Sexual stability in the nearly dioeciousPinus johannis(Pinaceae)

Abstract

• Premise of the study: Even though dioecy is a dominant sexual system among gymnosperms, little is known about its evolutionary history. Pinus johannis may represent a model system because unisexual and monoecious individuals compose its populations. The presence of unisexual individuals in other Pinus species is a consequence of sexual lability. Here we determined whether P. johannis represents the first example of a dioecious or nearly dioecious reproductive system in conifers by evaluating its sexual stability. • Methods: To assess the stability of sexual expression, we quantified the proportion of male vs. female reproductive structures produced by trees over multiple years and tested for the presence of sexual dimorphism. Sexual lability hypotheses were also examined by looking at the relationship between environmental factors and sexual expression and by comparing the reproductive behavior of P. johannis with its closest labile relative, P. edulis. • Key results: Pinus johannis is nearly dioecious: ∼99% of individuals are unisexual or express a low proportion of the opposite gender with few changes in sexual expression through time. We found sexual dimorphism consistent with sexual stability. Sexual expression did not vary with tree size/age, abiotic environment, or herbivore removal, providing evidence against sexual lability. Individuals of P. johannis tended to produce only male or female strobili, whereas those of P. edulis were mainly monoecious with a gradient in the female to male strobili ratio. • Conclusions: This study represents the first report of a nearly stable dioecious Pinus species. The variety of sexual morphs coexisting in the same population makes P. johannis a model for studying the evolution of dioecy in gymnosperms.

Morphological and niche divergence of pinyon pines

“…, ; Flores‐Rentería et al. ), so niche divergence could be a consequence of speciation. Nevertheless, as in any niche modeling research, the pattern could be the result of the methodological artifacts discussed below.…”

“…); along with P. culminicola , they are considered a complex group with little morphological and genetic divergence (Flores‐Rentería et al. ). Our results show that between some pairs of these species there has been niche conservatism which can be expected given their close phylogenetic relations and shared geographic ranges.…”

“…; Flores‐Rentería et al. ), and the rest from our own efforts on P. rzedowskii cone and seed measurements.…”

“…We searched for localities of the 11 pinyon pines species recorded in the literature (Cuenca ; Flores‐Rentería et al. ), the Red Mundial de Información sobre Biodiversidad (INEGI‐CONABIO‐INE, ) and personal field collections by Patricia Delgado. We restricted the database to records with coordinates reporting seconds and certainty in the species identification, either by genetic confirmation from previous analyses (Cuenca et al.…”

“…; Flores‐Rentería et al. ) or by recent expert identification by David Gernandt. A total of 261 localities were used ranging from three localities ( P. culminicola ) to 57 localities ( P. pinceana ), representative of the known localities of the species (see Fig.…”