Do secondary sexual dimorphism and female intolerance to drought influence the sex ratio and extinction risk of Taxus baccata?

Abstract

Sex ratio and sexual dimorphism were studied in the dioecious tree Taxus baccata. We examined five populations of T. baccata in Poland and Ukraine to identify the differences between male and female individuals. The sex of all individuals, height and diameter, needle length and area, specific leaf area (SLA), the number of stomata rows, stomatal density, and content of carbon and nitrogen were measured to identify the differences between male and female individuals. The relationship between sex ratio and climatic conditions, age and population size were analysed using data collected from the field and the literature. Female trees were shorter than males, but needles of females were longer and had larger area. Although there were no differences among sexes in SLA, nitrogen and carbon concentration, we found a positive correlation between nitrogen concentration and SLA among females. The sex ratio changed with tree height within populations, and taller height classes were biased in favour of males. Regardless of population age, the percentage of females within populations was positively correlated with precipitation. Probably high reproductive effort caused female trees to lose in competition with males, and this loss may also be enhanced by lower drought tolerance in females and could contribute to risk of extinction for T. baccata. The continental geographic range of T. baccata may be restricted by limited occurrence of females, which demand higher water resources than males.

Relative strength of fine-scale spatial genetic structure in paternally vs biparentally inherited DNA in a dioecious plant depends on both sex proportions and pollen-to-seed dispersal ratio

“…The study populations also differ with respect to census density (Table 4, see also Figure 1). According to the sex allocation theory, females are generally less competitive than males and females of English yew may have a higher mortality (Iszkuło et al, 2009). As shown in our earlier study, both populations reveal a significant SGS at six nuclear microsatellite markers (Chybicki et al, 2011) as well as relatively high genetic variation and no signal of a recent bottleneck (Chybicki et al, 2012).…”

“…Females of T. baccata tend to be more abundant in wetter habitat (Vessela et al, 2015). Our previous study showed that there is a positive correlation between average rainfall and increased participation of females in T. baccata populations (Iszkuło et al, 2009), and this may explain differences in sex proportions between Cisy Staropolskie and Cisy w Czarnem (the average annual rainfall of 572 and 638 mm, respectively; based on DIVA-GIS software: Hijmans et al, 2005). The study populations also differ with respect to census density (Table 4, see also Figure 1).…”

“…On the contrary, 'Cisy Staropolskie' represents a yew population with sex proportions significantly biased towards males (67% males; estimated based on a sample of 242 individuals; see Iszkuło et al, 2009). It should be stressed that 'Cisy Staropolskie' seems to represent an exceptionally high proportion of males compared with the average sex proportions of the species (c. 50%; see Iszkuło et al, 2009;Litkowiec et al, 2015). Male-biased sex proportions can be, at least partly, attributable to limited availability of water and stand density.…”

Morphological and molecular data from Madeira support the persistence of an ancient lineage ofTaxus baccataL. in Macaronesia and call for immediate conservation actions

“…Three individuals were sampled within the island native forest, where natural vegetation appears to be a transition type between "Madeiran laurisilva" and "Madeiran cloud heaths" (nos. 31.32 and 45.62, CORINE Biotope Manual, EC 1991) or, more specifically, in the Vaccinio padifoliiEricetum maderinicolae Plant characterization and leaf morphology Leaf morphometric analysis was executed using the Digimizer image analysis software (MedCalc 2009); comparisons were made with the following Mediterranean provenances to check relative differences in the southern distribution range of the species: a natural yew population at Rosello, Italy (central-eastern Abruzzi Apennines, 41°52′ N, 14°17′ E), a sample from Greece (Mount Parnassus, Sterea Ellada, 38°32′ N, 22°32′ E), a population from Algeria (Chréa National Park, 36°25′ N, 02°52′ E), in addition to three Taxus baccata plants from the Azores and another Italian natural population at Carpineto Romano (Lepini Mountains, 41°33′ N, 13°0 6′ E) recently studied by Schirone et al (2010), plus 21 sample descriptions retrieved from literature (Dempsey and Hook 2000;Zarek 2007;Wyka et al 2008;Iszkuło et al 2009). A total of 11 trees were scanned, and four leaf morphometric parameters were calculated: length (mm), width (mm), area (mm 2 ) and length/width ratio.…”

Weak competitive ability may explain decline of Taxus baccata

“…The main reasons for seedling mortality are grazing by deer (Perrin et al 2006), excessive shading (Iszkuło and Boratyński 2006), interaction of low temperature and light availability (Iszkuło 2010) and drought in the Mediterranean region (Sanz et al 2009). Dioecy may also adversely affect the mortality of yew (Iszkuło et al 2009;Cedro and Iszkuło 2011). The passive protection of European yew populations and the lack of thinning in the natural reserves have resulted in excessive canopy density and, consequently, lack of reproduction success (Dhar et al 2008).…”