Angert AL, Schemske DW. The evolution of species' distributions: reciprocal transplants across the elevation ranges of Mimulus cardinalis and M. lewisii. Evolution 59: 1671-1684

Department of Plant Biology, Michigan State University, East Lansing 48824, USA.
Evolution (Impact Factor: 4.61). 09/2005; 59(8):1671-84. DOI: 10.1554/05-107.1
Source: PubMed


Every species occupies a limited geographic area, but it remains unclear why traits that limit distribution do not evolve to allow range expansion. Hypotheses for the evolutionary stability of geographic ranges assume that species are maladapted at the range boundary and unfit beyond the current range, but this assumption has rarely been tested. To examine how fitness varies across species' ranges, we reciprocally transplanted two species of monkeyflowers, Mimulus cardinalis and M. lewisii, within and beyond their present elevation ranges. We used individuals of known parentage from populations collected across the elevation ranges of both species to examine whether populations are adapted to position within the range. For both species we found the greatest average fitness at elevations central within the range, reduced fitness at the range margin, and zero or near-zero fitness when transplanted beyond their present elevation range limits. However, the underlying causes of fitness variation differed between the species. At high elevations beyond its range, M. cardinalis displayed reduced growth and fecundity, whereas at low elevations M. lewisii experienced high mortality. Weak differences in performance were observed among populations within each species and these were not related to elevation of origin. Low fitness of both species at their range margin and weak differentiation among populations within each species suggest that adaptation to the environment at and beyond the range margin is hindered, illustrating that range margins provide an interesting system in which to study limits to adaptation.

