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: 14.39). 11/2010; 60(1):45-59. DOI: 10.1093/sysbio/syq056
Source: PubMed


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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    • "Humulus lupulus (H. lupulus) is a medicinal herb wildly grown in Europe, Asia, and North America (Reeves & Richards, 2011 ▶). In traditional medicine, hop is most often used to treat the symptoms of anxiety such as nervousness, overexcitability, restlessness, and insomnia (Viesti et al., 2011 ▶). "
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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.
    Avicenna Journal of Phytomedicine 03/2014; 4(1):53-8.
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    • "We used a maximum entropy algorithm available in MaxEnt [78], [79]. Recent studies indicate [17], [80], [81] that MaxEnt performs well when compared with other ENM methods and has been widely used to delimit species boundaries and ecological niches [82], [83], [84], [85]. MaxEnt is a machine learning program that estimates the probability distribution for a species occurrence based on environmental constraints [79]. "
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    PLoS ONE 02/2014; 9(2):e87804. DOI:10.1371/journal.pone.0087804 · 3.23 Impact Factor
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    • "Although methodologies using molecular data (Templeton 2001; Hebert et al. 2003; Pons et al. 2006; Knowles and Carstens 2007), have accelerated and facilitated species recognition, they may not be sufficient for the delimitation of recently diverged species (Will et al. 2005; Brower 2006; Hickerson et al. 2006; Gonzales et al. 2009), stressing the importance of studies at the population level (Knowles and Carstens 2007; Shaffer and Thomson 2007). Furthermore, information on natural history, reproductive biology, and/or ecological characteristics in situ for species delimitation, and for the understanding of speciation, is rarely sought (Marshall et al. 2006; Leaché et al. 2009; Reeves and Richards 2011). "
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    ABSTRACT: In this study we explore morphological and ecological variation in sympatric populations of Pagamea coriacea s.l. - a species complex from white-sand vegetation in the Amazon. A total of 147 trees were sampled and monitored at three nearby sites in Central Amazon, Brazil. Multivariate analyses of morphology indicated two distinct groups (A and B), which also differed in bark type, each containing subgroups associated with sexual dimorphism. However, a single hermaphroditic individual was observed within group B. As expected, all pistillate plants produced fruits, but 23% of the staminate plants of group B, and 5% of group A also produced fruits. This variation suggests that the sexual systems of both groups are between dioecy and gynodioecy. There was an overlap in flowering phases between the two groups, but the pattern of floral maturation differed. Ecologically, plants of group B were found in more shaded habitats and over sandstone bedrocks, while group A was prevalent in deeper sandy soils as canopy plants. The significances of morphological and environmental differences were tested by a multivariate analysis of variance, and a canonical discriminant analysis assessed the importance of variables. The coexistence in sympatry of two discrete morphological groups in the P. coriacea s.l., with different habitat preferences and reproductive behaviors, indicates they represent distinct species.
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