Maintenance of species boundaries amid hybridization in two island gingers with similar ecological niches.

Understanding species boundaries maintenance in the face of hybridization/introgression is an intriguing yet complex topic in evolutionary biology. The underlying mechanisms, however, remain elusive. To address this, we propose to investigate the role of climatic shifts in shaping genetic structure and influencing species boundaries. We combine multilocus genetic data and species distribution modeling to explore how past and current climatic shifts affect the genetic structure and demographic history of two Taiwan endemic gingers, Zingiber pleiostachyum and Z. shuanglongense. We identified a well-delimited genetic structure with evidence of admixture, indicating incomplete reproductive isolation between the two gingers. This is likely due to secondary contact and range overlap during the last glacial maximum, leading to sporadic instances of hybridization. Niche overlap tests based on climate and soil data indicate that these two gingers occupy similar but nonidentical ecological niches. Furthermore, we found that the considerable differences in their current geographic distribution and altitude preferences might have resulted from different seed dispersal capabilities and competitive exclusion due to their similar niche preferences. Our results reveal a model where altitudinal differentiation and dispersal strategy synergistically reinforce the species divergence, thereby illuminating the importance of these factors in shaping and maintaining the island's biodiversity.

[Profile nutrient distribution and sedimentary characteristics in typical marshes of Sanjiang Plain].

Profile distribution characteristics of organic carbon (C), total nitrogen (N), total phosphorus (P) and total sulfur (S) were studied in two typical marshes including Carex lasiocarpa marsh and Phragmites australis marsh in the Sanjiang Plain. Sedimentary characteristics of typical mashes were analyzed. The results showed that vertically these soil chemical elements also varied, showing obvious stratification and enrichment. In a soil profile, soil organic C under both vegetation communities gradually decreased; soil total N first increased and then decreased under both; total P under Carex lasiocarpa first decreased and then increased, whereas it decreased with the increasing depth under Carex lasiocarpa; total S was reduced with increasing depth under both marshes. Total N, total P and total S were all strongly correlated with soil organic C (P < 0.01); soil organic C was strongly correlated with bulk density (P < 0.01). Our study also illustrated that the vegetation types had different influences for organic C, total N, total P and total S of the marsh profiles. Environmental 137Cs and 210Pb dating techniques were applied to determine recent sedimentation rates, and the constant rate of supply (CRS) was applied to deduce the age of sediment core, and the results showed that the mean sedimentation rate was 0.33 cm x a(-1), and the sedimentation fluxes ranged 0.03-0.48 g x (cm2 x a)(-1) [Mean = 0.29 g x (cm2 x a) -1].