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Available from: Amy Angert, Jun 24, 2014
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    • "Although some sister species in a variety of taxonomic groups replace each other along elevational gradients (reviewed by Cadena, 2007), compelling empirical evidence for parapatric speciation in mountains is still largely lacking (but see Hall, 2005 for a promising example in butterflies and Savolainen et al., 2006 for a case of ecological speciation involving minor differences in elevation in plants). In birds and other organisms, there are well-documented examples of local adaptation of populations along elevational gradients (Angert & Schemske, 2005; Dingle et al., 2008; McCormack & Smith, 2008; Cheviron & Brumfield, 2009; McCracken et al., 2009; Mil a et al., 2009; Storz et al., 2012), but we are unaware of conclusive evidence that this mode of divergence has 'scaled up' and led to reproductive isolation and thus to the origin of two distinct species from a single, continuously distributed ancestral lineage as a result of divergent selection. Multiple analyses, including those in this study, indicate that speciation in tropical montane organisms often involves an allopatric phase and that elevational replacements result from secondary contact between populations (reviewed by Cadena, 2007; see also Fuchs et al., 2011). "
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    ABSTRACT: Behavioural barriers to gene flow can play a key role in speciation and hybridisation. Birdsong is well-known for its potential contribution to such behavioural barriers as it may affect gene flow through an effect on territorial and mating success across population boundaries. Conspecific recognition and heterospecific discrimination of acoustic variation can prevent or limit hybridization in areas where closely related species meet. Here we tested the impact of song differences on territorial response levels between two adjacent Henicorhina wood-wren species along an elevational gradient in Colombia. In an earlier study, playback results had revealed an asymmetric response pattern, with low-elevation H. leucophrys bangsi responding strongly to any conspecific or heterospecific song variant, whereas high-elevation H. anachoreta birds discriminated, responding more strongly to their own songs than to those of bangsi. However, in that study we could not exclude a role for relative familiarity to the song stimuli. In the current study we confirm the asymmetric response pattern with song stimuli recorded close to and on both sides of the distinct acoustic boundary. Furthermore, we also show a previously unnoticed divergence in singing style between these two wood-wren species, which may contribute to an acoustically guided barrier to hybridization in this secondary contact zone.
    Behaviour 07/2015; DOI:10.1163/1568539X-00003309 · 1.23 Impact Factor
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    • "Microhabitat and climatic variation, including water availability, are likely drivers of adaptive differentiation in ecological and physiological traits (Turreson 1922; Stebbins 1952; Lexer and Fay 2005). Furthermore, extensive empirical data indicate that plant populations (Clausen and Heisey 1958; Bennington and McGraw 1995; Dudley 1996a; McKay et al. 2001; Hall and Willis 2006; Lowry et al. 2008; Agren and Schemske 2012) and species (Angert and Schemske 2005; Lexer et al. 2005; Wu and Campbell 2006; Dorman et al. 2009; Campbell et al. 2010) are often locally adapted to environmental conditions (reviewed in Arntz and Delph 2001; Geber and Griffen 2003; Leimu and Fischer 2008; Hereford 2009). For adaptation to habitats with limited water availability , three broad strategies are described: tolerance, avoidance , and escape (Ludlow 1989). "
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    ABSTRACT: Flowering time and water-use efficiency (WUE) are two ecological traits that are important for plant drought response. To understand the evolutionary significance of natural genetic variation in flowering time, WUE, and WUE plasticity to drought in Arabidopsis thaliana, we addressed the following questions: (1) How are ecophysiological traits genetically correlated within and between different soil moisture environments? (2) Does terminal drought select for early flowering and drought escape? (3) Is WUE plasticity to drought adaptive and/or costly? We measured a suite of ecophysiological and reproductive traits on 234 spring flowering accessions of A. thaliana grown in well-watered and season-ending soil drying treatments, and quantified patterns of genetic variation, correlation, and selection within each treatment. WUE and flowering time were consistently positively genetically correlated. WUE was correlated with WUE plasticity, but the direction changed between treatments. Selection generally favored early flowering and low WUE, with drought favoring earlier flowering significantly more than well-watered conditions. Selection for lower WUE was marginally stronger under drought. There were no net fitness costs of WUE plasticity. WUE plasticity (per se) was globally neutral, but locally favored under drought. Strong genetic correlation between WUE and flowering time may facilitate the evolution of drought escape, or constrain independent evolution of these traits. Terminal drought favored drought escape in these spring flowering accessions of A. thaliana. WUE plasticity may be favored over completely fixed development in environments with periodic drought.
    Ecology and Evolution 11/2014; 4(23). DOI:10.1002/ece3.1270 · 2.32 Impact Factor
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    • "The study of distributional range limits is a fundamental goal in ecology, evolution and conservation, since it is related to processes involved in specialization (like local adaptation or tolerance to variable environments) and speciation (like reproductive and geographic isolation). However, studies on local adaptation among populations of closely related taxa located along an elevational gradient or beyond their current ranges are scarce (Angert and Schemske 2005; Gerber and Eckart 2005), especially in Mediterranean mountains (Milla et al. 2008; Ross et al. 2012). Overall in our study, plants performed better at high than at low elevation, especially in terms of growth (TPDW) and seedling survival. "
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    ABSTRACT: Abstract Aims Phenotypic plasticity and local adaptation of populations at their distributional limits are crucial to understand species colonization and persistence in novel or marginal environments, as well as species divergence and niche width evolution. We assess the contribution of these processes to shape current elevational limits and determine elevational phenotypic divergence between two subspecies of Aquilegia vulgaris (subsp. vulgaris and nevadensis). Methods We conducted sowing and transplant experiments considering four elevations throughout the current elevational range of Aquilegia vulgaris in southern Iberian Peninsula. Experiments were designed to explore, on the one hand, local adaptation through three components of performance (germination, survival and growth) and, on the other hand, the phenotypic differentiation and/or plasticity associated to local adaptation. Four populations per subspecies (three from the elevational core and one from the elevational boundary) were used as seed sources. Patterns of local adaptation and phenotypic differentiation are examined in the context of the “centre-periphery” hypothesis. Important Findings Central populations of both subspecies performed better at their local elevations while marginal populations were maladapted, confirming the hypothesis and contributing to explain the current elevational segregation of these subspecies. Density of glandular pubescence and germination timing seem to be related to local adaptation, through phenotypic differentiation between subspecies or elevations. The widespread subsp. vulgaris showed signals of adaptive plasticity in the timing of germination while it was not the case in the endemic subsp. nevadensis.
    Journal of Plant Ecology 05/2014; 8(3). DOI:10.1093/jpe/rtu017 · 2.65 Impact Factor
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