Species delimitation under the general lineage concept: an empirical example using wild North American hops (Cannabaceae: Humulus lupulus).

United States Department of Agriculture, Agricultural Research Service, National Center for Genetic Resources Preservation, 1111 South Mason Street, Fort Collins, CO 80521, USA.
Systematic Biology (Impact Factor: 12.17). 11/2010; 60(1):45-59. DOI: 10.1093/sysbio/syq056
Source: PubMed

ABSTRACT There is an emerging consensus that the intent of most species concepts is to identify evolutionarily distinct lineages. However, the criteria used to identify lineages differ among concepts depending on the perceived importance of various attributes of evolving populations. We have examined five different species criteria to ask whether the three taxonomic varieties of Humulus lupulus (hops) native to North America are distinct lineages. Three criteria (monophyly, absence of genetic intermediates, and diagnosability) focus on evolutionary patterns and two (intrinsic reproductive isolation and niche specialization) consider evolutionary processes. Phylogenetic analysis of amplified fragment length polymorphism (AFLP) data under a relaxed molecular clock, a stochastic Dollo substitution model, and parsimony identified all varieties as monophyletic, thus they satisfy the monophyly criterion for species delimitation. Principal coordinate analysis and a Bayesian assignment procedure revealed deep genetic subdivisions and little admixture between varieties, indicating an absence of genetic intermediates and compliance with the genotypic cluster species criterion. Diagnostic morphological and AFLP characters were found for all varieties, thus they meet the diagnosability criterion. Natural history information suggests that reproductive isolating barriers may have evolved in var. pubescens, potentially qualifying it as a species under a criterion of intrinsic reproductive isolation. Environmental niche modeling showed that the preferred habitat of var. neomexicanus is climatically unique, suggesting niche specialization and thus compliance with an ecological species criterion. Isolation by distance coupled with imperfect sampling can lead to erroneous lineage identification using some species criteria. Compliance with complementary pattern- and process-oriented criteria provides powerful corroboration for a species hypothesis and mitigates the necessity for comprehensive sampling of the entire species range, a practical impossibility in many systems. We hypothesize that var. pubescens maintains its genetic identity, despite substantial niche overlap with var. lupuloides, via the evolution of partial reproductive isolating mechanisms. Variety neomexicanus, conversely, will likely persist as a distinct lineage, regardless of limited gene flow with vars. lupuloides and pubescens because of ecological isolation--adaptation to the unique conditions of the Rocky Mountain cordillera. Thus, we support recognition of vars. neomexicanus and pubescens as species, but delay making a recommendation for var. lupuloides until sampling of genetic variation is complete or a stable biological process can be identified to explain its observed genetic divergence.

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    ABSTRACT: Objective: Many biological studies have been done to determine the activity of medicinal plants on gastrointestinal function. Since acetylcholine is the major transmitter involved in the gastrointestinal motility and there are some evidences regarding the cholinergic modulatory effect of hops extract, in the present study spasmolytic and antispasmodic action of hops (Humulus lupulus) on acetylcholine-induced contraction in isolated rat's ileum was evaluated. Material and Methods: In this study, pieces of isolated rat's ileum were mounted in the internal chamber of an organ bath which was filled with Tyrode's solution and tightly tied to the lever of an isotonic transducer. The contractile responses were recorded by using an oscillograph device. In the presence of normal saline and different concentrations of hops (0.1, 0.3, and 0.5 mg/ml), the amplitude of contractions induced by10(-12) up to 10(-2) M acetylcholine was determined. The spasmolytic action of the same extract concentrations was also examined on contraction induced by 10(-4) acetylcholine. Results: Our findings indicate that hops extract reduces acetylcholine-induced contraction in all concentrations. The significant inhibitory effects of 0.1, 0.3, and 0.5 mg/ml hops extract on contraction induced by 10(-3) M acetylcholine were 81.9, 77, and 29.3, respectively (p<0.05). Conclusion: According to our findings, hops extract poses a potent spasmolytic and antispasmodic action on acetylcholine-induced contraction in isolated rat's ileum which may be mediated by cholinergic systems.
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