in gynodioecious populations male steriles require a fecundity advantage to compensate for their gametic disadvantage, southern Spanish populations of the long-lived shrub Daphne laureola do not show any fecundity advantage over hermaphrodites in terms of seed production and early seedling establishment. By using allozyme markers, we assess the mating system of this species in five populations differing in sex ratio, and infer levels of inbreeding depression over the whole life cycle by comparing the inbreeding coefficients at the seed and adult plant stages. Extremely low outcrossing rates (0.001oto0.125) were consistently found for hermaphrodites in all populations, whereas, as expected, female progeny were entirely outcrossed. In most populations, offspring were much more inbred than their parents, and heterozygosity of adults was greater than expected from outcrossing rate estimates, with very few selfed progeny appearing to reproduce in the field. The combination of extensive selfing in hermaphrodites and a strong inbreeding depression expressed late in the life cycle (and thus, only estimable by indirect measures based on genetic markers) may explain the persistence and high frequency of D. laureola females in southern Spanish populations.

Modelling the maintenance of male-fertile cytoplasm in a gynodioecious population

“…Whether or not limit cycles do occur in populations is not known, because of a lack of suitable observations, but, as postulated by Gouyon et al (1991) the high variation in female frequencies observed in some gynodioecious species could reflect such dynamics (for example, Dommée et al, 1978;Wolfe and Shmida, 1997;Graff, 1999;McCauley et al, 2000;Bailey, 2002;Asikainen and Mutikainen, 2003;Delph and Mutikainen, 2003;Barr, 2004;Murayama et al, 2004;Medrano et al, 2005). However, since our results showed that the approach of point equilibria was usually slow, even without a predicted limit cycle, populations displayed wide variations of female frequencies.…”

Dioecious plants are more precocious than cosexual plants: A comparative study of relative sizes at the onset of sexual reproduction in woody species

“…However, empirical data suggested that the fecundity of dioecious plants at a flowering event was lower than the required value (Asikainen & Mutikainen, 2003; Ibarra‐Manriquez & Oyama, 1992; Medrano et al, 2005). Smaller size at the onset of flowering may enhance reproductive success over a lifetime by increasing reproductive opportunities.…”

The effect of disease on the evolution of females and the genetic basis of sex in populations with cytoplasmic male sterility

“…In natural plant populations, disease incidence is often both spatially and temporally heterogeneous, with pathogens only persisting at the metapopulation level [52][53][54][55]. Spatial variation in sex ratio has also been observed in many different gynodioecious species [56][57][58][59][60] and there is good reason to believe that, in many species, metapopulation dynamics play a large role in the maintenance of gynodioecy [56,61,62]. McCauley & Taylor [63] showed that once among population differences in sex ratio are established, females can be maintained at the metapopulation-level through frequencydependent selection, and can persist even in the absence of fertility advantages or costs.…”